JP2012243569A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug superior in stress corrosion cracking resistance, which is obtained by appropriately regulating a composition of an oil film layer that is formed by using a rust preventive oil and on a surface of a main metal fitting.SOLUTION: The spark plug comprises: a center electrode that extends in a shaft direction; a cylindrical insulator that is provided at a circumference of the center electrode; and the cylindrical main metal fitting that is provided at a circumference of the insulator and covered with the oil film layer. The oil film layer contains at least one of a Ca element and a Na element, and a C element and a S element. A weight ratio of the C element and the S element satisfies 20≤C/S≤125, and a deposited amount of the oil film layer is 0.02 mg/cm2 or more per unit surface area of the main metal fitting.

Description

  The present invention relates to a spark plug for an internal combustion engine.

  A spark plug used for ignition of an internal combustion engine such as a gasoline engine is provided with an insulator on the outside of the center electrode, and a metal shell is provided on the outside of the spark plug to form a spark discharge gap with the center electrode. The electrode has a structure attached to the metal shell. The metal shell is generally made of an iron-based material such as carbon steel, and its surface is often plated for corrosion protection. As a plating layer, a technique that employs a two-layer structure of a Ni plating layer and a chromate layer is known (Patent Document 1).

JP 2002-184552 A JP 2007-141868 A JP 2003-257583 A JP 2007-023333 A JP 2007-270356 A

  In the above-described prior art (Patent Document 1), an electrolytic chromate treatment is performed so that 95% by mass or more of the chromium component in the chromate layer becomes trivalent chromium. The aim was to reduce the environmental load and to improve the corrosion resistance against salt water (salt corrosion resistance).

  However, the inventors have found that even when two or more plating layers are used for the metal shell, the corrosion resistance becomes a big problem at a portion that deforms during caulking. That is, it has been found that the corrosion resistance for preventing stress corrosion cracking is a serious problem because a large residual stress is generated in the portion deformed by the caulking process of the metal shell. In particular, when heat caulking is used, there is a possibility that stress corrosion cracking may occur more because of the high hardness due to the structural change due to heating and the presence of large residual stress. Thus, in the spark plug, the inventor has found that not only the salt corrosion resistance but also the stress corrosion cracking resistance becomes a big problem in the portion deformed by the caulking process of the metal shell. Such a problem is particularly remarkable when a metal shell made of a material having a large amount of carbon (for example, carbon steel containing 0.15% by weight or more of carbon) is used. Moreover, it is remarkable when heat caulking is adopted as the caulking process.

  In order to suppress this stress corrosion cracking, the inventors have not only specifications for Ni plating layers and chromate layers, but also specifications for oil film layers formed by rust-preventing oil applied on these layers. The present invention has been reached with the recognition that it is important to study the above.

  An object of the present invention is to provide a spark plug excellent in stress corrosion cracking resistance by appropriately defining the configuration of an oil film layer formed on the surface of a metal shell by rust preventive oil.

  In order to solve at least a part of the above problems, the present invention can be realized as the following aspects or application examples.

[Application Example 1]
A central electrode extending in the axial direction;
A cylindrical insulator provided on the outer periphery of the center electrode;
A spark plug provided on the outer periphery of the insulator and having a cylindrical metal shell covered with an oil film layer,
The oil film layer contains at least one of Ca element and Na element, C element and S element, the weight ratio of C element and S element is 20 ≦ C / S ≦ 125, and the unit surface area of the metal shell The spark plug is characterized by having an adhesion amount of 0.02 mg / cm ² or more.

According to this configuration, the weight ratio of C element and S element contained in the oil film layer is 20 ≦ C / S ≦ 125, and the amount of oil film layer deposited per unit surface area of the metal shell is 0.02 mg / cm ² or more. By doing so, the stress corrosion cracking resistance of the spark plug can be improved.

[Application Example 2]
In the spark plug described in Application Example 1,
The metal shell is covered with a nickel plating layer, and the oil film layer is formed on the nickel plating layer.

  According to this configuration, it is possible to improve the stress corrosion cracking resistance of the spark plug in which the nickel plating layer is formed on the metal shell.

[Application Example 3]
In the spark plug described in Application Example 2,
The metal shell has a polygonal shape in the cross-sectional shape perpendicular to the axis, and includes a tool engaging portion having a plurality of flat portions for engaging with the tool,
The nickel plating layer is a spark plug in which the number of pinholes is 10 locations / cm ² or less per unit surface area in the planar portion.

According to this configuration, the number of pinholes per unit surface area of the nickel plating layer is set to 10 places / cm ² or less in the flat portion for engaging with the tool of the metal shell, whereby the stress corrosion resistance of the spark plug is reduced. It is possible to improve the cracking property.

[Application Example 4]
In the spark plug described in Application Example 1,
The spark plug, wherein the metallic shell is covered with a nickel plating layer, a chromate layer is formed on the nickel plating layer, and the oil film layer is formed on the chromate layer.

  According to this configuration, in the metal shell, since the chromate layer is formed on the nickel plating layer and the oil film layer is formed on the chromate layer, the stress corrosion cracking resistance of the spark plug can be further improved. it can.

[Application Example 5]
In the spark plug described in Application Example 4,
The metal shell has a polygonal shape in the cross-sectional shape perpendicular to the axis, and includes a tool engaging portion having a plurality of flat portions for engaging with the tool,
The nickel plating layer is a spark plug in which the number of pinholes in the planar portion is 13 places / cm ² or less per unit surface area.

