When talking with customers who manage production scale extrusion I am often asked to comment on the amount of heat generated and the issues that this can cause. In reality it is just something that we have to live with as all extrusion processing will generate heat. The amount of heat generated will vary depending on the formulation of the product, the rate of extrusion, the physical specifications of the extruder and the type of extruder being used (screw, gear or basket are the common ones).
It is also noted that with some formulations and extruder types, compression of the material can cause water migration through the compressed material - exacerbating an already unwanted issue.
The generation of heat during the extrusion process is sometimes a useful and preferred part of the process but generally it’s something that is not welcome and for a constant process through the extruder of homogeneous product, this needs to be managed.
Management of the inevitable heat generation can benefit from two distinct approaches.
This is not always possible but in some cases the addition of a material to help the flowability of product can be used. The materials suggested may be:
1. a higher content of lubricants (such as calcium stearate, glycerine and mineral oil amongst others) and/or
2. glidants (such colloidal silicon dioxide) starch or talc amongst others)
In many cases the issue can be significant improved with a small amount of these materials added to the formulation.
Whilst all extruders generate heat, different types of extruders generate different amounts of heat.
1. Screw extruders generally develop the most heat
2. Basket (or screen) extruders generating a lower amount of heat
3. Gear extruders generate the least amount of heat for a fixed extrusion quantity
There will always be exceptions with different formulations but this is generally true. This is reflected in the fact that most screw extruders for productions have the facility to have water cooling, some production screen extruders (for example these from Caleva) have this facility for water cooling. There are no gear extruders with the facility for water cooling.
Finally, for some materials, it may also be important that a specific high temperature point is avoided. In these cases temperature measurements should be determined exactly and not determined by subjective guesswork. Both production screw extruders and production screen extruders offered by Caleva have remote temperature sensing with an instantaneous digital readout so that in the case of excess temperature, remedial action can be taken immediately. In addition, all Caleva production and screen extruders have the facility to have cold water circulating around the compression chamber to allow the removal of heat and thus manage a generally unwanted part of the extrusion process.