JP6931480B2 - Metal gasket and its manufacturing method - Google Patents

Description

The present invention is a technique relating to a metal gasket such as a metal cylinder head gasket or the like, which is used for a seal portion where a metal bead is deformed by repeatedly receiving a load.

When the metal cylinder head gasket is incorporated between the cylinder head and the cylinder block of the engine, the metal bead is compressed in the plate thickness direction to generate a repulsive force and obtain a sealing property.
In such a metal gasket, since the metal bead is repeatedly subjected to a load and deformed, the metal bead cracks over time due to metal fatigue or the like, leading to fatigue fracture.
On the other hand, Patent Document 1 proposes that the structure of the substrate surface is made ultrafine and the origin of cracks is eliminated by performing shot peening at least at the position where the metal bead is formed before or after the bead formation. Has been done.

Japanese Unexamined Patent Publication No. 2011-163493

However, in the shot peening process proposed in Patent Document 1, since the dry particles collide with the metal surface, a device for preventing the collided particles and the metal powder from scattering is required, and the powder adhering to the surface is further required. A step is required to remove the particles. Further, since the particles are large and the impact force applied to the substrate 1 is also large, there is a possibility that the unevenness of the surface is rather increased and the fatigue property is deteriorated.
The present invention has been made focusing on the above points, and an object of the present invention is to improve the fatigue resistance of a metal gasket.

With the use of the metal gasket, cracks occur in the bead bending portion of the metal bead, leading to fatigue fracture. This fatigue fracture occurs when a crack base point is generated on the surface of the substrate and the crack propagates inside the substrate. Generally, it is said that the base point of a crack is that the stress amplitude is applied to the metal by a repeated load, so that the dislocation of the metal crystal is repeated and minute irregularities are generated on the surface.
On the other hand, when the inventors examined the cracks generated in the metal bead, when the bead bending portion immediately after the bead formation was observed in detail, the surface of the bead bending portion was formed by press molding to have a minute size of about 1 μm to 5 μm. We have obtained a new finding that streaky irregularities (wrinkles) of a size are generated, and that irregularities are formed not only by repeated stress but also by one processing step. Then, cracks are likely to be formed from the valleys of the wrinkles as the base point, and when stress amplitude is applied to the substrate, the cracks propagate inside the substrate and lead to fatigue fracture, but the valleys have a notch effect and are extremely durable. I got a new finding that it would reduce the sex.

Then, based on such a finding, the present inventor reduces the unevenness (wrinkles) generated in the bead bending portion by the bead formation and suppresses the generation of cracks starting from the valley portion of the unevenness (wrinkles). Therefore, the present invention has been made in consideration of improving the fatigue resistance of the metal gasket.
That is, in order to solve the problem, one aspect of the present invention is a method for manufacturing a metal gasket provided with a substrate having a metal bead bent in the plate thickness direction, after the metal bead is press-molded. It is characterized in that at least the bead bent portion formed on the substrate by press molding of the metal bead is subjected to a wet blast treatment.

Here, the bead bent portion refers to a corner portion where the substrate is bent due to the formation of a metal bead. For example, the bead bent portion refers to a portion where the substrate is bent due to the metal bead rising from the flat portion of the substrate.
Further, the metal gasket of the present embodiment based on the present invention is characterized in a structure in which wrinkles at the bent portion of the bead are suppressed by performing a wet blast treatment after forming a metal bead by press working.

That is, one of the features (invention-specific matters) of the present invention is that "fine wrinkles in the bead bent portion of the metal bead are reduced by the wet blast treatment". This has the effect of improving the fatigue resistance of the metal gasket, but it is difficult to directly identify its characteristics by the structure and properties of the bead bent portion in the manufactured substrate. This is because the wrinkle structure formed at the time of bead formation varies depending on the pressing conditions such as the material of the substrate used, the shape of the bead, and the die used when forming the bead. Further, by performing wet blasting on it, the unevenness of wrinkles is suppressed as shown in FIG. 6, but since the suppressed unevenness shape varies under the above-mentioned press conditions, it is possible to specify it within a numerical range. Impractical.

According to one aspect of the present invention, it is possible to provide a metal gasket having improved fatigue resistance.
In addition, the wet blasted surface also has the effect of improving the adhesiveness. Therefore, it is preferable that the wet blast treatment is performed on the entire surface of the substrate to be coated, including the bead bending portion.

