Research On The Humidity Resistance Of The Sodium Silicate Sand Hardened By Microwave

Sodium silicate,green binder,is often used in sand mould casting.The casting process of sodium silicate sand can reduce the casting pollution and conform to the time background of green casting.With the development of microwave heating technology and the upgrading of microwave equipment,the microwave hardening process of sodium silicate sand has become possible.The instant strength of sodium silicate sand is high after microwave hardening.However,the strength of sand mold in the wet environment decreases greatly,which brings a lot of inconvenience to the actual production.If the microwave hardening process of sodium silicate sand is to be applied in a wide range,it is the general trend to find a new method and approach to solve the problem of moisture absorption of sand mold.The effects of microwave heating time,sand mold placement position and other parameters on surface temperature and macroscopic mechanical properties of sand mold were systematically studied.The results show that when the heating time of the first microwave is 30 s,the second microwave heating time is 40 s,the microwave power is 700 w,the mass fraction of the sodium silicate is 1.5%,and the heating position of the sand mold is the center of the disk,the microwave energy utilization rate is high and the sand mold performance index meets the casting requirements.Through the comprehensive analysis of the storage strength,moisture absorption rate and micro-bonding bridge of the microwave hardened sand mold,it is determined that the storage strength is the main index and the moisture absorption rate is the auxiliary index.Through single factor experiment,the humidity resistance of sand mold was improved from the perspectives of reducing the number of hydrophilic sodium ions and targeted microwave heating.The results showed that polyquaternium-7,polyquaternium-10,castor oil potassium salt,silane coupling agent KH-602,silane coupling agent KH-570,titanate coupling agent CS-201,tremella fuciformis sporocarp extract,lithium tetraborate,ethylene diamine tetraacetic acid,and graphene all had effects on the hygroscopicity of sodium silicate sand.Among them,the polyquaternium-7 is more effective in improving the storage strength and moisture absorption rate of sand mold in the constant temperature and humidity tank for 4 hours.When 4% polyquaternium-7 was used to modify sodium silicate sand,the increase rate of strength was 68.97% and the decrease rate of moisture absorption was 27.34%.The best formula of modifying sodium silicate sand with the action of various modifiers was explored by means of orthogonal experiment to improve the humidity resistance of microwave hardened sodium silicate sand.The results showed that 4% polyquaternium-7,0.5‰ lithium tetraborate and 0.3% graphene were the best solutions.After the mixed reagent was used to modify sodium silicate sand,the storage strength improvement rate of the sand mold in the constant temperature and humidity tank for 4 hours was 58.49%,the indoor strength improvement rate was 50%,the moisture absorption rate of the constant temperature and humidity tank for 4 hours was 0.38%,it is possible to modify the sand mold with multiple reagents and multi-angle action.In this paper,the coating process of sand surface was discussed,the optimal process flow was determined,and the results of single and combined coating tests were compared.The results show that the coating procedure should be carried out immediately when the surface temperature of sand mold reaches 90-100? after microwave hardening;the coating effect of PE film is better than that of EVA film with the same thickness;the decrease rate of strength of coated sand mold in 10 days was 13.93% of PE film and 13.38% of EVA film respectively;the strength of the sand mold decreased by 8.85% in the combination test,the instant strength and surface temperature of the sand mold were higher than that of the single coated sand mold.The laminating process can isolate the moisture into the sand mold from the source and improve the humidity resistance of the sand mold.