JP2001316846A - Metallic member with chromate film, spark plug and method for production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metallic member with a chromate film a little in hexavalent chromium content of the chromate film and also excellent in corrosion resistance and thermal resistance, a spark plug equipped with the above metallic member and a production method therefor. SOLUTION: A metallic member 55 (wherein a zinc plating layer 56 is formed for corrosion prevention) is immersed in a chromate treating bath prepared by blending a trivalent chromium salt and a complexing agent for the trivalent chromium. A chromate film 57 with a film thickness of 0.2-0.5 μm wherein 95 mass % or above of contained chromium component are trivalent, is formed on at least a part of the metallic member 55. Thereafter, the chromate film 57 is heat treated at 130 deg.C or above. Thus, the metallic member with the chromate film can be obtained wherein the formed chromate film 57 has a reduction rate of average chromate film thickness of 10% or below when a baking treatment of heating at 200 deg.C and 30 min in air is carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal member with a chromate film having a chromate film formed on at least a part of its surface, and a spark plug comprising a metal shell and / or a gasket using the metal member with a chromate film. , And methods for their manufacture.

[0002]

2. Description of the Related Art In order to prevent corrosion on the surface of a metal member,
The surface is often plated. For example,
In iron-based materials, zinc plating is often formed on the surface, and it is well known that the zinc plating exhibits excellent corrosion protection due to sacrificial corrosion. However, zinc plating is disadvantageous in that it is severely consumed by sacrificial corrosion, and its appearance is easily impaired due to white discoloration due to the generated zinc oxide. Therefore, the surface of the zinc plating layer is covered with a chromate film to prevent the corrosion of the plating layer.

[0003] Among the above chromate films, the yellow chromate film has excellent corrosion resistance, and is therefore used in a wide range of fields including, for example, a film inside a can. In addition, a spark plug used for ignition of a gasoline engine in an internal combustion engine, for example, an automobile or the like, is often provided with the yellow chromate film in order to prevent corrosion due to an attack of an acidic component from inside the engine.

[0004]

However, in the yellow chromate film described above, interest in environmental issues has been increasing on a global scale in recent years due to the disaster that a part of the chromium component is contained in the form of hexavalent chromium. Then they are gradually being shunned. For example, in the automobile industry where a large amount of spark plugs are used, studies are being made to completely abolish the use of a chromate film containing hexavalent chromium in the future in consideration of the environmental impact of waste spark plugs. Further, since a treatment bath containing a relatively high concentration of hexavalent chromium is used for the treatment bath for the yellow chromate film treatment, there is also a problem that a large cost is required for waste liquid treatment.

[0005] Further, the yellow chromate film has a drawback of poor heat resistance. For example, in an automobile engine or the like,
Since the cylinder head to which the spark plug is attached is water-cooled, the spark plug rarely becomes extremely hot. However, if the operation of the engine is continued under the condition that the heat load is large, or if the spark plug is mounted at a position relatively close to the exhaust manifold, sometimes the temperature of the metal shell is about 200 to 300 ° C. May rise to Under such circumstances, there is a problem that the chromate film is apt to deteriorate and the anticorrosion performance is rapidly reduced. Further, the conventional chromate film receives an attack of acidic components such as acid rain, carbon dioxide gas, nitrogen oxide or sulfur oxide contained in exhaust gas, and acid water generated from the engine in the case of a gas engine or the like. Then, there is a problem that the performance is further likely to deteriorate.

An object of the present invention is to provide a metal member with a chromate film having a low hexavalent chromium content in a chromate film and having excellent corrosion resistance and heat resistance, a spark plug provided with the metal member, and a method of manufacturing these. To provide.

[0007]

Means for Solving the Problems and Functions / Effects To solve the above problems, a metal member with a chromate film of the present invention has a chromium content of 95% by mass or more of trivalent chromium, The surface is covered with a chromate film having a thickness of 0.2 to 0.5 μm.
When a baking treatment of heating at 00 ° C. for 30 minutes is performed, a reduction rate of the thickness of the chromate film is within 10%.

In the method of the present invention for producing the above metal member, the chromium component contained in at least a part of the surface of the metal member is immersed in a chromate treatment bath. 0.2-thick chromium
The method includes a chromate treatment step of forming a chromate film having a thickness of 0.5 μm, and a heat treatment step of heat-treating the chromate film at 130 ° C. or higher. By applying such a heat treatment to the metal member on which the chromate film is formed, a chromate film in which the reduction rate of the average film thickness when performing the above-described baking treatment is within 10% can be obtained.

[0009] In the above-described structure, the surface of the metal member is formed such that 95% by mass or more of the contained chromium component is trivalent chromium and the film thickness is 0.2 to 0.5 µm.
m (hereinafter referred to as a trivalent chromium-based chromate film). That is, in a normal yellow chromate film, about 25 to 35% by mass of the chromium component is hexavalent chromium, whereas in the film of the present invention, the content of hexavalent chromium with respect to the chromium component is as small as 5% by mass or less. So
The effect on environmental measures to reduce hexavalent chromium can be enhanced, and the chromate treatment solution used contains no hexavalent chromium component as described below,
Even if it is contained, the amount thereof can be greatly reduced as compared with a treatment solution such as a yellow chromate film, so that a problem of waste liquid treatment hardly occurs.

