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 Trouble Shooting


The main faults in the Machine may be of three types: Electrical, Mechanical or Hydraulic. Electrical faults may be due to loose contacts or malfunctioning of any of the instruments. Hydraulic faults include damaged oil seals, non-development of system pressure or non-working of solenoid valves. The general faults and remedies are given below:

On every fault ensure whether the power supply is reaching the concerned solenoid coil, if not, electrical fault exists. Then you check the circuit and get the solution. If supply is reaching, then either hydraulic, pneumatic or mechanical fault is there. Please note that on each hydraulic operation power should reach the unloading valve (wire no. 49) and (wire no. 68) concerned solenoid coil.

Mould Opens while air blow is on. This will result in a weaker parting line of the article. The possible causes are:

1.      Oil seal of the clamping cylinder is leaking inside. To check this, set the cooling time to maximum and turn off the system. Loosen the opening pipes from the cylinder and press the "Close" push-button. If the seals are damaged, the oil will leak from them.  Hence, replace them.

2.      Oil leakage in the pipeline of closing, in between the manifold block and cylinder. Tighten the pipes if necessary.

3.     Pilot operated check valve is leaking. This will cause pressure drop in the closing system. The leakage may be caused by small foreign particles in the spool of the check-valve. Clean the valve with kerosene.

Mould Does Not Close. First check whether the supply is reaching the solenoid coil of OPEN-CLOSE valve (wire no. 73). If power does not reach, check the following:

1.      Wire no. 73 is coming from the Limit switches (LS-6&7) at the Stretching unit. Supply to these Limit switches comes from the Closing Contactor through Opening Contactor, Unloading Timer and AUTO MANUAL Selector switch (wire nos. 27, 25, 38 & 71).

2.      If the Closing contactor is not energising, check the supply to the contactor coil (wire no. 33) from "Closing" push-button. If the supply  reaches, then check the coil and replace if necessary.

3.      If power supply is reaching the solenoid coil and the valve is not energising, the solenoid coil should be replaced.

4.      If power is reaching and valve is energising, check the hydraulic pressure. Hydraulic system pressure should be developed with any of the hydraulic operation.

5.    For non-development of pressure, check whether power is reaching the Unloading valve solenoid coil (wire no. 49) & (wire no. 68). If not, trace the line as discussed earlier. Note that the line for wire no. 49 and wire no. 68 are coming through wire no. 28 and Unloading Timer.

6.   If supply reaches the unloading solenoid and it doesn't energise, the solenoid coil should be replaced.

7.      If unloading valve is energising and pressure is not developing, then the unloading valve may be faulty due to foreign particles inside. Clean the valve using kerosene and re fit.

Mould Does Not Open. If mould not opens while working in either AUTO or MANUAL modes, check the electrical supply is reaching and valves are operating properly.

1.      Check whether power is reaching to the Opening solenoid coil (wire no. 37). If not trace the line coming through the wire no. 26 and Closing Contactor.

2.      Check the opening contactor is energising or not. If supply is not reaching trace the line to contactor coil wire no. 31 and if supply is reaching check and replace the contactor coil.

3.      If supply is reaching the Opening valve solenoid coil, check and if necessary replace the solenoid coil.

4.      If the opening valve is energising, check whether the system pressure is developing or not. Trace the line for unloading valve (wire no. 49), (wire no. 68) and check the solenoid coil. If the valve energises and the pressure is not developing, dismantle and clean the unloading valve and the main Relief valve.

5.      If both the valves are working and pressure is developing satisfactorily and still the mould does not open, check whether the check valve is OK. There is a small pilot line in the manifold block which connects the opening line to check-valve. It activates the check-valve during opening and it should not be blocked.

System Pressure Not Developing

1.      Check the power supply (wire no. 49) & (wire no. 68) to the unloading valve & main valve with any of the manual function. If it is not reaching trace it with the hydraulic control circuit.

2.      If the supply is reaching and solenoid coil is not energising the coil is to be replaced with new one.

3.      If the coil is energising and pressure is not developing, the unloading valve is faulty. Dismantle and clean it.

4.      Also check for leakage in any of the pipelines. If there is a leakage pressure may not develop.

Parison Not Dropping

1.     Check whether the supply is coming to Accumulator solenoid coil wire no. 44 or not. It comes from Accumulator Contactor through wire no. 19 and Half-Close Timer.

2.   If the power is not coming from the Accumulator Contactor, check if the contactor is energising or not. The power for coil comes through wire no. 35. Replace the contactor coil if it is not energising even after the supply reaches.

3.      If power reaches the Accumulator valve solenoid coil, check whether the solenoid is energising with power. If not replace the coil.

4.      Check whether the pressure is developing. If not check the wire no. 49, wire no. 68 and unloading valve.

5.      If the pressure is developing and valve is actuating check whether the Accumulator is filled with molten material or not.

6.      Check the heating in the Accumulator Head and ensure sufficient heating is attained. If You are restarting the Machine and not emptied the Accumulator when You shut off, it will take double the normal time to attain heating.

7.      Check the Flow Control Valve in the Hydraulic circuit on the Accumulator B line. If it is closed fully the Parison will not come out.

Parison Control Not Functioning

1.      Check the Parison Control Time. It should be less the Parison Length Time.

2.      After completion of the Parison Control Time the Parison control Cylinder actuates and the Core comes down. The movement is controlled by the Parison Control Nut in the top of the Parison Control Cylinder. If the nut is in fully closed position, the Parison Control will not work.

3.      Check the Flow Control Valve in the Parison Control Circuit. If it is fully closed the Parison Control will not work.

