Method for Applying Heat Insulating Material to Piston

Abstract

To improve coating efficiency in coating of heat shield material for a piston crown surface.SOLUTION: A coating method of heat shield material for a piston 100 is a coating method which coats heat shield material for formation of a heat shield layer on a crown surface 110 of the piston 100. A masking component 200 includes: a first part 211 which has a first clearance C1 between a side face 120 of the piston 100 and the first part and covers at least one part of the side face 120; and a second part 221 which has a second clearance C2 between an outer periphery part 114 of the crown surface 110 and the second part and covers the outer periphery part 114. The coating method thereof performs coating of the heat shield material while masking the piston 100 with the masking component.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for applying a heat insulating material to a piston.

Background Art

[0002] Generally, in order to reduce the cooling loss of an engine and improve fuel efficiency, a heat insulating layer is provided on the wall surface forming the combustion chamber of the engine (such as the crown surface of the piston, the lower surface of the cylinder head, etc.). 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 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 general spray coating, there is a problem that the amount of overspray of the heat insulating material scattered on the wall surface other than the crown surface of the piston is large, and the coating efficiency is low. Considering the high paint cost, from the viewpoint of suppressing the manufacturing cost of the piston, the development of a coating method capable of improving the coating efficiency is desired.

[0005] Therefore, in the present disclosure, in the application of the heat insulating material to the crown surface of the piston, the coating efficiency is improved.

Means for Solving the Problems

[0006] In order to solve the above problems, a method for applying a heat insulating material to a piston according to an embodiment of the present disclosure is Inserted into the cylinder bore of the engine's cylinder block a method for applying a heat insulating material for forming a heat insulating layer to the crown surface of the piston, The piston includes the crown surface, a skirt portion, and a side surface extending from the outer peripheral end of the crown surface toward the skirt portion side. of the piston TheA first portion having a first clearance from a side surface and covering at least a part of the side surface, and the Including the outer peripheral end A second portion having a second clearance from an outer peripheral portion of the crown surface and covering the outer peripheral portion, mask the piston with a masking member, While blowing air from the skirt portion side to the crown surface side of the piston through the first clearance and the second clearance Characterized in that the heat insulating material is applied.

[0007] According to this configuration, since the amount of the heat insulating material adhering to the wall surface other than the crown surface of the piston can be reduced, the coating efficiency of the heat insulating material on the crown surface can be improved. In addition, since the heat insulating layer formed on the outer peripheral portion of the crown surface of the piston contributes little to reducing the cooling loss of the engine and improving the fuel efficiency, appropriate application of the heat insulating material can be realized by appropriately suppressing the application amount of the heat insulating material on the outer peripheral portion.

[0008] In this configuration While blowing air from the skirt portion side to the crown surface side of the piston through the first clearance and the second clearance, apply the heat insulating material Yes.

[0009] If spray dust due to overspray of the heat insulating material adheres to the side surface of the piston, it may damage the cylinder bore surface when the piston reciprocates, leading to deterioration of fuel efficiency due to compression leakage. According to this configuration, the adhesion of the heat insulating material to the side surface of the piston can be effectively suppressed by blowing air.

[0010] The flow velocity of the air at the outlet of the second clearance is preferably more than 0.03 m / s and less than 0.69 m / s.

[0011] By setting the flow velocity of the air at the outlet of the second clearance within the above range, while effectively reducing the adhesion amount of the spray dust to the piston side surface, a high coating efficiency on the piston crown surface can be ensured.

[0012] The flow velocity of the air at the air outlet is preferably more than 0.1 m / s and less than 4 m / s.

[0013] By setting the air flow velocity at the air outlet within the above range, it is possible to effectively reduce the amount of spray dust adhering to the piston side surface while ensuring a high coating efficiency on the piston crown surface.

[0014] The masking member includes a cylindrical housing member that houses the piston inside, and a ring-shaped lid member that is connected to the housing member so as to cover one axial end of the housing member and has an inner diameter smaller than the inner diameter of the one end. Preferably, the first part is constituted by the part on the one end side of the housing member, and the second part is constituted by the inner peripheral part of the lid member.

[0015] According to this configuration, it is possible to reduce the amount of spray dust adhering to the wall surface other than the crown surface of the piston with a simple configuration.

[0016] Preferably, the radial width of the inner peripheral part of the lid member is 0.5 mm or more and 5 mm or less.

