Polyurethane Potting

[LukeBayly]

Hello

The company i am doing work experience at has been having issues with a product they are making. The product is basically a 900mmm long polyurethane filled ABS tube about 30mm OD with a taper. The polyurethane is used as a potting filler to fill a circuit board that runs the length of the tube.

There has been issues with the rods deforming especially when heated, but it also happens at room temperature when it is leaned up against a wall. The deformation is noticeable as it bends in one direction.

One thing i have thought of is maybe changing the ABS to a poly-carbonate as it is more thermally stable and may restrict the movement.

Any other ideas?

Any idea on what might be causing it. I think it is odd that such a large amount of polyurethane is deforming.

Just a few points
- These rods have not been put under any major stress
-The deflection is large and noticable


Thankyou
Luke

 

[CoryPad]

Is the polyurethane elastomeric or is it rigid? How thick is the tube wall?

 

[Compositepro]

A circuit board has much higher stiffness and lower thermal expansion than polymers. You could probably mount a switch close to your tube and use it as a thermostat to control room temperature (the point is that this is how mechanical thermostats do work).

You need to allow things to expand and contract without creating stress. Fillers can be added to potting compounds to lower the CTE (coefficient of thermal expansion), but these will also make the potting compound stiffer. You could create gaps or voids in the compound to allow for free expansion (mold in some rods that you later extract).