[en] To manufacture good-quality, uniform CR-39 nuclear track detectors, the polymerization rate should be chosen below a critical value to avoid the development of undesirable thermal gradients and internal temperature fluctuations in the sheet being cast. To improve curing cycles, especially for thick Cr-39 sheets, a computer programme was developed by which the trends of thermal effects under different casting conditions can be studied. The calculations are based on the solution of the one dimensional heat transport equation, taking into account the relations for describing the chemical kinetics of CR-39 polymerization. The empirical parameters available to such calculations were revised. With new 'Dial constants' the critical initial bath temperature (which results in thermal runaway at the central plane of the sheet being cast) was calculated as a function of the CR-39 thickness and IPP initiator concentration. Results are also presented for the temperature profile developing in the depth of cast Cr-39 sheets. (author)