JP5852413B2 - Manufacturing method of spark plug - Google Patents

Description

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

  A spark plug used for ignition of an internal combustion engine such as a gasoline engine includes an axial center electrode, a cylindrical insulator that holds the center electrode inside, and a metal shell that holds the insulator inside. Have. The metal shell is provided with a substantially L-shaped ground electrode so as to form a spark discharge gap with the center electrode. The metal shell and the ground electrode are generally made of an iron-based material such as carbon steel, and the surface thereof is subjected to a plating treatment for corrosion protection (Patent Document 1 below). However, even when a plating layer is formed on the outer surface of the metal shell or the ground electrode, it is known that the plating layer may be peeled off at a location that is deformed in a caulking process or the like. Yes. Until now, the actual situation is that no sufficient contrivance has been made to suppress the peeling of the plating layer in the metal shell.

JP 2006-222098 A

  An object of this invention is to provide the spark plug which suppressed peeling of the plating layer in a main metal fitting, and was excellent in corrosion resistance.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
An insulator having a shaft hole, a center electrode held by the shaft hole with its own tip protruding from the tip surface of the insulator, and holding the insulator with the tip of the insulator protruding A spark plug comprising: a metal shell, and a ground electrode having one end fixed to the metal shell and the other end forming a spark discharge gap with the tip of the center electrode,
The method of manufacturing a spark plug, wherein the metal shell is a metal shell obtained by the following process.
(A) Step of preparing a base material of the metal shell (b) In the first alkaline solution bath, the base material is used as electrolytic cleaning in which the base material and the electrode are immersed in an alkaline solution in a state of being separated from each other and energized. In the second alkaline solution bath, the cathode and the anode are periodically switched at a cycle shorter than the energization time of the anode electrolytic cleaning in the second alkaline solution tank. (C) A step of forming a nickel plating layer on the outer surface of the electrolytically cleaned substrate.
According to this manufacturing method, the anodic electrolytic cleaning is performed as the first electrolytic cleaning, and then the PR electrolytic cleaning is performed as the second electrolytic cleaning. The cleaning effect on can be improved. Therefore, it is possible to manufacture a metal shell in which adhesion between the base and the plating layer is improved and peeling of the plating layer is suppressed. By using the metal shell, a spark plug excellent in corrosion resistance can be obtained. .

[Application Example 2]
A manufacturing method according to Application Example 1,
In the step (b), the alkaline solution has a pH of 8 or more and 15 or less.
According to this manufacturing method, a higher cleaning effect can be obtained in the electrolytic cleaning process. Therefore, peeling of the plating layer in the metal shell can be suppressed.

[Application Example 3]
A manufacturing method according to application example 1 or 2,
In the step (b), the second alkaline solution tank contains cyanide ions.
According to this manufacturing method, since the impure metal deposited on the surface of the base material in the electrolytic cleaning step is removed by the cyanide ions in the solution tank, the cleaning effect in the electrolytic cleaning process is improved.

[Application Example 4]
The production method according to any one of Application Examples 1 to 3,
The step (b) includes a step of washing the substrate with an acidic solution after the PR electrolytic washing.
According to this manufacturing method, impurities attached to the substrate can be removed by the acidic solution in anodic electrolytic cleaning and PR electrolytic cleaning. Therefore, the adhesion between the substrate and the plating layer can be further improved.

[Application Example 5]
The manufacturing method according to Application Example 4,
The acidic solution has a concentration of 4% to 15%.
According to this manufacturing method, impurities attached to the substrate surface can be effectively removed while suppressing deterioration of the state of the substrate surface.

  The present invention can be realized in various forms. For example, it can be realized in the form of a metal shell or a spark plug manufactured by the manufacturing method of the metal shell or the spark plug, or the like. it can.

The principal part sectional drawing which shows an example of the structure of a spark plug. Explanatory drawing which shows an example of the manufacturing process of a metal shell in order of a process. Explanatory drawing which shows the procedure of the metal-plating process. Schematic which shows the structure of an electrolytic treatment apparatus. Explanatory drawing which shows each characteristic of a cathodic electrolytic degreasing process and an anodic electrolytic degreasing process. Explanatory drawing which shows the evaluation result about the adhesiveness of the plating layer for every sample group. The schematic diagram for demonstrating the evaluation site | part about the adhesiveness of a plating layer. Explanatory drawing which shows the experimental result of the experiment for investigating the suitable conditions of pH of the alkaline solution used for an electrolytic degreasing process. Explanatory drawing which shows the experimental result of the experiment for investigating the preferable process conditions of the washing process by an acidic solution.

