What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
According to the properties of nuts, there are mainly national standard (GB), German standard (DIN), international standard (ISO), Japanese standard (JIS), American standard (ASTM/ANSI) and other standards. Among them, the national standard, German standard, and Japanese standard are represented by M (such as M8, M16), and the American system and the British system are represented by fractions or # (such as 8#, 10#, 1/4, 3/8). Commonly used national standard GB41 Ⅰ type hexagonal nut - C grade GB6170 Ⅰ type hexagonal nut - A, B grade GB6171 I type hexagonal nut - fine thread - A, B grade GB6172 hexagonal thin nut - A, B grade - chamfering GB6173 Hexagonal Thin Nut - Fine Thread - A, B Grade GB6174 Hexagon Thin Nut - B Grade - No Chamfer GB6175 II Hexagonal Nut - A, B Grade GB6176 II Type Hexagonal Nut - Fine Thread - A, B Grade GB6177 Hexagon Method Blue face nut - grade A GB55 hexagonal thick nut GB56 hexagonal super thick nut GB1229 large hexagonal nut (high strength for steel structure)
Hydraulic wrench or pulling method Use hydraulic torque wrench or puller to fasten large screws, which saves effort and has high precision. However, hydraulic tools are expensive, screws of different sizes need to be equipped with different wrenches, and now the hydraulic pullers in the world are generally only M160×6. If the screws are too large, special specifications or very few in number, it is extremely uneconomical to equip them with hydraulic tightening tools.
Nuts cooperate with screws to achieve the fixing and connection of components. SMD nuts are generally used in the circuit board industry to fix electronic components. That is, the chip nut is soldered on the circuit board by solder, and the electronic components are fixed by turning the screw. However, when the current chip nut is soldered on the circuit board, there may be uneven soldering, which makes the soldering untidy. At the same time, during soldering, the excess solder overflows from the periphery of the nut, which affects the appearance and may affect its appearance. electrical properties. In addition, the nut is only welded with the circuit board on one end face, and its firmness and reliability after welding are low.
When the mechanical components are installed on the concrete foundation, the J-shaped and L-shaped ends of the bolts are embedded in the concrete for use. The tensile capacity of the anchor bolt is the tensile capacity of the round steel itself. The size is equal to the cross-sectional area multiplied by the allowable stress value (Q235B: 140MPa, 16Mn or Q345: 170MPA), which is the allowable tensile capacity at the time of design. The anchor bolts are generally made of Q235 steel, which is smooth and round. Rebar (Q345) is strong, and the thread of the nut is not as easy to be round. For light round anchor bolts, the burial depth is generally 25 times its diameter, and then a 90-degree hook with a length of about 120mm is made. If the bolt diameter is large (such as 45mm) and the buried depth is too deep, a square plate can be welded at the end of the bolt, that is, a large head can be made (but there are certain requirements). The burial depth and hook are all to ensure the friction between the bolt and the foundation, so as not to cause the bolt to be pulled out and damaged.
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