1. Most OEM ( Original Equipment Manufacturer) recommend that you pull and clean your screw at least once a year to check for signs of wear on both the screw and barrel. Excessive wear will reduce the output and efficiency.
2. You may have carbon build up at the root of the screw which result in black specks in your product.
3. Degraded polymer- build up on the back side of screw flight can cause taste and odor issues in some of your Food Contact Products.
4. With proper planning, you can pull and clean a 4 Inch screw and have it back into the extruder in 90 minutes or less when purging with Bamberko 9016 or Ultimax 9100 Purging Compound. This does not include time required to remove the die and barrel adapter.

Procedure

• Remove die, adapters, clamp rings, breaker plate and screen pack before starting to purge the equipment.
• Opening must be free of restrictions.
• Clean out previous resin from the hopper.
• Raise the extruder temperatures to 450 degrees F. Use temp. 450 - 550 F when purging ABS, Nylon, Polycarbonate, PET or other high temperature resins. Barrel temperatures should be kept within a 350-550 F(176-287 Celcius) range.
• Back out the pressure transducer and the rupture disc, 2 to 3 turns to protect the surfaces.
• After the extruder temperatures are reached, start the screw rotating at 80 to 100 rpms.
• Feed Bamberko 9016 or Ultimax 9100 Purging Compound into the extruder, a small quantity at a time.
• Observe the motor load (amps) to insure it can handle the load. Estimated amount of purge compound to use is 2 pounds per inch of screw diameter. The Purging Compound should come out unmelted to produce the scrubbing effect. One or two volumes of the extruder capacity are all that is needed.
• Minimize possible smoke and odor by purging into water.
• Clean out the hopper, run until the barrel and screw are empty.
• Immediately push screw out of the barrel and finish cleaning it with a wire cloth or a wire brush. This will prevent any of the purge compound, that is left on the screw, from melting to the screw.
• Clean the inside of the barrel with a flue brush on a copper pipe. Follow up with a cotton cloth draped over the flue brush to wipe the barrel clean.
• Make sure that all purge residue (dust) is removed from the hopper, feed throat, and barrel.
• Clean pressure transducer and rupture disc holes. Reapply anti-seez to the threads.
• Re-assemble the extruder.

Reprinted here with the permission of John L. Kelley and Earl E. Herriman Jr.