JP2018012875A - Film deposition method of spray deposit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of a damage in the periphery of a convex-shaped curve face in the periphery of a convex curved face joining such a valve hole outer circumference of the outer circumference of a spray deposition formed by a masking and a combustion chamber outer peripheral surface formed along the outer edge of a combustion chamber constituting face.SOLUTION: A masking jig 52 is formed with a plurality of grooves 52c in a confronting face 52b confronting to the bottom face 12 of the masking jig 52. The grooves 52c are formed by digging the confronting face 52b. The individual grooves 52c extend gently from eight concave curved faces 52a existing in each cylinder, gently toward the outer circumference 52d of the masking jig 52.SELECTED DRAWING: Figure 12

Description

  The present invention relates to a method for forming a sprayed film, and more particularly to a method for forming a sprayed film on the bottom surface of a cylinder head of an engine.

  The combustion chamber of an engine is generally a space surrounded by a bore surface of the cylinder block, a top surface of a piston accommodated in the bore surface, and a bottom surface of the cylinder head when the cylinder head and the cylinder block are combined. Is defined as For the purpose of reducing the cooling loss in the engine and protecting it from the heat generated by combustion, the components of the combustion chamber, that is, the bore surface of the cylinder block, the top surface of the piston, and the bottom surface of the cylinder head are used. A thermal barrier film may be formed.

  Patent Document 1 discloses a cylinder head in which a thermal spray film as a thermal barrier film is formed on a combustion chamber constituting surface. The cylinder head is formed with valve holes such as an intake valve hole and an exhaust valve hole. The sprayed film is formed in a region excluding the opening of the valve hole in the combustion chamber constituting surface.

Japanese Patent Laid-Open No. 2006-98407

  By the way, although not mentioned in Patent Document 1, in order to obtain a cylinder head in which a sprayed film is formed on the combustion chamber constituting surface, a non-deposition region of the combustion chamber constituting surface or the combustion chamber constitution It is necessary to mask the area outside the surface. Such masking is effective in a film forming method by spraying film material particles typified by thermal spraying or cold spray, and is widely performed.

  However, of the outer peripheral surface of the sprayed film formed by masking, the outer peripheral surface of the valve hole formed along the outer edge of the opening of the valve hole and the outer periphery of the combustion chamber formed along the outer edge of the combustion chamber constituting surface There is a problem that damage (breaking, chipping, peeling) is likely to occur around the convex curved surface connecting the surfaces. This is because the convex curved surface is formed corresponding to the concave curved surface provided in the masking jig, but the molten state of the thermal spray powder is insufficient around the concave curved surface. This is because something is easy to be collected. When damage occurs around the convex curved surface, the constituent particles fall off from the damaged portion, and it is predicted that scuffing occurs due to biting into the cylinder bore. Therefore, it has been necessary to make improvements to suppress the occurrence of such problems.

  The present invention has been made in view of the above-described problems, and an object thereof is the outer periphery of the valve hole formed along the outer edge of the opening of the valve hole in the outer peripheral surface of the sprayed film formed by masking. It is to suppress the occurrence of damage around the convex curved surface that connects the surface and the outer peripheral surface of the combustion chamber formed along the outer edge of the combustion chamber constituting surface.

The present invention is a method for forming a sprayed film to achieve the above object, and is a cylinder head base material having a cylinder block mating surface and an engine combustion chamber constituting surface on the same surface, and an intake valve Preparing a cylinder head base material in which at least two valve holes corresponding to a hole and an exhaust valve hole open to the combustion chamber constituting surface, a non-deposition region of the combustion chamber constituting surface, and the cylinder block alignment A plate-shaped masking jig for masking the surface is attached to the cylinder head base material, and after the masking jig is attached to the cylinder head base material, the thermal spray powder is sprayed onto the combustion chamber constituting surface. And a step of forming a film.
The masking jig includes a concave curved surface that connects an outer peripheral surface of a portion that masks the opening of the valve hole and an outer peripheral surface of a portion that masks the cylinder block mating surface. Further, the masking jig includes a groove extending from the outer peripheral surface of the masking jig to the concave curved surface on a surface facing the cylinder head base material in the attaching process to the cylinder head base material.

  According to the present invention, it is possible to move the sprayed powder, which is insufficiently melted and easily sprayed around the concave curved surface, along the groove portion and discharge it from the outer peripheral surface of the masking jig. Accordingly, of the outer peripheral surface of the sprayed film formed by masking, the outer peripheral surface of the valve hole formed along the outer edge of the opening of the valve hole and the outer periphery of the combustion chamber formed along the outer edge of the combustion chamber constituting surface It is possible to suppress the occurrence of damage around the convex curved surface connecting the surfaces.

