Arc ablation-resistant tungsten alloy switch contact and preparation method thereof

Abstract

An arc-ablation resistant tungsten alloy switch contact and preparation method is disclosed. A contact member has a three-layer structure, wherein a first layer is a hydrophobic rubber layer, a second layer is a sheet metal layer, and a third layer is a tungsten alloy chemical deposition layer. A plating bath adopted in the chemical deposition contains 25-125 g/L soluble tungsten compound, 0-60 g/L soluble compound of a transition metal like ferrum, nickel, cobalt, copper or manganese, and 0-30 g/L soluble compound of tin, stibium, lead or bismuth. When a layered complex of the hydrophobic rubber layer and the sheet metal layer is chemically plated by the plating bath, a tungsten alloy plated layer is selectively deposited on a metal surface, and chemical deposition of the tungsten alloy does not occur on a surface of the hydrophobic rubber fundamentally.

Claims

1. An arc-ablation resistant tungsten alloy switch contact, wherein the switch contact is a layered complex having a three-layer structure, comprising: a first layer, which is a hydrophobic rubber layer composed of a vulcanized hydrophobic rubber material, and having a thickness of 0.1-10 mm; a second layer, which is a sheet metal layer having a thickness of 0.01-1.0 mm and containing magnesium, aluminum, titanium, chromium, manganese, ferrum, cobalt, nickel, copper, zinc, niobium, molybdenum, silver, tin or aurum, wherein the hydrophobic rubber layer is adhered with self-adhesiveness directly to the sheet metal layer by heat vulcanization adhesion or by heat vulcanization shaping of the hydrophobic rubber material; and a third layer, which is a tungsten alloy plated layer having a thickness of 2*10.sup.5-0.02 mm, wherein the tungsten alloy plated layer of the third layer is deposited on a surface of the second layer, and the tungsten alloy plated layer in the third layer contains no less than 30 weight % tungsten.

2. The arc-ablation resistant tungsten alloy switch contact according to claim 1, wherein the third layer is chemically deposited on the surface of the second layer.

3. The arc-ablation resistant tungsten alloy switch contact according to claim 1, wherein the hydrophobic rubber material enables a water contact angle on a rubber surface of the hydrophobic rubber layer to be greater than 65 degrees.

4. The arc-ablation resistant tungsten alloy switch contact according to claim 3, wherein the hydrophobic rubber layer is prepared from nonpolar or weak polar rubber.

5. The arc-ablation resistant tungsten alloy switch contact according to claim 4, wherein the hydrophobic rubber layer is an ethylene propylene diene monomer, methylvinylsiloxane gum or polymethylvinylphenylsiloxane gum.

6. The arc-ablation resistant tungsten alloy switch contact according to claim 1, wherein the sheet metal layer is a metal sheet having a convex point or a concave point, a metal sheet having a convex line or a concave line, a metal sheet having a convex surface or a concave surface, a metal sheet having a small hole with an area less than 1 mm.sup.2, a metal gauze, metal foams or a metal fiber sintered felt; and wherein the sheet metal layer is a single metal material or composited by different metal materials in a layered manner.

7. The arc-ablation resistant tungsten alloy switch contact according to claim 1, wherein the sheet metal layer is a stainless steel sheet, a copper sheet, a copper alloy sheet, a nickel sheet, or a nickel alloy sheet having a thickness of 0.01-1.0 mm, and a pure nickel layer, a nickel alloy layer, a pure cobalt layer, or a cobalt alloy layer having a thickness of 0.1-10 m is vacuum plated, electroplated, or chemical plated on one side or two sides of the sheet metal layer.

