Magnetic Shielding

Magnetic Shielding Properties

Magnetic shields serve two basic needs. Preventing strong field radiation from sources such as magnets, motors and transformers, and to shield instruments and devices from magnetic fields within an environment. Typical materials for magnetic shielding are:

1) high permeability

2) medium permeability

3) high saturation

Conducting magnetic lines of force is called permeability. The degree of permeability is expressed numerically. Base line or the standard is free space with a rating of one, compared to magnetic shielding materials usually range from about 200 to 350,000.

A minimum permeability value of 80,000 at B-40 and a maximum of 350,000 with a saturation point of about 7,500 gauss after heat treating would be considered a High Permeability Material. Materials having values of 12,500 to 150,000 with a saturation point of about 15,500 gauss would be "Medium Permeability".

High saturation materials have permeability ranging from 200 to 50,000 with saturation points between 18,000 to 21,000 gauss.

MuShield high permeability magnetic shielding material meets ASTM A-753-78 standard specification and military specs MIL-N-14411 C (MR). MuShield high permeability magnetic shielding material offers extremely high initial permeability and maximum permeability with minimum hysteresis loss and is a 'non-oriented' 80% nickel-iron-molybdenum alloy.

Working with Magnetic Shielding Materials

MuShield's high permeability magnetic shielding material may be drawn, cold rolled, stamped, heat treated, welded and is fully machinable.

• Cold Forming: Rockwell B 90 minimum should be purchased for the best blanking characteristics. For best drawing characteristics, strips should be purchased as annealed, Deep Drawn Quality.
  
  
• Heat Treatment: MuShield anneals finished parts in an oxygen-free dry hydrogen atmosphere with a dew point below -40° F (-40° C) for two to four hours at 2050° F (1121° C) to 2150° F (1177° C). Furnace cool to 1100° F (593° C) from 1100/700° F (593/371° C), cool at a rate between 350° F (194° C) and 600° F (334° C) per hour. Oil, grease, lacquer and all other contaminants must be removed before annealing.
  
  
• Machining: High Permeability Material machines a lot like austenitic stainless alloys. It develops gummy chips but it does not work harden as rapidly as the stainless alloys. Work hardened bars, Rockwell B 90 minimum, offer the best machining characteristics.
  
  Lard oil should be used for drilling and machining operations which must be done at slow speeds. If sulfur-bearing and water-soluble cutting compounds are used, the parts should be thoroughly cleaned within 48 hours and heat treated. High-speed steel or carbide tools are suggested for cutting operations.
  
  
• Welding: MuShield's high permeability magnetic shielding material may be welded by following typical practices for ferrous alloys. Do not Braze or Solder prior to final heat treatment.

MuShield's high permeability magnetic shielding materials can be designed around your specific application. Should you need assistance or consultation, please feel free to contact us. Our engineers will be more than happy to guide you through the design process, application implementation or additional detailed technical specifications.