It is a figure explaining the composition of the cylinder head to which the method concerning an embodiment of the invention is applied. 2 is a cross-sectional photograph showing an example of a sprayed film 22 shown in FIG. It is the photograph which showed an example of the thermal spraying powder used for the intermediate | middle layer 24 shown in FIG. It is the photograph which showed an example of the thermal spraying powder used for the thermal insulation layer 26 shown in FIG. It is a figure explaining the film-forming method using a plasma spraying apparatus, and its problem. It is a cross-sectional photograph of the periphery of the outer peripheral surface of a sprayed film. It is a figure explaining the film thickness profile of the sprayed film formed by the conventional film-forming method. It is a partial enlarged photograph of the thermal spray film | membrane 46 immediately after thermal spraying. FIG. 9 is a photograph of the periphery of the convex curved surface 46a after polishing the sprayed film 46 shown in FIG. It is a cross-sectional schematic diagram when the concave curved surface 48a of the masking jig | tool 48 shown in FIG. 11 is cut | disconnected along the AA line shown in the figure. It is a figure explaining the shape of the masking jig which this inventor developed in relation to the method which concerns on embodiment of this invention. It is a figure explaining the shape of the masking jig | tool 52 used in the method which concerns on embodiment of this invention. It is an expansion schematic diagram of the periphery of the concave curved surface 52a shown in FIG. It is a figure explaining the effect by the method concerning this embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

[Cylinder head configuration]
FIG. 1 is a diagram illustrating a configuration of a cylinder head to which a method according to an embodiment of the present invention is applied. FIG. 1 illustrates a cylinder head 10 of an in-line four-cylinder diesel engine as an example of a cylinder head to which the method according to the present embodiment is applied. On the bottom surface 12 of the cylinder head 10, two intake valve holes 14 that are opened and closed by an intake valve (not shown) and two exhaust valve holes 16 that are opened and closed by an exhaust valve (not shown) are formed per cylinder. ing. In each cylinder, an injector hole 18 into which an injector (not shown) is inserted is formed at the center surrounded by the intake valve hole 14 and the exhaust valve hole 16. In each cylinder, a glow plug hole 20 into which a glow plug (not shown) is inserted is formed in the middle of the intake valve hole 14.

[Composition of sprayed film]
The thermal spray film 22 shown in FIG. 1 corresponds to the thermal spray film formed by the method according to the present embodiment. In each cylinder shown in FIG. 1, the sprayed film 22 is formed in a region corresponding to the combustion chamber constituting surface. More specifically, the sprayed film 22 is formed so as to cover the combustion chamber constituting surface. Further, the sprayed film 22 is not formed in the region outside the combustion chamber constituting surface, and the bottom surface 12 is exposed. Incidentally, the region where the bottom surface 12 is exposed constitutes a mating surface with a cylinder block (not shown).

FIG. 2 is a cross-sectional photograph showing an example of the sprayed film 22 shown in FIG. As shown in FIG. 2, the sprayed film 22 includes an intermediate layer 24 (Ni-50Cr + 35 wt% bentonite) and a heat shield layer 26 (ZrO ₂ −33 wt% SiO ₂ ). The intermediate layer 24 has a thickness of 50 μm, and the heat shield layer 26 has a thickness of 100 μm.

  FIG. 3 is a photograph showing an example of the thermal spray powder used for the intermediate layer 24 shown in FIG. This sprayed powder is obtained by granulating bentonite particles (inorganic particles) having a particle size of 45 μm or less into Ni-50Cr alloy powder having a particle size of 10 to 45 μm and an average particle size of 20 μm by sintering. The average particle size is 70 μm. In addition, the mixing ratio of Ni-50Cr alloy powder and bentonite particles is 65:35 in mass ratio. With such a mixing ratio, the area ratio of bentonite in the intermediate layer 24 is 60%.

The thermal expansion film composed of the alloy-based material described with reference to FIG. 3 has a smaller linear expansion coefficient than that of the cylinder head base material (as an example, an aluminum alloy), and ZrO ₂ —SiO ₂ constituting the heat shield layer 26. It becomes larger than the linear expansion coefficient of ceramics (details will be described later). Therefore, according to the sprayed film 22 including the intermediate layer 24, it is possible to reduce the difference in the linear expansion coefficient between the layers as compared with the sprayed film formed of only the thermal barrier layer 26 without the intermediate layer 24. Therefore, according to the sprayed film 22, it is possible to suppress the peeling of the heat shielding layer 26 due to the thermal stress generated during the cooling cycle.

