Shrink Packaging Equipment
Terminology

There are two types of impulse sealing systems in the marketplace today: electromechanical gap compensation (oldest type) and electronic heat control (newest type).

Electromechanical Gap Compensation
The seal wire is stretched between two points and spring loaded toward one side with an adjustable gap compensator switch. Opening and closing of the gap is the switching function. When the seal bar is down, voltage is provided to the seal wire which heats and expands (heating portion of the cycle only). As the wire continues to expand, the gap begins to close. When the gap is closed, voltage is turned off and the sealing head remains down, applying pressure, during dwell time (the cooling or curing portion of the cycle). The width of the gap determines how long the wire will remain hot. The advantage to this process is it is simple, effective, proven and maintainable.

Electronic Heat Control
A printed circuit board or microprocessor is utilized to measure and control temperature and time. The trend today is to utilize electronic controls since the specific temperature is more accurately controlled and is more resistant to benign tampering.

Pressure during cycle dwell is critical. There are three common methods for controlling seal pressure:

Manual L-Sealers with no magnetic hold down
Pressure is applied by the operator who pushes down on the seal bar until the seal process is completed. Usually, a buzzer or light indicates a completed cycle.

Manual L-Sealers with magnetic hold down
The operator brings the seal bar down manually; magnets then engage to hold the seal bar against the sealing pad until electronically released by the machine timer (dwell time). The advantage to using magnetic clamping systems is that they accurately control dwell time and maintain uniform pressure during dwell (consistent with all operators).

Air-actuated semi-automatic and automatic machines
Use air pressure to hold the seal bar against the pad at the proper pressure. In some cases the bar is brought to the pad mechanically with cycling arms; in other cases the sealing bar is brought into contact with electronic magnets.

Most problems with seal pressure are encountered when the seal pad is uneven as a result of excessive use, or poorly designed/low volume equipment. Proper pressure depends upon a flat seal pad of the correct height and density. Further, if the seal bars are out of alignment it is difficult to provide correct pressure.

Adjustable inverted film forming plow allows centerfolded film to be utilized in-line by accommodating film behind the machine (transverse direction) and inverting it 90 degrees so that the film web runs in the machine direction. This system is commonly utilized on semi-automatic and intermittent automatic L-sealers, and automatic side-seal equipment.

Film separating rods are often utilized to separate film that may have some residual static caused by winding and to improve film openability and machinability.

Seal height position adjustment (seal tray height or take-away conveyor height adjustment) e nsures that the seal is properly placed (centered) on the package - allowing for product height flexibility on the machine for a range of products.

Power take-away conveyors automatically transfer the product into the shrink tunnel after
sealing is complete.

Film clamps are used on semi and automatic L-sealers to hold the film in position during the
sealing cycle.

When shrinking film around a product, the air within the film envelope expands and causes the film to "balloon" around the product. Air venting devices are required to ensure proper shrinkage by allowing air to escape from the product. Residual air, left unreleased because air holes were insufficient, could eventually cause the seals to burst or may leave the air trapped within the package; after the air cools and/or escapes, the film will appear as though it has not been completely shrunk or has relaxed. In some extreme cases when there are too many air evacuation holes or where poor seals occur, the air escapes too rapidly and the film may have ineffective shrink (excessive wrinkles). Typical devices include thermal, electric, pneumatic and rotary mechanical perforators.

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Shrink Packaging Equipment Terminology

Shrink Packaging Equipment
Terminology