Are All Metals Magnetic?

Only a few metals are attracted to a magnet. Iron is the main one. Most other metals, such as aluminium, copper, brass and lead, are passed over by a magnet.

This guide explains which metals are magnetic, why, and what that means when you use magnets to protect a product line.

The metals a magnet will pick up

Three common metals are strongly magnetic:

• Iron, and every steel made mainly from iron
• Nickel
• Cobalt

These are called ferromagnetic metals. A magnet pulls them with real force. A steel bolt, a nail, a piece of swarf and a broken machine part are all picked up easily.

Some rare metals are also magnetic, such as gadolinium. These are unusual in a factory and you will seldom meet them.

The metals a magnet will pass over

Most metals are not attracted to a magnet in any useful way. Common examples are:

• Aluminium
• Copper
• Brass and bronze
• Lead
• Zinc
• Gold and silver
• Titanium

A magnet has no useful pull on these. A magnetic separator will leave them in the product. If these metals are a risk on your line, a magnet alone will not remove them.

Why some metals are magnetic

Every atom acts like a very small magnet. In most materials these small magnets point in random directions, so they cancel each other out. In iron, nickel and cobalt, the atoms line up in small groups called domains. When a magnet comes near, the domains turn to face the same way and the metal is pulled towards it.

The strength of the pull depends on how much iron the metal contains, how the metal was made, and its shape. A thin, sharp piece is pulled less strongly than a solid block of the same weight.

Stainless steel is a special case

Stainless steel is made mostly from iron, so many people expect all of it to be magnetic. Some grades are, and some are not. Grades 304 and 316, which are common in food and chemical plants, are only weakly magnetic. Grades such as 430 are strongly magnetic. See our guide Are All Stainless Steels Magnetic? for the detail.

Work hardening changes this. When a 304 stainless part is cut, bent or ground, the worked area becomes weakly magnetic. A high strength separator will still catch most fine stainless particles from wear on stainless equipment.

What this means on a production line

Most metal contamination in a factory is iron or steel. It comes from worn machine parts, screens, bolts, tools and the raw material itself. A magnetic separator removes this at low cost, with no power and very little maintenance.

The strength of the magnet decides how small a particle it can hold. Standard rods of 7,000 to 8,000 gauss remove ordinary tramp iron. High strength rods of 9,500 gauss and above hold fine particles and weakly magnetic stainless steel.

Aluminium, copper and brass need another method, such as a metal detector or a sieve.

The SMAG range

Santosh Magnetic Works makes magnetic rods, grids, drawer housings, liquid traps and plate magnets in strengths up to 13,500 gauss. Every unit is supplied with a tested certificate of magnetic strength. See the full magnetic separation range or contact us with a sample of your contamination and we will advise the right strength.