FIG. 4 is a photograph showing an example of the thermal spray powder used for the thermal barrier layer 26 shown in FIG. The spray powder is zircon sand _{(composition: ZrO 2 -33wt% SiO 2 -0.7wt} % Al 2 O 3 -0.15TiO 2 -0.1wt% Fe 2 O 3) a pulverized powder classifying the ZrO ₂ - SiO ₂ powder. For example, a ZrO ₂ —SiO ₂ powder having a particle size of 10 to 45 μm and an average particle size of 20 μm is used for the heat shield layer 26 shown in FIG.

The thermal spray film composed of the ZrO ₂ —SiO ₂ based ceramic described with reference to FIG. 4 is lower in thermal conductivity and volumetric heat capacity than the cylinder head substrate (an aluminum alloy as an example). Therefore, according to the thermal spray film 22 including the thermal barrier layer 26, the temperature of the thermal spray film (more precisely, the temperature of the thermal barrier layer is changed to the temperature of the working gas in the engine combustion chamber, that is, the temperature of the intake air and the temperature of the combustion gas. Temperature) can be made to follow. Therefore, the sprayed film 22 can improve the fuel consumption by reducing the cooling loss in the expansion stroke, and can also suppress the occurrence of abnormal combustion due to the heating of the working gas in the intake stroke.

[Spraying conditions]
An example of spraying conditions in the method according to the present embodiment is shown below. This thermal spraying is performed using a plasma spraying device (F4 gun manufactured by METCO) after shot blasting is performed on the bottom surface of the cylinder head to make the surface roughness Ra 7 μm.
<Intermediate layer 24>
Plasma gas: Ar—H ₂ , gas flow rate: 30 L / min (Ar), 8 L / min (H ₂ )
Plasma current: 450A, plasma voltage: 60V
Powder supply amount: 30 g / min
Thermal spray distance: 150mm
<Heat shield layer 26>
Plasma gas: Ar—H ₂ , gas flow rate: 40 L / min (Ar), 12 L / min (H ₂ )
Plasma current: 600A, plasma voltage: 60V
Powder supply amount: 50 g / min
Thermal spray distance: 100mm

  FIG. 5 is a diagram for explaining a film forming method using a plasma spraying apparatus and its problems. First, the configuration of the plasma spraying apparatus will be briefly described. A plasma spray apparatus 30 shown in FIG. 5 includes a spray gun 38 that injects a plasma flame 36 toward the bottom surface 34 of the cylinder head base material 32, and a nozzle 42 that introduces the spray powder 40 into the plasma flame 36. . It is assumed that the intake valve hole 14 and the exhaust valve hole 16 described with reference to FIG.

  Most of the thermal spray powder 40 introduced from the nozzle 42 to the plasma flame 36 is melted by the plasma flame 36. The molten thermal spray powder 40 is flattened by being sprayed on the bottom surface 34 and is deposited while being bonded to the adjacent molten thermal spray powder 40. In FIG. 5, the thermal spray powder 40 drawn in the range of the plasma flame 36 becomes a part of the thermal spray film through the melting process described above.

  However, on the other hand, for example, there is also a thermal spray powder 40 that reaches the bottom surface 34 in an unmelted state because it is not successfully introduced into the plasma frame 36 because of its small mass. In FIG. 5, the thermal spray powder 40 drawn outside the range of the plasma flame 36 corresponds to this.

  By the way, in the film-forming method using the plasma spraying apparatus 30, the non-film-forming area | region of a combustion chamber structure surface and the area | region outside a combustion chamber structure surface are masked. A masking jig 44, partially depicted in FIG. 5, is a plate-like member that covers these regions and is attached to the bottom surface 34 to expose only the film formation region. However, as shown in FIG. 5, the sprayed powder 40 that has reached the bottom surface 34 in an unmelted state is easily sprayed and accumulated at the boundary portion between the exposed region and the masking jig 44. When spraying is continued in a state where the unmelted sprayed powder 40 is still accumulated, the unmelted sprayed powder 40 becomes a part of the sprayed film.

  FIG. 6 is a cross-sectional photograph of the periphery of the outer peripheral surface of the thermal spray film, and approaches the outer peripheral surface of the thermal spray film as it goes to the right. As shown in FIG. 6, the thermal spray powder constituting the heat shield layer is flattened moderately in the left region, whereas many spherical spray powders are present in the heat shield layer in the right region. This spherical spray powder is derived from the above-mentioned unmelted spray powder and can be said to be a spray powder that is insufficient as a flat state.

