Method for applying heat insulation material to piston

Abstract

To improve coating efficiency and productivity in applying a heat insulation material to a crown surface 9 of a piston 1 of an engine.SOLUTION: A method for applying a heat insulation material for a piston includes the steps of: disposing a dispenser 21 for discharging a heat insulation material linearly toward a crown surface 9; discharging the heat insulation material toward the crown surface 9 from the dispenser 21 while rotating a piston 1 about the axial center thereof; and moving a position of applying the heat insulation material inward in a radial direction of the piston 1 per rotation of the piston to form a heat insulation layer at the crown surface 9.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a method for applying a heat insulating material to a piston of an engine.

Background Art

[0002] It is generally known that by providing a heat insulating layer on the wall surface (such as the crown surface of the piston, the lower surface of the cylinder head, etc.) forming the combustion chamber of the engine, the cooling loss of the engine can be reduced and the fuel consumption can be improved. For example, Patent Document 1 describes that a liquid heat insulating material obtained by mixing hollow particles and a binder is applied to the crown surface of the piston by a spray coating gun to form a heat insulating layer, and this heat insulating layer is fired.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the case of spray coating, the amount of overspray where the heat insulating material scatters around the crown surface of the piston increases. That is, the coating efficiency of the heat insulating material is poor. In addition, spray dust due to overspray adheres to the side surface of the piston, and when the piston reciprocates, it damages the cylinder bore surface. To prevent this, it is necessary to mask the side surface of the piston, resulting in low productivity (mass productivity).

[0005] The present invention aims to improve the coating efficiency and productivity in applying a heat insulating material to the crown surface of a piston.

Means for Solving the Problems

[0006] In order to solve the above problems, the present invention uses a dispenser for applying a heat insulating material to the crown surface of a piston.

[0007] The heat insulation material coating method disclosed herein is a method for coating a heat insulation material to form a heat insulation layer on the crown surface of a piston of an engine, arranging a dispenser for discharging the heat insulation material linearly toward the crown surface, while discharging the heat insulation material from the dispenser toward the crown surface, moving the coating position of the heat insulation material on the crown surface in the circumferential direction of the crown surface 、 The above-mentioned crown surface is provided with a cavity at the center, and the area around this cavity is an annular flat portion. Regarding the above-mentioned annular flat portion, the heat insulation layer is formed by the above-mentioned dispenser with the discharge direction of the above-mentioned heat insulation material being the axial direction of the piston. After that, the inner surface of the above-mentioned cavity is sprayed with the above-mentioned heat insulation material by a spray coating gun to form a heat insulation layer following the heat insulation layer of the above-mentioned annular flat portion. which is characterized by the above.

[0008] According to this, different from spray coating, the heat insulation material is discharged linearly (in a continuous line shape or a dotted line shape) toward the crown surface of the piston without diffusing from the dispenser, so that scattering of the heat insulation material around the crown surface can be avoided. Therefore, the coating efficiency of the heat insulation material is increased, and masking of the side surface of the piston can be simplified or the masking becomes unnecessary, which is advantageous for improving productivity. Further, since the coating position of the heat insulation material is moved in the circumferential direction of the crown surface, it becomes easy to form a heat insulation layer that spreads to the edge (extreme) of the crown surface without the heat insulation material protruding outside the crown surface.

[0009] Furthermore, regarding the annular flat portion around the cavity, since the heat insulation material is applied by the dispenser with the discharge direction being the axial direction of the piston, the heat insulation material can be applied efficiently. And, since the annular flat portion is dispenser-coated and the spray coating is applied to the inner surface of the cavity, it becomes easy to avoid the scattering of the heat insulation material around the crown surface due to the spray coating. Also, the inner peripheral surface of the cavity that slopes downward in the axial direction of the piston from the inner peripheral edge of the annular flat portion to the deepest part of the cavity is a curved surface. Since spray coating, which has a large selection width of the coating (spray) pattern instead of dispenser coating, is applied there, it becomes easy to apply the heat insulation material efficiently and evenly. Furthermore, since spray coating is performed after dispenser coating, it is easy to make the heat insulation layer by spray coating continuous with the heat insulation layer by dispenser coating.

