Guide to Magnetic Strength
Magnets are objects or materials that attract or repel other magnets through a force known as magnetism. Available in several shapes, sizes, and strengths, magnets are an essential component of everything from MRI machines to magnetic pick-up tools and sweepers. Although size and shape are important selection criteria, strength is the most critical factor when choosing a magnet for an application or device.
Magnet Grades
Permanent
With permanent magnets, the magnetic field is generated by the material’s own internal structure. More specifically, it results from a combination of the nuclear spins, electron spins, and electron orbits that occur within the material’s atoms and crystals. This phenomenon allows the material to retain its magnetic properties, even in the absence of an electrical current or inducing field.Temporary
Unlike permanent magnets, temporary magnets only exhibit magnetism when exposed to a permanent magnetic field or electric current. This exposure causes the atomic domains to align in a common orientation, giving the material temporary magnetic properties. In general, the stronger the applied magnetic field, the more powerful the resulting temporary magnet. When the magnetic field is removed, the atomic domains return to a non-aligned orientation and the magnetic properties are lost.
How Do You Measure Magnet Strength?
Two measurements can be used to quantify the strength of a magnet:
Pull force
Expressed in pounds or kilograms, a magnet’s pull force measures the amount of force required to break the magnet away from a flat steel surface. This measurement is influenced by the grade of the material as well as the steel’s surface condition and the angle of pull.
Magnetic field strength.
Magnetic field strength indicates the strength and direction of the magnet’s magnetic field at a given location near the magnet. This measurement is typically expressed in units of Gauss (G) or Tesla (T). Factors that influence this measurement include:
- Magnet size, shape, and grade
- Location of measurement
- Presence of nearby magnets or ferromagnetic materials
However, measuring “Magnet Strength” isn’t the same as measuring magnetic sweeper pickup power. Learn more about How to Measure Magnetic Sweeper Pickup Power
Magnet Material
In most materials, an equal number of electrons are rotating in opposite directions, causing their magnetic moments to be canceled out. This includes most textiles and paper, which fall into the category of weakly magnetic materials. In contrast, strongly magnetic materials are composed of electrons that are primarily spinning in the same direction.
Neodymium iron boron (NdFeB) magnets are the most powerful permanent magnets currently available. These rare earth magnets generate deep magnetic fields, allowing them to attract other magnets from remarkable distances. Even a small neodymium magnet weighing only a few grams can attract and lift an object that is up to 1,000 times its own weight.
Questions to Ask When Choosing a Magnet
When choosing a magnet for an application, five important questions to ask are:
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- What operating or storage temperatures will the magnet be exposed to? Temperature can strengthen or weaken the attractive force of a magnet. For example, higher temperatures cause the particles within a magnet to move faster and more sporadically, resulting in a reduction in magnetic field strength. Extremely high temperature (+450 C) can permanently weaken the attractive force of a magnet.
- Will the magnet be placed in a horizontal or vertical position? The placement of the magnet within the application should also be considered since this can impact the weight or tension the magnet will be capable of holding.
- What is the ideal magnet shape for the application? The shape of the magnet influences the distribution of magnetic energy within the space. U-shaped or horseshoe magnets tend to be the strongest option since their shape allows the magnetic field to be concentrated between the poles.
- What is the ideal magnet size for the application? In addition to shape, it is also important to consider the size of the magnet as it relates to your application’s space availability.
- Will a coating be necessary? Coatings can be applied to the outer surface of magnets to protect against corrosion and mechanical damage in harsh environments.
Factors That Contribute to a Magnet's Performance
The factors that contribute most to a magnet’s performance include:
- Maximum energy product. The maximum energy product is the most important strength indicator of a magnet. In general, magnets with a higher maximum energy product will generate a stronger magnetic field in a given application.
- Remanence describes the magnetization remaining in the material once the external magnetic force is removed.
- Coercivity refers to the energy required to lower the magnetization of a fully magnetized material to zero. This essentially measures the material’s resistance to demagnetization.
- Open circuit flux density. The open circuit flux density of a magnet measures the number of field lines passing through a given area in open circuit conditions.
- Pull strength. Usually measured in kilograms, a magnet’s pull strength indicates its highest possible holding power.
- Pull-gap curve. Provided in graph format, a pull-gap curve illustrates the attractive force exerted by a magnet on a flat steel workpiece as the distance between the two objects gradually increases.
Applications of Magnets
Magnets are an integral component of several commercial, industrial, and domestic applications. At Bluestreak Equipment, we leverage our extensive knowledge of magnets to create the following magnetic solutions:
- Magnetic sweepers. From lightweight handheld sweepers to powerful push-style designs, our magnetic sweepers include options to suit a range of spaces and terrains. These products are designed to simplify the process of cleaning metal debris.
- Magnetic tools. Our versatile and ergonomic magnetic tools allow objects or loads to be safely lifted, manipulated, or moved in industrial applications.
- Magnetic separators. Our magnetic separators allow metallic contaminants to be quickly removed from powder and bulk solids in a range of processing applications.
- Magnetic material handling equipment. Our magnetic lifting and handling equipment ensures speed, safety, and accuracy in everything from steel stock lifting to light pick-and-place operations.
