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 is disclosed for controllably heating cylinders in extruders and drawing machines for processing plastics, rubbers and the like. The electric thermal unit comprises a spiral coil resistance heater 4 incorporated to a ring-like structure 1 formed by mutually fastened ceramic strips 2. Said structure is surrounded by two coaxial interspaces 9,17 communicating with each other at the upper region of the cylinder 6 mounting the structure itself. In particular, cooling air id admitted into the outer interspace 17 and may be tapped in a heated condition, off the bottom of the inner interspace 9 for use in subsequent processing operation.