The quality of double-wall heat shrink tubing needs to be identified from two dimensions, and compared before and after shrinkage.

1. Before shrinking, you can focus on comparing the following factors:

1. Compare the softness under the same wall thickness. Generally, the quality of double-walled heat shrinkable tubes with good softness will be better than that of harder tubes;

2. Wall deflection rate. This is easy to understand. It means that on the same double-walled heat shrinkable tube, there will be a certain error in the wall thickness on the upper and lower sides. The smaller the error value, the better the dimensional accuracy, generally within 20%.

3. Surface flatness, no bamboo knots on the surface, no impurities and oil stains. The higher the surface flatness of double-wall heat shrinkable tubes of the same material, the better the quality.

4. The quality of the hot melt adhesive layer on the inner wall. After cutting the double-walled heat shrinkable tube along the tube wall, you should clearly see a uniform and bright layer of hot melt adhesive. If the brightness is not high or there is one bright surface and one matte surface, it means If the hot melt adhesive is applied unevenly, there is a risk that the sealing effect will not be achieved.

2. After shrinkage

1. Shrinkage speed. The shrinkage temperature of double-wall heat shrinkable tube is 70-110℃. If it is in the same temperature environment, the shrinkage should be uniform without bubbling.

2. Axial shrinkage rate. During the shrinkage process, the tube wall should move closer to the center instead of leaning to one side of the tube wall.

3. Surface cleanliness: after the shrinkage is completed, the surface of the pipe wall will have no impurities, no color difference, no bulges, and will be smooth and free of cracks.

4. The fluidity of the hot melt adhesive layer. After the double-wall heat shrink tube shrinks, the hot melt adhesive on the inner wall should evenly adhere to the tube wall. If it shrinks on the cable, a circle of hot melt adhesive should overflow from the port.

    There are no mandatory requirements for the bonding strength of hot melt adhesive on double-walled heat shrink tubes, because depending on the materials to be bonded, special corresponding hot melt adhesives need to be used to achieve better bonding effects.

    From the above points, you can roughly identify the quality of double-wall heat shrink tubing. The insulation and sealing properties require professional testing equipment to test.