[0017] According to this configuration, it is possible to suppress the amount of heat insulating material applied to the outer peripheral part while ensuring a sufficient amount of heat insulating material applied to the crown surface of the piston.

[0018] Preferably, the spray gun arranged on the crown surface side of the piston is fixed and the piston is moved to apply the heat insulating material to the crown surface.

[0019] According to this configuration, by fixing the spray gun, the straightness of the droplets sprayed from the spray gun can be ensured. Then, by moving the piston, the adhesion of spray dust to the wall surface other than the crown surface of the piston can be suppressed, and the coating efficiency of the heat insulating material on the crown surface can be improved.

[0020] The heat insulating material is applied to the crown surface by the spray gun arranged on the crown surface side of the piston, and it is preferable to maintain the relative position of the spray gun with respect to the piston inside the outer peripheral end of the crown surface.

[0021] According to this configuration, since the relative position of the spray gun with respect to the piston is maintained inside the outer peripheral end of the crown surface, it is possible to suppress the spray gun from being positioned outside the crown surface with respect to the crown surface of the piston, and overspray of the heat insulating material is suppressed.

[0022] Preferably, the second clearance is larger than the first clearance.

[0023] According to this configuration, by setting the second clearance to be larger than the first clearance, it is possible to effectively suppress the adhesion of spray dust to the piston side surface while appropriately ensuring the coating amount of the heat insulating material on the outer peripheral portion of the piston crown surface.

[0024] Preferably, the first clearance is 0.1 mm or more and 0.5 mm or less.

[0025] By setting the first clearance within the above range, it is possible to effectively suppress the adhesion of spray dust to the piston side surface.

[0026] Preferably, the second clearance is 0.3 mm or more and 1.0 mm or less.

[0027] By setting the second clearance within the above range, it is possible to appropriately form the heat insulating layer on the outer peripheral portion of the piston crown surface while ensuring a high coating efficiency on the piston crown surface.

Effect of the Invention

[0028] As described above, according to the present disclosure, since the amount of the heat insulating material adhering to the wall surface other than the crown surface of the piston can be reduced, the coating efficiency of the heat insulating material on the crown surface can be improved. Further, by appropriately suppressing the coating amount of the heat insulating material on the outer peripheral portion of the crown surface, appropriate coating of the heat insulating material can be realized.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

MODE FOR CARRYING OUT THE INVENTION

[0030] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the present disclosure, its applications, or its uses.

[0031] A method for applying a heat insulating material to a piston according to an embodiment of the present disclosure is a method for applying a heat insulating material for forming a heat insulating layer to the crown surface of the piston. FIGS. 1 to 3 are diagrams showing an example of the configuration of a heat insulating material applying apparatus for carrying out the heat insulating material applying method. FIG. 4 is a diagram for explaining the steps of the heat insulating material applying method. Note that FIGS. 1, 2, and 4 may include partial cross-sections, but hatching is omitted for simplicity.

[0032] <Piston> As shown in FIGS. 1 and 2, the piston 100 includes a crown surface 110, a side surface 120, and a skirt portion 130. The crown surface 110 includes a cavity 111 at the center thereof, and a raised portion 112 is formed around the cavity 111. The outside of the raised portion 112 is an annular flat portion 113. The outer peripheral portion 114 of the annular flat portion 113 corresponds to the outer peripheral portion of the crown surface 110 including the outer peripheral end of the crown surface 110.

[0033] The piston 100 is made of, for example, an aluminum alloy and is inserted into a cylinder bore (not shown) of a cylinder block (not shown) of the engine. The combustion chamber of the engine is formed by the crown surface 110 of the piston 100, the inner peripheral surface of the cylinder bore, a cylinder head (not shown), and the front surface of the umbrella portion (the surface facing the combustion chamber) of an intake / exhaust valve (not shown) that opens and closes the intake / exhaust ports (not shown) of the cylinder head.

[0034] The above shape and the like of the piston 100 are merely examples and can be appropriately changed according to the configuration of the engine and the like. Note that the engine may be a gasoline engine or a diesel engine.

[0035] [Heat insulation layer] The heat insulation layer formed on the crown surface 110 of the piston 100 is not limited as long as it can be formed by the method for forming the heat insulation layer described later. Specifically, the heat insulation layer may include, for example, a large number of hollow particles made of inorganic oxides or ceramics, and a resin binder that fixes the hollow particles to the crown surface 110 and fills the spaces between the hollow particles to form the base material (matrix) of the heat insulation layer. Nano particles may be dispersed in the resin binder.

