GB1588365A

GB1588365A - Permanent magnetic system for magnetic retention of ferromagnetic articles

Info

Publication number: GB1588365A
Application number: GB42603/77A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-10-16
Filing date: 1977-10-13
Publication date: 1981-04-23
Also published as: NO144254B; DE2646784A1; JPS5349667A; CA1100178A; IT1087778B; FR2368132A1; ES463017A1; NO144254C; BE859307A; FI772993A7; LU78261A1; DE2646784C3; SE7711078L; AT348301B; DD132218A5; NO773404L; DE2646784B2; DK451777A; NL7711339A; ATA732377A

Description

(54) PERMANENT MAGNETIC SYSTEM FOR MAGNETIC RETENTION OF FERROMAGNETIC ARTICLES (71) I, HEINRICH SPODIG, a subject of the Fed. Rep. of Germany, of Netteberge 202, 4714 Selm-Bork/Westfalen, Fed. Rep.

of Germany, do hereby declare the invention for which I pray that a Patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a permanent magnet system, particularly in the form of a clamping plate, for magnetic retention of ferromagnetic articles.

The object of the invention is to provide a permanent magnet system which has an improved magnetic retention property.

According to the invention there is provided a permanent magnet system for the magnetic retention of ferromagnetic articles, comprising a plurality of individual bar-like permanent magnets mounted in a ferromagnetic housing and arranged in alternating, polar sequeence between a base of the housing and a cover plate of ferromagnetic material seating directly on pole surfaces of the permanent magnets and presenting a magnetic retention surface, said cover plate being provided with holes or perforations and having a thickness so dimensioned in relation to the magnetic flux induced therein by the permanent magnets that an external magnet retention field exceeding the magnetic saturation in the plate is developed.

As a result of the holes or perforations which, advantageously are distributed over at least most of, or a distinctly substantial part of, the area of entire magnetic retention surface of the cover plate and have a size which is synchronised with the size of the articles to be retained, the external magnetic retention field existing adjacent or beside the magnetic short circuit becomes more intensive, due to the fact that the magnetic lines of force must pass through a labyrinth formed by the bridges caused by the holes or perforations and discharge at the edge of the holes or perforations in concentrated form.

In this way, a ferromagnetic article placed on the cover plate will be magnetised by the external magnetic retention field and thus be incorporated in the magnetic circuit of the system resulting in a retention of the article by the plate.

Thus, powerful individual external magnetic retention fields form, in contrast with a cover plate having an imperforate or closed surface, which are distributed practically uniformly over the entire magnetic retention surface, as far as the centre of gravity is concerned.

The cover plate may be of any reasonably practical thickness, that is to say, it may be designed thicker than the known short circuit plates, because the maintaining and the strength of the external magnetic retention field is determined more or less by the number of holes or perforations reducing the mass of material of the cover plate. With a thicker cover plate, the advantage exists that the wear caused by prolonged use and occurring on the surface of the cover plate can be repaired by reworking for example sanding or grinding, and a fullreplacement plate is not required. Conveniently, the thickness of the cover plate may be 0.6 to about 2 cm., more or less.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a schematic view of one embodiment of a permanent magnet system constructed in accordance with the present invention in the form of a clamping plate with one sidewall eliminated to allow for a view into a housing of the sytem, Figures 2 to 5 show partial sections through different cover plate of the permanent magnet system, with perforations of different designs, Figure 6 represents a schematic view of another permanent magnet system of the invention in the form a clamping plate with one sidewall partly eliminated to allow for a view into a housing of the sytem, and with a different distribution of the perforations on the cover plate.

Figure 7 shows a schematic view of an embodiment with a further modified distribution of the perforations in the cover plate.

