JPH0465158B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to surface treatment of a metal shell of a spark plug for an internal combustion engine used under conditions of high temperature and high pressure. (Prior art) Conventionally, the metal shell with a threaded part for installing spark plugs for internal combustion engines used at high temperatures and high pressures requires heat resistance and corrosion resistance, so the surface of the metal shell is finished with zinc plating or chromate. , those that have been treated with nickel plating are now in practical use. (Problems to be Solved by the Invention) However, in the above-mentioned conventional products, when the steel material is galvanized, since the standard electrode potential of the galvanized material is lower than that of the steel material, it acts as an anode, and therefore the galvanized material serves as a sacrificial anode and is selectively corroded and oxidized, but since the galvanized layer and the steel maintain electrical contact, corrosion of the steel does not progress and exhibits good corrosion resistance. However, in the surface treatment of the main metal fittings of spark plugs, which are exposed to solutions under high temperature conditions where the pH is acidic due to the reaction between components emitted as combustion components and water, zinc plating is not treated with any kind of chromate treatment on its surface. Even if zinc is applied, red rust will soon occur as the zinc itself reacts with the acid. In addition, to meet the demands for higher performance and more compact engines, smaller plugs are required, and the thread diameter has to be made smaller for this purpose.However, since Metsuki's own zinc is flexible, solid lubricants Even at low torque, considerable stress is applied to the material of the main metal fittings, making them prone to breakage.Furthermore, regarding heat resistance, the zinc plating will discolor at 300 to 400 degrees Celsius. There are some methods that cannot be applied to a so-called heat crimping structure in which the thin-walled part of the metal fittings is heated and crimped. On the other hand, in the case of nickel plating, if the surface is completely covered, it will exhibit excellent corrosion resistance due to the properties of nickel itself, but in the case of spark plugs, the thickness of the plating cannot be made thinner because the threaded portions are screwed together. In addition, pinholes and cracks are likely to occur, making it easy for corrosive liquids to enter through these.For this reason, nickel, which has a higher standard electrode potential than steel, acts as a cathode.
Red rust progresses quickly. As a result, in order to prevent pinholes, etc., it is considered that double or triple nickel plating or chrome plating is applied, but in the former case, considering the fitability of the threaded part, it is necessary to make it thicker. Not only is it impossible to do so, but it also increases costs, and in the latter case,
The chrome plating layer cannot follow the deformation of the material during the caulking process, resulting in peeling of the chrome plating layer, but it has superior corrosion resistance to acid solutions and heat resistance compared to zinc plating, and is resistant to breakage due to screwing. Sufficient strength can also be ensured. Therefore, this invention aims to improve the drawbacks of the above-mentioned conventional ones,
It has excellent heat resistance and corrosion resistance, and can be applied to threaded parts at a low cost without impairing the strength of the material such as breakage. (Means for solving the problem) To this end, in spark plugs for internal combustion engines, the surface of the metal shell is nickel-plated and activated, and then a colored electrolytic chromate film of 3 μm or less is applied on the nickel-plated layer. It is made by coating. (Function) With the above configuration, the breaking strength of nickel plating is the same as that of one without plating treatment, due to the nickel plating layer coated and laminated on the base of the metal shell and the colored electrolytic chromate film. , prevents damage at threaded parts, etc., and maintains properties under high temperature and high pressure due to its excellent corrosion resistance and heat resistance. Furthermore, by activating the nickel plating film, it is possible to effectively form a colored electrolytic chromate film with a thickness of 3 μm or less at a low current density.Moreover, it adheres to the nickel plating layer and covers it, making it possible to prevent pinholes from occurring in the nickel plating layer. , cracks, etc. can be completely hidden, and corrosion resistance can be further improved. (Example) This invention will be further explained with reference to an example shown in the drawings. 1 is a spark plug equipped with an embodiment of the present invention, and this spark plug 1 includes a terminal portion 2;
An insulator 3, a metal shell 4, a threaded portion 5 necessary for screwing and fixing to an engine head of an internal combustion engine, etc.
Furthermore, a center electrode 6 and side electrodes 7 are provided at the tip. As shown in FIG. 2, this metal shell 4 is provided with a nickel plating film 9 electrolytically or electrolessly on the surface of a formed steel portion 8 that is the base of the metal shell 4, and further, the nickel plating film 9 is degreased. After cleaning and removing contaminants such as surface rust and oxides by rinsing with water and activating with an acidic solution with a pH of approximately 1, such as hydrochloric acid solution, for example, for zinc plating colored chromate treatment or chromium-based black plating. The surface of the nickel plating film 9 is coated with an electrolytic chromate film 10 (usually XCr ₂ O ₂ / YCrO ₃ /
(expressed in the form of ZH ₂ O). At this time, the thickness of the electrolytic chromate film 10 is 3 μm for the nickel plating of approximately 5 μm.
The thickness may be less than m, preferably less than 2 μm; if the thickness is greater than this, interference occurs when the threaded portion 5 is screwed together, and peeling is likely to occur. In addition, chromate film 10
is thicker than the above 3μm, the insulator 3 inside the metal shell 4
is inserted, the upper end 12 of the metal shell 4 is crimped inward to buckle the thin wall portion 13, and when the insulator 3 is fixed, the chromate coating 10 on the upper end 12 and the thin wall 13 is peeled off. This will impair quality and make rust more likely. Furthermore, the nickel metal layer 9
The surface treatment is completed by washing and drying the surface coated with the electrolytic chromate layer 10. In a test to determine corrosion resistance by immersing the metal shell of the spark plug of the present invention, which has undergone surface treatment, in an electrolyte solution (20% salt water), as shown in Table 1, it was found that
Corrosion tests that take 100 to 150 hours and report at high temperatures and in a strongly acidic atmosphere require more than 48 hours as shown in Table 2.
It will rust over time. ) No red rust occurred even after a certain period of time. In addition, even when measuring the breaking strength of the screw neck, the
As shown in the table, while the conventional plated product had a value of 100 to 120 based on zinc plating, the value of this invention was about 150, which is almost the same as that without plating (about 160). It became the same thing. Furthermore, as shown in the fourth example, in a heat resistance test in which the temperature of the plated surface was increased, galvanized ones discolored at 300 to 400°C, while nickel plated and this invention did not discolor to some extent at 700 to 800°C. Although peeling occurred, it showed excellent heat resistance, and as shown in the same table, it became clear that the product of the invention had excellent properties overall. In addition, 11
is the internal electrode part of the center electrode.

