Study On Surface Modification Of Flat Die Of Granulator Based On Laser Cladding

As the critical component of the flat die granulator,the flat die was subject to the press roll’s extrusion pressure,the feed particles’friction,and the heat generated by the extrusion for a long time.The flat die wear is severe,affecting the granulator’s working efficiency and service life.In order to study the wear of flat die,this thesis uses Glycyrrhiza uralensis as the wear material to study the wear mechanism of the flat die.In order to improve the wear resistance of the flat die surface,Ni60A/Ti C composite coating was prepared by laser cladding with Ni60A as the base powder and Ti C as the reinforcing phase by selecting the flat die sample as the research object.First of all,through the orthogonal test and friction and wear test,the influence of different process parameters on the quality of the cladding layer was studied,and the combination of process parameters was optimized.Then,the cladding layer’s phase composition,microstructure,element distribution,wear resistance,and corrosion resistance was analyzed.The effect of adding h-BN and SiO₂ on the microstructure and properties of Ni60A/Ti C composite coating was studied,and the optimal powder material ratio was finally determined.The main work and conclusions are as follows:（1）The wear characteristics of glycyrrhiza powder and glycyrrhiza rod on carbon steel（20Cr,20Cr Mn Ti）and stainless steel（4Cr13）flat die materials were studied.Compare and analyze the microstructure and element content of three kinds of the flat die surface wear marks.It found that the wear mechanism of glycyrrhiza on the flat die is mainly abrasive wear,adhesive wear,and fatigue wear,and a thermal oxidation reaction accompanies the friction surface.The damage of the glycyrrhiza rod to the flat die is more severe than that of glycyrrhiza powder.When the loading force is 30 N,the friction coefficient of the 20Cr Mn Ti flat die and glycyrrhiza rod after wear is 0.88,and the average wear depth is 2.0μm,which is lower than the wear parameters of the 20Cr and 4Cr13 flat die.20Cr Mn Ti flat die has good wear resistance and plastic resistance.（2）The influence of laser cladding process parameters on the forming quality of the Ni60A/Ti C cladding layer studied.Three factors and three levels of orthogonal experiments used dilution ratio and microhardness as indicators.It found that the factors affecting the quality of the cladding layer were powder feeding speed,scanning speed,and laser power from the largest to the smallest.The optimum combination of process parameters obtains by analyzing the coating’s structure,element distribution,and wear resistance:laser power 1.4 k W,scanning speed 7 mm/s,and powder feeding speed 21 g/min.Under this process parameter,the worn form of the coating is mainly abrasive wear,and the wear depth is 8.20μm.Compared with 20Cr Mn Ti,the wear depth of the matrix is reduced by 82.1%,and the wear resistance of the composite coating is significantly improved.（3）The effect of h-BN content on the microstructure and properties of the Ni60A/Ti C cladding layer was studied.The cladding layer’s phase composition,microstructure,element distribution,tribological properties,and corrosion resistance were analyzed.The results showed that with the increase of h-BN content,the hardness and wear resistance of the cladding layer first increased and then decreased.Hard phases such as Ti C and Cr B precipitated in the cladding layer,and adhesive and abrasive wear occurred on the worn surface.0.75%h-BN cladding layer has the best wear and corrosion resistance,with a friction coefficient of 0.66 and wear depth of 5.92μm.Compared with the matrix,the wear depth is reduced by87.0%,and the self-corrosion current is reduced by one order of magnitude.（4）The effect of SiO₂ nano powder content on the microstructure and properties of the Ni60A/Ti C cladding layer was studied.The results show that with the increase of SiO₂ content,the hardness and wear resistance of the cladding layer first increase and then decrease,and the corrosion resistance of the cladding layer decreases.The addition of nano-SiO₂ increases the density of the coating produces hard phases such as Ti C,Cr B,and Si C in the coating,and adhesive wear and abrasive wear occur on the worn surface of the coating.The wear resistance of 1%SiO₂ cladding layer is the best,the friction coefficient is 0.66,and the wear depth is 7.15μm.Compared with the substrate,the wear depth is reduced by 84.4%.The 0.5%SiO₂cladding layer has good corrosion resistance;the self-corrosion current is the smallest.