Manufacturing method of the stirring shaft

Abstract

To realize production of a precise agitation shaft with a vacuum double pipe having a little thermal deformation, into which a flow passage of the agitation shaft is inserted.SOLUTION: A method for producing an agitation shaft including the following steps: preparing a shaft body 11 inside which a flow passage 11a extending in an axial direction is formed; attaching agitation blades to an outer periphery of the shaft body 11; and inserting a vacuum double pipe into the flow passage of the shaft body 11. The vacuum double pipe has a vacuum inside by closing an end surface of a cylindrical space composed of an inner pipe 14a and an outer pipe 14b and placed between the inner pipe 14a and the outer pipe 14b. The vacuum double pipe 14 is produced by the following sub steps: installing a double pipe with a hole opened on an outer surface thereof, and evacuating air from the cylindrical space; and keeping the cylindrical space in a vacuum state by closing the hole by electron beam welding. The influence of heat is limited to a section around the hole, with which an electron beam collides. Therefore, it is possible to produce the precise agitation shaft 10 with the vacuum double pipe 14 having a little thermal deformation.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a stirring shaft used in a kneader or the like.

Background Art

[0002] Inside a kneader, a reactor, a dryer, etc., a stirring shaft for stirring the object to be processed is provided. The stirring shaft has a shaft body and stirring blades provided on the outer periphery thereof. The shaft body is supported by a bearing portion so as to be rotatable around its axis, and the object to be processed is stirred by the stirring blades as it rotates. Here, in order to heat or cool the object to be processed, a flow path extending in the axial direction is provided inside the shaft body, and a heat medium can flow through this.

[0003] When the heat medium flows, the stirring shaft is heated. However, since the gland packing that seals the bearing portion and the shaft end that supports this may have poor heat resistance, if the heat of the stirring shaft is directly transmitted to the bearing or the gland packing, it may cause deterioration, failure, etc. Therefore, attempts have been made to insert a vacuum double tube into the flow path in the vicinity of the support portion by the bearing portion of the stirring shaft and the sealing portion by the gland packing as in Patent Document 1. The vacuum double tube consists of an inner tube and an outer tube, and the cylindrical space between the inner tube and the outer tube has its end faces closed and the inside is vacuum. Therefore, the space between the inner tube and the outer tube is heat-insulated, and even if a heat medium flows through the inside of the inner tube, the heat does not transfer to the outer tube side, and it is suppressed that the bearing portion and the gland packing are affected by heat.

[0004] By the way, as a manufacturing method of this kind of conventional vacuum double tube, first, a double tube before completion in a state where a hole is opened in the outer tube so that the above-mentioned cylindrical space communicates with the outside air, for example, a vacuum degree of 10 -2 Pa to 10 -4 is installed in a vacuum furnace of Pa. The general procedure involved raising the temperature inside the vacuum furnace to a high temperature of around 1040°C, using wax such as nickel wax, melting it, and sealing the hole in the outer tube to create a vacuum inside the cylindrical space. The vacuum double tube thus constructed was inserted into the flow path from the end of the shaft body and secured as needed to create the stirring shaft. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-137746 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, with this manufacturing method, the entire vacuum double tube would be heated in the vacuum furnace, which could cause it to deform, such as warping or bending. Therefore, it was sometimes impossible to insert the double vacuum tube into the internal flow path of the shaft body, or attempting to force it in could damage the double vacuum tube or the shaft body.

[0007] Therefore, the problem to be solved by the present invention is to reduce thermal deformation of the vacuum double tube inserted into the flow path of the stirring shaft and to realize the manufacture of a highly accurate stirring shaft. [Means for solving the problem]

[0008] To solve the above-mentioned problems, the invention provides a method for manufacturing a stirring shaft, comprising the steps of: preparing a shaft body having a flow channel extending axially inside; attaching stirring blades to the outer circumference of the shaft body; and inserting a vacuum double tube, consisting of an inner tube and an outer tube, with the cylindrical space between the inner and outer tubes having its end faces closed and the interior being a vacuum, into the flow channel of the shaft body. The vacuum double tube is manufactured by a sub-step of installing a double tube with a hole drilled in its outer surface into a vacuum welding chamber to vent the air from the cylindrical space; and a sub-step of impacting the hole in the outer tube with an electron beam and sealing the hole by electron beam welding to fix the vacuum state of the cylindrical space. Note that the order in which the step of attaching the stirring blades to the outer circumference of the shaft body and the step of inserting the vacuum double tube into the flow path of the shaft body do not matter.