It is sectional drawing which shows the example of the substrate of the metal gasket which concerns on embodiment based on this invention. It is sectional drawing explaining the full bead which concerns on embodiment based on this invention. It is a figure explaining the manufacturing method of the metal gasket which concerns on embodiment based on this invention. It is a figure explaining the process of a wet blast process. It is a top view which shows the shape of the test piece of an Example. It is a figure explaining the surface shape of the bead bending part, (a) is a figure explaining the observation position of a half bead, (b) is a profile shape before wet blasting, (c) is a profile shape after wet blasting. It is a figure exemplifying.

Next, an embodiment of the present invention will be described with reference to the drawings.
It should be noted that the present embodiment is specifically described in order to better understand the gist of the invention, and is not limited to the present invention unless otherwise specified. In addition, the drawings are schematic, and the thickness ratio of each layer is different from the actual one.
In the present embodiment, the case of a cylinder head gasket, which is interposed between the cylinder head and the cylinder block as the metal gasket, will be described as an example. However, the metal gasket of this embodiment is not limited to the cylinder head gasket, and is suitably used as a metal gasket used for a seal portion where the metal bead is deformed by repeatedly receiving a load.

<Example of metal gasket configuration>
A configuration example of the metal gasket will be described. However, the configuration example of the metal gasket that is the subject of the present invention is not limited to the following configuration.
The metal gasket includes a substrate 1. The metal gasket may be formed by stacking a plurality of substrates 1. Further, the metal gasket may have a secondary plate for adjusting the thickness separately from the substrate 1.
As the material of the substrate 1 constituting the metal gasket, for example, a thin metal plate such as a stainless steel plate, a mild steel plate, or an aluminum plate can be appropriately adopted. The material of the substrate 1 of this embodiment is a stainless steel plate.

Further, as shown in FIG. 1, an inner peripheral side seal line L1 is set so that one or more combustion chamber holes 2 are opened in the substrate 1 and surround the outer periphery of each combustion chamber hole 2. , Water holes, bolt holes, and the like are appropriately formed on the outer peripheral side of the inner peripheral side seal line L1, and the outer peripheral side seal line L2 is set at a portion requiring sealing. Then, along the inner peripheral side seal line L1, the substrate 1 is bent and molded in the plate thickness direction to form a metal bead 3 made of a convex step-shaped half bead on the upper side. Further, a metal bead 3 made of a convex step-shaped half bead is formed on the upper side along the outer peripheral side seal line L2.

The metal bead 3 does not have to be a half bead as shown in FIG. 1, and may be composed of a full bead having an arcuate cross section as shown in FIG.
A thickened portion (not shown) for a stopper is appropriately formed on the inner peripheral side of the inner peripheral side seal line L1. The thickened portion serving as a stopper may be composed of an auxiliary plate or the like separate from the substrate 1. Further, the thickened portion may not be provided.

Here, the surface of the substrate 1 includes a bead region A1 on which the metal bead 3 is formed and a flat region A2 formed of a flat flat portion. The boundary portion between the bead region A1 and the flat region A2 continuous therewith becomes the bead bending portion 4. The bead bending portion 4 is a region having a width of about 1 mm on both the left and right sides in the bead width direction, for example, about the boundary line between the bead region A1 and the flat region A2. However, performing wet blasting only on such a narrow width is inconvenient, such as labor, and therefore the width of the bead bent portion 4 is not particularly significant, but the bead bent portion 4 is flat. It is shown that it is also located on the region A2 side.
Further, a rubber coating film 5 (an elastic coating film) is formed on the surface of the substrate 1.

<Manufacturing method of metal gasket>
As shown in FIG. 3, the method for manufacturing the metal gasket of the present embodiment includes a punching step P1, a bead forming step P2, a flat pushing step P3, a wet blasting step P4, and a coating step P5, and the treatments are carried out in this order. NS.
(Pulling process P1)
The punching step P1 is a cutting process for forming an outer contour shape of a material to be a substrate 1 into a target shape or forming holes such as water holes before forming a bead. It is a process.

(Bead forming step P2)
The bead forming step P2 is a step of forming the material to be the substrate 1 by press working such as embossing to form a metal bead 3 bent in the plate thickness direction with respect to the substrate 1. The metal bead 3 is bent and molded in the plate thickness direction by press molding so as to project in the plate thickness direction, and as described above, a full bead having an arc-shaped cross section or a stepped half bead can be exemplified.
When the thickened portion is formed on the substrate 1, it is performed before and after the bead formation.

