Powder coating nozzle

Abstract

To provide a powder paint nozzle which can discharge a powdery paint in a more uniform manner.SOLUTION: A powder paint nozzle 1 of the invention is used to discharge a powdery paint toward an inner surface of a pipe body while moving along a traveling direction X1 relative to the inner surface of the pipe body. The powder paint nozzle 1 includes multiple discharge ports 12, 13 inclining toward the traveling direction X1.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a powder coating nozzle.

Background Art

[0002] For flowing fluids such as water supply and drainage, a pipe body such as a ductile iron pipe is used. The inner surface of the pipe body is coated with a powder paint to protect the inner surface. The pipe body is required to have a uniformly formed coating film not only for efficient coating but also for more reliably protecting the inner surface.

[0003] For example, a ductile iron pipe includes a socket capable of receiving another ductile iron pipe and a straight pipe portion communicating with the socket. The ductile iron pipe is connected to another ductile iron pipe by receiving the other ductile iron pipe at the socket. On the inner surface of the socket of the ductile iron pipe, a rubber ring, a lock ring, etc. are provided to suppress fluid leakage at the connection part and the withdrawal of another ductile iron pipe, and irregularities for providing such a rubber ring, a lock ring, etc. are formed. Therefore, the ductile iron pipe is formed such that the irregularities on the inner surface of the socket are larger than the irregularities on the inner surface of the straight pipe portion.

[0004] [[ID=第十九]] In the ductile iron pipe as described above, when coating the inner surface by spraying a powder paint, there is a problem that it is difficult to form a coating film with a uniform thickness on the inner surface of the socket with large irregularities. In particular, for the socket to receive another ductile iron pipe, the dimensional tolerance of the thickness of the applied coating film is also severely limited. Therefore, in the coating apparatus disclosed in Patent Document 1, for example, an attempt has been made to form a uniform coating film on the inner surface of the socket with large irregularities by inclining the discharge direction of the powder paint with respect to the pipe axis direction.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] In the coating apparatus described in Patent Document 1, the powder coating discharge nozzle is connected to the supply tube at an angle with respect to the direction in which the powder coating supply tube extends. In this case, the powder coating passes mostly along the radially outer side at the inclined connection between the supply tube and the discharge nozzle, making it impossible to discharge the powder coating uniformly in the axial direction of the tube. Therefore, the coating apparatus described in Patent Document 1 cannot uniformly coat surfaces with large irregularities, such as the socket of a ductile cast iron pipe.

[0007] The present invention has been made in view of the above problems, and aims to provide a powder coating nozzle capable of dispensing powder coating more uniformly. [Means for solving the problem]

[0008] The powder coating nozzle of the present invention is a powder coating nozzle for discharging powder coating toward the inner surface of a tube while moving relative to the inner surface of the tube along the direction of travel, and is characterized in that the powder coating nozzle has a plurality of discharge ports that are inclined toward the direction of travel.

[0009] Furthermore, it is preferable that each of the plurality of discharge ports has a discharge angle for the powder coating that is different from the other in terms of the angle with respect to the direction of travel.

[0010] Furthermore, it is preferable that each of the multiple discharge ports is arranged in line along the direction of travel.

[0011] Furthermore, it is preferable that the powder coating nozzle includes a plurality of powder coating nozzles that are inclined toward opposite directions of travel to discharge the powder coating, and that the plurality of powder coating nozzles are arranged such that at least a portion of the areas on the inner surface of the tube to which the powder coating discharged by each of the plurality of powder coating nozzles reaches overlaps with each other. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a powder coating nozzle that can dispense powder coating more uniformly. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional view of an exemplary pipe to which a powder coating nozzle according to several embodiments of the present invention is applied. [Figure 2] This is a schematic diagram showing an exemplary coating apparatus incorporating and using powder coating nozzles according to several embodiments of the present invention. [Figure 3] This diagram schematically shows the state in which powder coating is discharged from a first discharge unit (powder coating nozzle) in an exemplary coating apparatus that incorporates and uses a powder coating nozzle according to some embodiments of the present invention, where (a) shows the state in which the first discharge unit is discharging powder coating while moving relative to a first direction, and (b) shows the state in which the first discharge unit is discharging powder coating while moving relative to a second direction. [Figure 4] This figure schematically shows a modified version of the first discharge section shown in Figure 3. [Figure 5] This is a schematic diagram of a powder coating nozzle according to one embodiment of the present invention, where (a) is a front view showing the inlet and the first and second discharge ports, (b) is a side view of one side showing the inlet and the first discharge port, and (c) is a side view of one side showing the inlet and the second discharge port. [Figure 6]This is a schematic diagram of a powder coating nozzle according to one embodiment of the present invention, where (a) is a front view showing the inlet and the first and second discharge ports, (b) is a side view of one side showing the inlet and the first discharge port, and (c) is a side view of one side showing the inlet and the second discharge port. [Figure 7] This is a schematic diagram of a powder coating nozzle according to one embodiment of the present invention, where (a) is a front view showing the inlet and the first, second, and third discharge ports, and (b) is a side view of one side showing the inlet and the first, second, and third discharge ports. [Figure 8] This is a schematic diagram of a powder coating nozzle according to one embodiment of the present invention, where (a) is a front view showing the inlet and the first, second, and third discharge ports, and (b) is a side view of one side showing the inlet and the first, second, and third discharge ports. [Modes for carrying out the invention]

[0014] Hereinafter, powder coating nozzles according to several embodiments of the present invention will be described with reference to the attached drawings. However, the embodiments shown below are merely examples, and the powder coating nozzles of the present invention are not limited to the embodiments shown below.

[0015] Powder coating nozzles according to some embodiments of the present invention are used to coat the inner surface of a pipe with powder coating. Examples of pipes to which the powder coating nozzle can be applied include cast iron pipes such as known ductile cast iron pipes. However, the pipes to which the powder coating nozzle can be applied are not particularly limited as long as they have the structure of pipe P described below, and may be pipes made of other materials. Furthermore, the powder coating nozzle can also be applied to objects other than pipes.

[0016] As shown in FIG. 1, the pipe body P is formed in a cylindrical shape with both ends open in the direction of the pipe axis X, and the inside thereof functions as a flow path through which fluids such as water supply and drainage flow. The pipe body P forms a longer flow path by being connected to other pipe bodies P. In the illustrated example, the pipe body P is formed in a substantially cylindrical shape in which the pipe axis X extends in a substantially straight line. However, as long as fluids can flow inside the pipe body P, its shape is not particularly limited, and the pipe axis X may be curved, or it may be formed in a cylindrical shape of other shapes such as a substantially square tube shape.

[0017] As shown in FIG. 1, the pipe body P includes a first pipe portion A and a second pipe portion B. As will be described in detail below, the inner surface of the first pipe portion A has relatively large irregularities compared to the inner surface of the second pipe portion B. The powder coating nozzle of the present embodiment can be suitably applied to the inner surface portion having such large irregularities inside the pipe body P. Describing the illustrated pipe body P in detail, the pipe body P includes a receiving port P1 provided at one end in the direction of the pipe axis X, an insertion port P2 provided at the other end in the direction of the pipe axis X, and a straight pipe portion P3 extending along the direction of the pipe axis X between the receiving port P1 and the insertion port P2. In the illustrated example, the receiving port P1 constitutes the first pipe portion A, and the insertion port P2 and the straight pipe portion P3 constitute the second pipe portion B.

[0018] The receiving port P1 is formed in a cylindrical shape and is a portion for receiving the insertion port P2 of another pipe body P inside it. When the receiving port P1 of the pipe body P receives the insertion port P2 of another pipe body P, the pipe body P and the other pipe body P are connected. The receiving port P1 is formed to have an internal space larger than the outer shape of the insertion port P2 in order to receive the insertion port P2 of another pipe body P. In the illustrated example, the receiving port P1 is formed in a substantially cylindrical shape extending along the direction of the pipe axis X and has an inner diameter larger than the outer diameter of the insertion port P2. An opening P12 into which the insertion port P2 of another pipe body P is inserted is provided at one end of the receiving port P1 in the direction of the pipe axis X, and a step portion P13 defining the boundary with the straight pipe portion P3 is provided at the other end of the receiving port P1 in the direction of the pipe axis X. By providing the step portion P13 at the other end of the receiving port P1, when the insertion port P2 of another pipe body P is received inside the receiving port P1, the insertion port P2 is restricted from penetrating beyond the step portion P13 into the straight pipe portion P3.

[0019] As shown in Fig. 1, the inner surface P11 of the receiving port P1 has relatively large irregularities compared to the inner surface P21 of the insertion port P2 and the inner surface P31 of the straight pipe portion P3. Here, relatively large irregularities mean, for example, that the height difference between the convex portion and the concave portion is large compared to the comparison target. In the illustrated example, on the inner surface P11 of the receiving port P1, in order to provide a rubber ring (not shown) that suppresses fluid leakage to the outside at the connection portion between the pipe bodies P, P and a lock ring (not shown) that suppresses the other pipe body P from coming out of the pipe body P, a plurality of convex portions P14 protruding from the inner surface P11 toward the pipe axis X continuously in the circumferential direction of the inner surface P11 and a plurality of concave portions P15 formed between the plurality of convex portions P14 are provided. The rubber ring and the lock ring are attached to the inner surface P11 of the receiving port P1 by fitting into the concave portion P15. The receiving port P1 fits with the insertion port P2 of another pipe body P through the rubber ring and the lock ring provided on the inner surface P11.

[0020] The insertion port P2 is a portion that is received inside the receiving port P1 of another pipe body P. When the insertion port P2 of the pipe body P is received in the receiving port P1 of another pipe body P, the pipe body P and the other pipe body P are connected. The insertion port P2 is formed in a cylindrical shape, and its interior communicates with the interior of the straight pipe portion P3. In the illustrated example, the insertion port P2 is formed in a substantially cylindrical shape extending along the pipe axis X direction, has an inner diameter substantially the same as the inner diameter of the straight pipe portion P3, and has an inner diameter smaller than the inner diameter of the receiving port P1. The insertion port P2 has an inner surface P21 with relatively small irregularities compared to the inner surface P11 of the receiving port P1. In the illustrated example, the inner surface P21 of the insertion port P2 has substantially the same smoothness as the inner surface P31 of the straight pipe portion P3 and is formed smoother than the inner surface P11 of the receiving port P1.

[0021] One end of the spigot P2 is in communication with the straight pipe section P3, and the other end of the spigot P2 is provided with an opening P22. The outer surface of the spigot P2 is provided with a projection P23 that prevents the pipe body P from coming out of the other pipe body P. When the pipe body P and the other pipe body P are connected, if the pipe body P tries to come out of the other pipe body P, the projection P23 of the spigot P2 will come into contact with a lock ring (not shown) provided on the inner surface P11 of the receiving opening P1 of the other pipe body P, thereby preventing the pipe body P from coming out of the other pipe body P.

[0022] The straight pipe section P3 constitutes the main body of the pipe P, and is configured so that fluid flows through its interior between the socket P1 and the spigot P2. As shown in Figure 1, the straight pipe section P3 is formed in a cylindrical shape, communicating with the socket P1 at one end and with the spigot P2 at the other end. In the illustrated example, the straight pipe section P3 is formed in a substantially cylindrical shape extending along the pipe axis X direction, has an inner diameter that is substantially the same as the inner diameter of the spigot P2, and has an inner diameter that is smaller than the inner diameter of the socket P1. The straight pipe section P3 has an inner surface P31 with relatively small irregularities compared to the inner surface P11 of the socket P1. In the illustrated example, the inner surface P31 of the straight pipe section P3 has a smoothness that is approximately the same as the inner surface P21 of the spigot P2, and is formed to be smoother than the inner surface P11 of the socket P1.

