How to Fix Burning and Weak Sealing Issues on Your Plastic Bag Making Machine

In the competitive packaging market of the UAE and the Middle East, many factory owners run into a common problem when they switch production to biodegradable materials or thicker eco-friendly films: the bag making machine starts acting up, and the sealing quality is usually the first thing to fail. Bottom seals either split open under a light tug or get burned through by the cutting knife. Every rejected bag on the line is one you have already paid to produce and cannot sell — film, power, and operator time are spent before the defect shows up. On a busy shift the scrap stacks up fast, and a machine that used to run clean on conventional film now needs constant watching.

Why Bio-Film Seals Fail in UAE Plants

The trouble usually starts with the material. Traditional HDPE and LDPE offer a wide melting window, so operators have room for error. The biodegradable grades — PLA or PBAT blends, which are being pushed by the UAE’s phase-out of single-use plastic bags — are far more heat-sensitive, with a much narrower window. A drop of one or two degrees gives poor bonding and weak seals; an increase of a few degrees burns through the film and leaves holes.

There is a quick way to tell the two apart on the shop floor. A seal that peels apart in your fingers is usually running too cold or with too little dwell time; a burned, brittle edge that breaks when you bend it means too much heat or too much time at the knife. Reading that correctly first saves you from adjusting the wrong knob and making the problem worse.

To make things harder, many older machines rely on mechanical thermostats or standard relays that lag behind. The panel may read 140°C while the sealing knife is actually swinging between 130°C and 150°C — which is why a machine seals well in the first minutes after startup and starts burning film half an hour later.

Step 1: Get the Temperature Right — PID Control and Dwell Time

The first fix is precision. A PID micro-computer controller holds the knife temperature to about ±1°C, and that stability is the foundation of a clean run on bio-films. When you first install one, run a test batch rather than trusting the readout at face value, and watch the first twenty minutes after startup — that is where the lag shows up most.

Dwell time matters just as much. Operators often push the heat up to chase speed, but for thicker films or bio-compounds the better move is to raise the sealing pressure and dwell time and lower the temperature slightly. Low temperature plus high pressure lets the heat reach through the layers for a solid bond without overheating and scorching the outer layer. Adjust in small steps and run a few bags after each change to judge the seal before committing the whole shift.

Step 2: Keep the Sealing Hardware in Shape — Teflon and Bar Balance

Precision control only works if the hardware is sound. Check the Teflon tape or coating on the knife regularly: with the heat common in UAE plants, worn anti-stick coating lets molten film stick to the knife, and when the sealing bar lifts, the film tears apart into a defect that looks exactly like a burn-through. You can usually spot the wear before it fails — film residue clinging to the knife line, or seals that tear on one side at the lift. Check it as part of the daily start-up routine, and replace the element when it starts to wear; let the knife cool and wear heat-resistant gloves first.

Also check the mechanical balance of the sealing bar. If the spring tension on the two ends is uneven, you get a weak seal on one side and a burned hole on the other. A quick tell: run a few bags and look at the seal across the width — strong at one end and weak at the other points to the spring tension before you even take the covers off. Have the technicians calibrate the pressure across the whole blade line before each shift, with the machine cool and locked out.

Temperature precision, dwell time, Teflon condition, and bar balance cover most sealing failures. Work through them in that order and your line can run clean on bio-films, staying in line with the UAE’s move away from single-use plastics.

If your factory is seeing persistent seal failures, or you are comparing machines that handle biodegradable films well, our technical team would be glad to review your setup.