Research On A New Crosslinkling Agent Of CO₂Cured Phenolic Resin Binder And The Mechanism Of Crosslinking

The foundry industry plays an important role in the machinery industry, with therequirement of environmental protection,it is very urgent to prevent the pollution problemin casting production,and it is more and more important to develop the binder materialsand process with no pollution. So a new crosslinking agent of phenolic resin binder and themechanism cured by CO₂were researched in this paper.First, theoretical analysis had been done on the principles of resol synthesis and theinfluencing factors, an optimization of the synthesis process was studied and a bestsynthesis process was determined as follwed:KOH was used as catalyst, the amount offormaldehyde （nP/nF） was1/2.0, the amount of catalyst （nOH-/nP） was0.2/1, theformaldehyde was added in a directly manner, the materiel was slowly warmed to90°C,and kept in the temperature for1hour, and then kept at85°C temperature for a certain timeuntil the viscosity reached35S.Secondly, the resol resin was used as a main part of the binder with waterglass as acrosslinking agent and alkali as a dispersing agent, silane as a coupling agent to form thebinder system, and the ratio of each component was selected by experiment. Throughorthogonal test,the optimum proportion of them: the amount of resol resin was49%to thebinder, the amount of NaOH was22%to the binder, the amount of water glass was28%tobinder, the amount of silane was1.0%. because the initial strength of the binder wasvery low, a acrylic acid was used as a modifier at the late of synthesize of resol resin, aappropriate amount of Ca（OH）₂was added into sand and the initial strength was0.82MPa,the final strength achieved3.25Mpa.Next, by means of nuclear magnetic resonance spectroscopy and infraredspectroscopy, the structure of phenolic resin was determinated and characterited and thehardening mechanism of binder was analysed as followed:with amont of CO₂blown intothe sand,the PH of the binder system was reduced and crosslinking between the silicate anion and the phenolic hydroxyl of resol resin happened to built a certain initial strength; ahigher final strength thereby was obtained with a further crosslinking andpolycondensation of the binder system in the next more time.Finally, process performance of the resin binder was tested and the results showed thatgas evolution of binder was lower and collapsibility of binder was good. By verification ofproduction and economic analysis, the binder was shown with a high practical value.