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Foundry Products --> Melt
Shop Equipment --> Portable Rotary Degasser for
Aluminum Foundry
Products:
Portable Rotary
Degasser for Aluminum


Easy
assembly.

Easy
positioning.

Typical Results of
Nitrogen - Before and After Reduced
Pressure Test Samples
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Features:
- Low Cost
With High Efficiency
- Stainless
Steel Construction
- Variable
Speed Air Motor
- Portable and
Lightweight - Under 50 Pounds
- Versatile -
Can be used in dip-out or crucible
furnaces with capacities from 40 to 3000#
- Unique one
piece lance reduces cost by eliminating
shaft / impellor design
- Eliminates
use of hazardous degassing tablets and
chlorine or Freon gasses.

Complete Degasser
Kit |
General
Specifications
- Motor
Horsepower - 3/4 HP
- Motor RPM -
3600 RPM Variable Speed
- Lances -
24" and 36" are available. Note
that 12" of lance length are
contained within the unit shroud
- Body Size -
8" Diameter x 17" Long x
12" Base Flange - Suspension Hook
14" above body
- Customer
Requirements - Compressed air source
(90-100 PSI), Overhead Hoist, Dry Nitrogen
or Argon
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Included with
Purchased Unit
- Degas unit,
combination air regulator / filter / lubricator
for air motor, four standard lances
(non-impellor). See system picture to the upper
left.
- Regulation of
inert gas to be done with customer
equipment.
- Customer supplies
interconnecting hoses for compressed air and
inert gas to suit the needs of the installation.
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See the Palmer Degasser
video.

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Degas Times
(Estimated)
- 70-500 pound
crucible - 1-5 minutes
- 500-3000 pound
crucible - 5-10 minutes
Options
- Three leg mounting
for support on flat top crucible furnaces
- Impellor style
lances available
- Reduced pressure
tester for sample comparison to national and
metallurgical standards
Degassing
Principles
Hydrogen degassing of
aluminum is based on the principle that hydrogen gas
will move from an area of high pressure (in the
melt) to an area of low pressure (the inert gas).
Hydrogen gas disperses in the molten metal as it
would if it were released in any confined space. It
will maintain a constant pressure throughout the
melt. The ability of hydrogen gas to move through
and equalize its pressure in liquid metal is almost
as fast as it is in air. Therefore, it is
unnecessary to bring every bit of metal in contact
with the inert gas. How well and how fast a heat of
aluminum can be degassed is determined by two
factors, the transfer rate across the metal/gas
interface and the surface area of the gas exposed to
the metal.
Gas bubbling hydrogen
degassing systems work on the principle of using
specialty gasses (chlorine, Freon, or SF6) to speed
up the hydrogen transfer across the metal/gas
interface into large bubbles of gas in the metal.
There was a practical limit to hydrogen removal on
humid days because the large bubbles break the
surface and expose metal to the humid atmosphere
where more hydrogen is picked up. Chlorine was the
original gas of choice but due to its hazardous
nature, most foundries switched to other gasses.
What most foundries have not considered are the
hazardous materials released by the breakdown of any
specialty gas used.
Rotary degassing
works on the principle of increasing the surface
area of an inert gas exposed to the metal. The
greater the surface area, the faster the degassing.
For a given volume of gas, the smaller the bubble
size, the greater the surface area and the faster
the degassing. For example, a 1" inch diameter
bubble of gas has a surface area of 6 square inches.
If the same bubble is divided into 1/16"
diameter bubbles, the surface area is increased to
96 square inches. In other words, for the same
volume of gas used, the surface area is increased by
16 times, increasing the effectiveness of the
degassing by 16 times. Additionally, the small
bubbles disturb the surface of the melt less,
causing less hydrogen pickup on release.
This degassing unit
is recommend for dry nitrogen and argon. The
compatibility with specialty gasses cannot be
guaranteed. With the exception of the graphite, all
parts of the unit which are exposed to the gas are
stainless steel or Buena-N (seals). A four minute
degas time for a 400 pound crucible is common using
dry nitrogen as the gas. This being said, there is
no practical reason to use expensive specialty
gasses (costing up to $500 per bottle) when a $20
bottle of nitrogen will do the same job. Also, no
toxic emissions are produced from nitrogen gas.
Options
Reduced Pressure
Tester
Whenever
degassing is a requirement of the melting process,
it is desirable to verify the effectiveness of the
degassing process. Palmer supplies a simple, easy to
use partial pressure test unit for this
verification.
To use, the operator
warms a sample cup, dips the cup into the furnace
for a metal sample, quickly places the sample into
the vacuum chamber, and starts the vacuum pump.
The aluminum
solidifies under a vacuum causing any entrained
hydrogen gas bubbles to expand greatly. Once solid
and cooled, the sample is cut in half and compared
to the chart below for gas level analysis.
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