Polyethylene

Terephthalate (PET)

•Processing Guidelines •Troubleshooting Guide Injection Moulding Stretch Blow Moulding •Recommended Tests & Equipment INDEX PROCESSING GUIDELINES Drying Drying Conditions Dryer Startup Dryer Specification Injection Moulding Resin Inlet Temperature Barrel Temperature  Nozzle Temperature Manifold Hot Runner Temperature Injection Speed Stretch Blow Moulding 

TROUBLESHOOTING GUIDE

Injection Moulding Defects 1) Short Shots 2) Sink Marks 3) Flash 4) Water Marks 5) Black Specs / Contamination 6) Flow Lines 7) Heat Splay 8) PET Inclusion 9) Concentricity 10) Crystalline Gate 11) Long Gate 12) Air Bubbles 13) Stress Pattern

14) Stringing 15) Cloudy Preforms 16) Hollow Gates 17) Discolored Preforms 18) Line Over Finish 19) Burnt Gates 20) Oval Finish 21) Gas Burns 

22) High Acetaldehyde 

Stretch Blow Moulding Defects 1) Blown Finish 2) Sealing Surface Damage 3) Chocked Neck  4) Bent Neck  5) Hard Neck  6) Thin Shoulder  7) Hot Bottles 8) Excessive fill point drop 9) Pearlescence 10) Flat Sides 11) Deformation at mold parting lin 12) Chocked Body 13) Heavy Base Weight 14) Light Base Weight 15) Feet not fully formed 

16) Hot Sides

17) Low Head Load 18) Low Burst Pressure (Body) 19) Low Burst Pressure (Base) 20) Poor Clearance

 21) Fold in End Cap Line 

22) Fold Around Stretch Rod 23) Cracked Base 

24) Swung Gate 25) Stress Cracking

26) Explosion 27) Drop Test Failures

PROCESSING GUIDELINES THE processing guidelines set out below cover the two major processes involved in the conversion of PET resin into preforms and containers, namely:1. INJECTION MOLDING2. STRETCH BLOW MOLDING.

The resin preparation conditions and barrel temperature profile recommended on the injection molder could also be used on extrusion barrel, in converting PET resin into amorphous sheet.

DRYING: Drying Conditions: This is the first and most crucial step in converting PET resin into perform/container/sheet. If the drying equipment is not adequate or is not functioning efficiently then it is highly unlikely that you will produce an acceptable product. The dried resin should have a moisture content not more than 50 PPM.Recommended Drying Temperature: 160 - 180 °CRecommended Drying Time5- 6 hours

Dryer Start-Up : The time / temperature profile recommended when first starting the dryer or starting from a major shut down is as below. The first hour at 120 °The next two hours 150 °The next two hours 180 °C

Dryer Specification:  Able to heat air up to 200 °C Able to deliver air flow rate in the order of 0.062 metre cube/ min per kg/ hr of resin being processed. Able to deliver hot dehumidified air with a minimum of 40.0°C dew point.

Dryer Resin Level: To give approximately 5 to 6times the kg/hr capacity of the injection molder or extruder incase of sheet extrusion.

INJECTION MOLDING PROCESS: This is the process by which the resin is converted from dried pellets to perform.Resin Inlet Temperature: It is better to have a temperature of 160 -170 °C on the resin entering the feed zone of the

extruder.

Barrel Temperature Profile: For other than water grade resin it is recommended to use a temperature of 265°C in the feed zone gradually increasing towards the metering zone 280 °C. For the water grade resin however, it is recommended to use a reverse temperature profile, with highest temperature in the feed zone, say 280 °C and gradually lowering towards the metering zone.Recommended temperature: 265 - 280 °C Nozzle Temperature: Recommended temperature: 270 - 280 °C Manifold Hot Runner Temperature: Recommended temperature: 270 - 280 °C Mold Cooling Water Inlet Temperature: Recommended temperature: 7 to 8 °C Injection Speed:As required to fill the cavity with minimum shear and dependent on the gate size.

