Porosity in molded Delrin 500

You did not mention what kind of seal you are using between the 2 halves.

If you are just using plastic to plastic mating surfaces you could be getting capillary action between the 2 halves when they do not mate together completely. An O ring that fits in a groove between the 2 pcs. could give you a better seal, if your not using one already.

Yes, an "O" ring is being used between the two halves. That is not where we are seeing the leaks. The leaks appear to be in the halves themselves. When we xrayed the halves, they show area that are less dense. Could this area be the cause of the pressure pushing glycerin into the material itself?

There has been known to be some porosity problems with Delrin. May want to try so of its copolymers.

Hello Eagle zz

Almost all moulded plastics absorb water, to a greater or lesser degree.

Most also have micropores, which may allow water to transfer by capillary action.

Glycerine itself should not cause problems with either the PC Board, or 9V battery, but invariably there will be water transferred to both, and if this is supposed to be a permanent underwater arrangement, you will need to ensure that the PC Board, battery and connecting wires are kept dry.

An easy way of ensuring the battery, wires and PC Board remain dry, is to coat them with silicone grease, before assembling the unit.

Advise if this assists you

Kind Regards....

Hi,

very often there is an unexpected solubility of organic fluids in plastics.

(Benzene, xylene and toluene will readily pass through PE and PP).

The plastic remains solid and the fluid can readily diffuse through the plastic.

We had big problems with longterm diffusion of water through epoxi (mineralic filler),

we did measure any available plastic, all showed this diffusion.

Requirements were much longer "tightness" for that application, so may not be comparable.

So: this may be solubility, this may be porosity.

To test against porosity take some ink and let the colored glycerin-water be in contact with your part with pressure applied: if there are pores you will see a coloration that is not evenly distributed, you may not see the pores not by naked eyes nor by microscopic examination. (Pores in anodised surfaces are 30nm wide and suck rapidly any ink, these dry rapidly and leave the ink in the pores, some of the ink can be washed out later but some is remaining).

Real tightness can be achieved only with a multi-layer sheet of 5 layers, one is aluminum. Search for the material that is used to pack milk and similar material. They had extreme difficulties with tightness (outside smells and oxygen going inside) until this multi-layer material was introduced.

Our solution at that time was a 0.5mm aluminum shell covered with 0.5 to 1mm of hard rubber. The rubber protected the aluminum from corrosion by outside corrosive agents, the aluminum provided the water-vapor tightness. Brass-rubber is working too.

Ask the big producers of Delrin they may know! Else try other plastics.

RHABE