According to the study by the present inventors, conventional hexavalent chromium-based chromate films such as a yellow chromate film are inferior in corrosion resistance because when they are exposed to high temperatures, they shrink significantly. It was found that a large number of cracks were generated due to the shrinkage, and as a result, the anticorrosion performance against the base was reduced. The contraction of the coating is considered to be due to the dehydration of the chromate hydrate constituting the coating by heating.

As a result of further diligent studies, the trivalent chromium-based chromate film shrinks to some extent when heat history is applied, but hardly generates cracks and the like. It was found that the corrosion resistance was improved. Furthermore, it was also found that if the dehydration shrinkage of the coating by heating sufficiently proceeds, the coating thickness hardly changes even if the heat history is repeatedly applied thereafter, and more stable heat resistance can be secured.

Therefore, in the present invention, a positive heat treatment is performed after the formation of the trivalent chromium-based chromate film to promote the dehydration and densification of the film, so that the film thickness at the time of performing the above-described baking treatment is reduced. Can be obtained a trivalent chromium-based chromate coating having a reduction rate of 10% or less, and a metal member having such a chromate coating formed on the surface is
Its corrosion resistance and heat resistance can be greatly improved.
In the present invention, the fact that the thickness of the trivalent chromium-based chromate film is ensured to be 0.2 μm or more also contributes to the improvement of the anticorrosion performance. The rate of decrease in the thickness of the chromate film during the baking treatment is preferably as small as possible, more preferably within 5%.

The thickness of the chromate film is 0.2 μm
If it is less than 1, the anticorrosion performance and heat resistance cannot be sufficiently secured. On the other hand, if the thickness exceeds 0.5 μm, cracks may occur in the coating (for example, during processing in assembling with other members), or the coating may easily fall off, which impairs the anticorrosion performance. Leads to things. The thickness of the chromate film is desirably 0.3 to 0.5 μm. Further, it is desirable that the chromate film does not substantially contain hexavalent chromium. Further, the above-mentioned chromate film may be formed on a part of the metal member or on the entire surface.

The present invention also provides a spark plug having a metallic shell constituted by the metal member with a chromate film of the present invention. Spark plugs are susceptible to high-temperature loads and attacks of acidic components in view of their usage. Therefore, by covering the surface of the metal shell of the spark plug with the chromate film according to the present invention, it is possible to obtain a spark plug that can be used favorably even in a severe environment such as a high-temperature and acidic atmosphere. The chromate film formed on the metal shell may be formed on the entire surface, or may be formed only on a portion which is required to be exposed to a high temperature and an acidic atmosphere and has corrosion resistance and heat resistance.

Some spark plugs have a ring-shaped gasket to be fitted to the base end of a mounting screw formed on the outer peripheral surface of the metal shell. In this gasket, the screw portion of the metal shell is screwed into the screw hole on the cylinder head side, so that the gasket is crushed between the flange-shaped gas seal portion formed on the base end side of the screw portion and the opening peripheral portion of the screw hole. And serves to seal between the screw hole and the gas seal portion. In this case, at least a part of the surface of the gasket can be covered with the chromate film. This makes it possible to sufficiently impart corrosion resistance and heat resistance to the gasket as well as the metal shell.

The heat treatment step for improving the corrosion resistance of the chromate film may be performed, for example, in the air (or in the air) or in an inert atmosphere such as a nitrogen gas or an Ar gas. If the heat treatment temperature is lower than 130 ° C., it is difficult to keep the reduction rate of the average film thickness within 10% when the above-described baking treatment is performed, or the heat treatment time becomes extremely long even if it is possible. This causes a problem that lowers the production efficiency. On the other hand, when heat treatment is performed in air or in the air, if the heat treatment temperature exceeds 350 ° C., the deterioration of the coating proceeds during the heat treatment, which may lower the corrosion resistance. It is better to set below. On the other hand, even when the heat treatment is performed in an inert atmosphere, the upper limit may be appropriately set in consideration of the heat resistance of the base. For example, when the base is a Zn plating layer, the heat treatment temperature is set to 400 ° C. or lower. Is good. The heat treatment temperature is more desirably 180 to 2
It is good to carry out in the range of 50 ° C.

When the above heat treatment is performed on the metal shell of the spark plug, the heat treatment may be performed before the metal shell is attached to the spark plug. Alternatively, the heat treatment may be performed after the metal shell is mounted on the spark plug. Well,
A similar effect of improving corrosion resistance can be obtained. In the latter case, if the heat treatment is performed at a high temperature, the influence on other members of the spark plug cannot be ignored, and the heat sealing property is affected. Therefore, it is desirable to set the heat treatment temperature T (° C.) in the range of 130 to 200 ° C. . In addition, there is a concern that the influence on talc may be caused when the time for the heat treatment is long. Specifically, the temperature of the talc itself is 150 ° C.
Should be set to a time that does not exceed.

