Fasteners and thread knowledge

Release time:

2023-03-07

Fasteners are indispensable tools for our production and life. British Standard BS84 for Cylindrical Threads for General Use British Standard BS84 for British Threads with a profile angle of 55. Standard Wyeth Fine Tooth Series. Use cylindrical thread Whit.S additional Wyeth optional series, use cylindrical thread Whit Wyeth tooth type non-standard thread UN constant pitch series of the same thread American standard ANSIB1.1.

Fasteners and thread knowledge

Fasteners are indispensable tools for our production and life. British Standard BS84 for Cylindrical Threads for General Use British Standard BS84 for British Threads with a profile angle of 55. Standard Wyeth Fine Tooth Series. Use cylindrical thread Whit.S additional Wyeth optional series, use cylindrical thread Whit Wyeth tooth type non-standard thread UN constant pitch series of the same thread American standard ANSIB1.1.

China's 60 ° conical pipe screw GB/T12716-1991 is equivalent to it. ACME thread includes two kinds of matching trapezoidal threads for general purpose and centering. The performance of trapezoidal threads for general purpose is similar to that of trapezoidal threads specified in GB/T5796-1986 in China. Most fasteners are made of steel. As a staff member working in the fastener industry, it is necessary to understand the changes, distinctions and applications. If he is a technical staff member, he should have a deeper understanding.

The most commonly used screws are ISO Class 8.8 SAE Grade 5 screws. Generally, medium carbon steel is used. ML35 SAE 1035 DIN 35 JIS SWRCH35K is heat treated (quenched and tempered), or SAE5140 40Cr can be used. The increase of alloy elements is of great help to the hardenability of heat treatment. Therefore, alloy steel can be used for screws with large specifications, not to use medium carbon steel leads to the existence of the phenomenon of "quenching through" in the central part we often say.

ISO Class 9.8 10.9 SAE Grade 8 uses low to medium alloy steel materials. After heat treatment (quenching and tempering), alloy materials have a good combination in terms of mechanical properties of materials. Commonly used materials are 40Cr 35CrMo SAE5140 SCM435 SAE4135 SAE4137 JIS SCr440(H) DIN 41Cr4, etc. In fact, 45# can also meet the required mechanical properties, but it is slightly inferior to alloy steel in terms of comprehensive mechanical properties.

The author of my understanding of the material application, referring to the relevant information, and share this knowledge with you, for just engaged in the industry can be used as a guide, for senior people, we can further discuss.
　　
At present, our commonly used material standard parts include: ISO (International), GB (China), DIN (Germany), AISI/SAE (United States), JIS (Japan) bolts and other external thread materials, some low carbon steel fasteners without mechanical performance requirements or ISO Class 4.8 SAE Grade 1-2 and other low carbon steel fasteners, Q235A SAE 1015 DIN C15 is enough, no heat treatment at all, direct cold processing, however, for fasteners with a slightly higher grade, such as ISO Class 6.8 SAE Grade 3-4, steel with carbon content above 0.2, such as C1020 C1022 Ml20 ML35, etc., such screws do not need any heat treatment, and the cold working strength can fully meet the requirements. In fact, the higher the carbon content, the more difficult it is to cold-form, and there is no need to overuse 6.8-grade screws. Special circumstances are another matter.
　　
ISO Class12.9 SATM A574 is a high-strength bolt with high mechanical requirements. It must be heat treated (quenched and tempered) with medium carbon alloy steel, such as SCM435 35CrMo SAE 4137 SAE4135 DIN 34CrMo4. If the surface treatment of this high-strength bolt is to be pickled, hydrogen embrittlement will occur, so there must be a hydrogen-to-hydrogen process (especially fasteners with sharp corners), otherwise it will die miserably.