  When the sprayed powder having an insufficient flat state shown in FIG. 6 is included, a difference in film thickness occurs between the outer peripheral portion of the sprayed coating after spraying and the portion inside the sprayed coating. FIG. 7 is a diagram for explaining a film thickness profile of a sprayed film formed by a conventional film forming method. This film thickness profile represents the film thickness around the convex curved surface 46a when the sprayed film 46 immediately after spraying shown in FIG. 8 is cut along the line AA shown in FIG. Incidentally, the convex curved surface 46a includes a valve hole outer peripheral surface 46b formed along the outer edge of the opening of the intake valve hole 14 or the exhaust valve hole 16, and a combustion chamber outer periphery formed along the outer edge of the combustion chamber constituting surface. It is defined as a part of the outer peripheral surface of the sprayed film 46 that connects the surface 46c. As shown on the right side of FIG. 7, a protrusion approximately 50 μm larger than the surrounding is formed in the vicinity of the convex curved surface 46 a. This protrusion is caused by the fact that the sprayed powder having an insufficient flat state is included inside the convex curved surface 46a.

  When the protrusions as shown in FIG. 7 are formed around the convex curved surface, excessive stress is generated in the protrusions during the polishing process (finishing process) after thermal spraying. Damage (cracking, chipping, peeling) occurs on the curved surface. FIG. 9 is a photograph of the periphery of the convex curved surface 46a after the thermal spray film 46 shown in FIG. 8 is polished. As shown in FIG. 9, film chipping occurs around the convex curved surface 46 a.

  When damage due to the polishing process occurs on the convex curved surface 46a, the damage (cracking, chipping, peeling) is expanded by the thermal stress generated during the cooling cycle during actual operation of the engine. However, even if the convex curved surface 46a is not damaged due to the polishing process, damage (cracking, chipping, peeling) of the convex curved surface 46a occurs due to the thermal stress generated during the cooling cycle. there is a possibility. When damage (cracking, chipping, peeling) of the convex curved surface 46a occurs in this way, it is predicted that the constituent particles fall off from the damaged portion and become scuffed by being bitten into the cylinder bore.

  In fact, in the durability evaluation accompanied by the cooling and heating cycle, the occurrence of the damage on the convex curved surface described above has been confirmed. Incidentally, as can be seen from the shape of the sprayed film 46 shown in FIG. 8, examples of the outer peripheral surface of the sprayed film 46 include not only the convex curved surface 46a but also the valve hole outer peripheral surface 46b and the combustion chamber outer peripheral surface 46c. However, according to this durability evaluation, it was confirmed that the damaged part in the outer peripheral surface of the sprayed film 46 is limited to the convex curved surface 46a. One reason for this is that the valve hole outer peripheral surface 46b and the combustion chamber outer peripheral surface 46c have a larger radius of curvature than the convex curved surface 46a, and are more resistant to thermal stress.

The present inventor has studied from various directions in order to suppress the phenomenon on the convex curved surface 46a. The contents of these studies and the results of adoption are shown below.
Study 1. Increase powder particle size: Not adopted because the number of particle interfaces decreases and the thermal conductivity of the sprayed coating increases. Add air blow from outside: Some effect was seen, but not enough. Masking jig shape change: Adopted because most effective

  FIG. It is a figure explaining the shape of the masking jig which this inventor developed in relation to this. FIG. 10 corresponds to a schematic cross-sectional view when the concave curved surface 48a of the masking jig 48 shown in FIG. 11 is cut along the line AA shown in FIG. In the masking jig 48 shown in FIG. 10, a groove 48 c formed by digging out the facing surface 48 b is provided on the facing surface 48 b of the masking jig 48 facing the bottom surface 12. By forming the groove portion 48c, a space 50 is formed between the bottom surface of the cylinder head and the groove portion 48c when the masking jig 48 is attached to the cylinder head. Therefore, the unmelted thermal spray powder sprayed around the concave curved surface 48 a can be moved to the space 50. However, in practice, the sprayed powder that should have been moved to the space 50 rebounds in the groove 48c, and a sufficient effect cannot be obtained.

