Cautions for the use of threaded fasteners

- May 21, 2020-

Fasteners are a type of mechanical parts that are used for fastening and connection and are widely used. It is widely used in various industries, and can be seen on various machinery, equipment, vehicles, ships, railways, bridges, buildings, structures, tools, instruments, chemicals, instruments and supplies, etc. It is the most widely used mechanical basic part.

It is characterized by a wide variety of specifications, different performance and uses, and a high degree of standardization, serialization, and generalization. Therefore, some people refer to a type of fastener with existing national standards as standard fasteners, or simply standard parts.

Cautions for the use of threaded fasteners

1. Different thread types cannot be substituted for each other, otherwise the thread will be damaged. In order to prevent damage to the fastener, the first 3 to 5 turns of the bolt or nut must be tightened by hand (or finger) during assembly of the threaded fastener, otherwise damage may be caused.

2. According to the direction of bolts and nuts when they are screwed in, they are divided into right-hand and left-hand threads, but left-hand threads are not commonly used. The letter "L" is printed on them. The right-hand thread rotates clockwise to tighten (right-hand tighten, left-hand loose), and the left-hand thread counterclockwise tightens.

3. The use of predetermined tightening torques is the most common method of controlling fastener tension. Axial tension is directly proportional to the torque applied under certain conditions. The most common conditions are clean, dry and good threads. At this time, the friction on the thread consumes 40% of the torque used, the friction between the bolt head and the mating surface uses 50% of the torque, and the remaining 10% is used to tighten the bolt. The dry surface has the greatest friction, and when the fastener is coated with lubricant, the friction becomes smaller.

4. Note that the torque specified in the service manual for tightening threaded parts refers to clean and oil-free conditions. Even if the threaded parts with oil are tightened to the specified torque, the clamping force on the parts may still be unstable or insufficient. Therefore, unless otherwise specified in the service manual, it refers to dry and clean threads.