The Engineer's Troubleshoot: 20 Common Faults in Stretch Film Vacuum Machines and How to Fix Them

With 15 years in the trenches designing, commissioning, and maintaining vacuum packaging systems for the food industry, I've compiled a hard-won truth: 80% of downtime stems from 20 recurring, predictable faults. Stretch film vacuum packaging machines, while marvels of automation, are precision electro-mechanical systems. Their reliability is non-negotiable in food production. This guide distills my experience into a systematic fault catalog and resolution protocol. Our goal is not just to fix problems, but to understand their root causes and prevent recurrence.

 

 

Part 1: The Vacuum System – The Heart of the Process

 

The vacuum system's failure is immediate and catastrophic to product quality. These faults directly compromise shelf life and safety.

 

1. Fault: Slow Pump-Down Time or Failure to Reach Target Vacuum

• Symptoms: Cycle time increases; vacuum gauge stalls above target (e.g., 20 mbar instead of 5 mbar); persistent air in packages.

• Root Causes & Solutions:

  • Vacuum Pump Oil Degradation: Oil is the pump's lifeblood. Contaminated, watery, or carbonized oil loses viscosity and sealing ability. Solution: Change oil per manufacturer's spec (typically 500-1000 hrs), using only recommended grade. For humid environments, use a polymer-based oil resistant to moisture emulsification.

  • System Leak: The most common cause. Solution: Perform a staged isolation test. Isolate the pump and test its ultimate vacuum. Then, isolate the chamber. Use a helium leak detector or a "soap bubble" test on all fittings, valves, the chamber lid gasket, and solenoid valve diaphragms. A leak rate >0.5 mbar-L/sec is typically unacceptable for food packaging.

  • Clogged Vacuum Filter/Exhaust Muffler: A blocked filter strangles the pump. Solution: Replace or clean the inlet filter and exhaust muffler cartridge quarterly.

  • Worn Pump Vanes/Rotors: Internal wear reduces pumping capacity. Solution: Measure the pump's ultimate vacuum when isolated. If it cannot reach its rated value (e.g., <0.1 mbar for a rotary vane pump), a rebuild is due.

 

2. Fault: Oil Carry-Over into the Vacuum Chamber

• Symptoms: Oil mist or droplets inside the chamber, contaminating the sealing area and product.

• Root Causes & Solutions:

  • Overfilled Oil Reservoir: Causes excessive foaming and misting. Solution: Maintain oil level at the center of the sight glass.

  • Wrong Oil Viscosity: Oil too thin for operating temperature. Solution: Use the ISO VG grade specified for your ambient conditions.

  • Failed or Missing Oil Mist Filter/Exhaust Coalescer: Solution: Inspect and replace the exhaust filter element regularly. This is a consumable item.

 

3. Fault: Vacuum Valve Failure

• Symptoms: Vacuum not pulling, slow pumping, or valve audible but not functioning.

• Root Causes & Solutions:

  • Solenoid Coil Burnout: Check for power at the coil. Solution: Replace the solenoid coil. Investigate if voltage is correct and if the valve is binding, causing coil over-current.

  • Mechanical Binding or Diaphragm Rupture (for diaphragm valves): Debris or worn seals prevent operation. Solution: Dismantle, clean, and replace the diaphragm/seal kit. Install an inlet filter to protect the valve.

  • Pneumatic Actuator Failure (for pneumatic valves): Check air supply (typically 6 bar). Solution: Repair or replace the pneumatic actuator; ensure air lines are not kinked.

 

 

Part 2: The Sealing System – The Critical Barrier

A perfect vacuum is worthless with a failed seal. This system demands precision in temperature, pressure, and time.

 

4. Fault: Weak or Incomplete Seal (Leaking Seals)

• Symptoms: Packages leak under test; seals peel apart easily; visible wrinkles or channels in the seal.

• Root Causes & Solutions:

  • Insufficient Temperature: The top film's sealing layer (e.g., PE) is not melting fully. Solution: Verify heater bar temperature with a contact pyrometer. Recalibrate the PID controller if needed. Ensure heater bands are fully seated and making contact.

