South Asian Petrochem Limited TROUBLESHOOTING GUIDE - Injection Molding Problem 1. Short shot
Incomplete formation of preform.
2. Sink mark Depression in the preform surface / body 3. Flash Fins along the partings line created by out flowing polymer.
4. Water mark Wavy water marks, due to absorption of water by hot melt.
Possible causes
Possible Solutions
Injection Pressure low Barrel temperature low Mould manifold temp. low Mould cavity temp. low
Holding pressure low Holding time low High mold temperature Inadequate coolant supply Cooling time low Blocked venting Injection pressure high High injection speed Unwanted material in cores Unwanted material in splits Unwanted material in cavity High mold temperature High barrel temperature Clamping pressure low Leaking hoses Leaking mould Insufficient dehumidification Mold enclosure inadequate
Increase injection pressure Increase barrel temperature Increase mould manifold temperature Increase mould cavity temperature. Increase injection speed Increase back pressure Clean vent on split, core and cavity Check that no foreign object is in gate area. Check that the gate pin is moving all the way back (In valve gate hot runner) Increase holding pressure Increase holding time Decrease mould temperature Check cooling water flow / temperature. Increase cooling time Clean vents on split, core and cavity
Decrease Injection pressure Decrease injection speed Clean cores Clean splits Clean cavity Decrease mould temperature Decrease barrel temperature Increase clamp pressure
Check hoses on mould for damage Check mould for leaks Check that dehumidifier is working properly Check that the machine enclosures has no major gaps
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South Asian Petrochem Limited 5. Black specks /Contamination
Contaminated resin High residence time prior to machine start. Degradation of resin
6. Flow lines poor. Wavy flow lines, observed in the polarized light.
Injection pressure low Mould temperature low Barrel temperature low Injection speed low Drier inefficient Back pressure low Manifold and mold heater Malfunction. Barrel temperature high Foreign matter in the gate Low barrel temperature Low mould temperature Back pressure low Mixing head damage Check valve damage
7. Heat splay White / orange shaded flow marks, visible to naked eyes. 8. PET inclusions Un-melted polymer & fine dusty appearance in preform.
Check for resin cleanliness Clean the resin hopper Purge the barrel thoroughly on restart Reduce melt temperature Reduce back pressure Increase injection pressure Increase mould temperature Increase barrel temperature Increase injection speed Check resin drier Increase back pressure
Check temperature of mould cavity heaters and Manifold Check barrel temperature Check that no foreign material is in gate area
Check barrel temperature Check mould temperature Increase back pressure Check mixing head of the screw / screw is not broken. Inspect the check valve on the screw (not Husky Machine)
9. Concentricity
Injection speed high Injection core bent
Decrease injection speed Check that the injection core is not bent and straighten it.
10. Crystalline gate
Cavity heater malfunction Cavity temperature low Manifold temperature low Drier malfunction Hold pressure high Foreign material in gate Cooling at gate insufficient Core cooling inadequate
White crystalline appearance of area around gate.
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Check that the cavity heater is working Increase the cavity temperature Increase the manifold temperature Check that the drier is working Decrease injection hold pressure Check that no foreign object obstructs the cavity gate Increase cooling time Check water to injection core and cavity Check cooling tube in gate is straight and flow is ok.
South Asian Petrochem Limited 11. Long gate Extended Gate length
12. Air bubbles Entrapped air or gas or vacuum bubble.
13. Stress pattern Waviness in Polarized light. 14. Stringing Long fine string extending from the gate.
15. Cloudy preform Dull color preforms. Lack of clarity.
16. Hollow gate Hole in the center of gate.
Cavity heater malfunction Cavity heater low Gate valve malfunction Shut-off nozzle malfunction Short decompression time Barrel temperature low Inefficient drying Low back pressure Barrel temperature high. Mixing head damage High injection pressure High shot size Long hold time
Check cavity heater Increase cavity temperature Check that the gate valve is working Check that the barrel shut-off nozzle is working Increase decompression time
Check barrel temperature Check drier temperature Increase back pressure Lower temperature at last extruder zone Check extruder mixing head
High cavity temperature Low cooling time Low hold time Inadequate coolant to cavity Gate valve malfunction Inefficient Drying Blocked drier filters Air leaks on the drier Air leaks on machine hoppers Low air flow to drying hopper Low process air temperature Barrel temperature low Insufficient drying Back pressure low Holding pressure or time low Insufficient cooling time High cavity heater temperature Foreign material in gate
Reduce cavity temperature Increase cooling time Increase injection hold time Check water flow to cavities Check that gate valves are working
Check drier temperature and dew point Clean drier air filters Check for air leaks on drier Check for air leaks on machine hopper Check air flow to hopper Increase drier process temperature Increase barrel temperature Shut machine down for 1 hour and dry material Increase back pressure
Increase holding pressure Increase holding time Increase cooling time Lower cavity heater temperature Check for foreign material in gate area.
