Selection of fasteners for valve pressure bearing parts and calculation of preload torque
Release date:
2020-05-28
Author:
Shi Jianchang, Beijing Valve Research Institute
Source:
Abstract
1. The structure of commonly used fasteners for valves
(1) The pitch of threaded fasteners for pressure-bearing parts
Metric ordinary threads are the most used mechanical fastening threads for valves. Generally, each metric ordinary thread of nominal diameter has multiple pitch, divided into coarse teeth, fine teeth, and ultra-fine teeth. In HG/T 20613 "Fasteners for Steel Pipe Flanges PN Series", HG/T 20634 "Fasteners for Steel Pipe Flanges CLASS Series", DL-439 "Technical Guidelines for High Temperature Fasteners for Thermal Power Plants", GB/T 12234 "Steel Gate Valves with Studs Connecting Valve Caps for the Petroleum and Natural Gas Industry" In the valve design standards and fastener technical guidelines, the fastener pitch is specified.After analyzing these standards, it is concluded that fasteners with a nominal diameter ≤M27 generally use a coarse thread pitch, and fasteners with a nominal diameter >M27 use a fine thread pitch with a pitch of 3. From this, it can be concluded that when the nominal diameter of the thread is large, a smaller pitch (fine thread) is generally used. This is because fine thread threads have the characteristics of small thread lift angle, strong self-locking ability, small torsional stress when tightening, and large rotation angle when tightening the nut. Easy to control, but the pitch is not as small as possible, and the pitch of ultra-fine teeth is generally more expensive. , Commonly used in precision fit.
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