[0036] The thickness of the heat insulation layer 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, those having a particle size in the μm order smaller than the thickness of the heat insulation layer are used. The average particle size is preferably, for example, 30 μm or less. For example, hollow particles having 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 nano particles 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 restrictive.

[0037] As the hollow particles, inorganic hollow particles are adopted. For example, it is preferable to adopt ceramic hollow particles containing Si-based oxide components (such as silica) or Al-based oxide components (such as alumina) such as glass balloons, glass bubbles, fly ash balloons, shirasu balloons, silica balloons, and aluminosilicate balloons. The hollowness ratio of the hollow particles is preferably 60% by volume or more, and more preferably 70% by volume or more.

[0038] As the resin binder, for example, silicone resins composed of three-dimensional polymers with a high degree of branching, typified by methyl silicone resins and methylphenyl silicone resins, can be preferably used. Specific examples of the silicone resin include polyalkylphenylsiloxane.

[0039] As the nanoparticles, 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 a phenyl group can be preferably adopted. The nanoparticles may be hollow or solid.

[0040] The blending amount of the nanoparticles (the ratio of the nanoparticles in the total amount of the resin binder and the nanoparticles 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 (the ratio of the hollow particles in the heat insulation layer after firing. The same shall apply hereinafter.) can be adjusted according to the heat insulation performance required for the heat insulation layer, etc. The blending amount of the hollow particles can be, for example, 30% by volume or more and 60% by volume or less. The blending amount is more preferably 40% by volume or more and 55% by volume or less.

[0041] [Method for forming the heat insulation layer] Prepare a liquid heat insulation material, apply it to the crown surface 110 of the piston 100, and form a heat insulation layer by drying and baking. The heat insulation material contains, for example, the above-mentioned hollow particles, resin binder, nanoparticles and solvent as required. In preparing such a 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 as required and stirred, and further, hollow particles are added and stirred to obtain a liquid heat insulation material for application to the crown surface 110 of the piston 100. The baking after the application of the heat insulation material can be carried out by heating the piston 100 coated with the heat insulation material at a temperature of about 100 to 200 °C for several minutes to several hours.

[0042] Details of the method for applying the heat insulation material to the crown surface 110 will be described later.

[0043] <Heat Insulation Material Coating Device and Coating Method> As shown in FIGS. 3 and 4, the heat insulation material coating device 500 includes a conveyor 501, a first robot 510, a second robot 520, a painting booth 530, and a temporary placement table 540.

[0044] The piston 100 supplied by the conveyor 501 is placed at the pickup position (S1) and picked up by the first robot arm 511 of the first robot 510 (S2). The first robot arm 511 rotates around an axis perpendicular to the plane of FIG. 3 on the first base 512 of the first robot 510 and sets the piston 100 on the table 300 (see FIG. 4) at the piston set position 503 (S3). Then, the first robot 510 picks up the masking member 200 arranged on the temporary placement table 540 by the first robot arm 511. Then, the masking member 200 is placed over the piston 100 arranged at the piston set position 503 from above. Thus, the piston 100 is in a masked state by the masking member 200 (S4).

[0045] Next, the second robot arm 521 of the second robot 520 supports the masked piston 100. The second robot arm 521 rotates around an axis perpendicular to the plane of FIG. 3 on the second base 522 of the second robot 520, and sets the masked piston 100 at the painting position in the painting booth 530. Then, a heat insulation material is spray-coated on the crown surface 110 of the piston 100 in the masked state by a spray gun 531 (see FIG. 4) disposed on the crown surface 110 side (S5).

[0046] When the application of the heat insulation material is completed, the second robot arm 521 rotates around the axis of the second base 522 and returns the piston 100 with the masking member 200 set thereon to the piston setting position 503. Then, the masking member 200 is removed from the piston 100 by the first robot arm 511 (S6), and the masking member 200 is returned to the temporary placement table 540. Thereafter, the first robot arm 511 picks up the piston 100 coated with the heat insulation material (hereinafter also referred to as "painted product") (S7) and places it on the conveyor 501. Then, the painted product is carried out by the conveyor 501 (S8). The carried-out painted product becomes a product through processes such as baking as described above.

