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Knowledge of high strength bolts

Update:11 Jul 2017
Summary:

   Bolts made of high-strength steel or bolts requiring […]

   Bolts made of high-strength steel or bolts requiring greater pretension are all called high strength bolts. High strength bolts are used for bridge, rail, high pressure and extra high pressure equipment. The fracture of this bolt is mostly brittle fracture. High strength bolts applied to ultra high pressure equipment, in order to ensure the sealing of the container, the need for greater prestress
    With regard to the concept of high strength bolts, 1., according to the provisions of the performance of bolts in grades 8.8 or above, known as high-strength bolts. Now the national standard is only listed to M39, for large size specifications, especially the length of more than%10~15 times high-strength bolts, domestic production is still short-term.
    From the strength level point of view: high-strength bolts are used more and more widely. Commonly used 8.8s and 10.9s two intensity levels, of which 10.9 are mostly. Ordinary bolt strength level should be low, generally 4.4, 4.8, 5.6 and 8.8.
    From raw material: high strength bolts are made of high strength materials. High strength bolt screw, nut and washer are made of high-strength steel, 45 steel, 40 commonly used steel, 20 manganese titanium alloy steel, 35CrMoA etc.. Plain bolts are commonly made of steel, Q235 (equivalent to A3 in the past).
    From the force characteristics: high strength bolts apply pre tension and friction force to transfer external force. Ordinary bolt by bolt shear and hole wall pressure to transfer shear, tighten the nut when tension is very small, the effect is negligible, and the high strength bolt in addition to its material strength is high, a lot of the bolt pretension, the connecting member is generated between the extrusion pressure, so that the perpendicular to the direction of the screw a lot of friction and pretension, anti slip coefficient and steel types have a direct impact on the bearing capacity of high strength bolt.
    According to the force characteristics, it can be divided into pressure bearing type and friction type. The two methods of calculation are different. High strength bolts minimum specification M12, commonly used M16~M30, oversized bolts, unstable performance, should be used carefully in the design.http://www.lwhardware.com/