According to this configuration, the number of pinholes per unit surface area of the nickel plating layer is set to 13 places / cm ² or less in the flat portion for engaging with the tool of the metal shell, whereby the stress corrosion resistance of the spark plug is reduced. It is possible to improve the cracking property.

[Application Example 6]
In the spark plug according to any one of Application Examples 1 to 5,
The oil film layer is a spark plug in which an adhesion amount per unit surface area of the metal shell is 0.05 mg / cm ² or more.

According to this configuration, the stress corrosion cracking resistance of the spark plug can be further improved by setting the adhesion amount of the oil film layer per unit surface area of the metal shell to 0.05 mg / cm ² or more.

[Application Example 7]
In the spark plug according to any one of Application Examples 1 to 6,
The oil film layer is a spark plug having a Ba element content of 0.2 wt% or less.

  According to this configuration, the occurrence of discoloration in the appearance of the spark plug can be suppressed by setting the content of the Ba element in the oil film layer to 0.2% by weight or less. In addition, it is possible to reduce the environmental load when manufacturing the spark plug.

It is principal part sectional drawing for demonstrating the whole structure of the spark plug in a present Example. It is explanatory drawing which shows an example of the crimping process which fixes a metal shell to an insulator. It is a flowchart which shows the procedure of the metal-plating process. It is explanatory drawing which shows the influence which the component and pinhole amount which are contained in antirust oil have on an external appearance and corrosion resistance in the main metal fitting which is not provided with a chromate layer. It is explanatory drawing which shows the influence which the component and pinhole amount which are contained in antirust oil have on an external appearance and corrosion resistance in the metal shell provided with a chromate layer. It is explanatory drawing which shows the influence which the application quantity of rust prevention oil has on corrosion resistance. It is explanatory drawing which shows the influence which Ba density | concentration of rust preventive oil has on an external appearance.

  FIG. 1 is a cross-sectional view of an essential part for explaining the overall configuration of the spark plug in the present embodiment. The spark plug 100 includes a cylindrical metal shell 1, a cylindrical insulator 2 fitted into the metal shell 1 so that the tip portion protrudes, and the insulator 2 with the tip portion protruding. A center electrode 3 provided on the inner side and a ground electrode 4 disposed so that one end is coupled to the metal shell 1 and the other end faces the tip of the center electrode 3 are provided. A spark discharge gap g is formed between the ground electrode 4 and the center electrode 3.

  The insulator 2 is made of a ceramic sintered body such as alumina or aluminum nitride, for example, and has a through-hole 6 for fitting the center electrode 3 along the axial direction of the insulator 2. The terminal fitting 13 is inserted and fixed on one end side of the through hole 6, and the center electrode 3 is inserted and fixed on the other end side. In addition, the resistor 15 is disposed 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 through the conductive glass seal layers 16 and 17, respectively.

  The metal shell 1 is formed in a hollow cylindrical shape from a metal such as carbon steel, and constitutes a housing of the spark plug 100. The metal shell 1 is subjected to a plating process described later. A threaded portion 7 for attaching the spark plug 100 to an engine block (not shown) is formed on the outer peripheral surface of the metal shell 1. The hexagonal portion 1e is a tool engaging portion that engages a tool such as a spanner or a wrench when the metal shell 1 is attached to the engine block, and has a hexagonal cross-sectional shape. Between the inner surface of the opening on the rear side (upper side in the drawing) of the metal shell 1 and the outer surface of the insulator 2, a ring-shaped wire packing is provided on the rear edge of the flange-shaped protrusion 2e of the insulator 2. 62 is disposed, and on the further rear side, a packed layer 61 such as talc and a ring-shaped packing 60 are disposed in this order. At the time of assembly, the insulator 2 is pushed forward (downward in the figure) toward the metal shell 1, and in this state, the opening edge of the rear end of the metal shell 1 is used as a packing 60 (and thus a protrusion that functions as a crimping receiving portion). By crimping inward toward the portion 2 e), a crimped portion 1 d is formed, and the metal shell 1 is fixed to the insulator 2.

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

  FIG. 2 is an explanatory view showing an example of a process of caulking and fixing the metal shell 1 to the insulator 2 (the ground electrode 4 is omitted). First, for the metal shell 1 as shown in FIG. 2A, as shown in FIG. 2B, the center electrode 3 and the conductive glass sealing layers 16 and 17 in the through hole 6, the resistor 15 and the terminal metal 13 are provided. Is inserted through the insertion opening 1p at the rear end of the metal shell (the portion to be crimped 200 to be the crimping portion 1d is formed), and the engaging portion 2h of the insulator 2 is inserted. And the engaging portion 1 c of the metal shell 1 are engaged through the plate packing 63.

  Then, as shown in FIG. 2 (c), the line packing 62 is arranged on the inner side from the insertion opening 1p side of the metal shell 1, the filling layer 61 such as talc is formed, and the line packing 60 is further arranged. Then, the caulking die 111 is used to caulk the caulking scheduled portion 200 to the end surface 2n of the protruding portion 2e as the caulking receiving portion via the wire packing 62, the filling layer 61, and the wire packing 60, thereby FIG. As shown in (d), a caulking portion 1 d is formed, and the metal shell 1 is caulked and fixed to the insulator 2. At this time, in addition to the caulking portion 1d, the groove portion 1h (FIG. 1) between the hexagonal portion 1e and the gas seal portion 1f is also bent and deformed by the compressive stress during caulking. This is because the caulking portion 1d and the groove 1h are the thinnest in the metal shell 1 and are easily deformed. The groove 1h is also referred to as a “thin wall”. After the step of FIG. 2D, the spark plug 100 of FIG. 1 is completed by bending the ground electrode 4 to the center electrode 3 side to form a spark discharge gap g. Note that the caulking process described in FIG. 2 is cold caulking, but hot caulking can also be used.

