2.5. Shrinkage and warpage measurements
The shrinkage and warpage of rotomolded polyethylene parts was examined. Shrinkage of the parts was measured along the length of the box. Parts were kept at room temperature in an upright position for at least 24 h before measuring shrinkage or warpage. To measure shrinkage, two small
cuts were made in the mold wall at exactly 50mm apart. The positions of these cuts showed up sharply on the polyethylene parts, and the distance between them was measured. On the other hand, the warpage of rotationally molded parts was measured on the ‘‘flat’’ top part of the boxes in
a 1010mm2 mesh as the vertical distance of a mesh-node from the ideal plane. A Mitutoyo
profile-meter was used to measure the warpage. The mold itself did not show any measurable warpage.