Hello All: I have been trying to come up with the best method of
investing, Burn out and Casting over the last several years and I
think I got it now so I thought I would share it with Ya’ll. I
consistently invest as per the advice of Eddie Bell at Rio Grande
(http://www.riogrande.com/) thru and article in the summer 2003
edition of “Bench magazine”(http://www.bwsimon.com/bench/). I almost
exclusively cast hard green carving wax models using 2.5X2 inch
flasks. I use R&R (http://www.ransom-randolph.com/index.html) SJ-27
investment with a 38 ml. to 100 gr. mixing ratio. I use room
temperature distilled water and weigh out the investment carefully
every time to ensure consistency. I do however stray from common
practice by adding the water to the investment for mixing but I have
found that this keeps the dust down more than the other way around. I
have been consistently getting a 13 minute gloss off on this 100 lb.
keg of investment so I mix for 6 minutes,vacuum for 1.5 minutes,pour
and vacuum for 1.5 minutes and then let the flasks sit on the
investing table for 1 hour before numbering the flasks and putting
them in the over to sit overnight until my programmable thermominder
starts the burnout cycle. Using this investing process has eliminated
water marks on my castings and reduced my clean up time and wasted
metal. I am using an Ashurst Designs model 4 kilnminder programmed to
start the cycle at 5:30 am for a cast time of 4:30 pm. A total of 11
hours consisting of 300 F in 20 minutes with a 1.5 hour dwell. 400 F
in 20 minutes with a 1.5 hour dwell. 1250 F in 3 hours with a 2.5
hour dwell. 1000 F in 1 hour with at least a 1 hour dwell until I
cast.If you are using larger flasks the set time of the investment
will take longer of course and the dwell time before casting will be
longer. I added the extra 400 F dwell in the burnout on the advise
of JACMBJ Shannon Calloway, Instructor at the Texas Institute of
Jewelry Technology, Paris Texas because I cast hard carving wax
almost exclusively. Other advise from Shannon was to never invest
injected models and carving wax models in the same flask as the
difference in expansion in the two can damage the mold. I reduced the
maximum temperature of my cycle from 1350 F to 1250 F on the
suggestion of research presented to the Santa Fe Symposium that 1350
F is too hot as brought to my attention by James Binion of this
forum.
I preheat my crucible until it glows red, I then pull my flask out
of the oven and set it on my vacuum caster. I add the metal to the
crucible and melt with a bushy flame. I stir in flux, if required, by
dipping the heated quartz stir rod in the flux and adding it to the
melt without removing the flame from the melt. This reduces the
amount of Oxygen that can be absorbed by the melt by removing the
flame to add flux. Once the metal is completely melted with no more
solids I count to 10 and turn on the caster and pour while holding
the flame on the melt the entire time. I run the vacuum until the
sprue button solidifies and then remove the flask and set it aside
until the sprue stops glowing red and then quench immediately as
recommended by Hoover and Strong (http://www.hooverandstrong.com/)
for metals other than rose golds. I hope this helps someone out there
with water mark problems as I was having. Michael R. Mathews Sr.
Victoria,Texas Usa JACMBJ Yahoo | Mail, Weather, Search, Politics, News, Finance, Sports & Videos