SHRINKAGE AND PARTICLE PACKING DURING REMOVAL OF ORGANIC VEHICLE FROM CERAMIC INJECTION MOLDINGS.
J EUR CERAM SOC
109 - 116.
Alumina suspensions, containing 50 and 57 vol.% ceramic in isotactic polypropylene and microcrystalline wax, were prepared by high shear mixing and injection moulded. The test bars produced were heated in air at 5 degrees C h(-1) to four different temperatures in the range 155-225 degrees C and up to about 25 wt% of organic vehicle was removed. Shrinkage in the bars was measured after cooling to room temperature. The difference in the coefficient of thermal expansion of the suspension during heating and cooling, the changes in the crystallinity of the polypropylene and wax compared with the as-moulded state and the mobility of the ceramic particles due to removal of the organic vehicle are contributory factors to the measured shrinkage. The anticipated dimensional changes due to the first two factors have been determined experimentally and thereby the change in particle packing in the inner regions (core) of the test bars due to the mobility of the ceramic in the suspension have been calculated. Results shout that in both suspensions heating to just above the softening point caused appreciable particle packing. Subsequently, particle packing decreases substantially and the reasons for this are discussed, taking into account thermal expansion of the organic vehicle, capillary migration of the microcrystalline wax, loss of organic vehicle and development of porosity. Comparison of results with previous investigations show that particle packing is affected by the rate of heating and the atmosphere used during pyrolysis. Particle packing, during pyrolysis, in the more concentrated suspension (57 vol.% ceramic) was, as expected, smaller, except at 225 degrees C, when the core of each test bar containing this formulation showed a steep increase in weight loss. Otherwise, both formulations show similar trends in particle packing during the initial stages of the removal of organic vehicle.
|Title:||SHRINKAGE AND PARTICLE PACKING DURING REMOVAL OF ORGANIC VEHICLE FROM CERAMIC INJECTION MOLDINGS|
|Keywords:||MOLDED CERAMICS, BODIES, BINDER, MOLDINGS, FORMULATIONS, DEGRADATION|
|UCL classification:||UCL > School of BEAMS > Faculty of Engineering Science > Mechanical Engineering|
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