Every common bottle defect - streaks, thin walls, pear-shapes, flash, black specks - with its real cause and its real fix.
This guide exists because your production line does not stop at 5 pm. When bottles start coming off the machine wrong, every hour of confusion is scrap, lost output and a nervous sales team. What operators need is a plain-language map from what I see to what I fix.
So here it is: the eight defects we are asked about most, each with its true cause ranked by likelihood, and the fix in the order you should try it. Bookmark it - and when a fix needs a part, our spare parts desk dispatches worldwide within 7 days. Buying a machine instead? Start at the blow machines page.
The MethodEvery defect is the machine telling you exactly which system failed. Streaks point at the die head. Walls point at the parison. Shapes point at air and cooling. Specks point at material handling. Read the bottle like a diagnostic report and the fix is usually one adjustment away - the discipline is changing one variable at a time and logging it.
Causes: scratch on die lips, degraded material stuck in the die, melt temp too low.
Fix in order: raise melt temp 10°C and purge - clean and polish die lips - inspect die for damage and replace if scored.
Causes: uneven die head temperature, worn parison control, blow ratio beyond machine capability.
Fix in order: verify all die head heater zones - check parison programming settings - reduce bottle size or upgrade the machine.
Causes: blow pressure too low, parison too hot, clamp misalignment, wrong pinhole position.
Fix in order: raise blow pressure in 0.5 bar steps - reduce parison temp - check clamp parallelism and pinholes.
Causes: clamp force too low, melt temperature too high, die gap worn or open.
Fix in order: reduce melt temp slightly - increase clamp pressure - inspect and rework or replace the die gap.
Causes: moisture in the material, wet regrind, purge needed after material change. Fix: dry the material to spec before processing, screen regrind, purge completely.
Causes: burnt material from high temperature or long residence, dirty regrind, damaged screw flighting. Fix: full hot purge - lower temperatures - screen or replace regrind - inspect screw.
Causes: cooling time too short, mould temperature too high, bottles stacked hot. Fix: extend cooling 1-2 seconds - lower mould water temp - never pack bottles warm.
Causes: unstable screw speed, heater zone drift, inconsistent regrind blend. Fix: check drive stability - log zone temperatures hourly - standardise the regrind ratio.
Eighty percent of the defects above are prevented by a routine, not a repair:
Hydraulic oil level, air pressure at the regulator, mould water flow, all heater zones at setpoint.
Weigh five bottles and log the average - weight drift is the earliest warning of every problem on this page.
Clean die lips, check filter screens, verify chiller temperature, test safety interlocks.
Fixes not holding after two attempts means a worn part, not a setting - that is the moment for the spare parts desk, not more adjustments.
Every defect above has a wear-part behind it eventually: heater bands, thermocouples, seals, die lip sets, parison control components, filter screens. A shelf stocked at 5-10 percent of machine value converts most breakdowns from weeks of waiting into an afternoon of fitting.
Heater bands, thermocouples, hydraulic seals, filter screens, blow pins - the consumables of production.
Everything beyond the shelf ships from our spares catalogue within 7 days - see the catalog for any machine brand.
Vertical streaks or die lines come from a damaged or contaminated die head - a scratch on the die lips, degraded material stuck inside, or melt temperature too low. Clean and polish the die, check the melt temperature, and inspect for damage.
Uneven walls trace to the parison: temperature variation around the die head, a worn parison control, or the blow ratio pushed beyond the machine's capability. Start with a die head temperature check and parison programming.
Pear-shaping and lean come from unbalanced blowing - blow pressure too low or uneven air flow, a parison that is too hot, or clamp misalignment. Check pressure gauges, pinhole placement and clamp parallelism.
Black specks are degraded plastic: material burnt inside the barrel or die head from excessive temperature or residence time, or contaminated regrind. Purge the machine fully and screen your regrind.
Daily: check hydraulic oil, air pressure, water flow and heater zones. Monthly: clean die heads and inspect seals. Annually: full preventive service with worn-part replacement - a documented spare parts plan prevents most breakdowns.
Send photos of the bottle, your machine model and the parameters - our engineers diagnose it free, usually within 24 hours. Parts, if needed, ship within 7 days.