Function and classification of heat shrink tube
Heat shrink tubing is primarily utilized in the junctions or terminals of wiring harnesses, serving essential functions such as electrical insulation, mechanical protection, and corrosion sealing.
When heat shrink tubing is subjected to heat, the hot melt adhesive within it melts and flows to fill the internal spaces of the tubing.
rom a thickness perspective, heat shrink tubing can be categorized into thin-walled, medium-walled, and thick-walled varieties. Structurally, it can be divided into single-wall heat shrink tubing, which lacks an adhesive layer, and double-wall heat shrink tubing, which contains a layer of hot melt adhesive.
Among automotive wiring harness products, double-wall heat shrink tubing is the most commonly used.
Hot melt adhesive layer material and outer material
The materials for the hot melt adhesive layer primarily include two types: EVA (ethylene-vinyl acetate copolymer) based hot melt adhesive and PV (nylon) based hot melt adhesive.
The outer layer is typically made from PDX (polyolefin), PES (synthetic rubber), FBM (fluoropolymer), PVDF (polyvinylidene fluoride), and PTFE (polytetrafluoroethylene).
Select the key parameters of the heat shrink tube analysis
Depending on the specific application needs, the shrink ratio of heat shrink tubing varies from 2:1 to 6:1. To select an appropriate heat shrink tubing, we consider the following parameters:
- Wall Thickness of Heat Shrink Tubing: The material thickness is displayed in millimeters after complete shrinkage. “Nominal” refers to the size without any tolerances. Generally, individuals can distinguish between thin-walled, medium-walled, and thick-walled heat shrink tubing.
- Diameter of Heat Shrink Tubing: For thin-walled tubing with a shrink ratio of 2:1, the standard tube diameter is usually 25.4 millimeters (equivalent to one inch).
- Shrink Ratio: Depending on the composite materials used and the wall thickness, heat shrink tubing can undergo varying degrees of compression. The shrink ratio indicates the ratio between the provided diameter and the diameter after recovery, varying from 2:1 to 6:1. A higher shrink ratio allows for coverage of a broader range of object diameters, thus minimizing the number of sizes of heat shrink tubing required, which helps reduce inventory and free up space.
- Change in Length After Shrinkage: Heat shrink tubing not only shrinks in diameter but also in length. The change in length after shrinkage is expressed as a percentage.
- Minimum Shrink Temperature: Heat shrink tubing will not shrink at the same temperature; its shrinkage depends on the type of composite material used and the thickness of the tubing wall.
- Operating Temperature: Each type of tubing has a different operating temperature, which is determined by the type of composite material used.
When selecting the appropriate size of heat shrink tubing, the 80:20 principle should be followed: the tubing should shrink by at least 20% but not exceed 80% of the nominal diameter to achieve optimal performance.
Application of heat shrink tube technical standard in automotive industry
Automotive manufacturers focus on the functional aspects of heat shrink tubing, while wiring harness companies or manufacturers’ technical standards will also include material requirements.
Among the widely recognized technical standards for heat shrink tubing in the market are General Motors’ GMW17136 and Volkswagen’s TL82324. In the domestic market for new energy vehicles, GBT2408 and QC/T29106 are commonly adopted standards.