The strength of a magnet is an important factor that determines its utility in industrial applications. Several industries use magnets for various purposes during different stages of manufacturing. Certain applications need strong magnets while certain others might need only a mild magnetic strength.
The important question is – how do you measure the strength of a magnet? It might seem a difficult question to answer because several factors contribute to a magnet’s strength in different ways. However, the fact is that it is possible to measure the magnet’s strength based on these factors themselves.
Before proceeding further, it is important to clarify what is meant by a magnet’s strength. Generally, the pulling force and magnetic field strength are both considered strengths. Read on to understand how these can be measured.
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Maximum energy product
One of the common ways to measure the strength of a magnet is by measuring the maximum energy product. Measured in Mega Gauss Oersteds (MGOe), it is the key indicator of a magnet’s strength. As a rule, a magnet will generate a greater magnetic field in a particular application when the maximum energy product value rises. Maximum energy product or BHmax is determined by multiplying a magnet’s remanence (Br) and coercivity (Hc).
The remanence of a magnet is measured in Gauss. It is the magnetism that is left in a magnet after removing the external magnetic force used to magnetise it. Whenever a material is magnetised, it gets remanence because magnetism was induced by an external magnetic field at some point or other.
Coercivity refers to the energy required to reduce the magnetisation of a magnetised object to zero after being magnetised to the point of saturation. It measures a magnet’s resistance to demagnetisation. The coercivity of a magnet is measured in Oersteds (Oe).
It is to be noted that maximum energy product, remanence, and coercivity can only be measured with a hysteresis graph testing machine that plots a second quadrant hysteresis curve.
Open circuit flux density
Another method to test the strength of a magnet is by measuring the intensity of a magnetic field. It is measured in Gauss or Tesla (10,000 Gauss equals 1 Tesla). It is a common measurement of a magnet’s strength as it is a representation of flux density, which is the density of a magnetic field produced by a magnet. A magnet’s remanence value is the flux density held by the magnet when it is in a closed circuit. Open circuit flux densities are measured using a Gauss meter and hall probe.
With the increase in popularity of neodymium magnets, most manufacturers and suppliers require a pull strength for their magnets to demonstrate how much weight the magnet can hold. Measured in kilograms, pull strength is the highest achievable holding power of a magnet.
Pull gap curve
A pull-gap curve maps the pulling power of a magnet that is in direct contact with a thick and flat piece of steel and then through a gradually increasing range of air gaps. Magnets are tested over a variety of air gaps with a pull-gap testing machine.