[0010] In one embodiment, the dispenser is a dot coating gun that discharges the heat insulation material in dots at predetermined intervals, and the dot-shaped heat insulation material is wetted and spread to be continuous in the circumferential direction of the crown surface. That is, when the coating position of the heat insulation material on the crown surface of the piston moves in the circumferential direction of the crown surface, the dot-shaped heat insulation materials sequentially coated on the crown surface are wetted and spread to be connected, and a continuous heat insulation layer is formed in the circumferential direction of the crown surface.

[0011] When moving the coating position of the heat shield material in the circumferential direction of the crown surface, either a method of fixing the position of the dispenser and rotating the piston around its axis, or a method of fixing the piston and rotating and moving the dispenser around the axis of the piston can be adopted. Preferably, the former method of rotating the piston is used. According to this, since the dispenser does not move, the straightness of the heat shield material discharged from the dispenser is not disturbed. Therefore, it becomes easy to form a heat shield layer with a desired thickness at a desired position on the crown surface of the piston.

[0012] In one embodiment, every time the coating position of the heat shield material moves circumferentially on the crown surface and makes one revolution or several revolutions, the coating position of the heat shield material with respect to the crown surface is moved in the radial direction of the piston, thereby forming a heat shield layer continuous in the radial direction on the crown surface.

[0013] Thereby, a heat shield layer continuous in the radial direction of the piston can be easily formed on the crown surface of the piston.

[0014] In one embodiment, the dispenser is positioned so that the coating position of the heat shield material with respect to the crown surface becomes the peripheral edge of the crown surface, and in that state, the piston is rotated around its axis to start discharging the heat shield material, and the coating position of the heat shield material is moved inward in the radial direction.

[0015] By making the starting point of coating the heat shield material on the crown surface of the piston be the peripheral edge of the crown surface in this way, it becomes easy to prevent the heat shield material from adhering to the side surface of the piston.

[0016] In one embodiment, the dispenser is the dot coating gun, The discharge amount and discharge frequency per shot of the dot coating gun are made constant, and as the coating position of the heat shield material moves inward in the radial direction, the rotation speed of the piston is Ascent made to increase.

[0017] This facilitates the equalization of the thickness of the heat insulation layer in the radial direction on the crown surface of the piston.

[0018] In one embodiment, the dispenser is the dot coating gun, the discharge amount per shot of the dot coating gun and the rotation speed of the piston are kept constant, and the discharge frequency of the dot coating gun is decreased as the coating position of the heat insulation material moves inward in the radial direction.

[0019] This facilitates the equalization of the thickness of the heat insulation layer in the radial direction on the crown surface of the piston.

[0020] Another heat insulation material application method disclosed herein is a heat insulation material application method for forming a heat insulation layer on the crown surface of an engine piston, a dispenser for discharging the above-mentioned heat insulation material linearly is arranged facing the above-mentioned crown surface, while discharging the above-mentioned heat insulation material from the above-mentioned dispenser toward the above-mentioned crown surface, the coating position of the above-mentioned heat insulation material on the above-mentioned crown surface is moved in the circumferential direction of the above-mentioned crown surface. Up The crown surface has a cavity in the central part, and the area around this cavity is an annular flat part, and the central part of the cavity has a raised part. For the annular flat part and the raised part, the heat insulation layer is formed by the dispenser with the discharge direction of the heat insulation material in the axial direction of the piston. After that, the heat insulation material is sprayed between the annular flat part and the raised part by a spray coating gun to form a heat insulation layer spanning the heat insulation layer of the annular flat part and the heat insulation layer of the raised part.

[0021] According to this, different from spray coating, since the heat insulation material is discharged linearly (in a continuous line shape or a dotted line shape) toward the crown surface of the piston without diffusing from the dispenser, scattering of the heat insulation material around the crown surface can be avoided. Therefore, the coating efficiency of the heat insulation material is increased, and masking of the side surface of the piston can be simplified or the masking becomes unnecessary, which is advantageous for improving productivity. Also, since the coating position of the heat insulation material is moved in the circumferential direction of the crown surface, it becomes easy to form a heat insulation layer that spreads to the edge (extreme) of the crown surface without the heat insulation material protruding outside the crown surface.