(Flat pushing process P3)
In the flat pressing step P3, the substrate 1 on which the metal beads 3 are formed by the bead forming step P2 is subjected to a pressing load such that the metal beads 3 protruding in the plate thickness direction have a flat shape (total compression state). This is a step of performing a process of pressing in a direction. In addition, flat pressing is performed by a mold in which the thickened portion forming position is open. In the flat pressing step P3, flat pressing may be executed at least on the metal bead 3 position and the flat portion continuous with the metal bead 3 position. As a result, the bead bent portion 4 and its vicinity are flat-pressed. Flat pressing is performed with a pressing load having a magnitude of, for example, about 5 tons to 25 tons.
Here, the flat push is usually carried out for the purpose of alleviating the decrease in the bolt axial force due to the bead settling. On the other hand, in the present embodiment, the main purpose of flat pressing is to open minute wrinkles (unevenness) generated in the bead bending portion 4 (corner portion) by press molding of bead formation as a pretreatment for wet blasting. It is an object. That is, the flat push is performed to open the valley of the wrinkles.
Although the flat pressing step P3 may be omitted, the fatigue resistance is improved when the flat pressing step P3 is performed as a pretreatment for wet blasting.

(Wet blast process P4)
The wet blasting step P4 is a step of applying a wet blasting treatment to at least the bead bent portion 4. However, as described above, it is difficult to apply wet blasting only to the bead bending portion 4, so that the entire surface of the bead and the outer peripheral portion thereof are also subjected to wet blasting to ensure that the bead bending portion 4 is wet blasted. It should be.
The wet blasting step P4 of the present embodiment is carried out on both sides of the substrate 1 on the surface of the substrate 1 to be coated. For example, a wet blast treatment is applied to the entire surface of the substrate 1 in a state where the uncoated portion on the surface of the substrate 1 is masked. Wet blasting may be performed on only one side, but is preferably performed on both sides. When it is carried out on one side, it is carried out on the side (protruding side) where the bead 3 rises from the flat portion. In the half bead, since the bead stands up on both sides of the substrate, it is preferable to carry out the half bead on both sides.

Here, in wet blasting, solid particles and a liquid such as water are stirred and mixed to form a muddy water-like state (slurry), and the slurry is brought into a muddy water-like state (slurry) by using the force of compressed air from an injection nozzle to form a substrate 1. Inject at high speed toward the surface. By this process, the particles in the slurry process the surface of the substrate 1 by scraping, hitting, or rubbing the surface of the substrate 1.
As shown in FIG. 4, the wet blasting step P4 of the present embodiment includes a blasting step of injecting a slurry, a washing step, and a draining step in this order, and is applied to the surface of the substrate 1 which is a processing object moved by a conveyor. The steps are carried out in sequence. For the injection nozzle for injecting the slurry, for example, a wide slit-shaped nozzle is used.

The particles may be solid, and examples thereof include metal powder, stone, ceramic, glass, and plastic. The amount of processing of the particle size, hardness, and liquid flow velocity can be adjusted by the number of processing times. The particles used are extremely small particles that are dispersed in the liquid, and wrinkles can be smoothed without deteriorating the fatigue resistance, so it is possible to improve the adhesiveness of the paint while improving the fatigue resistance. Is.
In addition, fine dents are formed on the surface of the substrate 1 due to the collision of particles. On the contrary, a protruding portion is formed around the recess, but since the slurry is continuously injected and collides, the particles also collide with the protruding portion and a depression is generated in that portion as well. By this action, the surface of the substrate is uniformly hit, so that a large number of finely processed dents of particles are formed on the surface of the substrate. As a result, due to the anchor effect, the adhesiveness between the rubber coating film 5 (coating film) adhered by the coating treatment and the substrate 1 is improved.

Further, as described above, wrinkles are generated in the bead bent portion 4 due to the bead processing. The wrinkles of the bead bent portion 4 due to this bead processing were confirmed by the inventors to be peaks and valleys (unevenness) having a depth of about 1.5 μm to 5 μm. On the other hand, by applying the wet blast treatment, the protruding peaks are beaten by the particles and buried in the valleys. As a result, since the valley portion is substantially smoothed, even if a tensile stress is applied to the bead bent portion 4 during the use of the metal gasket, the degree of stress concentration is lowered and the possibility of crack progressing is reduced. In particular, when wet blasting is performed on both sides of the substrate 1, the wrinkle peaks are struck on both sides, so that the valleys are embedded from both sides, and the effect is further enhanced.

