Magnetic Filtration Benefits

10 Mar, 2022

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.

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)

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.