Tightening Torque Tightening Torque is the most important factor affecting the reliability of the threaded connection. Choosing the appropriate tightening torque is the key to ensuring preload and mechanical damage to the threaded fasteners. The size of the tightening torque is determined by the following factors: (1) The nominal diameter of the threaded fastener The nominal diameter of the threaded fasteneris the most important factor affecting the tightening torque. In other cases, the larger the diameter, The greater the required tightening torque, the specific value see 4.3. ⑵ thread fastener material grade general mechanical carbon steel and alloy steel external thread fastenersaccording to the mechanical properties are divided into 3.6,4.6,4.8,5.6,5.8,6.8,8.8,9.8,10.9,12.9 a total of 10 grades, Under normal circumstances, if not specifically mentioned, are 4.8. For each level, the data in front of the decimal point represents 1/100 of the tensile strength of the material, and the number after the decimal point represents the material yield strength or 10 times the yield point versus the tensile strength ratio, so the higher the level, the greater the corresponding torque. ⑶ thread connector material thread connector material considerations, the connection on the thread, the consideration and thread fasteners to consider the same; for threaded joints, should also consider other forces, if because of Other forces are more likely to cause damage, you should first consider. ⑷ thread connection applications Different applications on the tightening torque requirements are different, such as the general telecommunications products in the operation of the threaded connection of the mechanical connection strength requirements are not high, but for heat, shielding, sealing, grounding and other occasions, Requires a large tightening torque. ⑸ The degree of lubrication and roughness of the joint between the threaded fastener and the connecting force The tightening torque is mainly composed of three parts, 50% is used to overcome the friction torque between the threaded fastener and the threaded joint, 40% Used to overcome the friction between the screw torque, the remaining 10% used to overcome the screw between the reverse torque. It can be seen between the roughness and the degree of lubrication also directly affect the size of the tightening torque, in order to ensure adequate preload, the rough joint surface connection, should use a larger tightening torque; and for smooth joints, A smaller tightening torque can be used.
4.1.2 Thread fasteners The shape of the head The company commonly used screw connection is mainly screw connection, the other has studs, through the heart capacitors, cable joints and so on. In the fastening assembly selection tool, should pay attention to the following differences: different head shape using different tools; fasteners different diameter tools used in different sizes; according to different standards require the use of fasteners using tools are also different. The shape of the head according to the required fastening tools can be divided into hexagonal head, hexagonal, with cross recess and hexagonal flower type (hexagonal flower type): hexagonal head - hexagonal sleeve, sleeve approved head, wrench Wait. Hexagon - hexagonal hand or hexagonal head. With cross-slot - cross-batch or cross-head, cross-slot use the most common, the following will be described in detail. With a word slot - a word batch, on the word slot, it is recommended not to use electric screwdriver fastening, so as not to damage the word slot. Cross-slot company's most commonly used fastener head shape is with a cross-slot fasteners, screw cross-slot common Z-type and H-type 2, commonly used H-type, H-type cross slot in the fastening need to add a certain The axial force. The shape and depth of the screw cross groove directly determine the choice of the cross and the crosshead, and the shape and depth of the cross groove will not only vary depending on the size of the screw, but also the shape of the crosshead head. (P), countersunk head (K type), semi countersunk head (O type), flat round head (T head), spherical cone head (B head), semi-round head (V head) , With flange head (PW head) and small head (head plate head). Note: Under normal circumstances, the same diameter of different head shape of the cross slot can use the same type of tool; in demanding cases, according to Table 7 requirements, so that semi-countersunk head (O type) selection of large tools, Pan head using small tool # 1.
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