Study On The Optimization Of Synthesis Process Of Ester-hardened Phenolic Resin And The Regeneration Process Of Used Sand

At present,the casting industry is developing in the direction of green casting,so it is imperative to develop high performance casting binder and high efficiency used sand recycling technology.Ester hardened alkaline phenolic resin self-hardening sand has excellent technological properties,but the low strength of used sand and the difficulty of regeneration limit the popularization and application of this process.In this paper,the synthesis process of alkaline phenolic resin binder was optimized and its regeneration process was studied.First,the basic synthesis process of phenolic resin binder was determined through exploratory test:adding phenol,formaldehyde and 1/4 potassium hydroxide to three flasks,heating the solution slowly to 90?,reacting for 20 minutes⁴0 minutes,reducing the solution to 55?⁶0?by rapid cooling,adding the rest potassium hydroxide to three flasks,increasing the solution temperature to 95?meantime,reaction to viscosity of about 20s as the end of synthesis process,cooling to room temperature.The influencing factors such as phenol-formaldehyde molar ratio,phenol-potassium hydroxide molar ratio,reaction time and alkali catalyst were investigated through the optimization synthesis process.The optimum reaction conditions were determined by orthogonal test:the molar ratio of phenol to formaldehyde was 2.2,the molar ratio of phenol to potassium hydroxide was 0.85,and the reaction time of 90?was 40 minutes.The 24-hour tensile strength of the new sand is1.76MPa,and the content of free formaldehyde was reduced to 0.08%by adding dealdehydes.Secondly,aiming at the problem of difficult regeneration of ester-hardened phenolic resin used sand,the tensile strength and burning reduction of recycled sand were examined by mechanical method,thermal method and wet scrubbing method,mechanical impact method,thermal mechanical impact method respectively.The test results show that the wet scrubbing regeneration effect is acceptable,the mechanical impact method and the thermal mechanical impact method have better regeneration effect,and the 24h tensile strength of the regenerated sand by the thermal mechanical impact method can reach 0.52 MPa.Finally,a composite reinforcing agent of reclaimed sand was prepared by using double-fast cement and micro-silica powder,which further improved the tensile strength of reclaimed sand.When the addition ratio of double-speed cement and micro-silica powder is1:1,and the addition is 1.2%of reclaimed sand,the reinforcing effect was the best.By means of scanning electron microscope,the cracks in the binder after the addition of the reinforcing agent are greatly reduced;and the phenolic resin is investigated before and after the reinforcing agent is added by using the infrared spectrum,and the analysis is that the quick-drying cement can be hydrated with the adhesive,The micro-silicon powder reacts with the cement hydration product Ca?OH?₂ to form the C-S-H gel,and the micro-silicon powder can cross-link with the resin binder.