On 06 Feb 2004 01:27:13 GMT, osspam (Joe Bobst) wrote:



Any potting compound that you use will shrink when it cures, worse if it is
heat cured. The least shrinkage will be a filled epoxy, room temperature cured.
There are probably dozens of decent commercial compounds available; do a Google
search to start.


Thanks for all the replies. To undertake the project I had engaged an
industrial design engineer and we came up with the current design. We
had tried all sorts of combinations, based on Sanaprene, a food grade
plastic, without success. The plastics experts at the Alberta
Research Council and another at the Technical College, NAIT) pretty
much have the same solution we had tried so far and that is to keep
trying different resin combinations and vary the injection and
temperature parameters. They are very interested in how things will
turn out.

I had thought of dental acrylics to think outside the box so to say.
To move things along. Of course neither the injection plastics people
nor the dental people have an idea how to implement this application
nor do they want to spend lab time on it since I am not paying them to
do so. So I am doing this out of curiosity as much as of necessity.
Fortunately this project opened for me many doors to meet all sorts of
interesting people and experts who volunteered gratis their time and
expertise.

If your device doesn't have to be monolithic, consider
elastomeric compounds, silicones or polyurethanes. Even quicker, cheaper and
shock resistant are closed cell urethane foams. HTH

It has to be monolithic, for mechanical strength and to hermetically
seal the electronics as the device will be cleaned regularly with soap
and water. Silicone does not bond to the injected plastic body, it
doesn't cure evenly or fast enough and it is mechanically weak.
Urethane, I'll try it but it will probably open another can of worms
with regard to health, taste and other properties.