[0023] Next, with reference to Figure 2, a coating apparatus PD to which a powder coating nozzle according to several embodiments of the present invention is applied will be described. However, the following coating apparatus PD is just an example, and the powder coating nozzle of the present invention may be applied to other known coating apparatuses besides the coating apparatus PD.

[0024] As shown in Figure 2, the coating apparatus PD comprises a rotating device R for relative rotation of the pipe P and a dispensing device D for dispensing powder coating. The coating apparatus PD coats the inner surface of the pipe P by dispensing powder coating toward the inner surface of the pipe P using the dispensing device D while rotating the pipe P relative to the pipe P using the rotating device R. The coating apparatus PD may also be equipped with a heating device (not shown), such as a gas furnace or electric furnace, for preheating the pipe P to cure the powder coating that adheres to the inner surface of the pipe P.

[0025] The rotating device R supports the pipe body P and rotates the pipe body P relative to it around the pipe axis X. As shown in Figure 2, the rotating device R comprises a rotating roller R1 for rotating the pipe body P relative to it around the pipe axis X, a support base R2 that rotatably supports the rotating roller R1, and a drive device (not shown) such as a motor for rotating the rotating roller R1. The rotating device R rotates the pipe body P over a predetermined range (e.g., the entire circumference) around the pipe axis X while the dispensing device D dispenses powder coating toward the inner surface of the pipe body P. As a result, the coating device PD can coat the inner surface of the pipe body P with powder coating over a predetermined range (e.g., the entire length) along the inner circumference. The speed at which the rotating device R rotates the pipe body P is not particularly limited and can be set appropriately according to the required coating film thickness, etc.

[0026] In this embodiment, the coating apparatus PD is configured to coat the inner surface of the pipe P with powder coating by rotating the pipe P around the pipe axis X using a rotating device R. However, the coating apparatus PD does not necessarily have to be equipped with a rotating device R. For the purpose of coating the inner surface of the pipe P with powder coating, for example, a discharge unit provided in the discharge device D described later may be configured to rotate around the pipe axis X, or the discharge unit may be configured to discharge powder coating to a predetermined range in the circumferential direction on the inner surface of the pipe P.

[0027] Dispensing device D dispenses powder coating from the inside of pipe P toward the inner surface of pipe P in order to coat the inner surface of pipe P. Dispensing device D comprises a first dispensing device D1 and a second dispensing device D2, which dispense different powder coatings, as shown in Figure 2. The first dispensing device D1 and the second dispensing device D2 are configured to dispense a first powder coating Dp1 and a second powder coating Dp2, respectively. However, dispensing device D does not necessarily have to consist of two dispensing devices; for example, one dispensing device may be configured to dispense the first powder coating Dp1 and the second powder coating Dp2 alternately, or the first dispensing device D1 and the second dispensing device D2 may be configured to dispense the same powder coating.

[0028] The first dispensing device D1 is used to coat the inner surface P11 of the socket P1 of the pipe body P (the inner surface of the first pipe section A) with the first powder coating Dp1. For this purpose, the first dispensing device D1 is configured to dispense the first powder coating Dp1 from the inside of the socket P1 of the pipe body P toward the inner surface P11 of the socket P1. As shown in Figure 2, the first discharge device D1 includes a first discharge section D11 (powder coating nozzle) that discharges the first powder coating Dp1 toward the inner surface P11 of the receiving port P1, a first powder coating supply pipe D12 such as a lance that supplies the first powder coating Dp1 to the first discharge section D11, a first drive device D13 that moves the first discharge section D11 relative to the receiving port P1 over a predetermined range in the direction of the pipe axis X (for example, the entire length from the opening P12 to the stepped section P13), and a first powder coating supply device D14 that contains the first powder coating Dp1 and supplies the first powder coating Dp1 to the first powder coating supply pipe D12 and the first discharge section D11. The first discharge device D1 is configured such that the first discharge section D11 is moved relative to the receiving port P1 over a predetermined range in the pipe axis X direction by the first drive device D13, thereby coating the inner surface P11 of the receiving port P1 with the first powder coating Dp1 over a predetermined range in the pipe axis X direction. However, the first discharge device D1 may also be used to coat the inner surface P11 of the receiving port P1 of the pipe body P with the second powder coating Dp2, or it may be used to coat the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3 (the inner surface of the second pipe section B) of the pipe body P with either the first or second powder coating Dp1 or Dp2.

[0029] The first dispensing device D1 may be configured to move the first dispensing section D11, which dispenses the first powder coating Dp1, relative to the inner surface P11 of the receiving port P1 in both a first direction X1 (Figure 3(a), also called the "forward path") along the pipe axis X direction from the receiving port P1 to the insertion port P2, and a second direction X2 (Figure 3(b), also called the "return path") along the pipe axis X direction from the insertion port P2 to the receiving port P1. In this case, the first dispensing device D1 may be configured to dispense the first powder coating Dp1 from the first dispensing section D11 at a first dispensing angle θ1 with respect to the first direction X1 while moving the first dispensing section D11 relative to the first direction X1. Furthermore, the first discharge device D1 may be configured to discharge the first powder coating Dp1 from the first discharge section D11 at a second discharge angle θ2 with respect to the second direction X2, while relatively moving the first discharge section D11 in the second direction X2. The first discharge device D1 may paint the same location in the forward and return journeys (reciprocal painting), or it may paint different locations in the forward and return journeys (forward painting, return painting). The first discharge angle θ1 and the second discharge angle θ2 are the angles approximately at the center of the spread of the first powder coating Dp1 discharged from the first discharge section D11.

[0030] The first discharge angle θ1 and the second discharge angle θ2 are not particularly limited, as long as they are set so that at least the first powder coating Dp1 advances toward the inner surface P11 of the receiving opening P1, but it is preferable that both are acute angles. By having both the first discharge angle θ1 and the second discharge angle θ2 be acute angles, the inner surface P11 of the receiving opening P1, which has relatively large irregularities, can be coated uniformly. This is because, for example, if the first discharge angle θ1 and the second discharge angle θ2 are obtuse angles (discharging in the opposite direction to the direction of travel of the first discharge unit D11), the movement speed of the first discharge unit D11 is subtracted from the discharge speed of the first powder coating Dp1, and the spraying angle of the first powder coating Dp1 becomes close to the direction perpendicular to the inner surface P11 of the receiving port P1. However, by making both the first discharge angle θ1 and the second discharge angle θ2 acute angles, the first powder coating Dp1 can be sprayed more reliably along a direction inclined from the direction perpendicular to the inner surface P11 of the receiving port P1, so that the first powder coating Dp1 can easily enter the corners of the unevenness on the inner surface P11 of the receiving port P1.

[0031] The first discharge angle θ1 and the second discharge angle θ2 are not particularly limited, as long as they are acute angles in order to uniformly coat the inner surface P11 of the receiving port P1. However, it is preferable that the angles be set such that the first discharge angle θ1 is larger than the second discharge angle θ2. By making the first discharge angle θ1 larger than the second discharge angle θ2, the inner surface P11 of the receiving port P1 can be coated more uniformly. This is thought to be because there is a difference in inclination between the side wall on the first direction X1 side and the side wall on the second direction X2 side of the recess P15 present on the inner surface P11 of the receiving port P1, and the difference in discharge angles θ1 and θ2 corresponds to this difference in inclination, allowing the first powder coating Dp1 to penetrate into the corners of the uneven surface.

[0032] The first discharge angle θ1 is not particularly limited, but it should be set to be greater than the second discharge angle θ2 in order to coat the inner surface P11 of the socket P1 more uniformly. However, from the viewpoint of coating the inner surface P11 of the socket P1 even more uniformly, it is preferably in the range of 50 to 80°, more preferably in the range of 60 to 70°, and even more preferably in the range of 60 to 65°. The first powder coating Dp1 may also be discharged from the first discharge section D11 so as to spread at a first spreading angle α1 centered on the first discharge angle θ1. The first spreading angle α1 is not particularly limited, but from the viewpoint of coating the inner surface P11 of the socket P1 even more uniformly, it is preferably smaller than the second spreading angle α2 described later, more preferably in the range of 10 to 30°, and even more preferably in the range of 15 to 25°.

[0033] The second discharge angle θ2 is not particularly limited, but it should be set to be smaller than the first discharge angle θ1 in order to coat the inner surface P11 of the socket P1 more uniformly. However, from the viewpoint of coating the inner surface P11 of the socket P1 even more uniformly, it is preferably in the range of 40 to 70°, more preferably in the range of 45 to 60°, and even more preferably in the range of 50 to 55°. The first powder coating Dp1 may also be discharged from the first discharge section D11 so as to spread at a second spreading angle α2 centered on the second discharge angle θ2. The second spreading angle α2 is not particularly limited, but from the viewpoint of coating the inner surface P11 of the socket P1 even more uniformly, it is preferably larger than the first spreading angle α1, more preferably in the range of 30 to 50°, and even more preferably in the range of 40 to 50°.

[0034] In the example shown in Figures 3(a) and (b), the first dispensing device D1 is shown as having one first dispensing section D11 that can change the dispensing angle and / or spread angle according to the directions of travel X1 and X2. However, the first dispensing device D1 may have multiple dispensing sections with different dispensing angles and / or spread angles, and the multiple dispensing sections may be used interchangeably according to the directions of travel X1 and X2. That is, the first dispensing section D11 (powder coating nozzle) may include multiple powder coating nozzles D111, D112, each inclined toward opposite directions of travel X1 and X2 to dispense powder coating (e.g., first powder coating Dp1), as shown in Figure 4. In this case, it is preferable that the multiple powder coating nozzles D111 and D112 be arranged such that at least a portion of the regions PR1 and PR2 on the inner surface of the pipe P (for example, the inner surface P11 of the receiving opening P1 of the pipe P) to which the powder coating discharged by each of the multiple powder coating nozzles D111 and D112 reaches overlaps with each other. This allows for coating almost the same area on the inner surface of the pipe P before and after switching the powder coating nozzles D111 and D112 used according to the direction of travel X1 and X2. Therefore, it becomes unnecessary (or unnecessary) to adjust the relative movement positions of the powder coating nozzles D111 and D112 before and after switching the powder coating nozzles D111 and D112 according to the direction of travel X1 and X2 in order to make the coating film thickness approximately uniform along the direction of travel X1 and X2. This simplifies the reciprocating coating process.

