Re: bubbles and investment

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Posted by bpfink on June 29, 19100 at 10:13:02:

In Reply to: Re: bubbles and investment posted by Lyle Landstrom on June 23, 19100 at 12:17:06:

So many good approaches guys. Thanks.

Since my filled flasks run in the 300 to 2000 lb range I am confronted with the same problems but

on a larger scale. Maybe some of these thoughts will also help if you start to get to bigger flasks.

First is to prefill the vat of water to be used days in advance. It makes all the volume one

temperature so that variable is under control. This is done with several 120 gallon plastic farm

animal watering type tubs set in a row.

Then since the waxes are often super fragile and can barely hold their own weight standing this is

used to float them in it till the investment date sometimes days or weeks later.

I noticed that a very slight form of algae would form to cover the wax after a period and while not

really visible it broke down and made it more slippery when invested. Since these tubs are usually

set up right outside the garage door and also to keep anyone or anything from dipping into it or

thinking they are for garbage (especially when a lid is not practical) I also sometimes put Uranine

C20H10Na2O5 coloring into the water at the rate of about 1/8th teaspoon per 100 gallons. This

has nothing to do with it's function eliminating bubbles, but makes it pretty. Who said this had to be

like work... (Uranine Florescein Sodium Salt is the same stuff they put into antifreeze to give it that

iridesent yellow/green color so you can forget this if clear water is all you want.)

Occasionally I also find that a pre coat of superfine ground sand / clay / graphite mixed with

alcohol and sprayed on to the finished piece gives another better chance of eliminating any

bubbles. This is only a thickness of about 1/32 inch or so as it does not have it's own binder yet

and is a surface fineness coating. It's composition varies from time to time but currently is a mold

wash sold by the Asbury Graphite Mill, Asbury NJ 08802.

Reason for the alcohol is to both continue surface tension cutting and to evaporate off fast when

put on just before investing (may have to continue holding it a good part of that time, or have it on

a soft pillow, etc.).

It is also followed up later or mixed in with a time retarded sprayed or flicked on coating of the

sifted sand / plaster @ 50 : 50 used just seconds before investing. The main investment is then

either poured in down a temporary 3 inch dia. PVC pipe (the usual method for them when real

fragile as it keeps the mix from hitting it, and also prevents bubbles from getting remixed in), or is

first poured in before the wax piece is lowered into it (more risky on these sizes). The obvious

problem is that more bubbles can be created when the pour is done with the 3 to 6 foot drop

down into the mold flask.

Also don't ignore the water temperatures of the various investments when poured. A very cold

surface wash or coating with retarder gives you more time to handle it before it sets, and the next

main poured mix with much warmer water will combine with it to set up as one unit (that is part

theory since these pours are done in a depth progression by mixing about 20 to 30 gallons per

pouring).

A warm or hotter water in the main pour also gets the wax to slightly expnad before the set and

therefore lessens later meltout cracks causing flashing if due to wax expansion.

These pourings are timed so the first pour is set up as the 2nd still is setting and the third is still

liquid while you are mixing up the next. And on and on.

This also helps keep the fragile wax from bending or changing shape as it wants to float if any

depths are involved.

Again, it does not always work that way as is attested when the full 2000 lb investment is burned

out and a fine layer of bubbles is seen to have not had a chance to rise about any layer. Usually this

does not affect the surface of the piece though as the surface coats on that gave it additional

protection.

Hope this might help show some more possibilities to consider.

bpfink


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