[0047] [Masking member] As shown in FIGS. 1 and 2, the masking member 200 includes a cylindrical housing member 210 and a ring-shaped lid member 220.

[0048] The housing member 210 houses the piston 100 inside. The first portion 211 of the housing member 210 is constituted by a portion on the one end 213 side in the axial direction of the housing member 210, has a first clearance C1 with the side surface 120 of the piston 100, and covers at least a part of the side surface 120. Specifically, the inner peripheral surface of the first portion 211 covers the portion of the side surface 120 on the crown surface 110 side over the entire circumference of the side surface 120. Note that the inner peripheral surface of the first portion 211 may cover the entire side surface 120.

[0049] The lid member 220 is connected to the housing member 210 so as to cover one end 213 of the housing member 210. The inner diameter of the lid member 220 is smaller than the inner diameter of the one end 213. A second portion 221 formed by the inner peripheral portion of the lid member 220 has a second clearance C2 with the outer peripheral portion 114 and covers the outer peripheral portion 114.

[0050] By applying the heat insulation material in a state where the piston 100 is masked by such a masking member 200, the amount of the heat insulation material adhering to the wall surface other than the crown surface 110 of the piston 100 can be reduced, so that the coating efficiency of the heat insulation material on the crown surface 110 can be improved. In addition, since the heat insulation layer formed on the outer peripheral portion 114 contributes little to reducing the cooling loss of the engine and improving the fuel efficiency, appropriate application of the heat insulation material can be achieved by appropriately suppressing the application amount of the heat insulation material on the outer peripheral portion 114.

[0051] Note that the radial width 221A of the second portion 221 of the lid member 220 is preferably 0.5 mm or more and 5 mm or less from the viewpoint of ensuring a sufficient amount of the heat insulation material applied to the crown surface 110 while suppressing the amount of the heat insulation material applied to the outer peripheral portion 114. Also, in the piston 100 shown in FIG. 1, the width 221A is desirably 5 mm or less from the viewpoint of the configuration in which the second portion 221 does not contact the raised portion 112.

[0052] Also, the second clearance C2 is preferably larger than the first clearance C1. Thereby, while appropriately ensuring the application amount of the heat insulation material on the outer peripheral portion 114, the adhesion of the spray dust to the side surface 120 can be effectively suppressed.

[0053] Incidentally, the first clearance C1 is preferably 0.1 mm or more and 0.5 mm or less. If the first clearance C1 is less than the lower limit value, the masking member 200 may come into contact with the side surface 120. Further, as will be described later, when blowing air from the air mechanism 400, if the first clearance C1 is less than the lower limit value, the blowing speed and blowing amount of air toward the crown surface 110 side may excessively decrease. On the other hand, if the first clearance C1 exceeds the upper limit value, the adhesion amount of spray dust to the side surface 120 may increase. By setting the first clearance C1 within the above range, the adhesion of spray dust to the side surface 120 can be effectively suppressed.

[0054] Also, the second clearance is preferably 0.3 mm or more and 1.0 mm or less. If the second clearance C2 is less than the lower limit value, the second portion 221 of the lid member 220 may contact the surface of the heat insulation material coating film formed by the heat insulation material entering the second clearance C2 and the surface may be disturbed. If the second clearance C2 exceeds the upper limit value, the amount of heat insulation material entering the second clearance C2 may increase, which may lead to a decrease in the coating efficiency on the crown surface 110. By setting the second clearance C2 within the above range, while ensuring a high coating efficiency on the crown surface 110, the heat insulation layer of the outer peripheral portion 114 can be appropriately formed.

[0055] However, the above numerical range is a preferred range and is not limiting.

[0056] Incidentally, the housing member 210 and the lid member 220 may be integral or separate. The material of the masking member is not particularly limited and may be a general material such as metal or resin.

[0057] [Air mechanism] In the step S5 of coating the heat insulation material, as shown in FIG. 1, while blowing air from the skirt portion 130 side of the piston 100 toward the crown surface 110 side through the first clearance C1 and the second clearance C2 by the air mechanism 400 disposed on the table 300, the heat insulation material may be applied.

[0058] When spray dust due to overspray of the heat shield material adheres to the side surface 120 of the piston 100, it may damage the cylinder bore surface (not shown) when the piston 100 reciprocates, leading to deterioration of fuel efficiency due to compression leakage. By blowing air, the amount of spray dust of the heat shield material adhering to the side surface 120 of the piston 100 can be effectively reduced.