[0035] To explain in detail using the example shown in Figure 4, the first discharge section D11 (powder coating nozzle) includes a first powder coating nozzle D111 (for example, powder coating nozzles 1 and 3 described later) and a second powder coating nozzle D112 (for example, powder coating nozzles 2 and 4 described later). The first and second powder coating nozzles D111 and D112 correspond to the first discharge section D11 described in relation to Figure 3(a) and the first discharge section D11 described in relation to Figure 3(b), respectively. The first powder coating nozzle D111 is configured to discharge powder coating (for example, the first powder coating Dp1) toward the inner surface of the pipe P (for example, the inner surface P11 of the receiving opening P1 of the pipe P) at a first discharge angle θ1 which is acute with respect to the first direction X1, while moving relative to the inner surface of the pipe P (for example, the inner surface P11 of the receiving opening P1 of the pipe P). Furthermore, the first powder coating nozzle D111 is configured to discharge powder coating such that the powder coating spreads with a first spreading angle α1 centered on a first discharge angle θ1. The second powder coating nozzle D112 is configured to discharge powder coating (for example, the first powder coating Dp1) toward the inner surface of the pipe P (for example, the inner surface P11 of the receiving opening P1 of the pipe P) at a second discharge angle θ2, which is acute with respect to the second direction X2, while moving relative to the inner surface of the pipe P (for example, the inner surface P11 of the receiving opening P1 of the pipe P). Furthermore, the second powder coating nozzle D112 is configured to discharge powder coating such that the powder coating spreads with a second spreading angle α2 centered on the second discharge angle θ2. In the example shown in Figure 4, the first discharge section D11 includes two powder coating nozzles D111 and D112, but it may include three or more powder coating nozzles.

[0036] The first powder coating nozzle D111 and the second powder coating nozzle D112 are configured to move relative to each other along the directions of travel X1 and X2 with respect to the inner surface of the pipe P while maintaining their relative positions to each other at a substantially constant level. In this embodiment, the first powder coating nozzle D111 and the second powder coating nozzle D112 are fixed to each other so that their relative positions remain substantially constant while they move relative to the inner surface of the pipe P. However, it is sufficient that the first powder coating nozzle D111 and the second powder coating nozzle D112 maintain their relative positions at a substantially constant level when moving relative to the inner surface of the pipe P, and for example, they may be configured to be separated from each other and move relative to each other at the same speed.

[0037] As shown in Figure 4, the first powder coating nozzle D111 and the second powder coating nozzle D112 are positioned such that, at any relative position while moving relative to each other along the directions of travel X1 and X2, the first region PR1 on the inner surface of the pipe P reached by the powder coating discharged by the first powder coating nozzle D111 and the second region PR2 on the inner surface of the pipe P reached by the powder coating discharged by the second powder coating nozzle D112 overlap each other by at least a portion. Therefore, when painting is performed in both the first direction X1 and the second direction X2 (reciprocating painting), it is possible to paint almost the same area on the inner surface of the pipe P before and after switching between the first powder coating nozzle D111 and the second powder coating nozzle D112 when painting in the first direction X1 (forward painting) and when painting in the second direction X2 (return painting). Therefore, in order to achieve a nearly uniform coating film thickness along the directions of travel X1 and X2, it is not necessary (or the need is reduced) to adjust the relative movement positions of the first and second powder coating nozzles D111 and D112 in the directions of travel X1 and X2 before and after switching between the first and second powder coating nozzles D111 and D112. This simplifies the reciprocating coating process.

[0038] The first region PR1 and the second region PR2 only need to overlap each other in at least a portion on the inner surface of the pipe P, and the proportion of the overlapping region to the total overlapping region is not particularly limited. For example, for the purpose of coating the same region on the inner surface of the pipe P as much as possible before and after switching between the first powder coating nozzle D111 and the second powder coating nozzle D112, it is preferable that one of the first and second regions PR1 and PR2 is included in the other of the first and second regions PR1 and PR2 (in the example shown in Figure 4, the first region PR1 is included in the second region PR2). Furthermore, if a portion of the first region PR1 and a portion of the second region PR2 overlap each other, from the same viewpoint as above, the ratio of the area of ​​the overlapping region in the first and second regions PR1 and PR2 to the area of ​​the first and second regions PR1 and PR2 is preferably 7 / 10 or more, preferably 8 / 10 or more, and more preferably 9 / 10 or more.

[0039] The first dispensing device D1 is configured to dispense the first powder coating Dp1 over a predetermined range in the direction of the pipe axis X on the inner surface P11 of the receiving port P1 by moving the first dispensing section D11 relative to the first dispensing section D11 along the direction of the pipe axis X using the first drive device D13. However, the first dispensing device D1 does not necessarily have to be configured to move the first dispensing section D11 along the direction of the pipe axis X. For the purpose of dispensing the first powder coating Dp1 over a predetermined range in the direction of the pipe axis X, for example, the position of the first dispensing section D11 in the direction of the pipe axis X may be fixed and the pipe body P may be moved along the direction of the pipe axis X, or the dispensing section may be provided to extend over a predetermined range in the direction of the pipe axis X.

[0040] The first dispensing device D1 may be equipped with a known electrostatic coating device (not shown), such as a triboelectric coating device, for electrostatically coating the inner surface P11 of the receiving port P1 by charging the first powder coating Dp1. The electrostatic coating device includes, for example, a charging device (e.g., a coating gun) for charging the first powder coating Dp1. The first powder coating Dp1 is charged by the charging device and adheres to the inner surface P11 of the receiving port P1 by electrostatic force. By performing electrostatic powder coating with the first powder coating Dp1, the first dispensing device D1 can coat the inner surface P11 of the receiving port P1 more efficiently and uniformly.

[0041] The second dispensing device D2 is used to coat the inner surface P21 of the spit P2 and the inner surface P31 of the straight section P3 (the inner surface of the second section B) of the pipe body P with the second powder coating Dp2. For this purpose, the second dispensing device D2 is configured to dispense the second powder coating Dp2 from the inside of the spit P2 and the straight section P3 of the pipe body P toward the inner surface P21 of the spit P2 and the inner surface P31 of the straight section P3. As shown in Figure 2, the second discharge device D2 includes a second discharge section D21 (powder coating nozzle) that discharges the second powder coating Dp2 toward the inner surface P21 of the inlet P2 and the inner surface P31 of the straight pipe section P3, a second powder coating supply pipe D22 such as a lance that supplies the second powder coating Dp2 to the second discharge section D21, a second drive device D23 that moves the second discharge section D21 relative to the inlet P2 and the straight pipe section P3 over a predetermined range in the direction of the pipe axis X (for example, the entire length from the opening P22 to the stepped section P13), and a second powder coating supply device D24 that contains the second powder coating Dp2 and supplies the second powder coating Dp2 to the second powder coating supply pipe D22 and the second discharge section D21. The second discharge device D2 is configured such that the second discharge section D21 is moved relative to the spigot P2 and the straight pipe section P3 over a predetermined range in the X-axis direction of the pipe axis by the second drive device D23, thereby coating the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3 with the second powder coating Dp2 over a predetermined range in the X-axis direction of the pipe axis. However, the second discharge device D2 may also be used to coat the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3 of the pipe body P with the first powder coating Dp1, or it may be used to coat the inner surface P11 of the receiving end P1 of the pipe body P (the inner surface of the first pipe section A) with either the first or second powder coating Dp1 or Dp2.

[0042] The second discharge device D2 may be configured, similar to the first discharge device D1, to move the second discharge section D21 for discharging the second powder coating Dp2 relative to the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3 in both a first direction X1 (see Figure 2) along the pipe axis X direction from the receptacle P1 to the spigot P2 and a second direction X2 (see Figure 2) along the pipe axis X direction from the spigot P2 to the receptacle P1. In this case, the second discharge device D2 may be configured to discharge the second powder coating Dp2 from the second discharge section D21 while moving the second discharge section D21 relative to each of the first direction X1 and the second direction X2. The second discharge device D2 may paint the same location in the forward path (first direction X1) and the return path (second direction X2) (reciprocal painting), or it may paint different locations in the forward path and the return path (forward painting, return painting). The discharge angle and spread angle for discharging the second powder coating Dp2 from the second discharge section D21 are not particularly limited as long as the inner surface P21 of the inlet P2 and the inner surface P31 of the straight pipe section P3 can be painted with the second powder coating Dp2, and may be the same as or different from the discharge angle and spread angle of the first discharge device D1. Furthermore, the second discharge section D21 may also be equipped with a plurality of powder coating nozzles arranged such that they are inclined toward opposite directions of travel X1 and X2 to discharge the second powder coating Dp2, and the areas on the inner surface of the pipe P to which the discharged second powder coating Dp2 reaches overlap with each other.

[0043] The second discharge device D2 is configured to discharge the second powder coating Dp2 over a predetermined range in the direction of the pipe axis X on the inner surface P21 of the inlet P2 and the inner surface P31 of the straight pipe section P3 by moving the second discharge section D21 along the direction of the pipe axis X using the second drive device D23. However, the second discharge device D2 does not necessarily have to be configured to move the second discharge section D21 along the direction of the pipe axis X. For the purpose of discharging the second powder coating Dp2 over a predetermined range in the direction of the pipe axis X, for example, the position of the second discharge section D21 in the direction of the pipe axis X may be fixed and the pipe body P may be moved along the direction of the pipe axis X, or a powder coating nozzle may be provided so as to extend over a predetermined range in the direction of the pipe axis X.

[0044] Here, "powder coating" refers to a coating in powder form, and more specifically, a coating in powder form that does not contain organic solvents or water, and consists only of film-forming components. The first powder coating Dp1 and the second powder coating Dp2 used here are not particularly limited, and for example, known epoxy resin powder coatings that harden with heat after adhering to the inner surface of the pipe P can be used. The first powder coating Dp1 and the second powder coating Dp2 are not particularly limited and may be made of the same material or of different materials.

[0045] For example, epoxy resin powder coatings contain epoxy resin that is solid at room temperature, a hardening agent for epoxy resin, and various pigments and additives as needed.

[0046] Examples of epoxy resins include bisphenol-type epoxy resins such as bisphenol A-type epoxy resin and bisphenol F-type epoxy resin, naphthalene-type epoxy resin, biphenyl-type epoxy resin, novolac-type epoxy resin, cyclic aliphatic epoxy resin, glycidylamine-type resin, heterocyclic epoxy resin, and polyfunctional epoxy resin. Among these, bisphenol F-type epoxy resin, synthesized from bisphenol F and epichlorohydrin, is preferably used from a safety standpoint.

[0047] The curing agent is not particularly limited as long as it has the property of curing epoxy resin, but examples include amine compounds, amide compounds, imidazole compounds, imidazoline compounds, hydrazide compounds, acid anhydrides, phenolic resins and their derivatives. Among these, modified aromatic amine adducts mainly composed of aniline, imidazole / imidazoline compounds mainly composed of ethylenediamine and benzonitrile, hydrazides mainly composed of hydrazine and a dibase, and acid anhydrides mainly composed of trimellitic acid and ethylene glycol are preferably used from the viewpoint of corrosion resistance, flexibility, adhesion, and strength of the coating film.

[0048] Examples of coloring pigments include carbon black, titanium dioxide, iron oxide, and yellow iron oxide. Examples of extender pigments include barium sulfate, silica, and calcium carbonate.

[0049] The first powder coating Dp1 and the second powder coating Dp2 may be prepared such that, for example, the average particle size of the first powder coating Dp1 is smaller than the average particle size of the second powder coating Dp2. That is, the first powder coating Dp1 with a relatively small average particle size may be used to coat the inner surface P11 of the socket P1 (the inner surface of the first pipe section A), which has relatively large irregularities, and the second powder coating Dp2 with a relatively large average particle size may be used to coat the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3 (the inner surface of the second pipe section B), which have relatively small irregularities. By using the first powder coating Dp1 with a relatively small average particle size to coat the inner surface P11 of the socket P1, which has relatively large irregularities, the inner surface P11 of the socket P1, which has relatively large irregularities, can be coated more uniformly. This is thought to be because, when the relatively small first powder coating Dp1 is discharged from the discharge device, the first powder coating Dp1 is dispersed relatively uniformly, making it easier to penetrate into the corners of uneven surfaces. In contrast, by using the second powder coating Dp2 with a relatively large average particle size to coat the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3, which have relatively small uneven surfaces, the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3 can be efficiently coated. This is thought to be because, when the relatively large second powder coating Dp2 is discharged from the discharge device, the second powder coating Dp2 travels relatively straight towards the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3. This prevents it from floating inside the pipe body P or flowing out towards the openings P12 and P22 on both sides of the pipe body P, resulting in a good yield and adhesion to the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3.

[0050] The term "particle size" in relation to powder coatings is used in its usual sense, but for example, it refers to the diameter of a sphere if the particles constituting the powder coating were assumed to be spheres with the same volume as those particles. The average particle size of powder coatings can be measured using a known particle size measuring device.

[0051] The size of the first powder coating Dp1 and the second powder coating Dp2 is not particularly limited and can be appropriately selected according to the size of the irregularities on the inner surface of the pipe P to be coated. For example, the average particle size of the first powder coating Dp1 is preferably 20 to 50 μm. By setting the average particle size of the first powder coating Dp1 to 20 μm or more, the inner surface P11 of the socket P1 can be coated more efficiently. Also, by setting the average particle size of the first powder coating Dp1 to 50 μm or less, the inner surface P11 of the socket P1 can be coated more uniformly. Also, for example, the average particle size of the second powder coating Dp2 is preferably 70 to 80 μm. By setting the average particle size of the second powder coating Dp2 to 70 μm or more, the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3 can be coated more efficiently. Furthermore, by setting the average particle size of the second powder coating Dp2 to 80 μm or less, the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3 can be coated more uniformly.

[0052] The first powder coating Dp1 only needs to have the property of hardening with heat after adhering to the inner surface of the pipe P, and is not particularly limited, but it is preferable that it be prepared so that the gel time at 170°C is in the range of 90 to 250 seconds. By having a gel time of 90 seconds or more for the first powder coating Dp1, the inner surface P11 of the socket P1 can be coated more uniformly. This is thought to be because the longer the time it takes for the first powder coating Dp1 to harden, the easier it is for the first powder coating Dp1 to penetrate into the corners of the unevenness on the inner surface P11 of the socket P1. From a similar viewpoint, it is more preferable that the gel time of the first powder coating Dp1 be 135 seconds or more, and even more preferable that it be 180 seconds or more. Furthermore, by having a gel time of 250 seconds or less for the first powder coating Dp1, the coating efficiency is increased and the uniformity of the coating film is improved. From a similar viewpoint, the gel time of the first powder coating Dp1 is more preferably 235 seconds or less, and even more preferably 220 seconds or less.

[0053] The second powder coating Dp2 only needs to have the property of hardening with heat after adhering to the inner surface of the pipe P, and is not particularly limited, but it is preferable that it be prepared so that the gel time at 170°C is in the range of 50 to 250 seconds. A gel time of 50 to 250 seconds for the second powder coating Dp2 improves coating efficiency and the uniformity of the coating film. From a similar viewpoint, the gel time of the second powder coating Dp2 is more preferably 70 to 235 seconds or less, and even more preferably 90 to 220 seconds or less.

[0054] Gel time generally refers to the time it takes for a specified amount of powder coating to become undeformable under specified conditions after melting. For example, gel time can be determined by placing 2g of powder coating on a hot plate heated to 170°C and melting it. At this time, a metal rod is used to pull up a portion of the coating 10cm and check for stringiness. The time until the coating stops stringing and breaks at 10cm or less is determined. Furthermore, gel time can be controlled by the type and amount of hardener, the degree of polymerization of the epoxy resin, etc.

[0055] As described above, in the coating apparatus PD, for example, by using a first powder coating Dp1 with a relatively small average particle size to coat the inner surface P11 of the socket P1 which has relatively large irregularities, and a second powder coating Dp2 with a relatively large average particle size to coat the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3 which have relatively small irregularities, the inner surface of the pipe P can be coated more efficiently and uniformly. Furthermore, by adjusting the discharge angle of the powder coating as described above, and / or by adjusting the gel time of the powder coating as described above, the inner surface of the pipe P can be coated more efficiently and uniformly. Furthermore, in order to efficiently and uniformly coat the inner surface of the pipe body P, it is not only necessary to make the average particle size of the first powder coating Dp1 smaller than that of the second powder coating Dp2, but also, regardless of the difference in the average particle sizes of the first powder coating Dp1 and the second powder coating Dp2, the inner surface of the pipe body P can be efficiently and uniformly coated by adjusting the discharge angle of the powder coating as described above, and / or by adjusting the gel time of the powder coating as described above.

[0056] Next, powder coating nozzles 1, 2, 3, and 4 according to the first to fourth embodiments of the present invention will be described with reference to Figures 5 to 8. Figures 5 to 8 each illustrate powder coating nozzles 1, 2, 3, and 4 according to the first to fourth embodiments. Powder coating nozzles 1, 2, 3, and 4 of these embodiments can be suitably used as the first discharge section D11 and the second discharge section D21 of the coating apparatus PD described above, and in particular can be suitably used as the first discharge section D11 for coating the inner surface P11 of the receiving opening P1 of the pipe body P, which has relatively large irregularities. However, the powder coating nozzles of the present invention are not limited to the coating apparatus PD described above, and can be applied to other known powder coating apparatuses.

[0057] The powder coating nozzles 1, 2, 3, and 4 of the first to fourth embodiments are nozzles that discharge powder coating toward a coating object while moving relative to the coating object along the direction of travel. Here, the term "coating object" means an object that can be coated while the powder coating nozzle moves relative to the coating object along the direction of travel, and is not particularly limited. For example, the inner surface of the pipe P (for example, a known ductile cast iron pipe) described above, in particular the inner surface P11 of the socket P1 of the pipe P, is an example. The term "direction of travel" means the direction of relative movement with respect to the coating object, and is not particularly limited. For example, the direction along the pipe axis X direction of the pipe P, in particular the first direction X1 from the socket P1 toward the insertion port P2 along the pipe axis X direction (see Figure 3(a)) and the second direction X2 from the insertion port P2 toward the socket P1 along the pipe axis X direction (see Figure 3(b)). Furthermore, the term "powder coating" is synonymous with the powder coating described above and is not particularly limited; for example, the first powder coating Dp1 and the second powder coating Dp2, and especially the first powder coating Dp1, are given as examples. Also, the term "relative movement" is a concept that includes both the movement of the powder coating nozzle relative to the object to be coated and the movement of the object to be coated relative to the powder coating nozzle. In the following, the object to be coated is the inner surface P11 of the socket P1 of the pipe P, the direction of travel is the first and second directions X1 and X2 along the pipe axis X, and the powder coating nozzles 1, 2, 3, and 4 are described assuming that the powder coating nozzles move relative to the object to be coated.

[0058] The powder coating nozzles 1, 2, 3, and 4 of the first to fourth embodiments are all equipped with a plurality of discharge ports 12, 13, 22, 23, 32, 33, 34, 42, 43, and 44 that are inclined toward the first and second directions X1 and X2, which are the directions of travel, as shown in Figures 5 to 8. More specifically, the powder coating nozzles 1, 2, 3, and 4 are each equipped with a plurality of discharge ports 12, 13, 22, 23, 32, 33, 34, 42, 43, and 44 such that the angle between the discharge direction from which the powder coating is discharged and the directions of travel X1 and X2 is acute. As described above, the inclination of the discharge ports 12, 13, 22, 23, 32, 33, 34, 42, 43, and 44 toward the directions of travel X1 and X2 allows for more uniform coating of the inner surface P11 of the receiving opening P1, which has large irregularities. Furthermore, the powder coating nozzles 1, 2, 3, and 4 have multiple discharge ports 12, 13, 22, 23, 32, 33, 34, 42, 43, and 44 that are inclined toward the directions of travel X1 and X2, allowing the powder coating to be discharged in a dispersed manner, thereby enabling more uniform coating of the inner surface P11 of the receiving opening P1, which has large irregularities.

[0059] Next, the powder coating nozzles 1, 2, 3, and 4 of the first to fourth embodiments will be described with reference to Figures 5 to 8. The powder coating nozzle 1 of the first embodiment can be used to discharge powder coating toward the inner surface P11 of the receiving opening P1 of the pipe P while moving in a first direction X1 relative to the inner surface P11 of the receiving opening P1 of the pipe P (see Figure 3(a)). The powder coating nozzle 1 has a plurality of discharge ports 12, 13 that are inclined toward the first direction X1, which is the direction of travel, as shown in Figure 5. The plurality of discharge ports 12, 13 are arranged to discharge the powder coating in a dispersed manner along the first direction X1. For this purpose, each of the plurality of discharge ports 12, 13 has a powder coating discharge angle θ3, θ4 which is different from the angle with respect to the first direction X1. The powder coating nozzle 1 is equipped with multiple discharge ports 12 and 13, each having different discharge angles θ3 and θ4 with respect to a first direction X1, thereby enabling more uniform discharge of powder coating along the first direction X1. For example, if a powder coating nozzle has only one discharge port, the powder coating will be unevenly distributed within the discharge port, which is inclined toward the direction of travel, resulting in uneven discharge of powder coating. In contrast, in this embodiment, the powder coating nozzle 1 is equipped with multiple discharge ports 12 and 13, each having different discharge angles θ3 and θ4 with respect to a first direction X1, so that the multiple discharge ports 12 and 13 disperse the powder coating along the first direction X1. This allows for more uniform discharge of powder coating in the first direction X1, and thus more uniform coating of the inner surface P11 of the receiving port P1 of the pipe P.

[0060] In this embodiment, the powder coating nozzle 1, as shown in Figure 5, comprises an inlet 11 into which the powder coating flows and a plurality of outlets 12 and 13 for discharging the powder coating. The inlet 11 is formed to extend from a proximal end 11a to a distal end 11b. At its proximal end 11a, the inlet 11 communicates with the first powder coating supply pipe D12 of the first discharge device D1 of the coating apparatus PD described above, and the first powder coating Dp1 is supplied from the first powder coating supply pipe D12 (see Figure 2). The inlet 11 also communicates with the plurality of outlets 12 and 13 at its distal end 11b, and supplies the first powder coating Dp1 supplied from the first powder coating supply pipe D12 to the plurality of outlets 12 and 13. The inlet 11 is not particularly limited as long as it can supply the supplied powder coating to the discharge ports 12 and 13, but in the illustrated example, it extends from the proximal end 11a to the distal end 11b along the pipe axis X direction, i.e., the first direction X1, and is formed to have a substantially constant inner diameter along its entire length.

[0061] The multiple discharge ports 12 and 13 are formed to extend from proximal ends 12a and 13a to distal ends 12b and 13b, as shown in Figure 5. The multiple discharge ports 12 and 13 communicate with the inlet 11 at their proximal ends 12a and 13a, and the first powder coating Dp1 is supplied from the inlet 11. The multiple discharge ports 12 and 13 also open at their distal ends 12b and 13b, and discharge the first powder coating Dp1 supplied from the inlet 11 toward the inner surface P11 of the receiving opening P1 of the pipe body P. The multiple discharge ports 12 and 13 are formed to branch from the distal end 11b of one inlet 11 and have approximately equal inner diameters. This allows the multiple discharge ports 12 and 13 to discharge powder coating at approximately equal discharge volumes. Furthermore, each of the multiple discharge ports 12 and 13 is provided to extend at an inclination (at discharge angles θ3 and θ4) with respect to the inlet 11 which extends along the pipe axis X direction. When the discharge ports are inclined with respect to the inlet in this way, a large amount of powder coating flows outwards within the flow path at the connection point between the inlet and the discharge port, causing unevenness in the amount of powder coating discharged in the direction of travel. However, as in this embodiment, by providing multiple discharge ports 12 and 13 that are inclined at different angles, unevenness in the amount of powder coating discharged in the first direction X1 can be suppressed, and the powder coating can be discharged more uniformly. As a result, the inner surface P11 of the receiving opening P1 of the pipe body P can be coated more uniformly.

[0062] The multiple discharge ports 12 and 13, as shown in Figure 5, include a first discharge port 12 that discharges powder coating at a third discharge angle θ3 with respect to a first direction X1, and a second discharge port 13 that discharges powder coating at a fourth discharge angle θ4 with respect to the first direction X1. The first and second discharge ports 12 and 13 are provided so as to branch from both ends of the inlet 11 in a direction substantially perpendicular to the respective discharge direction and the first direction X1 (left and right direction in Figure 5(a)). The third and fourth discharge angles θ3 and θ4 are both acute angles and are set to be different from each other. In this embodiment, the powder coating nozzle 1 has two discharge ports 12 and 13, but it may have three or more discharge ports.

[0063] The third and fourth discharge angles θ3 and θ4 are not particularly limited, but it is preferable that they have an average value greater than the average value of the fifth and sixth discharge angles θ5 and θ6, which will be described later. This allows for more uniform coating of the inner surface P11 of the socket P1 of the pipe body P, as described above in relation to the painting apparatus PD. The third and fourth discharge angles θ3 and θ4 are preferably set within a range such that the flow of powder coating discharged from the first and second discharge ports 12 and 13 overlap each other in the first direction X1. For example, the third discharge angle θ3 is preferably in the range of 50 to 70°, more preferably in the range of 55 to 65°, and even more preferably in the range of 58 to 62°, from the viewpoint of further uniform coating of the inner surface P11 of the socket P1 of the pipe body P. Furthermore, the fourth discharge angle θ4 is preferably in the range of 60 to 80°, more preferably in the range of 65 to 75°, and even more preferably in the range of 68 to 72°, from the viewpoint of more uniformly coating the inner surface P11 of the receiving opening P1 of the pipe body P.

[0064] The powder coating nozzle 1 of the first embodiment can be used in combination with the powder coating nozzles 2 and 4 of the second and fourth embodiments, which can be used as the first powder coating nozzle D111 as described in relation to Figure 4, and as the second powder coating nozzle D112.

[0065] The powder coating nozzle 2 of the second embodiment can be used to discharge powder coating toward the inner surface P11 of the receiving opening P1 of the pipe P while moving in a second direction X2 relative to the inner surface P11 of the receiving opening P1 of the pipe P (see Figure 3(b)). The powder coating nozzle 2 has a plurality of discharge ports 22, 23 that are inclined toward the second direction X2, which is the direction of travel, as shown in Figure 6. The plurality of discharge ports 22, 23 are arranged to discharge the powder coating in a dispersed manner along the second direction X2. To this end, each of the plurality of discharge ports 22, 23 has a powder coating discharge angle θ5, θ6 that is different from the other with respect to the second direction X2. By having a plurality of discharge ports 22, 23 with different discharge angles θ5, θ6 relative to the second direction X2, the powder coating nozzle 2 can discharge the powder coating more uniformly along the second direction X2. For example, if a powder coating nozzle has only one discharge port, the powder coating will be unevenly distributed within the discharge port, which is inclined toward the direction of travel, resulting in an uneven discharge of powder coating. In contrast, in this embodiment, the powder coating nozzle 2 has multiple discharge ports 22, 23 with discharge angles θ5, θ6 with respect to the second direction X2 that are different from each other. As a result, the multiple discharge ports 22, 23 disperse the powder coating along the second direction X2, allowing for more uniform discharge of powder coating in the second direction X2 and more uniform coating of the inner surface P11 of the receiving port P1 of the pipe body P.

[0066] In this embodiment, the powder coating nozzle 2, as shown in Figure 6, comprises an inlet 21 into which the powder coating flows and a plurality of outlets 22 and 23 for discharging the powder coating. The inlet 21 is formed to extend from a proximal end 21a to a distal end 21b. At its proximal end 21a, the inlet 21 communicates with the first powder coating supply pipe D12 of the first discharge device D1 of the coating apparatus PD described above, and the first powder coating Dp1 is supplied from the first powder coating supply pipe D12 (see Figure 2). The inlet 21 also communicates with the plurality of outlets 22 and 23 at its distal end 21b, and supplies the first powder coating Dp1 supplied from the first powder coating supply pipe D12 to the plurality of outlets 22 and 23. The inlet 21 is not particularly limited as long as it can supply the supplied powder coating to the discharge ports 22 and 23, but in the illustrated example, it extends from the proximal end 21a to the distal end 21b along the pipe axis X direction, i.e., the second direction X2, and is formed to have a substantially constant inner diameter along its entire length.

[0067] The multiple discharge ports 22 and 23 are formed to extend from proximal ends 22a and 23a to distal ends 22b and 23b, as shown in Figure 6. The multiple discharge ports 22 and 23 communicate with the inlet 21 at their proximal ends 22a and 23a, and the first powder coating Dp1 is supplied from the inlet 21. The multiple discharge ports 22 and 23 also open at their distal ends 22b and 23b, and discharge the first powder coating Dp1 supplied from the inlet 21 toward the inner surface P11 of the receiving port P1 of the pipe body P. The multiple discharge ports 22 and 23 are formed to branch from the distal end 21b of one inlet 21 and have approximately equal inner diameters. This allows the multiple discharge ports 22 and 23 to discharge powder coating at approximately equal discharge volumes. Furthermore, each of the multiple discharge ports 22 and 23 is provided to extend at an inclination (at discharge angles θ5 and θ6) with respect to the inlet 21 which extends along the pipe axis X direction. When the discharge ports are inclined with respect to the inlet in this way, a large amount of powder coating flows outwards within the flow path at the connection point between the inlet and the discharge port, causing unevenness in the amount of powder coating discharged in the direction of travel. However, as in this embodiment, by providing multiple discharge ports 22 and 23 that are inclined at different angles, unevenness in the amount of powder coating discharged in the second direction X2 can be suppressed, and the powder coating can be discharged more uniformly. As a result, the inner surface P11 of the receiving opening P1 of the pipe body P can be coated more uniformly.

[0068] The multiple discharge ports 22 and 23, as shown in Figure 6, include a first discharge port 22 that discharges powder coating at a fifth discharge angle θ5 with respect to a second direction X2, and a second discharge port 23 that discharges powder coating at a sixth discharge angle θ6 with respect to the second direction X2. The first and second discharge ports 22 and 23 are provided so as to branch from both ends of the inlet 21 in a direction substantially perpendicular to the respective discharge direction and the second direction X2 (left and right direction in Figure 6(a)). The fifth and sixth discharge angles θ5 and θ6 are both acute angles and are set to be different from each other. In this embodiment, the powder coating nozzle 2 has two discharge ports 22 and 23, but it may have three or more discharge ports.

[0069] The fifth and sixth discharge angles θ5 and θ6 are not particularly limited, but it is preferable that they have an average value smaller than the average value of the third and fourth discharge angles θ3 and θ4 described above. This allows for more uniform coating of the inner surface P11 of the socket P1 of the pipe P, as described above in relation to the painting apparatus PD. The fifth and sixth discharge angles θ5 and θ6 are preferably set within a range such that the flow of powder coating discharged from the first and second discharge ports 22 and 23 overlap each other in the second direction X2. For example, the fifth discharge angle θ5 is preferably in the range of 52 to 72°, more preferably in the range of 57 to 67°, and even more preferably in the range of 60 to 64°, from the viewpoint of further uniform coating of the inner surface P11 of the socket P1 of the pipe P. Furthermore, the sixth discharge angle θ6 is preferably in the range of 42 to 62°, more preferably in the range of 47 to 57°, and even more preferably in the range of 50 to 54°, from the viewpoint of more uniformly coating the inner surface P11 of the receiving opening P1 of the pipe body P.

[0070] The powder coating nozzle 2 of the second embodiment can be used in combination with the powder coating nozzles 1 and 3 of the first and third embodiments, which can be used as the first powder coating nozzle D111, as the second powder coating nozzle D112 as described in relation to Figure 4.

[0071] The powder coating nozzle 3 of the third embodiment can be used to discharge powder coating toward the inner surface P11 of the receiving opening P1 of the pipe P while moving in a first direction X1 relative to the inner surface P11 of the receiving opening P1 of the pipe P (see Figure 3(a)). The powder coating nozzle 3 has a plurality of discharge ports 32, 33, 34 that are inclined toward the first direction X1, which is the direction of travel, as shown in Figure 7. The plurality of discharge ports 32, 33, 34 are arranged to disperse the powder coating along the first direction X1. For this purpose, each of the plurality of discharge ports 32, 33, 34 is arranged in a line along the first direction X1. Preferably, the inner diameter of each of the plurality of discharge ports 32, 33, 34 is set such that the amount of powder coating discharged from each of the plurality of discharge ports 32, 33, 34 is approximately equal. The powder coating nozzle 3 has discharge ports 32, 33, and 34 arranged along a first direction X1 so that the discharge amounts of powder coating are approximately equal. This allows for more uniform discharge of powder coating along the first direction X1, and thus more uniform coating of the inner surface P11 of the receiving port P1 of the pipe P. Each of the multiple discharge ports 32, 33, and 34 may have different inner diameters from each other in order to ensure that the discharge amounts of powder coating are approximately equal.

[0072] In this embodiment, the powder coating nozzle 3, as shown in Figure 7, comprises an inlet 31 into which the powder coating flows and a plurality of outlets 32, 33, and 34 for discharging the powder coating. The inlet 31 is formed to extend from a proximal end 31a to a distal end 31b. At its proximal end 31a, the inlet 31 communicates with the first powder coating supply pipe D12 of the first discharge device D1 of the coating apparatus PD described above, and the first powder coating Dp1 is supplied from the first powder coating supply pipe D12 (see Figure 2). The inlet 31 also communicates with a plurality of outlets 32, 33, and 34 arranged along a first direction X1 in the flow path from the proximal end 31a to the distal end 31b, and supplies the first powder coating Dp1 supplied from the first powder coating supply pipe D12 to the plurality of outlets 32, 33, and 34. The inlet 31 is not particularly limited as long as it can supply the supplied powder coating to the discharge ports 32, 33, and 34. However, in the illustrated example, it extends along the pipe axis X direction, i.e., the first direction X1, and is formed so that its inner diameter decreases from the proximal end 31a to the distal end 31b (continuously decreasing in the illustrated example). This allows the amount of powder coating reaching each position from the proximal end 31a to the distal end 31b to decrease as the distance from the proximal end 31a increases. For example, if multiple discharge ports are branched along the direction in which an inlet with a constant inner diameter extends, the amount of powder coating supplied to the discharge ports on the distal end side will be greater than that on the proximal end side. However, by setting the inlet 31 as in this embodiment so that the amount of powder coating reaching it decreases as the distance from the proximal end 31a increases, a more uniform or substantially uniform amount of powder coating can be supplied to the multiple discharge ports 32, 33, and 34.