[0009] In this way, the entire vacuum double tube is not heated, and the effects of heat are limited to a small area around the hole where the electron beam collides (spot diameter of about 0.2 mm). As a result, the vacuum double tube does not undergo significant thermal deformation, and a highly accurate stirring shaft can be manufactured. Furthermore, since the double-walled tube itself is melted to seal the holes, and no other materials such as nickel wax are used, there is no risk of other materials peeling off from the stirring shaft, thus preventing foreign matter from contaminating the processed material. Because the entire vacuum double tube is not overheated to high temperatures during its manufacture, it is possible to use different materials with different coefficients of thermal expansion for the inner and outer tubes (for example, using relatively expensive but high-strength SUS630 stainless steel for the inner tube and relatively inexpensive SUS304 stainless steel for the outer tube), allowing for the selection of the optimal material according to the purpose and characteristics of each of the inner and outer tubes. As a result, the entire stirring shaft can be made low-cost and highly durable.

[0010] In the method for manufacturing a stirring shaft according to the invention, it is preferable that the double tube is installed in the welding chamber in a horizontal position such that the hole is provided on the circumferential surface of the outer tube and the hole is directly facing the electron gun of the electron beam welding machine.

[0011] By doing so, after laying the long and difficult-to-handle vacuum double tube horizontally, the electron beam can be accurately made to collide with the holes provided on its outer periphery, enabling electron beam welding and thus facilitating the work of closing the holes.

[0012] In the manufacturing method of the stirring shaft according to the invention, it is preferable that a plurality of holes on the outer periphery of the outer tube are provided in parallel in the axial direction of the double tube.

[0013] By doing so, when the double tube is installed in a vacuum welding chamber, air can be smoothly exhausted from the cylindrical space between the inner tube and the outer tube through the plurality of holes, enabling the rapid creation of a vacuum state in the cylindrical space.

Effect of the Invention

[0014] Since the manufacturing method of the stirring shaft according to the invention is configured as described above, with respect to the vacuum double tube inserted into the flow path of the stirring shaft, thermal deformation is reduced and it becomes possible to manufacture a stirring shaft with high precision.

Brief Description of the Drawings

[0015] [Figure 1] Overall longitudinal sectional view of the kneader [Figure 2] Enlarged longitudinal sectional view of the main part of the kneader [Figure 3] Longitudinal sectional view of the vacuum double tube [Figure 4] Schematic diagram showing the manufacturing process of the stirring shaft [Figure 5] Schematic diagram showing the manufacturing process of the vacuum double tube

Mode for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described while referring to the drawings. The kneader 1 shown in FIGS. 1 and 2 is manufactured by the manufacturing method of the embodiment for its stirring shaft 10 and is used as a heat exchange device or the like. Needless to say, the configuration of such a kneader is merely an example and is not limited thereto.

[0017] As shown in Fig. 1, the kneader 1 has a stirring shaft 10 rotatably supported within a casing 2. A supply port 2a is provided at the upper part of one end of the casing 2, and a discharge port 2b is provided at the lower part of the other end. The workpiece is supplied into the casing 2 through the supply port 2a, processed by the stirring shaft 10, and then discharged out of the casing 2 through the discharge port 2b. As shown in Fig. 1, a jacket 3 is provided outside the casing 2, and a heat medium can be circulated in the jacket 3 by a general-purpose circulation device 4. Thereby, during the operation of the kneader 1, the inside of the casing 2 is heated to, for example, about 350 °C.

