The Important Stuff
This is the important information about the properties of neodymium magnets that will help you to make an informed decision. Understanding the following bullet points below will help you to get the most out of your magnets and what they are suitable for and what they are not.
- As with most magnets, neo magnets are hard and brittle. The brittle nature combined with the incredible pull force means that if the magnets collide unimpeded with another magnet or a steel object, the magnets will probably break or chip. Particularly the larger magnets which will impact with a higher force. Therefore the magnets should not be used where they will collide. Ideally a gap should be left between the magnet and the object, or alternatively, line the magnet with plastic, steel or any other material to protect the magnet from direct impact.
- Because the magnets are so strong and are brittle, even pulling them apart can break them. This is mainly an issue with the thinner magnets. To be safe we recommend separating the magnets by sliding them apart. For larger magnets we provide spacers between the magnets to make separating them easier.
- Neo magnets are highly corrosive, but the nickel coating prevents the magnets from rusting. However they are not intended for outdoor use. For outdoor use we’d recommend protecting the magnets from the elements. In the past customers have used epoxy to encase the magnets.
If you have any questions about neo magnets, please email us via our contact page.
General Useful Information About Neo Magnets
In the 1980s using powdered neodymium iron boron, magnets were produced with forces almost 75 times stronger than magnetite. These are now commonly referred to as neo magnets or rare earth magnets and are also referred to as NdFeB or NIB magnets. These are the most powerful permanent magnets commercially available today and hence can be dangerous if not handled with care. They can also damage devices such as magnetic strips (credit cards) and various computer accessories and components.
Neo magnets are a sintered magnet, which means they are produced from a powder. They are highly corrosive and rely on a plating, typically a nickel plating to protect them from corrosion. The coating is very thin, typically 10 – 30 microns and should not be used as a wearing surface. To extend the life of the magnets a sacrificial wearing surface is recommended as you see used on magnetic latches.
Although they rank as superior permanent magnets, they begin to lose their magnetism at temperatures above 80 degrees Celsius, so they are not suited to high-temperature applications.
One of the most appealing characteristics of neodymium magnets is their relatively low cost. Neodymium is the third most abundant rare-earth element, and is far more prevalent than samarium, the prime component of the samarium-cobalt magnets that neodymium magnets have largely replaced. Also due to their superior strength they allow for reductions in size and have good resistance to external demagnetisation fields. Neo magnets are hard and brittle and generally should avoid being machined.
The Manufacturing ProcessThe process of producing neo magnets is extremely complex.
Just as the materials are different for different kinds of magnets, the manufacturing processes are also different. This is a typical powdered metallurgy process used to produce neo magnets:
Preparing the powdered metalThe appropriate amounts of neodymium, iron, and boron are heated to melting in a vacuum. The vacuum prevents any chemical reaction between air and the melting materials that might contaminate the final metal alloy.
Once the metal has cooled and solidified, it is broken up and crushed into small pieces. The small pieces are then ground into a fine powder in a ball mill.
PressingThe powdered metal is placed in a mold, called a die, that is the same length and width (or diameter, for round magnets) as the finished magnet. A magnetic force is applied to the powdered material to line up the powder particles. While the magnetic force is being applied, the powder is pressed from the top and bottom with hydraulic or mechanical rams. Typical pressures are about 70 MPa to 100 MPa (10,000 psi to 15,000 psi). Some shapes are made by placing the powdered material in a flexible, air-tight, evacuated container and pressing it into shape with liquid or gas pressure. This is known as isostatic compaction.
HeatingThe compressed "slug" of powdered metal is removed from the die and placed in an oven. The process of heating compressed powdered metals to transform them into fused, solid metal pieces is called sintering. The process usually consists of three stages. In the first stage, the compressed material is heated at a low temperature to slowly drive off any moisture or other contaminants that may have become entrapped during the pressing process. In the second stage, the temperature is raised to about 70-90% of the melting point of the metal alloy and held there for a period of several hours or several days to allow the small particles to fuse together. Finally, the material is cooled down slowly in controlled, step-by-step temperature increments.
The sintered material then undergoes a second controlled heating and cooling process known as annealing. This process removes any residual stresses within the material and strengthens it.
The annealed material is very close to the finished shape and dimensions desired. This condition is known as "nearnet" shape. A final machining process removes any excess material and produces a smooth surface where needed. The material is then given a protective coating to seal the surfaces.
Up to this point, the material is just a piece of compressed and fused metal. Even though it was subjected to a magnetic force during pressing, that force didn't magnetise the material, it simply lined up the loose powder particles. To turn it into a magnet, the piece is placed between the poles of a very powerful electromagnet and oriented in the desired direction of magnetisation. The electromagnet is then energized for a period of time. The magnetic force aligns the groups of atoms, or magnetic domains, within the material to make the piece into a strong permanent magnet.