Next, the time of the heat treatment is as long as necessary and sufficient so that the rate of decrease in the average film thickness after baking of the chromate film obtained after the treatment is within 10%, and the heat resistance can be sufficiently ensured. Although it is necessary, the lower limit of the heat treatment time differs depending on the heat treatment temperature to be adopted. Specifically, assuming that the heat treatment temperature is T (° C.) and the heat treatment time is t (second), at T ≧ 250, t ≧ 90, at T ≧ 190, t
It is desirable to perform under conditions that satisfy any of t ≧ 210, T ≧ 150, T ≧ 270, T ≧ 130, and T ≧ 130 at T ≧ 170, T ≧ 130, and T ≧ 130. Under any conditions, by setting the heat treatment time to be longer than the above lower limit, the resulting chromate film has a reduction rate of the average film thickness after the baking treatment of 10% or less, and thus greatly improves heat resistance. It becomes possible. The heat treatment is more desirably performed at T ≧ 250 and t ≧ 15.
0, at T ≧ 190, t ≧ 210, at T ≧ 170, t
≧ 270, T ≧ 150, and t ≧ 540, preferably under the condition that satisfies any of t ≧ 540.

On the other hand, according to an experiment conducted by the present inventors,
It has been found that the necessary and sufficient heat treatment time becomes exponentially shorter as the heat treatment temperature becomes higher. As a result of further intensive studies, assuming that the heat treatment temperature is T (K) and the heat treatment time is t (sec), t ≧ 90 and t ≧ 1.768 × exp (2311 / T)... It has been found that performing the heat treatment under the conditions (that is, performing the heat treatment using the right side of the above formula 1 as the lower limit of the heat treatment time) is effective. By setting the heat treatment time longer than the above, the resulting chromate film is
The rate of decrease in film thickness after baking is within 10%,
As a result, heat resistance can be greatly improved.
The heat treatment time t (sec) is more desirably t ≧
150, and t ≧ 4.818 × exp (1981 / T)... It is preferable to set so as to satisfy Expression 2. More preferably, t ≧ 150 and t ≧ 0.105 × exp (4140 / T) T) It is better to set so as to satisfy Expression 3.

The heat treatment time can be set to an arbitrary time longer than the above lower limit value. However, even if the heat treatment time is extremely increased, further improvement of the heat resistance improvement effect may not be expected. It is appropriate to determine the upper limit appropriately in consideration of (for example, up to about three times the lower limit).

As described above, the heat treatment improves the corrosion resistance and heat resistance of the chromate film. On the other hand, however, excessive heat treatment may reduce the sliding property between the formed chromate film and other members. For example, in a spark plug, if a chromate coating formed on a metal shell has poor sliding slidability, the metal shell and other members are slid and slidably assembled to produce a spark plug. In some cases, a defect such as a crack may occur in the chromate film formed on the metal shell, or an undesired force may be applied at the time of assembling, and the dimensions of the tool engaging portion (so-called hexagonal portion) of the metal shell may be widened. Therefore, it is necessary to suppress excessive heat treatment. Therefore, when the sliding sliding property of the chromate film is particularly important, the heat treatment temperature is T (° C.) and the heat treatment time is t.
(Seconds), at T ≦ 155, t ≦ 2000, T ≦ 1
70, t ≦ 1650, T ≦ 190, t ≦ 135
0, at T ≦ 205, at t ≦ 1050, at T ≦ 215,
When t ≦ 750 and T ≦ 230, t ≦ 540 and T ≦ 245
It is preferable that the heat treatment is performed under a condition satisfying any one of t ≦ 360, T ≦ 255 and t ≦ 270. More preferably, at T ≦ 145, t ≦ 2000 and T ≦ 155.
, T ≦ 1650, T ≦ 170, t ≦ 1350,
At T ≦ 190, t ≦ 1050, at T ≦ 205, t ≦
750, T≤215, t≤540, T≤230, t≤360, T≤245, t≤270, T≤2
At 55, it is preferable to perform the heat treatment under a condition satisfying any one of t ≦ 210.

The heat treatment conditions effective for improving the sliding property are a heat treatment time t (sec) and a heat treatment temperature T
As (K), t ≦ 0.094 × exp (4201 / T)... The condition represented by the formula A may be satisfied. By setting the heat treatment time t (sec) to be shorter than the above upper limit, excessive heat treatment is suppressed, and as a result, the sliding property can be improved. The heat treatment time t (s)
ec) is more desirably set so that t ≦ 0.038 × exp (4489 / T) formula B

The chromate film which satisfies the heat treatment conditions of the present invention and is heat-treated under the heat treatment conditions in the above-mentioned range has excellent corrosion resistance and heat resistance and good sliding and sliding properties. The metal member on which is formed can easily slide and slide with other members. In particular, when using the metal member of the present invention as a metal shell of a spark plug, even if the metal shell is slid and slid and assembled with other members, peeling of the chromate film,
In addition, deformation of a tool engaging portion (a so-called hexagonal portion) and the like is suppressed.

The chromate treatment is a kind of chemical conversion treatment in which the chromium component is replaced and deposited as it is while oxidizing and eluting the base metal. Therefore, in an electroless chromate treatment in which power is not supplied from the outside, the base metal needs to be a metal that can be eluted into the chromate treatment bath. On the surface of a metal member made of an iron-based material such as carbon steel (for example, a metal shell of a spark plug or a gasket), a zinc-based plating layer in which a main component of a metal component is zinc is formed for corrosion protection. can do. This zinc-based plating layer is advantageous as a base metal for forming a chromate film in the above sense. In this case, the eluted zinc component is often taken into the chromate film. The zinc-based plating layer can be formed by known electrolytic zinc plating or hot-dip galvanizing. On the other hand, if the electrolytic chromate treatment method is employed, a chromate film can be formed even if the metal component is mainly a nickel-based plating layer made of nickel.

