Preparation And Hardening Process Of Modified Water Glass With Compound Hardening

The method of CO₂ hardened water glass sand has been used for more than 70 years in foundry.It has the advantages of fast hardening,low gas evolution,non-toxic,low cost in the production process and sufficient raw material resources,etc.It is a kind of environment--friendly inorganic binder.However,many problems have plagued foundry workers for many years,such as the amount of water glass is high?6%-8%?,a poor collapsibility,a low level of regeneration and strong moisture absorption capacity.In order to solve these problems in this study,the water glass was modified to improve the bonding strength and collapsibility of the sand,the hardening strength and anti-moisture absorption of sand core were improved further more by add of powdery hardening agent.Through the optimization of the composite hardening process of the powdery hardening agent+CO₂+compressed air,the optimum technological process was determined and the problem of over blown of CO₂was solved.Under the addition 2%of binder,hardened by the powdery hardening agent+CO₂+compressed air process,a good comprehensive technological property was got then.First of all,water glass was used as the main body of binder in this paper.In order to further improve the tensile strength of the binder,the method of organic and inorganic compound modification were carried out.The variety of the modifiers were determined by comparison test.The optimum ratio of the modifier was determined by the orthogonal test.The results showed that the best ratio of compound modifier was as followed:water glass:potassium hydroxide:A agent:silane:sodium hexametaphosphate=1000:80:5:1:4.Then,on the basis of the composite modification of water glass,the processes of the composite hardening process of powdery hardener agent+CO₂+compressed air was further selected and optimized.Through the test,some kinds of the powdery hardening agent were selected and compounded,and the optimum ratio of the hardening agent was determined by orthogonal test,that is:microsilica powder:coal powder:N powder=3.5:0.2:0.4.The tensile strength was used as the test object of the blowing air process,and the optimum combination of the parameters of the hardening process was determined through orthogonal test.The process should be:the blowing flow of CO₂ is 30LPM,and the blowing time of CO₂ is 25s,the blowing flow of compressed air is 30LPM,the blowing time of compressed air is 45s.The viscosity of the modified binder is 140mPa·s,and the density is 1.23g/cm³.under the addition 2%of binder?to sand weight?,the addition of powdery hardening agent?to sand weight?0.41%,blowing air time of 70s,the sample's instant tensile strength can reach0.27MPa,4h tensile strength can reach 1.09MPa,24h tensile strength can be 1.28MPa.The core sand has a good flow ability,a low gas evolution and a good collapsibility.Overall,it has a good comprehensive process performance.Finally,the production verification test was conducted.When the modified water glass binder and the compound blowing process were adopted,the test results showed that the core making was rapid,sand core surface was smooth,the strength of core was very high,casting corresponding surface was bright and clean,and the cores could be cleaned easily.It showed that the material and hardening process can meet the requirement of casting production.