Study On Structure Optimization And Wear Resistance Of Straw Extruder Screw

With the gradual popularization of straw extruder applications,higher requirements are placed on the service life of the key components of the straw extruder screw.The research on extending the service life of the screw mainly starts from the structure and material of the screw.The rationality of the screw structure is one of the key factors affecting the service life of the screw;the optimized heat treatment system can obtain excellent wear resistance of the screw material and also plays a key role in extending the service life of the screw.At the same time,the screw structure is complicated,and it is also one of the difficult points to prepare a screw with high precision and high size.This article comprehensively considers the practical conditions of the screw and the three-stage theory of the screw,and rationally optimizes each parameter of the screw.At the same time,the screw is designed in sections to facilitate the production,transportation,processing and manufacturing of the screw.Material Research Through the heat treatment test of the screw material,the best heat treatment process is explored to obtain the best wear resistance.On this basis,the wear resistance test comparison and the study of the wear mechanism between different grades of high chromium cast iron were carried out.Finally,the screw was prepared by designing a lost foam mold and a 3D printed sand casting model.The research shows:(1)The structure parameters of the screw are optimized based on the three-screw theory of the screw.The screw diameter is designed to reduce the diameter.The solid conveying section is 84-90mm,the extrusion melting section is 70-90mm,and the metering and homogenizing section is equipped with a 70-84mm.The aspect ratio solid conveying section is set to 4.5,and the extrusion melting section is set to 2-3;the compression ratio solid conveying section plays a preliminary extrusion role,set to about 1.5,and the extrusion melting section is set to 2.2;The pitch is variable:S=πDtanβ;When the screw edge gap is set to 2mm on one side,the efficiency is the highest.(2)The heat treatment optimization of the screw material Cr20 high chromium cast iron was carried out.The optimal heat treatment process was explored:the quenching process was air-cooled at 990℃×1h,combined with primary tempering at 250℃×1h(air cooling)and secondary tempering at 400℃×1h.(Air cooling),at this time its wear resistance is the best.Better than Cr26 high chromium cast iron with higher Cr content,it can effectively save the cost of raw materials.(3)The wear mechanism of the abrasion resistance test is mainly divided into three stages.The first stage of the wear mechanism is that the substrate is a softer phase at the beginning of the wear.The micro-cutting process of the substrate is firstly performed;The contact changed to point contact,the stress concentration increased,and the edge s of the carbides were cut.In the third stage,the support of the matrix to the carbides decreased,causing the carbides to break off and increase weight loss.(4)The screw is a variable diameter and pitch structure.After comprehensive analysis,it is prepared by the lost foam casting method.Based on the structural design optimization,the lost foam mold is designed.The optimized heat treatment process is applied to the cast screw.The batch tracking statistics show that the average service life is 66%longer than before optimization.