In addition, a zinc plating layer is used as the base metal layer, and a chromate film having the above-mentioned thickness range is formed on the zinc plating layer. When the “test method” was carried out, the durability time until white rust resulting from corrosion of the galvanized layer appeared at about 20% or more of the entire surface was 3
More than 00 hours can be secured. This is, for example, a sufficient level of corrosion resistance to be provided in a metal shell of a spark plug or a gasket.

Also, as a problem peculiar to the spark plug,
If the engine continues to operate under conditions where the heat load is high, or if the spark plug is installed at a position relatively close to the exhaust manifold, the temperature of the metal shell sometimes rises to about 200 to 300 ° C. May be. However, by forming the underlayer metal layer as a galvanized layer and forming a chromate film having the above-described thickness, good durability performance can be obtained even in the following test assuming such a situation. That is, after heating in air at 200 ° C. for 30 minutes, the JIS
When performing “5. Neutral salt spray test method” in the corrosion resistance test method for plating specified in H8502, white rust resulting from corrosion of the galvanized layer was approximately 20% of the entire surface.
The endurance time until the above appears is secured for 300 hours or more.

The metal shell and gasket of the spark plug are susceptible to attack by acidic components such as carbon dioxide, nitrogen oxides and sulfur oxides contained in exhaust gas and the like. However, by forming the undercoat metal layer as a galvanized layer and forming a chromate film having the above-described thickness, good durability performance can be obtained even in the following test assuming such a situation. That is, when the “7. Cass test method” in the corrosion resistance test method for plating specified in JIS H8502 was performed, the durability time until white rust resulting from corrosion of the galvanized layer appeared about 20% or more of the entire surface. For more than 40 hours.

Next, in the present invention, a metal member (for example, a metal shell of a spark plug or a gasket) is immersed in a chromate treatment bath containing a trivalent chromium salt and a complexing agent for trivalent chromium. By doing so, the above-described chromate film can be formed on the surface of the metal member.

By using a bath containing a complexing agent for trivalent chromium together with a trivalent chromium salt as a chromate treatment bath, a dense and thick trivalent chromium-based chromate film, which is difficult with a general chromate treatment method, is obtained. This makes it possible to easily form a trivalent chromium-based chromate film having a preferable thickness of 0.2 to 0.5 μm, which is the gist of the metal member of the present invention. A method for forming such a chromate film is disclosed in German Published Patent Application DE.
Details are disclosed in 19638176A1. The outline will be described below.

As described above, in the process of forming the chromate film, the underlying metal (eg, zinc) is first oxidized and eluted in the treatment bath, and the eluted underlying metal component reacts with the solution containing chromate ions. It is a common theory that trivalent chromium mainly forms a polymer-like complex by a hydroxyl group or an oxygen bridge and precipitates and deposits in a gel state on the surface of the underlying metal. In this case, in order for the chromate film to grow, the elution of the base metal and the reaction and deposition of the eluted base metal with the chromate ions in the bath must proceed in parallel. However, when the chromate film is deposited to some extent, the elution reaction of the underlying metal layer, which is a non-uniform reaction via the interface with the solution, is prevented, and the film growth stagnates.

According to the disclosure of the above-mentioned German Patent Publication, in order to increase the thickness of the coating, dissolution of the base metal and
It is important that the rate of reverse dissolution of the deposited chromate film be as small as possible while increasing the rate of film deposition by the reaction between the dissolved base metal component and trivalent chromium. Then, in the above method, it is considered that by adding an appropriate complexing agent to the bath and complexing trivalent chromium, the precipitation of the film is promoted and the film can be made thicker.

As complexing agents, various chelating agents (dicarboxylic acid, tricarboxylic acid, oxyacid, hydroxyl dicarboxylic acid or hydroxyl tricarboxylic acid, etc .: for example, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid) , Coric acid, aseleic acid, sebacic acid, maleic acid, phthalic acid, terephthalic acid, tartaric acid, citric acid,
It is effective to use malic acid, ascorbic acid, etc., but other complexing agents may be used. The complexing agents that can be used are as described in the above-mentioned German published patent application.

In order to increase the thickness of the coating, it is effective to raise the temperature of the chromate treatment bath to about 20 to 80 ° C. If the bath temperature is lower than 20 ° C., the effect of increasing the coating thickness by increasing the temperature can hardly be expected, and if the bath temperature is 80 ° C. or higher, control of bath conditions becomes difficult due to severe evaporation of water from the bath. In addition, an object to be treated in a chromate bath (metal member: for example, a metal shell of a spark plug, or a gasket)
The dipping time is preferably 20 to 80 seconds. If the immersion time is less than 20 seconds, the thickness of the formed chromate film may not be sufficiently secured. On the other hand, the immersion time is 80
When the time exceeds seconds, the formed chromate film becomes too thick, causing cracks in the film (for example, at the time of processing in assembling with other members), or easily falling off of the film, so that the anticorrosion performance is rather deteriorated. May be impaired.

In order to promote the dissolution of the underlying metal, it is effective to lower the pH of the chromate treatment solution within a range in which the re-dissolution of the deposited film does not become severe. A desirable pH range is, for example, about 1.5 to 3. Further, in order to suppress the re-dissolution of the deposited film, it is effective to incorporate a hardly re-dissolved hydroxide such as nickel, cobalt or copper into the film. For this purpose, the compounds of the above metals are dissolved in a chromate treatment bath.
Can be blended.

