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Cold-drawn parts for super magnets.

The Fermi National Accelerator Laboratory, Batavia, IL, recently started using two cold-drawn shaped parts produced by Rathbone Precision Metals Inc for research on superconducting accelerator magnets.

The Rathbone parts are alignment keys used in several prototype superconducting magnets that Fermilab is developing for the Superconducting Super Collider (SSC) being built near Dallas. The SSC, a twenty-trillion-electron-volt proton synchrotron, will be the world's largest and highest energy particle accelerator for scientific exploration of subatomic particles.

The alignment keys produced by Rathbone were designed by Fermilab and are used as a component in one of the magnet's major subsystems to help achieve the required manufacturing precision.

According to john Carson, manager of Fermilab's superconducting magnet facility, "The alignment keys are used as part of the magnet's cold-mass assembly. The assembly contains the superconducting coils, coil-support structure, and magnetic iron. It is also the containment vessel for liquid helium used to cool the coils to their operational temperature of 4.5 K."

The containment vessel consist of two 3/16"-thick stainless-steel semi-cylindrical "skins" connected via the alignment keys by welding to form a tube around the coil and iron assembly. The vertical alignment of the magnetic field created by the coils must meet critical tolerances less than one milliradian along the length of the 56-ft-long assembly.

Special Fixturing

The problem here is to ensure that all the components are properly aligned before and during welding. The alignment keys provide a convenient means of achieving the required precision during assembly. The alignment keys index to components within the stainless-steel skin, while a V-notch in the keys indexes to specialized fixturing that aligns the cold-mass components to their required precision. Once aligned, the assembly is welded together.

Rathbone's alignment keys are made by a combination of cold rolling and cold drawing and feature a smooth surface finish. The overall width tolerance is +0.000" to -0.0010". The overall height tolerance is +0.000" to -0.005". The V-notch is centralized on the key within 0.001". One alignment key uses 316 stainless steel; the other uses 304 stainless.

Commenting on the challenges associated with producing the alignment key for Fermilab, Raymond Lydon, Rathbone's VP of marketing, says, "Shaping a part from a round piece of stainless steel is always a challenge. There aren't too many manufacturers in North America who could make this shape out of stainless steel unless they machined it, and that would be very costly. After the part's design is given to us, it's up to us to meet the tolerance that the customer specifies."

The Rathbone cold-draw process offers many advantages to designers and manufacturers whose products can use cold-drawn shapes. Cold drawing has close tolerances, higher tensile and yield strengths, and offers a smooth surface finish.

For more information, contact Rathbone Precision Metals Inc, 241 Park St, Palmer, MA 01069 or circle 382.
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Title Annotation:Rathbone Precision Metals Inc.'s alignment keys
Publication:Tooling & Production
Date:Feb 1, 1991
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