Bottle blowing lines are built for repeatability, but small shifts in heat, air, water cooling, or Mold alignment can quickly turn into defects, downtime, and scrap. Below is a practical troubleshooting guide that focuses on the issues operators and maintenance teams see most often, with checks you can do on the floor and durable fixes you can implement at the process and equipment level.

As a manufacturer, BOHANG supports bottle blowing systems along with related automation like Manipulators, molds, and packing equipment, so troubleshooting can be handled as a complete production cell instead of isolated machines.

Before troubleshooting: lock your “4 utilities” baseline

Most recurring problems trace back to utilities drifting during shifts. Before changing molds or rewriting recipes, confirm these baselines are stable:

• Compressed air: pressure, dryness, and flow reserve for peak blow demand

• Cooling water: inlet temperature, flow rate, and filtration

• Power supply: voltage stability, grounding, heater/servo load spikes

• Ambient conditions: airflow around the oven, dust, and temperature swings

If any of the above fluctuate, the same settings can produce different bottles hour to hour.

Quick diagnosis table

Problem 1: Uneven wall thickness and unstable bottle weight

What it looks like: one side of the bottle is thin, bottles feel inconsistent by hand, or weight variation fails QC.

Typical root causes

• Heating imbalance between zones, or heater aging causing “invisible” hot/cold bands

• Preform is not centered when entering the mold, so stretching is asymmetric

• Stretch rod timing and pre-blow timing not synchronized to the actual material temperature

Floor checks

• Pull 10 bottles across a 15–20 minute window, record weight and thickness points

• Mark preforms with a line and observe whether the line stays centered after blowing

• Verify heater zone setpoints match actual readings, not only controller display

Durable fixes

• Rebuild the heating map: focus on shoulder and base transitions first

• Improve preform guidance and centering, especially after maintenance

• Adjust pre-blow delay and pre-blow pressure ramp to match preform temperature, not “last week’s” recipe

Problem 2: Bottle haze, pearlescence, or whitening

What it looks like: cloudy appearance, whitening near the shoulder/base, or a “stress haze” after cooling.

Typical root causes

• Overheating the preform surface, creating orientation stress

• Moisture issues in preforms or material handling

• Cooling water temperature too high, or flow restricted by scale/filters

Floor checks

• Compare haze rate at shift start vs mid-shift (often points to utilities drift)

• Check cooling water inlet temperature and differential across mold

• Inspect oven reflectors and airflow for dust buildup or blocked circulation

Durable fixes

• Standardize drying and storage conditions for preforms

• Increase cooling efficiency: clean filters, stabilize inlet temperature, verify flow

• Reduce overheating by smoothing heater transitions instead of cutting all zones equally

Problem 3: Neck finish deformation and cap fit failures

What it looks like: oval necks, threads out of tolerance, caps cross-threading, or leaks in torque testing.

Typical root causes

• Neck area receiving too much radiant heat

• Transfer/handling stress while the neck is still warm

• Neck ring cooling insufficient or uneven

Floor checks

• Use a go/no-go gauge and track which cavities fail more often

• Observe transfer timing: look for micro-delays that cause gripping while hot

• Check neck ring cooling passages for blockage

Durable fixes

• Shield the neck area during heating and concentrate heat lower on the body

• Improve neck cooling and reduce handling shock

• If failures are cavity-specific, inspect that cavity’s neck ring wear first

Problem 4: Bottom blowout, weak base, or base cracks

What it looks like: occasional base burst during blowing, weak “petaloid” base, or cracks after filling.

Typical root causes

• Pre-blow curve too aggressive or too weak for the current temperature

• Base overheated, then stretched too fast

• Venting or blow pin sealing issues causing unstable pressure delivery

Floor checks

• Review pressure curves and confirm actual pressure response matches the recipe

• Inspect base vents and exhaust paths for blockage

• Check seals and blow pin alignment for air loss

Durable fixes

• Tune pre-blow to “prepare” material before final blow, not to do all shaping

• Improve base cooling and venting consistency

• Replace worn seals early; small leaks become big defects at scale

Problem 5: Flashing, parting lines, and mold-related defects

What it looks like: excess plastic at the parting line, rough seams, or inconsistent finish.

Typical root causes

• Mold misalignment after changeover

• Clamp force not reaching target, or mechanical wear

• Parting surfaces damaged by debris or improper cleaning tools

Floor checks

• Do a simple closure test and inspect contact uniformity

• Compare defect rate right after mold change vs later in the day

• Inspect mold faces for embedded debris

Durable fixes

• Implement a repeatable mold changeover checklist with alignment validation

• Service clamp mechanisms and verify force calibration

• Use cleaning methods that protect parting surfaces

Preventive maintenance that actually reduces downtime

A strong PM routine is less about doing “more work” and more about doing the right checks at the right frequency:

• Daily: air leak walkdown, water filter inspection, oven lens/reflector wipe

• Weekly: sensor calibration spot-check, heating zone verification, mold water flow confirmation

• Monthly: full pressure curve validation, pneumatic seal review, oven airflow deep clean

• Quarterly: mold alignment audit, clamp system inspection, electrical grounding review

Where BOHANG fits in when problems keep repeating

If you’re fighting the same defect after multiple recipe changes, it’s usually time to look at the system design: heating stability, control logic, mold compatibility, and how automation handles preforms and bottles. BOHANG’s bottle blowing equipment is positioned as a modular solution with intelligent control and customization support, and the product range includes Bottle Blowing Machines plus supporting items like molds and manipulators for more consistent loading/unloading.

For energy-sensitive operations, BOHANG also describes energy-saving design approaches such as servo drive and energy-saving technology claims on certain models, which can be relevant when air and heating costs dominate your per-bottle expense.

Closing note

Most bottle blowing “mystery problems” become straightforward once you separate utility drift from process settings and mechanical alignment. Start with stable air/water/power, confirm heating reality versus controller numbers, then tune timing and pressure curves. If defects remain cavity-specific or return right after changeovers, focus on mold condition and alignment before chasing the recipe.