Heat Shrink Tube Process (II）

Chemical crosslinking
Add chemical crosslinking agents such as peroxides to the raw materials.
After extrusion molding, the chemical crosslinking agent is activated by heating to trigger the intermolecular crosslinking reaction.
This method is less used for high-end heat shrink tubes due to the control difficulty and residue issues.
After this step, the plastic pipe changes from thermoplastic to thermosetting and acquires the ability to "remember" its current shape.
Step 3: Heating for expansion and cooling for setting
Heating: The already cross-linked plastic pipe is sent into the heating box and heated to a "high elastic state" temperature higher than its crystallization melting point. At this point, the material becomes soft and elastic, but does not melt.
Expansion: When a material is in a highly elastic state, pressure is applied to its interior (usually compressed air or nitrogen), just like blowing up a balloon, to radially expand it to 1.5 to 6 times or even more of its original size (this multiple is called the "contraction ratio").
Cooling and setting: Rapidly cool the expanded tube under the condition of maintaining the expansion pressure (for example, by water cooling or air cooling). After cooling, the expanded form is fixed.