| Copper alloy are widely used in mechanical,electronic and marine fields because of their excellent electrical and thermal conductivity,corrosion resistance and wear resistance.The copper mold casting has the advantages of good technological performance,high dimensional precision and good casting surface quality.However,the thermal conductivity of the copper mold is good,and the cooling rate of the alloy solution is fast,and the failure modes such as wear are prone to occur.The castings are prone to defects such as air holes,cold septa,and insufficient pouring.In this paper,a new type of mold surface treatment coating was developed aiming at the problems of short mold life and casting surface quality during the casting process of the copper alloy water meter shell,focusing on the influence of coating formulation and spraying process parameters of the water meter housing on coating performance.The influence of different proportion of refractory filler on the properties of metal casting coatings is experimentally studied.The results show that when the amount of refractory filler is talc 55%,mica powder 20%and boron nitride powder 25%,the comprehensive performance of the metal-type coating is good.Through the single factor test method and the orthogonal test method,the effect of different content of suspending agent and binder on the performance of the coating was studied,and the formula of the water meter shell copper mold coating was optimized.The best coating formula(mass fraction of refractory filler):talcum powder 55%,mica powder 30%,hexagonal boron nitride powder 15%,sodium bentonite 6%,CMC 0.5%,water glass 10%,sodium hexametaphosphate 1.2%,solid to liquid ratio 1:2.The morphology of the mold coating under different spraying process parameters was analyzed by SEM,Stereomicroscope and other means.With the increase of die pretreatment temperature,the pores and cracks on the surface and interface of the coating decrease first and then increase.When the preheating temperature of the mold is 240,the surface of the coating is dense and smooth,the refractory filler on the coating interface is dense and has no crack.At this time,the quality of the coating is the best and the adhesive strength of the coating is high.With the increase of spraying distance and pressure,the holes and cracks on the surface of the coating appear to decrease first and then increase.When the spraying distance is 20cm and the spray pressure is 0.4MPa,the surface of the coating is smooth without cracks and holes.The surface quality of the coating is the most.The morphology and properties of the optimized coating were analyzed by SEM,wear resistance and adhesion test methods.The results show that the coating surface after the optimization of spray coating process is smooth and dense,and the interface between the coating and the substrate is tight and there is no obvious crack.The coating has good adhesion and wear resistance.The thermal resistance of the coating was analyzed by thermogravimetric analysis.The results show that the thermal weight loss of the coating at 969°C is only 15.27%,which has good thermal stability and chemical stability.The influence of two different mold surface treatment coatings on the surface quality of dies and castings is analyzed through experiments.The results show that the developed new coating has good environmental protection performance,high bond strength between the coating and the mold surface,no peeling of the coating,better protection of the mold surface from erosion and wear of the alloy liquid,and prolongs the service life of the mold;The mold has good mold release,smooth surface,dense internal structure,no shrinkage cavity and porosity,porosity and cold septum defects,and effectively improve the surface quality of the water meter shell. |
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