Patent GB-1469463-A (GB)
Title: Permanent magnet holding system for ferromagnetic materials
IPC: H01F7/02
Filed: 1974-09-04
Abstract: 1469463 Magnetically retaining loads on conveyer belts DEUTSCHE EDELSTAHLWERKE AG 4 Sept 1974 [13 Sept 1973] 38690/74 Heading B8A [Also in Division H1] A P.M. retaining system comprises two or more permanent magnets with ferromagnetic polepieces such that the external magnetic retaining force is controllably variable and removable by polarity reversal of at least one permanent magnet in response to energization of an electromagnetic coil; the permanent magnet or magnets to be reverse polarized being of low coercivity material and the remaining magnets of high coercivity material. The system is applicable to the lifting, handling, or conveying of ferromagnetic material. Two permanent bar magnets 1, 2 (Figs. 1, 2) with ferromagnetic polepieces 3, 4 are connected by a non-magnetic plate 5; magnet 1 of low coercivity being surrounded by electromagnet coil 6 while magnet 2 of high coercivity generates the same field as magnet 1 and is of corresponding polarity therewith, similar poles abutting in corresponding polepieces. When a current pulse engages the coil, magnet 1 is reverse polarized and the magnetic polarities in polepieces 3, 4 cancel to remove the retaining attractive force. On further reversal by another pulse the original polarisation is re-established. Polepiece 3 may be a ring, polepiece 4 a bar, and magnets 1, 2 as ring segments one of which has a polarising coil 6, and the system may be extended by multiplication. In a further modification (Figs. 3, 4 not shown), three permanent magnets are provided of which the centre one has low coercivity embraced by a coil, and the flanking magnets are of high coercivity with like poles abutting common polepieces. Pulse reversal of the centre magnet cancels the retaining force by closure of the field within the polepieces. In a further modification (Figs. 5, 6) a cup 31 encloses a circular low coercivity permanent magnet 32 surrounded by a high coercivity ring magnet 34; both being covered by poleplate 35, surrounded by coil 36, and embedded in casting compound 33. In a further modification (Figs. 7, 8 not shown) two permanent magnets are provided as annular segments and two others as interposed rods embraced by energization coils. The magnets are contained within magnetic rings separated by interposed non-magnetic rings and a shaft traverses a central bush. The device is externally effective as a handling roll when similar polarities are induced in the surrounding rings, and is magnetically de-energized on reversal of polarity of the rod shaped magnets. In a further modification applicable to a belt conveyer with plural rows of retaining magnet devices placed in a box between the conveyer runs (Figs. 9, 10 not shown) the devices comprise systems in which a U-section ferromagnetic member 45 (Figs. 11, 12) has a central high coercivity permanent magnet 46 flanked by low coercivity permanent magnets 47 each surrounded by energizing coil 48; the three magnets being covered with a common poleplate 49 which when the magnets are activated has opposite polarity to that of the flanges of the U- section, so that ferromagnetic material is retained on the conveyer belt until at a required location a magnet device or group of devices is reversed in polarity by pulsing the associated coils, so that the external field collapses to release the material in transit.