4.      Check whether power reaches the Parison Control valve coil. If not trace the supply (wire no. 45). It comes from the Accumulator Contactor through wire no. 20 and Parison Control Timer.

5.      If the power reaches the valve and the coil does not energise, then the coil has to be replaced.

6.      You can check the Parison Control only by taking the Parison. This is due to the fact that the Parson Control Cylinder actuates by the Parison push out pressure and not by the Hydraulic. The Hydraulic pressure only holds the Cylinder in the UP position and the pressure drops when the solenoid coil energises.

Clamping Slow Down Not Functioning

1.      Check whether power reaches the Slowdown Valve Solenoid coil (wire no. 68). It comes from the Closing Contactor through wire no. 43 and Slowdown Limit switch LS-2

2.      If the power reaches the solenoid coil and not energise then replace the coil.

3.      If the valve actuates and the required slow down is not achieved, check the Flow Control Valve in the Slow Down Circuit. The slow down can be adjusted by setting the Flow Control Valve.

Blowing Does Not Take Place

1.      Check whether the power reaches the solenoid coil on the Blowing Valve. If not check the line (wire no. 66). It comes through the Blowing Limit switch and Cooling timer.

2.      If power reaches, check the solenoid coil is energising or not, if necessary replace it.

3.      Check the pipeline for any damage.

Stretching Unit Not Functioning

1.      Check for any mechanical misalignment or loosening of the bolts and nuts.

2.      Check the pipeline for any damage.

3.      Check the air pressure.

4.      Check whether power is reaching the respective coil or not and trace the circuit if necessary.

5.      If the solenoid coil is not energising even after the supply is reaching the coil, replace it.

6.      Check the exhaust port of the Pneumatic valve, and ensure it is not blocked.

Noise in Hydraulic System.
If excessive noise is coming while hydraulic motor ON check the following.

1.      Check the mounting bolts of Hydraulic motor and pump. If necessary tighten them.

2.      Check the SPIDER on the pump motor coupling. If it is worn-out replace it.

3.      Check the Hydraulic oil filter. If it is blocked with foreign particles clean with kerosene and air stream.

4.      Check for the oil leakage in the system and rectify.

Feeding Of Material Is Improper.

1.      Check the temperature at the feeding zone, i.e., first zone. Too high and too low temperature results in feeding problem. Adjust it as per the requirement and quality of the resin.

2.      Check the cooling water circulation through the Barrel Cooling Jacket. If necessary, clean the cooling jacket.

3.      Remove the head from Barrel and clean the Breaker Plate inside. If some foreign particles blocked the small holes in the Breaker plate, the resin flow through it will be reduced.

4.      Note that if overheating caused the feeding problem, reduce the heating and put some strips of article, i.e., 2 or 3 cms wide and 2 or 3 mm thick, to the feeding zone manually. It will clear off the overheated resin from the feeding zone.



Possible cause

Suggested Solutions

Pitted surface appearance

Air trapped inside the mould





         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 grooves and lines in the part.

Dirty and / or damaged die

         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.

Water condensation or water leakage in the mould.

         Run faster cycle

         Run warmer mould

         Stop leakage in the mould

Rough part surfaces and / or poor gloss.




Rippling on parison / melt fracture.


Rough parison




Unsuitable die shape


Extrusion rate too high

         Increase die temperature

         Increase melt temperature

         Increase extruder speed

         Use low molecular weight resin

         Clean die core

         Increase die land

         Increase die diameter

         Reduce extruder speed

Thin areas or holes on the part surface.

Airflow in head is faster.

Parison is not straight.

Moisture in resin.

Contaminated resin in head or die.

         Reduce airflow through head.


         Set parison.


         Pre-heat the resin.

         Clean the head and die core.

Poor wall thickness distribution - longitudinal -

Parison sagging.



Parison control not working.

         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.

         Check parison control nut opening.

Poor wall thickness distribution - circumferential -

Non-symmetrical parison


Non-symmetrical article.

         Set parison straight.

         Use larger die.

         Optimise article weight.

         Use larger die.

Excessive dimensional shrinkage of article.




Low blow pressure.

Insufficient cooling.


Melt temperature is too high.

Insufficient cooling.

         Increase blow pressure.

         Decrease mould temperature.

         Increase cooling time

         Decrease melt temperature.

         Reduce mould temperature.

         Check for efficiency of water flow in mould channels.

         Increase cooling time.



Non uniform cooling.

         Check efficiency of mould venting.

         Provide more cooling, especially in pinch of area of the mould.

Parison doughnut formation.

Core temperature is low.

Core has gone inside the die.

         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.

Low blow pressure.


Pinch-off is too sharp.

         Increase blow pressure.

         Check efficiency of air line.

         Widen pinch-off land.

         Reduce head and die temperature.

Parison tail sticking to the article.

Parison too long.

         Shorten Parison length.

         Increase pinch-off land to compression cool the tail.

Black specks in parison.

Degraded resin.


 Hold ups in the die head.

         Thoroughly clean and purge extruder. Avoid prolonged shutdowns with resin held at high temperature.

         Improve streamlining of the melt inside.


Poor house keeping

         Keep production area clean.

Part blow-out / Flash appearance.

Blow up rate too high or too low.

Mould opening due to high air pressure.

Pinch off too hot.


Pinch off too sharp.

Part blows too fast.

         Use appropriate die.

         Increase clamping force.

         Decrease air pressure.

         Increase cooling of pinch off land.

         Reduce melt temperature.

         Widen pinch off land.

         Reduce air pressure.


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