FAQ

Magnets are used all over the world in almost all modern devices from computer hard drives to the latest environmentally friendly cars and transportation. A Magnet is a material which produces an invisible magnetic field which can attract ferromagnetic materials. Magnets can also attract or repel other Magnets. All Magnets have at least 2 magnetic poles.

There are 3 types of magnets:
Permanent magnets emit a magnetic field without the need for any external source of magnetism or electrical power.
Temporary magnets behave as magnets while attached to or close to something that emits a magnetic field but lose this characteristic when the source of the magnetic field is removed.
Electro-magnets require electricity to behave as a magnet.

There are five types of modern permanent magnets, each made from different materials with different characteristics. The strongest magnets, referred to as rare earth magnets, are commonly known as neodymium magnets which are made from an alloy of neodymium, iron and boron (NdFeb) and samarium cobalt magnets which are made from samarium, cobalt and small amounts of iron, copper and other materials. Other types of permanent magnets include ferrite magnets, made from a compound of ceramic material and iron oxide (SrO.6Fe2O3) and alnico magnets made from aluminum, nickel and cobalt and flexible rubber.

A permanent magnet is a solid material that produces its own consistent magnetic field because the material is magnetized. Unlike permanent magnets, the magnetic field exerted by an electromagnet is produced by the flow of electric current. The magnetic field disappears when the current is turned off. Typically, an electromagnet consists of many turns of copper wire which form a solenoid. When an electric current flows around the solenoid coil, a magnetic field is created. If an iron core is inserted into the bore of this solenoid, then magnetism is induced into it and it becomes magnetic, but when the current stops flowing it immediately becomes nonmagnetic.

Rare earth magnets are made of the rare earth group of elements in the periodic table and are famous for their strength. The most common are neodymium-iron-boron (NdFeb) and samarium cobalt (SmCo) varieties. Despite the name, rare earth elements are relatively abundant in the earth’s crust, however, they are not typically found in economically exploitable deposits and are often dispersed, deriving the term rare earth.

A permanent magnet, if kept and used in optimum working conditions, will keep its magnetism for years and years. For example, it is estimated that a neodymium magnet loses approximately 5% of its magnetism every 100 years. Optimum working conditions include not subjecting the magnet to temperatures above its maximum operating temperature, protecting from corrosion and not subjecting them to strong demagnetizing fields.

There are 3 classifications of magnetic metals:

Ferromagnetic: These are truly magnetic with a strong attraction to magnets
Paramagnetic: These metals only have a weak attraction to magnets
Diamagnetic: These metals display a slight repulsion to magnets

Ferromagnetic metals include Iron, Nickel, Cobalt, Steel, Some Stainless-Steel, Rare-earth metals including Neodymium, Samarium and Gadolinium.

Magnetization is the process that turns a ferromagnetic material into a magnet.  The level of magnetization can be measured by the strength of the magnetic field over a given area.

Yes, the main risk to humans lies in the misuse of magnets. These magnets are incredibly dangerous and can cause injuries. If part of your body is caught between two attractive magnets, then pinch injuries can be caused, the stronger the magnets the worst the injuries will be.

Children should always be supervised when playing with magnets. Neodymium magnets are too strong for children and small neodymium magnets are very dangerous if a child swallows more than one as they can attract in the intestines requiring immediate surgery. Small alnico magnets are strong enough for children to experience magnetism without the risk of trapping fingers. For example, the traditional alnico horseshoe magnet and educational alnico bar magnets are widely used in schools.

The operation of heart pacemakers will be affected by the proximity of a magnet as they can cause pacemakers to operate in a mode that does not respond to the user’s own heart rhythm. The way a pacemaker responds to a magnetic field differs between manufacturers and therefore people with pacemakers should not put strong magnets close to their chest.

Small and medium sized magnets should not have any detrimental effect on your smartphone or tablet. It is quite possible that these devices already contain small magnets which enable them to perform certain functions. However, it is always wise to keep large, powerful magnets away from any electronic device as strong magnetic fields could possibly damage mechanical parts.

The magnetic field generated by any magnet is always strongest at either pole. The magnetic force is equally as strong at both the north and south pole.

A magnet’s poles are the surfaces from which lines of magnetism leave a magnet and reconnect on return to the magnet. The pole of a magnet is the area which has the greatest magnetic field strength in each direction. Each pole is either north facing or south facing. If you break a magnet into two pieces each piece will still have a north pole and a south pole. No matter how small the piece of magnet is, it will always have a north pole and a south pole.

Most magnets can be bonded in place with two-part epoxy adhesives. We recommend Araldite Rapid which sets hard in about 5 minutes. We also recommend Loctite Industrial strength Adhesive which has a similar setting time. Both these have a proven track record of reliably bonding magnets to most surfaces except for certain polythene type plastics.