[0022] Furthermore , the annular flat part around the cavity and the central raised part of the cavity about Since the heat insulation material is applied by the dispenser with the discharge direction in the axial direction of the piston, the heat insulation material can be efficiently applied. And since the annular flat part and the central raised part of the cavity are applied by the dispenser, and the spray coating is applied to the inner surface of the cavity between the annular flat part and the raised part, it is easy to avoid the scattering of the heat insulation material around the crown surface by the spray coating. to This is achieved. Also, in the part where the inner peripheral surface of the cavity, which descends in the axial direction of the piston from the inner peripheral edge of the annular flat portion to the deepest part of the cavity, is a curved surface, spray coating, which has a wider selection range of coating (spray) patterns than dispenser coating, is applied here, making it easy to efficiently and evenly apply the heat insulation material. Further, since spray coating is performed after dispenser coating, it is easy to make the heat insulation layer formed by spray coating continuous with the heat insulation layer formed by dispenser coating.

[0023] In one embodiment, the viscosity of the heat insulation material discharged from the spray gun is made lower than the viscosity of the heat insulation material discharged from the dispenser.

[0024] Since the heat insulation material applied by spray coating is likely to spread due to its low viscosity, it is easy to prevent coating leakage at the boundary between the dispenser coating part and the spray coating part.

Advantages of the Invention

[0025] According to the present invention, while linearly discharging the heat insulation material from the dispenser toward the crown surface of the piston, the coating position of the heat insulation material with respect to the crown surface is moved in the circumferential direction of the crown surface, so that the coating efficiency of the heat insulation material is increased, and masking can be made simple or unnecessary, which is advantageous for improving productivity.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0027] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following description of the preferred embodiments is merely illustrative in nature and is not intended to limit the present invention, its applications, or its uses.

[0028] In the diesel engine shown in FIG. 1, 1 is a piston made of an aluminum alloy, 2 is a cylinder block, 3 is a cylinder head, 4 is an intake valve for opening and closing the intake port 5 of the cylinder head 3, 6 is an exhaust valve for opening and closing the exhaust port 7, and 8 is a fuel injection valve. The combustion chamber of the engine is formed by the crown surface 9 of the piston 1, the cylinder block 2, the cylinder head 3, and the front surfaces of the umbrella parts (the surfaces facing the combustion chamber) of the intake and exhaust valves 4 and 6.

[0029] As shown in FIG. 2, the crown surface 9 of the piston 1 is provided with a cavity 11 that is recessed in the piston axis direction at its central part, and an annular flat part 12 is formed around the cavity 11. A raised part 13 is formed at the center of the cavity 11. A heat insulation layer 14 is formed on the crown surface 9 composed of the inner surface of the cavity 11 including the raised part 13 of the piston 1 and the annular flat part 12.

[0030] The heat shield layer 14 includes a large number of hollow particles 15 made of inorganic oxides or ceramics, and a silicone-based resin binder 16 that fixes the hollow particles 15 to the piston 1 and fills the spaces between the hollow particles 15 to form the base material (matrix) of the heat shield layer 14. Nanoparticles 17 are dispersed in the resin binder 16. In Fig. 2, the nanoparticles 17 are represented by dots.

[0031] The thickness of the heat shield layer 14 is, for example, set to be 20 μm or more and 150 μm or less, preferably 30 μm or more and 100 μm or less, and more preferably 50 μm or more and 70 μm or less. As the hollow particles 15, those having a particle size in the order of μm smaller than the thickness of the heat shield layer 14 are used. The average particle size is preferably, for example, 30 μm or less. For example, hollow particles with an average particle size of 10 μm or less, and more preferably 3 μm or more and 5 μm or less can be preferably adopted. The average particle size of the nanoparticles 14 is preferably 500 nm or less, more preferably 1 nm or more and 200 nm or less, and even more preferably 1 nm or more and 120 nm or less. However, the above numerical ranges are preferred ranges and are not limiting.

[0032] As the hollow particles 15, inorganic hollow particles are adopted. For example, it is preferable to adopt ceramic-based hollow particles containing Si-based oxide components (for example, silica) or Al-based oxide components (for example, alumina) such as glass balloons, glass bubbles, fly ash balloons, shirasu balloons, silica balloons, and aluminosilicate balloons. The hollow ratio of the hollow particles is preferably 60% by volume or more, and more preferably 70% by volume or more.

[0033] As the resin binder 16, for example, a silicone-based resin composed of a three-dimensional polymer with a high degree of branching, typified by methyl silicone-based resins and methyl phenyl silicone-based resins, can be preferably used. Specific examples of the silicone-based resin include polyalkylphenylsiloxane, for example.