8. A method of preparing the arc-ablation resistant tungsten alloy switch contact according to claim 1, the method comprising: (1) treating the sheet metal layer, which is a stainless steel sheet, a copper sheet, a copper alloy sheet, a nickel sheet, or a nickel alloy sheet, by using a cleaning agent and an organic solvent to deoil and clean the sheet metal layer; or by mechanically roughing a surface of the sheet metal layer through sand blasting and polishing; or by processing the sheet metal layer through chemical etching to form concave pits or convex points having a diameter less than 1 mm; then using the cleaning agent and the organic solvent to deoil and clean the sheet metal layer; (2) adhering the hydrophobic rubber material onto the sheet metal layer through heat vulcanization shaping; or adhering the hydrophobic rubber material with self-adhesiveness on the sheet metal layer through heat vulcanization adhesion, thus forming a layered composite sheet; (3) separating or punching the layered composite sheet into a cylinder having a diameter of 2-10 mm; or separating or punching the layered composite sheet into an object having a cross section in a shape of ellipse, polygon, crisscross, star or crescent or any combinations thereof; using a basic cleaning liquid to wash the cylinder or the object for about 5 minutes, washing the cylinder or the object with water, then using 5% hydrochloric acid to clean the cylinder or the object for about 3 minutes, using deionized water to clean the cylinder or the object, and then draining off the cylinder or the object; (4) dipping the cylinder or the object in a chemical plating bath containing a soluble tungsten compound and stirring to form the tungsten alloy plated layer on a metal surface of the cylinder or the object using a method of chemical plating; or putting the cylinder or the object into a roller for the chemical plating bath to make the roller rotate and form the tungsten alloy plated layer on the metal surface of the cylinder or the object using the method of chemical plating, thus obtaining a plated object or a plated cylinder; wherein the chemical plating bath contains 25-125 g/L of the soluble tungsten compound, 0-60 g/L of a soluble compound of a transition metal of ferrum, nickel, cobalt, copper or manganese or any combination thereof, 0-30 g/L soluble compound of tin, stibium, lead or bismuth or any combination thereof, 20-100 g/L reducing agent, 30-150 g/L complexing agent, 20-100 g/L pH adjuster, 0.1-1 g/L stabilizer, 0.1-1 g/L surfactant, and 0-50 g/L brightener or roughness adjuster; wherein if sodium hypophosphite is adopted as the reducing agent, the chemical plating bath has a temperature of 60-85 C., the cylinder or the object remains in the chemical plating bath for 30-300 min, and a pH value of the chemical plating bath is 8.0-10.0; and (5) taking out the plated object or the plated cylinder from the chemical plating bath, using distilled water or deionized water to clean the plated object or the plated cylinder multiple times, then draining off the plated object or the plated cylinder, and putting the plated object or the plated cylinder in a 75 C. constant temperature drying oven to dry, thus obtaining the switch contact with the metal surface layer coated with the tungsten alloy.

9. The method of claim 8, wherein the reducing agent in the plating bath is sodium hypophosphite.

10. The method of claim 8, wherein the stabilizer is a mixture of one or more of potassium iodide, potassium iodate, benzotriazole, 4,5-dithiaoctane-1,8-disulfonate, 3-mercapto-1-propanesulfonate, sodium thiosulfate and thiourea.

11. The method of claim 10, wherein the stabilizer is sodium thiosulfate, thiourea or a mixture of the two.

12. The method of claim 8, wherein the reducing agent includes sodium hypophosphite, sodium borohydride, alkylamine borane, hydrazine or titanium trichloride.

13. The method of claim 12, wherein the reducing agent is sodium hypophosphite.

14. The method of claim 8, wherein the surfactant is one or more of dodecyl benzene sulfonate, lauryl sulfate and sodium n-octyl sulfate.

15. The method of claim 14, wherein the surfactant is sodium dodecyl sulfate or sodium dodecylbenzene sulfonate.

16. The method of claim 8, wherein the brightener or roughness adjuster is one or more of formaldehyde, acetaldehyde, -naphthol, 2-methyl aniline-aldehyde condensates, benzalacetone, cuminaldehyde, benzophenone, chlorobenzaldehyde, peregal, schiff base, butynediol, propiolic alcohol, 1-diethylaminoprop-2-yne, propynol ethoxylate, saccharin, sodium benzosulfimide, sodium vinylsulfonate, sodium proparagylsulfonate, pyridine-2-hydroxypropanesulfonate inner salt, alkylphenol polyoxyethylene.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of a sectional structure of the present invention; in the figure: 1 refers to rubber layer; 2 refers to sheet metal layer; and 3 refers to tungsten alloy plated layer; and

(2) FIG. 2 is a process flow diagram of a preparation method of the present invention.

DETAILED DESCRIPTION

(3) The present invention will be further described in details hereunder with reference to the specific embodiments.

(4) Embodiment 1:

(5) An embodiment of preparing a contact of a tungsten alloy plated layer is as follows.

(6) The compositions of the plating bath were as follows: 100 g/L sodium tungstate, 35 g/L sodium hypophosphite, 50 g/L sodium citrate, 30 g/L potassium sodium tartrate, 30 g/L ammonium sulfate, 24 g/L sodium pyrophosphate, 40 mg/L potassium iodate, 32 mg/L sodium thiosulfate, and 1 g/L sodium dodecyl sulfate. Proper aqueous ammonia was added to make the pH of the plating bath within 8.5-9.5.

