When is a “Bar Magnet” Not a “Bar Magnet”?

Simple answer — when it’s a magnetic tube. Often, we receive inquiries about our “bar magnets” but this is a misnomer. MPI provides magnetic tubes in our separators with a level of sophistication and science that goes way beyond those of a simple bar magnet.

Simple answer — when it’s a magnetic tube.

You can buy a good bar magnet at Staples. And it’s still fun to watch young children as they discover the “magic” of magnetism. Often, we receive inquiries about our “bar magnets” but this is a misnomer. MPI provides magnetic tubes in our separators with a level of sophistication and science that goes way beyond those of a simple bar magnet. A magnetic tube is not a solid bar but a tube filled with many magnets and circuits. What’s inside that tube makes a significant difference in performance. Don’t be fooled by grandiose promises of the “strongest magnetic tube on the market”. It’s not as simple as a catchy marketing phrase. MPI’s magnetic tubes remove small to medium size ferrous tramp metal contaminant from a variety of product streams. Typical uses include removing metallic grit from hydraulic reservoirs. This minimizes wear on the machine’s seals and bushings. Or they can remove unwanted ferrous contaminants in food and chemical processing systems. This improves product quality. The product stream flows around one or more 1” diameter magnetic tubes. These are within the product streams that attach to the housing via the tapped end holes. 

Tramp metal contaminants are captured and moved to the underside of the tubes — eliminating tramp metal “wash-off”. Magnetic tubes are easy to install and clean. They provide efficient and economical ferrous metal filtration protection of your processing equipment. The tubes may be used as individual units or part of multiple row arrangements. Our standard magnetic tubes utilize powerful ceramic magnet material. The tube is 1” diameter, Type 304 stainless steel. The ends are tapped to accommodate ¼” – 20 fasteners. When a manufacturer claims that they have the “strongest magnet tube on the market” what exactly are they saying? It boils down to their magnet having the highest holding force or highest Gauss level at the surface of the magnet. But, this may not always be the right solution for your application. At its core, a tube magnet’s job is to capture and retain unwanted metals from your product stream.

What differentiates one magnetic tube from another?

The answer is variations in the assembly — raw material strength, protective coatings, wall thickness, size of the magnet material, and size of pole pieces. These internal variations affect the circuit characteristics outside of the magnet, in what we refer to as the working area. This is where the product is moving through the magnetic field. Manufacturers have kept the conversation about magnetic tubes performance on the surface, or in the working area. The working area is where we conduct our testing with either pull or gauss testing. Let’s take a look inside the stainless steel tube to understand how these variations can affect performance.

Understanding MGOe

Neodymium rare earth magnets are a mixture containing neodymium, iron, boron, cobalt and varying levels of dysprosium and praseodymium. The exact amounts of these ingredients determine the Maximum Energy Product, or MGOe. 52 MGOe is currently the highest energy product available for commercial use.

The most important thing to understand is that the MGOe of any grade magnet material is finite and only has that maximum energy available. Creating 52 MGOe material is an exact scientific recipe. Therefore, it doesn’t matter which magnet supplier you buy from. One manufacturer’s 52 MGOe will have the same maximum energy as any other manufacturer’s 52 MGOe material. But, because a manufacturer uses 52 MGOe material does not mean that they have the most powerful magnetic circuit. Other factors can also influence the performance of the magnetic circuit. Let’s explore these other factors.

Reducing Tube Wall Thickness

Besides using a stronger magnet material, another way to increase performance on the surface of the magnet is by reducing the air gap.

The air gap is the amount of space between the magnetic pole pieces inside the magnet and the working area on the surface of the magnet. The closer the pole piece is to the working area of the magnet, the higher the measure of gauss or pull value will be on the surface of the magnet.

To do this, the manufacturer can use thinner walled tubing. This results in higher performance values. But, be aware, this reduces the thickness of the magnets protective cover and the protection that the layer provides.

You will often see dents and wear on magnets from manufacturers who use thinner tubes to lay claim to “the strongest magnet on the market.”

You may observe that your Magnet Audit reports reflect your magnet pull is getting stronger. Do not be fooled into thinking that this is a good thing. This is a sign that abrasion from your product flow is wearing through the thin wall of the magnet tube. It will soon need replacement.

Uncoated Magnet Slugs

If you have ever held a rare earth magnet in your hand (be careful!), it likely looked very shiny, as if it was chrome plated. Most magnet material manufacturers coat the raw magnet material in a nickel coating to protect the magnet from oxidation.

When installed into an assembly such as a magnetic tube, it increases the air gap. So, some manufacturers reduce the air gap by using uncoated neodymium magnet material. Neodymium is one of the more reactive rare earth elements and is very sensitive to oxidation. If left uncoated, a one-centimeter sample of neodymium will completely oxidize within a year.

The oxidization process is very similar to rusting. The structure of the magnet changes resulting in a progressive loss of magnetic performance. The magnet will break down into a powder state.

Using uncoated magnet slugs can be especially detrimental in applications where wet product are being filtered. Moisture penetrates the tube and an uncoated magnet slug will begin to swell as oxidization accelerates. This will lead to loss of magnetism and a potential to blow out of the tube. At MPI we are passionate about providing you the correct solution suited to your application.

We offer several models of magnetic tubes because there are many factors to consider when installing a magnet into a production line. A one-size-fits-all or “strongest magnetic tube” solution is not the right solution for everyone. MPI offers several solutions. Talk to our magnet experts. They will help you choose a product with the right balance of performance, cost and durability. This is a critical step before installing a thin-wall magnet into any application. To bridge the gap between performance and durability MPI has developed the new Hi-G Magnetic Tube.

MPI’s Hi-G Tube provides comparable pull values to any strongest on the market non-thin-walled tubes. But, without compromising the durability and longevity of your magnetic separator. We want to offer you the RIGHT magnet. For performance without compromise contact MPI today.