Study On Water-Based High Alumina Coating For Sand Casting

Sand casting is the most widely used casting method,brushing coatings on the surface of sand mold(core)is an effective measure to reduce casting defects and improve the quality of castings.Shandong is an important source of flint clay.Using the dust collection powder that is produced during the production of ceramic casting sand with flint clay as refractory aggregate to prepare casting coatings,not only realized the reuse of solid waste,reduced the discharge of solid waste,but also reduced the production cost,which has important practical significance.Therefore,the research work on the preparation of casting coatings using the dust collection powder produced from the preparation of ceramic casting sand as refractory aggregate was carried out.With the method combining experimental research and theoretical analysis,the rheological and thixotropic properties of commonly used suspending agent was studied.It was found that the aqueous solution of sodium-based bentonite with concentration less than 10.5% exhibited plastic fluid characteristics,and the aqueous solution of sodium-based bentonite with concentration greater than 10.5% showed pseudoplastic fluid characteristics with yield value.With the increase of solution concentration,viscosity and yield value increased.The aqueous solutions of sodium-based bentonite with concentrations of 5.5%,6.5%,7.5%,8.5%,9.5%,10.5%,11.5%,and 12.5% all had thixotropy,and as the concentration increased,the thixotropy increased.The concentrations of 7.5%,9.5%,11.5%,and 12.5% lithium-based bentonite aqueous solutions exhibited plastic fluid characteristics,as the concentration increased,the viscosity and the yield value increased,and it had low thixotropy only when the concentration reached 12.5%.The aqueous solutions of attapulgite with concentrations of7.5%,8.5%,9.5%,10.5%,11.5%,12.5%,13.5%,and 14.5% showed plastic fluid characteristics as a whole,and all had thixotropy.The aqueous solutions of CMC with concentrations of 1.0%,1.5%,2.0%,2.5%,3.0%,and 3.5% exhibited pseudoplastic fluid characteristics.When the concentration of CMC aqueous solution was low,it had little thixotropy.The suitable kinds of suspending agent,binder and defoaming agent were determined bysingle factor experiment.Sodium-based bentonite and CMC were used as the suspending agent,PVA as the binder,and mineral oil defoamer as the defoaming agent.The mineral oil defoamer was added half before and after ball milling,and the coating needed to be aged for48 hours.The effects of the addition of sodium-based bentonite,CMC and PVA on the properties of the coating were also studied.It was found that with the increase of sodium-based bentonite content,the anti-flow performance improved,the leveling time,coating thickness,suspension rate,viscosity and yield value increased,the pseudoplastic characteristic was more obvious,and the thixotropy improved,but the abrasion resistance changed little.When the addition amount of sodium-based bentonite was 5% of the refractory aggregate,the leveling property was poor,the thermal exposure crack resistance was grade ?,the number of cracks on the coating surface was large,the width was large,and the addition amount of sodium-based bentonite should not exceed 5% of the refractory aggregate.With the increase of the addition amount of CMC,the coating thickness,suspension rate,leveling time and viscosity of coating increased,but the anti-flow performance,abrasion resistance,yield value and thixotropy of coating changed little.With the increase of the addition amount of PVA,the coating thickness,suspension rate and viscosity increased,the abrasion resistance improved,but the changes of leveling time,yield value and thixotropy of the coating were not much.When the addition amount of PVA was 2% of the refractory aggregate,the abrasion resistance of coating was high.With orthogonal test,the main factors affecting the performance of the coating were studied,and the suitable formula of the coating was determined.The performance of the coating under the appropriate formula was also researched.The main factor affecting the coating thickness,fluidity,leveling,24 h suspension rate and 48 h suspension rate of the coating was sodium-based bentonite,and PVA was the main factor affecting the abrasion resistance of the coating.Based on the amount of refractory aggregate,the suitable formula of the coating was:100% aggregate,4% sodium-based bentonite,0.4% CMC,2%PVA,0.4% mineral oil defoamer,and the amount of water was appropriate.Under the proper formula,the leveling,anti-flow performance,abrasion resistance,drying crack resistance and thermal exposure crack resistance of coating were excellent.There was no cracks on the surface of the coating,and the suspension rate of the coating was 100% in 24 h and 48 h.It was a pseudoplastic fluid withthixotropy and yield value.The particle size of the refractory aggregate in the coating was alternated between coarse and fine,which maked the coating more compact.The bond bridge between the refractory aggregates was good.Through casting experiments,it can be obtained that the coating with proper formula can effectively prevent the casts from adhering sand defects.