You should never attempt to cut or drill a magnet as most magnets (excluding flexible magnets) are very hard and brittle due to the manufacturing process. These magnets cannot be drilled with HSS drills or even carbide drills, they need to be drilled or cut with diamond tooling and plenty of coolant as the dust is flammable.

The magnetic field is the area around a magnet where its magnetic force is exerted.  In other words, it is the area around the magnet where the magnet is effective move outside of the magnetic field and there is no magnetic force and the closer you get to the pole within the magnetic field the stronger the magnetic force.

Although invisible, the magnetic field of a magnet can be simply demonstrated by using iron filings and it can be very accurately simulated using complex modelling software.

There are several terms used to describe the strength of a magnet, these include:

Pull – This is how much force is needed to pull the magnet off a steel surface, and is usually referenced in kilograms.

Gauss reading (flux density) – If a Gauss meter or flux meter hall probe is placed on the pole of a magnet, a reading can be taken showing the number of lines of magnetism in every cm2 (1 Gauss = 1 line of magnetism in 1cm2), also known as flux density. This reading is an ‘open circuit’ value which will be substantially lower than the Br value and will be directly related to the material and the length to diameter ratio of the magnet. Long magnets with small diameters will have a much higher open circuit flux density than short magnets with relatively large diameters, even when they are manufactured from the same grade of magnetic material. If you had a rod magnet measuring 5,000 Gauss on the poles and you cut it in half, you would not expect the two smaller length magnets to have the same Gauss reading in open circuit.

Gauss is a measure of magnetic induction and a value of density. Simply put, a magnet’s Gauss measurement represents the number of magnetic field lines per square centimeter emitted by a magnet. The higher the value, the more lines of magnetism emitted by a magnet, however, alone, it isn’t necessarily a representation of a magnet’s strength. As well as the material, geometry also influences a magnet’s Gauss value, for example, if you have two different sized magnets made from the same material with the same surface Gauss, the larger magnet will always be stronger. Sometimes, a small magnet may have a high surface Gauss but will be able to support less weight than a larger magnet with a lower surface Gauss.

Non-Ferrous metals are metals or alloys that do not contain iron and have benefits such as low weight, higher conductivity, resistance to corrosion and of course they are non-magnetic.

Yes. Ferrous metals are defined as any metal that contains iron and it is this iron content that enables a magnetic field to attract.

Ferrofluid is a very special liquid that is magnetized when brought into the presence of a magnetic field. The Ferrofluid created wild, spikey shapes and patterns as it is near a magnet. Most pictures of Ferrofluid depict it with a very ‘spikey’ shape which is caused as the ferrofluid forms the most stable shape it can to minimize the total energy of the system, this is known as normal-field instability.

The strongest permanent magnets are Neodymium (Nd) magnets. Neodymium magnets are from the family of Rare Earth Magnets and are manufactured from a magnetic material consisting of neodymium, iron and boron forming the commonly seen structure of NdFeB.  Neodymium magnets offer incredible performance from a very small volume of magnet. They are available in many different grades, N55 is the highest grade available whereas the grades N42 and N52 are most readily available.

Neodymium magnets are permanent magnets and lose a fraction of their performance every 100 years if maintained within their optimum working conditions.
There are two factors which can shorten a magnet’s lifespan.

Heat
If the temperature of a magnet exceeds the maximum operating temperature (e.g. 80oC for N42 grade neodymium magnets), then the magnet will lose magnetism that will not be recovered on cooling. Samarium cobalt magnets are not quite as strong as neodymium magnets, but they do have a much higher operating temperature of up to 350 degrees Celsius. 

Corrosion
If the plating on a magnet is damaged and water can get inside, the magnet will rust and again this will result in a deterioration in magnetic performance. Samarium cobalt magnets and ferrite magnets are both resistant to corrosion but aren’t as strong as neodymium magnets.

Neodymium magnets are available in many different grades but most common are N35, N42 and N52 grade magnets.

Standard Neodymium magnets have a max operating temperature of 80°C and are available in different strengths. These magnets are prefixed with the letter ‘N’ followed by a number, the higher the number the stronger the magnet. N35 is the starting point and increases through to N52 as standard.  The number relates to the Maximum Energy Product of the magnet.

Neodymium can also be manufactured to operate at higher working temperatures and these magnets are identified with a different letter or letters at the end of the code:

• N = 80°C
• M = 100°C
• H = 120°C
• SH = 150°C
• UH = 180°C
• EH = 200°C
• AH = 230°C

Magnetic fields will pass through plastic, wood, aluminum and even lead as if it was not there. There is no material that will block magnetism. Ferrous materials such as iron, steel or nickel can conduct magnetic fields and redirect magnetism. All magnetic fields seek the shortest path from north to south and a piece of steel can provide a short cut making the journey from north to south much easier than flowing through air. To remove magnetism from where you do not want it to be, you can use steel to provide the magnet with a shortcut to redirect the magnetism flow via an alternative route.

