Comparative study of warpage, global shrinkage, residual stresses, and mechanical behavior of rotationally molded parts produced from different polymers

Abstract

A comparative study of warpage, global shrinkage, and residual quench stresses developed in rotational molding is made for a series of thermoplastics including various polyethylenes, polypropylene, polyamide-6, polycarbonate, and polystyrene. The influence of rate of quench on uniaxial stress strain and impact behavior of rotomolded parts was also studied. Generally, warpage, global shrinkage, and residual stresses increase with increasing quench rate for all the polymers. Further, the levels of warpage and global shrinkage increases with extent of crystallization, i.e., products from glassy polymers exhibit little warpage and those from highly crystalline polymers are highly warped. Increasing rate of quench tends to increase elongation to break and impact strength.

Simulation of heat transfer during rotational molding

“…The geometry of the system has been assumed to be constant, even if during the process the polymer experiences a continuous specific volume decrease as a consequence of sintering phenomena 22,45,46 during melting and crystallization effects during cooling. 7,47,48 The numerical values of parameters listed in Eqs. (6)- (20) are shown in Table I.…”

Warpage–crystallinity relations in rotational molding of polypropylene

“…In earlier experimental works on RM [4][5][6], warpage has been related to cooling rate, crystallinity, and the effect of mold release agent. In [5], Bawiskar and White related warpage to residual stresses as measured by a layer removal method. Studying metallocene polyethylene (PE), Pop-Iliev et al [7] concluded that warpage increased with increasing part thickness.…”

Rotational moulding of polymers

“…Some studies claim that the warpage and shrinkage are related to the cooling process (Shih-Jung and Chung-Yuan, 1999;Bawiskar and White, 1994). The level of shrinkage correlates with the extent of crystallization during solidification and is minimal in vitrifying plastics according to tests performed on polyethylene, Nylon-6, polycarbonate and polystyrene (Bawiskar and White, 1994).…”