Impact of Air Gap on Lifting Capacity of Lifting Magnets
Posted on June 20, 2016
The lifting capacity of any permanent
decreases with increases in air gap, but the decreasing rate can
vary among different brand products. Allow
us to explain the secret to you.
First, let's take a look
at two brands of permanent lifting magnets and compare their decreasing
rates of lifting capacity with increasesing air gap.
1) NL-2200B (Rated Lifting Capacity of 2200 lb) Permanent Lifting Magnets
The Lifting Capacity of NL-2200B Derated by
2) Brand X (Rated Lifting Capacity of 2200 lb) Permanent Lifting Magnets of this shape,
similar to our discontinued products - NL lifting magnets.
When you compare two charts above carefully, you can find that the lifting capacities of
NL-2200B and Brand X are almost the same when the air gap is less
than 1/64”(0.4mm). However, the decreases in NL-2200B lifting
capacity would be less with increases in air gap than Brand X when the air gap
becomes greater than 1/64”. In conclusion, NL-2200B is better
for a load with dirt or uneven surface.
The secret is that the magnets installed in NL-2200B are thicker than that installed in Brand X!
Please look at the following sketch of Neodymium magnet demagnetization curve.
When a load to be lifted is clean and flat, the air gap between
the permanent lifting magnets and the load is almost nil. Both
NL-2200B and Brand X would have same magnetic flux
density B1 at their poles which contact the load and therefore have equal attractive
If the load is not clean or not flat there should be an air gap,
1/32” long for example, between the load and the permanent lifting
magnet. In such case, NL-2200B could have larger magnetic flux
density B2 in the air gap than B3 of Brand X and consequently
NL-2200B produces greater attractive force to the load because thicker magnets
magnetomotive force and has its work point higher than that of thinner magnet at the
be any other factors which influence the decreasing rate of the
lifting capacity with increases in air gap except the thickness of
the Neodymium magnets (assuming they are the same magnetic grade)? Of course yes. But the thickness of the Neodymium magnets
is the key reason.