(7) Process route was as follows:

(8) The zinc-cupro-nickel sheet having a thickness of 0.1 mm, an HV hardness of 120 to 180, and a copper content of about 55% was used as the metal substrate to prepare the sheet metal layer 2. The reason for choosing zinc-cupro-nickel was that the zinc-cupro-nickel has excellent comprehensive mechanical properties, excellent corrosion resistance, and good hot and cold shaping property, and is suitable for manufacturing various elastic elements. The smooth zinc-cupro-nickel sheet was mechanically rolled into a sheet having fine rippers by a mechanical method, which had a crest height of 0.2 mm and a peak pitch of 0.4 mm. The sheet was cleaned and deoiled by industrial alcohol, then a basic cleaning liquid having a pH value around 9 was used to further clean and deoil the sheet under a temperature 60 C., then the sheet was washed by water, washed by 12.5% sulfuric acid solution under a temperature of 50 to 70 C. for 1 min, and washed by water. Then a nickel layer having a thickness of 2.5-5.0 m was plated on both sides of the zinc-cupro-nickel sheet having fine ripples by electroless plating. The nickel-plated zinc-cupro-nickel sheet having fine ripples was cleaned up by deionized water, and blow-dried by cold air.

(9) Polymethylvinylphenylsiloxane gum (for example, Elastosil R 401/60 produced by Wacker Chemie AG), vinyl tris-tert-butyl peroxy silane (VTPS) and dicumyl peroxide (DCP) were uniformly mixed by an open mill. The content of the VTPS in a rubber compound was 1%, and the content of the DCP in the rubber compound was 0.5%. VTPS was an unstable coupling agent containing a peroxide component, which not only can crosslink silicone rubber containing vinyl but also can promote the bonding between the silicone rubber containing vinyl and metals.

(10) Heat vulcanization adhesion and heat vulcanization shaping were performed between the zinc-cupro-nickel sheet having fine ripples and plated with nickel layer and the foregoing rubber compound under 165 C., wherein a curing time was 10 min, to form a layered composite sheet of zinc-cupro-nickel and silicone rubber having a thickness of 1.25 mm. A mold cavity of a mold for preparing the composite sheet has a Teflo coating on a surface of the mold cavity. The composite sheet was punched into a small wafer having a diameter of 5 mm. The small wafer was cleaned for various minutes by basic cleaning liquid, washed by water, then dip into 5% hydrochloric acid for 3 min, put into 10% dilute sulfuric acid for activation for 1 min, and then cleaned by distilled water or deionized water, and drained off.

(11) 500 small wafers above were put into 300 mL plating bath above under a temperature of 80 C. and stirred, taken out after 200 min, rinsed by distilled water or deionized water, drained off, and put into a 70 C. constant temperature drying oven to dry, thus obtaining small wafers with a sheet metal player 2 plated with tungsten alloy. During the process of chemical tungsten, attentions should be always paid to the change of the pH value, and the pH value of the solution should be controlled by ammonia water or sodium hydroxide solution in time, so as to make the pH value within 8.5 to 9.5. The thickness and density of the plated tungsten alloy were related to the time of the small wafers placed in the plating bath. The longer the deposition time was, the thicker the tungsten alloy plated layer 3 became. The tungsten alloy was deposited only on the surface of the stainless steel in the small wafer and rather than deposited on the surface of the rubber layer 1 in the small wafers as shown in FIG. 1.

(12) Heat vulcanization adhesion was performed between the small wafer plated with tungsten alloy of the silicon-containing rubber layer and the silicone rubber (heat vulcanization adhesion was performed between the a silicone rubber face in the small wafer and other silicone rubber, wherein one face plated with tungsten alloy faced outwards), so that the small wafer might be used as the contact of the circuit switch in the rubber keypad. The contact was contacted with the gold-plated contact of the PCB. The contact resistance between the contacts was smaller than that between small wafer directly prepared by stainless steel sheet and the gold-plated contact of the PCB, and the small wafer plated with tungsten alloy had better conduction performance: after electrifying a 300 mA direct current between the small wafer made of stainless steel sheet and not plated with tungsten alloy plated layer 3 and the PCB gold-plated contact, and switching about 2000 times, due to the arc-ablation during switching on or off, the contact resistance between the small wafer and the PCB gold-plated contact was significantly increased (from about 1 to 100 or more, or even non-conductive condition during multiple tests); however, in the same circuit conditions, after electrifying a 300 mA direct current between the small wafer plated with tungsten alloy and the PCB contact, and switching about 1000 times, the contact resistance between the small wafer and the PCB gold-plated contact is still below 1.

(13) Embodiment 2:

(14) An embodiment of preparing a contact containing the tungsten alloy plated layer is as follows.

