What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
Ordinary thread Ordinary coarse thread: Feature code M+ Nominal diameter + Rotation + thread tolerance zone code (pitch diameter, top diameter) - Rotation length Ordinary fine thread: Feature code M+ Nominal diameter * thread pitch + direction of rotation + thread tolerance With code (middle diameter, top diameter) - the length of screwing is omitted for right-handed threads, and the left-handed thread is represented by LH. M 16-5g6g means coarse thread ordinary thread, nominal diameter 16, right-handed, the thread tolerance zone is 5g in the middle diameter and 6g in the major diameter, and the screwing length is considered as the medium length. M16×1 LH-6G means fine thread ordinary thread, nominal diameter 16, pitch 1, left-handed, thread tolerance zone medium diameter and major diameter are both 6G, and the screwing length is considered as medium length. The labeling format is: feature code (cylindrical pipe thread is represented by G, conical pipe thread is represented by NPT) + size code + tolerance grade code + rotation direction G1A--LH represents inch non-threaded sealing pipe thread, size code 1in, left-handed, tolerance The grade is A grade. Rcl/2 means inch thread seal taper pipe thread, size code 1/2in, right-handed.
Reference standard GB 90 Fastener acceptance inspection, marking and packaging GB 196 Basic dimensions of ordinary threads (1～600mm in diameter) GB 197 Tolerance and fit of ordinary threads (1～355mm in diameter) GB 230 Test method for Rockwell hardness of metals GB 699 High-quality carbon Plain structural steel technical conditions GB 1237 Marking method of fasteners GB 5267 Electroplating layer of threaded fasteners GB6394 Determination of average grain size of metals
According to the development and evolution process of self-tapping screws, we believe that the main types of self-tapping screws are as follows: 1. Common self-tapping screw threads are self-tapping threads, also known as wide thread. The surface is mostly electroplated. 2. Self-cutting and self-tapping screws are called scraping ends of self-tapping screws in my country's standard. The threads are self-tapping threads or machine threads, and the cross grooves are also H type. There are several types of self-cutting self-tapping screws: cross recessed pan head self-cutting self-tapping screws, cross recessed countersunk head self-cutting self-tapping screws. Cross recessed countersunk head self-cutting self-tapping screws, hexagon head self-cutting self-tapping screws. 3. Self-extrusion and self-tapping screws (self-tapping locking screws) The threads of self-extrusion and self-tapping screws are generally machine threads, and self-tapping threads are rarely used. In the wrenching method, in order to ensure the use of high-speed automatic assembly wrenches, slotting is generally not recommended. The cross section of the screw of the self-extrusion self-tapping screw is triangular. So it is also called triangular thread screw. 4. Self-drilling and self-tapping screws (self-drilling screws) The threads of self-drilling and self-tapping screws are self-tapping threads according to Chinese, German and international standards. In the American ASME and SAE standards, the BSD self-drilling self-tapping screws are self-tapping threads, and the CSD self-drilling self-tapping screws are machine threads. Self-drilling self-tapping screws are not recommended for slotted and normal hex head. 5. Metal driving screws (metal tapping screws) The metal driving screws have multiple threads and special threads with a certain helix angle. Only the American standard has metal drive screws, and there are no Chinese and German standards. 6. Wallboard self-tapping screws (dry wall screws) Wallboard white tapping screws are special threads with horn head, cross groove (H type) and 60° profile angle, and the surface is mostly phosphate treatment (phosphating). 7. The cross groove of the fiberboard nail is Z-shaped, and the surface treatment is mostly electroplating. There are several types of fiberboard nails: countersunk head, double countersunk head fiberboard nails, pan head, pan head flange (with pad) fiberboard nails, semi-countersunk head, semi-countersunk head flange (with cushion) fiberboard nails. 8. Combination self-tapping screws Ordinary self-tapping screws, self-cutting self-tapping screws, self-drilling self-tapping screws, etc., and flat washers, elastic washers (including spring washers, elastic locking washers, etc.). 9. Others Self-tapping screw types High and low thread double lead self-tapping screws, coarse and fine thread (different pitch) thread self-tapping screws, threads coated with sealing material (fall resistance) self-tapping screws, various composite groove self-tapping screws, Other special self-tapping screws, etc. In short, there are many types of self-tapping screws. With the development of production, the advancement of technology, new materials, new structures, and new thread forms, new self-tapping screw products will continue to appear.
As shown in FIG. 1 and FIG. 2 , a rivet die in the prior art includes a set of top die 1 and cover die 2 arranged opposite to each other. The top die 1 is provided with a cavity 1 in the center that matches the shape of the rivet dome head 3-1. -1, the center of the cover mold 2 is provided with a mold cavity 2-1 that matches the shape of the rivet dome head 3-3.
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