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Home » FAQ » Shrinking H.S. tubing

How to -  Heat Shrinkable Tubing

However application of Heat Shrinkable Tubing is quite uncomplicated, we advice you to follow the below steps for the best possible result. It will help you to avoid disappointments and possible quality issues.

In the case you are still left with questions, please contact us.

Shrinking, the short version

  1. Select the largest H.S. tubing size that can just shrink far enough to snugly fit your object
  2. Cut the H.S. tubing with a pure square cut, and take in account a few percents extra length to compensate for a possible minor lengthe shrinkage.
  3. Apply the H.S. tubing on your object, possible centering it over a certain point and if applicable make sure you have enough overlapping with underlaying insulation to assure sealing.
  4. Slowly heat the H.S. tubing circularly all around by moving the heat source (heater or flame) around the object.
  5. Continu doing point 4, until the H.S. tubing is all around snugly fit to the object, and than move slowly to the end of the H.S. tubing while continuing the circular movements. Don't push it to much to avoid irragular surfaces and air bubbles.
  6. Now you should have a good result without irregularities, 'craters' or air bubbles. When using H.S. tubing with adhesive, the adhesive should have flown a little out of the tubing all around, indicating good flow which enables a proper seal.
  7. Allow the H.S. tubing to cool down

Good luck!

A comprehensive desciption of the above:

STEP 1: Select the proper size

Select the proper size for your application. To assure a snug fit you best choose a size that can shrink just a bit smaller than the smallest diameter of your object. On the other hand make sure that the size as supplied is large enough to allow applying it over the object. This may lead to multiple available sizes that meet these demands. We advice to choose to largest of these possible sizes, as this size will have to shrink further, giving a thicker and stronger wall and avoid damage during or after shrinkage. Take in account that H.S. tubing is vulnerable during heating!

 

STEP 2: Cutting the Heat Shrinkable Tubing at length

Cut the H.S. tubing at a usable length for your application. Take in account that sometimes an overlap with underlaying insulation is necessary and that H.S. tubing can show a length shrinkage of up to 5%. Make also sure that you make a proper cut in one move and as sqare as possible. This avoids extra chance of the H.S. tubing to tear apart during shrinkage.

 

STEP 3: Applying the H.S. tubing over the object

Apply the H.S. over the object. If applied over a cable or wire connection, make sure it is centered properly over the area to be protected.

 

STEP 4: Heating the H.S. tubing

Especially unexperienced users are recommend to shrink using an electrical heating gun (heater) instead of using a torch. We have special heaters available for this application with various nozzles to direct the air, depending on tubing diameter and specific application.

Though less professional and quickly, you could also use any commercially available heater like for removing paint.

Using a torch requires some more experience, but for large or thick tubing, or for application of the heat shrinkable tubing on metal surfaces it can even be necessary. Preferably use a yellow flame. A yellow flame is hot enough, has a more even temperature and is much better visible. You can clearly see the flame flowing around your object.
Handling a torch requires som experience to constantly move the torch to spread heat and not overheat the object. It's certainly not difficult but as stated before; it requires some experience. See also the video on the page Shrinking with a torch.

 

STEP 5: Circularly applying heat; from end to end

When shrinking a relatively long piece of heat shrinkable tubing, you will mostly start shrinking from one of the ends, towards the opposite end. Continuously apply the heat circular all around the tubing and continue doing so until the tubing has fully shrunk and any adhesive has clearly flowed, allowing adherance to your object. Then continue circularly applying heat and kind of follow the end of the area that has been fully shrunk. You will see that the shrinking part of the tubing will slowly 'walk' towards the end, thus avoiding airtraps. Be patient, as your experience grows, it will automatically speed up and the quality of your work will improve.

Why circularly?

  • it causes an even wall thickness all around (un unshrunk area will stay thin!)
  • an unshrink areau will prevent the heat shrinkable tubing to reach it's specified end diameter
  • adhesive under an unshrunk and unheated area will not adhere to the underlaying surface

 

STEP 6: Cooling down

The result of your work should now be a smooth tubing surface, following the structure of your object. No airtraps, craters (indicating unheated areas), and folded parts. Let the heat shrinkable tubing cool down before applying any mechanically stress.

Like riding a bicycle this is quite simple, but you will need to learn it by experience!

Some more advice

Preheating

When shrinking on a relatively cool and heat absorbing surface, like (tich) metal tubes, it can be sensible to preheat that object. It will improve both the result and speed up the installation time! A cool metal surface will immediatel cool down the part of the heated heat shrinkable tubing under it's shrinking temperature. It wil stop shrinking, while the surrounding tubing will continue shrinking. This results in a crater like surface. It mostly can be solved by carefully continue applying heat to these areas, but this is time consuming and you have to avoid overheating the outer surface of the tubing. In fact you are trying to heat up a metal object through a thermal insulater (the heat shrink tubing)!

Preheating saves time and improves the quality of the job. Heating to a specific temperature is not necessary, but you can use 60°C as a rule of thumb for Polyolefin (PE, Polyethylene) heat shrinkable tubing. You can use your had as a sensor for this temperature: to hot to take in your hands, but to cool to immediately burn your hands. (you can tap the surface and feel the sensation of heat without burning your hands).

 

Avoid overheating

Particularly the combination of a thicker wall heat shrink tubing and a cold heat absorbing object, the outer surface of the tubing can get overheated when using very hot air or a torch. This can easily be avoided, as overheat is mostly visible before damage occurs.

  • Polyolefin heat shrink tubing get extra shiny when mildly overheated
  • Further increase of temperature will cause the tubing to generate smoke
  • When also neglecting that signal, the surface can get irregular, show bubbles and/or tear apart

When one or more of these symptoms are visible, take the heat source away for a moment (or direct it at an other part or more evenly over a larger area), allowing the heat to spread down the tubing and the surface to cool down a bit.

 

Silicone- or Teflon-spray (PTFE)

A spray can be applied on tubes, cables etc. prior to applying the heat shrinkable tubing, to ease application. On inner- and outerside of bends this will dramatically improve speed and result.

Shrinking on bends

Read the part about Silicone or PTFE spray first. Start shrinkage at one end, apply heat as mentioned before while pulling the tubing at the unshrunk side when nearing a bend. Pull just hard enough to expand the heated tubing enough to avoid wrinkles on the inner side of the bend. This requires heating the tubing all around the bend as the tubing has to expand on the outside of the bend (apply enough heat to the outside to allow shrinkage there first, so the material thickens in this areau that has to stretch in the length direction!).

We will be pleased to help you choosing your shrinking tools, of which we supply a whole range.

 

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