Permanent Magnets Overview
SDM Magnetics stocks and supplies standard and premium grades of all commercially available permanent magnet materials. We specialize in building and manufacturing custom magnets and magnetic materials to meet our customers’ exact specifications.
There are several types of permanent magnets, each manufactured differently from different materials with different properties. The six types of permanent magnets are alnico, smco, samarium cobalt, ferrite, ceramic magnets, fecrco, flexible rubber and the strongest permanent magnets, neodymium magnets.
Comparison Magnet Materials
Understanding permanent magnets / rare earth magnets and how their application can play into the innovative devices of today’s markets is the foundation of our business. At SDM, our long history of magnetic expertise – including supporting all patent, trademark and license requirements of magnets – allows us to partner with you to deliver the permanent magnet product for your needs.
There are a number of major families of permanent magnets available. They range from ferrite, which is low cost and low energy, to rare earth materials, which are more expensive and offer higher performance. Many factors affect the choice of magnetic material, such as operating temperature, size, weight constraints, environmental concerns and required magnetic energy.
Diversity exists between the varieties of magnetic alloy materials and grades. Each permanent magnetic material has unique advantages and disadvantages. We suggest that you contact our customer support team so your application can be reviewed. We will then be able to select appropriate magnetic material for your application.
Magnetic Strength of Permanent Magnet
There are several measurements that all contribute to a permanent magnet’s strength, which can often seem confusing. Magnetic field strength (remanence), resistance to demagnetisation (coercivity) and pulling force are all often summarised as strength and all are desired attributes of a permanent magnet. The single primary indicator of a permanent magnet’s strength is its maximum energy product value measured in Mega Gauss Oersteds (MGOe). The higher the maximum energy product value, the greater the magnetic field the magnet will generate in a particular application.
Maximum energy product, also referred to as BHmax is calculated by multiplying a magnet’s remanence (Br) and coercivity (Hc). The strongest magnets in the world are neodymium magnets, which are manufactured in different grades, however, each grade is given a handy name that allows you to instantly judge which magnet is stronger. Commercially available neodymium magnets range from N35 to N52 grade; the number after the letter ‘N’ represents the magnet’s maximum energy product.
A magnet’s individual performance is altered by temperature and some types of magnets perform better at high temperatures than others, such as alnico and samarium cobalt magnets. All magnets lose a percentage of their magnetism per ℃ rise in temperature and the five types of magnetic material lose magnetism at different rates and have different maximum operating temperatures. If the temperature exceeds the maximum operating temperature of the individual grade it will be permanently demagnetised.
Permanent Magnets Magnetization Patterns
Isotropic magnets, such as Bonded Nd-Fe-B, are unoriented and have no preferred direction; therefore it is possible to magnetize them in any direction. Almost all other materials are anisotropic and have a preferred direction of magnetization. They will exhibit the best magnetic properties when magnetized in the direction of the grain. Higher magnetic flux densities can be achieved with anisotropic magnets that are magnetized in their direction of orientation than with isotropic magnets.
Permanent magnets can be produced with various magnetic directions, which inclueds Oriented through thickness, Oriented through length, Multi-Pole segments on single face, Axially oriented in segments, Axially oriented through thickness, Multi-Pole on outside diameter, Multi-Pole, Diametrically magnetised, Radially magnetised, Oriented through diameter, Oriented through ring diameter …
The term ‘magnetic length’ refers to the dimension of a magnet which follows the direction of a magnet’s magnetic axis. A magnet’s magnetic axis is always listed last when referring to a magnet’s physical dimensions. The following diagrams show the types of magnetic direction, magnetization patterns of permanent magnets.
Permanent Magnets Physical Properties
Most permanent magnets are inherently brittle and should not be utilised as structural components. Dimensions and tolerances vary from manufacturer to manufacturer but most will produce magnets to the tolerance of +/- 0.1mm for all dimensions quoted. Permanent magnets are produced in many shapes such as standard rings, bars and discs plus custom shapes such as trapezoid, arc, mitre and even the ‘top hat’.
Permanent magnets are often coated to improve their performance. Take neodymium magnets for example, they are the strongest permanent magnets available but they are the most prone to corrosion due to their high iron content, therefore they are virtually always supplied with a coating. Typical coatings include, nickel, stainless steel, PTFE (Teflon), epoxy, rubber, gold, titanium, chrome and many more.
Permanent magnets have several advantages that electromagnets do not. For example, permanent magnets do not require any power source and usually produce a powerful magnetic field compared to their size. Contrastingly, electromagnets must be continuously connected to a power source that may be quite large depending on the magnetic field needed.
Although permanent magnets are advantageous, they do have several disadvantages. For example, permanent magnets constantly produce a magnetic field and cannot be turned off like electromagnets. Likewise, it is not easy to control the intensity of a permanent magnet’s magnetic field. Furthermore, permanent magnets do not usually have a very large magnetic field, a property that makes it difficult to use them over long distances.
Permanent Magnets Industrial Application
Permanent magnets have a variety of uses. Most people would be surprised by the uses of magnets in everyday life. Every time you drive your car, magnets are being utilized to help you perform certain operations. Magnets are used in permanent magnet motors. These motors control the power windows and windshield wipers of your car.
Permanent magnets are used in the following major groups: acoustic transducers, motors and generators, magneto mechanical devices, and magnetic field and imaging systems. You will find permanent magnets in many products, such as televisions, telephones, computers, audio systems and automobiles.
A lot of sensors cannot work without magnets. Take position and displacement sensors as examples, magnetostrictive and magnetoresistive sensors need magnets as position giver. These sensors are applied to robotics, automation machines and machine tools etc. Many electric motors, generators and measuring instruments cannot work without permanent magnets.
Alnico magnets are used in radar and telephones. They even play an important role in amplifiers and loudspeakers. Ceramic magnets are great for performing attraction and repulsion experiments. Ceramic magnets are even used on lawnmowers.
Rare earth magnets such as NdFeB can ruin computer monitors, media and even credit cards. They are often used for physics education or research in the electrical engineering.