Magnetic Filtration Applications And Benefits

There are many benefits to using magnetic filtration.

According to Machinery Lubrication:

Oil filtration in automotive and industrial machinery is essential to achieving optimum performance, reliability and longevity. Lubricant cleanliness is highly important and lubrication practitioners are provided with numerous options for filtering and controlling contamination, including disposable filters, cleanable filters, strainers and centrifugal separators.

This article discusses the mechanism of particle separation and reviews the many applications of magnetic filters and separators in the lubrication industry today. A brief guide to commercial filtration products is also presented.

From its origin in the beneficiation of iron ores, the magnet has played a prominent role in the separation of ferrous solids from fluid streams. Even in the control of contamination from in-service lubricants and hydraulic fluids, magnetic separation and filtration technology has found a useful niche.

Currently, there are a number of conventional and advanced products on the market that employ the use of magnets in various configurations and geometry.

Magnetic Filtration Applications And Benefits

Magnetic Filtration Applications And Benefits

Role of Magnetic Filters
Car owners, car mechanics, equipment operators, maintenance technicians and reliability engineers know the importance of clean oil in achieving machine reliability. Tribologists and used oil analysts are also aware that in some machines as much as 90 percent of all particles suspended in the oil can be ferromagnetic (iron or steel particles).

Typically, one or both lubricated sliding or rolling surfaces will have iron or steel metallurgy. These include frictional surfaces in gearing, rolling-element bearings, piston/cylinders, etc.

While it is true that conventional mechanical filters can remove particles in the same size range as magnetic filters, the majority of these filters are disposable and incur a cost for each gram of particles removed.

There are other penalties for using conventional filtration, including energy/power consumption due to flow restriction caused by the fine pore-size filter media. As pores become plugged with particles, the restriction increases proportionally, causing the power needed to filter the oil to escalate.

How do Magnetic Filters Work?
While a large number of configurations exist, most magnetic filters work by producing a magnetic field or loading zones that collect magnetic iron and steel particles. Magnets are geometrically arranged to form a magnetic field having a nonuniform flux density (flux density is also referred to as magnetic strength) (Figure 1).

Magnetic filter showing pattern of flux distribution of flux distribution and the collected dirt.

Particles are most effectively separated when there is a strong magnetic gradient (rate of change of field strength with distance) from low to high. In other words, the higher the magnetic gradient, the stronger the attracting magnetic force acting on particles drawing them toward the loading zones. The strength of the magnetic gradient is determined by flux density, spacing and alignment of the magnets.

Various types of magnets can be used in these filters (see sidebar). Magnets used in some filters can have flux density (magnetic strength) as high as 28,000 gauss. Compare this level to an ordinary refrigerator magnet of between 60 and 80 gauss. The higher the flux density, the higher the potential magnetic gradient and magnetic force acting on nearby iron and steel particles.

While there are many configurations of magnetic filters and separators used in process industries, the following are general classifications for common magnetic products used in lubricating oil and hydraulic fluid applications.

Magnetic Plug
The most basic type of magnetic filter is a drain plug (Figure 2), where a magnet in the shape of a disc or cylinder is attached to its inside surface (typically by adhesion). Periodically, the magnetic plug (mag-plug) is removed and inspected for ferromagnetic particles, which are then wiped from the plug.

Magnetic Drain Plug Filter

Today, such plugs are commonly used in engine oil pans, gearboxes and occasionally in hydraulic reservoirs. One useful advantage of mag-plugs relates to examining the density of wear particles observed as a visual indication of the wear rate occurring within the machine over a fixed period of running time.

The appearance of these iron filings on magnets are often described in inspection reports using terms such as peach fuzz, whiskers or Christmas trees. If one normally sees peach fuzz, but on one occasion sees a Christmas tree instead, this would be a reportable condition requiring further inspection and remediation. After all, abnormal wear produces abnormal amounts of wear debris, leading to an abnormal collection of debris on magnetic plugs.

Rod Magnets
While magnetic plugs are inserted into the oil below the oil level (for example, drain port), rod magnets may extend down from reservoir tops (Figure 3), special filter canisters (Figure 4) or within the centertube of a standard filter element.

These collectors consist of a series of rings or toroidal-shaped magnets assembled axially onto a metal rod. Between the magnets are spacers where the magnetic gradient is the highest, serving as the loading zone for the particles to collect.

Periodically the rods are removed, inspected and wiped clean with a rag or lint-free cloth. A conceptual example of a particular rod magnet filter is shown in Figure 1. When the rod is removed, the sheath or shroud can be slid off the magnet core to remove the collected debris. This debris can then be prepared for microscopic analysis to aid in assessing machine condition.

Flow-through Magnetic Filters
Figure 5 illustrates an example of a commercially available flow-through filter.

Flow-through Magnetic Filter Figure 5. Flow-through Filter
In this configuration, sold by Fluid Condition Systems under the MAGNOM trademark, the magnets are sandwiched between metal collection plates that have specific flow slots.

Coillection Plates

As fluid passes through the slots, ferromagnetic particles accumulate in the gap between the plates. However, they do not interfere with flow (clogging), or risk particles being washed off by viscous drag.

One advantage of flow-through magnetic filters is the large amount of debris they hold before cleaning is required. The cleaning process typically involves removing the filter core and blowing the debris out from between the collection plates with an air hose.

What Are Magnetic Strainers And Filters?

Pros and Cons of Magnetic Filters

Inductors, Filters and Chokes

U-type Grooved Strong Rare Earth Ndfeb Magnet

Funnel Magnets Funnel Type Filters

Magnet Rotor Assembly with Neodymium Segment Magnets

Permanent Magnet Rotor Assembly on Non-magnetic Shaft

Flat Magnetic Rotor Assembly with Neodymium Rectangular Magnet