  FIG. 3 is a flowchart showing the procedure of the metal plating process. In step T100, nickel strike plating is performed as necessary. This nickel strike plating is performed in order to clean the surface of the metallic shell made of carbon steel and improve the adhesion between the plating and the base metal. However, nickel strike plating may be omitted. As processing conditions for nickel strike plating, processing conditions that are normally used can be used. Examples of specific preferable processing conditions are as follows.

<Examples of nickel strike plating treatment conditions>
・ Plating bath composition:
Nickel chloride: 150-600 g / L
35% hydrochloric acid: 50-300 ml / L
Solvent: deionized water / treatment temperature (bath temperature): 25-40 ° C
Cathode current density: 0.2 to 0.4 A / dm ²
・ Processing time: 5-20 minutes

  In step T110, an electrolytic nickel plating process is performed. As the electrolytic nickel plating treatment, a barrel type electrolytic nickel plating treatment using a rotating barrel can be used, and other plating treatment methods such as a static plating method may be used. As processing conditions for electrolytic nickel plating, processing conditions that are normally used can be used. Examples of specific preferable processing conditions are as follows.

<Examples of electrolytic nickel plating treatment conditions>
・ Plating bath composition:
Nickel sulfate: 100-400 g / L
Nickel chloride: 20-60g / L
Boric acid: 20-60 g / L
Solvent: Deionized water / bath pH: 2.0 to 4.8
Processing temperature (bath temperature): 25-60 ° C
Cathode current density: 0.02-3.0 A / dm ²
・ Processing time: 5 to 600 minutes

  In the above-mentioned electrolytic nickel plating treatment, the number of pinholes in the nickel plating layer was adjusted to 13 or less, preferably 10 or less, per unit area of the metal shell by adjusting the cathode current density and the treatment time. The processing conditions for setting the number of pinholes as described above will be described later together with the experimental results.

  In step T120, electrolytic chromate treatment is performed. A rotary barrel can also be used in the electrolytic chromate treatment, and other plating treatment methods such as a static plating method may be used. Examples of preferable treatment conditions for the electrolytic chromate treatment are as follows.

<Example of treatment conditions for electrolytic chromate treatment>
・ Composition of treatment bath (chromate treatment solution):
Sodium dichromate: 20-70 g / L
Solvent: Deionized water / bath pH: 2-6
Processing temperature (bath temperature): 20-60 ° C
Cathode current density: 0.02 to 0.45 A / dm ² (particularly 0.1 to 0.45 A / dm ² is preferable)
・ Processing time: 1-10 minutes

  As the dichromate, potassium dichromate can be used in addition to sodium dichromate. In addition, other treatment conditions (amount of dichromate, cathode current density, treatment time, etc.) may employ a combination different from the above depending on the desired chromate layer thickness. This electrolytic chromate treatment is an electrolytic trivalent chromate treatment in which most of the chromium component in the chromate layer is trivalent chromium.

  When the Ni plating treatment and the electrolytic chromate treatment are performed, a coating having a two-layer structure of a nickel plating layer and a chromate layer is formed on the outer surface and the inner surface of the metal shell. However, the electrolytic chromate treatment can be omitted. Moreover, you may form the plating layer by metals other than nickel instead of a nickel plating layer. Further, another protective film may be formed on the two-layer structure of a plating layer such as nickel and a chromate layer.

  In step T130, rust preventive oil is applied as a protective coating. Various commercially available rust preventive oils can be used as the rust preventive oil. In this example, a rust preventive oil containing a mineral oil as a main component and containing a Ca, Na salt or the like and a solvent such as kerosene was used. The applied rust preventive oil has water-replaceability and is dried after application to form a thin soft film.

  In addition to C as mineral oil, this rust-preventing oil contains at least one of Ca and Na, and S and Ba as additives. The rust preventive oil of this example is adjusted so that the weight ratio (C / S) of C and S is 20 ≦ C / S ≦ 125. Further, the content of Ba is adjusted to be 0.2% by weight or less. In general, as the weight ratio of C and S (C / S) increases, the corrosion resistance of the rust-preventing oil may decrease, and as it decreases, color unevenness and discoloration may occur after application. is there. Moreover, when there is too much Ba for rust preventive oil, discoloration may occur in the appearance of the metal shell, and there is a risk that the environmental load during production and the like will increase.

The application of the rust-preventing oil can be performed, for example, by putting the entire metal shell into a basket and immersing it in the rust-preventing oil. The amount of rust-preventive oil applied is determined by the number of revolutions of the centrifugal dryer when the metal shell immersed in the rust-proof oil is left in the cage and drained, and then the oil is removed by the centrifugal dryer. And by adjusting the drying time. As another method, the application of the rust preventive oil and the adjustment of the amount of the rust preventive oil are not performed separately, and may be performed at once in a centrifugal dryer. In that case, it is necessary to make the hole diameter of an appropriate cage so that the rust-preventing oil is accumulated in the cage, and a mechanism that can collect the rust-preventing oil and supply it again after the oil has been cut is necessary. In either method, the rust preventive oil applied to the metal shell may be dried by applying heat. In this embodiment, the coating amount of rust preventive oil, 0.02 mg / cm ² or more per unit area of the metal shell, preferably, is adjusted to be 0.05 mg / cm ² or more. In addition, the preferable application | coating conditions of rust prevention oil are mentioned later with an experimental result.

