Trouble Shooting Guide

What: List of most common problems and solutions

When to Use: When you experience a problem, this is the starting point

Why to Use: To decrease downtime, increase speed of resolution, and decrease scrap

Troubleshooting Guide

Problem Action/Issue
Top side of pipe has uneven wall thickness around the corrugation a. Center the die tooling if not pre-centered with the bolts in the die body.

b. If pre-centered, check heater bands for uneven heating around die

c. If problem continues, remove centering spiders
Downstream corrugations are thinner than upstream corrugations a. Adjust blow pressure down on impacted side
Inner wall is not equal a. Adjust second stages center caliper with the centering bolts
Pipe walls are equal but inner and outer wall not fusing a. Pipe weight is too low
Only one side of the inner wall is loose a. Move the corrugator sideways toward the side that is loose
Inner wall has a sawtooth like appearance a. The mold blocks are moving faster than the inner liner melt stream
Inner wall not flat, it is carved into the corrugation a. Increase air pressure slightly

b. Recheck and repeat until solved
Inner wall not flat, it curves to the inside of pipe a. Decrease air pressure slightly

b. Recheck and repeat until solved
Large diameter double wall bell forming requires the outer wall NOT to be vacuum formed into the cuff blocks until the inner wall & cuff air can assist in lifting the plastic into the cuff blocks a. Vacuum pumps become highly inefficient during an approximate 10 minute timeframe

b. Vacuum pump overheating and oil expulsion are the unfortunate side effects
Thinning inner wall of the last corrugation prior to bell formation a. Related to the purposeful ‘thinning’ of the bell’s outer wall – the thinning of the bell’s outer wall is required to ‘hover’ the plastic above the 2nd stage outer caliper
Annular rippled bell surface located where the gasket seats on the inner surface of the bell a. This is caused by 10. the exterior bell stiffening ridges create the rippling effect
Bell thickening as one approaches the flared end of the bell a. caused by the need to slow the cuff formation process down while initiating cuff air – unfortunately, this thickens both the inner wall and outer wall at the same time, just in different locations as it relates to the bell
Bell flaring inwardly instead of outwardly a. due to bell thickening – can cause gasket rolling issues when assembling pipes

 

Problem Action/Issue
Small bubbles or clusters
  1. moisture in resin
Blow outs
  1. moisture in resin
  2. too high blow pressure
  3. melt temperature too high
  4. uneven wall thickness distribution
  5. corrugator and die not lined up
  6. resins of different melt characteristics
  7. wet re-grind material
Rough finish
  1. melt temperature too low
  2. mold blocks too cold
  3. blow pressure too low – worn seals
  4. wrong type of plastic
  5. fine impurities in plastic
  6. vacuum / vent slots in mold blocks are plugged
Drag marks
  1. plug too large
  2. pipe is too hot
  3. plastic sticking on plug
Large parting line
  1. top and bottom housing not lined up
Longitudinal streaks
  1. dirt in die
  2. scratch or dent on inside or outside caliper
  3. dirt in screen
Tube sticking to moldblocks
  1. moldblocks temperature too high
  2. internal cooling not working
  3. melt temperature too high
  4. aftercooler is not working
Die head back pressure too high
  1. dirty screens
  2. melt temperature too low

 

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