  FIG. 1 is a cross-sectional view of an essential part showing an example of the structure of a spark plug. 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. And a center electrode 3 provided inside. A ground electrode 4 is joined to the metal shell 1. The ground electrode 4 is disposed so that one end is coupled to the metal shell 1 and the other end faces the tip of the center electrode 3, and 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 a through-hole 6 for fitting the center electrode 3 and the terminal fitting 13 along the axial direction of the insulator 2 is formed therein. Has been. The center electrode 3 is inserted and fixed on the front end side (the lower side of the drawing) of the through hole 6, and the terminal fitting 13 is inserted and fixed on the rear end side of the through hole 6 (the upper side of the drawing in FIG. 1). A 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. A threaded portion 7 for attaching the spark plug 100 to a combustion chamber (not shown) of the internal combustion engine is formed on the outer peripheral surface of the metal shell 1 on the front end side (the lower side in FIG. 1). The threaded portion 7 has a thread groove that is screwed into a threaded hole for attaching a spark plug provided in the combustion chamber. A hexagonal portion 1e is provided on the rear end side (upper side of the drawing) of the screw portion 7. 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 combustion chamber, and has a hexagonal cross-sectional shape.

  Between the inner wall surface of the opening on the rear end side of the metal shell 1 and the outer wall surface of the insulator 2, a packed layer 61 filled with powder such as talc is formed. The filling layer 61 is formed between the flange-shaped protrusion 2e of the insulator 2 and a crimped portion 1d in which the opening end of the metal shell 1 is crimped inward. Ring-shaped wire packings 62 and 60 are arranged at the end portions of the filling layer 61 on the protruding portion 2e side and the crimped portion 1d side. In addition, the formation process of the filling layer 61 and the crimping part 1d is mentioned later.

  A flange-shaped gas seal portion 1 f is provided between the hexagonal portion 1 e of the metal shell 1 and the screw portion 7, and a gasket 30 is fitted on the screw portion 7 side of the gas seal portion 1 f. 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 gas seal portion 1f and the opening peripheral portion of the screw hole are provided. Between the screw hole and the threaded portion 7 to seal the gap between the screw hole and the threaded portion 7. A groove portion 1h is formed between the gas seal portion 1f and the hexagonal portion 1e. The groove 1h is formed to be the thinnest in the metal shell 1 and is slightly curved outward. Hereinafter, in this specification, the groove portion 1h is also referred to as a “thin wall portion 1h”.

  2A to 2D are explanatory views illustrating an example of the manufacturing process of the metal shell in the order of processes. In the step of FIG. 2A, a base material 1a of the metal shell 1 to which the ground electrode 4 is bonded is prepared. In the base material 1a, the caulking scheduled portion 1da to be the caulking portion 1d is formed as a wall portion extending to the rear end side, the thin portion 1h is not curved, and the ground electrode 4 is also bent. It is almost the same as the metal shell 1 described in FIG. In addition, the surface of the base material 1a has already been subjected to a plating treatment for corrosion prevention.

  Next, in the step of FIG. 2B, the insulator 2 is inserted into the through hole of the base material 1a from the insertion opening 1p on the rear end side of the base material 1a, and the insulator 2 and the base material 1a are respectively inserted. The provided engaging portions 2 h and 1 c are engaged with each other via the plate packing 63. The insulator 2 is preassembled with a center electrode 3, conductive glass seal layers 16 and 17, a resistor 15 and a terminal fitting 13.

  In the step of FIG. 2C, the line packing 62 is disposed from the insertion opening 1p of the substrate 1a, and then a filling layer 61 such as talc is formed, and the line packing 60 is further moved to the insertion opening 1p side. Deploy. Then, the caulking die 111 is used to caulk the caulking scheduled portion 1da through the wire packing 62, the filling layer 61, and the wire packing 60 with the end surface 2n of the protruding portion 2e as the caulking receiving portion. Thereby, as shown in FIG. 2D, the caulking scheduled portion 1 da is deformed to form the caulking portion 1 d, and the base material 1 a is caulked and fixed to the insulator 2. Note that the thin portion 1h is bent by the compressive stress during the caulking. After the caulking process, the ground electrode 4 is bent toward the center electrode 3 to form the bent portion R, thereby forming a spark discharge gap g and completing the spark plug 100 of FIG.

  Thus, the caulking portion 1d of the metal shell 1, the bent portion of the ground electrode 4, and the thin-walled portion 1h are deformed in the process after the surface is plated. Accordingly, residual stress is generated in the caulking portion 1d, the bent portion R of the ground electrode 4, and the thin portion 1h, and the plating layer is easily peeled off. In particular, peeling of the plating layer tends to occur at the bent portion R of the ground electrode 4. Therefore, in the present embodiment, peeling of the plating layer is suppressed by a plating process described below.