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Decrease injection pressure Reduce shot size Decrease injection hold time
South Asian Petrochem Limited High barrel temperature High mold temperature High drying temperature Contaminated splits Low packing pressure Insufficient packing time High cavity temperature
Lower barrel temperature Lower injection mould temperature Lower drier process temperature
20. Oval finish
Insufficient cooling Hold time low Insufficient cooling
21. Gas burn
High injection speed Contaminated splits Improper air venting in neck rings, causing melt flow unequally and form a weld line at this point. Extreme high packing at neck finish area, leading to expansion crack. More prevalent in unbalanced gating system. High residual AA in resin High barrel temperature High plasticizing back pressure & speed High injection speed High manifold & nozzle tip temperature Long cycle time High extruder / screw cushion Low inlet resin temperature Unsuitable screw
Decrease injection speed Clean splits
17. Discolored preforms
18. Over size finish
19. Burnt gate
22. Cracks between threads & NSR (Horizontal) 23. Vertical crack in the preform lip surface. 24. High AA
Clean splits Increase packing pressure Increase packing time Reduce cavity temperature
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High core and cavity temperatures Increase cooling time Increase injection hold time Check water temperature and water flow to injection Mould Check temperature of injection cores and cavities
Check equal air vents along the circumference of the neck ring core insert. Clean dirt accumulations around vent area. Reduce packing pressure. Reduce barrel / melt temperature.
Check for resin AA levels Reduce the barrel temperature Reduce back pressure Reduce screw RPM Reduce injection speed Reduce mold manifold temperature Reduce cycle time Reduce cushion Increase inlet resin temperature
South Asian Petrochem Limited TROUBLESHOOTING GUIDE - Stretch Blow Molding Problem 1. Pearlescence White Pearl shade on the bottle surface.
Possible causes
Possible Solutions
Pearlescence results from stretching of molecules faster than they can respond past it's natural stretch limit. Small tears appear on material surface. This can also be due to the Pre bottle condition considerably smaller than the mold cavity, > 20 %.
Material too thin at pearlescent area. Increase heat other than where pearl is evident. Material too thick at pearlescent area. Increase heat at pearl area. Increase overall preform temperature. Pearlescence on the bottle shoulder may be the result of a blow air leak through nose from either pre-valve, high blow valve or stretch rod. Reduce Pre blow volume, increase Pre blow time and reduce Pre blow pressure. Ensure Pre blow bottle is not to large. Excessive petal formation in Pre blow will cause pearl in the petal area. Pearlescence in the body in the form of a ring is the result of insufficient Pre blow. Reduce over all perform temperature allowing the bottle to be blown closer to its natural stretch limit. Under this condition slight pearlescence may be evident
2. Excessive fill point drop Low fill volume of the bottle
Low levels of orientation results in the material not having enough strength to resist the stretch force.
3. Clear break along NSR ( rough feel the crack surface)
Weld line formation along this circumference due to low melt temperature, low fill velocity, improper venting. (Preform defect) Over heating of area near the NSR, leading to separation of softened and hard amorphous portions.
Check “Preform Problem & Remedy” point no.22. There may be chances a fine crack at injection molding stage, is not noticed. Check crack presence by polarized light table.
Insufficient orientation (Too hot)
Reduce preform temperature. Reduce body heat.
4. Burst below NSR (smooth feel of crack surface) 5. Low burst pressure (BODY)
Low IV
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Reduce lamp heat in zone 1. Raise the level of lamp in zone 1. Check preform mandrel are not too cold.
South Asian Petrochem Limited 6. Low burst pressure (BASE)
Excessive crystallinity at the gate Low IV Excessive stress in preform
7. Heavy base weight
Incorrect heating profile, resulting in a poor distribution of material.
8. Thin shoulder
Over stretching of the body / shoulder. Excessive stretching of the taper. Stations producing a smaller Pre blow container will be typically affected.
9. Swung gate
Poor shield positioning, allowing excessive stretching of the thin part of the taper. First impacted mark is evident and is not centered to the gate, an alignment problem is usually the cause. Inadequate mould cooling, If the gate is centered to the stretch rod impact mark and yet not centered to the mould base at the end of blow. If the first impact mark is centered, the stretch rod has lost control of the gate during blow. Often gate control is lost due to excessive rate of growth of expanding film during pre blow. Ideally growth should start high in the preform and should reach the base after the stretch rod has reached the base.
