Troubleshooting Guide. PET Blow moulding. Blown finish. Sealing surface damage. Chocked neck

Transcription

1 Troubleshooting Guide PET Blow moulding Blown finish Overheating of the finish area which allows blow pressure air to stretch the material Move shield away from finish into a thicker part of the preforms taper. Oven ambient temperature to high Bring shield close to preform. Incorrect loading height, too much of the finish is exposed to the elements Increase oven exhaust. Reduce neck element heat. Sealing surface damage Misalignment of the preform, blow mould and blow nozzle usually caused by poor transfer arm positioning Realign transfer arm. Blow mold position Realign blow mold or nozzle if necessary. Nozzle position Chocked neck Over stretching of the preform by the stretch rod prior to blow Reduce air delay time.

2 Low blow delayed or missing 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. Bent neck Misalignment of the preform to the mould or nose Realignment of the preform to the nose or mould. Distortion below the flange Reduce material thickness in the shoulder by reducing heat in the body. Insufficient mould cooling Increase high blow time. One mould half with poor cooling Improve mould cooling. Excessive material remained in the neck and shoulder Hard neck Initial stretching occurs too low into the preforms taper Reduce heat in the body and/ or base until pearlescence occurs then increase neck temperature. Preform location incorrect through oven Increase stretch rod pressure. Air leak into preform before the start of low blow Increase air delay time. Reduce low blow pressure.

3 Move shield into the thinner part of the taper. Check height of preform though oven. Check for air leak through nose. Thin shoulder Excessive stretching of the taper. Stations producing a smaller low blow container will be first with the fault or the thinnest. Move shield into a thicker part of the preforms taper. Poor shield positioning, allowing excessive stretching of the thin part of the taper Reduce air delay time. Increase low blow pressure. Reduce heat in the neck. If thickening occurs below desired area Increase heat below the neck element. Hot bottles Preform temperature above crystal growth range for to long Reduce heat adjacent to the haze until pearlescence is evident somewhere on the bottle. Insufficient cooling of the outside surface for the amount of heat absorbed by the P.E.T. Reduce heat over all until pearlescence is evident. Excessive equilibration time o Preform wall thickness excessive blowers Increase air circulation through oven, increase blower speed, clean blowers. Excessive fill point drop Low levels of orientation results in the material not having enough strength to resist the pressure applied Reduce over all perform temperature allowing the bottle to be blown closer to its natural stretch limit.

4 Under this condition slight pearlescence may be evident. Pearlescence 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. Material to thin - Increase heat other than where pearl is evident. Where the pearlescent area may be allowed to stretch further increase heat at pearl. Increase overall preform temperature. Pearlescence opposite a swung gate (see"swung gate"). 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. Reduce low blow volume, increase low blow time and reduce low blow pressure. Ensure low blow bottle is not to large. Excessive petal formation in low blow will cause pearl in the petal area. Pearlescence in the body in the form of a ring is the result of insufficient low blow. Flat sides Poor venting due to excessive parting of the blow moulds allowing air to be trapped along the mould seams Ensure excessive mould parting does not occur. 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 Increase low blow pressure ensuring bottle diameter is close to blow mould size at the end of low blow to minimize air that remains in the blow mould before high blow starts. Low blow bottle blown to fast Reduce low blow pressure and extend low blow time if the body of the bottle has reached the mould.

5 Excessive high blow pressure Reduce high blow pressure. Deformation at mold parting lines Pressure remaining in the bottle when blow moulds open Inadequate exhaust time, check exhaust valve activation. Insufficient high blow cooling time Increase high blow time or reduce material thickness. Material too hot and/or too thick Reduce material thickness. Reduce preform temperature. Chocked body Insufficient or no low blow Increase low blow pressure. Insufficient heat beside choke Increase heat in the body. Reduce heat in the base and/ or neck. Reduce air delay time. Heavy base weight Incorrect heating profile resulting in a poor distribution of material, over stretching of the body or 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.

6 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/or 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. Feet 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. Check high pressure. If possible. If station related check for high blow leaks from nozzle or stretch rod o Increase high blow time. Insufficient high blow time. If adding high blow time does not fix the problem look for another cause. Reduce base weight by reducing preform temperature until pearlescence is evident then increase prefroms lower body temperature. Heavy base weight. High blow pressure inadequate to move material into the corners. Check low blow bottle size. Reduce if necessary. 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. Fix swung gate. Swung gate. Feet will not form in the corners opposite the gate movement unless extra heat is applied near the end cap. Hot sides

7 Inconsistent preform rotation through the oven Check the preform for a drag marl. Ensure oven shields are not touching the preform. Check collect, spindle or mandrel rotation. Insufficient surface cooling of the preform Increase air flow onto the surface of the preform. Low head 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. Low burst pressure (body) Insufficient orientation (too hot) Reduce preform temperature. Material to thin Reduce body heat. Confirmation Low IV Low burst pressure (base) Base of bottle blown too cold producing excessive stress Increase heat below the preform.

8 Stretch rod clearance too short Reset stretch rod clearance. Excessive crystallinity at the gate Low IV Excessive stress in preform Poor clearance Preform temperature too high Base weight correct or light, reduce heat beside and/or below the gate. Heavy base weight Base weight to heavy, reduce preform temperature. End cap temperature too high Increase high blow time. Aged preforms Insufficient mould cooling Excessive inherent preform stress Fold in base at end cap line Preform temperature to hot Reduce heat in the areas other than the base. If the fold remains after pearlescence has formed. Heat may

9 be applied to the preform end cap area. Preform end cap area to cold Increase low blow pressure. An excess of material in the vicinity of the fold Reduce air delay time. Lack or loss of low blow volume Excessive force applied by the stretch rod Aged or stressed preforms Fold around the 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 or below the end cap area. Increase low blow pressure. Cracked base Preform end cap too cold Increase heat beside or below the gate. Excessive stretch rod pressure Clearance between the stretch rod and mould base too small Check preform for excessive crystallinity, if so change preforms.

10 Thick crystallinity above the gate Increase stretch rod, mould base gap. Swung gate 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. Misalignment of the preform to the mould, nozzle or stretch rod. Check blow mould cooling 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. 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. Lower half of preform too hot. before diameter the rod must travel further than normal to keep up. Low blow pressure too high. Reduce low bottle size Air delay time too short. Increase air delay time Stretch rod length too short. Reset stretch rod height Excessive stretch rod cushioning. Worn stretch rod guides. Excessive preform eccentricity. Thick crystallinity near gate.

11 Stress cracking Off center gates. Webs with the thinnest material will stress crack early. Fix swung gate. Excessive post mould change. As clearance deteriorates web shape changes increasing the risk of stress cracking. Reduce preform temperature to pearlescence, reduce base weight if necessary. Increase high blow time. Excessive growth at the base cust line. Temperature of the lower half of the preform's body is to high. Reduce heat in the preform's lower body. Chemical reaction by some line lubricants Line lubricants generally cause severe stress cracking in all feet. Low I.V. material Increase base weight. Light base weight. Inadequate thickness to resist movement. Explosions Hot bottles (see "Hot bottles") Folds in the base Light base weight Excessive post mold growth Low I.V.

12 Chemical Reaction (see "Stress cracking") Contamination Air bubbles above the gate Stress Cracking Cracked bases Excessive crystallinity Drop test failures 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. Excessive crystallinity above gate Large air bubbles above the gate