General Tips on Selecting, Applying and Shrinking Heatshrink
1. Selection:
Confirm the OD(Outside Diameter) of the cable / object you need to cover.
Decide on the wall thickness you require. Based on the thickness you may need to choose one size up or select a heatshrink with a higher shrink ratio. Standard thin wall heatshrink has a 2 : 1 ratio which means it will shrink to half its supplied size. (Example: 25.4will shrink to 12.7).
Take note that all heatshrink sizes are given as the ID (Inside Diameter) and not in mm² or layflat (see pages 4, 5, 7, 12).Should you not have the ID refer to pages 4, 5, 7 and see the calculation necessary to determine the ID.
When choosing the heatshrink always allow for at least a 20% shrink and a maximum of 80% as this will ensure the product performs according to the specifications stated.
Will the heatshrink be placed onto the cable before or after a lug or ferrule has been crimped into place? If afterwards confirm that the heatshrink size is suitable to fit over the lug / ferrule and if it will still recover to the OD of the cable. If not, a heatshrink with a higher shrink ratio must be selected.
Other considerations include:
- Do you need a moisture seal / watertight connection, this will require an adhesive lined heatshrink (see pages 16, 17, 18, 25)-- Will it be exposed to cleaning fluids, fuel, oils or more aggressive chemicals? This may require diesel resistant, Kynar, Viton or Teflon heatshrink.
- What will the minimum or maximum operating temperature be? Typically diesel resistant, Kynar and Teflon material offer higher operating temperatures, up to 330°C.
- Are you covering identification labels that must be clearly visible after shrink and must it be moisture free? Various grades of clear heatshrink exist, including adhesive lined.
- Do you need any specific specifications, approvals and accreditations? This may include Military, Halogen Free, RoHS, Flame Retardant, REACH, UL, IEC, UV stability etc.
- What will the operating voltage be?
- Do you require high abrasion properties?
- Standard or specialised colours. (Standard - Black, Clear, White, Red, Blue, Yellow, Green /Yellow).
2. Application and Shrinking
Always keep the work area and cables / application as clean as possible.
When cutting the heatshrink to the required size bear the following in mind.
- Always cut with a sharp knife / guillotine. Make sure that there are no jagged edges as this will lead to the heatshrink splitting / tearing during application of heat (see page 7).Should you need to trim the heatshrink to size after shrunk, allow sufficient time for the product to cool down first.
- In order to allow for continuation of insulation determine a suitable overlap.
- Allow for the longitudinal shrinkage by cutting slightly longer. This could be as much as 5% (see page 7).
Slide the heatshrink sleeve into place by positioning it centrally over the ferrules / object.
Before shrinking:
- Carefully read the installation instructions first as improvements and amendments may have been introduced.
- Confirm that all other heatshrink or components have been placed over the cable and that all ferrules / lugs are crimped / connected.
- Remove all sharp edges that may cause the heatshrink to split.
- Ensure that the surface has been abraded (if required) and that it is clean and de-greased.
- If an adjustable heat gun is used, confirm the suitable setting / temperature. Incorrect temperature may lead to uneven shrinkage / wall thickness, incorrect insulation properties, damage to heatshrink and undesired air entrapment.
Commence shrinking by starting from the middle working towards the outer ends applying heat circumferentially outwards until the internal sealant (adhesive) has melted, sleeves have a uniform wall thickness and are fully recovered (see below).
When shrinking long lengths of heatshrink tubing (on cables for example), commence shrinking at one end and gradually move towards the other end.
When shrinking thicker wall heatshrink (shrinks at higher temperatures) you may also use a propane gas torch (see below). When doing this keep the following in mind:
- Ensure that this is done in a well ventilated area.
- Use a “clean burning torch” e.g. a propane gas torch which does not leave any conductive contamination deposits.
- Adjust the torch to a soft blue flame with an orange / yellow tip. A “pencil-like” blue flame should be avoided (see below).
- As this heatshrink has a very thick wall the torch / flame has to be moved continuously to ensure proper shrinkage and avoid damage due to overheating in one place.
Keep the following in mind during the shrinking process:
- Keep the heat aimed in the shrink direction to pre-heat the material (see below).
- Always apply the heat circumferentially around and outwards on all tubes, this ensures correct heat application which results in the correct material wall thickness.
- Shrink the tubing and moulded parts as recommended and indicated in the instructions & manufacturer’s guidelines.
Once shrunk, all of the tubing should be smooth and free of any wrinkles. Signs of wrinkles indicate incorrect heating and possible air entrapment. With regards to Medium Voltage (MV) applications this may lead to failure over time.
Allow the heatshrink to cool before applying any mechanical strain or trimming / cutting it to size.
How to calculate / determine the correct size Airshrink or Heatshrink for your busbar dimensions.
1. Add all four sides.
2. Divide by 3.1415 (π)
3. This result gives the actual OD (outer diameter) of your busbar and thus the min ID (inner diameter) that your Airshrink / Heatshrink
needs to shrink down to.
4. Add 10% to this result to allow sufficient clearance. This will ensure that your Airshrink / Heatshrink slips over easily.
Example
Busbar Size: 50 x 10
= (50+50+10+10) / 3.1415
= 120 / 3.1415
= 38.198
Add 10%
= 42.02mm
This is the most suitable diameter (ID) for your application. Now choose the Airshrink / Heatshrink
size that suits this busbar size. (AS3510 / 50.8)
2. Layflat to Diameter
Heatshrink sizes are given as the internal diameter (ID) as supplied and NOT the layflat (LF) size. If you are not sure of the correct ID you can calculate as follow:
Example:
Heatshrink size: 25.4mm
ID = (LF x 2 ) / 3.1415 (π)
= (40 x 2) / 3.1415
= 80 / 3.1415
ID = 25.46mm
3. Circumference to Layflat
To calculate the Layflat if you have the diameter (D) it can be done as follow:
Example:
Heatshrink Size: 25.4mm
Circumference (C) is the same as 2 x Layflat (LF)
C = 3.1415 x ID
2LF = 3.1415 x ID
2LF = 3.1415 x 25.4
2LF = 79.79
LF = 79.79
2
LF = 39.9mm
4. Imperial to Metric
Heatshrink sizes are given as the internal diameter (ID) as supplied and NOT the layflat (LF) size. If you are not sure of the correct ID you can calculate as follow:
