MuMetal Toroids PDF Print E-mail

What strip widths do we cater for? What coatings do we offer? How do we test a core? What handling restrictions are there?

Stock Strip Widths

AEM Cores has a slitting line and carries slit strip from 15mm wide in increments of 5mm to 60mm depending on availability. Special orders requiring a set up and slit run can be accommodated as production volumes dictate. Our maximum strip width is 60mm, we reserve the right to use multiple strip widths to build up a stack for larger sizes if required. Slitting Mumetal is an involved process, we cannot simply set up to slit one strip width off the parent coil, all slit operations must take into account other strip requirements and slit disc combinations. For this reason the strip you request may not be instantly available, yet may be programmed into the next slit run for Mumetal. We will always offer our best alternative in the event the strip is not available.

Test Regime

After annealing each core is inspected and degaussed to above 0.55T, it is then tested and the unique core number noted on the label. Each core is assigned a unique number against which all test data and dimensional information is stored.This number should be quoted in any correspondence concerning the performance of a core.

Refer to the sheet Performance Data - Mumetal for the graph of the Total Magnetising Field resolved into Loss and Reactive components.

Inlac Coating

After slitting we coat the strip on either side with Inlac to assist in the heat treatment of the steel. After drying the carrier fluid has evaporated leaving a fine, consistent layer of inert magnesium oxide powder adhered to the surface of the strip. When wound into a toroid, this powder physically separates the laminations and reduces the possibility of inter lamination welding. It also helps prevent shot spots and wicking in the core, to ensure the material is consistently annealed.

Inlac burns off at the temperatures involved with annealing mumetal, you may find a fine film of white powder on the core, this is the remnant MgOx which is inert.

Material Selection

AEM Cores currently stocks Vacoperm 100, made in Germany. In the sheet Performance Data - Mumetal you may download a PDF file of the core response at various flux densities for a population of cores made at AEM from Vacoperm 100. We are continually researching alternative suppliers of mumetal in an effort to reduce costs, improve quality and maintain consistent magnetic performance.

As new materials become available and pass our test regime, we will post details.

Handling Considerations

HANDLE Mumetal WITH CARE

  • Mumetal is EXTREMELY sensitive to adverse stress.
    A satisfactory core can be magnetically damaged simply by dropping it on the table, squeezing     it with finger force, incorrect copper winding tension, incorrect mounting and assembly or even by vibration from transit or whilst in operation. It cannot be stressed enough that delicate handling, correct winding procedures and careful consideration for induced stress must be paramount when dealing with mumetal.
  • Stress is additive from the time the parent roll leaves the annealing furnace at AEM Cores. Every effort is made to ensure the cores are at peak performance by the time they leave our store. We will not accept responsibility for transit damage or end user handling errors leading to increased stress and reduced magnetic response. We often CANNOT re-anneal a damaged mumetal core, therefore we encourage our customers to handle these cores with care.
  • NEVER stand a mumetal core on it's edge,
    ALWAYS use two hands to pick them up, NEVER flex or deform a core, the material is extremely strain sensitive.
  • The colour and outer texture of a mumetal core will vary depending on the quality of the atmosphere and impurity level within the furnace. It has NO effect on the magnetic properties nor is it an indication of the core performance.