JPH0370595B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a positioning pin for projection welding used for welding nuts etc. to steel plates, and in particular, the pin surface is formed by chemical densification. This is a proposal for a method of forming a reinforced composite ceramic coating.

(Prior Art) Japanese Patent Laid-Open No. 61-27185 discloses a positioning pin for projection welding coated with a plasma sprayed layer.

The positioning pin for projection welding is the second
As shown in FIG. 3 and FIG. 3, it is used to position the steel plate 1 and the nut 2, for example, when projection welding the nut 2 to the steel plate 1. Figure 2 shows the state before welding, in which the positioning pin 3 is constantly lifted upward by biasing means such as air pressure or a spring, and the nut 2 is held apart from the steel plate 1. are doing.
FIG. 3 shows the state in which the upper electrode 6 is lowered for welding, and the nut 2 and positioning pin 3 are pushed down against the upward force.

The material of this positioning pin is the same as that of the lower electrode 7.
Since it moves up and down while slidingly contacting the inner wall surface, it needs to be wear resistant and electrically insulating.

Conventional positioning pins are made by insulating the base material of the steel pin by covering it with Bakelite, etc., or by oxidizing the surface of the pin made of a special metal material (KCF material) to form a metal oxide film. By forming a ceramic film by the plasma spraying method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 61-27185, improvements in electrical insulation properties and wear resistance have been achieved.

(Problems to be Solved by the Invention) The above-mentioned positioning pins have problems such as insufficient wear resistance and the nut groove becoming rough due to the passage of minute currents. There were problems in that pores were inevitable, adhesion was insufficient, and peeling occurred due to repeated thermal shocks. Therefore, there is a need for a positioning pin that has sufficient wear resistance and insulation properties, does not cause peeling of the coating due to thermal shock, is non-porous, has excellent adhesion, wear resistance, is sufficiently strong, and has excellent electrical insulation properties. was.

(Means for Solving the Problems) The present invention aims to eliminate and improve the above-mentioned problems that pins manufactured under the conventional technology have. This problem was solved by forming a reinforced composite ceramic film on the surface using a chemical densification method.

That is, in the present invention, on the surface of the pin made of steel,
Add the same weight to a 50% chromic acid aqueous solution.
A porous ceramic layer is formed by applying a slurry obtained by mixing powders consisting of SiO ₂ : 50 to 95% by weight, Al ₂ O ₃ : 5 to 50% by weight, and unavoidable impurities, and then firing. Next, the process of applying a CrO ₃ aqueous solution to the surface of this porous ceramic layer and then firing it is repeated at least twice to impregnate Cr ₂ O ₃ into the porous ceramic layer, thereby chemically infiltrating the porous ceramic layer. The present invention relates to a method for forming a ceramic film on a positioning pin for projection welding, which comprises forming a composite ceramic film having a thickness of 30 to 200 μm and having a highly densified layer.

(Function) The method of the present invention is to first apply a 50% chromic acid aqueous solution to the surface of a pin base material made of steel that has been previously degreased, derusted, and, if necessary, subjected to pretreatment such as sandblasting. SiO ₂ at the same weight: 50-95
A ceramic slurry prepared by mixing a powder consisting of 5 to 50% by weight of Al ₂ O ₃ and unavoidable impurities was applied by dipping or spraying, and the pins coated with this slurry were then dried. After that, a porous ceramic layer is formed by further firing at 400 to 600°C, and then a CrO ₃ aqueous solution is coated on the surface of the porous ceramic layer by dipping or brush coating, and then dried. and another 400-600
This is a method of forming a composite ceramic film having a chemically densified layer by impregnating it with an oxide deposit (Cr ₂ O ₃ ) by firing at ℃. By repeating the application two or more times, a positioning pin is formed that is coated with a composite ceramic film with a layer thickness of 30 to 200 μm that is non-porous, has excellent adhesion and wear resistance, is sufficiently strong, and has excellent electrical insulation properties. This is the way to get it.

Figure 1 is a photograph of the cross-sectional structure of a composite ceramic film strengthened by chemical densification according to the present invention. 660). Figure 1a,
An intermediate layer containing iron and chromium is formed at the boundary between the composite ceramic coating and the pin base material shown in b, and this intermediate layer generates high adhesion and forms a strong oxide bond with the hard ceramic particles formed by ceramic slurry coating. This results in a pore-free, highly hard composite ceramic film.

