Knowledge of fasteners and threads

Fasteners are indispensable tools for our production and life. General purpose cylindrical thread British standard BS84 inch thread B.S.F. standard Wyeth fine pitch series with a tooth profile angle of 55. Use cylindrical thread Whit.S additional Wyeth optional series, use cylindrical thread Whit Wyeth tooth profile non-standard thread UN constant pitch series of the same thread American standard ANSIB1.1.

Our country's 60° conical pipe screw GB/T12716-1991 is equivalent to it. ACME thread includes two types of cooperating trapezoidal threads for general purpose and centering. Among them, the performance of general purpose is similar to the trapezoidal thread specified in GB/T5796-1986, and most of the fastener materials are steel. An employee who works in the fastener industry needs to understand the changes, distinctions and applications. If it is a technical employee, he should have a deeper understanding. (Guide: The real cause of damage to threaded fasteners) 　　

The most commonly used screws are ISO Class 8.8 SAE Grade 5. Medium carbon steel is generally used. ML35 SAE 1035 DIN 35 JIS SWRCH35K is heat treated (quenched + tempered), and SAE5140 40Cr, etc. can also be used. The alloy elements are increased It is of great help to the hardenability of heat treatment, so you can choose to use alloy steel for screws with large specifications, so that the use of medium carbon steel will not lead to the existence of the phenomenon of impermeability in the central part that we often say.　　

ISO Class 9.8 10.9 SAE Grade 8 should use low to medium alloy steel material, after heat treatment (quenching + tempering), the alloy material has a good combination of mechanical properties of the material, the commonly used material is 40Cr 35CrMo SAE5140 SCM435 SAE4135 SAE4137 JIS SCr440(H) DIN 41Cr4, etc. In fact, 45# can also achieve the required mechanical properties, but it is slightly inferior to alloy steel in terms of comprehensive mechanical properties.　　

With regard to the material application that I know, I refer to related materials and share this knowledge with you. It can be used as a guide for those who have just started in the industry, and for senior people, we can further discuss.

Now we commonly use material standard parts: ISO (international), GB (China), DIN (Germany), AISI/SAE (United States), JIS (Japan) bolts and other external thread materials, some without machinery For performance requirements or low-carbon steel fasteners such as ISO Class 4.8 SAE Grade 1-2, Q235A SAE 1015 DIN C15 is sufficient, no heat treatment is required at all, and directly cold-worked, and fasteners with higher grades such as: ISO Class 6.8 SAE Grade 3-4 uses steel with a carbon content of more than 0.2%, such as C1020, C1022, Ml20, ML35, etc. This type of screw does not require 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 use a grade 6.8 screw for overkill. Special circumstances are a different matter.　　

ISO Class12.9 SATM A574 is a high-strength bolt with high requirements for mechanical properties. Medium-carbon alloy steel must be heat treated (quenched + tempered), such as SCM435 35CrMo SAE 4137 SAE4135 DIN 34CrMo4. If the surface treatment of the strength bolt undergoes the pickling process, hydrogen embrittlement will occur, so the process of hydrogen transfer (especially the fasteners with sharp corners) must be carried out, otherwise it will die miserably.

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