An electric thermal unit surrounded by a double air circulating interspace, for controllably heating cylinders in extruders, injection presses, and drawing machines for plastics, rubbers and the like

摘要

An electric thermal unit comprises a spiral coil resistance heater incorporated in a ring-like structure formed by mutually fastened ceramic strips. This structure is surrounded by two coaxial interspaces communicating with each other at the upper region of the cylinder mounting the structure itself. In particular, cooling air is admitted into the outer interspace and may be tapped, in a heated condition, off the bottom of the inner interspace for use in subsequent processing operations.