Epoxy Pressure Sealing

[courtl]

Please can someone advise on the best epoxy to use for pressure sealing?

I am trying to seal a cavity on top of an RF filter which contains the tuning screws. The unit is pressurised to 3.5bar and the leak rate has to be better that 5cc/hr.

We have tried eccobond type epoxies, but after aging it begins to leak around the ends of the epoxy seal.

I think that the epoxy is not sticking properly to the filter housing (aluminium, painted with two part black epoxy paint).

We have tried stripping the paint off to leave bare metal but the epoxy still seems to leak at the edges as if it has crept away.

I don't think we are using the right epoxies (eccobond and the like are adhesives or used for encapsulating components, not for pressure sealing).

Any suggestions?

 

[rnd2]

To be effective, seal material like has to be located 'upstream' much like a plug in a sink so that pressure bearing on it causes it to deflect and assists making the seal.
Consider trying one of the many elastomeric materials that are available.

 

[Tofflemire]

Courtl

You should be able to use 5 minute epoxy made by Devcon. Cheap

There is another epoxy that I have used which is called Stycast 2850 made by Emerson & Cuming. This sticks to aluminum very well. This stuff is not reworkable and costs more money than the 5 minute epoxy.

You still have to try each for application.

Tofflemire

 

[sreid]

Another possibility is Moglice.

http://www.moglice.com

Although sealing is not the primary application it has extremely low shrinkage while curing.

 

[unclesyd]

Another approach is this product
Click on the Sonolok and go to Sealing Grades

http://www.parsonadhesives.com/

An Epoxy supplier that I have used is:

http://www.masterbond.com

 

[Fracball]

Courtl:

You might look at Armstrong A-2 and A-706 epoxies. They are both basically the same, but A-706 has a 400 degree F temperature limit and it is a bit harder to work with. A-2 is very simple to use. Good luck.

 

[courtl]

Thanks everyone for your suggestions, I am looking into all the ideas, hopefully I can find something that will work!!

Fingers crossed

 

[Tmoose]

How much room do you have in the cavity? Is the cavity round? If you could place a weak plastic cup with a small OD upside down in the cavity before potting then the pressure would tend to expand the cup lips and epoxy outward, tightening the seal.