On the other hand, a predetermined amount of sodium salt (for example, sodium nitrate) is blended in the chromate treatment bath so that the content of the sodium component in the chromate treatment film is 2 to 7% by mass, so that the density of the chromate treatment film can be increased. It becomes easier to form a thick chromate film into a thick film. Although the detailed mechanism is unknown, it is presumed that if sodium ions are taken into the chromate film, the chromate film is less likely to be redissolved in the treatment bath. If the content of the sodium component in the chromate treatment film is out of the range of 2 to 7% by mass, it may be difficult to secure the thickness of the chromate film to 0.2 μm or more. The content of the sodium component in the chromate treatment film is more desirably 2 to 6% by mass.

When the chromate film is formed on another metal member, it goes without saying that the same method as in the above steps can be applied.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example (for example, a bolt or the like) of a metal member 55 which is a metal member with a chromate film of the present invention. A zinc plating layer 56 is formed on the metal member 55 to prevent corrosion. The zinc plating layer 56 is formed by a known electrolytic zinc plating method, and the thickness of the formed zinc plating layer 56 is, for example, about 3 to 5 μm. The thickness of the galvanized layer 56 is 3
If the thickness is less than μm, the effect of preventing corrosion is poor, and the corrosion resistance cannot be sufficiently secured due to the consumption of the galvanized layer 56 due to the sacrificial corrosion, which is not preferable.
On the other hand, a film thickness exceeding 10 μm is an excessive specification from the viewpoint of ensuring corrosion resistance, and also reduces the production efficiency due to a long plating time. In addition, there is a problem that plating peeling and the like are apt to occur at the time of assembling with another member or bending or the like.

A chromate film 57 is further formed on the surface of the galvanized layer 56 as described above. The thickness of the chromate film 57 is set to 0.2 to 0.5 μm. Further, 95% by mass or more of the chromium component contained in the chromate film is trivalent chromium. Desirably, all of the chromium components contained are substantially trivalent chromium components.

FIG. 2 shows an example of a method for forming a chromate film 57 on a metal member. That is, the metal member 55 having a galvanized layer having a predetermined thickness formed by a known electrolytic galvanizing method or the like is immersed in a chromate treatment bath. The type of the chromate treatment bath 50 to be used has already been described. As a result, as shown in FIG.
A chromate film 57 is formed on the surface of the substrate. In addition,
FIG. 2 is an explanatory view showing a conceptual process.
Is simply immersed in a chromate treatment bath, but in actuality, in order to improve the treatment efficiency, a known barrel treatment method (the metal members 55 are inserted in bulk in a liquid-permeable container and inserted into the treatment bath 50) Process performed while rotating the container).

After the chromate treatment, the metal member 55 is washed with water and further heated to 130 to 350 ° C. in the air (or an inert atmosphere made of Ar gas or nitrogen gas) by a heat treatment furnace F as shown in FIG. As a result, the chromate film 57 shrinks and densifies.
Even if a heat history up to about 00 ° C. is applied, the shrinkage of the film thickness can be suppressed to 10% or less. As a result, heat resistance is greatly improved. The metal member 55 after the chromate treatment
May be dried at 50 to 80 ° C. by warm air after washing with water, and then the above heat treatment may be performed. The metal member 55 can be used, for example, as a screw jig such as a bolt or a nut. However, this is merely an example, and the present invention is not limited to the knowledge of a person concerned without departing from the spirit thereof. Based on the above, the present invention can be implemented in a mode in which other changes are added.

For example, the metal shell or gasket of the spark plug can be constituted by the metal member of the present invention. Hereinafter, embodiments of the spark plug of the present invention will be described. A spark plug 100 with a resistor as an example of the present invention shown in FIG. 4 has a cylindrical metal shell 1, an insulator 2 fitted into the metal shell 1 so that the tip protrudes, and a tip protruding. A center electrode 3 provided inside the insulator 2 in this state, and a ground electrode 4 and the like, one end of which is coupled to the metal shell 1 and arranged so that the multi-end side faces the tip of the center electrode 3. A spark discharge gap g is formed between the ground electrode 4 and the center electrode 3.

The insulator 2 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride, and has a through hole 6 for fitting the center electrode 3 along its own axial direction. . The terminal fitting 13 is inserted and fixed to one end of the through hole 6, and the center electrode 3 is inserted and fixed to the other end of the through hole 6. A resistor 15 is arranged between the terminal fitting 13 and the center electrode 3 in the through hole 6. Both ends of the resistor 15 are electrically connected to the center electrode 3 and the terminal fitting 13 via conductive glass seal layers 16 and 17, respectively.

The metallic shell 1 is formed of a metal such as carbon steel into a cylindrical shape, and forms a housing of the spark plug 100 and has a plug 100 on its outer peripheral surface.
Is formed on the engine block (not shown). Reference numeral 1e denotes a tool engagement portion that engages a tool such as a wrench or a wrench when the metal shell 1 is attached, and has a hexagonal axial cross-sectional shape. On the other hand, between the inner surface of the rear opening of the metal shell 1 and the outer surface of the insulator 2, a ring-shaped wire packing 62 that engages with the rear peripheral edge of the flange-shaped protrusion 2e is arranged. On the rear side, a ring-shaped packing 60 is arranged via a filling layer 61 such as talc. Then, the insulator 2 is pushed forward toward the metal shell 1 and, in this state, the opening edge of the metal shell 1 is swaged inward toward the packing 60 to form a swaged portion 1d. It is fixed to the insulator 2.