[0018] The stirring shafts 10 are provided in parallel in a front-rear pair in the depth direction of Fig. 1. Each stirring shaft 10 is supported and sealed at one end by a gland packing 5 and at the other end by a gland packing 5 and a bearing portion 6. One end of the stirring shaft 10 that is supported and sealed only by the gland packing 5 is connected to a motor 7 and is driven to rotate. Also, the other end of the stirring shaft 10 that is supported and sealed by the gland packing 5 and supported by the bearing portion 6 is connected to a rotary joint 8. The rotary joint 8 is capable of supplying and recovering the heat medium from the circulation device 4.

[0019] As shown in the figure, the stirring shaft 10 includes a shaft body 11 and stirring blades (paddles) 12 provided on the outer periphery of the shaft body. As the material of the shaft body 11 and the stirring blades 12, stainless steel is exemplified. The shaft body 11 has an elongated cylindrical shape. The stirring blades 12 each project in the outer diameter direction of the shaft body 11, and a plurality of them are arranged in parallel at a predetermined interval in the axial direction of the shaft body 11. The workpiece introduced from the supply port 2a of the casing 2 is stirred by the stirring blades 12 as the shaft body 11 rotates due to the motor 7. Furthermore, a screw paddle (screw blade) 13 for forward feeding is provided on the outer circumference of the shaft body 11 on the motor 7 side, and a screw paddle 13 for reverse feeding is provided on the rotary joint 8 side, enabling continuous and smooth processing of the workpiece.

[0020] The shaft body 11 is provided with a flow path 11a that extends in the axial direction, and it is possible to circulate the heat transfer medium from the circulation device 4 through this flow path 11a. The flow path 11a penetrates to the end of the shaft body 11 connected to the rotary joint 8, but does not reach the end connected to the motor 7, terminating just before the gland packing 5. Therefore, the gland packing 5 that supports and seals the end connected to the motor 7 is less susceptible to the effects of heat caused by the heat transfer medium flowing through the flow path 11a. On the other hand, the gland packing 5 and bearing portion 6 that support and seal the end connected to the rotary joint 8 are susceptible to the effects of heat caused by the heat transfer medium flowing through the passage 11a.

[0021] A partition member 11b is inserted into the flow path 11a. The partition member 11b is supported by known means so as to rotate integrally with the stirring shaft 10. The partition member 11b divides the flow path 11a into an upstream side and a downstream side at positions corresponding to the stirring blade 12. Here, a flow path 12a is also provided inside the stirring blade 12, and the upstream side of the flow path 11a of the shaft body is connected to one end of the flow path 12a of the stirring blade 12, and the downstream side of the flow path 11a is connected to the other end of the flow path 12a of the stirring blade 12, thereby enabling the circulation of a heat transfer medium inside the stirring blade 12.

[0022] As described above, the gland packing 5 and bearing portion 6 that support the end connected to the rotary joint 8 are susceptible to the effects of heat caused by the heat transfer medium flowing through the flow path 11a of the shaft body. Therefore, as shown in Figure 2, a vacuum double tube 14 is inserted and fixed at the relevant location in the flow path 11a.

[0023] As shown in Figures 2 and 3, the vacuum double tube 14 consists of an inner tube 14a and an outer tube 14b, and the inside of the inner tube 14a is in communication with the inside of the partition member 11b, allowing the heat transfer medium to flow through. Furthermore, the cylindrical space between the inner tube 14a and the outer tube 14b forms a vacuum section 14d, which is closed off by the caps 14c at both ends. This vacuum section 14d has a vacuum level of, for example, 2.4·10. -3 It is sealed to achieve a pressure of Pa. Of the caps 14c at both ends, the cap that faces forward when inserted into the flow path 11a is provided with a flange 14e. The flange 14e abuts against the opening edge of the flow path 11a, thereby determining the amount of insertion of the vacuum double tube 14 into the flow path 11a. Furthermore, a seal groove 14f is provided on the outer circumference of each cap 14c. By fitting a seal ring into this groove, watertightness is ensured when the vacuum double tube 14 is inserted into the flow path 11a.