Here, the wet blast has a degreasing effect as well as being able to use smaller particles than the dry blast. Further, in the case of dry last, embedding residue is generated due to the particles driving the particles, and the residue may contribute to cracking. On the other hand, in the case of wet blasting, the particles after processing can be washed away by water having a large mass, so that the residue of the particles can be suppressed. Furthermore, due to the buffer effect, water collects in the valley part and functions like a cushioning material, which makes it difficult to blast the valley part compared to the mountain part, and the valley part is affected. Excessive blasting is suppressed. That is, as described above, the protruding mountain portion is mainly hit by the particles, and it becomes easy to be buried in the valley. However, since the average particle size of the particles is usually larger than the width of the wrinkle valley, it is difficult for the particles to collide directly with the bottom of the valley, but depending on the shape of the particles, the particles also collide with the bottom of the valley. There is a possibility of doing.

(Coating step P5)
The coating step P5 is a step of applying a coating liquid for coating to the surface of the substrate 1 and applying a rubber coating film (coating film) to the surface of the substrate 1.
(Operation and others)
The metal cylinder head gasket has an embossed metal bead 3 formed on the substrate 1 by press working with a mold having a male mold and a female mold. When the metal bead 3 is incorporated between the head blocks of the engine, the metal bead 3 is compressed in the plate thickness direction to generate a repulsive force and obtain a sealing property.
Here, the deck surface (joint surface) of the engine head and the block usually has a cutter mark having a surface roughness of about 1 μm to 20 μm due to flat surface processing. A rubber coating is applied to the surface of the substrate 1 in order to fill the gaps with respect to the minute irregularities. As the rubber material, NBR, FKM, silicone coating or the like is usually selected in consideration of heat resistance to the temperature range of the engine.

In particular, the engine deck surface is in contact with combustion gas, cooling water, engine oil, or exhaust gas, and in order to seal these fluids, the metal cylinder head gasket has an appropriate metal bead 3 shape and coating. Need to be set. The metal bead 3 needs a spring force to fill the minute dent on the engine deck surface with the rubber coating film 5. Therefore, the metal bead 3 is designed to give a large contact pressure (surface pressure). .. For example, the metal bead 3 for a bore often has a full bead shape. In addition, the temperature of the engine changes depending on the operating conditions, and the amount of clearance on the engine deck surface changes due to thermal expansion. In particular, since there is a portion exceeding 100 μm in the outer peripheral portion and a restoring force is required, half beads are often selected for the cooling water and the oil seal.

Further, the metal bead 3 generates pressure when the surface of the metal bead 3 comes into contact with the mating surface at the time of tightening. The metal gasket forms a fluid seal by making the contact portion an endless ring.
In addition, metal cylinder head gaskets must be designed to seal against openings for multiple fluids such as combustion gas, cooling water, oil and exhaust gas, especially rubber coatings that are chemically degraded during engine operation. Not only must it withstand the relative movement of the head block due to the thermal expansion and contraction of the engine. Therefore, in order to improve the adhesive strength of the coating paint, there is a method of applying an adhesive such as a primer to the boundary with the substrate 1 or containing a primer component in the paint, but a separate step such as heat treatment is required. It causes the price to rise. Further, when the material is made of stainless steel, a passivation film is present on the surface of the stainless steel, which hinders the adhesiveness. Therefore, there is a method of peeling off this passivation film and covering it with zinc plating, but the plating treatment of thin plates is special and the production bases are limited, and the pickling treatment of the plating base treatment surface causes intergranular corrosion of the substrate 1. There is a risk of reducing the strength of the substrate 1.

Further, in order to reduce the residual stress of the metal bead 3 and reduce the settling, a low temperature annealing treatment may be performed after the bead is formed, but this treatment causes an oxide film to adhere to the surface, which is also the adhesiveness of the coating. It becomes a factor to reduce.
Furthermore, fatigue fracture is a problem peculiar to metal gaskets. During the use of the gasket, a crack occurs in the bead bent portion 4 of the metal bead 3, leading to fatigue failure.
When the inventors closely observe the bead bending portion 4 immediately after the bead formation, the surface of the bead bending portion 4 on the flat portion side (the position of the flat portion where the beads are continuous) has a minute unevenness having a size of about 1 μm to 5 μm. It was found that (wrinkles) were generated, and that the unevenness was formed not only by the repeated stress when using the gasket but also by one processing step, that is, bead formation.