 STRETCH BLOW MOLDING PROCESS: The most commonly available stretch blow molding machines are the:Single stage stretch blow molder ( preform & bottle made on the same machine).They are AOKI, NISSEI, UNILOY, etc.Two stage stretch blow molder (reheating and blowing of preforms made onInjection molder).They are SIDEL, KRUPP, SIPA, etc.The processing conditions depend on the type of process used and the mostcommon parametersto be controlled are:o Preform Temperature.o Re-heating oven profile and over all oven percentage.o Oven sheilds o Bottle blowing speed, bottles/hour.o Stretch rod speed o Air delay time o Pre-blow pressure.o High blow time.o High blow pressure.o Blow mold cooling.

Optimizing of the above parameters depend on several factors such as :o Preform design.o Preform intrinsic viscosity.o Preform infrared absorbing characteristics.o Bottle design.

TROUBLESHOOTING GUIDE

Injection Moulding 1 Problem: SHORT SHOTS POSSIBLE CAUSES o Injection Pressure lowo Barrel temperature lowo Mould manifold temp. lowo Mould cavity temp. low

POSSIBLE SOLUTIONS oIncrease injection pressureo Increase barrel temperatureo Increase mould manifold temperatureo Increase mould cavity temperatureo Injection speed lowo Back pressure lowo Increase injection speedo Increase back pressureo Clean vent on split, core and cavityo Check that no foreign object is in gate area.o Check that the gate pin is moving all the way back

2 Problem: SINK MARKS POSSIBLE CAUSESo Holding pressure lowo Holding time lowo High mold temperatureo Inadequate coolant supplyo Cooling time lowo Blocked venting

POSSIBLE SOLUTIONSo Increase holding pressureo Increase holding timeo Decrease mould temperatureo Check cooling water o Increase cooling timeo Clean vents on split, core and cavity

3 Problem: FLASH POSSIBLE CAUSESo Injection pressure higho High injection speedo Unwanted material in coreso Unwanted material in splits

o Unwanted material in cavityo High mold temperatureo High barrel temperatureo Clamping pressure low

POSSIBLE SOLUTIONSo Decrease Injection pressureo Decrease injection speedo Clean coreso Clean splitso Clean cavityo Decrease mould temperatureo Decrease barrel temperatureo Increase clamp pressure

4 Problem: WATER MARKS POSSIBLE CAUSES o Leaking hoseso Leaking mouldo Insufficient dehumidificationo Mold enclosure inadequate

POSSIBLE SOLUTIONS o Check hoses on mould for damageo Check mould for leakso Check that dehumidifier is working properlyo Check that the machine enclosures has no major gaps

5 Problem: BLACK SPECS /CONTAMINATION POSSIBLE CAUSES o Contaminated resino High residence time prior to restart of the machineo Degradation of resin

POSSIBLE SOLUTIONS o Check for resin cleanlinesso Clean the resin hopper o Purge the barrel thoroughly on restarto Reduce melt temperatureo Reduce back pressure

6 Problem: FLOW LINES POSSIBLE CAUSES o Injection pressure lowo Mould temperature lowo Barrel temperature lowo Injection speed lowo Drier inefficiento Back pressure low

POSSIBLE SOLUTIONS o Increase injection pressureo Increase mould temperatureo Increase barrel temperatureo Increase injection speedo Check resin drier o Increase back pressure

7 Problem: HEAT SPLAY POSSIBLE CAUSES o Manifold and mold heater Malfunction.o Barrel temperature higho Foreign matter in the gate

POSSIBLE SOLUTIONS o Check temperature of mould cavity heater sand Manifoldo Check barrel temperatureo Check that no foreign material is in gate area

8 Problem: PET INCLUSIONS POSSIBLE CAUSES o Low barrel temperatureo Low mould temperatureo Back pressure lowo Mixing head damageo Check valve damage

POSSIBLE SOLUTIONS o Check barrel temperatureo Check mould temperatureo Increase back pressureo Check that the mixing head of the screw or the screw is not broken. Of Inspect the check valve on thescrew (not Husky Machine)

9 Problem: CONCENTRICITY POSSIBLE CAUSES o Injection speed higho Injection core bent

POSSIBLE SOLUTIONS o Decrease injection speedo Check that the injection core is not bentand straighten it.