  FIG. 3 is a flowchart showing the procedure of the plating process of the metal shell in the present embodiment. This plating process is performed on the base material 1a of the metal shell 1 before the process described in FIG. In step S100, an electrolytic degreasing process (electrolytic cleaning process) is performed. In this electrolytic degreasing treatment, the oil and fat adhering to the surface of the base material 1a of the metal shell 1 made of carbon steel is washed, so that the plating layer formed on the surface of the base material 1a and the underlying metal are adhered to each other later. This is done to improve the performance.

  4 (A) to 4 (C) are schematic views each showing a configuration of an electrolytic treatment apparatus that performs different types of electrolytic degreasing treatments. Generally, three types of electrolytic degreasing treatment are known: anodic electrolytic degreasing treatment, PR electrolytic degreasing treatment, and cathodic electrolytic degreasing treatment. In the electrolytic degreasing process in the present embodiment, the anodic electrolytic degreasing process and the PR electrolytic degreasing process are executed. FIG. 4A is a schematic diagram showing a configuration of an electrolytic treatment apparatus 200 for performing anodic electrolytic degreasing treatment. The electrolytic treatment apparatus 200 includes an electrolytic bath 201, two electrodes 202a and 202b, a base material container 203, and a rectifier 204. The electrolytic bath 201 stores an alkaline solution, and two electrodes 202a and 202b and a base material container 203 are disposed in the alkaline solution.

  The base material container 203 is a container for holding a plurality of base materials 1a, and is generally called a barrel. Here, the base material 1a is the same as that described with reference to FIG. 2A except that the plating treatment is not performed. In the electrolytic degreasing process, the plurality of base materials 1 a are stacked in the base material container 203. The container wall of the base material container 203 is configured to be porous so that the alkaline solution permeates into the container. Accordingly, the plurality of base materials 1 a are immersed in the alkaline solution in the base material container 203. The base material container 203 is disposed so as to be rotatable around the central portion 203c in an alkaline solution, and is rotated at a substantially constant cycle by a drive motor (not shown) during the electrolytic degreasing process. To do. Thus, the plurality of base materials 1a stacked in the base material container 203 are stirred in the alkaline solution during the electrolytic degreasing process.

  The two electrodes 202a and 202b are conductive plate members made of iron, stainless steel (registered trademark), or carbon. The two electrodes 202a and 202b are arranged so as to sandwich the base material container 203 in an alkaline solution. Note that the two electrodes 202a and 202b are preferably arranged at substantially equal distances from the base material container 203. The rectifier 204 functions as a direct current power source, and is electrically connected to the two electrodes 202a and 202b and the central portion 203c of the base material container 203 via the direct current power line DCL. More specifically, the cathode of the rectifier 204 is connected in parallel with each of the two electrodes 202 a and 202 b, and the anode of the rectifier 204 is connected to the center portion 203 c of the base material container 203. That is, in this cathodic electrolytic degreasing treatment, electrolytic cleaning is performed by energizing the substrate 1a side as a cathode. In addition, the example of the preferable preferable process conditions of an anodic electrolytic degreasing process is as follows.

<Examples of processing conditions for anodic electrolytic degreasing>
・ Alkaline solution: Sodium hydroxide solution (NaOH solution)
Concentration around 2-6%
pH 7 or more, 15 or less ・ Processing temperature (solution temperature): 40 to 65 ° C.
Applied current density: 0.1 to 0.6 A / dm ²
・ Processing time: 5-15 minutes

  As the alkaline solution, a solution other than the above sodium hydroxide solution may be used. Further, at least one of the two electrodes 202a and 202b of the electrolytic treatment apparatus 200 may be omitted.

  FIG. 4B is a schematic diagram illustrating a configuration of an electrolytic treatment apparatus 220 that performs PR electrolytic degreasing treatment. FIG. 4B is almost the same as FIG. 4A except that two changeover switches 221a and 221b are provided on the DC power supply line DCL and a switch drive unit 223 is added. . The first changeover switch 221a is connected to the cathode of the rectifier 204, and the connection destination of the cathode of the rectifier 204 can be switched to one of the two electrodes 202a and 202b or the central portion 203c of the base material container 203. . The second changeover switch 221b is connected to the anode of the rectifier 204, and the connection destination of the anode of the rectifier 204 can be changed in the same manner as the first changeover switch 221a.