Then, a crack is formed from the valley portion of the wrinkle as a base point, and when the stress amplitude is added, the crack propagates inside the substrate 1 and leads to fatigue fracture. I will drop it.
In contrast to the above, the present embodiment has the following effects.
That is, in the present embodiment, by performing a wet blast treatment on the surface of the substrate 1 including the surface of the bead bent portion 4, minute irregularities (dents) are generated on the surface of the metal substrate 1. Therefore, the adhesiveness of the coating is improved. Here, in wet blasting, since the liquid in which the particles are dispersed in the liquid is sprayed, the colliding particle diameter is small and the energy given to the surface of the substrate 1 is small, so that the processing amount can be easily adjusted, and fatigue resistance and adhesiveness are achieved. Can be improved.

Further, since the wet blasting process also serves as a cleaning step, the oil component adhering when the metal bead 3 is press-molded can be removed in this step, so that the oil component removing cleaning process for surface coating can be omitted.
Further, by applying a flat push to the substrate 1 after molding of the metal bead 3 to widen the concave portion and then performing a wet blast treatment, the wrinkles of the bead bent portion 4 are expanded due to the compression behavior of the metal bead 3. However, as a result of pre-smoothing the surface against the wrinkles, the durability of the metal gasket is improved.

Here, the substrate 1 on which the metal beads 3 are formed may be subjected to a low temperature annealing treatment. The low-temperature annealing treatment is preferably performed before the flat pressing step P3. By performing the low-temperature annealing treatment, the residual stress of the metal beads 3 formed by press molding can be reduced. Further, by the subsequent wet blasting treatment, good adhesiveness can be ensured even in the substrate 1 subjected to the low temperature annealing treatment, and as a result, it becomes possible to provide a metal gasket having a strong coating with less settling.
As described above, according to the present embodiment, the "wet" blasting improves the fatigue resistance and the adhesiveness, and further, the cleaning step can be omitted.
Further, when flat pressing is performed as a pretreatment for the wet blast treatment, the wrinkle valley formed in the bead bending portion 4 is opened by the flat pressing, and the opened portion is filled with blast to further resist fatigue. Improves sex.

Next, an example based on the present invention will be described.
A rectangular test piece having a combustion chamber hole 2 opened in the center and an opening imitating a bolt hole was prepared on all sides. As the material of the test piece, a blank material made of stainless steel (SUS301H) having a thickness t of 0.2 mm was used.
Then, a full bead as a metal bead 3 was press-molded by a mold so as to surround the combustion chamber hole 2 of the test piece in an endless annular shape as shown in FIG. For the full bead, the bead width was set to 2.5 mm and the bead height was set to 0.2 mm.

Next, the test piece on which the metal bead 3 was formed was passed through the wet blasting apparatus, and the entire surface of both sides of the test piece was subjected to wet blasting treatment.
As the wet blasting device, PFE-300 (device size: 2125W * 2125D * 1800H) manufactured by Macoho Co., Ltd. was used.
When the bead bending part 4 (bending part on the combustion chamber hole 2 side) of the full bead was observed with an electron microscope (× 2000 times) for the test piece before the wet blasting treatment, the plate was found to be a plate with respect to the flat surface as a whole. It was confirmed that minute grooves were formed by rolling and streaky wrinkles of a predetermined depth were formed by bead forming.

On the other hand, when the bead bending portion 4 (combustion chamber hole 2 side) of the full bead was observed with an electron microscope (× 2000 times) for the test piece after the above wet blasting treatment, streaky wrinkles were observed. It was buried and smoothed, and innumerable minute irregularities were confirmed throughout.
FIG. 6 shows the surface profile of the substrate 1 before and after the bead bending portion 4 before and after the wet blasting treatment.
In this example, the position of the bead bending portion 4 of the rising portion in the half bead as shown in FIG. 6A is set as the observation position. FIG. 6B is a profile before the wet blast treatment, and the vicinity of the position marked with a cross is a wrinkled portion. FIG. 6 (c) is a profile after the wet blast treatment. As can be seen from FIG. 6, it can be seen that the unevenness of the wrinkles is smoothed by performing wet blasting, and the profile of the bead bent portion 4 and its vicinity becomes a gentle shape.