A gasket 30 is fitted into the base end of the screw 7 of the metal shell 1. The gasket 30 is a ring-shaped part obtained by bending a metal plate material such as carbon steel, and the screw portion 7 is screwed into a screw hole on the cylinder head side to form a flange-shaped gas seal portion 1f on the metal shell 1 side. Between the screw hole and the opening peripheral portion of the screw hole, it is compressed in the axial direction and deformed so as to be crushed, and serves to seal a gap between the screw hole and the screw portion 7.

Next, a zinc plating layer 41 for corrosion protection is formed on the entire outer surface of the underlayer (for example, carbon steel) 40 of the metal shell 1.
(A zinc-based plating layer) is formed, and further outside thereof is covered with a chromate film 42. Gasket 30
Similarly, a galvanized layer 45 and a chromate film 46 are also formed on the outer surface. These galvanized layers and chromate coatings are both formed by the same method, and will be described below as representative on the metal shell 1 side.

The galvanized layer 41 of the metal shell 1 (or the gasket 30) of the spark plug is formed by the same method as the above-mentioned metal member. The thickness of the zinc plating layer 41 formed on the metal shell 1 is set to about 3 to 10 μm in the same manner as the above-mentioned metal member in consideration of the effect of ensuring corrosion resistance. If the film thickness exceeds 10 μm, the metal shell 1
In a portion that is deformed when caulking and fixing to the surface or when bending the ground electrode 4, plating peeling is likely to occur. In consideration of the usage of the spark plug 100 and the manufacturing situation, the thickness of the zinc plating is preferably about 3 to 9 μm. On the other hand, the chromate film 42 formed on the zinc plating is a trivalent chromium-based chromate film in which 95% by mass or more of the contained chromium component is trivalent chromium, and has a thickness of 0.2 to 0.2%. It is set to 0.5 μm. Preferably, the chromium component has a trivalent chromium component as much as possible, and it is desirable that substantially all of the chromium component be a trivalent chromium component. The thickness of the chromate film 42 is more preferably about 0.3 to 0.5 μm in consideration of the usage of the spark plug 100 and the manufacturing conditions.

The chromate film 42 is formed by the following chromate treatment. That is, the metal shell 1 on which the above-described galvanized layer 41 is formed is placed in the chromate treatment bath 50.
Soak in As the chromate treatment bath 50, those described above are preferably used. Thereby, the chromate film 42 is formed on the metal shell 1. The metal shell 1 may be simply immersed in a chromate treatment bath. However, in order to improve the treatment efficiency, a known barrel treatment method (the metal members 55 are piled up in a liquid-permeable container and inserted into the treatment bath 50). (A process performed while rotating the container inside). Further, the bath temperature of the chromate treatment bath is set to 20 to 80 ° C., and the immersion time in the chromate treatment bath is set to 20 to 80 seconds. Thereby, the above-mentioned chromate film having a suitable thickness can be formed.

After the chromate treatment, the metal shell 1 (or the gasket 30) is washed with water, and then further heated by the heat treatment furnace F.
The heat treatment is performed at 130 to 350 ° C. in the air (or an inert atmosphere made of Ar gas or nitrogen gas), whereby the chromate film 42 shrinks and densifies. Even if added, the shrinkage ratio of the average thickness of the coating can be suppressed to 10% or less. As a result, heat resistance is greatly improved. The heat treatment may be performed after the metal shell 1 after the chromate treatment and after temporary washing at 50 to 80 ° C. with hot air or the like after washing with water.

The metal shell 1 after the heat treatment is assembled into the spark plug 100 shown in FIG. In the metal shell 1 or the gasket 30, the chromate film formed on the galvanized layer has significantly higher anticorrosion performance and heat resistance than the conventional hexavalent chromium chromate film, and is resistant to corrosion against the galvanized layer. Property can be sufficiently imparted. After the metal shell 1 is assembled into the spark plug 100, the above-described heat treatment may be performed.

[0050]

EXAMPLE A metal shell of a spark plug was taken as a metal member with a chromate film, and the effect of the present invention was examined.
Although the present embodiment shows a metal shell of a spark plug as an example, this is merely an example, and the present invention is based on the knowledge of the parties and includes other modifications without departing from the spirit thereof. It can be implemented in.

Using a carbon steel wire SWCH8A for cold heading specified in JIS G3539 as a raw material, a metal shell 1 having a shape shown in FIG. 4 was manufactured by cold forging. In addition, the nominal size of the threaded portion 7 of the metal shell 1 was M14, and the length in the axial direction was about 19 mm. Next, a zinc plating layer 41 having a film thickness of about 6 μm was formed by subjecting this to electrolytic zinc plating using a known alkaline cyanide bath.

Next, the chromate treatment bath 50 was filled with chromium (III) chloride (Cr
Cl ₃ · _6H 2 O) of 50 g, cobalt nitrate (II) (C
o (NO ₃ ) ₂ ) and sodium nitrate (NaN
A bath was prepared by dissolving 100 g of O ₃ ) and 31.2 g of malonic acid, and the solution was maintained at a liquid temperature of 60 ° C. with a heater, and the pH of the bath was adjusted to 2.0 by adding an aqueous solution of caustic soda. The zinc-plated metal shell 1 was immersed in the chromate treatment liquid 50 for 60 seconds, washed with water, and temporarily dried with warm air at 70 ° C. for 60 seconds to form a trivalent chromium-based chromate film (test sample). A).