[0059] Note that the flow velocity of the air blown out from the outlet 221B of the second clearance C2 is not intended to be limited, but is preferably more than 0.03 m / s and less than 0.69 m / s, more preferably 0.04 m / s or more and 0.52 m / s or less, still more preferably 0.05 m / s or more and 0.40 m / s or less, and particularly preferably 0.09 m / s or more and 0.35 m / s or less.

[0060] If the flow velocity of the air blown out from the outlet 221B of the second clearance C2 is 0.03 m / s or less, the amount of spray dust adhering to the side surface 120 may increase. Also, if the flow velocity of the air blown out from the outlet 221B is 0.69 m / s or more, the floating amount of the heat shield material may increase and the coating efficiency on the crown surface 110 may decrease. By setting the flow velocity of the air at the outlet 221B within the above range, it is possible to effectively reduce the amount of spray dust adhering to the side surface 120 while ensuring high coating efficiency on the crown surface 110.

[0061] Also, the flow velocity of the air blown out from the air outlet 403 of the air mechanism 400 is not intended to be limited, but is preferably more than 0.1 m / s and less than 4 m / s, more preferably 0.2 m / s or more and 3 m / s or less, still more preferably 0.3 m / s or more and 2 m / s or less, and particularly preferably 0.5 m / s or more and 2 m / s or less.

[0062] If the air flow velocity blown out from the air outlet 403 is 0.1 m / s or less, the adhesion amount of spray dust to the side surface 120 may increase. Further, if the air flow velocity blown out from the air outlet 403 is 4 m / s or more, the amount and velocity of the air blown out to the crown surface 110 side through the second clearance C2 increase, and the floating amount of the heat insulating material increases, which may reduce the coating efficiency on the crown surface 110. By setting the air flow velocity blown out from the air outlet 403 within the above range, while effectively reducing the adhesion amount of spray dust to the side surface 120, a high coating efficiency on the crown surface 110 can be ensured.

[0063] [Relative position of the spray gun with respect to the piston] In the step S5 of applying the heat insulating material, in order to apply the heat insulating material to the entire crown surface 110, it is preferable to change the relative position of the spray gun 531 with respect to the piston 100. As a method of changing the relative position, the piston 100 may be fixed and the spray gun 531 may be moved, or the spray gun 531 may be fixed and the piston 100 may be moved. Preferably, the method is to fix the spray gun 531 and move the piston 100. By fixing the spray gun 531, the straightness of the droplets sprayed from the spray gun 531 can be ensured. Then, by moving the piston 100, the adhesion of spray dust to the wall surfaces other than the crown surface 110 can be suppressed, and the coating efficiency of the heat insulating material on the crown surface 110 can be improved.

[0064] Note that the movement path, that is, the trajectory of the piston 100 or the spray gun 531 is not particularly limited, but from the viewpoint of efficiently applying the heat insulating material to the crown surface 110, it is preferably a trajectory that linearly reciprocates parallel at a constant line interval in a certain direction (see FIGS. 5 and 6).

[0065] Also, it is preferable to maintain the relative position of the spray gun 531 with respect to the piston 100, in other words, inside the outer peripheral end of the crown surface 110 of the above trajectory, preferably within 1 mm to 5 mm in the radial direction of the crown surface 110 from the outer peripheral end of the crown surface 110. Thereby, it is suppressed that the spray gun 531 is positioned outside the crown surface 110 with respect to the crown surface 110, and overspray of the heat insulating material is suppressed.

[0066] [Adhesion ratio of heat insulating material] The coating efficiency, which is the adhesion ratio of the heat insulating material to the crown surface 110 of the piston 100, is preferably 66% or more, although not intended to be limiting.

[0067] Also, the adhesion ratio of the heat insulating material to the side surface 120 of the piston 100 is preferably 0.31% or less, more preferably 0.07% or less, and particularly preferably 0.05% or less, although not intended to be limiting.

Example

[0068] Next, the specifically implemented examples will be described.

[0069] The ratio (%) of the heat insulating material adhering to each part or becoming floating droplets when the heat insulating material was spray-coated on the crown surface of the piston was calculated by computer simulation using a thermal fluid program. The calculation conditions and results of Comparative Examples 1 to 3 and Examples 1 to 12 are shown in Table 1, Figure 7, and Table 2.