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Base of bottle blown too cold producing excessive stress Increase heat below the preform Stretch rod clearance too short. Reset stretch rod clearance. Reduce stretch rod pressure. Reduce heat in the body and/ or shoulder until pearlescence occurs, then increase heat at the base. Repeat until the base weight is correct.
Move shield into a thicker part of the preforms taper. Reduce pre blow delay time Reduce stretch rod pressure Increase Pre blow pressure Reduce heat in the neck. If thickening occurs below desired area.
Misalignment of the preform to the mould, nozzle or stretch rod.
Check blow mould cooling Lower half of preform too hot
Reduce low bottle size Increase air delay time Reset stretch rod height Low blow pressure too high Air delay time too short Worn stretch rod guides Excessive preform eccentricity Thick crystallinity near gate
South Asian Petrochem Limited 10. Drop test failure
Excessive crystallinity above gate. Lower base weight.
11. Fold around stretch rod.
12. Blown finish
13. Sealing surface damage
14. Chocked neck
15. Bent neck
Over heating of the preform end cap, material wraps around the end of the stretch rod. In effect another thick/ thin transition forms Overheating of the finish area which allows blow pressure air to stretch the material. Oven ambient temperature to high. Incorrect preform loading, too much of the finish is exposed. Misalignment of the preform, blow mould and blow nozzle usually caused by poor transfer arm positioning. Blow mold position. Nozzle position. Over stretching of the preform by the stretch rod prior to pre blow. Low blow delayed or missing
Misalignment of the preform to the mould or nose. Distortion below the flange Insufficient mould cooling One mould half with poor cooling Excessive material remained in the neck and shoulder.
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Preform end cap blown too cold. Increasing heat at the gate or below without loosing base weight usually improves drop test failure. Light base weight. Increase base weight. Reduce heat around gate area. Increase pre blow pressure. Reduce stretch rod pressure. Move shield away from finish into a thicker part of the preforms taper. Bring shield close to preform Increase oven exhaust Reduce neck element heat
Realign transfer arm Realign blow mould or nozzle if necessary
Reduce air delay time Reduce stretch rod pressure Move shield into a thicker part of the taper Increase heat in the body or base Increase low blow pressure Reduce heat in the neck Realignment of the preform to the nose or mould. Reduce material thickness in the shoulder by reducing heat in the body. Increase high blow time Improve mould cooling
South Asian Petrochem Limited 16. Hard neck
17. Hot bottles
18. Flat sides
19. Deformation at mold parting line
20. Chocked body
Initial stretching occurs too low into the preforms taper. Preform location incorrect through oven. Air leak into preform before the start of low blow.
Preform temperature above crystal growth range for to long. Insufficient cooling of preform outside surface for the amount of heat absorbed by the P.E.T. Poor venting of mold.
Pressure remaining in the bottle when blow moulds open. Insufficient high blow / cooling time Material too hot and/or too thick Insufficient or no low blow Insufficient heat beside choke
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Reduce heat in the body and/ or base until pearlescence occurs then increase neck temperature. Increase stretch rod pressure Increase air delay time Reduce low blow pressure Move shield into the thinner part of the taper Check height of preform though oven. Check for air leak through nose Reduce heat adjacent to the haze portion until pearlescence is evident somewhere on the bottle. Reduce heat over all until pearlescence is evident. Increase air circulation through oven. Increase blower speed, clean blowers Ensure adequate mold venting, and clean clogs. Increase low blow pressure ensuring bottle diameter is close to blow mould size. Low blow bottle too small. In this case the volume of air trying to escape during high blow is more than the venting can allow. Low blow bottle blown to fast. Excessive high blow pressure at the end of low blow to minimize air that remains in the blow mould before high blow starts. Reduce low blow pressure and extend low blow time if the body of the bottle has reached the mould. Reduce high blow pressure. Inadequate exhaust time, check exhaust valve activation. Increase high blow time or reduce material thickness Reduce material thickness Reduce preform temperature
Increase low blow pressure Increase heat in the body Reduce heat in the base and/ or neck. Reduce air delay time Reduce stretch rod pressure
South Asian Petrochem Limited 21. Light base weight
22. Not fully formed
23. Hot sides
24. Low top load
25. Poor base clearance
Poor heating profile resulting in poor distribution of material, insufficient stretching of the body or shoulder.