On the other hand, as a yellow chromate treatment bath, 7 g / l of chromic anhydride and 3 g of sulfuric acid with respect to deionized water.
Per liter and nitric acid at a rate of 3 g / liter were prepared and maintained at a liquid temperature of 20 ° C. Then, a metal shell was immersed therein for about 15 seconds, pulled up, and dried with hot air at 70 ° C. (Test article B: Comparative example).

The existence state of chromium in each chromate film of each of the test samples was examined by X-ray photoelectron spectroscopy (XPS). FIG. 5 shows the peak portions of chromium (2p _2/3 ) in the photoelectron spectra of the test sample A and the test sample B.
In the test sample A (solid line), no peak appears at the position corresponding to hexavalent chromium, and it can be confirmed that almost all of the chromium component is trivalent chromium. On the other hand, in the test sample B, the peak of hexavalent chromium overlaps the peak of trivalent chromium, and a bump-like bulge appears on the shoulder on the high energy side of the peak.

FIG. 6 shows the shape of each peak as I = exp {, where the intensity of the photoelectron X-ray is I (vertical axis in the figure: cps) and the binding energy value is x (horizontal axis in the figure: eV). − (X−
μ) ² / 2σ ² } Equation 4 (where μ is the peak x
The coordinates and σ represent the half-width of the peak curve), and are the results of peak separation analysis. According to this, assuming that the peak height of trivalent chromium is I1 and the peak height of hexavalent chromium is I2, I2 / (I1 + I2) is about 0.2 (from the viewpoint of hexavalent chromium reduction, I2 /
It can be said that (I1 + I2) is desirably 0.05 or less.) Further, a calibration curve was prepared using a standard sample of dichromium trioxide, and the mass content of hexavalent chromium in the total amount of chromium components was calculated based on the calibration curve. About 15% by mass was hexavalent chromium, and the balance was trivalent chromium. It turned out to be chrome.

Next, the test sample A after the preliminary drying was heated in a heat treatment furnace F at a temperature of 70 to 300 ° C. for 30 to 1800.
Heat treatment was performed for 2 seconds to obtain a final corrosion resistance evaluation test piece. Also,
The test article B of the comparative example was used as a corrosion resistance evaluation test piece without heat treatment. Then, each test piece was baked at 200 ° C. for 30 minutes in the air, and the change in the thickness of the chromate film before and after the treatment was measured by actual measurement from a cross section by SEM. In order to facilitate observation of the chromate film, an Au thin film is formed on the surface of the film by a sputtering method. In the SEM image, the chromate coating layer having a low conductivity is darker than the zinc plating layer having a high conductivity and the Au coating layer, so that the image of the chromate coating can be easily confirmed from the contrast. .

When the film thickness is measured by the SEM as described above, a destructive inspection is performed. Therefore, the film thickness is measured by comparing before and after baking at a place where the same film thickness is expected to be formed. do it. For example, in the case of a metal shell of a spark plug as in the present embodiment, the following method may be used. First, the galvanized layer and the chromate film are peeled off at a predetermined location in the tool engaging portion 1e, and the thickness of the chromate film before the baking treatment is measured. Next, after the metal shell is baked, the galvanized layer and the chromate film are peeled off at other portions of the tool engaging portion 1e, and the thickness of the chromium film after the baking process is measured. Then, the reduction rate of the film thickness is calculated from the measured values after the baking process. Note that film thickness measurement using a laser interferometer is also possible. In this case, since non-destructive inspection is performed, measurement can be performed at the same place before and after baking.

For the above test items, JIS H8502
Perform the “5. Neutral salt spray test method” in the corrosion resistance test method for plating specified in, and evaluate the durability by the time until white rust resulting from corrosion of the galvanized coating appears at least about 20% of the entire surface. Was. In this embodiment, the metal shell is used as a sample as it is, and one of the tool engaging portions (hexagonal portions) is used.
One surface is used as the sample surface. FIG. 7 shows the results. The evaluation criteria are as follows: （(excellent): 400 hours or more in endurance time. The rate of decrease in thickness of the chromate film before and after baking is 5% or less. Δ (good): Durable time of 300 hours or more and less than 400 hours.
The chromate film thickness reduction rate before and after baking is 5
% And 10% or less. X (bad): Durability time less than 300 hours. Chromate coating thickness reduction before and after baking is greater than 10%.

According to the results, the test piece A heat-treated within the range of the present invention had a good durability time of 300 hours or more in the salt spray test, and showed a decrease in the thickness of the chromate film before and after the baking treatment. The rate was also found to be small. On the other hand, for the test sample B, the rate of decrease in the thickness of the chromate film before and after the baking treatment was large, and the durability time in the salt spray test was insufficient.