10 Problem: CRYSTALLINE GATE POSSIBLE CAUSES o Cavity heater malfunctiono Cavity temperature lowo Manifold temperature low

o Drier malfunctiono Hold pressure higho Foreign material in gateo Cooling insufficiento Core cooling inadequateo Fountain in core rod damage 

POSSIBLE SOLUTIONS o Check that the cavity heater is workingo Increase the cavity temperatureo Increase the manifold temperatureo Check that the drier is workingo Decrease injection hold pressureo Check that no foreign object obstructs the cavity gateo Increase cooling timeo Check water flow through the injectioncore and cavityo Check that the fountain in the injectioncore is not bent 11 Problem: LONG GATE POSSIBLE CAUSES o Cavity heater malfunctiono Cavity heater lowo Gate valve malfunctiono Shut-off nozzle malfunctiono Short decompression time

POSSIBLE SOLUTIONS o Check cavity heater o Increase cavity temperatureo Check that the gate valve is workingo Check that the barrel shut-off nozzle is workingo Increase decompression time

12 Problem: AIR BUBBLES POSSIBLE CAUSESo Barrel temperature lowo Inefficient dryingo Low back pressureo Barrel temperatureo Mixing head damage

POSSIBLE SOLUTIONS o Check barrel temperatureo Check drier temperatureo Increase back pressureo Lower temperature at last extruder zoneo Check extruder mixing head

13 Problem: STRESS PATTERN 

POSSIBLE CAUSES o High injection pressureo High shot sizeo Long hold time

POSSIBLE SOLUTIONS o Decrease injection pressureo Reduce shot sizeo Decrease injection hold time

14 Problem: STRINGING POSSIBLE CAUSES o High cavity temperatureo Low cooling timeo Low hold timeo Inadequate coolant to cavityo Gate valve malfunctionPOSSIBLE SOLUTIONS o Reduce cavity temperatureo Increase cooling timeo Increase injection hold timeo Check water flow to cavitieso Check that gate valves are working15 Problem: CLOUDY PREFORMS POSSIBLE CAUSES o Inefficient Dryingo Blocked drier filterso Air leaks on the drier o Air leaks on machine hopperso Low air flow to drying hoppero Low process air temperatureo Barrel temperature lowo Insufficient dryingo Back pressure low

POSSIBLE SOLUTIONS o Check drier temperature and dew pointo Clean drier air filterso Check for air leaks on drier o Check for air leaks on machine hopper o Check air flow to hopper o Increase drier process temperatureo Increase barrel temperatureo Shut machine down for 1 hour and dry materialo Increase back pressure

16Problem: HOLLOW GATESPOSSIBLE CAUSESo Packing pressure lowo Hold time low

o Insufficient cooling timeo High cavity temperatureo Foreign material in gate

POSSIBLE SOLUTIONSo Increase packing pressureo Increase holding timeo Increase cooling timeo Lower cavity temperatureo Check for foreign material in gate area.

17 Problem: DISCOLORED PREFORMS POSSIBLE CAUSESo High barrel temperatureo High mold temperatureo High drying temperaturePOSSIBLE SOLUTIONS o Lower barrel temperatureo Lower injection mould temperatureo Lower drier process temperature

18 Problem: LINE OVER FINISH POSSIBLE CAUSESo Contaminated splitso Low packing pressureo Insufficient packing timePOSSIBLE SOLUTIONSo Clean splitso Increase packing pressureo Increase packing time

19 Problem: BURNT GATES POSSIBLE CAUSES o High cavity temperature

POSSIBLE SOLUTIONS o Reduce cavity temperature

20 Problem: OVAL FINISH POSSIBLE CAUSESo Insufficient cooling Hold time lowo Insufficient cooling

POSSIBLE SOLUTIONSo High core and cavity temperatureso Increase cooling timeo Increase injection hold time

o Check water temperature and water flow to injection Mouldo Check temperature of injection cores and cavities

21Problem: GAS BURNS POSSIBLE CAUSES o High injection speedo Contaminated splitsPOSSIBLE SOLUTIONSo Decrease injection speedo Clean splits

22 Problem: HIGH ACETALDEHYDE POSSIBLE CAUSESo High residual AA in resino High barrel temperatureo High back pressureo High screw speedo High injection speedo High mold manifold temperatureo High nozzle tip temperatureo Long cycle timeo High extruder / screw cushiono Low inlet resin temperatureo Unsuitable screw