  After various protective coatings are formed in this way, the metal shell is fixed to an insulator or the like by a caulking process to manufacture a spark plug. As the caulking step, heat caulking can be used in addition to cold caulking.

(1) 1st Example (Ni strike + Ni plating + rust prevention oil):
In the first embodiment, step T100 (Ni strike plating process), step T110 (electrolytic Ni plating process) and step T130 (rust preventive oil application) in FIG. 3 are executed, and step T120 (electrolytic chromate process) is omitted. Thus, a plurality of metal shell samples having different component ratios of C and S contained in the rust preventive oil and pinhole amounts of the nickel plating layer were manufactured. Then, an evaluation test of appearance and corrosion resistance (salt corrosion resistance and stress corrosion cracking resistance) was performed on these metal shells.

First, the metal shell 1 was manufactured by cold forging using a cold forging carbon steel wire SWCH17K defined in JIS G3539 as a material. The ground electrode 4 was welded and joined to the metal shell 1 and degreased and washed with water, and then subjected to nickel strike plating using a rotating barrel under the following processing conditions.
<Processing conditions for nickel strike plating>
・ Plating bath composition:
Nickel chloride: 250-350 g / L
35% hydrochloric acid: 90-110 ml / L
Processing temperature (bath temperature): 25 to 35 ° C
Cathode current density: 0.3 A / dm ²
・ Processing time: 15 minutes

Next, the nickel plating layer was formed by performing an electrolytic nickel plating process on the following process conditions using a rotating barrel.
<Processing conditions for electrolytic nickel plating>
・ Plating bath composition:
Nickel sulfate: 230-270 g / L
Nickel chloride: 40-60g / L
Boric acid: 30-50 g / L
Solvent: Deionized water / bath pH: 3.8-4.2
Processing temperature (bath temperature): 50-60 ° C
Cathode current density: 0.15 to 1.2 A / dm ²
・ Processing time: 15 to 120 minutes

Next, rust preventive oil was applied under the following conditions.
<Example of application conditions of rust preventive oil>
・ Rustproof oil immersion time: 10 minutes ・ Standing time after immersion: 15 minutes ・ Centrifuge drying treatment:
Processing time: 5 minutes Number of revolutions: 600 rpm
Application amount: 0.5 mg / cm ²

FIG. 4 shows the sample ratios S101 to S125 prepared by the above processing, the component ratio of C and S contained in the rust preventive oil, the pinhole amount of the nickel plating layer, the appearance and the corrosion resistance (salt corrosion resistance and stress corrosion cracking resistance). It is explanatory drawing which shows the test result of property. In FIG. 4, it is possible to read mainly the influence of the antirust oil component on the appearance and durability of the metallic shell in the metallic shell having no chromate layer. In samples S101 to S125, the weight ratio (C / S) of C and S contained in the rust preventive oil was changed between 17 and 143. Moreover, in the electrolytic nickel plating treatment, the number of pinholes in the nickel plating layer was changed between 0 and 16 by changing the cathode current density and the treatment time. The amount of rust preventive oil applied was constant at 0.5 mg / cm ² .

About the component contained in the antirust oil of sample S101-S125, the quantitative analysis was performed using the electron beam microanalyzer (EPMA: Electron Probe Micro Analyzer). As the X-ray spectrometer, a wavelength dispersive X-ray spectrometer (WDS) was used. The analysis conditions were an acceleration voltage of 15 kV, an irradiation current of 5.1 × 10 ⁻⁸ A, and a beam diameter of 50 μm. The measurement locations were six plane portions (hexagon plane portions) that engage with the tool in the hexagon portion 1e. The average value of the values measured from the four locations of the hexagonal plane portion was taken as the measurement result.

  As a result of the analysis, the rust preventive oils of samples S101, S106, S111, S116, and S121 were 10% by weight for C, 0.6% by weight for S, and 17 for C / S. In the rust preventive oils of samples S102, S107, S112, S117, and S122, C was 10% by weight, S was 0.5% by weight, and C / S was 20. In the rust preventive oils of samples S103, S108, S113, S118, and S123, C was 10% by weight, S was 0.1% by weight, and C / S was 100. In the rust preventive oils of samples S104, S109, S114, S119, and S124, C was 10% by weight, S was 0.08% by weight, and C / S was 125. In the rust preventive oils of Samples S105, S110, S115, S120, and S125, C was 10% by weight, S was 0.07% by weight, and C / S was 143.

In the electrolytic nickel plating treatment, samples S101 to S105 had a cathode current density of 0.15 A / dm ² and a treatment time of 120 minutes. Samples S106 to S110 had a cathode current density of 0.3 A / dm ² and a treatment time of 60 minutes. Samples S111 to S115 had a cathode current density of 0.45 A / dm ² and a processing time of 45 minutes. Samples S116 to S120 had a cathode current density of 0.6 A / dm ² and a processing time of 30 minutes. Samples S116 to S120 had a cathode current density of 1.2 A / dm ² and a processing time of 15 minutes.

In order to confirm the number of pinholes formed in the nickel plating layers of samples S101 to S125, a ferroxyl test based on JIS H8617 was performed. The number of pinholes was confirmed by the number of blue spots of iron complex ions that appeared on the filter paper soaked with the test solution. The confirmation place was a hexagonal plane part. The number of pinholes per unit area in the whole metal shell was estimated by calculating the number of pinholes (unit / cm ² ) per unit area in the hexagonal plane portion.

