After the heat shrinkable sleeve is baked to the welded junction, we need to carry out some tests to check whether it is qualified and meets the standards. One of the most important is peel strength.
The peel strength test of heat shrinkable joint material can reflect the bonding performance from two aspects. The first is the peel strength value, the second is the peel phenomenon, which reflects the adhesion of the interface between the base material of the heat shrinkable sleeve and the adhesive, the adhesive and the reducing primer or the overlapping area, the primer and the steel pipe, and the cohesion of each layer of materials. Generally, it can be divided into five categories:
1. Completely cohesive peel. The peeling section is adhesive layer, and the surface of primer or base material is evenly covered with adhesive layer.
2. Partial cohesive peel / partial non cohesive peel. Part of the peeling section is occupied by the adhesive layer, and part of it shows non cohesive peeling with primer or base material (there is peeling strength value, but the adhesive layer is pulled away from the surface of primer or base material)
3. Completely non cohesive peeling. That is, the peeling section is pulled away from the surface of the adhesive layer and the primer or base material.
4. Partial non cohesive peeling / partial viscosity loss. That is to say, the stripped part of the section is full of primer, and the part is layered with primer or base material.
5. Complete loss of viscosity. That is to say, the peel strength is zero, and the primer or base material is layered with the heat shrinkable sleeve material.
Test method for general peel strength:
First, the anticorrosive coating shall be cut along the circular direction with a strip of 20-30mm in width and more than 100mm in length. When it is cut, the anticorrosive coating shall be completely scratched and one end shall be lifted. Use a dynamometer to pull up the anticorrosive coating at a rate of 10 mm / min perpendicular to the steel pipe surface at a constant speed, and record the value of the dynamometer. During the measurement, the surface thermometer shall be used to monitor the external surface temperature of the anti-corrosion coating, and the peel strength test shall be completed between 45-55 ℃.
The value recorded by the dynamometer divided by the peeling width of the anticorrosive coating is the peeling strength, in N / cm. The results are expressed as the average of three determinations.
Normally, we measure the peel strength of the heat shrinkable sleeve, generally at the normal ambient temperature, about 24 ℃. It cannot be carried out at low or high temperature.
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