Ceralloy
- NPG is a nickel-Chromium
high heat-casting alloy made to strictest specifications
to alloy its use in fabrication of ceramic crowns and bridgework
using porcelains such as Ceramco. Using purest raw materials
available and employing vacuum melting process, Emdin alloys
are able to insure consistent dependable quality from batch
to batch.
Mechanical Properties:
Yield Strength…………..….83,500 psi (576 Mpa)
Percent of Elongation……..10%
Coefficient of Expansion….13.8 x 106
Liquidous Temperature……2120-2280 F
(1160-1250 C)
Tensile Strength…………...120,000 psi (828 Mpa)
Modulus of Elasticity………29.5 x 106
Hardness, Vickers…………380
Alloy Composition:
Nickel…………..74.8%
Chromium……..12.7%
Molybdenum…..9.00%
Aluminum…..….2.00%
Titanium………..0.32%
Beryllium……….1.95% (Max.)
Cobalt…………..0.45%
Wax-Up:
Wax up copings to a thickness of approximately 0.3
mm. Use of hard wax is recommended. Dipping waxes can also
be used. Use of plastic copings would require adjusting
(increasing) expansion of the casting investment. Use Emdin's
STARVEST
micro-fine casting investment for best results.
Spruing:
Use indirect or running bar
spruing technique. For bulky pontics and occlusals use a
larger 8-gauge sprue. For standard copings a 10-gauge sprue
should be adequate. The horizontal bar and feeder sprues
should be made of still larger 6-gauge round wax. Use softer
waxes for these and sprues to copings. Keep distance from
the sprue bar to the copings to about 0.24 (1/4) inch. For
casting one or two single units use a ball reservoir type
sprue.
Investing and Burnout
Follow the recommendations of the investment
manufacturers. Because the non-precious requires more compensation
for the alloy shrinkage it is advisable that a good investment
be used. Investment consistency from batch to batch is the
single most important factor in reducing repairs and rework
of the castings.
We highly recommend Emdin's STARVEST
micro-fine casting investment. STARVEST
provides the smoothest castings and is the most consistent
investment from batch to batch. Moreover it is a multi-purpose
investment so that no other investment is needed to cast
the other type of alloys (precious and semi-precious).
Casting:
A high volume multi-orifice tip torch should be used
in casting CERALLOY. The torch needs to melt the alloy rapidly
and cleanly and therefore it has to have a flame, which
is hot enough to accomplish the task. Propane and oxygen
or city gas and oxygen are recommended. Acetylene gas is
not recommended due to possible contamination of the alloy
resulting in subsequent difficulties in soldering etc. Follow
the recommendation of the torch manufacturer with respect
to the gas and oxygen pressure. Generally a high volume
torch would require a 35 lb. of oxygen to 4 lbs. of propane.
However, start with the recommendations of the torch manufacturer.
Adjust the flame so that the inner cones of the flame extend
about 3/8 inch in length.
Due to low specific gravity wind the casting machine one
or two time more than normal for precious alloys. Replace
the crucible if is too corroded from previous meltings.
Use a good melting crucible. Zirconia based crucibles will
give better results longer.
Preheat the crucible and then place the alloy into it.
Bring the flame to within 1 and 1/2 inch distance of the
alloy and heat it to bright red, moving the flame around
to cover the entire alloy to ensure uniformity of heating.
Cast when the molten alloy slumps into the crucible. The
alloy ingots will not merge into one during melting like
gold alloys. Further heating beyond the point when the alloy
ingots have slumped would burn the alloy and might change
the chemistry of the alloy.
Quench the ring after the button has become dull. The buttons
can be remelted 50/50 with new alloy. Do not use button
after two meltings and do not use alloy that has been overheated.
For casting in Induction casting machines set the casting
temperature at 2700 degrees F with a 5 second soak time.
Do not use carbon inserts in the crucible. Place the ingots
on the floor of the casting crucible for most efficient
melting. Avoid stacking the alloy ingots on top of each
other.
The casting should be bright and free from casting oxides.
The investment would separate cleanly from the casting surface.
Heavy sticking of the investment indicates overheating of
the alloy. Heavy green oxide indicates severe burning of
the alloy.
Degassing:
Follow normal degassing procedures. Fire copings
at 1950 F under vacuum for 3 minutes. Reblast to remove
the oxide surface with 50 micron white aluminum oxide and
place it in distilled water in an ultrasonic for 5 minutes.
Do not touch the alloy with your fingers. Opaque and build
porcelain in the usual manner.
High Fusing Solder:
Use standard soldering techniques for non-precious
alloys.