As a result of the confirmation, Samples S101 to S105 had a blue spot number of 0 (months / cm ² ). Samples S106 to S110 had a blue spot number of 7 (months / cm ² ). Samples S111 to S115 had a blue spot number of 10 (months / cm ² ). Samples S116 to S120 had a number of blue spots of 13 (months / cm ² ). Samples S121 to S125 had a blue spot number of 16 (months / cm ² ). In addition, the measuring method of the application quantity of antirust oil is demonstrated in the below-mentioned 3rd Example.

  As an appearance inspection of samples S101 to S125, the ratio of the color change occurrence area to the surface area of the metal shell after the application of the rust preventive oil was measured. In this measurement, the ratio of the color change generation area to the surface area of the metal shell of the sample was measured. When determining the value of the generated area ratio, take a photograph of the sample after the test, and measure the area Sa of the discolored portion in the photograph and the area Sb of the metal shell in the photograph. The ratio Sa / Sb was calculated as a ratio of occurrence of discoloration.

  In samples S103 to S105, S108 to S110, S113 to S115, S118 to S120, and S123 to S125, the appearance of the metal shell was good and almost no discoloration occurred. In samples S102, S107, S112, S117, and S122, the ratio of the color change occurrence area was more than 0% and 5% or less. There was no discoloration area ratio of more than 5% and 10% or less. In samples S101, S106, S111, S116, and S121, the ratio of the color change occurrence area was greater than 10%. From this, it can be seen that the weight ratio (C / S) of C and S contained in the rust preventive oil is preferably 20 or more and more preferably 100 or more in terms of the appearance of the metal shell. .

  As an evaluation test regarding the salt corrosion resistance of samples S101 to S125, a neutral salt spray test defined in JIS H8502 was performed. In this test, after the salt spray test for 48 hours, the ratio of the area where red rust was generated to the surface area of the metal shell of the sample was measured. The method for determining the value of the generated area ratio is to take a photograph of the sample after the test, measure the area Sa of the portion where red rust is generated in the photograph, and the area Sb of the metal shell in the photograph, The ratio Sa / Sb was calculated as a red rust generation area ratio.

In samples S101 to S103, S106, red rust did not occur. In samples S104, S107, S108, S111, and S112, the area ratio of red rust generation was more than 0% and 5% or less. In samples S109, S113, S114, S116, and S121, the area ratio of red rust generation was more than 5% and 10% or less. In samples S105, S110, S115, S117 to S120, and S122 to S125, the ratio of the red rust generation area exceeded 10%. From the viewpoint of salt corrosion resistance, the number of blue spots (units / cm ² ) is preferably 10 (units / cm ² ) or less, and more preferably 7 (units / cm ² ) or less. Further, it is understood that the weight ratio (C / S) of C and S contained in the rust preventive oil is preferably 125 or less, and more preferably 100 or less.

  The following accelerated corrosion test was performed as an evaluation test regarding the stress corrosion cracking resistance of samples S101 to S125. First, after four holes having a diameter of about 2 mm were formed in the groove 1h of each sample (main metal shell), an insulator or the like was fixed by caulking. The reason for making the hole is to allow the test corrosive liquid to enter the metal shell. The test conditions for the accelerated corrosion test are as follows.

<Test conditions for accelerated corrosion test (stress corrosion cracking resistance evaluation test)>
・ Corrosion composition:
Calcium nitrate tetrahydrate: 1036g
Ammonium nitrate: 36g
Potassium permanganate: 12g
Pure water: 116g
-PH: 3.5-4.5
-Processing temperature: 30-40 ° C
Here, the reason why potassium permanganate as an oxidizing agent is added to the corrosive solution is to accelerate the corrosion test.

A sample was taken out after 10 hours under these test conditions, and the groove 1h was observed from outside using a magnifying glass to examine whether or not cracks occurred in the groove 1h. If no cracking occurred, the corrosion solution was replaced and an additional 10 hour accelerated corrosion test was added under the same conditions. This test was repeated until the cumulative test time reached 80 hours. A large residual stress is generated in the groove 1h as a result of the caulking process. Therefore, it is possible to evaluate the stress corrosion cracking resistance in the groove 1h by this accelerated corrosion test. In samples S101 to S103 and S106, no crack occurred in the groove 1h even when the cumulative test time reached 80 hours. In samples S104, S107, S108, S111, and S112, cracks occurred in the groove 1h when the cumulative test time was more than 50 hours and less than 80 hours. In samples S109, S113, S114, S116, and S121, cracks occurred in the groove 1h when the cumulative test time was more than 20 hours and less than 50 hours. In samples S105, S110, S115, S117 to S120, and S122 to S125, cracks occurred in the groove portion 1h when the cumulative test time was 20 hours or less. From the viewpoint of resistance to stress corrosion cracking, the number of blue spots (units / cm ² ) is preferably 10 (units / cm ² ) or less. Further, it is understood that the weight ratio (C / S) of C and S contained in the rust preventive oil is preferably 125 or less, and more preferably 100 or less.