[0070]

Table 1

[0071]

Table 2

[0072] Note that the physical property values and spraying conditions of the heat insulating material were as shown in Table 3.

[0073]

Table 3

[0074] During spraying of the heat insulating material, one of the piston and the spray gun was fixed and the other was moved so that the heat insulating material was applied to the entire crown surface of the piston. In Tables 1 and 2, only the fixing members are shown.

[0075] Also, as the locus indicating the relative position of the spray gun with respect to the piston, the locus A shown in FIG. 5 and the locus B shown in FIG. 6 were used.

[0076] In both of the locus A and the locus B, the relative position linearly reciprocates and translates in a constant direction at a constant line interval as indicated by the arrows in FIGS. 5 and 6. In both of the locus A and the locus B, the linear speed which is the moving speed of the relative position was 150 mm / s and the line interval was 8 mm.

[0077] The locus A is set such that the width in the direction parallel to the moving direction of the relative position is ±60 mm with the bore center O of the piston being zero, and the width in the direction perpendicular to the moving direction of the relative position is ±44 mm with the bore center O of the piston being zero. That is, the locus A is set such that the relative position of the spray gun reaches a position beyond the outer peripheral end of the piston crown surface.

[0078] The locus B is set such that the width in the direction parallel to the moving direction of the relative position is 4 mm inside the outer peripheral end of the piston crown surface in the radial direction of the crown surface, and the width in the direction perpendicular to the moving direction of the relative position is ±32 mm with the bore center O of the piston being zero. That is, the locus B is set such that the relative position of the spray gun with respect to the piston is maintained inside the outer peripheral end of the crown surface.

[0079] <Comparative Examples 1 to 3> In Comparative Examples 1 to 3, spraying of the heat insulating material was performed without using a masking member.

[0080] In the piston-fixed setting, comparing Comparative Example 1 of locus A with Comparative Example 2 of locus B, the adhesion ratio of the heat insulation material to the piston crown surface, that is, the coating efficiency, increased from about 26% to about 62%. That is, from the perspective of improving the coating efficiency, it can be seen that locus B is more desirable than locus A. Therefore, in Comparative Example 3 and Examples 1 to 12, locus B is adopted.

[0081] Next, comparing Comparative Example 2 with piston fixation and Comparative Example 3 with spray gun fixation, it was found that the coating efficiency on the piston crown surface is improved with spray gun fixation compared to piston fixation. Although the coating efficiency on the piston crown surface is improved in Comparative Example 3 compared to Comparative Example 2, the adhesion ratio of spray dust to the piston side surface also increased as a result.

[0082] <Examples 1 to 4> In Examples 1 to 4, the heat insulation material was sprayed using a masking member.

[0083] The coating efficiency in Example 1 was improved compared to Comparative Example 2.

[0084] Also, compared with Example 1 with piston fixation, in Example 3 with spray gun fixation, it was found that the coating efficiency is further improved and the adhesion amount of spray dust to the piston side surface also slightly decreases.

[0085] Furthermore, in Examples 2 and 4 where air was blown out at an air flow rate of 0.5 m / s at the air outlet using an air mechanism, although the coating efficiency slightly decreased compared to Examples 1 and 3 without using the air mechanism, it was found that the adhesion amount of spray dust to the piston side surface became zero.

[0086] As shown in FIG. 7, when comparing Comparative Example 3 in which the spray gun is fixed and no masking member is used with Example 3 in which a masking member is used, it was found that the amount of spray dust adhering to the piston side surface was significantly reduced due to the presence of the masking member. Further, when comparing Example 3 in which no air mechanism is used with Example 4 in which an air mechanism is used, it was found that the amount of spray dust adhering to the piston side surface was further reduced due to the use of the air mechanism.

[0087] <Examples 5 to 8> Under the calculation conditions of Example 4, the air flow velocity at the air outlet in the air mechanism was changed to 0.1 m / s (Example 5), 0.3 m / s (Example 6), 2 m / s (Example 7), and 4 m / s (Example 8), and the air flow velocity at the outlet of the second clearance C2 and the adhesion ratio of the heat insulating material were calculated.

[0088] As shown in Example 5, when the air flow velocity at the air outlet was reduced to 0.1 m / s, although the coating efficiency on the piston crown surface increased, the amount of air blown out and the blowing speed from the outlet of the second clearance became small, and the amount of spray dust adhering to the piston side surface tended to increase.

