| As a crucial part of high speed elevator,safety pliers was installed on the bottom of the lift car in order to ensure it can be safely clamped on the track during an event of an accident.With the development of the super high rise building,high speed heavy load elevator(operation speed is 4 to 8 m/s,some even as fast as 12.5 m/s;operation load is 16000 kg)is being used more and more frequently.Among many brake materials(such as rubbers,metals,ceramics and C/C composite materials),C/C composite materials are extensively valued by researchers around the world due to its high strength,high modulus,high temperature performance,low coefficient of thermal expansion(CTE)and excellent abrasive ability.However,there have not been many research literatures reported on the research and application of C/C composite material on the safety pliers material of the high speed elevator.As a result,this paper has studied the C/C composite material synthesized with chemical vapor infiltration(CVI)method using fiber produced domestically and abroad with different weaving structure,different pyrocarbon matrix structure and different volume fraction.In addition,the materials were analyzed using modern technique to study their mechanical property,thermal physical property and friction and wear performance.The main research content and conclusions are as below:1.The imported carbon fiber with different weaving structure and volume fraction was adopted to produce C/C composite materials.The friction and wear performance were also studied.The result mainly shows that:(1)The friction factor of the needle punched C/C composite materials(fraction volume: 25%;matrix structure: smooth layer pyrocarbon)increased as the friction load increased.(2)The volume fraction of the fiber(38% and 25%)does not have obvious influence on the friction factor and abrasion loss of the fibers punched through structure C/C composite material.2.The carbon fiber non-woven carbon felt needle punched perform(volume fraction 25%)was adopted as reinforcement,micro positive pressure and low pressure CVI technique were used to prepare the smooth layer and rough layer pyrocarbon matrix C/C composite materials of which the mechanical property and friction and wear performance were studied.The result mainly shows that:(1)Smooth layer pyrocarbon matrix C/C composite material has the compressive strength in XY and Z direction of 136.8MPa and 198.0MPa which were 66.6% and 36.4% higher than that of rough layer pyrocarbon matrix C/C composite.(2)The friction factors of smooth layer and rough layer pyrocarbon matrix C/C composite materials were relatively close with each other around 0.16,and were fluctuated as friction time increased.(3)Smooth layer pyrocarbon matrix C/C composite material have higher friction performance than that of rough layer pyrocarbon matrix C/C composite material.3.Domestically produced carbon fiber was adopted to weave needle punched structure preform and was densified using CVI process,followed with high temperature treatment.The mechanical,physical,friction and wear performance of the ultimate smooth layer pyrocarbon matrix C/C composite were studied with different heat treatment temperatures.The result mainly shows that:(1)With higher heat treatment temperature,comes with better dimensional stability of C/C composite material.Under 1500℃,No.13 specimen had a CTE of 6.4×10-6/K and dropped to 4.2×10-6/K after high temperature heat treatment.(2)Under the same braking test conditions of the C/C composite materials,compared with specimen No.1 with high temperature treatment,specimen No.13 with low temperature treatment has a shorter range of friction factor(No.13 materials:0.30~0.45,No.1 materials:0.20~0.50)),brake time(No.13 materials: 0.35~3.10 s,No.1 materials: 0.35~3.37s),and a slightly lower braking energy(0.50-6.00 k J).During the braking test,specimen No.13 with low temperature treatment experienced more stable friction and wear performance and higher brake efficiency.(3)Specimen No.11 dissimilar materials friction pair(C/C composite material and No.45 steel mate plate)has a brake time ranging from 0.35 s to 2.67 s,which is 0.7s shorter than No.11 same material friction pair;however compared with dissimilar material friction pair,No.13 dissimilar material has a slight increase of the dispersion of the friction factor.(4)The C/C composite material for friction brake block of safety pliers treated with low temperature exhibit excellent comprehensive property.Not only does the brake satisfy the technical requirement and test specification of the high speed elevator brake,it also maintains a relatively intact apparent structure with suitable friction factor,low wear loss and no obvious impact on the quality and service time of the steel track.Figure 41,table 14,reference 69. |
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