Heat Shrink Tubing

Introduction

Heat Shrink Tubing is a shrinkable plastic tube used to insulate wires and provide abrasion resistance. It is also used to bundle groups of wires, or provide identification. Heat shrink tubing will shrink its diameter when heated to a specific temperature, with little or no shrinkage along its length.
Polyolefin is the most commonly used heat shrink tubing material. It is used by military, automotive, railway and aerospace industries.
Other materials include PTFE, Viton, Silicone Rubber and PVC.

Single v/s Dual Heat Shrink

Single / Thin wall tubing is the most common. This tubing provides a good seal against water and other contaminants. It also strengthens connections, reducing the likelihood they can pull apart. However it achieves this through friction only and typically does not bond with the material it shrinks to.
Dual Wall or Adhesive Lined tubing features an adhesive lining. It melts as the tubing contracts forming a truly sealed connection. It also dramatically increases the strength of connections, even making it stronger than the wires themselves.

Importance

Heat Shrink tubing has many uses. Some are listed below:

• Seal water and other contaminants out of wire connections
• Provide electrical insulation
• Insulate against extreme heat
• Color code wire for easy identification
• Bundle multiple wires together
• Cleanly terminate ends of braided sleeving
• Improve the overall look of large amounts of wiring

Why should we use heat shrink tubing instead of traditional insulation?

Heat shrink tubing provides extensive durability and heat resistance. In most cases, it outperforms basic insulation. Additionally, heat shrink tubing is built to provide the perfect fit and will not come off with age or use (the same cannot be said for electrical tape). Heat shrink tubing is also generally easy to install. Some heat shrink tubing requires costly heat shrink machinery, but some tubing can be installed manually.

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Additional Information
Heat shrink tubing was invented by Raychem Corporation. It is manufactured from a thermoplastic material such as polyolefin, fluoropolymer (such as FEP, PTFE or Kynar), PVC, neoprene, silicone elastomer or Viton.
The material is often cross-linked through the use of electron beams, peroxides, or moisture. This cross-linking creates the memory in the tubing so that it is able to shrink back to its original extruded dimensions upon heating.

Heat Shrink Insulated Terminals

Ring Terminals

These terminals offer superior performance over standard crimp terminals. After crimping, the hot-melt glue lined heat shrink sleeve is heated and shrunk down onto the cable. This increases the mechanical strength of the termination and its resistance to corrosion, as the melted glue effectively seals the joint.

Female Terminals - Fully Insulated

Male Terminals

Buying Heat Shrink Tubes

Heat shrink tubing comes in a wide range of colors and sizes. It also comes with a variety of protection levels, including heavy wall, multiple wall, and single wall.
Here are some things to consider if you’re buying heat shrink tubing:

• Maximum diameter of your cable bundle: This will help you choose the correctly-sized heat shrink tubing.
• Temperature range of your environment : Some heat shrink tubing is rated to extremely high and low temperatures, while other tubing is designed for more moderate environmental conditions.
• Wall thickness: Heat shrink tubing is typically categorized by heavy wall, multiple wall, and single wall tubes. Thicker walls provide enhanced durability, rigidity, and abrasion resistance – but come at an extra cost and can unnecessarily thicken your cable arrangement.
• Required resistance properties: For example, your wires may be exposed to chemicals and oils

It’s also a good idea to buy heat shrink tubing that is slightly longer than you need. When heat is applied, you’ll notice that the tubing slightly shrinks lengthwise as well as widthwise, though ideally they are expected to shrink only along the diameter.

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Additional Information
Heat shrink tubing comes with a range of different ratios. You’ll see these ratios advertised directly on heat shrink product descriptions or packaging. Here are the most common ratios and their uses:
2:1 ratio: These tubes shrink to half its original size when heat is applied
3:1 ratio: These tubes shrink to one third of its original size when heat is applied

Types of Heat Shrink Tubes

Image reproduced from here

Elastomeric Tubes

They maintain high flexibility even at low temperatures and meet stringent international specifications. Their operating temperature range is -75 to 150 °C. A common shrink ratio is 2:1.

Fluorinated Ethylene Propylene (FEP)

It is a versatile electrical insulator and is inert to most chemicals and solvents. Additionally, it is highly resistant to extreme heat, cold, and ultraviolet radiation, making it an excellent material for heat-shrink tubing applications.

Polyolefin Tubes

The are most commonly used and have maximum use for temperatures from -55 to 135 °C, and are used by the military, aerospace and railway industries. They are flexible and fast-shrinking, and manufactured in a wide range of colors (including clear), which can be used for color-coding wires. Polyolefin tubing shrinks at 143°C. Polyolefin heat-shrink tubing typically shrinks 2:1 diametrically, but high-grade polyolefin heat-shrink is also available with a 3:1 ratio. Polyolefin tubing may withstand being touched with a soldering iron.

References

• http://ramproducts.com/6-things-need-know-heat-shrink-tubing/
• http://www.jttproducts.com/jt-t-tech-articles/An-Introduction-to-Heat-Shrink-Tubing
• https://en.wikipedia.org/wiki/Heat-shrink_tubing
• https://www.youtube.com/watch?v=ak-9BxjWMlw

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