[0073] The multiple discharge ports 32, 33, and 34 are each formed to extend from proximal ends 32a, 33a, and 34a to distal ends 32b, 33b, and 34b, as shown in Figure 7. The multiple discharge ports 32, 33, and 34 communicate with the inlet 31 at their proximal ends 32a, 33a, and 34a, and the first powder coating Dp1 is supplied from the inlet 31. The multiple discharge ports 32, 33, and 34 also open at their distal ends 32b, 33b, and 34b, and discharge the first powder coating Dp1 supplied from the inlet 31 toward the inner surface P11 of the receiving opening P1 of the pipe body P. The multiple discharge ports 32, 33, and 34 are arranged along a first direction X1, branching off from a single inlet 31. Multiple discharge ports 32, 33, and 34 are arranged in a line from the proximal end 31a to the distal end 31b of the inlet 31. The inner diameter of each discharge port 32, 33, and 34 decreases from the proximal end 31a to the distal end 31b of the inlet 31. As a result, the discharge port closer to the proximal end 31a of the inlet 31 has a larger allowable capacity for powder coating, while the discharge port closer to the distal end 31b of the inlet 31 has a smaller allowable capacity for powder coating. As described above, when multiple discharge ports are branched along the direction in which the inlet extends, the discharge ports on the distal end side will supply more powder coating than those on the proximal end side. However, as in this embodiment, by increasing the inner diameter of the discharge port closer to the proximal end 31a of the inlet 31 and decreasing the inner diameter of the discharge port closer to the distal end 31b of the inlet 31, a more uniform or nearly uniform amount of powder coating can be supplied to the multiple discharge ports 32, 33, and 34. As a result, the powder coating can be discharged more uniformly in the first direction X1, and the inner surface P11 of the receiving end P1 of the pipe body P can be coated more uniformly.

[0074] The multiple discharge ports 32, 33, and 34, as shown in Figure 7, include a first discharge port 32 that discharges powder coating at a seventh discharge angle θ7 with respect to a first direction X1, a second discharge port 33 that discharges powder coating at a seventh discharge angle θ7 with respect to a first direction X1, and a third discharge port 34 that discharges powder coating at a seventh discharge angle θ7 with respect to a first direction X1. The first, second, and third discharge ports 32, 33, and 34 are arranged in order along the first direction X1 from the distal end 31b to the proximal end 31a of the inlet 31. Preferably, the first, second, and third discharge ports 32, 33, and 34 are arranged in close proximity to each other such that the flow of powder coating discharged from adjacent discharge ports overlaps with each other in the first direction X1. Furthermore, the first, second, and third discharge ports 32, 33, and 34 are formed such that the inner diameter of the second discharge port 33 is larger than the inner diameter of the first discharge port 32, and the inner diameter of the third discharge port 34 is larger than the inner diameter of the second discharge port 33. The inner diameters of the first, second, and third discharge ports 32, 33, and 34 can be set to, for example, 2 mm, 3 mm, and 4 mm. In this embodiment, the multiple discharge ports 32, 33, and 34 all have the same acute seventh discharge angle θ7, but they may have different discharge angles. Also, in this embodiment, the powder coating nozzle 3 has three discharge ports 32, 33, and 34, but it may have two or more discharge ports.

[0075] The seventh discharge angle θ7 is not particularly limited, but is preferably larger than the eighth discharge angle θ8, which will be described later. This allows for more uniform coating of the inner surface P11 of the socket P1 of the pipe P, as described above in relation to the painting apparatus PD. From the viewpoint of further uniform coating of the inner surface P11 of the socket P1 of the pipe P, the seventh discharge angle θ7 is preferably in the range of 50 to 80°, more preferably in the range of 60 to 70°, and even more preferably in the range of 60 to 65°.

[0076] The powder coating nozzle 3 of the third embodiment can be used in combination with the powder coating nozzles 2 and 4 of the second and fourth embodiments, which can be used as the first powder coating nozzle D111 as described in relation to Figure 4, and as the second powder coating nozzle D112.

[0077] The powder coating nozzle 4 of the fourth embodiment can be used to discharge powder coating toward the inner surface P11 of the receiving opening P1 of the pipe P while moving in a second direction X2 relative to the inner surface P11 of the receiving opening P1 of the pipe P (see Figure 3(b)). The powder coating nozzle 4 has a plurality of discharge ports 42, 43, 44 that are inclined toward the second direction X2, which is the direction of travel, as shown in Figure 8. The plurality of discharge ports 42, 43, 44 are arranged to disperse the powder coating along the second direction X2. For this purpose, each of the plurality of discharge ports 42, 43, 44 is arranged in a line along the second direction X2. Preferably, the inner diameter of each of the plurality of discharge ports 42, 43, 44 is set such that the amount of powder coating discharged from each of the plurality of discharge ports 42, 43, 44 is approximately equal. The powder coating nozzle 4 has discharge ports 42, 43, and 44 arranged along the second direction X2 so that the discharge amounts of the powder coating are approximately equal. This allows for more uniform discharge of the powder coating along the second direction X2, and thus more uniform coating of the inner surface P11 of the receiving port P1 of the pipe P. Each of the multiple discharge ports 42, 43, and 44 may have different inner diameters from each other in order to ensure that the discharge amounts of the powder coating are approximately equal.

[0078] In this embodiment, the powder coating nozzle 4, as shown in Figure 8, comprises an inlet 41 into which the powder coating flows and a plurality of outlets 42, 43, and 44 for discharging the powder coating. The inlet 41 is formed to extend from a proximal end 41a to a distal end 41b. At its proximal end 41a, the inlet 41 communicates with the first powder coating supply pipe D12 of the first discharge device D1 of the coating apparatus PD described above, and the first powder coating Dp1 is supplied from the first powder coating supply pipe D12 (see Figure 2). The inlet 41 also communicates with a plurality of outlets 42, 43, and 44 arranged along the second direction X2 in the flow path from the proximal end 41a to the distal end 41b, and supplies the first powder coating Dp1 supplied from the first powder coating supply pipe D12 to the plurality of outlets 42, 43, and 44. The inlet 41 is not particularly limited as long as it can supply the supplied powder coating to the discharge ports 42, 43, and 44. However, in the illustrated example, it extends along the pipe axis X direction, i.e., the second direction X2, and is formed so that its inner diameter decreases from the proximal end 41a to the distal end 41b (continuously decreasing in the illustrated example). This allows the amount of powder coating reaching each position from the proximal end 41a to the distal end 41b to decrease as the distance from the proximal end 41a increases. For example, if multiple discharge ports are branched along the direction in which an inlet with a constant inner diameter extends, the amount of powder coating supplied to the discharge ports on the distal end side will be greater than that on the proximal end side. However, by setting the inlet 41 as in this embodiment so that the amount of powder coating reaching it decreases as the distance from the proximal end 41a increases, a more uniform or substantially uniform amount of powder coating can be supplied to the multiple discharge ports 42, 43, and 44.

[0079] The multiple discharge ports 42, 43, and 44 are each formed to extend from proximal ends 42a, 43a, and 44a to distal ends 42b, 43b, and 44b, as shown in Figure 8. The multiple discharge ports 42, 43, and 44 communicate with the inlet 41 at their proximal ends 42a, 43a, and 44a, and the first powder coating Dp1 is supplied from the inlet 41. The multiple discharge ports 42, 43, and 44 also open at their distal ends 42b, 43b, and 44b, and discharge the first powder coating Dp1 supplied from the inlet 41 toward the inner surface P11 of the receiving opening P1 of the pipe body P. The multiple discharge ports 42, 43, and 44 are arranged along a second direction X2, branching off from a single inlet 41. Multiple discharge ports 42, 43, and 44 are arranged in a line from the proximal end 41a to the distal end 41b of the inlet 41. The inner diameter of each discharge port 42, 43, and 44 decreases from the proximal end 41a to the distal end 41b of the inlet 41. As a result, the discharge ports closer to the proximal end 41a of the inlet 41 have a larger allowable capacity for powder coating, while the discharge ports closer to the distal end 41b of the inlet 41 have a smaller allowable capacity for powder coating. As described above, when multiple discharge ports are branched along the direction in which the inlet extends, the discharge ports on the distal end side will supply more powder coating than those on the proximal end side. However, as in this embodiment, by increasing the inner diameter of the discharge port closer to the proximal end 41a of the inlet 41 and decreasing the inner diameter of the discharge port closer to the distal end 41b of the inlet 41, a more uniform or nearly uniform amount of powder coating can be supplied to the multiple discharge ports 42, 43, and 44. As a result, the powder coating can be discharged more uniformly in the second direction X2, and the inner surface P11 of the receiving end P1 of the pipe body P can be coated more uniformly.

[0080] The multiple discharge ports 42, 43, and 44, as shown in Figure 8, include a first discharge port 42 that discharges powder coating at an eighth discharge angle θ8 with respect to a second direction X2, a second discharge port 43 that discharges powder coating at an eighth discharge angle θ8 with respect to a second direction X2, and a third discharge port 44 that discharges powder coating at an eighth discharge angle θ8 with respect to a second direction X2. The first, second, and third discharge ports 42, 43, and 44 are arranged in order along the second direction X2 from the distal end 41b to the proximal end 41a of the inlet 41. Preferably, the first, second, and third discharge ports 42, 43, and 44 are arranged in close proximity to each other such that the flow of powder coating discharged from adjacent discharge ports overlaps with each other in the second direction X2. Furthermore, the first, second, and third discharge ports 42, 43, and 44 are formed such that the inner diameter of the second discharge port 43 is larger than the inner diameter of the first discharge port 42, and the inner diameter of the third discharge port 44 is larger than the inner diameter of the second discharge port 43. The inner diameters of the first, second, and third discharge ports 42, 43, and 44 can be set to, for example, 2 mm, 3 mm, and 4 mm. In this embodiment, the multiple discharge ports 42, 43, and 44 all have the same acute eighth discharge angle θ8, but they may have different discharge angles. Also, in this embodiment, the powder coating nozzle 4 has three discharge ports 42, 43, and 44, but it may have two or four or more discharge ports.

[0081] The eighth discharge angle θ8 is not particularly limited, but is preferably smaller than the seventh discharge angle θ7 described above. This allows for more uniform coating of the inner surface P11 of the socket P1 of the pipe P, as described above in relation to the painting apparatus PD. From the viewpoint of further uniform coating of the inner surface P11 of the socket P1 of the pipe P, the eighth discharge angle θ8 is preferably in the range of 40 to 70°, more preferably in the range of 45 to 60°, and even more preferably in the range of 50 to 55°.

[0082] The powder coating nozzle 4 of the fourth embodiment can be used in combination with the powder coating nozzles 1 and 3 of the first and third embodiments, which can be used as the first powder coating nozzle D111, as the second powder coating nozzle D112 as described in relation to Figure 4.

[0083] Next, a painting method using the powder coating nozzle of the present invention will be described. In the following, the painting method will be described using as an example a method in which the inner surface of a pipe body P is painted using the painting apparatus PD, with the powder coating nozzle of several embodiments used as the first discharge section D11 of the painting apparatus PD described above. However, the painting method of the present invention may be carried out using a painting apparatus having a different structure, as long as it is possible to achieve the same effects as those described below. In addition, although several steps and procedures will be described below, the steps and procedures may be carried out in an order different from the order of description, and several steps and procedures may be carried out simultaneously.

