Research On Safety And Reliability Of Worm Gear Material For As-cast High-aluminum-zinc-based Alloy (ZA27) Elevator Traction Machine

In recent years,with the development of materials technology,the domestic elevator industry began to use the cast state high aluminum zinc base ZA27 which has simple production process,excellent performance,low cost and other advantages to make worm gear in elevator traction machine. However at present,experts and scholars for the cast state high aluminum zinc based alloy ZA27 research focuse on improving the comprehensive mechanical properties of material,the system studied aspects on material of worm gear in elevator traction machine is still blank,As material worm gear in elevator traction machine which lacked safety and reliability assessment, also did not formulate relevant technical indicators. With the increase of the elevator,the cast state high aluminum zinc based alloy ZA27 worm gear in elevator traction machine failure caused by accidents have also increased,the cast state high aluminum zinc based alloy ZA27 can be used to challenge the worm gear in elevator traction machine. Therefore,it is of great significance to the research on the safety and reliability of the cast state high aluminum zinc based alloy ZA27 material of worm gear in elevator traction machine.The failure analysis of the elevator traction machine which appeared worm gear teeth broken. The results show that the content of the principal components of the worm gear was in accordance with the content of the grade composition in the GB/T1175-1997 ?casting zinc alloy?. Tooth fracture is fatigue fracture,fracture source at the root part of the gear. There is pitting corrosion pit on the surface of broken tooth. There are some casting defects such as loose and porosity and inclusions on the first tooth loss,partial loose to form defect area.These defects cause local stress concentration,reduce tensile strength of the material,crack initiation and propagation in the defect. Under cyclic loading,he crack extending,finally broken tooth. It is proved that the probability of pitting on the surface of gear teeth is related to the distribution and size of the casting defects in the microstructure.To characterize microstructure and properties of high aluminum zinc based alloy ZA27 worm gear blank in elevator traction machine from different manufacturing processes,andwith the comparison of the properties of cast tin bronze,then to comprehensive analysis the influence factors of normal use of casting state high aluminum zinc based alloy ZA27 worm gear in elevator traction machine. The results show that the best production process is squeeze casting,the microstructure of the worm gear is dense,grain morphology is fine equiaxed grain;there is not loose and porosity and inclusions in key parts;its tensile strength is 412 MPa and elongation is 6.5%, impact energy is 53.5J,micro hardness for is 27.9HV.The friction coefficient is 0.101~0.118. And its mechanical properties are better than cast tin bronze.Using finite element analysis to establish the cast state high aluminum zinc based alloy ZA27 worm gear in elevator traction machine dynamics mathematical model and calculate worm gear stress in different conditions and analysis the calculation results of finite element.The results show that the maximum stress occurs in the root area;When the car load 125% of rated load and static or car load 110% of rated load to 9.8m/s2 acceleration at the bottom to start or car load 125% of rated load to 9.8m/s2 acceleration in underlying emergency braking of three extreme conditions,the traction machine failure which does not occur. Therefore,to control casting defect degree in the key parts of the worm gear,and the working temperature,the cast state high aluminum zinc based alloy ZA27 can used safety for manufacturing worm gear in elevator traction machine.