SPE Extrusion Division 1-0-Wiki



Extrusion 1-0-Wiki Pages

Search the Wiki


Account Management


Brought to you by:
The SPE Extrusion Division
Board of Directors


Heating Modes for Extruder Barrels:

Modified on Saturday, 31 January 2015 01:23 PM by mpieler Categorized as Consultants Corner
Heating modes for extruder barrels: on/off or true current proportioning
Vol. 16 #2, December 1989

In attempting to simplify the elements that are critical in the extruder barrel temperature control, below is a list of some of the areas that are of primary concern:

1. Type of extruder - L/D, size, screw type

2. Air cooled — controls, altitude of facility

3. Liquid cooled

— water
— treated
— chilled
— heat transfer mediums

4. Instrumentation

— Micro processes
— Fully instrumented
— Partially instrumented

5. Maintenance of the extruder

Although much has been written about these areas, we tend to treat problems on a specific area rather than the system, and at best not with a complete understanding of these areas. To control the Barrel heat and maintain melt control levels, the extruders should contain equipment (instrumentation) with the latest revisions in the system. Controls should be maintained and have the degree of accuracy required, preferably with the latest calibration equipment incorporated for each zone. Additional equipment (microprocessor) controls and limits established with alarm signals (audio or trouble lights incorporated). There should be a print-out (at time intervals) dependent on the material and management requirements. This is also another tool for SPC control. The maintenance of this hardware cannot be taken too lightly; if controls are not maintained, product control cannot be achieved. In general, older equipment, shorter L/D cannot achieve the melt flux or temperature required. Extruder size also is limited due to the product size and outputs (lbs/hr) required, and should be scaled accordingly. Screw type should be considered with special considerations to type of material to be processed.

On/Off Systems Air cooled — On/Off or true current proportioning Disadvantages:

1. If chilled air is not used, it is then dependent upon the ambient temperature with summer or winter room temperature differentials.
2. Altitudes above 5000 ft. re quire special blower motors.
3. Environment considerations— during summer months various insects can be drawn into the blowers or fitters — moths, mites, flies, etc.
4. Accuracy of air transfer through zones (although baffled) may over-ride into the next higher temperature (zone) causing a wider temperature drift.


1. Least expensive in temperature proportioning per zone.
2. Easy to maintain, if followed daily/weekly/yearly.
3. Lower installation costs — does not require specially treated water chiller systems with recycled water. Piping systems would require solenoid, valve, piping repairs/replacement, cleaning lime or mineral depositions from the system frequently.
4. As contaminates build up in the system, (as outlined in #3) control is also lost.

Water or Heat Transfer Medium Disadvantages:

1. Water must be treated — use of closed loop distilled water is recommended.
2. Piping, valves, solenoids must be constantly checked and cleaned or replaced.
3. Costly system to install (including chillers).
4. Leaks in system can be a hazard in the work area.
5. Heat transfer mediums require complete purging of system frequently (dependent on whether system is used solely for heating or cooling).
6. Available water storage tank, wells, or ponds with ambient considerations (winter freeze, summer heat).


1. Most efficient/fastest temperature proportionally.
2. Accurate controls — temperature spread is narrower.
3. Water is the lowest cost temperature change medium.

Recommendations Over the years, I have recommended an air cooling system due to the simplicity of he operation. When properly addressed, it can be an excellent system for control and machine operating system (for extruder barrels). Water or heat transfer medium control should be used when a higher degree of accuracy is required especially when high volume output or product size control is important. Extruder dies, however, cannot be cooled with air and should be heat transfer medium cooled. I would suggest that micro processor systems be incorporated into the system with closed loop elements for degree of control required.

— Frank Lichtey

See also:
  • A case for shorter heating zones in the feed section of extruders
  • Barrel and screw wear
  • Barrel heater maintenance and installation
  • Feed stability
  • Heater replacement
  • On/off barrel cooling control
  • Temperature control
  • Two stage extrusion
  • Water cooling extruders
  • Worn barrel repair

Return to Consultants' Corner
Some of the icons were created by FamFamFam.