PTFE heat shrink tubing is available in 2:1 and 4:1 ratios. In use, the tube, or sleeve, is heated to about 340 °C and expanded by applying compressed air. Subsequently, the material cools under constant pressure and retains the expanded form. If the tube is subsequently heated again to around 340 °C, the so-called memory effect occurs: the material returns to its original shape.
Notes on heatshrink tubing application
PTFE shrinkable tubing should be shrunk at a temperature of 340 °C +/- 5 °C. PTFE changes to a gel state at 320 °C (crystalline to amorphous). This is visually apparent, as the heatshrink tube loses its milky white colour. PTFE is thermally damaged at around 350 °C. The part to be shrunk to must be able to withstand this temperature. Any material which is to be shrunk to, which could be destroyed or significantly altered at these temperatures, will only remain unaffected if highly specialized techniques are employed or through favourable technical combinations.
Damage through incorrect shrinking temperature
If the parts to be shrunk to absorb too much heat, the heatshrink tube can literally freeze when it comes into contact with the colder part. For a firm and smooth fit, the part to be shrunk to must also be brought approximately to the shrinking temperature. Overheating the shrinktube can destroy its plastic memory (shrinkage property) and make the tube unusable.
Best results through uniform heating and cooling
As a result of the manufacturing process, longitudinal shrinkage can occur during shrinking. The longitudinal shrinkage can be up to ten per cent. Uniform heating and cooling from all sides give the best results. Uneven heating and cooling can lead to wrinkling and cracking. Shrinkage begins when the PTFE reaches its gel point. It continues during the cooling phase.
The following heating methods are suitable:
- Ovens are very reliable. Uniform heating and cooling is easily possible. When the parts to be shrunk to and the shrink tube have reached their temperature, a built-in fan can be switched on for cooling.
- Hot air blowers have also proven their worth. The prerequisite is to achieve sufficient heating to heat the tube and the part to be shrunk to, without overheating.
- Clear gas flames have also been used successfully. Special care must be taken to ensure that the heatshrink tubing is not spot overheated, which could damage the tubing or the shrinkage effect.
- Infrared radiators are only useful if the parts to be shrunk to reflect the heat to the PTFE heat shrink tubing.
Should you have any further questions on the application of heatshrink tubing, please do not hesitate to contact us.