The simplest example is putting a steel keeper across the poles of a horseshoe magnet, all the magnetism flows through the steel and there is no external magnetic field. When we send highly magnetized materials overseas, the airlines stipulate that there should be no magnetism on the outside of the box. To achieve this, we put the magnets in the Centre of the box and then line all 6 sides of the inside of the box with steel sheets. Stray magnetism which would normally pass through the walls of the box are suddenly diverted as they conduct through the steel on their journey from north to south.

Using two magnets together wouldn’t be the same as having one magnet of their combined size. For example, if you stacked two 10mm diameter x 2mm thick magnets on top of each other you would have effectively created a 10mm diameter x 4mm thick magnet, this would not double the magnets strength and pull, it would provide an estimated 70% increase.

Once the length of the magnet exceeds the diameter of the magnet, the magnet is working at an optimum level and further additions to magnetic length will provide only small increases in performance.

Once a magnet is fully magnetized, it cannot be made any stronger as it is fully ‘saturated’. It is like the analogy of a full bucket of water, once it is full to the brim, it can’t be made any fuller. By adding one magnet to the other, e.g. stacking, the stacked magnets will work as one bigger magnet and will exert a greater magnetic performance. As more magnets are stacked together, the strength will increase until the length of the stack is equal to the diameter. After this point, any further magnets added will provide a negligible increase in performance.

Although the logical assumption would be that when using two magnets together the attracting force would be equal to that of both the individual pull forces combined, this isn’t the case. While the total combined attracting force will be slightly increased it won’t be anywhere near the total combined value.

When a magnet is not in direct, flush contact with a steel surface or another magnet, their ability to attract/repel does decline significantly. How much, is roughly exponential, however, every shape and size of magnet is different. We test the holding strength of all our magnets in direct contact with a steel plate and through a series of ‘air gaps’ ranging from 0.1mm to 20mm. If you would like to know how much weight one of our magnets will support over a distance, please give one of our technical experts a call on 0800 488 0288 

All magnets have a ‘pull’ rating measured in kilograms and this relates to how much force acting perpendicular to the magnet is required to pull the magnet from a steel plate or equal thickness when in direct, flush contact.

The ‘pull’ rating is obtained under the following ideal conditions:

– the test bed steel plate is thick enough to absorb all the magnetism (typically 10mm thick)
– it is clean and ground perfectly flat
– the pulling force is slowly and steadily increased and is perpendicular to the magnet face.

In actual applications, perfect conditions are unlikely, and the following factors will reduce the given pull: 

Steel thickness
If a magnet needs the contact steel to be 10mm thick to absorb all the magnetism and deliver maximum pull, then fixing the magnet to a 1mm thick sheet steel surface will result in 90% of the magnetism being wasted and the actual pull delivering only 10% of its capability. To test if the contact steel is thick enough to absorb all the magnetism from a given magnet, simply fix the magnet in place and then offer a small steel plate behind the contact steel, directly behind the magnet and if it sticks, then it is being held in place by stray magnetism which is breaking out from insufficiently thick steel. If it falls away, then the contact steel is absorbing and conducting all the magnetism and increasing the thickness of the steel will not increase the ‘pull’ from the magnet.
Air gap
If the contact steel is rusty, painted or uneven, then the resulting gap between the magnet and the contact steel will lead to a reduced ‘pull’ from the magnet. As this gap increases, the pull decreases using an inverse square law relationship.

Material
All pull tests use mild steel as a contact steel. Alloy steels and cast irons have a reduced ability to conduct magnetism and the pull of a magnet will be less. In the case of cast iron, the pull will reduce by as much as 40% because cast iron is much less permeable than mild steel.

Temperature
Subjecting a magnet to temperatures above its maximum operating temperature will cause it to lose performance that won’t be recovered on cooling. Repeatedly heating beyond the maximum operating temperature will result in a significant decrease in performance.

Sheer force
It is five times easier to slide a magnet than to pull it vertically away from the surface it is attracting to. This is entirely down to the coefficient of friction which is typically 0.2 for steel-on-steel faces. Magnets with a rated pull of 10kg will only support 2kg if they are being used on a vertical steel wall and the load is causing the magnets to slide down the wall.

Flexible magnetic tapes and sheets are not as strong as hard permanent magnets in small volumes, however, when used over a large surface area it can be effective. Typically, flexible magnetic tape or sheet provides a pulling force of 40 grams per cm2 and can offer a cost-effective solution for hanging signs and displays.

Unfortunately, as other types of magnets such as neodymium or ferrite have greater magnetic performance, they will damage the magnetic sheeting by realigning the magnetic particles in the sheet. The result is that the sheet will be significantly weakened in the area(s) that you have placed the magnets. If you are wanting to use a flexible sheet with neodymium magnets you should use a ferrous sheet or tape. While ferrous sheet or tape does not produce any of its own magnetism it is excellent for sticking magnets too.