JPH093686A - Silver coated phosphor bronze for spring and its production - Google Patents

Abstract

PURPOSE: To provide excellent corrosion resistance and to stabilize contact resistance by forming, via a copper layer, a coating layer composed of silver or silver alloy on the surface of phosphor bronze. CONSTITUTION: After a copper plating layer 2 is formed on the surface of phosphor bronze 1 for spring, a coating layer 3 composed of silver or silver alloy plating is further formed. It is preferable to apply low temp. annealing after copper plating and silver or silver alloy plating are successively performed. It is further preferable that, subsequently to this double layer plating, reduction of area is carried out, followed by low temp. annealing. The copper layer 2 is interposed as a barrier to the diffusion of tin from the phosphor bronze 1 into the silver type metal coating layer 3 at the time of annealing, and, although its thickness is not particularly limited, a thickness of 0.5-5.0μm is preferred in terms of function and cost. Moreover, it is desirable to regulate the thickness of the silver type metal coating layer 3 to 0.2-5.0μm in terms of practical use. It is preferable that low temp. annealing is done by performing holding for 1min to 2hr in the temp. region of 200-500 deg.C where the strain of the material can be sufficiently removed and the softening of phosphor bronze is not brought about.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to phosphor bronze for silver-coated springs and a method for producing the same, and more particularly to silver-coated springs which exhibit excellent corrosion resistance and stable contact resistance when used as spring contacts. TECHNICAL FIELD The present invention relates to phosphor bronze and a method for manufacturing the same.

[0002]

2. Description of the Related Art A material in which phosphor bronze for springs defined by JIS-H3732 is used as a base material and a coating layer made of silver or a silver alloy is formed on the surface of the base material is excellent in spring property of the base material. In addition, it is known as a high-performance conductor that simultaneously develops the corrosion resistance and electrical connectivity properties of the coating layer,
Switches for various electronic, communication, information, electricity, measuring instruments,
It is actually used in fields such as connectors and relays.

Regarding the production of this material, a silver alloy plating layer having a predetermined composition is directly formed on the surface of a phosphor bronze base material, for example, by an electroplating method, and then heat treatment is performed in a temperature range of about 85 to 150 ° C. A method of doing so has been proposed (Japanese Patent Publication Sho 5)
5-43073). Further, on the surface of the base material, a foil made of silver or a silver alloy is clad by, for example, a cold rolling method, and then surface-reducing processing is performed to a desired thickness by a rolling process or a drawing process, and then, for example, hydrogen is used. Alternatively, it is also manufactured by performing low temperature annealing at a temperature of 150 to 300 ° C. in a reducing atmosphere such as a mixed gas of hydrogen and nitrogen.

[0004]

However, the spring contact made of the material subjected to the heating (annealing) treatment as described above has a larger initial contact resistance than the spring contact made of the material not subjected to the annealing treatment. Become. Furthermore, when used in a corrosive environment, the contact resistance of the former spring contact increases with time, compared to the latter spring contact, and the characteristics of the spring contact deteriorate rapidly. The problem arises of doing so.

Such a problem is caused by the above-mentioned annealing process.
The tin component contained in the base material of phosphor bronze diffuses through the coating layer of silver or silver alloy to reach the surface layer, contaminates the coating layer to increase its contact resistance and lowers corrosion resistance. Is. The present invention solves the above-mentioned problems when using the silver-coated spring phosphor bronze in which the surface of the spring phosphor bronze is coated with silver or a silver alloy as a spring contact, and has excellent corrosion resistance. An object of the present invention is to provide a phosphor bronze for silver-covered springs, which has a low contact resistance at a low level even when used for a long time, and a method for producing the same.

[0006]

Means for Solving the Problems In the course of intensive research to achieve the above-mentioned objects, the present inventors changed from phosphor bronze as a base material to silver or a silver alloy when the atmosphere during low temperature annealing changed. It has been found that the components that diffuse into the coating layer change. That is, tin components preferentially diffuse in a reducing atmosphere such as hydrogen or a mixed gas of hydrogen and nitrogen which has been conventionally applied, and copper components preferentially diffuse in an atmosphere containing oxygen. The fact is that

The present inventors are based on this fact, and that the increase in contact resistance and the decrease in corrosion resistance in the spring contact of the low temperature annealed material are based on the diffusion of the tin component in the substrate to the surface layer. In consideration of the above, it was conceived to interpose a copper layer as a diffusion barrier of tin components between a phosphor bronze base material for springs and a coating layer of silver or a silver alloy, and as a result of various studies, the silver of the present invention was obtained. We have developed a phosphor bronze for coated springs and a manufacturing method for the same.

That is, the silver-coated spring phosphor bronze of the present invention is characterized in that a coating layer made of silver or a silver alloy layer is formed on the surface of the spring phosphor bronze via a copper layer, and the production thereof. The method is characterized in that the surface of phosphor bronze is successively plated with copper and plated with silver or a silver alloy, and then annealed at a low temperature. In the phosphor-coated bronze for silver of the present invention, as shown in FIG. 1, a coating layer 3 of silver or a silver alloy is formed on the surface of a phosphor bronze for spring 1 which is a base material via a copper layer 2. It is a thing.

As the phosphor bronze 1 for spring, any material conventionally used as a base material for a spring contact may be used, and for example, the material specified by JIS-H3732 may be mentioned. The copper layer 2 functions as a barrier for preventing the tin component of phosphor bronze from diffusing into the coating layer 3 during low temperature annealing described later, and the thickness of the copper layer 2 is not particularly limited. However, if it is too thin, it causes the above-mentioned deterioration of the function as a barrier layer, and if it is too thick, it lowers the spring property and raises the cost.
It is preferably about 5 μm.

