Heater Band Profile

The heat profile of conductive heat generated with heater bands is probably the most important and perhaps least understood factor in successful plastics processing. An incorrect heat profile is the single most important cause of wear in barrels and screws! Why? Because of the natural tendency to cool down the heater bands when a heat override condition occurs. Because most heat overrides are caused by excessive shear heat, the best way to decrease shear is to apply more, not less conductive heat. It will not increase the temperature of the melt but instead, change the source of the heat energy used to melt the plastic. It is the uncontrolled, excessive shear of material that causes most abrasive wear and, through melt blockage and screw deflection, adhesive wear. In addition, too much shear heat may cause extensive damage to the quality of the melt and have a negative impact on the physical properties of the plastic part.

What can you do?

We suggest that you measure the hydraulic pressure or electrical energy required by the screw motor during screw recovery. Readings of 800 to 1,200 PSI (on a 2,000 PSI system) suggest that the heat produced from shear energy is ranging from 40% to 60%, a desirable range. Greater pressure indicates that the screw is working very hard creating potential excessive shear. Lower readings, under 800 PSI, suggest that too little shear energy is being used, resulting in non-uniform melt temperature and viscosity.

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