Cleaning of Vent Hole
Procedures for Purging Vented Barrels
(Injection and Extrusion)
Background:
Vented barrels are typically used for applications in which volatile gasses need to be released – they are also used when hydroscopic (moisture-absorbing) materials are processed and moisture in the form of vapor must be released from the barrel. In this case, it is a less-expensive alternative to using dryers. It is also common to have vented barrels when a two-stage (barrier / mixing) screw is used (as shown above). Pressure increases within the barrel and is greatest at the point before the vent – this area represents a concentrated energy region (high pressure = high shear). For this reason, it is likely to find greater degraded contamination in this area. Pressure then drops sharply in the vent area and starts to build again after the vent.
ASACLEAN is a mechanical purge and requires agitation and pressure within the barrel to perform its best. Higher pressure allows ASACLEAN to better address the surfaces of the barrel and screw. Since there is little to no pressure in the vent area, it is likely that the ASACLEAN may not sufficiently remove all deposits.
Procedures:
These recommendations should be made if following our standard purging instructions has not proven successful.
- Use a vent plug or cap to close the vent – often, machine manufacturers supply plugs or the customer can make their own. Follow standard purging instructions. It is important to keep an eye on pressure gauges while purging to avoid machine damage or injury.
- If a vent plug is not available or a customer is reluctant to plug the vent, suggest adding ASACLEAN pellets directly through the vent while also feeding through the hopper. Note that these vents can sometimes be very small or even difficult to access and it may be necessary to feed the ASACLEAN pellet by pellet! Follow standard purging instructions.
- Vent-up method: For injection molding, block the nozzle and perform metering (turn the screw) while applying back pressure. ASACLEAN will be forced to come out of the vent. Continue until ASACLEAN coming from vent looks fairly clean. Proceed using standard purging instructions. This method can not be used for extrusion.
