1, screw torque requirements: the torque of the outer hex screw is relatively larger, the torque of the inner hex screw is smaller, and the torque of the cross slot is smaller (so this kind of screw is generally an ordinary grade screw).

2, the assembly of hexagonal bolts are generally assembled with adjustable wrenches, box wrenches and open wrenches. The assembly efficiency of the adjustable wrench is low, but the universality is very strong, and it is suitable for various head specifications of outer hexagonal screws; The wrench is the most efficient, but some occasions are not applicable, a wrench has only two heads, which can only be used in two specifications of the head of the outer hexagonal screws; An open wrench is similar to a box wrench, but it can be used with an extended socket. The smaller the specification of the outer hexagonal screw, the higher the angular requirements of the outer hexagonal bolt, otherwise its head is easy to slip when subjected to (wrench) force. Wenzhou people in order to save materials, invented the outer hexagonal cavity. The concave outer hexagonal screw is single weight and light, the thickness of the head is thin, the force is easy to slip, and the head may be twisted off.

3, hex screw assembly with hex wrench. This is very high requirements for the inner hexagonal hole, the hole is a little bit of wrench slip, a little wrench can not be inserted into the hole. The smaller the specifications of the hex, the higher the requirements for the hole. For some large hexagonal screws, as long as the opposite side of the hexagonal is qualified, it can be assembled normally with a wrench; For some small specifications of hexagonal screws, such as M2 hexagonal tight, the wrench inserted into the hex slightly harder will slip, so a slight opposite side is not qualified. Therefore, M2, M2.5, M3 hex screws (especially tight products) are easy to slip during the assembly process.

4, the cross slot screw assembly with a screwdriver, do not need to use too much strength, so the strength as long as 4.8, occasionally some need high strength screws, as long as carburizing heat treatment can be.

5, in the use of products, we generally recommend that the screw grade is higher than the nut grade, so as to have the most economic benefits. For example, 8.8 class screws, matching the use of 4 class nuts; In this way, the next time you change, you only need to change the nut.

Second, heat treatment:

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

1, tempering heat treatment: 8.8 grade and above strength grade products, are tempering heat treatment products. This heat treatment is characterized by a relatively uniform hardness 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, toughness is also guaranteed.

2, carburizing heat treatment: self-tapping screws basically need this treatment, characterized by a very hard surface, and the core is relatively soft; Because you need to break through the hard iron. The risk of self-tapping nails is higher, such as self-tapping nails often encounter severed heads, the possible reasons are: ① hydrogen embrittlements; ② The hardness is too high or too low to cause torsion; ③ The cross groove is too deep; ④ Too thin head; (5) No R Angle at the head and neck junction leads to stress concentration; ⑥ Operation is not standardized; Let’s wait.

Third, hydrogen embrittlement risk:

1, under normal circumstances, hardness >32HRC products, electroplating has the risk of hydrogen embrittlement. Therefore, all 10.9 grade or above (including 10.9 grade) products and products that have been carburized heat treatment (self-tapping nails) will have the risk of hydrogen embrittlement when electroplating.

2, hydrogen embrittleness that is, when the product is electroplated, H+ enters the metal to form bubbles, resulting in screws in use, on the spot, but within 24 hours of delayed fracture.

3, Products with hydrogen embrittlement risk need to be sent to the hydrogen dehydrogenation furnace within 4 hours after electroplating, and stored at 200 degrees Celsius for about 8 hours; This is called dehydrogenation.

4, hydrogen embrittlement treatment can greatly reduce the risk of hydrogen embrittlement, but can not completely avoid, so in the need to ensure 100% no hydrogen embrittlement risk, it is strictly prohibited to use electroplating products; Instead, dacromet, sandblasting and other surface treatment processes are used.

Fourth, fastener performance and processing technology development direction:

1, high strength at the same time to ensure toughness;

2, the same size can reduce the weight;

3, the mechanical strength can be guaranteed to make the volume smaller;

4, The toughness can be strengthened when the strength is guaranteed;

5, If the appearance is satisfied, the anti-corrosion ability can be enhanced;

6, the accuracy limit of the improvement;

Any of the above existing high processing cost processes, can have a relatively low cost to meet the requirements of the new process, will open up a new climate in our fastener industry.