Selecting
the Right Magnet
Two basic types of electromagnets are available: flat-faced
and bipolar.
FLAT FACED MAGNET
Used when the entire face of hte 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.
BIPOLAR MAGNET
Has two widely spaced poles or lifting surfaces which cause
the magnetic 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.
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MAGNETS
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EM-476
FLAT-FACED
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BP-1601
BI-POLAR
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Size
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4" x 7-1/2" x 4-3/4" high
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Face Area
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Pole Area
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Wattage
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Holding Power
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Through 1/32" air gap
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Through 1/16" air gap
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Through 1/8" air gap
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Through 3/16 " air gap
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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 460 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 1/4" 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 CAPABILITIES
For standard Magnetool Lift Magnets 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 theopposite side of hte 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 shown on the Small
Flat-Faced Electromagnets and the
Small Bi-Polar Electromagnets pages are the actual ratings.
They have not been derated.
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