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Proper torch adjustment can alleviate
a host of common problems in the dental
lab, including casting porosity, porcelain
bubbling, miscasts, and oxide problems.
This technique offers a very reproducible,
standardized way of adjusting a torch
that has given good results in our laboratory
over the years.
These instructions apply specifically
to the Harris model 16, but they can be
used with other torch models as well.
Some torches, such as those from Degussa,
have on the torch handle the recommended
gas pressures. If your torch specifies
gas pressures other than what we recommend,
use those that are recommended for the
torch. The Degussa torch and those similar
tend to utilize slightly lower pressures
than what is used in the Harris.
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| 1 |
Open the propane and oxygen
tanks. With the torch valves open,
set the regulators to the following pressures.
· Most Ceramic
Alloys: 10 psi propane and 20 psi oxygen.
· Most C&B
Alloys: 5 psi propane and 10 psi oxygen
When you close the torch valves, these pressures
will rise, so do it with the torch valves
open in a well ventilated area. |
| 2 |
Open the gas valve on the
torch handle, and light the torch. |
| 3 |
Open the oxygen valve on the
torch handle all the way (so that
further opening does not change the flame). |
| 4 |
Adjust the gas control on
the torch handle so that the bright blue
cones near the tip are 1/4 inch long. |
| 5 |
You will be melting the alloy
typically from 2 to 4 inches from the tip.
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A few words on torch maintenance:
If porcelain bubbling is the problem,
and you are following this technique,
buy a new torch tip. These parts do wear
over time. Don't sandblast your tip -
it won't burn quite right again if you
do. Clean tips with a torch tip cleaning
tool, and replace the tip once in a while.
(Jensen replaces their tips about twice
a year)
The Harris model 16 should have the following
parts:
· H-16-S
Mixer
· D-50-C
Tube
· "H"
Multi-orifice tip
If your Harris torch has a different mixer
than this, you may have a miss-matched
part on your torch which should be replaced.
Always use flashback arrestors!
Buy hoses that are approved for propane
(not all welding hoses are!) Propane approved
hoses are "Grade T."
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