The Practical Processor: July 2010

Your Processing Questions Answered

Q. How do I know when it’s necessary to disassemble and inspect my melt pump? —Southeast extruder


A. There are five major reasons to disassemble a melt pump:

  1. The output of the melt pump at a given speed—independent of material, temperature and pressure—begins to decrease over time.
  2. A repeatable surface defect in the finished product is traced to the gear pump, indicating possible damage to internal parts.
  3. An increase in current draw from the pump with no changes of product, temperature, or pump discharge pressure.
  4. The pump seizes and will not turn.
  5. Degraded material is traced to the pump, or color will not purge and can not be corrected by normal purging methods.

Since the pump is a positive-displacement device, output is affected by four factors: rotational speed; viscosity; pressure/orifice (die); and pump clearances. If items 1 to 3 have not changed, but pump output changes, then the clearances in the pump have likely increased due to wear. Since only the manufacturer knows the dimensional specification of the pump parts, it is advisable to return the pump for inspection. If you are relatively confident that the pump is worn, and are experienced, you may replace the parts yourself, strictly following the manufacturer’s instructions.

Dan Smith, sales manager
Maag Pump Systems Inc., Charlotte, NC
(704) 716-9081 •