The authoritative public forum
  for Metal Finishing since 1989
-----

Water Break Test vs Dyne Test - Stainless Steel and adhesion to PUR

November 9, 2009

Dear all,

This is my first post here, so please do bear with me should I accidentally violate some of your rules.

My question is about surface tension of stainless steel surfaces and their influence on adhesion til poly-urethane resins (PUR).

I need to waterproof some electronics that are submerged (at least part-time) under water. The project has decided to go with an open PA (poly-amide) box, stuff in the electronics, and fill it up with PUR.
For this to work we need adhesion in several critical areas (read adhesion to several different materials).

Amongst others a stainless steel surface. To prepare the surface we do the following:
- Ultrasonic washing in alkaline solution.
- Ultrasonic cleansing
- Blowing off excess water
- Drying in oven
- Application of primer

I have the option of incorporating a Water Break Test(WTB) just after the cleansing process. But I have also experimented with a Dyne test (basically a WTB but with different solutions with known surface tensions). Using the Dyne test I have found the stainless steel surface just after cleansing to have a surface tension of between 20-21 mN/m. This value seems rather low to me.
Unfortunately the direct correlation between adhesion to the PUR and surface tension of the stainless steel is not known to me.

Should I proceed with employing the Dyne test in production or does the extra information not 'pay back' in terms of process control?

Best regards,

Lars Glowien
process engineer - Bjerringbro, Jylland, Denmark

----
Ed. note: Sorry that you felt somewhat harassed by the "rules", Lars. That isn't our intention. Thanks for your interesting posting.