  Accordingly, the present inventor has developed a shape of a masking jig in which the groove portion 48c shown in FIG. FIG. 12 is a diagram for explaining the shape of the masking jig 52 used in the method according to the present embodiment. A masking jig 52 shown in FIG. 12 includes a plurality of groove portions 52 c on a surface 52 b facing the bottom surface 12 of the masking jig 52. The plurality of groove portions 52c are formed by digging the facing surface 52b (as an example, groove width: 3 mm, depth: 2 mm). Each of the groove portions 52c gently extends from the concave curved surfaces 52a present at eight locations per cylinder toward the outer peripheral surface 52d of the masking jig 52.

  FIG. 13 is an enlarged schematic view of the periphery of the concave curved surface 52a shown in FIG. Since the groove 52c as shown in FIG. 13 is formed, the non-molten sprayed powder sprayed around the concave curved surface 52a is moved along the groove 52c, so that the outer peripheral surface 52d shown in FIG. It becomes possible to discharge. A water jacket hole or the like is formed on the bottom surface of a general cylinder head in a region outside the combustion chamber constituting surface. Therefore, it is desirable that the groove 52c is formed avoiding these holes so that the sprayed powder moved along the groove 52c does not enter the inside of the cylinder head via these holes. Further, in order to prevent the sprayed powder in an unmelted state moved to the groove 52c from staying, it is desirable to form a low friction film such as a DLC coat on the surface of the groove 52c.

  FIG. 14 is a diagram for explaining the effect of the method according to the present embodiment. “Conventional” shown in the left column of FIG. 14 shows the film thickness profile (upper stage) and cross-sectional structure (middle stage) of the sprayed film formed using the masking jig in which the groove 52c described in FIG. 12 is not formed. It is an appearance photograph (lower stage). The film thickness profile (upper) is shown in FIG. 7, the cross-sectional structure (middle) is shown in FIG. 6, and the appearance photograph (lower) is shown in FIG.

  The “present invention” shown in the right column of FIG. 14 is a film thickness profile (upper part), a cross-sectional structure (middle part), and a photograph of the appearance (lower part) of the sprayed film formed using the masking jig 52 described in FIG. ). Note that the film thickness profile (upper stage) is obtained by cutting the thermal sprayed film formed using the masking jig 52 at the same position as the line AA shown in FIG. The film thickness around the convex curved surface is shown. As can be seen by comparing the right column and the left column in FIG. 14, according to the “present invention”, no protrusion is seen on the convex curved surface (upper stage), and no intervening spray powder in an unmelted state is seen ( Middle). In addition, no film chipping occurs around the convex curved surface.

  As can be seen from FIG. 14, by using the masking jig 52, it is possible to satisfactorily suppress the occurrence of damage due to the polishing process on the convex curved surface of the sprayed film. Further, when the cylinder head was subjected to a thermal endurance evaluation after this polishing process, damage to the sprayed film was not particularly confirmed, and product abnormalities such as scratches on the piston and cylinder bore and scuffing were not observed. From the above, it has been proved that the method according to the present embodiment is useful as a film forming technique capable of suppressing the occurrence of damage to the convex curved surface of the sprayed film.

10, 32 Cylinder head 12, 34 Bottom surface 14 Intake valve hole 16 Exhaust valve hole 22, 46 Thermal spray film 24 Intermediate layer 26 Thermal barrier layer 30 Plasma spray device 36 Plasma flame 38 Thermal spray gun 40 Thermal spray powder 42 Nozzle 44, 48, 52 Masking Jig 46a Convex curved surface 46b Valve hole outer peripheral surface 46c Combustion chamber outer peripheral surface 48a, 52a Concave curved surface 48b, 52b Opposing surface 48c, 52c Groove 50 Space 52d Outer peripheral surface

Claims (1)

A cylinder head base material having a cylinder block mating surface and a combustion chamber constituting surface of the engine on the same surface, and at least two valve holes corresponding to an intake valve hole and an exhaust valve hole open to the combustion chamber constituting surface. Preparing a cylinder head substrate;
A step of attaching a plate-shaped masking jig for masking the non-film formation region of the combustion chamber constituting surface and the cylinder block mating surface to the cylinder head substrate;
After attaching the masking jig to the cylinder head base material, spraying thermal spray powder onto the combustion chamber constituting surface to form a thermal spray film,
The masking jig includes a concave curved surface that connects an outer peripheral surface of a portion that masks the opening of the valve hole and an outer peripheral surface of a portion that masks the cylinder block mating surface;
The thermal spraying characterized in that the masking jig includes a groove extending from the outer peripheral surface of the masking jig to the concave curved surface on a surface facing the cylinder head substrate in the step of attaching to the cylinder head substrate. A film forming method.

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