[0024] The material of the inner tube 14a is not particularly limited, but among stainless steels, it is preferable that it be made of SUS630, which has excellent heat resistance, corrosion resistance, and strength, as it is through which a heat transfer medium flows. The material of the outer tube 14b is not particularly limited, but among stainless steels, it is preferable to use SUS304, which has excellent heat resistance and corrosion resistance and is relatively inexpensive, although the heat transfer medium does not flow through it and it does not need to have the same performance as the inner tube 14a.

[0025] Here, the heat transfer medium supplied from the rotary joint 8 passes through the inner tube 14a of the vacuum double tube 14 and is supplied to the upstream side of the flow path 11a, which is partitioned by the partition member 11b of the shaft body 11, and returns to the downstream side of the flow path 11a via the flow path 12a of the stirring blade 12. Furthermore, from the downstream side of the flow path 11a, it returns again through the inner tube 14a to the rotary joint 8 and is returned to the circulation device 4.

[0026] In this way, although a high-temperature heat transfer medium flows inside the inner tube 14a, the surrounding area is covered by a vacuum section 14d, making it difficult for heat to be transferred to the shaft body 11. This prevents the support parts and sealing parts, such as the gland packing 5 and bearing section 6, from deteriorating due to heat. Therefore, while making it difficult to transfer heat to support parts and sealing parts such as the gland packing 5 and bearing part 6, it becomes possible to stir the material to be processed by the stirring shaft 10, which is heated to a high temperature (for example, the same temperature as the jacket, 350°C, etc.) by the heat transfer medium.

[0027] Alternatively, an air layer may be formed between the outer surface of the outer tube 14b and the inner surface of the flow path 11a, thereby creating a gap. Alternatively, the shaft body 11 may be covered with the sleeve 15 so as to create a gap, thereby forming an air layer between the outer circumferential surface of the shaft body 11 and the inner circumferential surface of the sleeve 15. These air layers further reduce the transfer of heat from the stirring shaft 10 to the gland packing 5 and bearing section 6.

[0028] The configuration of the kneader 1 is as described above, and next, a manufacturing method relating to the embodiment of its stirring shaft 10 will be explained.

[0029] As shown in Figure 4(a), first prepare the shaft body 11. The shaft body 11 is assumed to have the necessary components, such as the flow path 11a, already installed through the previous process. Next, as shown in Figure 4(b), the stirring blades 12 and screw paddles 13 are attached to the shaft body 11 (only the stirring blades 12 are shown in this figure as an example). The manner in which the stirring blades 12 and other components are attached is not particularly limited. In the illustration, the stirring blades 12 are schematically attached to the shaft body 11 from the radial direction, but generally, they are spline-connected to a key and keyway by sliding them along the axial direction of the shaft body 11 together with a spacer. Here, it is assumed that the stirring blades 12 have the necessary components, such as the flow path 12a, already prepared through a previous process.

[0030] Furthermore, as shown in Figure 4(c), the vacuum double tube 14 is inserted into the flow path 11a of the shaft body 11 and fixed in place by appropriate means. In this way, the stirring shaft 10 is completed. In the illustration, the process of attaching the stirring blades 12 to the shaft body 11 is shown first, followed by the process of attaching the vacuum double tube 14. However, the order of these steps does not matter, and the vacuum double tube 14 may be attached to the shaft body 11 before the stirring blades 12.

[0031] The vacuum double tube 14 is manufactured by the following sub-steps, referring to Figure 5, prior to the main process (step) for manufacturing the stirring shaft described above. Specifically, first, a pre-completion double-walled pipe 14' is prepared, consisting of an inner pipe 14a and an outer pipe 14b, with both ends of the cylindrical space between the inner pipe 14a and the outer pipe 14b closed by caps 14c. The inner pipe 14a and outer pipe 14b and the caps 14c are assumed to have been fixed in advance by welding or other appropriate means. Here, before completion, multiple holes 14g are provided on the outer surface of the outer tube 14b of the double-walled tube 14', communicating with the cylindrical space. The holes 14g are small holes with a diameter of about 1 mm (0.5 mm to 1.5 mm) and are arranged in parallel at predetermined intervals (for example, about 150 mm to 250 mm) in the axial direction of the outer tube 14b.

