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Scheme
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Vice broken bolt coupling causes and prevention

Views: 53Date: 2013-09-12Typeface: Big Small
Common failure mode bolt loose in turn break the trip , such as several cases , analyze the causes , which are summarized as the following aspects :

1 , the stress and fatigue factors : Usually fasteners shearing , tensile, bending , compression, etc. The stress in four different ways , sometimes one or two combined stress , and sometimes there are some stress when several stress is applied to the bolt , in particular the case of overload , the bolt is prone to fracture. Under all load conditions for a long time , due to various stresses cross effect , resulting in fatigue , fatigue failure is the most common site of the tooth root Park , threads, and the screw at the threaded coupling , cross- stress producing a fatigue failure , such damage to account for about 80% of the total failure to use appropriate materials , use a larger size, increase strength to enhance the ability of the fastener resistance to stress .

2 , there is corrosion Corrosion is a major cause of bolt fracture , corrosion of general corrosion, chemical corrosion , electrolytic corrosion and stress corrosion , and other. It is worth mentioning that the electrolytic corrosion , most people do not know this corrosion when different materials connected pairs, fastened to the workpiece , since the electrolytic potential of each material type will result in the flow of electrons to form a " micro- cells" , in a wet environment, electrolytic corrosion is very serious. Serious electrolytic corrosion important humid environment , to take protective measures , the first to try to cut off the air , keeping the packaging of dry to prevent corrosion generation.

3 , high-strength bolts produce hydrogen embrittlement hydrogen embrittlement is a fatal flaw in the event of an external force , it is prone to fracture. Hydrogen embrittlement There are two main causes , one is internal, generated by the material smelting , this rarely happens . The second category is external, in pickling , plating free state is generated hydrogen atom , will be embedded into the substrate and spread , destroy the original state of equilibrium lattice distortion generated in the breakage under the action of external forces . Effective solution is to use dehydrogenation annealing .

4 , design and technology in the design of the tooth root neglected garden or in the rolling , the sharp cusp ; in hot molding screw wrinkles , pits . These sharp corners, grooves produce is the source of cracks in the design and manufacture of attention should be paid to this problem, avoid potential cracks. Bolt in the process of quenching and tempering brittleness to encounter the second category , such as possible to avoid the generation of temper brittleness .

5, the installation and connect the installation torque is within the predetermined range , the torque is too small, preload is too small , or the working state of the vibration less prone to loosening the locking force , but the torque is too large or exceeds a predetermined value , screw in the ultra- service load conditions , when the combination of various stresses applied, it is prone to drawing, tripping cause failure . Therefore, according to the specified torque for installation. In particular to understand the various materials, various surface treatments torque coefficient , using the correct torque value to prevent connection Vice lapse. When mounting coupling surface roughness and vice vertical links will also affect the use of sub- surface roughness installation part to overcome the friction loss torque tightening force correspondingly reduced. Vertical well, from the point when tightened into a surface contact with the contact process, a portion of torque loss , and tightened, the bolt head transverse stress increases , prone to break the head .

6 , the material and heat treatment according to the strength requirements to select different materials , the higher the strength , the content of alloying elements to increase, if the ordinary carbon steel, no Cr, Mo, V and other elements , the matrix strength of the difference in the effect of multiple stress prone to fatigue and fracture. Heat treatment is also very important factor in the process of bolt quenching and tempering, tempering at a high temperature area , prone to sulfur, phosphorus and other impurities , impurities in the grain boundary segregation , resulting in brittle fracture , especially when the hardness in HRC35 degrees, tend to be more serious brittleness . In short bolt coupling vice fracture involves a wide range , a careful analysis , especially to keep the specimen fracture , maintaining its original state , understand the material , hardness, use the installation and a series of circumstances in order to make the right judgments , for nature take appropriate measures to effectively prevent the failure or bolt fracture .