Selecting the Right Electromagnet

Two basic types of electromagnets are available, flat-faced and bi-polar.

FLAT-FACED MAGNET - used when the entire face of the magnet is in direct contact with the work to be held or lifted and the work surface is smooth and flat. This design usually requires less over-all height and is less expensive.

BI-POLAR MAGNET - has two widely spaced poles or lifting surfaces which cause the magnet field to "reach out" further. Use the bi-polar type when the magnet has only partial contact with the work piece, handle an irregular shape, or when it must work through an air gap.

When work surface is not flat and smooth the magnet cannot make close contact. Scale, rough surface, or nonferrous material between the magnet and work piece create an "air gap." The greater the gap, the further the magnetic lines of force must reach.

The chart below compares the EM-476 flat-faced magnet and the BP-1601 bi-polar magnet. It shows the effect of air gap on the holding power of each.

Size4" x 8" x 2-1/2" high 4" x 7-1/2' x 4-3/4" high
Face Area30 sq. in.32 sq. in.
Pole Area15 sq. in.15 sq. in.
Holding Power2000 lb.1100 lb.
Through 1/32" air gap200 lb.480 lb.
Through 1/16" air gap95 lb.250 lb.
Through 1/8" air gap35 lb.70 lb.
Through 3/16" air gap0 lb.9 lb.

SMALL MAGNETS: generally operate on 12 volts. They will require a rectifier to convert 115 VAC to 12 VDC. Another method of obtaining direct current for magnet operation is through the use of 12 volt batteries.

LARGE MAGNETS: will usually operate on 115 or 220 VDC. A rectifier is required to convert 115, 230 or VAC to 115 or 230 VDC.

TOTAL WATTAGE: of all magnets powered by a single rectifier must not exceed wattage rating of the rectifier, e.g., from one to five-3 watt magnets can be used with a 15-watt rectifier.

THIN GAUGE SHEET: Magnets to pick up thin gauge, flexible sheet, such as 1/8", 3/16", and " thick, may require variable power, multiple coil, or special poles to maintain holding power and prevent double sheet pickup. Two or more magnets on a spreader bar or "H" frame may be needed to eliminate "peel off."

LIFTING CAPACITIES for standard Magnetool Lift Magnets, as shown on page 6, have been derated 50%. Do not exceed the listed capacity. These ratings are established by applying force on the magnet under registered tension until the magnet is pulled from a flat, mild steel test plate. This plate is thick enough so that magnetism cannot be detected on the opposite side of the plate. When tubing, rounds, or odd shapes must be lifted, the de-rating of the magnet may have to be as much as 75%. The pounds pull of the smaller magnets as listed on pages 3 and 4 actual ratings. They have not been de-rated.

Let Us Help You Select the Right Magnet

There are many variables that must be considered in the selection of a proper magnet. To help you get the best magnet for your application, we should have the following information:

  1. Surface of the work - is it scaly, rough, flat, machined or of irregular shape?
  2. Size of the work - give thickness, width, length and weight, plus area of contact for the magnet.
  3. Air gap - distance from work surface to face of magnet, whether actually air or non-ferrous material.
  4. Composition of the work - hot or cold rolled steel, tool steel, high carbon content steel, nickel, carbide, etc.
  5. Heat - temperature in which the magnet will operate and temperature of the work.
  6. Duty Cycle - will magnet be on 100%, 50%, or 25% of the time?
  7. Method of operation - will magnet be turned on and off manually or automatically? If the latter, how many times per minute?
  8. Send prints or sketches, parts, Polaroid shots and whatever other information will help in selecting the proper magnet.
  9. Special Note - The economical pick-up and transfer of small parts or scrap require a scrap yard type magnet or a magnetic conveyor. Please consult us.