POSSIBLE SOLUTIONS o Check for resin AA levelso Reduce the barrel temperatureo Reduce back pressureo Reduce screw RPMo Reduce injection speedo Reduce mold manifold temperatureo Reduce cycle timeo Reduce cushiono Increase inlet resin temperature

 

TROUBLESHOOTING GUIDE

Stretch Blow Moulding

1 Problem: BLOWN FINISH POSSIBLE CAUSESo Overheating of the finish area which allows blow pressure air to stretch the material.o Oven ambient temperature to higho Incorrect loading height, too much of the finish is exposed to the elements

POSSIBLE SOLUTIONSo Move shield away from finish into a thicker part of the preforms taper o Bring shield close to performo Increase oven exhausto Reduce neck element heat

2 Problem: SEALING SURFACE DAMAGE POSSIBLE CAUSESo Misalignment of the preform, blow mould and blow nozzle usually caused by poor transfer arm positioning.o Blow mold position.o Nozzle position.

POSSIBLE SOLUTIONSo Realign transfer armo Realign blow mould or nozzle if necessary

3 Problem: CHOCKED NECK  POSSIBLE CAUSESo Over stretching of the preform by the stretch rod prior to blow.o Low blow delayed or missing

POSSIBLE SOLUTIONSo Reduce air delay timeo Reduce stretch rod pressureo Move shield into a thicker part of the taper o Increase heat in the body or baseo Increase low blow pressureo Reduce heat in the neck

4 Problem: BENT NECK  POSSIBLE CAUSESo Misalignment of the preform to the mould or nose.o Distortion below the flangea) Insufficient mould coolingb) One mould half with poor coolingo Excessive material remained in the neck and shoulder.

POSSIBLE SOLUTIONS o Realignment of the preform to the nose or mould.o Reduce material thickness in the shoulder by reducing heat in the bodyo Increase high blow timeo Improve mould cooling

5 Problem: HARD NECK  POSSIBLE CAUSESo Initial stretching occurs too lowinto the preforms taper.o Preform location incorrectthrough oven.o Air leak into preform before thestart of low blow.

POSSIBLE SOLUTIONS o Reduce heat in the body and/ or base until pearlescence occurs then increase neck temperature.o Increase stretch rod pressureo Increase air delay timeo Reduce low blow pressureo Move shield into the thinner part of the taper o Check height of preform though oven.o Check for air leak through nose

6 Problem: THIN SHOULDER  POSSIBLE CAUSESo Excessive stretching of the taper. Stations producing a smaller low blow container will be first withthe fault or the thinnest.o Poor shield positioning, allowing excessive stretching of the thin part of the taper.

POSSIBLE SOLUTIONSo Move shield into a thicker part of the preforms taper.o Reduce air delay timeo Reduce stretch rod pressureo Increase low blow pressureo Reduce heat in the neck. If thickening occurs below desired area Increase heat below the neck element.

7 Problem: HOT BOTTLES POSSIBLE CAUSESo Preform temperature above crystalgrowth range for to longo Insufficient cooling of the outsidesurface for the amount of heatabsorbed by the P.E.T.o Excessive equilibration time oPreform wall thickness excessiveblowers.

POSSIBLE SOLUTIONS o Reduce heat adjacent to the haze untilpearlescence is evident somewhere onthe bottleo Reduce heat over all until pearlescenceis evident.o Increase air circulation through oven,increase blower speed, clean blowers.

8 Problem: EXCESSIVE FILL POINT DROP POSSIBLE CAUSESo Low levels of orientation results in the material not having enough strength to resist the pressure applied.

POSSIBLE SOLUTIONSo 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

9 Problem: PEARLESCENCE POSSIBLE CAUSESo Pearlescence results from stretching of molecules faster than they can respond past it's natural stretch limit. Small tears appear on the material's surface.

