Plastic Carry Bag Machine Troubleshooting: Fixing Punching Cut-Off Failures, Scrap Jams, and Hydraulic/Pneumatic Synchronization

Downtime on a plastic carry bag manufacturing machine often comes from a small number of recurring problems: punching cut-off failures, scrap blocking, and timing mismatch between feeding, punching, and cutting. This article is written from a maintenance and service perspective to help you quickly diagnose issues and restore stable production.

It applies to many systems sold as a plastic carry bag making machine, carry bag cutting machine, or “banana handle” carry bag machine.

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1. Symptom: punching does not cut through cleanly

Common causes

• worn punching die / dull cutting edge
• incorrect punch clearance or misalignment
• insufficient pressure (hydraulic/pneumatic)
• film thickness changed but parameters not updated

Fix steps

1. Inspect die edge under magnification; regrind or replace if rounded
2. Check punch-to-anvil alignment and clearance; adjust to spec
3. Verify pressure stability and check for air leaks or hydraulic pressure drop
4. Reconfirm punching dwell time and feed stop timing

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2. Symptom: frequent scrap jams around the punch area

Common causes

• scrap removal suction too weak
• static attraction (scrap sticks to tooling)
• scrap path has sharp edges or narrow turns
• scrap bin overfilled or filter blocked

Fix steps

• clean and check suction fan/filter performance
• add/repair anti-static devices and grounding
• smooth the scrap channel and remove snag points
• schedule scrap bin checks in operator SOP

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3. Symptom: punching position drifts (hole not centered)

Common causes

• feeding roller slip
• unstable tension from unwinder
• worn encoder or sensor contamination
• servo parameter drift after maintenance

Fix steps

• check roller pressure and surface condition
• confirm tension settings and brake response
• clean sensors; verify encoder mounting
• recalibrate servo feeding length and registration

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4. Symptom: cutting unit and punching unit out of sync

This is often described as “timing mismatch” and can become worse at higher speed.

Common causes

• pneumatic cylinder response delay
• hydraulic valve wear or pressure fluctuation
• mechanical backlash in transmission
• controller parameter mismatch after speed changes

Fix steps

• test cylinder speed and replace worn seals/valves
• verify hydraulic oil condition and valve response
• inspect couplings, belts, gears for backlash
• re-tune timing parameters at target speed (not only low-speed)

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5. Preventive maintenance checklist (reduces repeat failures)

Daily:

• clean punch area and scrap channels
• verify pressure gauges within normal range
• quick check: unusual noise or vibration

Weekly:

• inspect die sharpness and alignment
• check suction system and filters
• test sensor stability and cable wear points

Monthly:

• full timing verification at production speed
• inspect pneumatic/hydraulic seals
• check grounding and anti-static system performance