What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
ANSI B1.1 Thread Pitch Comparison Table Nominal Diameter (inch〖mm〗) Coarse Thread Pitch (UNC) Fine Thread Pitch (UNF) Ultra Fine Thread Pitch (UNEF) Drilling Diameter (Coarse Thread) Drilling Diameter (Fine Thread) #0 0.060 〖1.524〗 80 1.2 # 1 0.073 〖1.5 1.5 # 2 0.086 〖2.8 # 3 0.099 〖2.515〗 48 56 2.0 2.1 # 4 0.112 〖2.4 # 5 0.125 〖 3.175〗 40 44 2.5 2.6 # 6 0.138 〖3.50〗 32 40 2.7 2.9 # 8 0.164 〖4.166〗 32 36 3.4 3.5 # 10 0.190 〖4.0 # 12 0.216 〖5.486〗 24 28 32 4.5 4.6 1/4 6.35 20 28 32 5.1 5.4 5/16 10.7 11.5 9/16 〖14.288〗 12 18 24 12.3 13.1 5/8 〖15.875〗 11 18 24 13.5 14.7 3/4 〖19.05〗 10 16 20 16.7 17.5 7/8 〖22.125 2.4 9 14 〗 8 12 20 22.2 23.4 The pitch is expressed by the number of teeth per inch, such as: 11 teeth per inch, then the pitch=25.4/11=2.309mm. The unit of pitch in the table is the number of threads per inch. The hole diameter is the recommended hole size for tapping, in millimeters.
Bolts are widely used as common fasteners. The traditional T-bolt consists of a head, a screw and a tail. The head is a long plane. During the use of the T-bolt of this structure, the T-bolt and the groove The contact surface of the track is a smooth surface, its friction force is not large, its connection is not firm enough, and it is easy to fall off. For this reason, some people design the head as a bevel to increase friction, but only one bevel is in contact with the part in this design, and the sealing is not very good
With the rapid development of China's automobile industry, the requirements of body assembly process are constantly improving. Riveting has the characteristics of short process cycle, low noise and low energy consumption, and is widely used in automobile bodies. In the automobile industry, due to the complexity of the body sheet metal structure, there are many cavities, and the riveting tools in some positions will interfere with the structure. Many assembly points cannot use the traditional two-way loading riveting technology, so single-sided riveting is used instead. craft.
The drawing process has two purposes, one is to modify the size of the raw materials; the other is to obtain basic mechanical properties of the fasteners through deformation and strengthening. For medium carbon steel, medium carbon alloy steel also has another purpose, that is, to make the wire rod. The flaky cementite obtained after controlled cooling is cracked as much as possible during the drawing process to prepare for the subsequent spheroidization (softening) annealing to obtain granular cementite. However, some manufacturers arbitrarily reduce the drawing in order to reduce costs. The excessive reduction rate increases the work hardening tendency of the wire rod, which directly affects the cold heading performance of the wire rod. If the distribution of the reduction ratio of each pass is not appropriate, it will also cause torsional cracks in the wire rod during the drawing process. In addition, if the lubrication is not good during the drawing process, it can also cause regular transverse cracks in the cold drawn wire rod. The tangential direction of the wire rod and the wire drawing die is not concentric at the same time when the wire rod is rolled out of the die, which will cause the wear of the unilateral hole pattern of the wire drawing die to aggravate, make the inner hole out of round, and cause uneven drawing deformation in the circumferential direction of the wire. The roundness of the steel wire is out of tolerance, and the cross-sectional stress of the steel wire is not uniform during the cold heading process, which affects the cold heading pass rate. During the drawing process of the wire rod, the excessive surface reduction ratio will deteriorate the surface quality of the steel wire, while the too low surface reduction ratio is not conducive to the crushing of the flaky cementite, and it is difficult to obtain as much granular cementite as possible. , that is, the spheroidization rate of cementite is low, which is extremely unfavorable to the cold heading performance of the steel wire. For the bar and wire rod produced by the drawing method, the partial surface reduction rate is directly controlled within the range of 10%-15%.
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