POSSIBLE SOLUTIONSo Material to thin - Increase heat other than where pearl is evident.o Where the pearlescent area may be allowed to stretch further increase heat at pearl.o Increase overall preform temperatureo Pearlescence opposite a swung gate (Refer Swung Gate)o Pearlescence on the bottle shoulder may be the result of a blow air leak through nose from either the low valve, high blow valve or stretch rod oReduce low blow volume, increase low blow timeand reduce low blow pressure.o Ensure low blow bottle is not to large. Excessive petal formation in low blow will cause pearl in the petal area.o Pearlescence in the body in the form of a ring is the result of insufficient low blow.

10 Problem: FLAT SIDES POSSIBLE CAUSESo Poor venting due to excessive parting of the blow moulds allowing air to be trapped along the mould seams

POSSIBLE SOLUTIONS o Ensure excessive mould parting does not occur o Increase low blow pressure ensuring bottle diameter is close to blow mould sizeo 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.o Low blow bottle blown to fast.o Excessive high blow pressure at the end of low blow to minimize air that remains in the blow mould before high blow starts.o Reduce low blow pressure and extend low blow time if the body of the bottle hasreached the mouldo Reduce high blow pressure

11 Problem: DEFORMATION AT MOULD PARTING LINES POSSIBLE CAUSES

 o Pressure remaining in the bottle when blow moulds open.o Insufficient high blow cooling timeo Material too hot and/or too thickPOSSIBLE SOLUTIONSo Inadequate exhaust time, check exhaust valve activation.o Increase high blow time or reduce material thicknesso Reduce material thicknesso Reduce preform temperature

12 Problem: CHOCKED BODY POSSIBLE CAUSESo Insufficient or no low blowo Insufficient heat beside choke

POSSIBLE SOLUTIONS o Increase low blow pressureo Increase heat in the bodyo Reduce heat in the base and/ or neck.o Reduce air delay timeo Reduce stretch rod pressure

13 Problem: HEAVY BASE WEIGHT POSSIBLE CAUSESo Incorrect heating profile resulting in a poor distribution of material, over stretching of thebody or shoulder POSSIBLE SOLUTIONS o Reduce heat in the body and/ or shoulder until pearlescence occurs then increase heat at the base. Repeat until the base weight is correct.

14 Problem: LIGHT BASE WEIGHT

POSSIBLE CAUSESo Poor heating profile resulting in poor distribution of material, insufficient stretching of the body or shoulder.POSSIBLE SOLUTIONS o Reduce heat near the base of the perform until pearlescence occurs then increase heat to the shoulder and/or body. Repeat until base weight is correcto Increase air delay timeo Increase stretch rod pressureo Reduce low blow pressureo Reduce oven shielding of the taper 

15 Problem: FEET NOT FULLY FORMED POSSIBLE CAUSES  o Insufficient high blow pressure. Rate of high blow too slow, material movement stalls before reaching the corners. Often as a result of blow nozzle leako Insufficient high blow time. If adding high

POSSIBLE SOLUTIONS

 o Check high pressure. If possible. If station related check for high blow leaks from nozzle or stretch rod o Increase high blow timeo Reduce base weight by reducing

16 Problem: HOT SIDES POSSIBLE CAUSESo Inconsistent preform rotation through the oveno Insufficient surface cooling of the preform

POSSIBLE SOLUTIONSo Check the preform for a drag marl. Ensure oven shields are not touching the preform. Check collect, spindle or mandrel rotationo Increase air flow onto the surface of the preform

17 Problem: LOW HEADLOAD POSSIBLE CAUSESo Insufficient orientation and/or material thickness to deliver the required physical strength

POSSIBLE SOLUTIONS o Reduce over all preform temperatureo Reduce heat beside failure pointo Where failures occur between neck and shoulder adjust shield into a thicker part of the taper  18 Problem: LOW BURST PRESSURE (BODY) POSSIBLE CAUSESo Insufficient orientation (Too hot)o Material to thino Confirmationo Low IV

POSSIBLE SOLUTIONS o Reduce preform temperatureo Reduce body heat

19 Problem: LOW BURST PRESSURE (BASE) POSSIBLE CAUSESo Base of bottle blown too coldproducing excessive stresso Stretch rod clearance too shorto Excessive crystallinity at the gateo Low IVo Excessive stress in preform

POSSIBLE SOLUTIONS o Increase heat below the performo Reset stretch rod clearanceo Reduce stretch rod pressure

20Problem: POOR CLEARANCE POSSIBLE CAUSES

o Preform temperature too higho Heavy base weight

POSSIBLE SOLUTIONS o Base weight correct or light, reduce heat beside and/or below the gateo Endcap temperature too higho Aged performso Insufficient mould coolingo Excessive inherent preform stresso Base weight to heavy, reduce perform temperatureo Increase high blow time.

