How to Choose & Use Lifting Magnets - ERIEZ - #5

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But if the same load offers a much larger contact area magnets of a differenttype, or smaller magnets of the same type, but more of them, can be used. These smaller magnets need not produce a field with such deep penetration into the load because the power of each magnet can be multiplied by the number used. Did you know? The number of poles a magnet has is determined by itsintended use. As a general rule of thumb, the more “poles”on the face of the magnet, the shallower the magnetic field.A two-pole magnet typically has a deeper field (extendingfarther from the face) than a magnet with 3 or more poles.The design of the magnet circut determines the depth of themagnet field produced Generally speaking, as gaps between poles increase, the depth of field, orpenetrating ability of the magnet, increases. For a given physical size, magnets with two poles will have greater gaps than those with three poles and, accord- ingly are usually better suited for thicker loads. Conversely, three-pole magnets are normally the logical choice for thinner loads.A billet and a flat plate are sketched, each with the same weight. The typeof magnet arrangement used for efficient lifting in each case is shown. As indicated above, a two-pole magnet is used for the billet and three pole magnets for the plate.The billet offers comparatively small contactarea in relation to its weight. The plate of the same weight offers a considerable contact area. A magnet for handling the billet must penetrate the billet material to get adequate holding or lift power. But this same magnet would be ineffi- cient for lifting the plate because the shape of its penetrating field would result in consider- able fringing outside the relatively thin plate. For lifting the plate an arrangement of multiple smaller lifting magnets is more efficient.
A A A A Section A-ASection A-A SURFACE CONDITION OF LOAD AND MAGNET Only when there is no space between the mating surfaces of the magnet andload can the full lifting ability of the magnet be put to work. The familiar “inverse square law” tells us that the pulling power of a magnetic pole decreases rapidly as the distance between magnet face and load is increased. The graph illustrates this effect. We see that a magnetic pole with a given pulling power at 1 unit of distance will have only 1/4 that pull at 2 units of distance, 1/9 that pull at 3 units of distance, etc. 5