Guidelines for Heat Sealing – how to join a Teflon belt
The Heat Sealing Unit must induce enough heat to allow proper bonding between the PFA-tape and PTFE (Teflon™) surfaces. The melting point of PFA-tape is around 380 to 390°C (716 to 752°F), but exposure time is another important factor for proper bonding. The choice of temperature is determined by a variety of factors like; thermal conductivity of the surface on which heat sealing take place, thickness of Teflon belts and bonding materials.
Applying a moderate pressure on the
Heat Sealing Unit may facilitate a stronger the bond. In order to achieve a good bond, the melting point of PFA-tape or PTFE bonding materials must be reached.
It is recommended to first make a trail with two smaller pieces of Teflon belts and PFA-tape to find out what time and temperature is required for a particular seal. A proper bond between Teflon surfaces and PFA-tape is stronger than the bond between Teflon and the fiberglass core. Prepare a trail by following the instructions below. Then try to pull the bond apart. If the Teflon and PFA-tape is bond properly then the fiberglass will be exposed when pulled apart and proper bonding has been achieved.
Prepare the Fixture upon which the ends are hold and sealing takes place. The Fixture have low thermal conductivity which help induce heat to the bond.
Align the ends with required angle and overlap, normally 90° and 50 mm (1,96 in) overlap. Use a marker pen to mark the 50 mm overlap.
Clean the overlapping areas with alcohol to ensure fats, dust and fingerprints are removed. Use latex gloves if necessary.
Carefully apply the PFA-tape along the entire length of the bond. Fix the ends with tape to hold the PFA-tape in place.
Heat up the Heat Sealing Unit to 380-400°C (716 to 752°F). Then apply heat on the bond for 90 to 120 seconds using no to moderate pressure. The first seal shall be at the centre of the bond, followed by a series of seals, every other on each side of the centre-seal towards the edges. Gently toggle the Heat Sealer to release it from the bond before removing it. Immediately rub the bond with a cloth or paper while it is still warm to remove air and enhance bonding. Be careful not to deform the warm bond as it is rubbed. -When the bond is completed, allow it to cool for a minute.
Check the bond before the Fixture is removed. Pay particular attention to the edges. Edges shall be bonded properly! If not, then apply heat with the Heat Sealer for another minute or so to bond edges properly. One can also apply heat at other areas where the bond may be deformed or partly open.
Trim the edges with a scissor or sharp carper knife before removing the Fixture.