Magnets play a vital role in our everyday lives. They’re in our vacuum cleaners, washing machines and various other electronic gadgets. Delve into your wallet and you’ll find magnetic strips on the back of credit and debit cards. In hospitals, MRI machines use powerful magnetic fields to generate incredibly detailed images of bodily organs, bones, tissue and muscles. In other words, magnets are everywhere.
Yet most of us don’t really understand how magnets work nor how magnets are made. So let’s get to the core of the matter. How are magnets produced? What’s more, how is an electromagnet made?
A Short History of Magnets
We’re exploring how magnets are made, but they’re also naturally occurring. Humans have been observing magnets since at least the sixth century BC, when ancient Greek philosopher Thales of Miletus noted that certain minerals, what we now call lodestone, attracted iron. Some even attribute the word ‘magnet’ to the Greeks, citing their use of ‘magnetis lithos’ or ‘the stone of Magnesia’ so-named for the region on the Aegean coast where these lodestones were first discovered.
Other civilisations also observed magnetic properties and, in the eleventh century, the Chinese used lodestone to make compasses, known as ‘Si Nan’ or ‘south pointer’. Medieval Europeans and the Islamic world followed soon after.
Over the centuries, scientific understanding of magnetism has evolved incrementally. In 1600, William Gilbert published his book De Magnete, including the discovery that the Earth is a magnet.
In around 1819, Hans Christian Ørsted discovered that electric currents produce magnetic forces. And, in 1824, English physicist William Sturgeon made the first electromagnet.
However, there’s still much to discover. And, in terms of the question “how are magnets made” scientists are still unsure how lodestone becomes magnetically charged. The current leading theory is that it occurs when the minerals that make it up are struck by lightning. But, shifting from the natural to the man made, how are magnets manufactured? Let’s take a look.
How are Magnets Made?
The most common method of magnet manufacturing is known as powder metallurgy. From mining to a finished product, this takes between four and six weeks to complete. Let’s examine this process step-by-step.
Raw Materials: Ferromagnetic Metals
The process of how magnets are made begins with metal; specifically, “ferromagnetic” metal, this being one that can generate its own magnetic field. Cobalt, nickel and iron are examples of ferromagnetic metals. Some alloys, such as steel, also qualify. One of the most common metal bases is barium ferrite.
Whatever is to be used, the required metals are mined and transported to the manufacturer. So, with the raw materials in situ, how are magnets made from metal? The first step is melting it down.
Vacuum Induction Melting
The metal is heated to its melting point within an induction melting furnace. This is done in a vacuum in order to prevent any chemical reactions or contamination.
The next phase in how magnets are produced is to turn the molten metal into a powder. First, it’s allowed to cool and solidify. It’s then broken into pieces which are placed inside a ball mill machine. As the machine rotates, heavy steel or ceramic balls drop onto the load to be crushed. This mechanised process has its roots in a manual version used for thousands of years to crush stones.The result is a fine powder, usually between three and seven microns in diameter.
It’s important to align the particles that make up the powder. This maximises the magnetic force by homogenising the direction of all magnetic regions. One of the ways of doing this is die pressing. The powder is placed into a mould known as a die, which is formed in the desired eventual shape of the magnet. It is then simultaneously pressed and subjected to a magnetic force known as an aligning field.
We’re about halfway through answering ‘how are magnets manufactured’ but there are a few more steps to complete before we have a finished magnet.
The next stage in terms of “how are magnets produced” involves heating the compressed powdered metal slugs which fuses them into a solid piece of metal. This is called sintering and is done in three stages.
1. The metal powder is heated at a low temperature to remove any moisture and contaminants from the pressing.
2. The temperature rises to around 80% of the metal’s melting point which allows the metal to permanently fuse together. This can last hours or even days.
3. The temperature is slowly reduced in small increments over a period of time to cool the metal.
Annealing is the process of reducing any stresses on the metal and strengthening it through further rounds of heating and cooling.
Testing, Polishing and Machining
Tests are carried out to assess and measure different aspects of the magnet’s strength, from field strength to pulling force. The metal is polished to remove any last remaining debris. Finally comes machining, this is the stage at which the magnet is machined into its final shape.
To prevent breakage or chipping, the magnet is covered with a protective coating, then cleaned, dried and plated.
Whilst it may seem counterintuitive, the final stage of how magnets are made is magnetising. That’s because all the work done thus far is to prepare for this step, when it actually becomes a magnet. This is done by placing it between the poles of a powerful electromagnet, which is energised and the magnetic force aligns the atoms, known as magnetic domains. And that is now a magnet.
So that answers ‘how are magnets manufactured’, but it’s not the end of the story. Because there is one more answer to draw out, namely, how is an electromagnet made?
How is an Electromagnet Made?
Electromagnets are made from coils of wire that conduct electricity. When a current passes through the wire, a magnetic field forms around it and it acts like a magnet. The more loops of wire in the coil, the stronger the magnetic field is. When the electricity stops flowing, there is no magnetism.
Electromagnets are used in a lot of electronic devices when magnetic forces are only required for a short amount of time. Electromagnets are used in all sorts of devices from the speakers we play our music on to the cars we drive. And that’s the final element in the process of ‘how are magnets produced’ as well as ‘how is an electromagnet made’.