  • Insufficient Pressure/Dwell Time: The films are not held together with enough force for enough time. Solution: Increase sealing pressure (via pneumatic regulator) and/or dwell time in the PLC program. Check that the sealing bar is parallel and the pneumatic cylinder is not sluggish.

  • Contaminated Sealing Surface: Product residue, oil, or water prevents polymer bonding. Solution: Implement a strict, frequent cleaning protocol for the sealing bar using approved, non-residue-leaving cleaners.

  • Cooling Time Insufficient: The molten seal is disturbed before solidifying. Solution: Increase the post-seal cooling/crimp time in the machine cycle.

 

5. Fault: Burnt Seals or Film Melting Through

• Symptoms: Seals are charred, brittle, or the film has a hole along the seal line.

• Root Causes & Solutions:

  • Excessive Temperature: Solution: Reduce heater bar setpoint. Use a pyrometer to map temperature profile; hot spots indicate a failing heater band or poor thermal transfer.

  • Excessive Dwell Time: The film is subjected to heat for too long. Solution: Reduce sealing dwell time.

  • Incorrect Film: Using a film with a low-melting-temperature sealing layer for a high-heat application. Solution: Consult your film supplier to match the film's thermal properties to the machine's parameters.

 

6. Fault: Sealing Bar Not Activating

• Symptoms: No heat or pressure applied during the seal phase.

• Root Causes & Solutions:

  • Failed Solid-State Relay (SSR) or Contactor: The SSR that switches power to the heater bar fails, often "open" or "closed." Solution: Test the SSR. If it's failed closed, the bar will be constantly hot. Replace it.

  • Broken Heater Band: Measure resistance of each heater band. An open circuit (infinite resistance) indicates a break. Solution: Replace the broken heater band. Consider replacing in pairs for even wear.

  • Faulty Temperature Sensor (Thermocouple): A false "high temperature" reading will prevent the controller from energizing the heaters. Solution: Check sensor calibration and replace if faulty.

  • PLC Output or Program Error: The control signal is not being sent. Solution: Monitor the PLC output for the seal command. Check the logic of the program sequence.

 

Part 3: The Film Handling System – Precision in Motion

This system dictates film waste, package appearance, and operational consistency.

 

7. Fault: Film Wrinkling or Misalignment

• Symptoms: Crooked packages; film gathers or folds before sealing, causing leakers.

• Root Causes & Solutions:

  • Incorrect Film Roll Alignment/Braking: The film is not feeding squarely off the roll. Solution: Ensure the film roll spindle is aligned and the mechanical or magnetic brake is providing even, adjustable tension.

  • Worn or Dirty Film Feed Grippers/Claws: These components, which index the film, must be sharp and clean. Solution: Inspect and clean daily. Replace worn grippers.

  • Uneven Pre-Stretch: The mechanical fingers that stretch the bottom film are not synchronized or are worn. Solution: Check the synchronization of the pre-stretch drive chain/belt. Replace worn stretching fingers.

 

8. Fault: Film Does Not Feed/Index

• Symptoms: Machine stops with "film fault" alarm; cavities are empty.

• Root Causes & Solutions:

  • Film Breakage: Solution: Check for sharp edges on the forming die, sealing bar, or cutting tools. Ensure film quality is consistent.

  • Faulty Film Feed Sensor: A photoelectric sensor that detects the film's registration mark is dirty, misaligned, or failed. Solution: Clean the sensor lens and reflector. Verify alignment and signal strength. Adjust sensitivity.

  • Insufficient Gripper Force/Pressure: The film slips. Solution: Increase the gripper pneumatic pressure or check for worn gripper pads.

  • Film Roll Finished or Tangled: Solution: Standard operating procedure check.

 

9. Fault: Inconsistent Cavity Depth

• Symptoms: Packages vary in depth; some are shallow, risking product overfill and seal contamination.

• Root Causes & Solutions:

  • Incorrect or Fluctuating Pre-Stretch Ratio: Solution: Recalibrate the pre-stretch system. The pre-stretch ratio (e.g., 250%) must be matched to the film grade and desired cavity depth.

  • Uneven Heater Plate Temperature for Forming: The bottom film is heated to be pliable for forming via compressed air. A cold spot will cause a shallow cavity. Solution: Use a thermal camera or surface probe to map the forming plate. Replace faulty heating elements.

