Foundry Products:
Portable Rotary Degasser for Aluminum

Easy assembly. Easy positioning.  Typical Results of Nitrogen - Before and After Reduced Pressure Test Samples

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

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.

See the Palmer Degasser video.

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.

• Click here for more information on the Reduced Pressure Tester. 
• Click here to view the Gas Comparative Analysis Chart