PET Processing V4 - Trouble Shooting

TROUBLESHOOTING GUIDE - Injection Molding

Problem

Possible causes

Possible Solutions

1. Short shot

Incomplete formation of

preform.

Injection Pressure low Barrel temperature low Mould manifold temp. low Mould cavity temp. low

 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)

2. Sink mark

Depression in the preform

surface / body

Holding pressure low Holding time low High mold temperature Inadequate coolant supply Cooling time low

Blocked venting

 Increase holding pressure  Increase holding time

 Decrease mould temperature

 Check cooling water flow / temperature.  Increase cooling time

 Clean vents on split, core and cavity

3. Flash

Fins along the partings line

created by out flowing

polymer.

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

 Decrease Injection pressure  Decrease injection speed  Clean cores

 Clean splits  Clean cavity

 Decrease mould temperature  Decrease barrel temperature  Increase clamp pressure

4. Water mark

Wavy water marks, due to

absorption of water by hot

melt.

Leaking hoses Leaking mould

Insufficient dehumidification Mold enclosure inadequate

 Check hoses on mould for damage  Check mould for leaks

 Check that dehumidifier is working properly

5. Black specks

/Contamination

Contaminated resin

High residence time prior to machine start. Degradation of resin

 Check for resin cleanliness  Clean the resin hopper

 Purge the barrel thoroughly on restart  Reduce melt temperature

 Reduce back pressure

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

 Increase injection pressure  Increase mould temperature  Increase barrel temperature  Increase injection speed  Check resin drier  Increase back pressure

7. Heat splay

White / orange shaded flow

marks, visible to naked eyes.

Manifold and mold heater Malfunction. Barrel temperature high

Foreign matter in the gate

 Check temperature of mould cavity heaters and Manifold  Check barrel temperature

 Check that no foreign material is in gate area

8. PET inclusions

Un-melted polymer & fine

dusty appearance in preform.

Low barrel temperature Low mould temperature Back pressure low Mixing head damage Check valve damage

 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

White crystalline appearance

of area around 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

 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

11. Long gate

Extended Gate length

Cavity heater malfunction Cavity heater low

Gate valve malfunction Shut-off nozzle malfunction Short decompression 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

12. Air bubbles

Entrapped air or gas or

vacuum bubble.

Barrel temperature low Inefficient drying Low back pressure Barrel temperature high. Mixing head damage

 Check barrel temperature  Check drier temperature  Increase back pressure

 Lower temperature at last extruder zone  Check extruder mixing head

13. Stress pattern

Waviness in Polarized light.

High injection pressure High shot size

Long hold time

 Decrease injection pressure  Reduce shot size

 Decrease injection hold time

14. Stringing

Long fine string extending from

the gate.

High cavity temperature Low cooling time Low hold time

Inadequate coolant to cavity Gate valve malfunction

 Reduce cavity temperature  Increase cooling time  Increase injection hold time  Check water flow to cavities  Check that gate valves are working

15. Cloudy preform

Dull color preforms. Lack of

clarity.

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

 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

16. Hollow gate

Hole in the center of gate.

Holding pressure or time low Insufficient cooling time High cavity heater temperature Foreign material in gate

 Increase holding pressure  Increase holding time  Increase cooling time

 Lower cavity heater temperature  Check for foreign material in gate area.

17. Discolored preforms

High barrel temperature High mold temperature High drying temperature

 Lower barrel temperature

 Lower injection mould temperature  Lower drier process temperature

18. Over size finish

Contaminated splits Low packing pressure Insufficient packing time

 Clean splits

 Increase packing pressure  Increase packing time

19. Burnt gate

High cavity temperature  Reduce cavity temperature

20. Oval finish

Insufficient cooling Hold time low Insufficient cooling

 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

21. Gas burn

High injection speed Contaminated splits

 Decrease injection speed  Clean splits

22. Cracks between threads

& NSR (Horizontal)

Improper air venting in neck rings, causing melt flow unequally and form a weld line at this point.

 Check equal air vents along the circumference of the neck ring core insert.

 Clean dirt accumulations around vent area.

23. Vertical crack in the

preform lip surface.

Extreme high packing at neck finish area, leading to expansion crack.

More prevalent in unbalanced gating system.

 Reduce packing pressure.  Reduce barrel / melt temperature.

24. High AA

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

 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

TROUBLESHOOTING GUIDE - Stretch Blow Molding

Problem

Possible causes

Possible Solutions

1. Pearlescence

White Pearl shade on the

bottle surface.

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.

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.

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

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)

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.

