Heating a mold with hot air may seem inefficient and that is the thought process developers have used to ingeniously create oil jacketed rotomolding machines. By circulating a heated fluid in a jacket surrounding a mold, more heat is concentrated directly on the target area and this yields lower costs when heating the materials to high temperatures. For example, polycarbonate materials require a high temperature and this method is considered successful for operating with this material.
This concept has been used on commercial machines such as the Leonardo automated rotomolding machine; this machine has been developed to run tooling which heats and cools the parts using an external jacket containing oil. Shown here is the fully automated Leonardo rotational molding machine (Reference, equiplast):
Disadvantages to using this type of machinery include the high temperature at which the oil is circulated; should there be any leaks, there are safety concerns such as injury or fire. Oil can also leak from rotating joints which also releases fumes and can possibly contaminate the plastic resin.
However, even though these disadvantages are present there are significant advantages with respect to product consistency and production control.