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Fastener Product Basics (Functional)

Mar. 06. 2020

High quality fasteners wholesaler to share with you:

i. functions:

1. Torque requirements for screws: The torque of the outer hexagonal screws is relatively large, the torque of the hexagonal screws is small, and the torque of the cross recess is smaller (so these screws are generally ordinary grade screws).

2. The assembly of hexagonal bolts is generally carried out with adjustable wrenches, plum wrenches and open-end wrenches. The assembly efficiency of the adjustable wrench is low, but the versatility is very strong, and it is suitable for various hexagon head screws. The Torx wrench has the highest efficiency, but it is not applicable in some occasions. A Torx wrench has only two heads. For more CNC programming knowledge, follow the WeChat public account (NC programming teaching), and it can only be applied to the two hexagon head screws. The open end wrench is similar to the Torx wrench, but it can Extension sleeves are used. The smaller the size of the external hex screw, the higher the requirements for the angle of the external hex bolt, otherwise the head will slip easily when subjected to (wrench) force. In order to save materials, Wenzhou people invented the outer hexagonal cavity. The recessed hexagonal screws are light in weight and have a thin head thickness, which tends to slip under stress, and the head may be unscrewed.

3. Carbon steel hex head is assembled with hexagon wrench. The requirements for the hexagon socket are very high. The larger the wrench, the smaller the wrench slips, and the smaller the wrench cannot be inserted. The smaller the size of the inner hexagon, the higher the requirements on the hole. For some large hex screws, as long as one of the opposite sides of the hex is qualified, the wrench can be assembled normally; for some small hex screws, such as M2, the hexagon is tightened, and the wrench is inserted slightly harder Hexagons will slip, so a little opposite side is too big to pass. Therefore, the hexagon socket screws of M2, M2.5, and M3 (especially tightening products) are liable to slip during the assembly process.

Carbon Steel Hex Head

Carbon Steel Hex Head

4. The Phillips screws are assembled with a screwdriver, and do not require too much force, so the strength is only 4.8. Occasionally, some high-strength screws are required, as long as carburizing heat treatment is sufficient.

5. In the use of supporting products, we generally recommend that the level of screws is one level higher than the level of nuts, which is the most economical. For example, a class 8.8 screw uses a class 4 nut; in this case, the next time you only need to change the nut.

Second, heat treatment:

Heat treatment is mainly for carbon steel screws, mainly quenching and tempering and carburizing heat treatment to meet the requirements of the screw strength in different environments.

1. Quenching and tempering heat treatment: Products of strength class 8.8 and above are all quenching and tempering products. The characteristic of this heat treatment is that the hardness is relatively uniform inside and outside.

When the same material is heat treated, the higher the hardness, the worse the toughness. Therefore, there is a need for safety matching. While meeting the hardness, the toughness is also guaranteed.

2. Carburizing heat treatment: Self-tapping screws are generally required for this type of treatment. The characteristic is that the surface is very hard and the core is relatively soft; because it needs to penetrate hard iron plates.

Self-tapping screws are more risky. For example, self-tapping screws often encounter broken ends. More CNC programming knowledge is concerned with WeChat public account (NC programming teaching). The possible reasons are: ① hydrogen embrittlement; ② hardness is too high or too low Induced twisting; ③ The cross groove is too deep; ④ The head is too thin; ⑤ There is no R angle at the head-neck junction to cause stress concentration; ⑥ The operation is not standardized; etc.

Too thin; ⑤ No R angle at the head-neck junction causes stress concentration; ⑥ Operation is not standardized; etc.

Third, the risk of hydrogen embrittlement:

1. In general, for products with hardness> 32HRC, there is a risk of hydrogen embrittlement in electroplating. Therefore, all products above 10.9 grade (including 10.9 grade) and products that have undergone carburizing heat treatment (self-tapping screws) will have the risk of hydrogen embrittlement when electroplating.

2. Hydrogen embrittlement means that when the product is electroplated, H + enters the inside of the metal to form bubbles, which causes the screw to continue on the spot during use, but delayed fracture occurs within 24 hours.

3. Products with a risk of hydrogen embrittlement need to be sent to a dehydrogenation furnace within 4 hours after plating, and stored at 200 degrees Celsius for about 8 hours; this is called dehydrogenation treatment.

4. The hydrogen embrittlement treatment method can greatly reduce the risk of hydrogen embrittlement, but it cannot be completely avoided. Therefore, when it is necessary to ensure that there is no risk of hydrogen embrittlement, it is strictly prohibited to use electroplated products; instead, use Dacromet, sandblasting and other surface treatment processes .

Development direction of fastener performance and processing technology:

1. High strength while ensuring toughness;

2. The weight can be reduced under the same size;

3. The volume can be reduced if the mechanical strength can be guaranteed;

4. The toughness can be strengthened under the condition of strength assurance;

5. The antiseptic ability can be enhanced if the appearance is satisfied;

6. Increase in accuracy limit;

A new process that can meet the requirements at a relatively low cost will start a new era in our fastener industry.