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A MAGNET IS NOT “JUST A MAGNET”

AN OVERVIEW OF MAGNETIC POLARITY AND COMPOSITION

WE BUILD THEM CORRECTLY! Let’s take figure (1) and (3) from our previous example. In fig (1), a ferrous
mild steel material 1/8” thick will be placed between each north and south
Contrary to popular belief, a magnet is not just a magnet. When making a pole within the magnet tube length. In fig (3), a nonferrous wood or metal
magnet purchase, it is advantageous to understand more about a magnet’s
material ½” thick will be placed between each north and south pole.
“inner” design as well as outer appearance. The inner design criteria are Furthermore, we will say this application involves locating the magnet
composed of three elements:
assembly in an environment which is within a heat range that will destroy the
wood spacers after an unknown extended period of time.
1) Magnet polarity design
2) Composite material construction Due to the fact that ferrous metal spacers act as a conductor to the magnetic
field, the fig (1) unit has greater magnetic strength on it’s working surface
3) Magnet material rating
when compared to the second unit, also the number of magnetic poles is
MAGNET POLARITY greater, so the magnet can hold more ferrous metal between cleanings.
Additionally, the mild steel will be able to handle the working environment
All magnets including Grates, Drawers and Plates can be assembled
internally in a variety of magnetic polarities. These internal differences, without any negative impact magnetically or structurally.
The second unit, on the other hand, being nonferrous, does not conduct
although not visually noticeable on the exterior, will produce a different magnetism, therefore is weaker magnetically and will not hold up in the
magnetic performance result. Selecting the best magnetic polarity design operating environment due to the wood spacers. Once again, both units
depends on (a) the specific application criteria, and (b) knowing the differences appear to be the same when making only a physical observation of the finished
when comparing these products offered by various manufacturers. Due to product.
the fact that equipment manufacturers operate as an unregulated industry
Another possible transparent difference is a non-magnetic stainless-steel
without uniform product standards, it is incumbent on the buyer to know how magnet housing compared to a cheaper mild steel housing. The mild steel
to compare “apples to apples.”
will become magnetized when placed around or near a magnetic field and
1” interfere with the magnetic field created by the internal magnets resulting in
TYP. PPE design ALL types a reduction of the magnets ability to do its job.
MAGNET MATERIAL RATING
1
Throughout the history of magnetics, like materials have generally
possessed like magnetic characteristics. Although Alnico and Ceramic magnet
Composite materials are available in a wide range of grades of magnetic values, the
Magnetic differences from one end of the range to the other has not been as significant
Material
Material as it is today. With the advent of new high energy Rare Earth magnet materials,
3” this generalization is no longer acceptable.
TYP. Typical Alnico Design Based on current rare earth magnet manufacturing technology,
Neodymium-Iron-Boron magnets dominate this segment of the
permanentmagnet market. Due to the lower costs as compared to Samarium-
2
Cobalt magnets and higher magnet strengths, nearly all rare earth magnets
manufactured for the Plastics Industry are made from Neodymium-Iron-Boron
magnetic materials. Unlike Ceramic and Alnico materials, Rare Earth materials
can vary greatly in strength. This variation is measured in MGOe (Mega
2” Gauss Orsteds) and represents a magnet’s peak energy. This can be
TYP. Typical Rare Earth Design compared to a magnet’s “horsepower” and will have a great impact on
maximum potential strength of the magnetic separator such as a Grate or
3 Drawer magnet.
Because the rare earth magnetic material component cost represents the
greatest cost component of the magnetic equipment, knowing the MGOe
The 3 illustrations above depict how these polarity differences can be grade of material is critical in the selection/comparison process.
created in what appears to be similar sized magnetic tubes.
Standard PPE Rare Earth Magnets have an MGOe rating of 52. It has
Figure (1) illustrates the most common design offered by manufacturers. been our practice to always offer the highest commercial grade available as
The 5 magnets and 6 magnetic poles offer the most powerful of the three we understand our customers are paying a significant price premium to have
designs shown. At PPE, we use this design for ALL types of magnet tubes. the most powerful permanent magnets when “buying up” to rare earth
magnets.
Figure (2) illustrates the most common design when Alnico magnetic materials The maximum temperature your PPE Magnets will be exposed to must be
are used. Alnico is used when high temperature applications up to about a consideration when selecting the proper magnet for the application. PPE
800°F exceeds Samarium Cobalt magnet limits. This 2 magnet and 3 Ceramic magnetic material may be placed in applications seeing
magnetic pole design provides improved magnetic field strength at gap but temperatures up to 400°F, while standard PPE Rare Earth Magnets may
due to the lower number of magnetic “poles” as compared to type 1 less be placed in applications with a maximum temperature up to 176°F.
volume of ferrous metal is retained along the tube. PPE High-Temperature Rare Earth Magnets may be placed in applications
with a maximum temperature up to 356°F.
Figure (3) illustrates how magnet manufacturers can reduce costs when
producing Rare Earth magnets when buyers do not know how to compare
PPE Magnetic Tube Performance
designs. This illustration shows smaller magnets and larger “poles” as
compared to figure 1 resulting in much weaker magnetic strength. The greatest Magnet Tube Type Ceramic Rare Earth Hi-Temp Rare Earth
component driving costs of rare earth magnets is the amount of magnetic 400°F 176°F 356°F
Maximum Temp.
material. Therefore, using smaller magnets, lower quality rare earth material,
and/or larger mild steel “poles” provide manufacturers with distinct cost MGOe Rating 4.5 52 38
advantages that are transparent to the naked eye.
Some of our competitors like to offer rare earth magnets with a rating of 27
PLASTIC PROCESS EQUIPMENT, INC. www.ppe.com
COMPOSITE MATERIAL CONSTRUCTION and only provide the higher quality magnets to informed customers who know
e-mail: sales@ppe.com
6385 MONTESSOURI STREET
W
E 8303 CORPORATE PARK DRIVE
Composite material construction variances can impact a product’s what to ask. Now you know what to ask.
Toll Free: USA, Canada & Mexico
A MACEDONIA, OHIO 44056-2300
E
LAS VEGAS, NEVADA 89113-1186
performance both structurally and/or magnetically depending on the product, As you can see, knowing a magnet’s “inner” design and construction will
800-362-0706
S
S 216-367-7000 • FAX: 216-367-7022
702-433-6385 • FAX: 702-433-6388
it’s application and composite material design.
help guide you in selecting the right magnet for your application.
T TOLL FREE: 800-321-0562 T TOLL FREE: 800-258-8877 Order Fax: 800-223-8305
Plastic Process Equipment, Inc. • 800-362-0706 • www.ppe.com 463