[0032] As shown in Figure 5(a), the unfinished double-walled tube 14' is laid on its side (meaning the axial direction of the double-walled tube 14' is roughly aligned with the horizontal direction), and placed on a trolley 21 or the like with the hole 14g facing upwards, and the electron beam welding machine 20 is set to a vacuum state (vacuum degree 10%). -2 Pa to 10 -4 It will be installed in welding chamber 22 (Pa). At this time, the air in the cylindrical space escapes through hole 14g, and the cylindrical space of the double tube 14' becomes a vacuum. Since there are multiple holes 14g, the air is removed smoothly.

[0033] From here, electron beam welding is performed on the periphery of hole 14g. However, since the double tube 14' is laid on its side and the hole 14g provided on the outer surface of its outer tube 14b is directly facing the electron gun (cathode 23, anode 24, grid 25) of the electron beam welding machine 20 in an up-and-down position, the work efficiency is improved. Referring to Figure 5(a), electrons emitted from the cathode 23 of the electron gun are accelerated to about two-thirds the speed of light by the voltage (60kV to 150kV) applied between it and the anode 24, and are controlled by the grid 25, and further focused and deflected by the electromagnetic coil 26, before being irradiated (collided) as an electron beam E around the hole 14g of the double tube 14'. The alignment of hole 14g and electron beam E is performed by moving the trolley 21 on which the double tube 14' is mounted and by deflecting the electron beam with the electromagnetic coil 26.

[0034] As shown in Figure 5(b), the thermal energy generated by the collision of the electron beam E melts the area around the hole 14g in the outer tube 14b, forming a welded joint 14h that seals the hole 14g. This process is carried out sequentially by moving the double tube 14' axially, etc., until all the holes 14g are sealed. In this way, the vacuum state in the cylindrical space is fixed, and the vacuum section 14d is formed, completing the vacuum double tube 14. Because all operations are performed in a vacuum, oxidation and nitriding of the weld are suppressed. Furthermore, electron beam welding produces a narrow weld width (spot diameter of approximately 0.2 mm) and a deep penetration weld (14h), resulting in high weld strength. Compared to filling holes with nickel solder, the holes (14g) can be made smaller.

[0035] The vacuum double tube 14 manufactured in this manner is used in the manufacturing process of the stirring shaft 10 described above, as shown in Figure 4. According to this manufacturing method, unlike conventional methods, the entire vacuum double tube 14 is not heated, and the effects of heat are limited to the local area where the electron beam E collides around the hole 14g. As a result, the vacuum double tube 14 does not undergo thermal deformation as a whole, and a highly accurate stirring shaft 10 can be manufactured using it.

[0036] Furthermore, in order to seal the hole 14g of the double tube 14', the outer tube 14b itself is melted, and no other materials such as conventional Ni brazing material are used. As a result, the welding strength is high, and there is no concern that other materials will peel off from the stirring shaft 10 in which this vacuum double tube 14 is used. Therefore, contamination of the processed material with foreign matter is prevented during processing by the kneader 1. Furthermore, since the entire vacuum double tube 14 is not overheated to a high temperature during its manufacture, different materials with different coefficients of thermal expansion can be used for the inner tube 14a and the outer tube 14b, allowing for the selection of the optimal material for each according to its purpose and characteristics. Therefore, the entire stirring shaft 10 can be designed to have sufficient heat resistance, corrosion resistance, and other functionalities while keeping costs down.

[0037] The embodiments disclosed herein are illustrative in all respects and not restrictive. The scope of the invention is defined by the claims and includes all modifications in the sense and scope equivalent to the claims.

