Most combination screws are composed of screws, washers, gaskets, nuts, etc. There are also many materials for combination screws. The material of the combination screw is generally divided into iron and stainless steel. Iron is made of different iron screws. General combination screw wire is used 1010,1018,10B21 and so on. 10B21 is used to make 8.8 class combination screws. For example, 8.8 hex socket combination screws are commonly used to do 10B21 wire. After finishing, go to heat treatment. After heat treatment, remove hydrogen and electroplate. This is to prevent the spring washer of the hexagon assembly screw from breaking. Stainless steel combination screws, combination screws on the market, generally refers to stainless steel SUS304 combination screws. 201 combination screws generally do very little. Very few combination screw manufacturers to produce 201 combination screws. Because the hardness of stainless steel 201 screw wire is not well controlled, it is easy to produce cracks.
The standard of combination screws and the quality of plating are mainly measured by their corrosion resistance, followed by their appearance. Corrosion resistance is to imitate the working environment of the product, set as the test conditions, and perform corrosion tests on it. The quality of electroplating products is controlled from the following aspects:
1, the appearance of the combined screw: the surface of the product is not allowed to have local coating, burnt, rough, gray, peeling, skin conditions and obvious stripes, not allowed to have pinhole pitting, black plating slag, passivation film loose, cracked, falling off and serious passivation traces. 2, composite screw coating thickness: the working life of fasteners in corrosive atmosphere is proportional to its coating thickness. Generally recommended economic plating coating thickness is 0.00015in~0.0005 in(4~12um). Hot-dip galvanizing: The average thickness of the standard is 54 um(name diameter ≤3/8 is 43 um), and the minimum thickness is 43 um(name diameter ≤3/8 is 37 um). 3, coating distribution: using different deposition methods, the coating on the surface of the fastener aggregation is also different. During electroplating, the coated metal is not uniformly deposited on the outer edge, and a thicker coating is obtained at the corner. In the threaded part of the fastener, the thickest coating is located at the top of the thread, gradually thinning along the side of the thread, and the thinnest deposit at the bottom of the tooth, while the hot dip galvanizing is the opposite, the thicker coating is deposited in the inner corner and the bottom of the thread, the mechanical plating metal deposit tends to be the same as the hot dip plating, but it is smoother and the thickness is much more uniform across the surface.
The combination screws manufactured by the general production, under normal circumstances, need to be electroplated. The electroplated screws not only look better in this way. There will be no oil. And it passes the salt spray test. Customer specified salt spray time may be reached. So the general combination screw plating, all those electroplating color! General electroplating has ordinary electroplating and environmental protection electroplating. Common electroplating colors are: white zinc, black zinc, blue zinc, color zinc, white nickel, black, black nickel, etc., environmentally friendly electroplating is to add two words "environmental protection" in front of these electroplating. But the electroplating is in line with environmental requirements. White nickel screw salt spray is generally 8-10 hours, but if the requirement is higher, it can be too oil. The salt spray of environmental protection color zinc is generally 48-72 hours, and the salt spray of environmental protection blue zinc is generally 48-72 hours. There is generally no standard for the use of combination screws and salt spray time. It's all done according to the customer's request. Hot-dip galvanizing of combination screws: by immersing the carbon steel parts in a bath of molten zinc at a temperature of about 510 ° C. The result is that the iron-zinc alloy on the surface of the steel gradually becomes the passivated zinc on the outer surface of the product. Hot dip aluminum plating is a similar process.
