Failure Analysis And Improvement Research Of Chain Grate Parts

Since the production process of chain grate machine-rotary kiln pellets was successfullyput into use in Shougang Qian in2000, this technology has been greatly developed in ourcountry. But in practice, chain grate parts are easily to fail because of improper selection ofmaterials and design deficiency, which results to great economic loss for the company. InXinyu Steel, the blast furnace pellets ratio has reached15%. But the production quantity ofpellets is only70000~90000tons for one month, which is far from the design capacity. And20000~30000tons of pellets are needed to buy from other company every month, whichleads to economic burden since the higher price. In order to increase self-produced pelletsproduction and economic efficiency, it is necessarily to reduce the fault rate.In Xinyu Steel, oxygenation loss of grate bed parts, deformation and fracture are the mainreason for failure for the parts of chain grate machine. In the present study, visual inspection,mechanical testing, chemical element analysis，metallographic analysis，linear expansioncalculation were used to explore the failure mechanism in detail. The antioxidant regularity ofheat resistant steel, the influence of various elements on the microstructure and mechanicalproperties of heat resistant steel constituent, and the material welding performance wereexamined. Based on the analysis, improvement experiments were carried out. The mainconclusions are as follows:(1) The working temperature is higher than600℃and the shear stress can be higherthan135.67MPa for the small shaft when it is used. In this condition,20CrMo is easy tocreep and fracture. And the2Cr13with addition of3%Ni and4%Mn can improve themicrostructure stability at high temperature, which satisfies the performance requirement ofsmall shaft parts.(2) The old grate plate structure was thin, and ZG30Cr26Ni5exhibited poor abrasion resistance and oxidation resistance at high temperature, which easily leads to failure. WhileZG35Cr24Ni7SiN can work at1100℃and shows better mechanical properties and oxidationresistance, so it is suitable to make grate plate and side panel parts.(3) The reason for oxidation burning of side panel mainly lies in the uneven distributionof pellets and the improper operation. The fracture failure of links is due to the displacementbecause of the loose of parts at high temperature.1Cr18Ni9Ti austenitic stainless steel wasused as slipping plate and the swing scale of the belt machine was adjusted to proper level,and so a better distribution of pellets can be achieved. Lock nuts were equipped on both sidesof the main shaft, and chain loose was prevented.(4) The addition of mandatory automatic reset device in the end of the chain gratemachine can force grate plate return and avoid empty of grate bed, it is also can play a goodprotective effect for the grate bed.