[0034] As the nanoparticles 17, inorganic nanoparticles composed of inorganic compounds such as zirconia, alumina, silica, and titania, metal nanoparticles such as Ti, Zr, and Al, etc. can be adopted. In particular, silica nanoparticles whose surface is modified with phenyl groups can be preferably adopted. The nanoparticles may be hollow or solid.

[0035] The blending amount of the nanoparticles 17 (the ratio of the nanoparticles 17 in the total amount of the resin binder 16 and the nanoparticles 17 after firing the heat insulation layer. The same shall apply hereinafter.) is preferably 10% by volume or more and 55% by volume or less. The blending amount of the hollow particles 12 (the ratio of the hollow particles 15 in the heat insulation layer 11 after firing. The same shall apply hereinafter.) can be adjusted according to the heat insulation performance required for the heat insulation layer 14, etc. The blending amount of the hollow particles 15 can be, for example, 30% by volume or more and 60% by volume or less. It is more preferably 40% by volume or more and 55% by volume or less.

[0036] <Formation of the heat insulation layer> A heat insulation material containing the hollow particles 15, the resin binder 16, the nanoparticles 17, and a solvent is prepared, applied to the crown surface 9 of the piston 1, and dried and fired to form the heat insulation layer 14. In preparing the heat insulation material, first, a reactive silicone-based resin solution for the binder is obtained by adding a solvent such as toluene to the raw material resin solution. Nanoparticles are added to this reactive silicone-based resin solution and stirred, and further, hollow particles are added and stirred to obtain a liquid heat insulation material for coating the crown surface 9 of the piston 1. The firing after coating the heat insulation material can be carried out by heating the piston 1 coated with the heat insulation material at a temperature of about 100 to 200°C for several minutes to several hours.

[0037] <Heat insulation material coating device> For coating the heat insulation material on the crown surface 9 of the piston 1, the robot 20 shown in Fig. 3 is used. That is, a dot coating gun (dispenser) 21 shown in Fig. 4 or a spray coating gun 22 shown in Fig. 5 is attached to this robot 20 to perform the coating of the heat insulation material.

[0038] As shown in FIG. 3, the robot 20 includes a robot head 24 that supports a dot painting gun 21 or a spray painting gun 22, a horizontal movement device 25 that horizontally moves the robot head 24, a pedestal 26 that supports the horizontal movement device 25 with a column, and a robot controller (not shown). The robot head 24 is provided with a vertical movement device 27 that vertically moves the gun mounting jig 23. Therefore, the gun mounting jig 23 can be horizontally moved by the horizontal movement device 25 and vertically moved by the vertical movement device 35. The gun mounting jig 23 is provided on the vertical movement device 27 so as to be rotatable about a horizontal axis orthogonal to the horizontal movement direction.

[0039] A support base 30 is movably provided on the pedestal 26 in a horizontal direction orthogonal to the horizontal movement direction, and a turning device 28 is supported on the support base 30. The turning device 28 is attached with a piston mounting base 29 that supports a piston 1 such that its axis is vertical. The turning device 28 rotates the piston 1 attached to the piston mounting base 29 about its axis.

[0040] As shown in FIG. 4, the dot painting gun 21 includes a discharge head 32 having a nozzle 31 that discharges a heat insulating material, a syringe 33 that stores the heat insulating material, and a silencer 34. The syringe 33 and the silencer 34 are connected to the discharge head 31. A pressurized air source for pressurizing the heat insulating material in the syringe 33 is connected to the upper end of the syringe 33 via a hose 35. A heater 36 for heating the heat insulating material to be discharged is provided at the tip of the discharge head 32.

[0041] As shown in Fig. 6, in the discharge head 32 of the dot painting gun 21, a plunger chamber 41 and a heat insulating material chamber 42 are provided with vertical partitioning. A plunger rod 44 provided on the plunger 43 in the plunger chamber 41 is inserted into the heat insulating material chamber 42. An air supply port 45 and an exhaust port 46 are provided in the front chamber of the plunger 43 in the plunger chamber 41, ahead of the most forward position of the plunger 43. A pressurized air source is connected to the air supply port 45 via the air supply hose 48 shown in Fig. 4. The connection of the air supply port 45 and the exhaust port 46 to the front chamber is switched by the valve 47. The heat insulating material is pressurized and supplied to the heat insulating material chamber 42 from the syringe 33.