Furthermore, the composite ceramic film formed by impregnating an oxide deposit into a porous ceramic layer by the chemical densification method according to the present invention is strengthened by chemical densification, which is not seen in ceramic films made by plasma spraying. is applied, so pores can be eliminated. Therefore, the nut groove does not become rough or the coating film becomes damaged due to the passage of a minute current.

The hardness of the composite ceramic film obtained by the formation method of the present invention is Hv1200-1500, and the hardness of the ceramic film obtained by the plasma spraying method is Hv700-1000.
It has high hardness and excellent wear resistance compared to other materials.

Furthermore, the size of the particles forming the coating formed by such chemical densification is very small, at 1 μm or less, whereas the plasma spray coating has a size of several tens of μm. This indicates that the composite ceramic coating formed by the method of the present invention is also effective in wear resistance. This is because the particles are very small, so even if some particles fall off the coating surface due to wear, the resulting holes can be ignored, but in the case of ceramic coatings made by plasma spraying, the particle size is much larger. Because of their large size, if they fall off due to wear and frictional resistance, the size of the holes will become large, causing spalling, peeling, or peeling of the film.

Next, the adhesion between the composite ceramic film formed by the method of the present invention and the pin base material is determined by applying a film thickness of 0.5 mm to one cross section of two steel bars with a diameter of 40 mm and a length of 40 mm.
The value is 800Kg/cm 2 or more by applying coating treatment, blasting the other cross section with molten alumina to make it a rough surface, joining these coated surfaces and the blasted rough surface with adhesive, and conducting a ^tensile test. Compared to the adhesion of 250 to 350 kg/cm ² between the ceramic coating and the pin base material obtained by plasma spraying, the coating has excellent adhesion and also has excellent thermal shock resistance. When the ceramic film was repeatedly subjected to a thermal cycle of dropping the material into water from 600°C, it peeled off after 20 to 30 times with the ceramic coating made by plasma spraying, but the film according to the present invention did not peel off even after 100 times.

Further, the electrical conductivity of the composite ceramic film formed by the method of the present invention is 10 ^-6 to 10 ^-7 Ω ^-1 cm, and has sufficient insulation properties to be used as a positioning pin.

In the forming method of the present invention, when first forming a porous ceramic layer, _SiO2 : 50 to 95% by weight,
Al ₂ O ₃ : 5 to 50% by weight is mixed with a 50% chromic acid aqueous solution to make a slurry, because the expansion coefficient of the pin base material and the ceramic film (S45C: 13.6×10 ^-6 /℃,
Al ₂ O ₃ : 5.4×10 ^-6 /℃, Cr ₂ O ₃ : 8.8×10 ^-6 /℃,
SiO ₂ : 10.3×10 ^-6 /°C), if SiO ₂ is less than 50% by weight, the expansion coefficient of the ceramic film will be small and it will be easy to peel off with repeated heating, and if Al ₂ O ₃ is less than 5% by weight, it will be easily peeled off. When applied to a base material, 5% by weight is required because it is difficult to coat. Therefore, _SiO2 is
It must be within the range of 50-95% by weight. _{Al2O3 _}
If it is over 50% by weight, the expansion coefficient of Al ₂ O ₃ is small and it becomes easy to peel off with repeated heating.
Al ₂ O ₃ should be in the range of 5 to 50% by weight.

In addition, the thickness of the composite ceramic film layer strengthened by the chemical densification method formed in the present invention is
The reason why the thickness is 30 to 200 μm is that if the thickness is less than 30 μm, the electrical insulation properties will be lowered and the life span will be shortened due to wear. Also, the maximum limit of 200μm is 200μm.
In the chemical densification treatment, CrO ₃
This is because it becomes difficult to diffuse when an aqueous solution is impregnated and fired. Therefore, the composite ceramic coating thickness is 30
It is necessary to keep it within the range of ~200 μm.

Next, examples of the forming method of the present invention will be described.

(Example) FIGS. 2 and 3 show an example of a projection welding method showing the relationship between the positioning pin 3, the upper electrode 6, and the lower electrode 7 when projecting the nut 2 to the steel plate 1. FIG.

FIG. 2 shows the positioning pin 3 with the nut 2 attached before welding. The nut 2 is biased to be pushed upward, and the nut 2 is held at a position apart from the steel plate 1, and is electrically insulated from the steel plate 1.