  • Insufficient or Unstable Forming Air Pressure: Solution: Check the regulator and solenoid valve for the forming air. Ensure the air supply is stable and dry.

 

10. Fault: Poor Film Cutting (Tearing, Not Cutting)

• Symptoms: Individual packages are not separated cleanly; ragged edges.

• Root Causes & Solutions:

  • Dull or Chipped Cutting Blades/Knives: Solution: Sharpen or replace the blades. They are wear items. A schedule based on operational hours should be established.

  • Insufficient Cutting Force or Misalignment: The upper and lower blades must meet perfectly. Solution: Adjust the blade alignment and the pneumatic pressure/spring force for the cut.

 

 

Part 4: The Control & Electrical System – The Brain and Nerves

Modern machines are run by PLCs. Electrical issues often manifest as illogical or intermittent faults.

 

11. Fault: PLC in "Stop" Mode or Program Error

• Symptoms: Machine dead; HMI shows a fault code or "STOP."

• Root Causes & Solutions:

  • Emergency Stop or Safety Circuit Activated: Solution: Check all E-Stop buttons, safety guard switches, and light curtains. Reset them.

  • Major Fault in a Critical Subsystem (e.g., Over-temperature, Motor Fault): Solution: Acknowledge the fault on the HMI. The diagnostic code will guide you to the specific subsystem. Clear the root cause before resetting.

  • Corrupted PLC Program or Memory Error: Solution: Reload the program from a known-good backup. This underscores the necessity of regular program backups.

 

12. Fault: Intermittent or "Ghost" Faults

• Symptoms: Random stoppages with varying error codes; faults that clear on reset.

• Root Causes & Solutions:

  • Loose Wiring Connections: Vibration causes intermittency. Solution: Perform a systematic check and tightening of all terminal blocks, especially on sensors, solenoids, and motor connections.

  • Failing Proximity or Photoelectric Sensor: A sensor on the edge of failure may work when cool but fail when warm. Solution: Monitor the sensor status on the HMI in real-time to catch the dropout. Replace the suspect sensor.

  • Electrical Noise Interference: From VFDs, welders, etc. Solution: Ensure all shield drains on sensor cables are properly terminated. Check grounding of the machine cabinet and main earth.

 

13. Fault: Touch Screen HMI Unresponsive or Blank

• Symptoms: No display or touch inputs ignored.

• Root Causes & Solutions:

  • Failed Power Supply to HMI: Solution: Check the DC voltage (e.g., 24VDC) at the HMI terminal. Replace the machine's switched-mode power supply if output is low or absent.

  • HMI Internal Failure: Solution: Cycle power. If no change, replace the HMI unit. Ensure the program is backed up and can be reloaded.

 

14. Fault: Servo/Stepper Motor Fault on Film Indexing

• Symptoms: "Drive Fault" alarm; film index jerky or inaccurate.

• Root Causes & Solutions:

  • Mechanical Overload/Binding: The motor is trying to move against a physical obstruction. Solution: Manually turn the drive mechanism to check for smooth movement. Look for seized bearings or physical damage.

  • Drive Parameter Mismatch or Fault: Solution: Check the drive's error code. Reset the drive. Ensure motor tuning parameters are correct. An overheated drive can indicate insufficient cooling.

  • Failed Feedback Device (Encoder/Resolver): Solution: Replace the encoder cable or the motor if the encoder is integral.

 

Part 5: Mechanical & Pneumatic Systems – The Muscle and Ligaments

These faults are often slow to develop but lead to increasing inaccuracy and wear.

 

15. Fault: Excessive Machine Vibration or Noise

• Symptoms: New or growing rattles, knocks, or harmonic vibrations.

• Root Causes & Solutions:

  • Loose Mounting Bolts or Frame Components: Solution: Go through the machine with a torque wrench and re-tighten all structural and sub-assembly bolts according to spec.

  • Worn Bearings in Gearboxes, Indexers, or Drive Shafts: Solution: Use a mechanic's stethoscope or vibration pen to isolate the noisy bearing. Replace it. Listen for a grinding or rumbling sound.

