how to make shrink tube mastic adhere to urethane tubing

I am looking for a way to make heat shrink tube mastic (the meltable
adhesive in certain shrink tubes) adhere to urathane tubing.
I am building a sensor that is to be used for winter maintenance
vehicles (plow trucks). The sensor element is potted in a 3/4 inch
steel tube with a 24 inch wire extending to a connector. The wire is
protected by flexible tubing covering the wire from the sensor to a
connector. A piece of shrink tube connects the tubing to the
connector. The tubing needs to have good adhesion in the potting
material and to the mastic liner of the shrink tube.
The problem I am finding is that it is hard to find a compatible tube
that will adhere well to the potting material (Locktite urathane has
been selected at this time) and the mastic liner of the shrink tube. I
see poor "wetting" and adhesive strength of the surface of several
types of tubing to either the potting or the mastic.
I tried urathane and various rubber tubing (1/4 ID, 3/8 OD). Rubber
seems to adhere best to the mastic. I'd like to use a urathane tubing
material, but I can't get the mastic to give good peel strength.
Are there materials I should try that "prepare" the surface of the
urathane to allow good adhesion of a urethane material to the heat
activated mastic of shrink tube?
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You've got at least three tubes here, right? The steel tube, the shrink tube, and the urethane tube, right?
Can I assume that in every case where you are referring to "tube" without further qualification, you are referring to the urethane tube? Otherwise, it is difficult to parse your screed.
My first thought is would it be possible to use wires 28" long, and tie three knots in the wires, an inch or two apart?
UV/ozone or electrostatic discharge is often used to improve adhesion to a polymer sufrace. Also various primers. Have you asked the shrink tube/mastic vendor for a primer recommendation?
Reply to
Mark Thorson
You are correct. The tube referred to without further qualification is the urethane tubing (1/4" ID, 3/8" OD) that protects the wires coming from the sensor. The sensor is in the steel tube. The urethane tubing goes to the connector. The shrink tube covers the urethane tubing and the connector. I have not asked the shrink tube distributor for a primer recommendation. I think that is a good idea, but my thought is that they will not have the sophistication in this area to answer the question of what might create good adhesion to the mastic.
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I just tried the Gorilla glue. I applied it to the urathane tube. Wiped it off. Put the shrink tube on the tube with the coating of Gorilla glue and...amazing!!!! It works like a charm!! The mastic adheres tenaciously. Got the clue from the newsgroups here. I just LOVE the newsgroups. We are so lucky we work in these times. If only the rest of the US business worked as well. wrote:
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