21Problem: FOLD IN BASE AT END CAP LINE POSSIBLE CAUSESo Preform temperature to hoto Preform endcap area to coldo An excess of material in the vicinityof the foldo Lack or loss of low blow volumeo Excessive force applied by thestretch rodo Aged or stressed preforms

POSSIBLE SOLUTIONS o 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.o Increase low blow pressureo Reduce air delay timeo Reduce stretch rod pressure

22Problem: FOLD AROUND THE STRETCH ROD POSSIBLE CAUSES o Over heating of the preformend cap, material wraps around the end of the stretch rod. In effect another thick/ thin transition forms

POSSIBLE SOLUTIONS o Reduce heat or below the end cap areao Increase low blow pressureo Reduce stretch rod pressure

23Problem: CRACKED BASE POSSIBLE CAUSESo Preform end cap too coldo Excessive stretch rod pressureo Clearance between the stretch rod and mould base too smallo Thick crystallinity above the gate

POSSIBLE SOLUTIONS o Increase heat beside or below the gateo Reduce stretch rod pressureo Check preform for excessive crystallinity, if so change preforms.

o Increase stretch rod, mould base gap

24Problem: SWUNG GATE / OFF- CENTERED POSSIBLE SOLUTIONSo First impacted mark is evident and is not centered to the gate, an alignment problem is usually the cause. Check for misalignment. Ensure transfer arm locates preform in mould correctly.o Check blow mould coolingo 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 growth in length during low blow. Ideally growth should start high in the preform reaching full diameter before full length if length is achieved before diameter the rod must travel further than normal to keep up.o Reduce low bottle size

o Increase air delay timeo Reset stretch rod heighto Check the gap between stretch rod tip and base mould. maintain .5 to 1mm. o Increse primary blow delay and secondary blow delay. o Increase l.p. air pressure. o check the stretch rod speed and increase if necassary.

POSSIBLE CAUSES o Misalignment of the preform to the mould, nozzle or stretch rod.o Inadequate mould cooling, one half only If the gate is centered to the stretch rod impact mark and yet not centered to the mould base at the end of blow the stretch rod has lost control during blow.o Lower half of preform too hoto Low blow pressure too higho Air delay time too shorto Stretch rod length too shorto Excessive stretch rod cushioningo Worn stretch rod guideso Excessive preform eccentricityo Thick crystallinity near gate

25Problem: STRESS CRACKING POSSIBLE CAUSESo Off center gates. Webs with the thinnest material will stress crack early.o Excessive post mould change. As clearance deteriorates web shape changes increasing the risk of stress cracking.o Excessive growth at the base cust line. Temperature of the lower half of the preform's body is to higho Chemical reaction by some line lubricants.o Low I.V. materialo Light base weight. Inadequate thicknesso resist movement.

POSSIBLE SOLUTIONSo Fix swung gate.

o Reduce preform temperature to pearlescence, reduce base weight if necessary. Increase high blow timeo Reduce heat in the preform's lower bodyo Line lubricants generally cause severe stress cracking in all feet.o Increase base weight

26Problem: EXPLOSIONS POSSIBLE CAUSESo Hot bottles (Refer Hot Bottles)o Folds in the baseo Light base weighto Excessive post mould growtho Low I.V.o Chemical Reaction (Refer stress Cracking)o Contaminationo Air bubbles above the gate

POSSIBLE SOLUTIONS o Refer Causes

o Stress Crackingo Cracked baseso Excessive crystallinity

27Problem: DROP TEST FAILURES POSSIBLE CAUSESo Preform end cap blown too coldo Light base weighto Excessive crystallinity above gate.o Large air bubbles above the gatePOSSIBLE SOLUTIONS o Increasing heat at the gate or below without loosing base weight usually improves drop test failure.o Increase base weight.