FIG. 8 shows the reciprocal of the value t1 at which the evaluation result changes from poor (x) to good (△) for the heat treatment time t at each temperature (represented by a plot point “△” in the graph). Good), good (△) to good (○)
Is a semilogarithmic plot of the reciprocal of the value t2 (indicated by a point “グ ラ フ” in the graph) that changes to the reciprocal of the heat treatment temperature T (absolute temperature display). In the graph, t1 = 1.768 × exp (2311 / T) ··· Equation 1 ′ t2 = 4.818 × exp (1981 / T) ··· Recommended lower limit expressed by Equation 2 ′ Straight lines representing the times t1 and t2 are also drawn. It can be seen that the evaluation result is good (△) on the longer side (below the straight line) than Equation 1 ′, and the evaluation result is excellent (○) on the longer side than Equation 2 ′. .

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a metal member with a chromate film of the present invention.

FIG. 2 is an explanatory diagram of a chromate treatment step in a metal member with a chromate film of the present invention.

FIG. 3 is an explanatory view of a heat treatment step in the metal member with a chromate film of the present invention.

FIG. 4 is a longitudinal sectional view showing an example of a spark plug as one embodiment of the present invention.

FIG. 5 is a view showing the result of X-ray photoelectron spectroscopy analysis of the chromate films of the test articles A and B of the example (peak portion of chromium (2p _2/3 ) in the photoelectron spectrum).

FIG. 6 shows the chromium (2
The figure which shows the result of having performed peak separation analysis with respect to the peak part of (p2 _{/ 3} ).

FIG. 7 is a view showing the results of a corrosion resistance test performed in Examples.

8 is a diagram in which the heat treatment upper limit time indicated by the experimental results in FIG. 7 is plotted against the heat treatment temperature.

[Explanation of symbols]

 55 Metal member 50 Chromate treatment bath 57, 42 Chromate coating 56, 41 Galvanized layer 100 Spark plug 1 Metal shell 2 Insulator 3 Center electrode g Spark discharge gap 4 Ground electrode 7 Mounting screw part 30 Gasket

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01T 13/02 H01T 13/02 21/02 21/02 F term (Reference) 4K026 AA02 AA07 AA12 AA21 BA06 BA11 BB08 CA13 CA19 CA32 CA38 DA13 DA16 EB11 4K044 AA02 AB05 BA10 BA15 BB03 BC02 CA16 CA18 CA62 5G059 AA03 GG09

Claims (13)

[Claims] 1. 95% by mass of the chromium component contained
The above is trivalent chromium, the surface of which is covered with a chromate film having a thickness of 0.2 to 0.5 μm, and which is subjected to a baking treatment of heating at 200 ° C. for 30 minutes in air. A metal member with a chromate film, wherein a reduction rate of a film thickness of the film is within 10%. 2. The metal member with a chromate coating according to claim 1, wherein the chromate coating does not substantially contain a hexavalent chromium component. 3. The metal member with a chromate film according to claim 1, wherein a zinc plating film is formed as a base metal layer of the chromate film. 4. When performing “5. Neutral salt spray test method” in the plating corrosion resistance test method specified in JIS H8502, white rust resulting from corrosion of a galvanized coating film is about 20% of the entire surface. The metal member with a chromate coating according to any one of claims 1 to 3, wherein a durability time until the above-mentioned appearance is 300 hours or more. 5. A spark discharge gap is formed between a center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and the center electrode. A spark plug comprising: an installation electrode disposed in a shape facing the spark plug; and wherein the metal shell is made of the metal member with a chromate coating according to any one of claims 1 to 4. Features spark plug. 6. A ring-shaped gasket to be fitted to a base end of a mounting screw portion formed on an outer peripheral surface of the metal shell, and the gasket is formed of the metal member with the chromate film. Item 6. A spark plug according to item 5. 7. The method for producing a metal member with a chromate film according to claim 1, wherein the metal member is contained in at least a part of the surface of the metal member by immersing the metal member in a chromate treatment bath. A chromate treatment step of forming a chromate film having a thickness of 0.2 to 0.5 μm in which 95% by mass or more of the chromium component is trivalent chromium; and a heat treatment step of heat treating the chromate film at 130 ° C. or more. A method for producing a metal member with a chromate film, characterized by the above-mentioned. 8. The method for producing a metal member with a chromate film according to claim 7, wherein a mixture of a trivalent chromium salt and a complexing agent for trivalent chromium is used as the chromate treatment bath. 9. The chromate treatment bath is at 20 to 80 ° C.
9. The method for producing a metal member with a chromate film according to claim 7, wherein the metal member is used in a state where the bath temperature is adjusted. 10. The method for producing a metal member with a chromate film according to claim 7, wherein the immersion time of the metal member in the chromate treatment bath is 20 to 80 seconds. 11. The heat treatment step includes setting a heat treatment temperature to T.
(° C.), the heat treatment time is t (second), T ≧ 250, t ≧ 90, T ≧ 190, t ≧ 150, T ≧ 170, t ≧ 210, T ≧ 150, t ≧ 150 The method for producing a metal member with a chromate film according to any one of claims 7 to 10, wherein the method is performed under a condition that satisfies any one of: ≧ 270, T ≧ 130, and t ≧ 540. 12. The heat treatment step includes setting the heat treatment temperature to T.
(K) The chromate film according to any one of claims 7 to 10, wherein the heat treatment time is t (sec), and t ≧ 90 and t ≧ 1.768exp (2311 / T). Method for manufacturing a metal member with an attachment. 13. The method for manufacturing a spark plug according to claim 5, wherein the metal shell and / or the gasket are provided.
13. A method for manufacturing a spark plug, wherein the spark plug is manufactured as the metal member with a chromate film by the method according to any one of claims 12 to 12.