[0042] In the dot painting gun 21, by switching the connection of the air supply port 45 and the exhaust port 46 in the front chamber of the plunger chamber 41, the plunger 43 moves forward and backward, and the heat insulating material is discharged in a dot (droplet) state from the discharge hole of the nozzle 31. The dot painting gun 21 of the present embodiment is a seating method in which the plunger rod 44 contacts the valve seat on the heat insulating material chamber 42 side so as to close the discharge hole of the nozzle 31 to form a dot (droplet). Note that a non-seating method may also be used.

[0043] As shown in Fig. 5, the spray painting gun 22 includes a discharge head 51 that discharges the heat insulating material, and a syringe 52 that stores the heat insulating material to be sent to the discharge head 51. At the upper end of the syringe 52, a pressurized air source for pressurizing the heat insulating material in the syringe 52 is connected via a hose 53. The discharge head 52 is provided with a heat insulating material nozzle and a needle valve for opening and closing this nozzle inside, an air cap 54 is provided at the tip, and a heat insulating material discharge portion 55 is provided on the air cap 54. An operating air supply hose 56, an atomizing air supply hose 57, and a pattern air supply hose 58 for operating the needle valve are connected to the discharge head 51.

[0044] In the spray painting gun 22, when the needle valve retracts, the heat insulating material supplied from the syringe 52 jets out from the nozzle, and the heat insulating material is atomized by the atomizing air and formed into an appropriate pattern by the pattern air and discharged from the discharge portion 55 of the air cap 54.

[0045] <Application of heat insulation material to piston crown surface> One application mode is to apply the heat insulation material to the annular flat part 12 (the hatched part in Fig. 7) of the crown surface 9 shown in Fig. 7 by dispenser coating, that is, by dot coating with the dot coating gun 21 in this embodiment, and then apply the heat insulation material to the inner surface of the cavity of the crown surface 9 (the blank part in Fig. 7) by spray coating with the spray coating gun 22.

[0046] Attach the dot coating gun 21 to the gun mounting jig 23 of the robot 20 shown in Fig. 3, operate the horizontal movement device 25 and the vertical movement device 27, and horizontally move the support base 30, so that, as shown in Fig. 8, the nozzle 31 of the dot coating gun 21 is vertically arranged facing the outer peripheral edge of the annular flat part 12 of the crown surface 9. That is, position the dot coating gun 21 so that the coating position of the heat insulation material is the outer peripheral edge of the annular flat part 12. The piston 1 is supported by the piston mounting base 29 via the support ring 60.

[0047] Then, while rotating the piston 1 around its axis by the turning device 28, operate the dot coating gun 21 to discharge the heat insulation material linearly (in a dotted line shape) from the nozzle 31 and apply it onto the annular flat part 12. Due to the rotation of the piston 1, the coating position of the heat insulation material on the annular flat part 12 moves in the circumferential direction of the annular flat part 12. The dot-shaped heat insulation materials 61 sequentially coated on the annular flat part 12 wet and spread to connect with each other, and a continuous heat insulation layer is formed in the circumferential direction of the annular flat part 12.

[0048] Every time the piston 1 makes one revolution, move the dot coating gun 21 inward in the radial direction of the piston 1 by a predetermined amount (a distance corresponding to the width of the heat insulation layer formed by the movement of the coating position of the heat insulation material in the circumferential direction of the annular flat part 12). In this way, as the coating position of the heat insulation material on the annular flat part 12 sequentially moves inward in the radial direction of the piston 1, a heat insulation layer spreading in the radial direction is formed. When the heat insulation material is applied to the inner peripheral edge of the annular flat part 12, stop the coating by the dot coating gun 21.

[0049] In the above dot coating, unlike spray coating, since the heat insulation material does not diffuse from the coating gun but travels straight as droplets toward the crown surface of the piston, scattering of the heat insulation material around the crown surface can be avoided. Therefore, the coating efficiency of the heat insulation material is increased, and masking of the side surface of the piston can be simplified or the masking becomes unnecessary, which is advantageous for improving productivity. Further, when moving the coating position of the heat insulation material in the circumferential direction of the annular flat portion 12, the piston 1 is rotated and the position of the dot coating gun 21 is fixed, so the straightness of the heat insulation material ejected from the nozzle 31 is not disturbed. Therefore, it becomes easy to form a heat insulation layer with a uniform thickness over the entire circumferential length of the annular flat portion 12.

