Overband magnets
Permanent magnetic overband magnets are supplied with or without discharge belt, depending on the task involved. Everywhere that it is a question of automatically separating foreign iron items from bulk goods of all types, such as coal, sand, grain, meal, etc., permanent magnetic overband magnets are used with very great success.
Design
The system comprises a permanent magnetic overband magnet and, in the case of the design with discharge belt, a sectional frame construction as well as a discharge belt made of non-wearing and impact-resistant rubber material with mounted discharge strip.
The overband magnet has been manufactured using high-quality magnetic materials, and its ideal design and construction guarantee a wide range of the magnetic field and thus a high separating power of ferromagnetic items from bulk goods of all types. A special design is made to screen the overband magnet on all sides with the exception of the working side; i.e. there are no interfering leakage fields which attract the iron items to the side or which might cause electromagnetic interference. In addition, this screening serves to protect against mechanical damage as well as powerful demagnetizing fields.
The permanent magnetic overband magnet has an unlimited service life with no diminishing of its magnetic power under normal operating conditions. The use of permanent magnets means that the overband magnet operates completely maintenance-free and without a supply of electric current, apart from the drive for the discharge belt.
The discharge belt is driven either by a completely enclosed three-phase current drum motor or by a three-phase current geared motor via roller chain and drive drum; the standard voltage is 230/240/400 Volt, 50 Hz.
Design and performance
The dimensioning of the overband magnet in respect of its magnetic power is determined by the level and nature of the bulk goods, the speed of the conveyor belt as well as the form and size of the iron items. The necessary size is specified by us in accordance with information on the respective operating conditions. The performance is presented in the form of the free transfer height of the various iron items for the various types of magnet. The sizes are here identical with or without discharge belt. If the iron items which are to be discarded are covered by bulk goods, the free transfer height is reduced; this occurs as a function of the type, grain size, the specific gravity and the degree of humidity of the bulk goods as well as that of the iron items which are to be separated. The dependence of the transfer height on the geometry of the parts is presented qualitatively on the following page.
Notes
The width of the overband magnet should be chosen in each case so as to be 100 mm greater than the respective flow of material on the transportation unit. To increase the extent of separation, conveyor belts should not be troughed where the overband magnet is located so that the level of the layer of the material which is to be separated is reduced and so that the material is additionally loosened up. It may be appropriate to use movable deflectors to regulate the height of the layer. Notes on the installation of overband magnets are sketched on the following page. At the time of installation, special attention should be paid to all parts of the conveyor units and of the construction in the range of action of the overband magnet being made of non-magnetizable material. This applies also to the drive drums of conveyor belts if the magnet is used as an overhead magnet.
It is generally the case that the wider the magnet is, the greater is its range also.