FIG. 3 shows that when the upper electrode 6 is lowered, the nut 2
The positioning pin 3 is shown in a state in which it slides against the inner wall surface of the lower electrode 7 and is pushed downward against the above-mentioned upward bias, and the nut 2 is pressed against the steel plate 1 and welded.

The positioning pin 3 used in such projection welding means is made of S45C and has a cylindrical shape with a collar 10 at one end and a conical part 11 at the other end, as shown in FIG. A positioning pin base material 8 is made, and the base material 8 is subjected to degreasing and grit blasting as a pretreatment, and then 50%
of chromic acid in an aqueous solution of chromic acid at a weight ratio of 1:
The SiO ₂ and Al ₂ O ₃ powders in Step 1 were mixed and kneaded for 18 hours using a magnetic ball mill to prepare a slurry, and as a coating process, the pretreated positioning pin was immersed in the slurry to form a powder with a thickness of 30 to 80 μm. After coating the film to a thickness of
After increasing the temperature at ℃/hour and holding at 550℃ for 1 hour,
The temperature was lowered and cooled at a rate of 100° C./hour to form a porous ceramic layer with a porosity of 10 to 25%.

Next, as a chemical densification process, the positioning pin with the porous ceramic layer formed thereon is
CrO ₃ aqueous solution and heated at 600℃/hour.
After holding at 550° C. for 1 hour, the temperature was lowered and cooled at a rate of 100° C./hour to convert CrO ₃ to Cr ₂ O ₃ to obtain a chemically densified composite ceramic film layer 9. After repeating this chemical densification treatment 8 to 15 times, the coating surface was finished with a nylon buff to obtain the desired positioning pin.

As a result of using a positioning pin with a film formed from conventional KCF material for the projection welding described above,
Due to the specifications of approximately 48,000 cycles, galling occurred on the surface and it had to be replaced.

On the other hand, it was confirmed that the positioning pin having the composite ceramic film formed by the method of the present invention showed almost no damage even after being used about 400,000 times, and had an excellent wear resistance of about 9 times or more. Furthermore, even if some particles have fallen off the surface of the film due to abrasion, etc., the holes are so minute that they can be ignored and are not large enough to cause spalling or peeling. The electrical conductivity of the film is 10 ^-6 ~ 10 ^-7 Ω ^-1 cm, which sufficiently prevents electrical shunt during projection welding, ensuring the quality of the locating pin for a long time without damaging the product. It was confirmed that it has excellent durability.

(Effects of the Invention) As explained above, according to the forming method of the present invention, the obtained positioning pin has higher wear resistance than the conventional plasma spraying method or the one in which a metal oxide film is formed using KCF material. It can prevent damage caused by insufficient properties and insulation, and has superior durability compared to conventional positioning pins, and the electrical conductivity of the film is 10 ^-6 to ^{10 -7} Ω ^{- 1} cm, it sufficiently prevents electrical shunt during projection welding, and can supply welded products with stable quality for a long period of time without damaging the product.Therefore, it greatly improves productivity. Contribute.

Although the embodiment has been described in which a nut is projection welded to a steel plate, it is also possible to apply the present invention to other positioning pins for projection welding.

[Brief explanation of drawings]

Figure 1 is a photograph of the cross-sectional structure of a composite ceramic film strengthened by the chemical densification method according to the present invention, where a is
SEM secondary electron image (×660), b is an optical micrograph (×660), and Figures 2 and 3 are partial fractures showing the relationship between the locating pin and electrode during projection welding of a nut to a steel plate. FIG. 4 is a partially cutaway front view showing an example of a positioning pin. 1... Steel plate, 2... Nut, 3... Locating pin, 4... Air supply port, 5... Camber, 6...
...Top electrode, 7...Bottom electrode, 8...Pin base material,
9... Composite ceramic film layer, 10... Tsuba, 11
...Conical part.

Claims (1)

[Claims] 1. On the surface of a pin made of steel material, SiO ₂ :50 to 95% by weight is added to the same weight of 50% chromic acid aqueous solution.
Applying a slurry obtained by mixing powder consisting of Al ₂ O ₃ :5 to 50% by weight and inevitable impurities,
A porous ceramic layer is then formed by firing, and then, on the surface of this porous ceramic layer,
By repeating the process of applying a CrO ₃ aqueous solution and then firing it at least twice, the porous ceramic layer is impregnated with Cr ₂ O ₃ , thereby creating a chemically densified layer. A method for forming a ceramic film on a positioning pin for projection welding, the method comprising forming a composite ceramic film with a thickness of 30 to 200 μm.