[0050] Hereinafter, although not intended to limit the invention, the requirements for dot coating will be described. The viscosity of the heat insulation material ejected from the dot coating gun 21 is preferably 0.20 dPa·s or more, more preferably 0.30 dPa·s or more, from the viewpoint of avoiding dripping from the nozzle 31, and is preferably 0.80 dPa·s or less so that the dot-shaped heat insulation materials 61 spread and connect to each other on the crown surface 9. The temperature of the heat insulation material is preferably 10°C or more from the viewpoint of good film-forming properties, and is preferably 50°C or less from the viewpoint of avoiding pre-curing due to solvent volatilization and catalytic reaction. If the clearance between the tip of the nozzle 31 and the annular flat portion 12 is 1 mm or more and 10 mm or less, it is easy to apply the heat insulation material to the intended coating position.

[0051] The discharge amount per shot of the heat insulation material (the amount of one dot-shaped heat insulation material) is preferably about 0.4 mg or more and 1.5 mg or less, for example. The rotation speed of the piston 1 is preferably 40° / s or more and 550° / s or less in terms of the rotation angle, for example, and the discharge frequency is preferably 10 Hz or more and 400 Hz or less, for example.

[0052] Here, the coating pitch of the dot-shaped heat insulating material 61 in the circumferential direction of the annular flat portion 12 depends on the rotational speed of the piston 1 and the discharge frequency. When the coating pitch is short, adjacent dot-shaped heat insulating materials 61 overlap more, the coating state is likely to be disturbed, and the heat insulating layer also becomes thicker. When the coating pitch is long, the interval between adjacent dot-shaped heat insulating materials 61 becomes wider, and the connection due to wet spreading deteriorates. Also, as the discharge amount increases, adjacent dot-shaped heat insulating materials 61 are more likely to overlap each other.

[0053] Therefore, with the discharge amount being constant, it is preferable to set an optimal coating pitch according to the rotational speed and the discharge frequency so that a linear heat insulating layer that is continuous in the circumferential direction and has less disturbance is formed by the movement of the coating position of the heat insulating material in the circumferential direction.

[0054] As the coating position of the heat insulating material moves from the outer peripheral edge to the inner peripheral edge of the annular flat portion 12, the circumferential length of the portion of the annular flat portion 12 where the heat insulating material is coated becomes shorter. Therefore, in order to make the coating pitch of the heat insulating material constant at each part in the radial direction of the annular flat portion 12, with the discharge amount and the discharge frequency being constant, as the coating position of the heat insulating material moves inward in the radial direction, the rotational speed of the piston 1 is decreased. Or, with the discharge amount and the rotational speed of the piston 1 being constant, the coating pitch is made constant by decreasing the discharge frequency as the coating position of the heat insulating material moves inward in the radial direction. By making the discharge amount and the coating pitch constant, a heat insulating layer with a uniform thickness can be formed over the entire annular flat portion 12.

[0055] After the dot coating of the annular flat portion 12, the inner surface of the cavity 11 of the crown surface 9 is spray-coated. That is, the spray coating gun 22 is attached to the gun mounting jig 23 of the robot 20 shown in FIG. 3, the horizontal movement device 25 and the vertical movement device 27 are operated, and the support base 30 is horizontally moved so that the discharge portion 55 of the spray coating gun 22 faces the inner circumferential surface of the cavity 11 of the crown surface 9 as shown in FIG. 9.

[0056] Then, while rotating the piston 1 supported by the piston mounting base 29 around the axis by the rotating device 28, the spray painting gun 22 is operated to spray the heat insulating material from the discharge part 55. Since the piston 1 is rotating, the heat insulating material is applied over the entire inner peripheral surface of the cavity 11. Subsequently, by operating the robot 20 to move the spraying position of the heat insulating material from the inner peripheral surface of the cavity 11 toward the raised part 13, the heat insulating material is applied over the entire inner surface of the cavity 11. Thereby, a heat insulating layer continuous with the heat insulating layer of the annular flat part 12 can be formed on the inner surface of the cavity 11.

[0057] Since the application of spray painting is limited to the inner surface of the cavity 11, it becomes easy to avoid the scattering of the heat insulating material around the crown surface by spray painting. Also, the inner peripheral surface of the cavity that descends in the axial direction of the piston 1 from the inner peripheral edge of the annular flat part 12 to the deepest part of the cavity 11 is a curved surface, and since spray painting, which has a large selection width of the coating (spraying) pattern rather than dispenser coating, is applied there, it becomes easy to apply the heat insulating material efficiently and evenly. Furthermore, since spray painting is performed after dot painting, it is easy to make the heat insulating layer by spray painting continuous with the heat insulating layer by dot painting.

