Some Helpful Hints on Grooved-Feed Extruders
There are a few things that are different between these and their smooth-bore cousins that processors should know.
Melt pumps are not normally used with grooved-feed extruders. Remember that grooved-feed extruders build their pumping pressure from the groove section, whereas a smooth-bore extruder builds it through the transition and metering section of the screw. This is primarily the reason for the the instability of a smooth bore, and also why it generally has less capability to overcome pressure. Grooved-feed extruders, on the other hand, are much more stable and capable of pumping against much higher pressures, and therefore don't need a melt pump to the same extent as a smooth-bore machine.
Another thing about grooved-feed extruders: they cannot be vented. This has been tested many times in Germany and in the U.S., never successfully. A grooved-feed extruder builds pressure in the rear of the screw, or directly in front of the groove bushing area. This area is typically the high-pressure area along the length of the screw, where resin is actually being pushed through the screw. If you try to vent, the screw will just push the resin right out the vent port.
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