During rotational molding, the mold exterior
surface is completely exposed to the air. In the oven,
the mold and the resin are heated by forced
convection of hot air. Therefore, according to the
heat transfer theory, the heat transfer rate at the free
surface of the metal mold will depend on the
temperature gradient of the mold surface temperature
and the oven temperature. The use of fins can
be better justified under conditions for which the
convective heat transfer is small (or the convection
coefficient is small) [8]. When the oven temperature
is high, the heat convection at the mold surface
increases as well. The effects of the enhancing fins
thus become less pronounced, as shown in Table 5.
Increasing the mold’s rotational speed also increases the convection at the surface. The enhancing effect of the fins reduces and the relevant HTR and CTR decreases accordingly (Table 6).