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Figure 2-8. 2-3.6 CORNER RADII Rao and Throne experimented with the aluminum corner mold shown in Fig. 2-8. Corner angles of 45, 75, 90, 135, 165, 180, 225, and 240 deg were included in this mold together with a 1 X 1 in. square section, and indentations with radii of 1/16, 1/8, 3/16, 1/4, and 1/2 in. Rotational molding with many plastics in this mold has shown that rarely will the 45- and 75-deg and 1/16- and 1/8-in. test areas be free of voids. For materials such as impact styrene or ABS, even 90-deg, 135-deg, and 3/16-in. test areas were incompletely filled. The square section was rarely filled, regardless of the material used. Based on this testing it is concluded that, for most materials, mold radii of 3/16 in. and parting lines placed on 180-deg walls are the safe lower limits for avoidance of voids in part surfaces1. 2-3.7 FLAT PANELS Flat panels should be avoided because they will shrink away from the mold as they cool, especially if they are cooled too rapidly with consequent warpage and brittleness. 2-3.8 CORE SECTIONS, RIBS, AND HAN- DLES Core sections can be made. Deep ribs, kissed off, and handle areas should be designed with a greater taper than normal for easy part removal. A 6- to 8-deg taper is recommended for crosslinked polyethylene4 . Deep handle core sections and other deep core sections that kiss-off from one side of the mold to the other should have an opening for hot air passage through the mold as illustrated in Fig. 2-9. This will help prevent thinning due to air being static in the bottom of the core section. 2-7 16" '< 12 " »1 1 " 1i 1/2UR ISS^N/^ V"\223° \. K |3SM i/4" R— a 14" J63» . 1/ v\ vwR^y l/W R ..„>*PDF Image | ROTATIONAL MOLDING OF PLASTIC POWDERS
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