  • Unbalanced Rotating Component (Fan, Pump Coupling): Solution: Check the vacuum pump coupling alignment. Inspect cooling fans for damage.

 

16. Fault: Low or Unstable Pneumatic Pressure

• Symptoms: Sealing, cutting, or clamping actions are weak and slow.

• Root Causes & Solutions:

  • Factory Air Supply Issue: Solution: Check the plant air pressure at the machine inlet filter/regulator. It should be stable at 6-7 bar.

  • Clogged Air Filter/Regulator/Lubricator (FRL) Unit: Solution: Service the FRL. Drain water from the filter bowl, replace the filter element, and ensure the lubricator has oil.

  • Air Leak in the Machine: Solution: Listen for hissing. Use a soapy water solution on air line fittings and valve bodies. Tighten or replace fittings/valves.

 

17. Fault: Cylinder Failure (Sealing, Cutting, Clamping)

• Symptoms: Cylinder does not extend/retract, or moves sluggishly.

• Root Causes & Solutions:

  • Seal Failure within the Cylinder: Internal leaks bypass pressure. Solution: Rebuild the cylinder with a new seal kit or replace the cylinder.

  • Bent Piston Rod: Caused by side-load impact. Solution: Replace the cylinder. Ensure the load is properly guided to prevent recurrence.

  • Blocked or Failed Solenoid Valve Controlling the Cylinder: Solution: Check the valve is energizing. Swap the valve coil or the entire valve with a known-good one to test.

  •  

Part 6: Operational & Process Faults

These are often "nuisance" faults that halt production but have simple triggers.

 

18. Fault: Product in the Seal Area (Contaminated Seal)

• Symptoms: Chronic leakers due to particles or liquid between the sealing films.

• Root Causes & Solutions:

  • Overfilling of Cavities: Solution: Adjust the filler head or check-weight system. There must be a clear "seal margin" (typically 3-5mm) around the product.

  • Product Splashing/Boiling Under Vacuum: Liquid products can erupt. Solution: Implement a slower, two-stage vacuum pull to gently remove air before pulling a hard vacuum. Use a defoaming program if needed.

  • Poor Cavity Registration: The top film is not aligned over the bottom cavity. Solution: Adjust the film tracking/alignment system.

 

19. Fault: Film Web Breaks Frequently

• Symptoms: Production stops for film splicing.

• Root Causes & Solutions:

  • Poor Film Quality or Incorrect Specification: Solution: Audit film thickness, tensile strength, and elongation at break. Work with your supplier.

  • Sharp Edge on Forming Die, Sealing Bar, or Machine Frame: Solution: Deburr and polish any edge the film travels over. Use protective nylon rollers or guides.

  • Excessive Tension from the Brake or Indexing System: Solution: Reduce the film unwinding brake tension to the minimum required to prevent film overspool.

 

20. Fault: Condensation Inside the Vacuum Chamber

• Symptoms: Water droplets on the chamber walls and lid, especially with cold or wet products.

• Root Causes & Solutions:

  • Lack of Chamber Heating: Most machines have a heated chamber to prevent condensation during the vacuum cycle. Solution: Ensure the chamber heater (often a ribbon heater on the lid) is enabled and functioning. Check its thermostat and heating element.

 

Conclusion: The Philosophy of Prevention

 

Treating these 20 faults reactively is a path to chronic downtime. The professional approach is Predictive and Preventive Maintenance (PM). Build your PM schedule directly from this list:

 

• Daily: Clean sealing bars, check film alignment, inspect for leaks/oil.

• Weekly: Check pneumatic pressure, clean sensors, verify safety circuits.

• Monthly: Check heater temperatures with a pyrometer, inspect grippers and cutting blades, tighten frame bolts.

• Quarterly/Annually: Change vacuum pump oil, replace air filters, service pneumatic valves, verify PLC program backup.

 

Document every intervention and fault. This log becomes your most powerful diagnostic tool, revealing patterns and wear rates specific to your operation. By mastering these 20 points, you transform from a technician who fixes machines into an engineer who ensures flow. The goal is for the machine to be the most reliable component on your production line.

If you have any production questions please contact with us.