  The connection destinations of the two changeover switches 221a and 221b are switched simultaneously and in parallel by a command from the switch driving unit 223. In the electrolytic treatment apparatus 220, the electrolytic degreasing process is performed while periodically switching the polarity of the current applied to the substrate 1a by the switching operation of the two changeover switches 221a and 221b. In addition, the example of the preferable preferable process conditions of PR electrolytic degreasing process is as follows.

<Examples of processing conditions for PR electrolytic degreasing>
・ Alkaline solution: Sodium hydroxide solution (NaOH solution)
Concentration around 2-6%
pH 7 or more, 15 or less ・ Processing temperature (solution temperature): 40 to 65 ° C.
Applied current density: 0.1 to 0.6 A / dm ²
・ Processing time: 5 to 15 minutes ・ Reversal period of current polarity: Repeating the following energizing time Time to energize using the substrate side as the anode 5 to 15 seconds Time to energize using the substrate side as the cathode Use the substrate side as the anode About half of the energization time

  FIG. 4C is a schematic diagram showing a configuration of an electrolytic treatment apparatus 240 for performing a cathodic electrolytic degreasing treatment as a reference example. 4C is substantially the same as FIG. 4A except that the electrical connection between the rectifier 204, the two electrodes 202a and 202b, and the central portion 203c of the base material container 203 is different. In this electrolytic treatment apparatus 240, the cathode of the rectifier 204 is connected to the central portion 203c of the base material container 203, and the anode is connected in parallel to each of the two electrodes 202a and 202b. That is, in this cathodic electrolytic degreasing process, electrolytic cleaning is performed by energizing the base 1a side as a cathode. Here, the characteristic of three types of electrolytic degreasing processes is demonstrated below.

  FIG. 5 is an explanatory diagram summarizing the characteristics of the cathodic electrolytic degreasing treatment and the anodic electrolytic degreasing treatment. In the cathode electrolytic degreasing treatment, as described above, the substrate 1a side is used as a cathode to energize. Therefore, hydrogen is generated on the surface of the substrate 1a, and the dirt attached to the surface of the substrate 1a due to the hydrogen can be effectively removed. However, when the cathodic electrolytic degreasing process is continuously performed for a long time, hydrogen embrittlement may occur in the base material 1a to be processed due to the generated hydrogen. Therefore, the cathodic electrolytic degreasing treatment is not suitable for cleaning the substrate 1a made of a so-called high C material having a large carbon content.

  On the other hand, in the anodic electrolytic degreasing treatment, since electricity is supplied using the base 1a side as an anode, oxygen is generated on the surface of the base 1a. In the anodic electrolytic degreasing treatment, dirt adhering to the surface of the substrate 1a due to the generation of oxygen can be decomposed by electrolytic oxidation. Thus, the anodic electrolytic degreasing treatment does not cause hydrogen embrittlement unlike the cathodic electrolytic degreasing treatment, and is suitable for removing smut (fine powdery black substance) generated on the surface of the substrate 1a. In the anodic electrolytic degreasing treatment, a passive film or an oxide film may be formed on the surface of the base material 1a. Therefore, the base material 1a is pickled after the anodic electrolysis treatment. It is preferable to activate the surface.

  In the PR electrolytic degreasing treatment, as described above, the polarity on the substrate 1a side is periodically switched. That is, the PR electrolytic degreasing process can be interpreted as a cleaning process that is performed by alternately switching the cathode electrolytic degreasing process and the anodic electrolytic degreasing process in a short cycle. Therefore, in the PR electrolytic degreasing treatment, it is possible to obtain a cleaning effect while complementing the respective disadvantages of the cathode electrolytic degreasing treatment and the anodic electrolytic degreasing treatment described above. However, in the PR electrolytic degreasing treatment, since the continuous energization time with the same polarity is shorter than the normal cathodic electrolytic degreasing treatment or anodic electrolytic degreasing treatment, the cleaning efficiency may be lowered. Further, as described above, in the PR electrolytic degreasing treatment, the polarity of the current is reversed while stirring the plurality of base materials 1a in the solution tank. Therefore, in each base material 1a, what may become non-uniform | heterogenous in the electricity polarity and time for electrolysis degreasing may arise. That is, in the PR electrolytic degreasing treatment, the cleaning effect on the base material 1a may be uneven.

  Here, the electrolytic degreasing treatment is generally repeated a plurality of times because there is a high possibility that a sufficient cleaning effect cannot be obtained if the number of treatments is one. However, when the same kind of electrolytic degreasing treatment is continuously performed, the inventors of the present invention have found that the disadvantages of each electrolytic degreasing treatment may be emphasized as follows. That is, when the cathodic electrolytic degreasing process is continuously performed, hydrogen embrittlement of the base material 1a is promoted, and the possibility of impure metal ions such as iron deposits on the surface of the base material 1a increases. . Moreover, when the anodic electrolytic degreasing process is continuously performed, the surface oxidation of the base material 1a may become remarkable. When the PR electrolytic degreasing process is continuously performed, there is a possibility that the cleaning effect as compared with the number of processes cannot be obtained, and the unevenness of the cleaning effect for each substrate 1a may be promoted.

