Frequently Asked Questions

Is the Earth's north pole a north or a south magnetic pole?
By definition, the tip of a compass which points toward the "north" pole of the earth is a magnetic north pole. Therefore, the north pole of the Earth is actually a south magnetic pole (unlike poles attract). Again: geographic north is a magnetic south; geographic south is a magnetic north.

What is a Helmholtz coil?

Used in pairs, these are coils of wire connected to an integrating (totalizing) fluxmeter so that when a magnet is moved relative to the coils, the resulting current in the coils is measured and totalled. The magnet must be positioned properly, relative to the coils, and can be extracted from the pair of coils or rotated 90 degrees in the pair of coils. When compared to a standard magnet measured this way, this is a fairly efficient test of the strength or out put of a magnet of the same size and shape.

	There are many manufacturers making "Silicon Steel" laminates. What is different about your products?
	Arnolds' oriented and non-oriented silicon steel is designed for high frequency uses with low core loss. Most silicon steels are designed for 60 hertz operations, while ours, depending on the gauge, can be used in applications of 400-10,000 Hz. This is done by rolling the material to very thin gauges (as low as .001") and therefore minimize the eddy current losses.

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I have many applications that use Cunife and Vicalloy. These materials give me good shape-forming freedom since they are wrought metallic material. However, I would like higher magnetic performance and/or lower cost. Are there any alternatives?

The ARNOKROMETM family of iron-chrome-cobalt alloys, from the Rolled Products Division, are excellent replacements for these older materials. They can exceed the magnetic performance of Cunife, and are more price-competitive than Vicalloy.

What materials can be used for magnetic shielding?

In general, magnetic field attenuation is a function of the permeability of the material. A better shielding material has high permeability per weight. For metallic foil and sheet, the most efficient shielding material is the 80 Nickel family (e.g., Molypermalloy), followed by the 50 Nickel alloys (e.g., Deltamax). The economical silicon-steel foils and sheets are also good shielding material when weight is not of a major issue. Bonded (rubber) sheets of softmagnetic powders, such as our FerrosheetTM can also serve as a shielding material.

What is meant by Reversible Temperature Coefficient of Induction (or of Coercivity)?

Two very important magnetic characteristics change (increase or decrease) with temperature: these are the induction (Br) and the coercivity (Hci) of the permanent magnet material. The word "reversible" is used to indicate that, even though the properties change as temperature is raised or lowered, that when the magnet is again brought to room temperature, the magnetic property returns to its original value. Since the amount of change per degree change in temperature is not the same at, for example, 100°C and at -20°C, it is necessary to specify the range of temperature over which the average is calculated. The Reversible Temperature Coefficient of Induction is often called (Greek letter) "alpha". The Reversible Temperature Coefficient of Coercivity is often called (Greek letter) "beta".

	Is there such a thing as a magnetic mono-pole?
	We are occasionally asked to supply a south pole without the north; or north without the south. Forgive us. We do not know how to do that. For all practical purposes, the presence of one pole dictates the presence of the opposite pole a bit like every battery has both positive and negative terminals.

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Can magnets be used as structural elements in an assembly?

Most magnetic materials are too brittle to be safely used as structural components. Samarium cobalt, neodymium-iron-boron, and ferrites are particularly brittle. Iron-chrome-cobalt is a malleable alloy and not likely to crack or shatter. However, its magnetic properties change under stress and work hardening. Bonded magnets have been successfully used as structural components, but only when subjected to low stresses. Unlike fiberglas reinforced plastics, the high magnetic material loading in bonded magnets means that they are not very strong. Alnico magnets are the toughest of the common materials. But even they are not recommended for structural use.

Can magnets be used in an application where they will rub against other surfaces?

Most magnetic materials are very abrasive and hard. This means that they have the capability to seriously abrade adjacent surfaces. As in the previous question: as a general rule, magnets do not make good structural members.

Are there any regulations for shipping magnetized materials?

According to the United States Department of Transportation and the Office of Hazardous Materials Safety, it is against regulations to ship a magnet by air that maintains a field of more than 0.00525 gauss measured at 4.5 meters (15 feet) from any surface of the package. This is to prevent the magnet from interfering with the operation of the aircraft's navigational compass. There are no federal regulations that restrict the shipping of magnetized materials by ground transportation. Please check with your commercial carrier for additional specifics.

Accuracy Statement
While we make every effort to ensure that the information contained in these documents is complete and accurate, we make no warranty regarding this. Please see our disclaimer statement. We would appreciate your input regarding corrections, additions and suggestions for improvement (contactus@arnoldmagnetics.com.

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