Hereinafter, the test piece on which the metal bead 3 is formed and subjected to wet blasting is referred to as an example product, and the test piece on which the metal bead 3 is formed and not wet blasted is a comparative example product. Called.
The following products were prepared as examples.
(Example product 1)
A test piece prepared by passing one pass through a wet blasting apparatus under the above-mentioned production conditions of the example product was designated as the example product 1. As the wet blasting abrasive, an alumina abrasive having a particle size of 9.5 μm (Macorandom A # 2000 manufactured by Macoho Co., Ltd.) was used.

(Example product 2)
A test piece prepared by passing 10 passes through a wet blasting apparatus under the manufacturing conditions of the above-mentioned Example product was designated as Example Product 2. The same abrasive as in Example 1 was used as the abrasive.
(Example product 3)
Example product 3 was produced in the same manner as in Example product 2 except for the abrasive material. As the wet blasting abrasive, an alumina abrasive having a particle size of 40 μm (Macorund A # 320 manufactured by Macoho Co., Ltd.) was used.

(Example product 4)
Example product 4 was produced under the same conditions as in Example product 1 except that the test piece was flat-pressed with a pressing load of 20 tons before being passed through the wet blasting device.
(Example product 5)
Example product 5 was produced under the same conditions as in Example product 2 except that the test piece was flat-pressed with a pressing load of 20 tons before being passed through the wet blasting device. The flat push was performed only once before one pass to the wet blasting device.

(Comparative example product 1)
It was prepared under the same manufacturing conditions as in Example Product 1 except that it was not subjected to wet blasting treatment, and was used as Comparative Example Product 1.
(Comparative example product 2)
A test product prepared under the same preparation conditions as that of Comparative Example Product 1 was subjected to a drive last treatment once to obtain Comparative Example Product 2.

<Evaluation>
Fatigue resistance of Examples 1 to 5 and Comparative Examples 1 and 2 was evaluated under the following test conditions.
The test conditions are as follows.
A Komatsu 80TON servo press (H1F80) was used to apply a repeated load to the full beads of each test piece with no gap (0 μm) and a press load of 15 TON for one shot to impart compression fatigue.
Then, the state of the test piece was observed with an electron microscope every 500 shots, and the surface texture thereof was evaluated.
The evaluation criteria are as follows.
◯: No cracks △: Groove depth progress can be confirmed ×: Cracks occur (groove width and depth can be clearly confirmed)
The evaluation results are shown in Table 1.

Comparing Example Products 1 and 2 with Comparative Example Product 1, it can be seen that Example Products 1 and 2 based on the present invention have improved fatigue resistance. Further, as can be seen from Examples 1 and 2, there was no clear change in fatigue resistance due to the difference in the number of wet blast passes. Further, as can be seen from Examples 2 and 3, no significant change in fatigue resistance was observed even when the wet blasting abrasive was changed.
Further, as can be seen from Example Product 1 and Example Product 4, it can be seen that fatigue resistance is further improved by performing flat pressing as a pretreatment.
Further, as can be seen from Example Product 1 and Comparative Example Product 2, it can be seen that the wet blast has improved durability as compared with the drive last.

1 Substrate 2 Combustion chamber hole 3 Metal bead 4 Bead bending part 5 Rubber coating film A1 Bead area A2 Flat area P1 Punching process P2 Bead forming process P3 Flat pressing process P4 Wet blasting process P5 Coating process

Claims (5)

A method for manufacturing a metal gasket having a substrate having a metal bead that is bent in the plate thickness direction.
After press molding the above metal beads
A method for producing a metal gasket, which comprises performing a wet blast treatment on at least a bead bent portion formed on the substrate by press molding of the metal bead. A method for manufacturing a metal gasket in which the surface of a substrate is coated after the metal beads are formed.
The method for manufacturing a metal gasket according to claim 1, wherein the wet blast treatment is performed on a substrate surface portion to be subjected to the coating treatment including the bead bending portion. The method for manufacturing a metal gasket according to claim 1 or 2, wherein the substrate on which the metal bead is formed is flat-pressed before the wet blasting treatment is performed. The method for manufacturing a metal gasket according to any one of claims 1 to 3, wherein the substrate on which the metal beads are formed is subjected to a low-temperature annealing treatment before the wet blast treatment is performed. The method for manufacturing a metal gasket according to any one of claims 1 to 4, wherein the metal gasket is a metal cylinder head gasket interposed between the cylinder head and the cylinder block.

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