JPH0336069Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Field of Industrial Application) This invention relates to a metal shell of a small spark plug used in an internal combustion engine, with a mounting screw diameter of 10 mm or less and a pitch of 1.0 mm or less. (Conventional technology) The main metal fittings of conventional spark plugs are made of
S10C to S20C low carbon steels for machine structures are mainly used in manufacturing, and the surfaces of these metal shells are treated with galvanized chromate finish or nickel plating to prevent rust. By the way, in recent years, the mounting space for spark plugs has become narrower in automobile engines due to higher output, lower fuel consumption, and lighter weight, and various studies are being conducted on the application of small spark plugs with a mounting screw diameter of 10 mm or less and a pitch of 1.0 mm. has been done. Conventionally, when low carbon steel of S10C to S20C is used for the main metal fittings of such plugs, there is a problem that the screw neck part breaks when the plug is tightened. It is also effective to increase the thickness of the insulator, but this will further reduce the diameter of the insulator and center electrode disposed inside, which will reduce the insulator strength and withstand voltage performance, and will also reduce the axial direction of the center electrode. Such a method cannot be adopted because the abrasion resistance and heat resistance deteriorate due to a decrease in thermal conductivity. Therefore, in order to improve the breaking strength of the screw neck of the metal shell, S30C and S35C with high carbonization content should be used, or the weight ratio should be 0.03 to 0.20% C, 0.25% or less Si, and 0.1 to 2.0% Mn. , P0.025% or less, S0.025% or less, A10.005~0.08%, and Zr0.005~0.25
%, Nb0.005~0.10%V0.03~0.25%, Ti0.005~
Japanese Patent Application No. 61-294409 proposes the use of a non-thermal alloy steel consisting of balance iron containing at least one of 0.25% Cr, 0.05-1.0% Cr, and 0.05-0.5% Ni. (Problem to be solved by the invention) However, in cases where the main metal fittings of small spark plugs are galvanized using materials such as carbon steel with a high carbon content and non-thermal alloy steel, the zinc itself is Because it is flexible, it acts as a solid lubricant, and at low torque, high stress is applied to the screw neck, which tends to cause breakage. Also, nickel plating + chrome plating, or chrome plating, has a high surface hardness and is smooth and has an excellent lubricating effect on the plating surface, but the breaking strength similarly decreases.
Furthermore, nickel plating has a low lubricating effect, reduces the drop in breaking strength, and exhibits excellent corrosion resistance, but since spark plugs are screwed together, the thickness of the plating cannot be made thinner. Because it does not move, pinholes, cracks, etc. are likely to occur.
Tests using saltwater corrosive liquids have the disadvantage that red rust progresses quickly. Therefore, this invention aims to solve the above problems and provide a main metal fitting for a small spark plug that has a good screw neck breaking torque close to that of the material and has a rust-proof surface with excellent corrosion resistance. . (Means for solving the problem) The feature of this invention is that the insulator that holds the center electrode in the shaft hole is fixed in the inner cavity of the metal shell, and the diameter of the mounting screw of the metal shell is 10 mm or less, and the pitch is 1.0 mm. mm
In a small ignition plug consisting of the following, the metal shell has a nickel plating layer on its surface and an electrolytic chromate treatment layer thereon, and the color tone is colored chromate. (Function) As in the above structure, the nickel plating layer and colored electrolytic chromate coating coated and laminated on the main metal fitting of the small spark plug provide the screw with the original breaking strength of the nickel plating and chromate coating. This prevents the neck from breaking, and the colored chromate treatment covers pinholes caused by nickel plating, resulting in excellent corrosion resistance. Furthermore, by combining carbon steel with a high carbon content and non-thermal alloy steel as materials for the metal shell,
It has a high breaking strength close to the strength of the raw material, making it useful as a small spark plug. (Example) This invention will be further explained with reference to an example shown in the drawings. Fig. 1 is a front view of a small spark plug showing an embodiment of this invention, and 1 is a metal shell whose mounting screw portion 1a has a diameter of 10 mm or less and a pitch of 1.0 mm or less, and its material has a tensile strength. big S30C,
It consists of S35C and a non-thermal alloy with a carbon content C of 0.03 to 0.20%. 2 is an insulator with a center electrode 3 in its shaft hole.
are heat-sealed together with the terminal electrode 4 via a known conductive glass and resistor. The insulator 2 is inserted into the inner cavity of the metal shell 1 and locked to the step seat 1b, and is fixed at the rear end 1c by a known method such as caulking. Reference numeral 5 denotes an outer electrode protruding from the metal shell, and is a spark plug having a spark gap formed between it and the end of the center electrode 3. The metal shell 1 of this invention is manufactured by cutting or plastic working into a predetermined shape using the above-mentioned materials,
After the outer surface 6 is plated with nickel to a thickness of 3 to 8 μm, the outer sheath is further subjected to colored electrolytic chromate treatment (usually XCr ₂ O ₂・YCrO ₃・
It is expressed in the form ZH ₂ O. ) has been applied. FIG. 2 shows a small ignition plug showing another embodiment of this invention, in which the main metal fitting 11 has a mounting screw portion (1
1a) is formed on the lower end side, and an unthreaded part 11a larger than the diameter of the threaded part is formed in the upper part.In particular, in this form, the mounting thread diameter is
Suitable for M8 and below. The other parts are the same as those in the embodiment shown in FIG. 1, so their explanation will be omitted. Next, in the embodiment shown in Fig. 1 of this invention, M8mm,
Using non-tempered steel for the metal shell with a pitch of 1.0 mm, the fracture torque (Kgm) of the screw neck (portion A) was compared for various plated products shown in Table 1. As a result, the material of this invention with nickel plating and colored electrolytic chromate treatment has the same breaking strength as the material without plating, and moreover, the material of this invention has no nickel plating in a 20% salt spray test. Red rust occurs in 12-48hr, 100-150hr
No abnormalities were observed, and as a combustion product, it was heated at 90°C in an oxidizing atmosphere of PH2 with nitrate roots like drain water.
In the 48-hour test, the nickel-plated product achieved 30~
Although red rust occurred for 40 hours, no abnormality was observed after 48 hours.

【table】

[Table] (Effects of the invention) This invention with the above structure provides a nickel plating layer on the surface of the metal shell of a small spark plug with a pitch of 1.0mm or less and a colored electrolytic chromate layer on the surface. This has the effect of providing excellent corrosion resistance without causing a decrease in the breaking strength of the screw neck.

[Brief explanation of the drawing]

FIGS. 1 and 2 are partially sectional front views of small-sized spark plugs that are embodiments of this invention, respectively. DESCRIPTION OF SYMBOLS 1, 11... Metal shell, 1a, 11a... Mounting screw part, 2... Insulator, 3... Center electrode, 6...
The outer surface is coated with colored electrolytic chromate on a nickel-plated jacket.

Claims (1)

[Scope of utility model registration request] An insulator that holds the center electrode in the shaft hole is fixed in the inner cavity of the metal shell, and the metal shell has a mounting screw diameter of 10 mm or less and a pitch of 1.0 mm or less, and the surface of the metal shell is coated with a nickel plating layer. and an electrolytic chromate treatment layer provided thereon, the small spark plug having a color tone of colored chromate.