[0038] For example, the position, number, and dimensions of the holes 14g in the double-walled tube 14' before completion, and the orientation of the double-walled tube 14' during electron beam welding, are not limited to the embodiment. For instance, the holes 14g may be provided in the cap 14c, the number of holes 14g may be limited to one, or the size of the holes 14g may be set to a diameter exceeding 1 mm (approximately a few mm). The direction in which the holes 14g of the double tube 14' are arranged in parallel is not limited to the embodiment; they may also be arranged in parallel in the circumferential direction of the outer tube 14b. In this case, it is conceivable to perform electron beam welding sequentially on all the holes 14g while rotating the double tube 14' around its axis. The spacing between the parallel holes 14g is also not limited to the embodiment. The cap 14c of the double-walled tube 14' may also be fixed to the inner tube 14a and outer tube 14b by electron beam welding.

[0039] The insertion and fixing positions of the vacuum double tube 14 on the stirring shaft 10 are not limited to this embodiment; for example, it may also be inserted and fixed at the end connected to the motor 7. If there are support parts other than both ends of the stirring shaft 10, the vacuum double tube 14 may be inserted and fixed at the corresponding positions. The method of closing the end of the vacuum double tube 14 is not limited to that using a cap 14c. The shape, number, mounting spacing (pitch), and material of the stirring blades 12 and screw paddles 13 of the stirring shaft 10 are not limited to the embodiment. The shape and material of the shaft body 11 are also not limited to the embodiment, as long as the vacuum double tube 14 can be inserted into the flow path 11a. [Explanation of Symbols]

[0040] 1. Mixing machine 2 Casing 2a Supply port 2b Outlet 3 Jackets 4 Circulation device 5. Gland packing 6 Bearing section 7 Motor 8 Rotary Joint 10 Stirring shaft 11 Axis body 11a Channel 11b Partition member 12 stirring blades 12a Flow channel 13 Screw paddles 14 Vacuum double tube 14´ double tube 14a inner tube 14b Outer tube 14c cap 14d Vacuum section 14e flange 14f seal groove 14g hole 14h Weld 15 sleeves 20 Electron beam welding machines 21 bogies 22 Welding Room 23 Cathode 24 Anode 25 grid 26 Electromagnetic coil E electron beam

Claims

1. The steps include preparing a shaft body in which a flow channel extending axially is formed inside, The steps include attaching stirring blades to the outer circumference of the shaft body, The step of inserting a vacuum double tube, which consists of an inner tube and an outer tube, and in which the cylindrical space between the inner and outer tubes is closed at its end face and the inside is a vacuum, into the flow path of the shaft body, The aforementioned vacuum double tube is A substep involves installing a double-walled tube with holes drilled in its outer surface into a vacuum welding chamber and venting the air from the cylindrical space, It is manufactured by a substep in which an electron beam is projected onto a hole in the outer tube, and the hole is sealed by electron beam welding to fix the vacuum state in the cylindrical space. A method for manufacturing a stirring shaft, wherein the double-walled pipe is installed in the welding chamber with the hole drilled in the outer circumference of the outer pipe and the end face of the cylindrical space between the inner pipe and the outer pipe pre-closed.

2. The steps include preparing a shaft body in which a flow channel extending axially is formed inside, The steps include attaching stirring blades to the outer circumference of the shaft body, The step of inserting a vacuum double tube, which consists of an inner tube and an outer tube, and in which the cylindrical space between the inner and outer tubes is closed at its end face and the inside is a vacuum, into the flow path of the shaft body, The aforementioned vacuum double tube is A substep involves installing a double-walled tube with holes drilled in its outer surface into a vacuum welding chamber and venting the air from the cylindrical space, It is manufactured by a substep in which an electron beam is projected onto a hole in the outer tube, and the hole is sealed by electron beam welding to fix the vacuum state in the cylindrical space. A method for manufacturing a stirring shaft, wherein the double tube has the hole drilled in the outer circumference of the outer tube and is installed in the welding chamber in a horizontal position so that the hole faces directly towards the electron gun of the electron beam welding machine.

3. The method for manufacturing a stirring shaft according to claim 1 or claim 2, wherein the holes on the outer circumference of the outer tube are arranged in parallel in the axial direction of the double tube.

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