  Therefore, in the present embodiment, the anodic electrolytic degreasing treatment that does not cause the hydrogen embrittlement of the base material 1a and the PR electrolytic degreasing treatment that can complement the disadvantages of the anodic electrolytic degreasing treatment and the cathodic electrolytic degreasing treatment are combined two times. By performing the electrolytic degreasing treatment, the degreasing property of the substrate 1a is improved. Here, when the anodic electrolytic degreasing process is performed as the second electrolytic degreasing process, there is a high possibility that the effect of the oxidation of the surface of the base material 1a will be noticeable in the subsequent plating process. Therefore, in this embodiment, an anodic electrolytic degreasing process is performed as the first electrolytic degreasing process, and a PR electrolytic degreasing process is performed as the second electrolytic degreasing process.

  By the way, the electrolytic degreasing treatment can be performed a plurality of times. However, when the electrolytic degreasing treatment is performed three times or more, the number of steps increases with respect to the obtained cleaning effect, which is not preferable. In addition, when the electrolytic degreasing treatment is performed five times or more, the surface of the substrate 1a is roughened, not only the adhesion of the plating layer is lowered, but also the appearance of the substrate 1a is defective. There is a possibility that.

  Each electrolytic degreasing process is preferably performed in different electrolytic baths 201. Thereby, reduction in the effect of electrolytic degreasing treatment due to deterioration of the alkaline solution can be suppressed. Further, the alkaline solution used for the electrolytic degreasing treatment preferably contains a surfactant, and more preferably contained in the alkaline solution used for the first electrolytic degreasing treatment. This is because the wettability of the surface of the substrate 1a can be increased by the surfactant, and the cleaning effect can be further improved. As the surfactant, the following can be used.

<Example of surfactant>
Higher fatty acid sodium, sulfated oil, higher alcohol sulfate sodium, alkylbenzene sodium sulfate, higher alkyl ether sulfate sodium, α-olefin sodium sulfate, alkyl polyoxyethylene ether, alkylphenyl polyoxyethylene ether, fatty acid ethylene oxide adduct, Polypropylene glycol ethylene oxide adduct (Buluronic), etc.

Further, it is preferable to add, for example, sodium cyanide as a complexing agent to the alkaline solution used in the last (second) electrolytic degreasing treatment to contain cyanide ions (CN ⁻ ). With this cyanide ion, it is possible to suppress the deposition of impure metal ions on the surface of the substrate 1a, or to promote the removal of oxides on the surface of the substrate 1a. The alkaline solution used for the second electrolytic degreasing treatment may contain the following complexing agent instead of sodium cyanide.
<Examples of complexing agents>
Ethylenediaminetetraacetic acid (EDTA), sodium gluconate, compounds with amino groups, etc.

In step S110 (FIG. 3), the base material 1a is washed with an acidic solution. Specifically, each substrate 1a is immersed in an acidic solution for a predetermined time. By this washing step, impurities such as smut and oxide attached to the surface of the substrate 1a are removed, and the adhesion between the surface of the substrate 1a and the plating layer is improved. In addition, the example of the specific preferable process conditions of the washing process by an acidic solution is as follows.
<Examples of processing conditions for cleaning with an acidic solution>
Acidic solution: A solution containing any one of hydrochloric acid, sulfuric acid and nitric acid Concentration: 2 to 20%, more preferably 4 to 15%
・ Processing time: 1 to 3 minutes ・ Solution temperature: 20 to 40 ° C.

  In step S120, a nickel plating process is performed on the substrate 1a. Specifically, a barrel electrolytic nickel plating process using a rotating barrel may be performed, or another plating process method such as a static plating method may be performed. Here, as the treatment conditions for electrolytic nickel plating, the following commonly used treatment conditions can be used.

<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
Applied current density: 0.2 to 0.4 A / dm ²
・ Processing time: 30-90 minutes

  In addition, as a plating process, it is also possible to perform a zinc plating process, for example. However, the plating layer delamination suppressing effect by the electrolytic degreasing treatment in the present embodiment is remarkably exhibited in the nickel plating layer having high hardness. Accordingly, in this respect, it is preferable to combine the electrolytic degreasing treatment of this embodiment with a nickel plating treatment.