From the results shown in FIG. 4, the weight of C and S contained in the rust-preventing oil is considered in the metal shell in which the oil film layer is formed on the nickel plating layer in consideration of the appearance and corrosion resistance (salt corrosion resistance and stress corrosion cracking resistance). The ratio (C / S) is preferably 20 ≦ C / S ≦ 125, more preferably around 100. Further, the number of pinholes per unit area in the nickel plating layer is preferably 10 (units / cm ² ) or less, and more preferably 7 (units / cm ² ) or less. Since the result of FIG. 4 is not affected by the type of metal constituting the plating layer, the same effect can be obtained even when an oil film layer is formed on a metal plating layer other than nickel. On the other hand, since pinholes are likely to occur in the nickel plating layer, it is thought that the appearance and corrosion resistance can be easily improved by using the oil film layer of the example.

(2) Second Example (Ni strike + Ni plating + electrolytic chromate + rust preventive oil):
In the second embodiment, the metal shell is obtained by executing step T100 (Ni strike plating process), step T110 (electrolytic Ni plating process), step T120 (electrolytic chromate process) and step T130 (rust-preventing oil application) in FIG. Manufactured and evaluated for appearance and corrosion resistance (salt corrosion resistance and stress corrosion cracking resistance) of these metal shells. The processing conditions of steps T100, T110, and T130 were the same as those in the first example. In the electrolytic chromate treatment in Step T120, a chromate layer was formed on the nickel plating layer by performing the treatment under the following treatment conditions using a rotating barrel.
<Processing conditions for electrolytic chromate treatment>
・ Composition of treatment bath (chromate treatment solution):
Sodium dichromate: 40 g / L
Solvent: deionized water / treatment temperature (bath temperature): 30-40 ° C
Cathode current density: 0.2 A / dm ²
・ Processing time: 5 minutes

  FIG. 5 shows the component ratios of C and S contained in the rust preventive oil, the pinhole amount of the nickel plating layer, the appearance and the corrosion resistance (salt corrosion resistance) with respect to the samples S201 to S225 of the second embodiment created by the above processing. And stress stress cracking resistance) is an explanatory view showing the test results. In FIG. 5, in the metal shell having a chromate layer, it is possible to read the influence of the rust preventive oil component on the appearance and durability of the metal shell. In samples S201 to S225, as in the first example, the weight ratio (C / S) of C and S contained in the rust preventive oil was changed between 17 and 143. In the electrolytic nickel plating treatment, the number of pinholes in the nickel plating layer was changed between 0 and 16. About the analysis method of the component contained in the rust preventive oil of samples S201 to S225, the cathode current density and the processing time in the electrolytic nickel plating process, and the confirmation method of the number of pinholes formed in the nickel plating layer, The same as in the first embodiment. Samples S201 to S225 correspond to the samples S101 to S125 of the first embodiment in terms of C / S and pinhole amount, respectively.

  As an appearance inspection of samples S201 to S225, the ratio of the color change occurrence area to the surface area of the metal shell after the application of the rust preventive oil was measured as in the first example. In samples S203 to S205, S208 to S210, S213 to S215, S218 to S220, and S223 to S225, the appearance of the metal shell was good, and almost no discoloration occurred. In samples S202, S207, S212, S217, and S222, the ratio of the color change occurrence area was more than 0% and 5% or less. There was no discoloration area ratio of more than 5% and 10% or less. In samples S201, S206, S211, S216, and S221, the ratio of the color change occurrence area was greater than 10%. From this, it can be seen that the weight ratio (C / S) of C and S contained in the rust preventive oil is preferably 20 or more and more preferably 100 or more in terms of the appearance of the metal shell. .

As an evaluation test regarding the salt corrosion resistance of samples S201 to S225, a neutral salt spray test defined in JIS H8502 was performed as in the first example. In samples S201 to S104, S206, S207, and S211, red rust did not occur. In samples S208, S209, S212, S213, S216, and S217, the ratio of the area where red rust was generated was more than 0% and 5% or less. In samples S214, S218, S219, and S221, the area ratio of red rust generation was more than 5% and 10% or less. In samples S205, S210, S215, S220, and S222 to S225, the ratio of the area where red rust was generated exceeded 10%. From the viewpoint of salt corrosion resistance, the number of blue spots (units / cm ² ) is preferably 13 (units / cm ² ) or less, and more preferably 10 (units / cm ² ) or less. Further, it is understood that the weight ratio (C / S) of C and S contained in the rust preventive oil is preferably 125 or less, and more preferably 100 or less. In the second example, the preferable range of the number of blue spots (months / cm ² ) is slightly wider than that in the first example. The reason for this is presumed that in the second example, the chromate layer formed by the electrolytic chromate treatment contributes to the improvement of salt corrosion resistance.

As an evaluation test regarding the stress corrosion cracking resistance of samples S201 to S225, the same accelerated corrosion test as in the first example was performed. In samples S201 to S204, S206, and S207, no crack occurred in the groove 1h even when the cumulative test time reached 80 hours. In samples S208, S209, S212, S213, S216, and S217, cracks occurred in the groove 1h when the cumulative test time was more than 50 hours and less than 80 hours. In samples S214, S218, S219, and S221, cracks occurred in the groove 1h when the cumulative test time was more than 20 hours and less than 50 hours. In samples S205, S210, S215, S220, and S222 to S225, cracks occurred in the groove 1h when the cumulative test time was 20 hours or less. From the viewpoint of stress corrosion cracking resistance, the number of blue spots (months / cm ² ) is preferably 13 (pieces / cm ² ) or less, and more preferably 10 (pieces / cm ² ) or less. . Further, it is understood that the weight ratio (C / S) of C and S contained in the rust preventive oil is preferably 125 or less, and more preferably 100 or less. In the second example, the reason why the preferable number of blue spots (months / cm ² ) is slightly wider than that in the first example is that the chromate layer is resistant to stress as in the case of the salt corrosion resistance described above. This is presumably because it contributes to the improvement of corrosion cracking property.

