Manifold heating and insulation

The heaters used for external heating of plate manifolds are of the cartridge or tubular resistance type operating on 230 V AC current. Tubular manifolds are heated by 230 V coil heaters or low-voltage 24 V or 5 V, heaters. 

Cartridge heaters in a metal body (available on the market) have a very high heating power, which, in combination with their small dimensions, enables a power density of as much as 40 W/cm to be achieved (for comparison, the power density of a band heater is around 5 W/ cm ). To prolong the life of a heater and to reduce the risk of local overheating in the manifold, it is best not to exceed a value of 20 W/cm. This applies to cases where the user/mould manufacturer selects the heaters himself. The heaters are set in reamed holes symmetrically positioned on both sides of the flow channels (wall thickness minimum 10 mm). 

Cartridge heaters may be cylindrical or conical in shape (see Chapter 5.1). 

K - distance between nozzle and end of manifold (Reproduced with permission from HOTSET Heizpatronen und Zubehoer GmbH) 

It depends not only on the heating method, but also on the insnlation method and the way the manifold is supported, i.e., its cooling curve. Typical of externally-heated manifolds is rapid cooling of the ends of the manifold (measurement points 1 and 6). This is why a certain minimum distance K between the nozzle and the end of the manifold is maintained. 

---