  In step S130, in order to prevent corrosion of the plated layer, an electrolytic chromate treatment for forming a chromate layer over the plated layer is performed. The electrolytic chromate treatment may use a rotating barrel, or may use another plating method such as a static plating method. 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
・ Processing time: 1-10 minutes

  As the dichromate, potassium dichromate can be used in addition to sodium dichromate. By the plating process in steps S120 and S130, a two-layered film of a nickel plating layer and a chromate layer is formed on the outer surface including the outer and inner surfaces of the substrate 1a. Further, another protective film may be formed on the outer surface of the substrate 1a. A spark plug is manufactured by the process described with reference to FIG. 2 using the base material 1a on which the protective film having a multilayer structure is formed. In addition, as a caulking process, in addition to cold caulking, heat caulking can also be used.

  In the following experiment, the base metal 1a of the metal shell 1 was subjected to a plurality of types of plating treatments with different electrolytic degreasing treatment contents, and the adhesion of the plating layer was evaluated. The base 1a of the metal shell 1 was manufactured by cold forging using a carbon steel wire SWCH17K for cold heading defined in JISG3539 as a material. The ground electrode 4 was made of a material containing nickel (Ni) as a main component and containing aluminum, and was welded to the tip side of the substrate 1a. The plating process was performed under the following processing conditions according to the flowchart of FIG.

<Common treatment conditions for anode electric degreasing / PR electrolytic degreasing>
・ Alkaline solution: Sodium hydroxide solution (NaOH solution)
Concentration 3% (only the last electrolytic treatment is 5%)
pH12 or more, 15 or less ・ Processing temperature (solution temperature): 55 ± 5 ℃
Applied current density: 0.3 A / dm ²
・ Treatment time: 10 minutes <treatment conditions for PR electrolytic degreasing>
-Current polarity reversal cycle: The following energization times are alternately repeated.
Energizing time when the substrate side is the anode 10 seconds
Energizing time when the substrate side is the cathode 5 seconds

  Between each electrolytic degreasing process, the base material 1a was washed with water at room temperature for about 2 minutes. And after the last electrolytic degreasing process was completed, the base material 1a was washed with water at room temperature for 1 minute. In any electrolytic degreasing treatment, the alkaline solution used for the first electrolytic degreasing treatment contained alkyl polyoxyethylene ether as a surfactant. Further, the alkaline solution used for the final electrolytic degreasing treatment contained sodium cyanide as a complexing agent.

After the electrolytic degreasing treatment, a washing treatment with an acidic solution was performed under the following treatment conditions. In addition, after this washing | cleaning process was completed, the base material 1a was washed with water at room temperature for about 30 seconds.
<Processing conditions for washing with acidic solution>
・ Acid solution: hydrochloric acid solution
Mixing water and hydrochloric acid in a ratio of 4: 1
(Specific gravity of hydrochloric acid 1.040 ± 0.005)
・ Processing time: 2 minutes ・ Solution temperature: 30 ± 5 ℃

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: 250 g / L
Nickel chloride: 50 g / L
Boric acid: 40 g / L
-Bath pH: 4.0
・ Processing temperature (bath temperature): 55 ± 5 ℃
Cathode current density: 0.3 A / dm ²
・ Processing time: 60 minutes

In addition, after the electrolytic nickel treatment, the substrate 1a was washed with water and neutralized under the following treatment conditions. And after the neutralization process, the base material 1a was washed with water again. The washing time of the base material 1a before and after the neutralization treatment was 1 minute.
<Neutralization treatment conditions>
・ Immersion solution: Sodium hydroxide ・ Solution concentration: 5%
pH12 or more, 15 or less ・ Processing temperature (bath temperature): 30 ± 5 ℃
・ Processing time: 2 minutes

Next, the chromate layer was formed on the nickel plating layer by performing electrolytic chromate 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 ・ Processing temperature (bath temperature): 35 ± 5 ℃
Cathode current density: 0.2 A / dm ²
・ Processing time: 5 minutes

  FIG. 6 is an explanatory diagram showing a table summarizing the evaluation results of the plating layers of the samples of the base material 1a created under the above processing conditions. 100 samples of the substrate 1a were prepared for each sample group in which the content of the electrolytic degreasing treatment was changed. In each sample group, the ground electrode 4 of each sample was bent as described below, and the occurrence of peeling of the plating layer at the bent portion was observed.