Insufficient high blow pressure. Rate of high blow too slow, material movement stalls before reaching the corners. Often as a result of blow nozzle leak. Insufficient high blow time. Heavy baseweight. High blow pressure inadequate to move material into the corners. Inconsistent preform rotation through the oven. Insufficient surface cooling of the preform. Insufficient orientation and/or material thickness to deliver the required physical strength Preform temperature too high. Heavy base weight.
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Reduce heat near the base of the preform until pearlescence occurs then increase heat to the shoulder and body. Repeat until base weight is correct Increase air delay time Increase stretch rod pressure Reduce low blow pressure Reduce oven shielding of the taper Check high pressure. Check for high blow leaks from nozzle or stretch rod. Increase high blow time. Excessive low blow pressure or time. If too much of the material will be left to form the feet correctly. Corners are likely to be thin. Swung gate. Feet will not form in the corners opposite the gate movement unless extra heat is applied near the end cap. Reduce preform temperature until pearlescence is evident then increase preforms lower body temperature Check pre bottle size. Reduce if necessary. Check the preform for drag marl. Ensure oven shields are not touching the preform. Check spindle or mandrel rotation Increase air flow onto the surface of the preform Reduce over all preform temperature Reduce heat beside failure point Where failures occur between neck and shoulder adjust shield into a thicker part of the taper Base weight correct or light, reduce heat beside and/or below the gate. End cap temperature too high Aged preforms. Insufficient mould cooling Excessive inherent preform stress Base weight too heavy, reduce preform temperature Increase high blow time.
South Asian Petrochem Limited 26. Fold in base at end cap line
27. Cracked base
28. Stress cracking
29. Explosion during blowing
30. Streaks (Thin thick vertical lines)
Preform temperature too hot Preform end cap area to cold An excess of material in the vicinity of the fold Lack or loss of low blow volume Excessive force applied by the stretch rod Aged or stressed preforms Preform end cap too cold Excessive stretch rod pressure Clearance between the stretch rod and mould base too small Thick crystallinity above the gate Off center gates. Webs with the thinnest material will stress crack early. Excessive post mould change. As clearance deteriorates web shape changes increasing the risk of stress cracking. Temperature of the lower half of the preform's body is too high. Chemical reaction by some line lubricants. Low I.V. material Light base weight. Inadequate thickness to resist movement. Hot bottles (Refer Hot Bottles) Folds in the base Light base weight Excessive post mould growth Low I.V. Contamination Air bubbles above the gate Due to stretching of highly crystalline portions of preform.
Reduce heat in the areas other than the base. If the fold remains after pearlescence has formed. Heat may be applied to the preform end cap area. Increase low blow pressure Reduce air delay time Reduce stretch rod pressure
Increase heat beside or below the gate Reduce stretch rod pressure Check preform for excessive crystallinity, if so change preforms. Increase stretch rod, mould base gap
Fix swung gate. Reduce preform temperature to pearlescence, reduce base weight if necessary. Increase high blow time Reduce heat in the preform lower body Line lubricants generally cause severe stress cracking in all feet. Increase base weight
Refer Causes Stress Cracking Cracked bases Excessive crystallinity
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Check & reset preform temperature. Rectify if haze is present in preforms.
South Asian Petrochem Limited TROUBLESHOOTING GUIDE - Injection Stretch Blow Molding Problems specific to ISBM is addressed here, general molding & blowing related problem, please refer „Trouble shooting guide – Injection Molding / Blow molding” Problem 1. Broken gate
2. Splay (Orange shaded)
3. Splay (White shade)
4. Small lumps / dotted marks in bottle
Possible causes
Possible Solutions
Curing time not enough. Insufficient gate cooling. Higher hold pressure. Higher back pressure Drooled material clogging HR nozzle top surface. Resin decomposing Restriction in melt flow in HR. Higher injection velocity. Poor drying. Sudden variation in melt temperature in melt path. Restriction in melt flow in HR. Higher injection velocity. Sudden variation in melt temperature in melt path. Water in blow air. Dust in blow air. Dirt and pitting in blow mold
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Increase cooling time. Reduce hold pressure Reduce back pressure Replace damaged Nomex paper / NF ring and clean HR nozzle surface. Reduce barrel temperature. Reduce back pressure & Speed. Reduce HR temperature. Reduce nozzle temperature. Reduce injection velocity & pressure. Check dryer performance. Balance flow path temperature. Maintain not more than 10 deg C variation in flow path. Clean HR flow path. Reduce injection velocity. Balance flow path temperature. Maintain not more than 10 deg C variation in flow path. Check moisture trap / dryer performance in air line. Check air filter performance. Clean and polish blow cavity.
