1. Mark: Hex head bolts and screws (thread diameter ≥ 5mm). A logo with a embossed or concave word on the top of the head or a concave one on the side of the head. The contents of the logo include performance levels (such as 4.8, 8.8, 10.9, 12.9, etc.) and the factory standard.
2. Performance: Tensile strength and yield strength
Tensile strength—The maximum tensile stress a material can withstand before tensile fracture.
Tensile strength is the critical value of the transition of metal from uniform plastic deformation to localized plastic deformation. It is also the maximum load carrying capacity of metal under static tensile conditions, which reflects the fracture resistance of the material. The unit is PMa (MPa) = 1n/mm2 (the cow's tonnage per unit area) 1Kgf (kg force) = 9.8N (cattle)
Yield strength—The stress at which the material begins to produce macroscopic plastic deformation.
The yield strength is the yield limit when the metal material yields, that is, the stress that resists the slight plastic deformation. For metal materials without significant yield, the stress value specified to produce 0.2% residual deformation is the yield limit, which is called the conditional yield limit or yield strength.
External forces greater than this limit will permanently disable the part and will not recover. For example, the yield limit of low carbon steel is 207 MPa. When the external force is greater than this limit, the parts will be permanently deformed. If it is smaller than this, the parts will return to their original appearance.
The tensile strength and hardness are different. If the customer says that the product is interrupted during use, then we will see if our grade has been reached. For example, the hardness of 8.8 has not been reached, then we will test whether our tensile strength meets the standard. Whether the yield strength meets the standard, if these are no problem, we must look at whether the customer is using more force than the screw can carry during the installation process.
When our business receives a customer complaint, we must first determine whether it is our problem or the customer's problem, where is the problem, and then make some improvements. Also, we have to give back some special requests from customers. But the standard, for example, the 8.8-level screw, do not need to talk so much, it can be said 8.8.
There are 10 performance levels of 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9, and 12.9. The grade mark code consists of two parts separated by ".". The meaning of the number in the front part of the point indicates the nominal tensile strength. For example, the "4" of the 4.8 level indicates 1/100 of the nominal tensile strength of 400 N/MM2. The meaning of the digits in the latter part of the point indicates the yield ratio, which is the ratio of the nominal yield point or the nominal yield strength to the nominal tensile strength. For example, the yield point of the 4.8 grade product is 320 N/mm2. The stainless steel product strength grade mark is divided into two parts by "-".
3, surface treatment, in simple terms, is to wear a variety of different clothes for the screw. The surface treatment of fasteners serves two functions, one is anti-corrosion (rust), and the other is decoration!
The surface treatment of fasteners is as follows:
Nickel plating (black, white), galvanizing (black, white, blue and white, color zinc, yellow zinc), gold plating, silver, copper, chrome, electrophoretic paint and spray, spray paint, etc., we have not touched gold yet, Silver and spray, others are involved.
In general, we recommend black black zinc plating and white blue white zinc plating.
The surface of the electrophoretic paint is like paint. It is actually not paint. This kind of black is brighter and brighter than normal black zinc, but the salt spray time is relatively short. Often the salt spray time of black things is relatively short. For example, the difference between black Dacromet and white Dacromet is that after Dacromet is done first, then a layer of black is dyed. This black often only plays a color role. That is to say, after washing, the black will fade. Some black products are resistant to falling, and the temperature is slightly higher and fades.
The plating quality is based on its corrosion resistance strength and appearance. The appearance should be smooth, the partial non-plating layer is certainly not allowed, the chrome-plated charred, the excessive pickling leads to the rough surface, the color is not bright, the peeling, the crust, the pitting, etc., our current electroplating is relatively external plating Be better.
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Chongqing Xingjida Import and Export Trade Co., Ltd. , https://www.xjdvalve.com