[0084] As shown in Figure 2, the painting method of this embodiment includes the steps of painting the inner surface P11 of the socket P1 (the inner surface of the first pipe section A) with a first powder coating Dp1, and painting the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3 (the inner surface of the second pipe section B) with a second powder coating Dp2.

[0085] In the step of coating the inner surface P11 of the socket P1 with the first powder coating Dp1, the pipe body P is first heated to a predetermined temperature. The heating temperature of the pipe body P is set to a temperature at which the first powder coating Dp1 hardens through the heat transferred when the first powder coating Dp1 comes into contact with or adheres to the inner surface P11 of the socket P1 (for example, 150°C or higher). In this embodiment, the pipe body P, which has been preheated by a heating device, is mounted on a rotating device R. However, the pipe body P only needs to be heated at least when the first powder coating Dp1 comes into contact with or adheres to the inner surface P11 of the socket P1, and may be heated after the pipe body P is mounted on the rotating device R, for example. Furthermore, the timing of heating the pipe body P in this step may be the same as the timing of heating the pipe body P in the step of coating the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3 with the second powder coating Dp2, which will be described in detail later.

[0086] Next, the first powder coating Dp1 is sprayed onto the inner surface P11 of the socket P1 of the pipe body P in a predetermined circumferential range (for example, the entire length) and a predetermined range in the pipe axis X direction (for example, the entire length from the opening P12 to the stepped portion P13). In this embodiment, the first powder coating Dp1 is sprayed onto the inner surface P11 of the socket P1 by being discharged from the inside of the socket P1 towards the inner surface P11 of the socket P1 by the first discharge device D1. At this time, since the pipe body P has been heated to a predetermined temperature in advance, the first powder coating Dp1 that comes into contact with or adheres to the inner surface P11 of the socket P1 hardens on the inner surface P11 of the socket P1 through the heat that is transmitted and is deposited on the inner surface P11 of the socket P1. When the first powder coating Dp1 is discharged by the first discharge device D1, the pipe P is rotated relative to it by the rotating device R around the pipe axis X, causing the first powder coating Dp1 to accumulate over a predetermined circumferential range on the inner surface P11 of the receiving opening P1. Furthermore, when the first discharge section D11 of the first discharge device D1 is moved relative to the receiving opening P1 along the direction of the pipe axis X, the first powder coating Dp1 accumulates over a predetermined range on the inner surface P11 of the receiving opening P1 in the direction of the pipe axis X.

[0087] The discharge speed and discharge amount of the first powder coating Dp1 discharged toward the inner surface P11 of the socket P1 of the pipe body P are not particularly limited and can be set appropriately according to the required coating thickness. The relative rotation speed of the pipe body P and the relative movement speed of the first discharge section D11 of the first discharge device D1 are also not particularly limited and can be set appropriately according to the required film thickness.

[0088] The step of coating the inner surface P11 of the socket P1 with the first powder coating Dp1 may include, as shown in Figures 3(a) and (b), moving the first discharge part D11 that discharges the first powder coating Dp1 relative to the inner surface P11 of the socket P1 in a first direction X1 toward the socket P2 along the pipe axis X, and discharging the first powder coating Dp1 from the first discharge part D11 at a first discharge angle θ1 with respect to the first direction X1, and moving the first discharge part D11 that discharges the first powder coating Dp1 relative to the inner surface P11 of the socket P1 in a second direction X2 toward the socket P1 along the pipe axis X, and discharging the first powder coating Dp1 from the first discharge part D11 at a second discharge angle θ2 with respect to the second direction X2. In this case, by using the powder coating nozzles 1 and 3 described above as the first discharge nozzle D11 that moves relative to the first direction X1, and / or by using the powder coating nozzles 3 and 4 described above as the first discharge nozzle D11 that moves relative to the second direction X1, the inner surface P11 of the receiving port P1 can be coated more uniformly. Here, the same location may be coated in the forward path (first direction X1) and the return path (second direction X2) (reciprocating coating), or different locations may be coated in the forward path and the return path (forward coating, return coating). In the case of reciprocating coating, as described in relation to Figure 4, the first discharge nozzle D11 is equipped with a plurality of powder coating nozzles D111 and D112 such that the regions PR1 and PR2 on the inner surface of the pipe P to which the first powder coating Dp1 reaches overlap each other, so that the same region on the inner surface of the pipe P can be coated before and after switching between the plurality of powder coating nozzles D111 and D112 in the forward and return paths. Therefore, in order to achieve a nearly uniform coating film thickness along the travel directions X1 and X2, it is not necessary (or the need is reduced) to adjust the relative movement positions of the multiple powder coating nozzles D111 and D112 before and after switching between them. This simplifies the process in reciprocating coating.

[0089] As described above, it is preferable that both the first discharge angle θ1 and the second discharge angle θ2 are acute angles. By having both the first discharge angle θ1 and the second discharge angle θ2 be acute angles, the inner surface P11 of the socket P1, which has relatively large irregularities, can be painted more uniformly. Furthermore, it is preferable that the angles of the first discharge angle θ1 and the second discharge angle θ2 are set such that the first discharge angle θ1 is larger than the second discharge angle θ2. By having the first discharge angle θ1 be larger than the second discharge angle θ2, the inner surface P11 of the socket P1, which has relatively large irregularities, can be painted more uniformly.

[0090] As described above, the first discharge angle θ1 is preferably in the range of 50 to 80°, more preferably in the range of 60 to 70°, and even more preferably in the range of 60 to 65°, from the viewpoint of more uniformly coating the inner surface P11 of the receiving port P1. Furthermore, when discharging the first powder coating Dp1, the first spreading angle α1 centered on the first discharge angle θ1 is preferably smaller than the second spreading angle α2, more preferably in the range of 10 to 30°, and even more preferably in the range of 15 to 25°, from the viewpoint of more uniformly coating the inner surface P11 of the receiving port P1.

[0091] As described above, the second discharge angle θ2 is preferably in the range of 40 to 70°, more preferably in the range of 45 to 60°, and even more preferably in the range of 50 to 55°, from the viewpoint of more uniformly coating the inner surface P11 of the receiving port P1. Furthermore, when discharging the first powder coating Dp1, the second spreading angle α2 centered on the second discharge angle θ2 is preferably larger than the first spreading angle α1, more preferably in the range of 30 to 50°, and even more preferably in the range of 40 to 50°, from the viewpoint of more uniformly coating the inner surface P11 of the receiving port P1.

[0092] In this embodiment, the first powder coating Dp1 is deposited over a predetermined range in the circumferential direction and the direction of the pipe axis X by rotating the pipe body P around the pipe axis X and moving the first discharge part D11 of the first discharge device D1 along the direction of the pipe axis X. However, the embodiment is not limited to this one, and the first powder coating Dp1 may be deposited over a predetermined range in the circumferential direction and the direction of the pipe axis X by other methods, such as rotating the first discharge part D11 of the first discharge device D1 around the pipe axis X and moving the pipe body P along the direction of the pipe axis X. Furthermore, the first powder coating Dp1 only needs to be deposited on at least a portion of the inner surface P11 of the receiving port P1, and for example, other powder coatings different from the first powder coating Dp1 may be deposited in portions other than the portion where the first powder coating Dp1 is deposited.

[0093] Finally, the pipe body P is cooled by natural cooling or other means, and the painting of the inner surface P11 of the socket P1 is completed. Note that the timing of cooling the pipe body P in this process may be the same as the timing of cooling the pipe body P in the process of painting the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3 with the second powder coating Dp2, which will be described in detail later.

[0094] As described above, the first powder coating Dp1 and the second powder coating Dp2 may be prepared such that, for example, the average particle size of the first powder coating Dp1 is smaller than the average particle size of the second powder coating Dp2. That is, in the coating method of this embodiment, the first powder coating Dp1 with a relatively small average particle size may be used to coat the inner surface P11 of the socket P1 (the inner surface of the first pipe section A) which has relatively large irregularities. By using the first powder coating Dp1 with a relatively small average particle size to coat the inner surface P11 of the socket P1 which has relatively large irregularities, the inner surface P11 of the socket P1 which has relatively large irregularities can be coated with a uniform thickness compared to the case where the second powder coating Dp2 with a relatively large average particle size is used. This is thought to be because, when the relatively small first powder coating Dp1 is discharged from the first dispensing device D1, the first powder coating Dp1 is dispersed relatively uniformly, making it easier to penetrate into the corners of uneven surfaces. By coating the inner surface P11 of the socket P1 with the first powder coating Dp1, the thickness of the formed coating film becomes uniform, effectively protecting the inner surface P11 of the socket P1. Furthermore, since the socket P1 is fitted to the spigot P2 of another pipe body P, high dimensional accuracy is required for the inner diameter of the socket P1 relative to the spigot P2. By making the thickness of the coating film formed on the inner surface P11 of the socket P1 uniform, the required high dimensional accuracy can be met.

[0095] The size of the first powder coating Dp1 is not particularly limited, as long as the average particle size of the first powder coating Dp1 is smaller than the average particle size of the second powder coating Dp2, and can be appropriately selected according to the size of the irregularities on the inner surface P11 of the socket P1. Among these, for example, the average particle size of the first powder coating Dp1 is preferably 20 to 50 μm. By setting the average particle size of the first powder coating Dp1 to 20 μm or more, the inner surface P11 of the socket P1 can be coated more efficiently. From this viewpoint, the average particle size of the first powder coating Dp1 is more preferably 34 μm or more, and even more preferably 38 μm or more. Furthermore, by setting the average particle size of the first powder coating Dp1 to 50 μm or less, the inner surface P11 of the socket P1 can be coated more uniformly. From this viewpoint, the average particle size of the first powder coating Dp1 is more preferably 46 μm or less, and even more preferably 42 μm or less.

[0096] As described above, the first powder coating Dp1 is not particularly limited, but it is preferable that it be prepared so that its gel time at 170°C is in the range of 90 to 250 seconds. A gel time of 90 seconds or more for the first powder coating Dp1 allows for uniform coating of the inner surface P11 of the socket P1. From a similar viewpoint, a gel time of 135 seconds or more for the first powder coating Dp1 is more preferable, and even more preferable to 180 seconds or more. Furthermore, a gel time of 250 seconds or less for the first powder coating Dp1 increases coating efficiency and improves the uniformity of the coating film. From a similar viewpoint, a gel time of 235 seconds or less for the first powder coating Dp1 is more preferable, and even more preferable to 220 seconds or less.

[0097] The thickness of the coating film formed by the process of coating the inner surface P11 of the socket P1 with the first powder coating Dp1 is not particularly limited, as long as it is thick enough to protect the inner surface P11 of the socket P1. Among these, the inner surface P11 of the socket P1 can be protected more reliably by making the thickness of the coating film 150 μm or more.

[0098] The step of coating the inner surface P11 of the socket P1 with a first powder coating Dp1 may include charging the first powder coating Dp1 and electrostatically coating the inner surface P11 of the socket P1. In this embodiment, the first powder coating Dp1 is negatively charged by a high voltage (for example, 40,000 to 80,000 volts) generated by the charging device of the electrostatic coating apparatus, and is adhered to the inner surface P11 of the socket P1 by electrostatic force. By using electrostatic coating when coating the inner surface P11 of the socket P1, the inner surface P11 of the socket P1 can be coated more efficiently and more uniformly.

