Temperature Control in Hot Runner System——Heaters

Hot runner system is always in thermal equilibrium status and heat loss must be compensated.

Elements that influence the heat balance of hot runner system are all kinds of variable factors and stable molds, injection molding machines and surrounding conditions. As a matter of fact, all various factors often act as the tool of auto temperature controlling. The deviation of hot runner temperature controlling must be kept to the minimum. The following initial conditions should be satisfied:

• Make sure every heating elements of hot runner system and pay attention to the process indicator.

• Implement the installation of heating elements in the structure.

• Identify the heating area and temperature test point.

Make sure the insulation:

• From the user’s point of view, the following requirements should be met:

• Durability

• Easy changed

• Resistance to mechanical damage, leakage and corrosion

• Safe and reliable connection

Heaters

Normally used heaters are:

• Coil or ribbon-coil heaters used to heat up nozzles.

• Cartridge or tube heaters used to heat up manifolds.

Usually, it is designed as two abreast heating coils inserted into a stainless steel and then filled with magnesium oxide which features high resistance and excellent heat conductivity. If the circular section of the heater is spirally connected to nozzle surface, the heat transfers mainly by radiation. For this reason, the density of hot runner at heater surface is restricted to 0.3W/cm².

A rectangular section or a flat ellipse of the heater coil, If the connecting surface of nozzles is big, part of heat conduction can help reduce heat load and improve heat balance. Hot runner density is 6~15W/cm² on this condition.

Heaters consist of a non-heating area which occupy at least 35mm of the heater tube. At the heater end near the nozzle is the place which thermocouple installs. Another non-heating area of 10-15mm is located there.

Casted in a knot or tube made of copper alloy, They all features durability, tolerate heat load and precise temperature control. Also they are easily replaced when damage occurs.