(15) The compositions of the plating bath were as follows: 90 g/L sodium tungstate, 10 g/L nickel sulfate, 16 g/L basic nickel carbonate, 25 g/L sodium hypophosphite, 50 g/L sodium citrate, 30 g/L potassium sodium tartrate, 30 g/L ammonium sulfate, 24 g/L sodium pyrophosphate, 40 mg/L potassium iodate, 32 mg/L sodium thiosulfate, 1 g/L sodium dodecyl sulfate, and 20 g/L sodium benzosulfimide. Proper aqueous ammonia is added to make the pH of the plating bath within 8.5-9.5.

(16) Process route was as follows:

(17) As shown in FIG. 2, a flat stainless steel sheet (Model 304) having a thickness of 0.075 mm was subjected to alkaline deoiling and anodic deoiling, then washed by tap water and cleaned up by distilled water and alcohol, one surface of the sheet was subjected to a primer treatment by a rubber-metal adhesion agent (Megum 3270 produced by Rohm and Haas Company, U.S.A.), and then the heat vulcanization adhesion was performed between the surface treated with the primer and a methylvinyl silicone rubber (e.g., KE 951U produced by Shin-Etsu Chemical Co., Japan) to form a stainless steel-silicone rubber composite sheet having a thickness of 1.0 mm. The composite sheet was punched into a small wafer having a diameter of 5 mm.

(18) The wafers were washed by basic cleaning liquid under a temperature of 70 C. for about 5 min, washed by water, then washed by 5% hydrochloric acid for 3 min, then cleaned by deionized water and drained off.

(19) 500 small wafers above were put into 300 mL plating bath above under a temperature of 80 C. and stirred, taken out after 240 min, rinsed by distilled water or deionized water, drained off, and blow-dried by cold air or put into a 700 constant temperature drying oven to dry, thus obtaining small wafers with a sheet metal player 2 plated with tungsten alloy. During the process of chemical tungsten, attentions should be always paid to the change of the pH value, and the pH value of the solution should be controlled by ammonia water or sodium hydroxide solution in time, so as to make the pH value within 8.5 to 9.5. The thickness of the plated tungsten alloy was related to the time of the small wafers placed in the plating bath. The longer the deposition time was, the thicker the tungsten alloy plated layer 3 became. The tungsten alloy was deposited only on the surface of the stainless steel in the small wafer and rather than deposited on the surface of the rubber layer 1 in the small wafers as shown in Figure.

(20) Heat vulcanization adhesion was performed between the small wafer plated with tungsten alloy and the silicone rubber in a heating mould pressing mode (heat vulcanization adhesion was performed between the a silicone rubber face in the small wafer and other silicone rubber, wherein one face plated with tungsten-nickel alloy faced outwards), so that the small wafer might be used as the contact of the circuit switch in the rubber keypad. The contact was contacted with the gold-plated contact of the PCB. The contact resistance between the contacts was smaller than that between small wafer directly prepared by stainless steel sheet and the gold-plated contact of the PCB, and the small wafer plated with tungsten alloy had better conduction performance: after electrifying a 300 mA direct current between the small wafer made of stainless steel sheet and not plated with tungsten alloy plated layer 3 and the PCB gold-plated contact, and switching about 2000 times, due to the arc-ablation during switching on or off, the contact resistance between the small wafer and the PCB gold-plated contact was significantly increased (from about 1 to 100 or more, or even non-conductive condition during multiple tests); however, in the same circuit conditions, after electrifying a 500 mA direct current between the small wafer plated with tungsten alloy and the PCB contact, and switching about 2000 times, the contact resistance between the small wafer and the PCB gold-plated contact is still below 1.

(21) Embodiment 3:

(22) A 400-mesh stainless steel plain net (the model of the stainless steel was 304) was used to replace the stainless steel sheet having fine ripples in embodiment 2, and the contact prepared using the process and the electroless plating bath in embodiment 2 also had lower contact resistance and preferable arc-ablation resistance.

(23) A mesh of the 400-mesh stainless steel net was very small, and the silicone rubber will not penetrate through the mesh of the stainless steel net when molding the stainless steel net with the silicone rubber. If a stainless steel net with a small mesh number, for instance, a stainless steel net with a mesh below 80, was selected, a technical problem that the silicone rubber penetrated through the mesh of the stainless steel net during molding will occur. Therefore, a stainless steel net with a larger mesh number needs to be adopted for preparing a switch contact having a tungsten alloy plated layer 3.

(24) Those having ordinary skills in the art may also make various improvements and polishing without departing from the principle of the invention, which shall all be deemed as the protection scope of the invention.