From the results shown in FIG. 5, in the metal shell in which the chromate layer is formed on the nickel plating layer and the oil film layer is further formed thereon, the appearance and corrosion resistance (salt corrosion resistance and stress corrosion cracking resistance) are considered. The weight ratio (C / S) of C and S contained in the rust oil is preferably 20 ≦ C / S ≦ 125, more preferably around 100. Further, the number of pinholes per unit area in the nickel plating layer is preferably 13 (units / cm ² ) or less, and more preferably 10 (units / cm ² ) or less.

(3) Third Example (Influence of coating amount of rust preventive oil):
In the first and second embodiments described above, the coating amount of the antirust oil was maintained at a constant value of 0.5 mg / cm ² , but in the third embodiment, the coating amount of the antirust oil was changed. The case was evaluated for corrosion resistance (salt corrosion resistance and stress corrosion cracking resistance).

  FIG. 6 is an explanatory diagram showing the test results of the coating amount of the rust preventive oil and the corrosion resistance (salt corrosion resistance and stress corrosion cracking resistance) regarding the samples S301 to S312 of the third example. In FIG. 6, it is possible to read mainly the influence of the coating amount of the antirust oil on the durability of the metal shell. In the manufacturing process of samples S301 to S312, the processing conditions of step T100 (Ni strike plating process), step T110 (electrolytic Ni plating process), and step T130 (rust preventive oil application) were the same as those in the first example. The processing conditions in step T120 (electrolytic chromate treatment) were the same as in the second example. The components contained in the rust preventive oils of Samples S301 to S312 were subjected to the same quantitative analysis as in the first example. As a result, the weight ratio (C / S) of C and S was 100.

The coating amount (mg / cm ² ) of the rust-preventing oil is determined by measuring the amount of oil contained in the liquid in which the oil film layer formed on the surface of the metallic shell is dissolved by applying the rust-preventing oil. It was calculated by dividing by the surface area. Specifically, first, 150 ml of dichloropentafluoropropane as a solvent for oil extraction, an oil content measuring device that has been prepared in advance, and five identical samples with the same coating conditions for rust preventive oil are prepared. did. Here, an oil concentration meter (product number: OCMA-355) manufactured by HORIBA, Ltd. was prepared as a measuring device. Five samples were immersed in the prepared oil extraction solvent and stirred to dissolve the oil film layer. The liquid temperature at this time is room temperature, and the dissolution time is 10 minutes. After dissolution, a liquid containing the solvent and the dissolved oil was set in a measuring device, and the amount of oil was measured. The measurement was performed at room temperature. The coating amount (mg / cm ² ) of the rust preventive oil per unit surface area of the metallic shell was calculated by dividing the measured oil content by the total surface area of the five metallic shells.

For example, when the oil concentration contained in the liquid (150 ml) containing the solvent and the dissolved oil is 100 (mg / l), the amount of oil is (100 mg × 150 ml) / 1000 ml = 15 mg. When the surface area of the metal shell is 30 cm ² , the total surface area of the five samples is 5 × 30 cm ² = 150 cm ² , so the coating amount of rust preventive oil per unit surface area of the metal shell is 15 mg / 150 cm. ² = 0.1 mg / cm ² .

  The surface area of the metal shell was calculated as the surface area of the rotating body of the cross section by measuring the dimensions of each part of the metal shell and using the cross section (FIG. 2 (a)) of the CAD diagram created using that value. . At this time, the threaded portion 7 was also approximated by a rotating body having an uneven cross section of the thread. However, as the surface area of the hexagonal portion 1e, a value calculated based on the three-dimensional CAD drawing of the metal shell was used instead of the value calculated as the rotating body.

  As a preliminary preparation of the measuring device, the measuring device was calibrated using a standard solution having an oil concentration of 0 ppm and a standard solution having an oil concentration of the detection limit concentration (for example, 200 ppm) of the measuring device. A new oil extraction solvent (dichloropentafluoropropane) was used as a 0 ppm standard solution. As a 200 ppm standard solution, a solution in which the above oil extraction solvent was added to 50 mg of the OCB mixed standard substance described later to make 500 ml was used. Prior preparation was performed at room temperature. The OCB mixed standard substance is obtained by collecting 15 ml of 2,2,4-trimethylpentane (isooctane), 15 ml of hexadecane (cetane), and 10 ml of benzene with a whole pipette, putting them in an Erlenmeyer flask, quickly plugging them and mixing well. It was prepared (specific gravity 0.769 / 20 ° C.). All chemicals used were reagent special grades or special grade equivalents.

With respect to the samples S301 to S312, evaluation tests for salt corrosion resistance and stress corrosion cracking resistance were performed. As an evaluation test regarding the salt corrosion resistance of samples S301 to S312, a neutral salt spray test defined in JIS H8502 was performed in the same manner as in the first example. In samples S306 to S312, red rust did not occur. In sample S305, the area ratio of red rust generation was more than 0% and 5% or less. In samples S303 and S304, the red rust generation area ratio was more than 5% and 10% or less. In samples S301 and S302, the ratio of the area where red rust was generated exceeded 10%. From the viewpoint of salt corrosion resistance, the coating amount of rust preventive oil is preferably at 0.02 mg / cm ² or more, more preferably 0.04 mg / cm ² or more, with 0.05 mg / cm ² or more It can be seen that it is most preferable.