[0099] In the process of coating the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3 with a second powder coating Dp2, the pipe body P is first heated to a predetermined temperature. The heating temperature of the pipe body P is set to a temperature at which the second powder coating Dp2 hardens through the heat transferred when the second powder coating Dp2 comes into contact with or adheres to the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3 (for example, 150°C or higher). In this embodiment, the pipe body P, which has been preheated by a heating device, is mounted on a rotating device R. However, the pipe body P only needs to be heated at least when the second powder coating Dp2 comes into contact with or adheres to the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3, and may be heated after the pipe body P is mounted on the rotating device R, for example.

[0100] Next, the second powder coating Dp2 is sprayed onto the inner surface P21 of the spout P2 and the inner surface P31 of the straight section P3 of the pipe body P in a predetermined circumferential range (for example, the entire length) and a predetermined range in the pipe axis X direction (for example, the entire length from the opening P22 to the stepped section P13). In this embodiment, the second powder coating Dp2 is sprayed onto the inner surface P21 of the spout P2 and the inner surface P31 of the straight section P3 by being discharged from the inside of the spout P2 and the straight section P3 by the second discharge device D2. At this time, since the pipe body P has been heated to a predetermined temperature in advance, the second powder coating Dp2 that has come into contact with or adhered to the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3 hardens on the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3 through the heat that is transmitted, and is deposited on the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3. When the second powder coating Dp2 is discharged by the second discharge device D2, the pipe body P is rotated relative to the pipe axis X by the rotating device R, so that the second powder coating Dp2 is deposited over a predetermined range in the circumferential direction on the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3. Furthermore, as the second discharge section D21 of the second discharge device D2 is moved relative to the spigot P2 and the straight pipe section P3 along the pipe axis X direction, the first powder coating Dp1 is deposited over a predetermined range in the pipe axis X direction on the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3.

[0101] The discharge speed and discharge amount of the second powder coating Dp2 discharged toward the inner surface P21 of the spit P2 of the pipe body P and the inner surface P31 of the straight pipe section P3 are not particularly limited and can be set appropriately according to the required coating thickness. The relative rotation speed of the pipe body P and the relative movement speed of the second discharge section D21 of the second discharge device D2 are also not particularly limited and can be set appropriately according to the required film thickness.

[0102] The step of coating the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3 with the second powder coating Dp2 may include discharging the second powder coating Dp2 from the second discharge section D21 while relatively moving the second discharge section D21 in the first direction X1 and the second direction X2, respectively, similar to the step of coating the inner surface P11 of the receptacle P1 with the first powder coating Dp1. In this case, the powder coating nozzles 1, 2, 3, and 4 described above may be used as the second discharge section D21. Here, the same location may be coated in the forward path (first direction X1) and the return path (second direction X2) (reciprocal coating), or different locations may be coated in the forward path and the return path (forward coating, return coating). Furthermore, the discharge angle and spread angle for discharging the second powder coating Dp2 from the second discharge section D21 are not particularly limited and may be the same as or different from the discharge angle and spread angle when discharging the first powder coating Dp1 from the first discharge section D11. Also, the second discharge section D21 may be equipped with multiple powder coating nozzles arranged such that they are inclined toward opposite directions of travel X1 and X2 to discharge the second powder coating Dp2, and the areas on the inner surface of the pipe P to which the discharged second powder coating Dp2 reaches overlap with each other. In this case, in reciprocating coating, almost the same area on the inner surface of the pipe P can be coated before and after switching between the multiple powder coating nozzles in the forward and return strokes. Therefore, in order to make the coating film thickness approximately uniform along the directions of travel X1 and X2, it is not necessary (or the need is reduced) to adjust the relative movement positions of the multiple powder coating nozzles before and after switching between the multiple powder coating nozzles. This simplifies the process in reciprocating painting.

[0103] In this embodiment, the second powder coating Dp2 is deposited over a predetermined range in the circumferential direction and the direction of the pipe axis X by rotating the pipe body P around the pipe axis X and moving the second discharge section D21 of the second discharge device D2 along the direction of the pipe axis X. However, the embodiment is not limited to this one, and the second powder coating Dp2 may also be deposited over a predetermined range in the circumferential direction and the direction of the pipe axis X by other methods, such as rotating the second discharge section D21 of the second discharge device D2 around the pipe axis X and moving the pipe body P along the direction of the pipe axis X. Furthermore, the second powder coating Dp2 only needs to be deposited on at least a portion of the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3. For example, other powder coatings different from the second powder coating Dp2 may be deposited in areas other than those where the second powder coating Dp2 is deposited.

[0104] Finally, the tube body P is cooled by natural cooling or other means, and the painting of the inner surface P21 of the spigot P2 and the inner surface P31 of the straight tube section P3 is completed.

[0105] Here, as described above, the second powder coating Dp2 may be prepared to have an average particle size larger than that of the first powder coating Dp1. That is, a second powder coating Dp2 with a relatively large average particle size may be used to coat the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3 (the inner surface of the second pipe section B), which have relatively small irregularities. By using a second powder coating Dp2 with a relatively large average particle size to coat the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3, which have relatively small irregularities, the inner surface P21 of the spigot P2 and the inner surface P31 of the straight pipe section P3 can be coated more efficiently than when using a first powder coating Dp1 with a relatively small average particle size. This is thought to be because, when the relatively large second powder coating Dp2 is discharged from the second discharge device D2, the second powder coating Dp2 travels relatively straight towards the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3. This prevents it from floating inside the pipe body P or flowing out towards the openings P12 and P22 on both sides of the pipe body P, resulting in a good yield and adhesion to the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3.

[0106] The size of the second powder coating Dp2 is not particularly limited, as long as the average particle size of the second powder coating Dp2 is larger than the average particle size of the first powder coating Dp1, and can be appropriately selected according to the size of the irregularities on the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3 to be coated. Among these, for example, the average particle size of the second powder coating Dp2 is preferably 70 to 80 μm. By setting the average particle size of the second powder coating Dp2 to 70 μm or more, the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3 can be coated more efficiently. From this viewpoint, the average particle size of the second powder coating Dp2 is more preferably 72 μm or more, and even more preferably 74 μm or more. Furthermore, by setting the average particle size of the second powder coating Dp2 to 80 μm or less, the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3 can be coated more uniformly. From that perspective, the average particle size of the second powder coating Dp2 is more preferably 78 μm or less, and even more preferably 76 μm or less.

[0107] The thickness of the coating formed by the process of coating the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3 with the second powder coating Dp2 is not particularly limited, as long as it is thick enough to protect the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3. Among these, setting the thickness of the coating to 300 μm or more provides more reliable protection for the inner surface P21 of the spout P2 and the inner surface P31 of the straight pipe section P3.

[0108] As described above, the second powder coating Dp2 is not particularly limited, but it is preferably prepared so that its gel time at 170°C is in the range of 50 to 250 seconds. A gel time of 50 to 250 seconds for the second powder coating Dp2 improves coating efficiency and the uniformity of the coating film. From a similar viewpoint, the gel time of the second powder coating Dp2 is more preferably 70 to 235 seconds or less, and even more preferably 90 to 220 seconds or less.

[0109] As described above, the painting method of this embodiment includes the steps of painting the inner surface having relatively large irregularities (inner surface P11 of the receiving opening P1) with a first powder coating Dp1 having a relatively small average particle size, and painting the inner surface having relatively small irregularities (inner surface P21 of the spigot opening P2 and inner surface P31 of the straight pipe section P3) with a second powder coating Dp2 having a relatively large average particle size. This makes it possible to paint the inner surface of a pipe body P having two parts with inner surfaces of relatively different sizes of irregularities in a simpler, more efficient, and uniform manner.

[0110] Furthermore, in the coating method of this embodiment, the step of coating an inner surface (inner surface P11 of the receiving opening P1) having relatively large irregularities may additionally or alternatively include discharging powder coating from a discharge unit that discharges powder coating at an acute angle with respect to the first direction X1 while relatively moving the discharge unit that discharges powder coating in the first direction X1, and discharging powder coating from a discharge unit that discharges powder coating at an acute angle with respect to the second direction X2 while relatively moving the discharge unit that discharges powder coating in the second direction X2. This makes it possible to coat the inner surface of a pipe body P having two parts with inner surfaces having relatively different sizes of irregularities in a simpler, more efficient, and uniform manner. In particular, by using the powder coating nozzles 1 and 3 described above as the discharge unit that moves relative to the first direction X1, and / or by using the powder coating nozzles 2 and 4 described above as the discharge unit that moves relative to the second direction X2, the inner surface (inner surface P11 of the receiving opening P1) having relatively large irregularities can be coated more uniformly.

[0111] Furthermore, in the coating method of this embodiment, a powder coating for coating the inner surface having relatively large irregularities (the inner surface P11 of the socket P1) may be prepared so that the gel time at 170°C is in the range of 90 to 250 seconds, either additionally or alternatively. This makes it possible to efficiently and uniformly coat the inner surface of a pipe body P having two parts with inner surfaces having relatively different sizes of irregularities in a simpler manner. [Explanation of Symbols]

[0112] 1, 2, 3, 4 Powder coating nozzles 11, 21, 31, 41 Inlet 11a, 21a, 31a, 41a Proximal end 11b, 21b, 31b, 41b distal end 12, 22, 32, 42 First discharge port 12a, 22a, 32a, 42a Proximal end 12b, 22b, 32b, 42b distal end 13, 23, 33, 43 Second discharge port 13a, 23a, 33a, 43a Proximal end 13b, 23b, 33b, 43b distal end 34, 44 Third discharge port 34a, 44a Proximal end 34b, 44b distal end A First pipe section B. Second pipe section D Discharge device D1 First Discharge Device D11 First discharge section D111 First powder coating nozzle D112 Second powder coating nozzle D12 First powder coating supply pipe D13 First drive unit D14 First powder coating supply device D2 Second Discharge Device D21 Second discharge section D22 Second powder coating supply pipe D23 Second drive unit D24 Second powder coating supply device Dp1 First Powder Coating Dp2 Second Powder Coating P-type body P1 socket P11 Inner surface of the socket P12 opening P13 Multilayered section P14 protrusion P15 recess P2 socket P21 Inner surface of the opening P22 opening P23 protrusion P3 straight pipe section P31 Inner surface of the straight pipe section PD coating equipment PR1, First Domain PR2 Second Domain R Rotating Device R1 Rotating Roller R2 support stand X tube axis X1 First direction (direction of travel) X2 Second direction (direction of travel) α1 First spreading angle α2 Second spread angle θ1~θ8 Discharge angles 1st to 8th

Claims

1. A powder coating nozzle for discharging powder coating toward the inner surface of a pipe while moving relative to the inner surface of the pipe along the direction of travel, The powder coating nozzle is equipped with a plurality of discharge ports that are inclined toward the direction of travel, Each of the plurality of discharge ports has a discharge angle of the powder coating that is different from the other, with respect to the direction of travel in which the powder coating nozzle moves relative to the inner surface of the tube. Powder coating nozzle.

2. Each of the aforementioned multiple discharge ports is provided in a line along the direction of travel, The powder coating nozzle according to claim 1.

3. The powder coating nozzle includes a plurality of powder coating nozzles that are each inclined toward opposite directions of travel and discharge the powder coating, The plurality of powder coating nozzles are arranged such that at least a portion of the areas on the inner surface of the tube to which the powder coating discharged by each of the plurality of powder coating nozzles reaches overlaps with each other. A powder coating nozzle according to claim 1 or 2.

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