Hi Tom and Peter: Long ago I decided to vacuum my investment in a
large bowl all in one batch, because I always try to invest five
2 1/2 x 3 1/2 flask with each batch and did not want to mess with
vacumming each flask after I poured the investment in them. I
vacuum the large bowl until it boils good and raise and falls,
then I pour into my flasks while I vibrate them one at a time. I
have no problems with bubbles. I had a student that did not have
a vibrator so she swore by doing the vacuum first, then pouring
the investment in the flask and tapping it with a spoon three
times. She never got any bubbles either, but it had to be three
taps!
If the investment starts to “freeze” while it is under vacuum
the tiny bubbles are actually expanded and freeze that way.
– Don Norris @Donald_Norris PO Box 2433 Estes Park, CO 80517
Mix investment. To a consistency of heavy cream that coats.
Vacuum in bowl for 1 min. (start time when your machine
reaches 28.?? or higher)
Remove bowl from under bell jar and pour investment into
flasks.
Place flasks under bell jar and vacuum for 1 1/2 min. ( start
time when your machine reaches 28.?? or higher) also after 1 min
and for the remaining 30 sec. hit or gentle bump, thump, or tap
the base on which the bell jar is setting, this dislodges any
trapped air bubbles. “Do not hit the bell jar as it could
collapse.”
Remove and let set for about 30 min. untouched
This should all be done in not more than 7 min. (Satin Cast) for
best results.
vacuum the large bowl until it boils good and raise and falls,
then I pour into my flasks while I vibrate them one at a time. I
have no problems with bubbles.
In the trade, many casters skip the vibrator, since sometimes it
can jar a wax model loose or move the tree in undesireable ways.
It’s not really needed. Some of us tap the vacuum table while
pouring the flasks to be sure to jar loose any large bubbles, but
again, it doesn’t really make much difference if you’re doing it
right in the first place. The usual schedule for investing is
to mix thoroughly for a couple minutes, vacuum in the bowl til
the investment rises and falls, pour the flasks, and THEN VACUUM
AGAIN. This is part of why a good vac pump is essential. You
can’t afford to be waiting and waiting and waiting for the
investment to boil, or you will exceed the working time of the
investment. Most investments have published working times, but it
will vary with each batch, and even with the age of the batch
you’re using. Keep it documented, so you know what to expect,
and run a small test with a new batch of investment. What you’re
interested in is the time between water hits the investment and
when the investment glosses off, which is the point where the wet
shine leaves the surface as the investment absorbs the surface
water. You need to be completely finished topping off the flask
about two or three minutes before gloss-off. Usually (at least
with Kerr satincast 20) this means you have a working time about
about 8 to 10 minutes during which you mix, vacuum, pour,
revacuum, and top off the flasks. It helps to have a wall clock
or similar timer with a second hand to keep exact track of where
you are in the process as you work. it’s important to take long
enough, as well as get it done quickly enough. If the poured
flask sits too long before the investment glosses off, the mix
can start to settle a little, creating “water marks” which look
like little tracks or lines of micro bubbles on the surface. The
result is also weaker. If you find you need a little more time,
use slightly cooler water, which slows the setting reaction. For
consistancy, all variables should be controlled. Water temp is
the biggie, but many casters also feel it important to use water
thats been allowed to sit long enough for dissolved gasses and
chlorine in the water to dissipate, so investing is often done
with water that was poured into a storage container the day
before. This also gives room temp water, rather than variable
temp cold water from the tap.
Have been using this Technique for over 20 years. I always say
that if it works, don’t change it, but you might want to try just
stopping with step 3. I do not vacuum the flasks after I pour
them because I have had waxes break off during that process,
especially with students doing the spruing. I stop with step 3,
and have not problems with bubbles, and it just saves one step.
(one exception is when I have a solid ring with a possible air
bubble that could be trapped by just pouring it.) –
Don Norris @Donald_Norris
PO Box 2433 Estes Park, CO 80517