  FIGS. 7A and 7B are schematic views for explaining an evaluation site for the adhesion of the plating layer in each sample. In the evaluation of the adhesion of the plating layer in this example, the ground electrode 4 of each sample was bent in two stages as shown in FIGS. 7 (A) and (B). Specifically, it is as follows. That is, in the first stage, the straight rod-shaped ground electrode 4 was bent at approximately 90 ° toward the virtual central axis 1cx of the substrate 1a (FIG. 7A). In the second stage, the same portion Rt that was bent in the first stage was bent 180 ° in the direction (outside) opposite to that in the first stage (FIG. 7A). Hereinafter, the portion Rt subjected to the bending process in the first stage and the second stage is referred to as “evaluation bent part Rt”.

  The evaluation of the plating adhesion in each sample group was evaluated according to the following criteria by observing the peeling of the plating layer at the evaluation bent portion Rt of each sample. That is, for each sample group, when none of the 100 samples in which the peeling portion of the plating layer occurred in the evaluation bent portion Rt, the evaluation was “と し た”. Moreover, when the number of the sample which produced the peeling site | part of the plating layer less than 1 mm in diameter was one, evaluation was set as "(circle)". If there were one or more samples where the peeling portion of the plating layer having a diameter of 1 mm or more was generated, or two or more samples where the peeling portion of the plating layer having a diameter of less than 1 mm was generated, the evaluation was “x”. It was.

  In addition, in each table | surface of FIG. 6, the kind of electrolytic degreasing process is abbreviate | omitted and described. Specifically, the anodic electrolytic degreasing treatment is indicated as “positive”, and the PR electrolytic degreasing treatment is indicated as “PR”. In each sample group, the number of times that the same type of electrolytic degreasing treatment is continuously performed, that is, the number of times that the anodic electrolytic degreasing treatment or the PR electrolytic degreasing treatment is continuously performed, is displayed as “the number of consecutive times of the same kind of treatment” It is. Furthermore, in each sample group, the number of times of switching from the anodic electrolytic degreasing process to the PR electrolytic degreasing process or the switching from the PR electrolytic degreasing process to the anodic electrolytic degreasing process is displayed as “positive / PR switching number”. It is.

  FIG. 6A summarizes the evaluation of the sample groups SG01 and SG02 in which the anodic electrolytic degreasing process or the PR electrolytic degreasing process is performed only once. Even if it is an anodic electrolytic degreasing process or a PR electrolytic degreasing process, when it is performed only once, a sufficient degreasing effect (cleaning effect) cannot be obtained, and a favorable evaluation is obtained. I couldn't.

  FIG. 6 (B) summarizes evaluations about sample groups SG03 to SG06 created by performing the electrolytic degreasing process twice. In each of the sample groups SG04 and SG06, the same type of electrolytic degreasing treatment was continuously performed twice. In these sample groups SG04 to SG06, the disadvantages of the respective types of electrolytic degreasing treatment were not compensated, and therefore, preferable results could not be obtained.

  In sample group SG05, a PR electrolytic degreasing process was performed as the first electrolytic degreasing process, and an anodic electrolytic degreasing process was performed as the second electrolytic degreasing process to create a sample. In this sample group SG05, as described above, a favorable evaluation result could not be obtained due to the influence of the oxidation of the sample surface by the second anodic electrolytic degreasing treatment.

  In sample group SG03, an anodic electrolytic degreasing process was performed as the first electrolytic degreasing process, and a PR electrolytic degreasing process was performed as the second electrolytic degreasing process to create a sample. In this sample group SG03, the most preferable evaluation result could be obtained. From these evaluation results, it can be seen that the highest cleaning effect can be obtained by performing the anodic electrolytic degreasing process first time and the PR electrolytic degreasing process second time as the electrolytic degreasing process.

  FIG. 8 is an explanatory diagram showing the results of an experiment for investigating suitable conditions for the pH of the alkaline solution used for the electrolytic degreasing treatment. In this experiment, the electrolytic degreasing treatment, the nickel plating treatment, the electrolytic chromate treatment, and the like under the same conditions as the sample group SG03 (FIG. 6B) except that alkaline solutions having different pH values were used. And 100 samples were prepared for each pH value of the alkaline solution. In each sample, as described with reference to FIG. 7, the evaluation bent portion Rt was formed in the ground electrode 4, and the evaluation was performed based on the same criteria as described with reference to FIG. 6.

  As can be seen from the experimental results, the pH of the alkaline solution used for the electrolytic degreasing treatment is preferably 8 or more, and more preferably 11 or more. The pH of the alkaline solution is particularly preferably 12 or higher. However, when the pH of the alkaline solution is higher than 15, there is a high possibility that the surface of the substrate 1a becomes rough. Therefore, it can be said that the range of the pH value of the alkaline solution used for the electrolytic degreasing treatment is preferably 8 or more and 15 or less, more preferably 11 or more and 14 or less. Furthermore, the pH value is particularly preferably 12 or more and 14 or less.

