| Erosion wear，especially the high temperature erosion，reduces the service life ofrefractories seriously, which whould affect the industrial production and even causegreat economic loss.Erosion wear tests were carried out at the sand blasting impact setunder room temperature and at the freely falling impact set at high temperaturerespectively with quartz sand，brown corundum and silicon carbide grain，on the threekinds of widely used alumina based refractories including Grade I high aluminabrick,grade III high alumina brick and silicon carbide－mullite brick.Surfaces oftargets and impacting particles after erosion were observed by SEM analysis.Effects ofhardness, particle size, and shape of the abrasives, erosion temperature, impact angle,and material properties on the erosion wear rate and erosion mechanism under differenttest conditions were studied systematically. Erosion models for such typical materials aslinear elastic and Johnson-Homquist (JH-2) in three dimensions exposed to the singleand multiple particles impact were proposed respectively to analysis the erosion processaccording to parameters of erosion experiments by means of a finite element dynamicanalysis software named ANSYS/LS-DYNA. Data relevant to the erosion process werecalculated such as displacement, stress magnitude and the distribution, contact time,energy, erosion rate, morphology on the worn surface,etc. The main studies werefocused on the effect of abrasive shape and particle size on the erosion wear rate anderosion stress of targets, which whould provide a theoretical basis for studies on theerosion of brittle materials.The results obtained in this paper are as following:The erosion wear rate was decreased with the increase of the circularity of the impact particles from the erosion test results，between which an exponential relationshipwith a value2.24of the abrasive shape factor is existed, indicating that the abrasiveshape of the impact particles plays a dominant role in the erosion experiment. Theerosion process of Grade III high alumina brick impacted vertically by erodent particleswith shape of sphere, cube and regular rectangular pyramid at room temperature wassimulated using finite element method model. Contact time,vertical indentation depthand impact efficiency resulted from the impact of cube and regular rectangular pyramidabrasives are about the same，and far more than those of sphere abrasive from thecalculation;the predicted decrease in erosion wear rate with the increase in thecircularity of erosion particles is consistent with the experimental results,but the valuesfrom the single particle erosion simulation are slightly lower than those from theexperimences while the values from the eight particle erosion simulation higher thanexperimental ones. In the experimental studies, the change in the circularity of theerodent particles is obtained through the selection of three kinds of erodent particles assilica sand, brown fused alumina and silicon carbide and the observation on theirmorphology by SEM. The erosion wear mechanism from impacting particles withobtuse angle e.g. silica sand is the resulted defects in microstructure and themicro-cutting of the matrix, meanwhile, the erosion wear mechanism impacted byerodent particles with sharp angle e.g. silicon carbide is intergranular and transgranularfracture of aggregates,other than the micro-cutting of the matrix.The erosion rate is changed little with the increase of the particle size of abrasivesimpacting on Grade III high alumina brick at an angle of30°, however there is a slightdownward trend at an angle of90°.The "grain size effect" is occurred when the particlesize of the abrasive is increased larger than0.28mm.The erosion rates are increased withthe particle size less than0.40mm of abrasives impacting on Grade I high alumina brickat both30°and90°, but they are changed little as the particle size is increased more than0.50mm.The"grain size effect" is happended only when the particle size is increasedlarger than0.50mm.The erosion process of Grade III high alumina brick impactedvertically by erodent particles with size0.27mm,0.40mm,0.50mm,0.80mm at roomtemperature was simulated by using finite element method model.The results are shownthat:in the erosion process, inside the contact zone the target is suffered compressive stress other than any tensile stress;the maximum tensile stress is occurred at theboundary of contact zone and outside the contact zone,which is increased with theincreased particle size of the abrasive;contact time,vertical indentation depth and impactefficiency are proportional to the particle size of the abrasive; in the multiple particleerosion model the erosion wear rate and maximum effective stress in targets will beincreased slowly with the particle size of the abrasive even greater than0.5mm,meaning that there is a deviation between finite element simulation results and erosiontest results. It is found in this paper that abrasives has been broken after the erosionprocess, whatsmore,the larger particle size of abrasive is, the more prone to breakout,which is considered to be the reason for the decline in the erosion wear rate.The influence of erosion temperature on erosion wear rate is deppened on theimpact angle. At impact angle of30°,erosion wear rate on both Grade I high aluminabrick and silicon carbide－mullite brick are increased at temperature lower than800℃at which it is obtained the maximum value and then it is decreased. At impact angle of90°,erosion wear rate on the two materials are decreased consistently with the increasederosion temperature. Erosion mechanism on two bricks are of the same: at impact angleof30°, erosion mechanism is mainly fructure happened in the defects and micro-cuttingof the matrix at temperature lower than800℃,but it is changed to micro-cutting ratherthan brittle fracture at temperature higher than800℃;at impact angle of90°, erosionmechanism is mainly the fracture and pull out of aggregates at temperature lower than800℃,and is changed to micro-cutting instead of brittle fracture.The erosion wear rates on Grade I high alumina brick and on silicon carbide－mullite brick are increased with the increased impact angle and reach the maximumvalue at90°at room temperature. At1200℃, the erosion wear rate on Grade I highalumina brick is increased slightly with the increased impact angle, remained a constantat angle more than60°,while that on silicon carbide－mullite brick is increased，reaching the maximum value at90°.Impact angle related to the maximum erosion wearrate moves forward at elevated temperature for both of the two materials.Influence of material properties on the erosion wear resistance is studied.It isimproved with the increased bulk density, strength and hardness, or the decreasedapparent porosity of the materials. The negative effects of the increase in apparent porosity on is far more serious than the positive effects of the increase in strength.It is shown from the erosion tests that the erosion wear rate is increased with theincrease in hardness of the erosion particle according to an exponential relationship witha hardness factor value0.27, indicating that the hardness of the abrasive excert littleinfluence on the erosion wear rate,in other words, it is not a dominant factor in thiserosion experiment. |
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