Preparation And Research Of Gypsum Casting Powder For High-performance Investment Casting

The rapid development of the manufacturing industry makes high-quality,high-precision parts more and more widely used,and the widespread use of precision parts has promoted the rapid development of the manufacturing industry.Investment casting gypsum-type precision casting technology has become an important bridge for rapid development between the two.Furthermore,the performance of investment gypsum casting has become the cornerstone of development of them.The fluidity of investment gypsum casting powder affects the success of grouting,and the strength and thermal crack resistance of the gypsum casting mold has a great influence on the complete filling of the molten metal,and the linear shrinkage of the gypsum casting mold affects the dimensional accuracy of the casting.Although investment gypsum molds are easy to form,their performance affects the quality of castings.This leads to the point of inquiry in this article-the casting performance of investment gypsum,the effects of fillers,additives and modified glass fibers on the casting performance of investment gypsum are studied,and the flowability of the casting powder of investment gypsum is analyzed by testing,The initial and final setting time and the strength,linear shrinkage,and thermal crack resistance of the gypsum mold,a more excellent gypsum casting powder formula was obtained,and the availability of investment gypsum casting powder circulation was further analyzed.The main contents are:(1)The effects of coal gangue and diatomaceous earth on the fluidity,setting time,mold strength and linear shrinkage of investment gypsum casting powder were investigated.Coal gangue and diatomaceous earth are porous refractory materials.Coal gangue and diatomaceous earth are mixed into gypsum casting powder at the same time.The roasted gypsum grains have good overlap,compactness and high mold strength.When the content of coal gangue is 20%and the content of diatomaceous earth is 10%,the flow diameter of the gypsum slurry is 90mm,the initial setting time is 7min,the final setting time is 17min,the wet flexural strength is2.02MPa,the compressive strength It is 2.3MPa,the flexural strength after firing is0.458MPa,the compressive strength is 1.07MPa,and the linear shrinkage is0.320%.When the coal gangue content is 10%and no diatomaceous earth is included,the flow diameter of the gypsum slurry is 240mm,the initial setting time is 13min,the final setting time is 26min,and the flexural and compressive strengths in the wet state are 1.17MPa and 1.78MPa,respectively.The flexural and compressive strengths after firing are 0.295MPa and 0.56MPa,respectively,and the linear shrinkage is 0.669%.(2)The effects of different additives on the fluidity,setting time and mold strength of roasted gypsum casting powder were investigated respectively.The additives mainly include polycarboxylic acid water reducer,melamine water reducer,silica sol And boric acid;with the increase of the amount of polycarboxylic acid water-reducing agent,it significantly enhances the fluidity of the gypsum casting powder slurry while seriously retarding the gypsum casting powder slurry.When the ratio of water:silica sol is less than 1:1,the silica sol can promote the fluidity of the gypsum casting powder slurry,prolong the setting time properly and enhance the strength of the gypsum casting mold.When water?silica sol is 4?1,the fluidity of gypsum casting powder slurry is best;when water?silica sol is 1?1,the strength of gypsum casting is best.Boric acid has little effect on the fluidity and setting time of investment gypsum casting powder slurry,but boric acid can significantly enhance the strength of gypsum casting.(3)The L9(3~4)orthogonal experiment method was used to investigate the length and dosage of the glass fiber after the silane coupling agent KH550 modified the glass fiber,and the curing time of the silane coupling agent KH550 on the surface of the glass fiber to the strength of the investment gypsum casting.And further explored the effect of glass fiber on the thermal cracking resistance of investment gypsum castings.The length and amount of modified glass fiber have a great influence on the strength performance of gypsum casting,and the curing time of coupling agent KH550 on the glass surface has a small effect on its strength performance.The flexural strength of the 10mm,0.6%fiber gypsum casting mold is 1.84MPa and the compressive strength is 1.91MPa,which is 178.79%and 17.90%more than the compressive strength of the gypsum casting matrix.It also have best resistance to thermal cracking.(4)The feasibility of reusing the gypsum casting powder by adding different contents to the original investment gypsum casting powder was analyzed.Through the loss of fluidity of the investment gypsum casting powder during the sample preparation process and the reduction of the strength of the test sample,it is concluded that the performance of reused investment gypsum casting powder is poor.Through the above experimental research,the formula of investment gypsum casting powder with excellent performance is obtained:gypsum:quartz powder?mullite?coal gangue?diatomaceous earth=35?8?27?20?10,the length of glass fiber is 10mm,the amount is 0.6%,water?silica sol=4?1.