Sweating operations were explored for various crystalline layers obtained in layer melt crystallizations. The crystalline layers used in sweating operations were obtained under the conditions of the cooling rates of 0.1, 1 and 5 K/min, and the feed compositions of 80, 85 and 90 wt% caprolactam mixtures. The purification effects of sweating parameters including the sweating time, amount of inclusions entrapped during the crystallization operation and the p degree of superheating were investigated. The crystalline layer formed in higher growth rate is purified more easily by C sweating operations. The more the amount of inclusions in the layer, the faster is the removal of impurity in sweating operations. (C) 2002 Elsevier Science B.V. All rights reserved.