  FIG. 9 is an explanatory view summarizing the results of an experiment for examining preferable processing conditions for the cleaning treatment with an acidic solution performed after the electrolytic degreasing processing is performed. In this experiment, electrolytic degreasing treatment, nickel plating treatment, and electrolytic chromate treatment were performed under the same conditions as the sample group SG03 (FIG. 6B) except that acidic solutions having different concentrations were used. 100 samples were prepared for each concentration of the acidic solution.

  And about the sample group for every density | concentration of a solution, the adhesiveness of plating and the airtightness between the insulators 2 (FIG. 1) were evaluated. Specifically, in each sample, as described with reference to FIG. 7, the evaluation bending portion Rt is formed on the ground electrode 4 and the evaluation bending portion Rt is observed to evaluate the adhesion between the plating layer and the base. Went. Evaluation of adhesion between the plating layer and the base was performed according to the same criteria as described in FIG.

  Moreover, each sample is crimped and attached to the insulator 2 (FIGS. 2C and 2D), and by observing the groove 1h curved by the crimping process, the airtightness between the sample and the insulator 2 is improved. Evaluation was performed. When the groove portion 1h had one or more lacerations having a width of 1 mm or more, or two or more lacerations having a width of less than 1 mm, the result was “X”. In the case where only one laceration having a width of less than 1 mm occurred in the groove portion 1h, “◯” was indicated, and in the case where no laceration occurred in the groove portion 1h, “◎” was indicated.

  As can be seen from this experimental result, the acidic solution used for the cleaning treatment with the acidic solution has a concentration of 4% or more at which evaluation of both adhesion and airtightness of the plating layer is evaluated as “◯” or more, An acidic solution of 15% or less is preferred. Further, an acidic solution having a concentration of 6% or more and 14% or less, in which the evaluation of “◎” is obtained for both the adhesion and the airtightness of the plating layer, is particularly preferable.

  As described above, by performing the electrolytic degreasing process described in the above embodiment, it is possible to manufacture a metal shell for a spark plug having higher adhesion between the base and the plating layer. Therefore, with the spark plug using this metallic shell, it is possible to suppress the peeling of the plating on the metallic shell main body and the ground electrode, and to obtain a spark plug with more excellent durability and ignitability.

DESCRIPTION OF SYMBOLS 1 ... Metal fitting 1a ... Base material 1cx ... Virtual center axis 1d ... Clamping part 1da ... Clamping part 1e ... Hexagon part 1f ... Gas seal part 1h ... Groove part (thin part)
DESCRIPTION OF SYMBOLS 1p ... Insertion opening part 2 ... Insulator 2e ... Protrusion part 2h, 1c ... 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 ... Conductive glass sealing layer 30 ... Gasket 60 ... Wire packing 61 ... Filling layer 62 ... Line packing 63 ... Plate packing 100 ... Spark plug 111 ... Mold 200, 220, 240 ... Electrolytic treatment apparatus 201 ... Electrolytic bath 202a, 202b ... Electrode 203 ... Base material container 203c ... Center part 204 ... Rectifier 221a ... First changeover switch 221b ... Second changeover switch 223 ... Switch drive part DCL ... DC power supply line R ... Bending part Rt ... Evaluation bending part g ... Spark discharge gap

Claims (5)

An insulator having a shaft hole, a center electrode held by the shaft hole with its own tip protruding from the tip surface of the insulator, and holding the insulator with the tip of the insulator protruding A spark plug comprising: a metal shell, and a ground electrode having one end fixed to the metal shell and the other end forming a spark discharge gap with the tip of the center electrode,
The method of manufacturing a spark plug, wherein the metal shell is a metal shell obtained by the following process.
(A) Step of preparing a base material of the metal shell (b) In the first alkaline solution bath, the base material is used as electrolytic cleaning in which the base material and the electrode are immersed in an alkaline solution in a state of being separated from each other and energized. In the second alkaline solution bath, the cathode and the anode are periodically switched at a cycle shorter than the energization time of the anode electrolytic cleaning in the second alkaline solution tank. (C) A step of forming a nickel plating layer on the outer surface of the electrolytically cleaned substrate. The manufacturing method according to claim 1,
In the step (b), the alkaline solution has a pH of 8 or more and 15 or less. The manufacturing method according to claim 1 or 2,
In the step (b), the second alkaline solution tank contains cyanide ions. It is a manufacturing method as described in any one of Claims 1-3,
The step (b) includes a step of washing the substrate with an acidic solution after the PR electrolytic washing. The manufacturing method according to claim 4,
The acidic solution has a concentration of 4% to 15%.

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