[0058] Hereinafter, although not meant to limit the invention, the requirements for spray painting will be described. The viscosity of the heat insulating material is preferably 0.20 dPa·s or more and 0.40 dPa·s or less from the viewpoints of atomization of the heat insulating material and thus film forming property. Although the viscosity of the heat insulating material in dot painting is preferably set higher from the viewpoint of preventing dripping as described above, the viscosity of the heat insulating material in spray painting is preferably lower than the viscosity of the heat insulating material in dot painting. Thereby, since the heat insulating material becomes easy to spread, it becomes easy to prevent coating leakage at the boundary between the dot painting part and the spray painting part.

[0059] In spray coating, the discharge rate of the heat insulating material is preferably, for example, 30 mg / s or more and 300 mg / s or less, and the temperature of the heat insulating material is preferably 10°C or more and 40°C or less. The rotation speed of the piston 1 is preferably 200° / s or more and 550° / s or less, and the gun movement speed is preferably 50 mm / s or more and 200 mm / s or less. Further, the gun distance from the discharge part of the spray coating gun 22 to the coating surface is preferably 10 mm or more and 200 mm or less.

[0060] In the coating method of the above embodiment, the entire inner surface of the cavity 11 is spray-coated. However, for the raised portion 13 in the cavity 11, dispenser coating may be applied. That is, as shown in FIG. 10, for the annular flat portion 12 and the raised portion 13 (the hatched portion in FIG. 10), the heat insulating layer is formed by a dispenser (dot coating gun 21 in the above embodiment) with the discharge direction of the heat insulating material in the axial direction of the piston, and then, between the inner peripheral surface of the cavity between the annular flat portion 12 and the raised portion 13 and the base of the raised portion 13 (the blank portion in FIG. 10), the heat insulating material is sprayed by the spray coating gun 22 to form a heat insulating layer straddling the heat insulating layer of the annular flat portion 12 and the heat insulating layer of the raised portion 13.

[0061] In the above embodiment, the nozzle 31 of the dot coating gun 21 has one nozzle, but a dot coating gun having a plurality of nozzles may also be used. The plurality of nozzles may be arranged side by side in the circumferential direction of the annular flat portion 12 or in the radial direction of the piston 1. When the plurality of nozzles are arranged side by side in the radial direction, in order to equalize the thickness of the heat insulating layer, when the discharge amounts of those nozzles are made the same, the discharge frequency of the inner nozzle in the radial direction is lowered, and when the discharge frequencies of those nozzles are made the same, the discharge amount of the inner nozzle in the radial direction is reduced.

[0062] Further, in the above embodiment, a dot coating gun is adopted as the dispenser, but the dispenser may be a continuous discharge type such as a screw method that continuously discharges the heat insulating material from the nozzle (discharges in a continuous line shape).

Explanation of reference numerals

[0063] 1 piston 9 crown surface 11 cavity 12 annular flat part 13 raised part 14 heat insulation layer 20 robot 21 dot painting gun (dispenser) 22 spray painting gun 28 swivel device 61 dot-shaped heat insulating material

Claims

1. A method for applying a heat insulating material to form a heat insulating layer on the crown surface of a piston of an engine, comprising: arranging a dispenser for linearly discharging the heat insulating material toward the crown surface; while discharging the heat insulating material from the dispenser toward the crown surface, moving the application position of the heat insulating material on the crown surface in the circumferential direction of the crown surface; the crown surface has a cavity in the central portion, and an annular flat portion is formed around the cavity; for the annular flat portion, forming the heat insulating layer by making the discharge direction of the heat insulating material by the dispenser in the axial direction of the piston, and then, spraying the heat insulating material onto the inner surface of the cavity by a spray gun to form a heat insulating layer following the heat insulating layer on the annular flat portion. A method for applying a heat insulating material to a piston, characterized by the above.

2. In Claim 1, moving the application position of the heat insulating material on the crown surface in the circumferential direction of the crown surface by fixing the position of the dispenser and rotating the piston around its axis. A method for applying a heat insulating material to a piston, characterized by the above.

