A VFFS machine rarely fails without warning. A seal that looked fine in the morning starts to leak by afternoon, the film drifts to one side after a roll change, or the jaws jam on a pinch of powder. Each of these faults has a short list of likely causes, and most of them can be found and fixed by an operator in minutes if the checks are done in the right order.
This guide is written for production supervisors, maintenance technicians and plant owners who run vertical form fill seal machines on powders, grains, snacks or granules. It covers the faults we are asked about most, the cause behind each, and the order in which to check. It does not replace the manual for your own machine, so always follow the safety rules and lock-out procedure before you open a guard.
How a VFFS Machine Makes a Pouch (and Where Faults Start)
Knowing the sequence helps you place a fault. Flat film unwinds from a roll, and a dancer arm or brake holds it at steady tension. The film passes over a forming collar and tube, which wrap it around the tube. Heated jaws or a sealing bar close the back seam, and servo belts pull the film down. The bag length is set by the servo motor or by a registration mark on printed film. Cross-seal jaws close below the tube, sealing the top of one pouch and the bottom of the next, and a knife cuts them apart. Product drops down the tube in the pause between seals.
Almost every fault falls into one of four zones: the film path (unwind, dancer, rollers), the forming tube and back seal, the cross-seal jaws, or the timing between the filler and the bagger. Start by deciding which zone the fault belongs to, and the search becomes much shorter.
Film Not Tracking: The Most Common Starting Point
When film wanders to one side, the back seam wanders with it and the pouch comes out crooked or the seal is weak at one edge. Common causes are a film roll that is not centred on the spindle, film threaded incorrectly, rollers and the dancer that are not parallel to each other, uneven film tension, a splice table that is still clamped, rollers that do not spin freely, an automatic tracking device that is not working, a damaged or incorrectly fitted forming tube, splice tape caught in the forming tube, pull belts that are set unevenly, and a dirty brake roller.
- Stop the machine and re-centre the roll on the air spindle, then re-thread the film along the marked path.
- Check that every roller and the dancer bar turn freely and sit parallel.
- Inspect the lower and upper film carriages for alignment, and look for tape or a burr on the forming tube.
- Clean the brake roller, since a film-dust or adhesive build-up changes tension from side to side.
- Check that both pull belts press on the film with equal force and are not worn smooth.
Film tracking should be solved before any seal setting is changed, because every other adjustment assumes the film is running straight.
Bad Vertical (Back) Seals
A poor back seal usually looks like a fine channel along the seam, a seam that peels open, or a seam that is wrinkled. The usual causes are a forming tube backstop set in the wrong position and an incorrect gap between the film and the forming tube. Worn foam or tape on the forming tube can also stop the film lying flat against the sealing bar.
- First confirm film tracking and correct loading and folding.
- Adjust the backstop and the film-to-tube distance so the overlap is even.
- Inspect the foam and tape on the forming tube and replace them if they are worn.
- Only then fine-tune sealing time, temperature and pressure in small steps, noting each change.
Leaking or Weak Cross Seals
The cross seal is the seal across the top and bottom of the pouch, and the main enemy of this seal is product caught between the jaws. Fine powders, spices and flour are the usual culprits, since a small amount of dust in the seal weakens the bond. Wrinkles in the film and jaws that are not parallel are the next most common causes.
- Clear any product from the jaw faces and the seal area.
- Check that the jaws meet squarely and that the sealing faces and Teflon tape are clean and undamaged.
- Remove film wrinkles by checking tension and the forming tube.
- Adjust the time the filler drops product so it does not reach the jaws before they close, and use a dust extraction or a longer fall delay for powders.
- Last, tune time, temperature and pressure, because raising temperature to hide dust in the seal only burns the film and shortens jaw life.
For dusty products, the filler matters as much as the jaws. A well-matched servo auger filler controls the dose and reduces dust at the seal, and our powder packing machine page explains the set-up.
Jaw Temperature Out of Range
If the control panel shows the jaw temperature outside its range, the problem is one of four things: the jaws have not finished warming up, the temperature sensor has failed, a heater cartridge has failed, or a fuse or breaker has tripped. Allow the jaws to warm up first. Then check the wiring against the electrical drawings, confirm the solid-state relay indicator is on, and inspect the sensor, the heater and the fuses in that order. Do not bypass an over-temperature alarm, since it protects the film and the operator.
Jaws Not Opening or Jamming
A jaw jam is usually caused by product in the end seal, incorrect timing between the filler and the bagger, jaws that are not set up as the manual specifies, or low air pressure at the jaws. A jaw that cannot open fully may also point to an assembly that is binding, a fault in the air cylinder or its slide, a faulty piston position sensor or a fault in the air distribution.
- Switch off and lock out, then clear product from the jaws.
- Check the filler-to-bagger timing, since a product drop that is late or early will land in the closing jaws.
- Verify the air pressure at the machine, and confirm the supply line is large enough for the machine.
- Move the jaw assembly by hand where the manual allows and feel for binding.
Short Bags, Uneven Bag Length and Print Registration
Bag length is controlled by the servo motor or by a registration sensor reading a mark on printed film. If bag lengths vary, check for slipping pull belts, which give short bags and inconsistent lengths, then check the registration sensor for dirt and the correct position on the mark. Printed film with a faint or inconsistent mark confuses the sensor, so ask your film supplier for a high-contrast registration mark. A printer or coder that does not fire is generally a simple cause: it is switched off, the cable is damaged or loose, or the ribbon has broken.
The Machine Does Not Start, Reset or Hold Air Pressure
If the machine will not power up, confirm that incoming power is present and the main disconnect is on. If it will not reset, look for open guard doors, an engaged emergency stop, a safety circuit that has not been reset, or low air pressure. Check the safety relay and wiring only after the simple items are ruled out. Low air pressure can come from an undersized supply line as well as a compressor fault, so verify both.
A Simple Daily and Weekly Maintenance Routine
Most faults described above are prevented by routine care. A short routine does more than a long repair.
- Every shift: wipe the jaw faces and the forming tube, clear dust from the seal area, check the Teflon tape on the jaws and confirm the air pressure.
- Every day: clean the brake roller and the dancer, check the pull belts for wear and look at the sensors for dust.
- Every week: check the jaw alignment, tighten fasteners, inspect cables and air lines, and note the jaw temperature against the setting.
- Every month: review the wear parts, namely jaws, knife, heater cartridges, belts and Teflon tape, and compare the stock of spares with your list.
Keep a log of the settings that work for each film and product. When a fault appears, the log shows what changed, and a new operator can reach a good pack in minutes instead of hours.
When the Fault Is Really a Specification Problem
Sometimes the machine is running correctly and the real problem is a mismatch. A film with a sealing layer that is too thin for the jaw temperature, a pouch that is too heavy for a seal designed for lighter packs, or a product that needs a different filler will keep causing faults however carefully the machine is adjusted. Our guide to why seal quality matters explains how film, jaw and product interact, and the main vertical form fill seal machine page shows the configurations we build for different products.
Get Help From VS Packit
VS Packit has built VFFS machines in Faridabad for more than two decades and supports customers with installation, operator training, spare parts and technical advice. If a fault keeps returning, send us the product, the film, the pouch size and a short video of the fault, and our engineers will tell you where to look. You can contact our team here or call +91 9811103573.