The coating layer 3 is composed of silver alone or a silver alloy, and examples of the silver alloy include Ag-Sb and Ag.
-Se, Ag-Pd, Ag-Cu, etc. can be mentioned. The thickness of the coating layer 3 is not particularly limited,
Due to the actual use as a spring contact, it is usually 0.2-5.0.
It is set to about μm. The phosphor bronze for silver-coated spring is manufactured as follows.

First, phosphor bronze is subjected to regular degreasing, pickling, and water washing to clean its surface, and then copper plating and silver or silver alloy plating are sequentially carried out to form a copper layer on the surface. A silver or silver alloy plating layer is formed in this order.
Then, the obtained material is annealed at a low temperature. Obviously, the temperature during annealing must be lower than the melting point of each of these materials, but in that case, the material strain cannot be sufficiently removed at a too low temperature, and the temperature is too high. Therefore, there arises a problem that the phosphor bronze is softened, so that it is usually set to a temperature range of 200 to 500 ° C.

Further, depending on the annealing temperature, if the annealing time is too short, the material strain is not sufficiently removed, and if it is too long, it is wasteful in terms of thermo-economy.
Usually, it is set to 1 minute to 2 hours in the above temperature range.
If the surface-reduced material is applied to the material that has been subjected to the plating treatment before the low temperature annealing, the bonding force between the plated crystal grains is strengthened and the wear resistance is improved. As the surface-reducing work in this case, for example, cold rolling work or drawing work can be applied. Further, in the surface reduction processing, the surface reduction rate is set so as to satisfy desired mechanical characteristics.

[0013]

Examples of the invention

Examples 1 to 7, Comparative Examples 1 and 2, electrolytic degreasing tank, water washing tank, pickling tank, water washing tank, copper plating tank, water washing tank, silver strike plating tank, silver (silver alloy) plating tank,
The washing bath and the dryer are serially arranged in this order, and the phosphor bronze strips for springs are continuously run to perform each treatment.
Phosphor bronze strips for silver plated springs were continuously manufactured.

In this line, copper plating, silver strike plating, silver plating, and silver alloy plating were performed under the following conditions. (1) Copper plating Composition of plating bath: CuSO ₄ 80 g / liter, H ₂ S
O ₄ 180 g / liter, NaCl 1 g / liter, bath temperature: 30 ° C., current density: 5 A / dm ² , plating thickness: 0.5
μm, 1.0 μm, 2.0 μm. (2) Silver strike plating Composition of plating bath: AgCN 3 g / liter, KCN60
g / liter, K ₂ CO ₃ 30 g / liter, bath temperature: 3
0 ° C., current density: 5 A / dm ² . (3) Silver plating Composition of plating bath: AgCN 50 g / liter, KCN6
0 g / liter, K ₂ CO ₃ 30 g / liter, bath temperature:
30 ° C, current density: 1 A / dm ² , plating thickness: 0.5 μm, 1.0 μm, 2.0 μm with different plating times. (4) Silver-antimony alloy plating Composition of plating bath: AgCN 12 g / liter, KCN4
0 g / liter, K ₂ CO ₃ 30 g / liter, antimony potassium tartrate 25 g / liter, potassium sodium tartrate 25 g / liter, bath temperature: 30 ° C., current density:
1 A / dm ² , plating thickness: 1 μm.

The phosphor bronze strips for silver-plated springs thus obtained were subjected to a rolling process in which one of them was kept as it was and the rest was subjected to a low-temperature annealing under the conditions shown in Table 1 respectively. And made a phosphor bronze strip for silver coated springs. The contact resistance of each material was measured according to the following specifications. Measurement of contact resistance: A probe made of sterling silver and having a head of 5.0 R is pressed against the material with a load of 49 mN, and a current of 10 mA is applied.

The above contact resistance is measured for the material immediately after the production (initial) and the material whose surface is subjected to the sulfurating treatment after being left in an atmosphere containing H ₂ S ₃ ppm at a temperature of 40 ° C. for 8 hours. went. Table 1 summarizes the above results.

[0017]

[Table 1]

As is apparent from the table, Example 2 and Comparative Example 1 are the same as Example 2 in spite of the fact that the other elements and manufacturing conditions are the same except for the presence or absence of the copper plating layer.
The material of (1) has extremely excellent corrosion resistance and its contact resistance is small, but in the case of Comparative Example 1, the contact resistance is extremely large.

[0019]

INDUSTRIAL APPLICABILITY As described above, the phosphor bronze for silver-coated spring of the present invention has excellent corrosion resistance and low contact resistance, and its industrial value as a spring contact material is extremely large.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a phosphor bronze for silver-coated spring of the present invention.

[Explanation of symbols]

 1 Phosphor bronze for springs 2 Copper layer 3 Coating layer of silver or silver alloy

Claims (3)

[Claims] 1. A phosphor bronze for a silver-coated spring, wherein a coating layer made of silver or a silver alloy is formed on the surface of phosphor bronze with a copper layer interposed therebetween. 2. A method for producing phosphor bronze for a silver-covered spring, which comprises sequentially performing copper plating and silver or silver alloy plating on the surface of phosphor bronze, and then annealing at a low temperature. 3. The surface of the phosphor bronze for spring is sequentially plated with copper and silver or silver alloy, and then surface-reduced.
The method for producing phosphor bronze for silver-covered springs according to claim 2, wherein low temperature annealing is further continued.