JPH03104897A - Surface treatment of sintered metal - Google Patents

Abstract

PURPOSE:To form a plating layer having high adhesion and superior rust preventing power on sintered metal stock by sealing the pores in the stock by treatment with steam, removing a coating film on the surface of the stock by shot blasting and carrying out plating. CONSTITUTION:When the surface of sintered metal stock is plated, the stock is subjected to treatment with steam as pretreatment. By this pretreatment, an oxidized film of Fe3O4, etc., is formed on the surface of the stock and in the pores in the stock in about 5-15mum thickness to seal the pores. The stock is then shot-blasted for about 2-10min to seal the pores in the surface of the stock as well as to remove only the film on the surface and the stock is plated. Blowoff from the pores is prevented and a plating film having high adhesion and superior rust preventing power is obtd.

Description

[Detailed Description of the Invention] Industrial Application Fields This invention relates to a method for surface treatment of sintered metal, and more specifically, to a method for treating the surface of sintered metal, and more specifically, to sintered metal parts that require severe rust prevention, such as anti-skid sensor rings. The present invention relates to an applied surface treatment method.

Conventional technology> Conventionally, when plating a member having pores such as sintered metal, the pores are impregnated with a resin in advance to seal them, and then the plating treatment is performed.

■ Plating is performed after filling the pores on the sintered metal surface with a barrel or shot blast.

(2) The sintered metal member is subjected to steam treatment, then pickled to dissolve the oxide film on the surface, pre-plated, and then subjected to main plating.

method is known.

Problems to be Solved by the Invention> The conventional plating methods described above have their own problems as described below.

That is, in the method (2), plating is performed after resin impregnation and sealing, but if resin adheres to the surface, the adhesion of the plating will deteriorate. In addition, some of the resin dissolves in the plating solution, making it difficult to manage the plating solution and increasing the cost.

In method (2), when the surface pores are mechanically closed by barrel or shot blasting, some of the pores are exposed again due to pickling or the like before plating, and spouting occurs from those areas after plating.

Method (2) involves dissolving the oxide film on the surface by pickling after steam treatment, but it is difficult to completely remove the oxide film with this pickling, and therefore the adhesion of preliminary plating and main plating deteriorates. Rust prevention ability decreases.

<Means for Solving the Problems> The present inventor has conducted intensive studies to solve the problems of the conventional surface treatment method for sintered metal materials described above, and has arrived at this invention. When performing plating treatment on the surface of a sintered metal material, the sintered metal material is sealed by steam treatment as a pretreatment, and then only the film on the surface of the sintered metal material is removed by shot blasting, and then the plating treatment is performed. The present invention provides a method for surface treatment of sintered metal.

<Function> As described above, in the present invention, a sintered metal material is first subjected to steam treatment before plating treatment, and the surface and interior of the material are sealed with a film of triiron tetroxide (Fea04).

However, since Fei04 is not a good conductor, if it is plated as is, the adhesion of the plating will deteriorate significantly.

Therefore, the Fe,04 film of about 10 um formed on the surface is removed by shot blasting to expose the metal surface, and then plating is performed.

When the surface treatment method of this invention is carried out, the pores on the surface of the material are closed by shot blasting, and the pores inside are also closed by a film of FesO<, so the acid used in the pre-plating treatment is This prevents the intrusion of alkali, alkali, or plating solution, and solves the problem of spouting after plating.

The steam treatment in this invention can be carried out under various conditions, but in the case of iron-based sintered members, the temperature is 500 to 600°C.
It is preferable to carry out the treatment for 1 to 2 hours, thereby forming a Fes04 film of 5 to 15 μm.

The temperature condition for steam treatment is 500 to 600℃ because
At temperatures below 500°C, it is difficult to obtain a good FeJ4 film.
Furthermore, at temperatures above 600°C, the degree of oxide film growth is large;
This is because it easily adheres to the surface and makes it difficult to seal the pores with an oxide film inside the sintered part.

The Fes04 film formed by this steam treatment is 51
If it is less than +m, the sealing of the internal pores is incomplete, and there is a concern that liquid may enter.If it exceeds 15 IIm, the removal of the surface film will be incomplete and the adhesion of the plating will deteriorate. .

The appropriate shot blasting time required to remove the Fl1!304 film at 5 to 15 urn is 2 to 10 minutes. If the film is removed for less than 2 minutes, the film will not be completely removed.
This is because even if it is carried out for more than 10 minutes, it will only become uneconomical.

Example Hereinafter, this invention will be explained in detail with reference to Examples.

Example l Ring shape (φ50mm x φ30mm x 110mm
) Fe-0.4%C sintered body (density 7..Og/C.)
m3) and steam treated under the conditions shown in Table 1.
Perform shot blasting, then JIS MFZ
Zn plating + chromate treatment was performed using n8G.

After the ring shape thus plated was left in the atmosphere for three days, a salt spray test according to JIS Z-2371 was conducted to examine the occurrence of rust. The results are shown in Table 1.

In addition, the evaluation of the rusting situation is ○: no rust, △: spot rust, ×
: I did this in a place where red rust was spreading.

From Example 1 in Table 1, it was found that if the steam treatment time was less than 1 hour, the internal pores were not sealed, and the plating solution etc. penetrated into the interior, causing embossment. It was also found that if shot blasting was insufficient, the adhesion of the plating would be reduced and the rust prevention ability would be poor.

Example 2 Ring shape (φ50mmXφ40+nmX j5n+m
) Fe-1.5%Cu-0.4%C sintered body density 6
．． 8g/cm”) and S45G rings (solid form) were prepared, and the sintered body was pretreated such as steam treatment under the conditions shown in Table 2, and then Ni plating was applied to 30Ilm and Cr plating was applied to 10um. S45C (Comparative example 1
In case 1), plating treatment was performed without pretreatment.

Two ring-shaped test beads plated in this way
One was held in a vise and the state of the fractured surface was observed.

The other side is the same as Example 1 < JIS Z-2371
The rusting status was investigated using a salt spray test. All the results are shown in Table 2.

Note that the evaluation of the rusting state was the same as in Example 1.

Table 2 From the results in Table 2 of Example 2, it was found that when the oxide film was dissolved and removed, if the immersion time in the HCf solution was short, the adhesion decreased and the rust prevention ability deteriorated. On the other hand, in the examples of the present invention, it was found that results equivalent to the rust prevention effect obtained when ingot S45G was plated.

<Effects of the Invention> As explained above, according to the surface treatment method of the present invention, sintered metals that conventionally had pores that prevented satisfactory adhesion or always caused problems of spouting. It is possible to form a plating layer on the surface of the material that has strong adhesion comparable to the plating layer applied to the surface of general melted lumber and also has high rust prevention properties, and its industrial value is extremely high. It's large.

Claims (1)

[Claims] When performing plating treatment on the surface of the sintered metal material, the sintered metal material is sealed by steam treatment as a pretreatment, and then only the film on the surface of the sintered metal material is removed by shot blasting, and then the plating treatment is performed. A method for surface treatment of sintered metal, characterized by subjecting it to.