As an evaluation test regarding the stress corrosion cracking resistance of samples S301 to S312, an accelerated corrosion test similar to that of the first example was performed. In samples S306 to S312, no crack occurred in the groove 1h even when the cumulative test time reached 80 hours. In sample S305, cracks occurred in the groove 1h when the cumulative test time was more than 50 hours and less than 80 hours. In samples S303 and S304, cracks occurred in the groove 1h when the cumulative test time was more than 20 hours and less than 50 hours. In samples S301 and S302, cracks occurred in the groove 1h when the cumulative test time was 20 hours or less. From the viewpoint of stress corrosion cracking resistance, the coating amount of the rust preventive oil is preferably 0.02 mg / cm ² or more, more preferably 0.04 mg / cm ² or more, and 0.05 mg / cm. It turns out that it is the most preferable that it is ² or more.

From the results shown in FIG. 6, in view of salt corrosion resistance and stress corrosion cracking resistance of the metal shell, the amount of the oil film layer formed on the metal shell is preferably 0.02 mg / cm ² or more, and 0.04 mg. / Cm ² or more is more preferable, and 0.05 mg / cm ² or more is most preferable.

(4) Fourth Example (Influence on Appearance by Containing Ba Content):
In the fourth example, an external appearance evaluation test was performed when the concentration of Ba contained in the rust preventive oil was changed.

  FIG. 7 is an explanatory diagram showing the Ba concentration (% by weight) of the rust preventive oil and the appearance test results for the samples S401 to S406 of the fourth example. In FIG. 7, the influence which the density | concentration of Ba contained in antirust oil mainly has on the external appearance of a metal fitting can be read. In the manufacturing process of samples S401 to S406, the processing conditions of step T100 (Ni strike plating process), step T110 (electrolytic Ni plating process), and step T130 (rust preventive oil application) were the same as those in the first example. Step T120 (electrolytic chromate treatment) was omitted. About the component contained in the antirust oil of sample S401-S406, when the same quantitative analysis as 1st Example was performed, all the weight ratios (C / S) of C and S were 100.

  As an appearance inspection of samples S401 to S406, the ratio of the color change occurrence area to the surface area of the metal shell after the application of rust preventive oil was measured in the same manner as in the first example. In samples S401 to S403, the appearance was good over the entire metal shell, and almost no discoloration occurred. In sample S404, the ratio of the color change occurrence area was more than 0% and 5% or less. In sample S405, the color change occurrence area ratio was more than 5% and 10% or less. In sample S406, the color change occurrence area ratio was larger than 10%. Therefore, in terms of the appearance of the metallic shell, the Ba concentration of the rust preventive oil is preferably 0.2% by weight or less, more preferably 0.15% by weight or less, and 0.1% by weight. It can be seen that the following is most preferable. Moreover, it can be said that it is preferable to reduce the Ba density | concentration contained in antirust oil also from a viewpoint of reducing environmental impact.

DESCRIPTION OF SYMBOLS 1 ... Metal shell 1c ... Engagement part 1d ... Clamping part 1e ... Hexagon part 1f ... Gas seal part (flange part)
1h ... Groove (thin wall)
DESCRIPTION OF SYMBOLS 1p ... Insertion opening part 2 ... Insulator 2e ... Protrusion part 2h ... Engagement part 2n ... End surface 3 ... Center electrode 4 ... Ground electrode 6 ... Through-hole 7 ... Screw part 13 ... Terminal metal fitting 15 ... Resistor 16, 17 ... Conductivity Glass sealing layer 30 ... gasket 60 ... wire packing 61 ... filling layer 62 ... wire packing 63 ... plate packing 100 ... spark plug 111 ... mold 200 ... scheduled part

Claims (7)

A central electrode extending in the axial direction;
A cylindrical insulator provided on the outer periphery of the center electrode;
A spark plug provided on the outer periphery of the insulator and having a cylindrical metal shell covered with an oil film layer,
The oil film layer contains at least one of Ca element and Na element, C element and S element, the weight ratio of C element and S element is 20 ≦ C / S ≦ 125, and the unit surface area of the metal shell The spark plug is characterized by having an adhesion amount of 0.02 mg / cm ² or more. The spark plug according to claim 1, wherein
The metal shell is covered with a nickel plating layer, and the oil film layer is formed on the nickel plating layer. The spark plug according to claim 2,
The metal shell has a polygonal shape in the cross-sectional shape perpendicular to the axis, and includes a tool engaging portion having a plurality of flat portions for engaging with the tool,
The nickel plating layer is a spark plug in which the number of pinholes is 10 locations / cm ² or less per unit surface area in the planar portion. The spark plug according to claim 1, wherein
The spark plug, wherein the metallic shell is covered with a nickel plating layer, a chromate layer is formed on the nickel plating layer, and the oil film layer is formed on the chromate layer. The spark plug according to claim 4, wherein
The metal shell has a polygonal shape in the cross-sectional shape perpendicular to the axis, and includes a tool engaging portion having a plurality of flat portions for engaging with the tool,
The nickel plating layer is a spark plug in which the number of pinholes in the planar portion is 13 places / cm ² or less per unit surface area. The spark plug according to any one of claims 1 to 5,
The oil film layer is a spark plug in which an adhesion amount per unit surface area of the metal shell is 0.05 mg / cm ² or more. The spark plug according to any one of claims 1 to 6,
The oil film layer is a spark plug having a Ba element content of 0.2 wt% or less.

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