3. In Claim 1 or 2, the dispenser is a dot coating gun that discharges the heat insulating material in a dot shape at a predetermined interval, and spreading the dot-shaped heat insulating material to make it continuous in the circumferential direction of the crown surface. A method for applying a heat insulating material to a piston, characterized by the above.

4. In Claim 3, each time the application position of the heat insulating material moves in the circumferential direction on the crown surface and makes one or several rounds, moving the application position of the heat insulating material on the crown surface in the radial direction of the piston to form a continuous heat insulating layer in the radial direction on the crown surface. A method for applying a heat insulating material to a piston, characterized by the above.

5. In Claim 4, Position the dispenser so that the application position of the heat insulation material on the crown surface is at the peripheral edge of the crown surface. In this state, rotate the piston around its axis to start discharging the heat insulation material, and each time the piston makes one full rotation, move the application position of the heat insulation material inward in the radial direction by a predetermined amount. A method for applying a heat insulation material to a piston, characterized by this.

6. In claim 5, The dispenser is the dot coating gun, The discharge amount per shot and the discharge frequency of the dot coating gun are kept constant, and as the application position of the heat insulation material moves inward in the radial direction, the rotation speed of the piston is increased. A method for applying a heat insulation material to a piston, characterized by this.

7. In claim 5, The dispenser is the dot coating gun, The discharge amount per shot of the dot coating gun and the rotation speed of the piston are kept constant, and as the application position of the heat insulation material moves inward in the radial direction, the discharge frequency of the dot coating gun is decreased. A method for applying a heat insulation material to a piston, characterized by this.

8. A method for applying a heat insulation material to form a heat insulation layer on the crown surface of a piston of an engine, Arrange a dispenser that discharges the heat insulation material linearly facing the crown surface, While discharging the heat insulation material from the dispenser toward the crown surface, move the application position of the heat insulation material on the crown surface in the circumferential direction of the crown surface, The crown surface has a cavity at the central part, and the area around this cavity is an annular flat part, and the central part of the cavity has a raised part. For the annular flat part and the raised part, form the heat insulation layer by making the discharge direction of the heat insulation material by the dispenser in the axial direction of the piston, and then, A method for applying a heat insulating material to a piston, characterized in that a heat insulating layer spanning the heat insulating layer of the annular flat portion and the heat insulating layer of the raised portion is formed by spraying the heat insulating material between the annular flat portion and the raised portion with a spray gun.

9. In claim 8, A method for applying a heat insulating material to a piston, characterized in that the position of the dispenser is fixed and the piston is rotated about its axis to move the application position of the heat insulating material on the crown surface in the circumferential direction of the crown surface.

10. In claim 8 or 9, the dispenser is a dot coating gun that discharges the heat insulating material in a dot shape at predetermined intervals, A method for applying a heat insulating material to a piston, characterized in that the dot-shaped heat insulating material is spread by wetting and made continuous in the circumferential direction of the crown surface.

11. In claim 10, A method for applying a heat insulating material to a piston, characterized in that each time the application position of the heat insulating material on the crown surface moves in the circumferential direction and makes one or several rounds on the crown surface, the application position of the heat insulating material on the crown surface is moved in the radial direction of the piston to form a continuous heat insulating layer in the radial direction on the crown surface.

12. In claim 11, A method for applying a heat insulating material to a piston, characterized in that the dispenser is positioned so that the application position of the heat insulating material on the crown surface becomes the peripheral edge of the crown surface, and in this state, the piston is rotated about its axis to start discharging the heat insulating material, and each time the piston makes one round, the application position of the heat insulating material is moved inward in the radial direction by a predetermined amount.

13. In claim 12, the dispenser is the dot coating gun, A method for applying a heat insulating material to a piston, characterized in that the discharge amount and discharge frequency per shot of the dot coating gun are kept constant, and the rotation speed of the piston is increased as the application position of the heat insulating material moves inward in the radial direction.

14. In claim 12, The dispenser is the dot coating gun, A method for applying a heat insulating material to a piston, characterized in that the discharge amount per shot of the dot coating gun and the rotational speed of the piston are kept constant, and the discharge frequency of the dot coating gun is decreased as the coating position of the heat insulating material moves inward in the radial direction.

15. In claim 1 or claim 8, A method for applying a heat insulating material to a piston, characterized in that the viscosity of the heat insulating material discharged from the spray coating gun is lower than the viscosity of the heat insulating material discharged from the dispenser.

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