Monday, June 14, 2010

Trouble Shooting of Blow Moulding Process

Pitted surface appearance

Possible Reasons:

  • Air entrapment inside the mould
  • Condensation
  • Low Blow Rate
  • Low Blow Pressure

Possible Solutions:

  • Vent the mould to reduce the air entrapment.
  • Check mould finishing, polished mould causes air entrapment. Very coarse mould surface results in rough part surface. Sand blasted mould surfaces are usually desirable.
  • Check mould for condensation coolant temperature
  • Increase the size of air orifice to allow faster blow rate
  • Increase blow pressure.

Vertical groves and lines in the part

Possible Reasons:

  • Dirty and / or damaged die

Possible Solutions:

  • Clean die surface.
  • Scratches in die or core, to be removed
  • Check for contamination.
  • Set the parison straight to eliminate hold up in die.

Irregular markings on the part

Possible Reasons:

  • Water condensate or water leakage in the mould

Possible Solutions:

  • Run faster cycle.
  • Run warmer mould.
  • Stop leakage in the mould.

Rough part surfaces and / or poor gloss.

Possible Reasons:

  • Rough parison

Possible Solutions:

  • Increase die temperature
  • Increase mould temperature
  • Increase melt temperature
  • Increase extruder speed
  • Use low molecular weight resin
  • Clean die core

Rippling on parison / melt fracture

Possible Reasons:

  • Unsuitable die shape
  • Extrusion rate too high

Possible Solutions:

  • Increase die land
  • Increase die diameter
  • Reduce extruder speed

Thin areas or holes on the part surface

Possible Reasons:

  • Airflow in head is faster
  • Parison is not straight
  • Moisture in resin
  • Contaminated resin in head or die

Possible Solutions:

  • Reduce airflow through head
  • Set parison
  • Pre heat the resin
  • Clean the head and die core

Poor wall thickness distribution – longitudinal

Possible Reasons:

  • Parison sagging
  • Parison control not working

Possible Solutions:

  • Change extrusion rate
  • Decrease melt temperature.
  • Use low M.F.I. resin.
  • Check parison control timings.
  • Check parison control pressure.
  • Check flow control valve setting.

Poor wall thickness distribution- circumferential

Possible Reasons:

  • Non symmetrical parison
  • Non symmetrical article

Possible Solutions:

  • Set parison straight
  • Use larger die
  • Optimise article weight
  • Use larger die

Excessive dimensional shrinkage of article

Possible Reasons:

  • Low blow pressure
  • Insufficient cooling
  • Melt temperature is too high

Possible Solutions:

  • Increase blow pressure
  • Decrease mould temperature
  • Increase cooling time
  • Decrease melt temperature.

Warpage

Possible Reasons:

  • Insufficient cooling
  • Non uniform cooling

Possible Solutions:

  • Reduce mould temperature
  • Check for efficiency of water flow in mould channels
  • Increase cooling time.
  • Check efficiency of mould venting.
  • Provide more cooling, especially in pinch of area of the mould.

Parison doughnut formation

Possible Reasons:

  • Core temperature is low
  • Core gone inside the die

Possible Solutions:

  • Allow core to reach temperature equilibrium with rest of the system
  • Lower the core slightly (to get the weight of the article, reduce the core diameter)

Thinning or stretching at parting line

Possible Reasons:

  • Low blow pressure
  • Pinch off is too sharp

Possible Solutions:

  • Increase blow pressure
  • Check efficiency of airline
  • Widen pinch of land
  • Reduce head and die temperature

Parison tail sticking to the article

Possible Reasons:

  • Parison too long

Possible Solutions:

  • Shorten Parison length.
  • Increase pinch-of land to compression cool the tail

Black specks in parison

Possible Reasons:

  • Degraded resin
  • Hold ups in the die head

Possible Solutions:

  • Thoroughly clean and purge extruder. Avoid prolonged shutdowns with resin held at high temperature
  • Improve streamlining of the melt inside

Contamination

Possible Reasons:

  • Poor house-keeping

Possible Solutions:

  • Keep production area clean

7 comments:

Haresh said...

It's really helpful
I have been applied it.
This post will be just like a sanjivani who are facing various problems in his vertical moulding machine.

faizan said...

thanks,i take help.by applying these techniques I am able to solve the problem

Anonymous said...

hello
i have an straight dark line in a forward part of the bottle, it wsnt der earlier, strtd all of a sudden, cleaned head, barrel, screw and even changed machine bt i am still facing da same problem. hope to find a solution here.
thank u

Reuben said...

What is the propotion of Preblow and Support air. I am struggling to make good 20L drums using cut and seal knife. The drum has got a tape hole on the base.

Tasnim said...

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Anonymous said...

I am having a lot of trouble with leaking bottles at the mould vents. Blowing 2Litre HDPE milk bottles on a reciprocating screw blow moulder. The vent lines are quite noticeable on the finished bottle and at times the area of the vent is thin and causes leaks
Thank you

AG Poly Pack Pvt. Ltd. said...

The information which you have provided is very good. It is very useful who is looking for HDPE Bottles Manufacturer.