Research On The Modified Furan Resin Used In Warm-box And Composite Curing Agent

To develop a core binder and a hardening process with a high binding strength,a low cost,an energy conservation and a good working condition,is the basic requirement for foundry production.Compared with the hot-core box process,the warm-box process decreases the heating temperature of the core box and is beneficial to the energy conservation during the coremaking procedure and the on-site labor protection of the operators.Firstly,a new and efficient furan resin used in warm-box process was prepared in this paper.According to the comparison of different types of furan resin,a phenolic modified furan resin was selected as the binder main body.Through the analysis of the reaction principle of phenolic modified furan resin,the main influence factors in the process of synthesis were determined,and the exploratory synthesis tests were carried out.On the basis of the exploration experiment,two orthogonal tests were done,and the optimized synthesis process of furan resin for warm-box was as followed: molar ratio of phenol to formaldehyde was 1:2.5,the percent of furfuryl alcohol was 55%,the pH value of alkaline reaction was 8.0,the reaction time was 60 min,the reaction temperature was 85?;the pH value of acidic reaction was 5.0,the reaction time was50 min,the reaction temperature was 90?,the amount of dehydration was 55% of the amount of formaldehyde,the viscosity was 56.0mPa?s,the content of water was 4.30%,the content of free formaldehyde was 0.21% and the content of nitrogen in the resin was 2.0%.Then,the preparation of the composite curing agent was studied.The single factor explorations were carried out on the acid species,metal salt species,solvent species and the addition of acid.Then according to the results of the exploration tests,the two groups of orthogonal tests were done,and finally the optimal ratio of composite curing agent was:phosphoric acid: compound salt: water=6:3:1,the composite salt ingredients was: ferric chloride:magnesium chloride: aluminum chloride=2:3:2.After been optimized,some of process performance were test,and performance indicators of furan resin for warm core box used in foundry were: core box temperature was 200?,the hardening time was 40 s,the addition of resin was 2.5% of the sand,the addition of composite curing agent was 20% of the resin,the hot tensile strength was 0.95 MPa,the room temperaturetensile strength was 3.23 MPa,the content of free formaldehyde was reduced to 0.09%,the collapsibility of the sand is good,the gas evolution is low,and the sand mixture can be used for4 h,all the indicators above can meet the requirements of casting production.Finally,the prepared furan resin was characterized by infrared spectroscopy,and the bonding bridge morphology of the sand core was observed by scanning electron microscopy and the type of fracture was a compound one.