4. Burst below NSR

(smooth feel of crack

surface)

Over heating of area near the NSR, leading to separation of softened and hard amorphous portions.

Reduce lamp heat in zone 1. Raise the level of lamp in zone 1. Check preform mandrel are not too cold.

5. Low burst pressure

(BODY)

Insufficient orientation (Too hot)

Low IV

Reduce preform temperature. Reduce body heat.

6. Low burst pressure

(BASE)

Excessive crystallinity at the gate

Low IV

Excessive stress in preform

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.

7. Heavy base weight

Incorrect heating profile, resulting in a poor distribution of material.

Over stretching of the body / shoulder.

Reduce heat in the body and/ or shoulder until pearlescence occurs, then increase heat at the base. Repeat until the base weight is correct.

8. Thin shoulder

Excessive stretching of the taper. Stations producing a smaller Pre blow container will be typically affected.

Poor shield positioning, allowing excessive stretching of the thin part of the taper.

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.

9. Swung gate

First impacted mark is evident and is not centered to the gate, an alignment problem is usually the cause.

Misalignment of the preform to the mould, nozzle or stretch rod.

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.

Check blow mould cooling Lower half of preform too hot

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.

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

10. Drop test failure

Excessive crystallinity above gate. Lower base weight.

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.

11. Fold around stretch

rod.

Over heating of the preform end cap, material wraps around the end of the stretch rod. In effect another thick/ thin transition forms

Reduce heat around gate area. Increase pre blow pressure. Reduce stretch rod pressure.

12. Blown finish

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.

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

13. Sealing surface

damage

Misalignment of the preform, blow mould and blow nozzle usually caused by poor transfer arm positioning.

Blow mold position. Nozzle position.

Realign transfer arm

Realign blow mould or nozzle if necessary

14. Chocked neck

Over stretching of the preform by the stretch rod prior to pre blow.

Low blow delayed or missing

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

15. Bent neck

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.

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

16. Hard neck

Initial stretching occurs too low into the preforms taper. Preform location incorrect

through oven.

Air leak into preform before the start of low blow.

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

17. Hot bottles

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.

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

18. Flat sides

Poor venting of mold. 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.

19. Deformation at mold

parting line

Pressure remaining in the bottle when blow moulds open.

Insufficient high blow / cooling time

Material too hot and/or too thick

Inadequate exhaust time, check exhaust valve activation. Increase high blow time or reduce material thickness Reduce material thickness

Reduce preform temperature

20. Chocked body

Insufficient or no low blow Insufficient heat beside choke

Increase low blow pressure Increase heat in the body

Reduce heat in the base and/ or neck. Reduce air delay time

21. Light base weight

Poor heating profile

resulting in poor distribution of material, insufficient stretching of the body or shoulder.

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

22. Not fully formed

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.

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.

23. Hot sides

Inconsistent preform rotation through the oven.

Insufficient surface cooling of the preform.

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

24. Low top load

Insufficient orientation and/or material thickness to deliver the required physical strength

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

25. Poor base clearance

Preform temperature too high. Heavy base weight.

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.

26. Fold in base at end

cap line

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

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

27. Cracked base

Preform end cap too cold Excessive stretch rod pressure Clearance between the stretch rod and mould base too small Thick crystallinity above the

gate

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

28. Stress cracking

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.

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

29. Explosion during

blowing

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

Refer Causes

Stress Cracking

Cracked bases

Excessive crystallinity

30. Streaks

(Thin thick vertical lines)

Due to stretching of highly crystalline portions of preform.

Check & reset preform temperature. Rectify if haze is present in preforms.

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

Possible causes

Possible Solutions

1. Broken gate _{Curing time not enough.}

Insufficient gate cooling. Higher hold pressure. Higher back pressure

Drooled material clogging HR nozzle top surface.

Increase cooling time. Reduce hold pressure Reduce back pressure

Replace damaged Nomex paper / NF ring and clean HR nozzle surface.

2. Splay (Orange shaded) _{Resin decomposing}

Restriction in melt flow in HR. Higher injection velocity. Poor drying.

Sudden variation in melt temperature in melt path.

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.

3. Splay (White shade) _{Restriction in melt flow in HR.}

Higher injection velocity. Sudden variation in melt temperature in melt path.

Clean HR flow path. Reduce injection velocity.

Balance flow path temperature. Maintain not more than 10 deg C variation in flow path.

4. Small lumps / dotted marks

in bottle Water in blow air.

Dust in blow air.

Dirt and pitting in blow mold

Check moisture trap / dryer performance in air line. Check air filter performance.