【table】

【table】

【table】

[Table] Note that the application of the present invention is not limited to the spark plug fittings of the above embodiments, but is also useful for fittings with threaded parts for mounting parts such as various sensors used in internal combustion engines. be. (Effects of the Invention) As described above, the surface of the main metal fitting of a spark plug for an internal combustion engine is nickel-plated and activated, and the nickel-plated film is effectively treated with a colored electrolytic chromate film.
The threaded part has high breaking strength, which prevents the threaded part from breaking due to tightening during screwing, and its excellent corrosion resistance and heat resistance allow it to withstand use under conditions of high temperature and high pressure, and its cost is also low. Since it can be achieved at a relatively low cost, it has the excellent effect of improving product reliability and reducing costs.The thickness of the electrolytic chromate is reduced to 3 μm or less, and the thickness of the threaded part is reduced. By preventing interference during screwing, it is possible to advantageously prevent peeling of the plating film or peeling of the film on the caulked portion of the tip of the metal shell of the spark plug.

[Brief explanation of the drawing]

FIG. 1 shows a front view of a spark plug comprising an embodiment of the invention, and FIG. 2 shows a cross-sectional view of FIG. 1. 1... Spark plug, 2... Terminal section, 3...
Insulator, 4... Metal shell, 5... Threaded part, 6...
Center electrode, 7... Side electrode, 8... Steel part, 9...
...nickel metal layer, 10...electrolytic chromate layer.

Claims (1)

[Claims] 1. A spark plug for an internal combustion engine, which is made by applying nickel plating to the surface of the metal shell, and then performing an activation treatment, and then forming a colored electrolytic chromate film of 3 μm or less on the nickel plating film.