[0089] Also, as shown in Example 8, when the air flow velocity at the air outlet was increased to 4 m / s, the amount of air blown out and the blowing speed from the second clearance excessively increased, and the amount of spray dust adhering to the piston side surface was zero, but the coating efficiency on the piston crown surface decreased as a result.

[0090] <Examples 9 to 12> Under the calculation conditions of Example 4, the first clearance C1 and the second clearance C2 were adjusted to the values shown in Table 2, and the air flow velocity at the outlet of the second clearance C2 and the adhesion ratio of the heat insulating material were calculated.

[0091] In Examples 9 and 10, the second clearance C2 was fixed at 0.5 mm and the first clearance C1 was changed to 0.3 mm and 0.5 mm, but a high coating efficiency of 66% or more was obtained, and the amount of spray dust adhering to the piston side surface was also zero.

[0092] In Examples 11 and 12, the first clearance C1 was fixed at 0.1 mm, and the second clearance C2 was changed to 0.3 mm and 1.0 mm. As a result, a high coating efficiency of 66% or more was obtained, and the amount of spray dust adhering to the piston side surface was also zero.

Industrial Applicability

[0093] The present disclosure is extremely useful because it can improve the coating efficiency in applying the heat insulating material to the crown surface of the piston.

Explanation of Signs

[0094] 100 Piston 110 Crown surface 114 Outer peripheral portion 120 Side surface 130 Skirt portion 200 Masking member 210 Housing member 211 First portion 220 Lid member 221 Second portion 221B Outlet (of the second clearance) 400 Air mechanism 403 Air outlet (of the air mechanism) 531 Spray gun C1 First clearance C2 Second clearance

Claims

1. A method of applying a heat insulating material for forming a heat insulating layer to a crown surface of a piston inserted into a cylinder bore of a cylinder block of an engine, comprising: The piston includes the crown surface, a skirt portion, and a side surface extending from an outer peripheral end of the crown surface toward the skirt portion side. While masking the piston with a masking member having a first portion that has a first clearance from the side surface of the piston and covers at least a part of the side surface, and a second portion that has a second clearance from an outer peripheral portion including the outer peripheral end of the crown surface and covers the outer peripheral portion, the heat insulating material is applied while blowing air from the skirt portion side to the crown surface side of the piston through the first clearance and the second clearance. A method for applying a heat insulating material to a piston, characterized by the above.

2. In Claim 1, The flow velocity of the air at the outlet of the second clearance is more than 0.03 m / s and less than 0.69 m / s. A method for applying a heat insulating material to a piston, characterized by the above.

3. In Claim 1 or Claim 2, The flow velocity of the air at the air outlet is more than 0.1 m / s and less than 4 m / s. A method for applying a heat insulating material to a piston, characterized by the above.

4. In any one of Claims 1 to 3, The masking member includes a cylindrical accommodating member that accommodates the piston inside, and a ring-shaped lid member that is connected to the accommodating member so as to cover one axial end of the accommodating member and has an inner diameter smaller than the inner diameter of the one end. The first portion is constituted by a portion on the one end side of the accommodating member. The second portion is constituted by an inner peripheral portion of the lid member. A method for applying a heat insulating material to a piston, characterized by the above.

5. In Claim 4, The radial width of the inner peripheral portion of the lid member is 0.5 mm or more and 5 mm or less. A method for applying a heat insulating material to a piston, characterized by this.

6. In any one of Claims 1 to 5, Fix the spray gun arranged on the crown surface side of the piston and move the piston to apply the heat insulating material to the crown surface. A method for applying a heat insulating material to a piston, characterized by this.

7. In any one of Claims 1 to 6, The heat insulating material is applied to the crown surface by the spray gun arranged on the crown surface side of the piston, and the relative position of the spray gun with respect to the piston is maintained inside the outer peripheral end of the crown surface. A method for applying a heat insulating material to a piston, characterized by this.

8. In any one of Claims 1 to 7, The second clearance is larger than the first clearance. A method for applying a heat insulating material to a piston, characterized by this.

9. In any one of Claims 1 to 8, The first clearance is 0.1 mm or more and 0.5 mm or less. A method for applying a heat insulating material to a piston, characterized by this.

10. In any one of Claims 1 to 9, The second clearance is 0.3 mm or more and 1.0 mm or less. A method for applying a heat insulating material to a piston, characterized by this.

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