In Purging – Part III of our Feedscrew and Barrel Maintenance blog series, we will focus on a two-step purging process for scheduled equipment maintenance and disassembly. This includes a high-viscosity resin purge followed by a cast acrylic purge. The high-viscosity resin scours the flow surfaces of the extruder, adapter and die system and is done with the downstream components assembled. Once the high-viscosity resin purge is complete, a cast acrylic compound is then processed through the extruder after the downstream components are removed in an open discharge configuration. This cleans the screw and barrel and removes any remaining material from the extruder. And voila! You have a clean system.
Note: These procedures should only be conducted by trained personnel. Please consult your equipment operating manuals for considerations regarding your specific system. This may include adjustments in temperature and time based on materials, and the size and design of your equipment.
High-Viscosity Purge Procedure (First step)
For this procedure, a high-viscosity HDPE is used. This is an excellent cleaning agent, easily releasing from the flow surfaces of the adapter and die after disassembly of downstream components.
1. Run material out of the extruder.
2. Back out the variable depth thermocouples.
3. Set the barrel profile temperatures to 280°F.
4. Add HDPE to the hopper.
5. Purging should be done at 25 to 40 percent of normal run speed.
6. Watch head pressure as barrels drop.
7. When the material runs out of extruder (amps start dropping), shut off the extruder and follow the second step for the cast acrylic purge.
Cast Acrylic Purge Procedure (Second step)
Care must be taken before processing the cast acrylic. The cast acrylic will not flow through a breaker plate, adapter or die. The breaker plate, adapter and downstream equipment must be removed. Also, ensure there is adequate ventilation before performing this step.
WARNING: When working around the discharge end of the barrel with the downstream components removed, wear appropriate PPE (i.e. face shield, high-temperature resistance clothing and gloves). Hot polymer may splatter during the process and could result in serious burns to exposed or inadequately protected body parts.
1. Set the barrel profile to 350 degrees F.
2. Remove the downstream components from the system.
WARNING: Once the downstream equipment has been removed, there is exposure to a rotating screw. Do not put finger/hands or any tools near the barrel discharge as serious injury may result.
3. Starve-feed the cast acrylic compound slowly to the extruder (1-1/2 five-gallon buckets should be sufficient).
4. Watch the amps closely as the acrylic compound will easily amp-out the extruder.
5. Start purging the extruder at 5 RPM. Do not go above 20 RPM.
6. When the acrylic exits in a powdery form, the purge is complete. Let the acrylic run out entirely before extracting the screw.
7. Push out the screw and place on a cart. Remove excess material with copper gauze.
8. Clean the barrel with a wire brush and copper gauze.
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The D-S Connect Blog Team