The Mechanism Research Of Heat Transfer And Friction In The Feeding Process Of WPC Extrusion

WPC(Wood Plastic Composites)is made by biomass fiber and plastic resin with polymer interface modification,through molding process such as extrusion,injection and molding,it is green environmental protection material and can be recycled.WPC has double properties of wood and plastic and can be applied to the fields of wood and plastic application,it is one of research priorities of current world environmental protection materials and has broad prospects,significant economic and social benefit.The most commonly processing method of WPC is extrusion molding.It is easy to have "bridging" phenomenon that leads to feeding discontinuous in the feeding process because of the wood powder fluffy property;And the cellulose molecular chain of wood powder contains a lot of hydroxys that have intense hydroscopicity.The moisture and volatile substance must be removed in WPC process,or products easily have stress concentration defects.The research works for these matters as follows:(1)It was firstly studied that the heat transfer characteristics of some commonly raw materials of WPC in this paper.Using semi-infinite body transient heat conduction theory model,the relationship between thickness and time and temperature rate of change over time in the materials temperature rising process have been analysed,and combining with finite element analysis and experiment,the thermal characteristics of materials were studied.Raw materials temperature gradient at any time reduced with thickness increasing and temperature rate of change reduced in the same thickness with time increasing;The experimental results were similar to simulation,temperatrue rapidly increase at first,and then wood powder temperature was fluctuant up state,HDPE and PVC were steady and then slowly increased because materials contain moisture and wood powder has more water.(2)The friction mechanism between raw materials and metal plate has been studied.Material friction properties play an important role in conveying,changing of friction coefficient influences conveying.Material friction coefficient is up to self-characteristic of friction system interface,and is influenced by temperature,pressure,sliding speed and contacting time of interface.This subject focuses on the influence of materials friction coefficient by temperature.(3)The friction coefficient of some commonly raw materials of WPC in different temperature has been tested by direct reading type variable temperature coefficient of friction tester,and variable temperature friction properties have been analysed,data references for conveying equipment designing were gained.The test results showed that wood powder friction coefficient increased with temperature increasing;PP aggregates friction coefficient increased with temperature increasing;HDPE powder friction coefficient reduced with temperature increasing,materials became softening and sticky when temperature was close to 110?;PVC powder friction coefficient increased with temperature increasing at first and then reduced,and rised again with fluctuant state,materials became softening and sticky in 80 0C;The greater the size,the smaller friction coefficient;Wood powder friction coefficient higher then the PP,HDPE and PVC;The mixture of wood powder and PVC friction coefficient with temperature changes overall reduced at first and then rise.(4)According to the materials heat transfer and variable temperature friction characteristics,using Pro/e 3d design software design two kinds of preheating dry and mixing feeding systems:double helix skateboard feeding system and straight back feeding system.Two systems feeding principle and structure parameters were introduced in detail,and two feeding systems materials stress state when feeding were analysed,providing technology references for practical production feeding system.