The permanent magnet system of Figure 1 consists, in a manner known from the prior art, of a clamping plate unit having a ferro-magnetic base plate 1, individual barlike permanent magnets 2 arranged thereon in alternating polar sequence, a cover plate 3, likewise of ferro-magnetic material, and lateral parts 4, 5, 6, 7. The lateral parts 4, 5, 6, 7 which seal the magnetic system box or housing-like construction consist of ferromagnetic material, for example, iron. The cover plate 3, which acts as a magnetic retention surface, is provided with holes 8 distributed substantially over its entire surface or in spaced sections or arrangements, as described hereafter, and seats directly on pole surfaces of the permanent magnets.

These holes are drilled continuously from the top side to the bottom side of the cover plate 3, or they can be formed in any other suitable manner, for example by a Laser beam. The magnetic lines of force, thus, flow only through the bridges 9, Figures 2 to 5, between the perforations and thus radiate with corresponding reinforcement at the externally disposed edges of the holes 8.

Depending on the number and the distribution of the holes 8 in the cover plate 3, a strong external magnetic retention field exists on the surface of the plate, this field being composed of a multiplicity of individual external magnetic retention fields.

The cross-section of the holes 8 can take different configurations. Thus, as shown in Figure 2, the holes 8 have a cylindrical cross-section. In Figure 3, the holes 8 have a tapered configuration. In case of holes 8 with a tapered cross-section configuration, the tapering may extend from the top side of the cover late 3 toward the bottom side as in Figure ), or in the opposite direction as in Figure 4. With the selected cross-section, it is possible to determine the thicknesses of the bridges 9 between the perforations 8 in a differential manner, and this also applies to the prevailing strength of radiation of the magnetic lines of force at the surface of the cover plate 3. Independently of the selection of the cross-section for the perforations 8, it is advisable to fill them with a nonmangentic conductive material 10, in order to restore a uniform surface on the cover plate 3. There is nothing critical about such non-magnetic materials and they may comprise non-magnetic metals or alloys such as brass, or synthetic or natural non-magnetic materials.

Instead of having a cylindrical or tapered cross-section, the perforations 3 can be made to have a cross-section different from the above, for example, a triangular, quadrangular or a stellate cross-section. For achieving the desired effect according to the present invention thsre exists practically no limitation on the cross-section configuration which the perforations 8 can have. Depending on whether there is a regular or irregular distribution of the holes 8 on the surface of the cover plate 3, the forces of magnetic retention may differ. With a close arrangement of the holes 8 the magnetic saturation of the cover plate is reduced and the external magnetic retention field, originating from the bridges 9 between the perforations 8, is increased. Conversely, the external magnetic retention field is reduced when the distance of the perforations 8 from each other is increased.

It also may be desirable in certain instances, as shown in Figure 6, to reduce the number of holes 8 in the area above the poles of the magnets 2, and/or to arrange them in these areas at larger distances from each other than the holes in the areas between the poles so as to limit the intensity of the magnetic retention field in the areas above the poles where the magnetic flux induced by the magnets in the plate is strongest. This increases the magnetic flux in the areas of the plate between the poles to the extent necessary to develop an external magnetic retention field of uniform intensity over the entire surface of the cover plate 3.

Figure 7 shows a further embodiment of the system of the invention in which a uniform retention field intensity over the entire surface of the cover plate is obtained by providing perforations 8 only in he area between the poles of the magnets 2.

In regard to the thickness of the cover plate 3, there is a relationship therebetween and the distance of the holes 8 from each other. Thus, for an optimal magnetic force of retention, the thicker the cover plate 3 the closer together should be the holes 8; and, conversely, if the thickness of the cover plate 3 is reduced, the distance from each other of the holes 8 must be increased for optimal results. The thickness is so dimensioned in relation to the magnetic flux of force of the permanent magnets that it provides a magnetic retention field exceeding the magnetic saturation.

The magnetic system of the present invention can be provided with means known per se for suppressing the magnetic retention field in order, for example, to facilitate removal of ferromagnetic articles from the cover plate.

WHAT I CLAIM IS: 1. A permanent magnet system for the magnetic retention of ferromagnetic articles, comprising a plurality of individual bar-like permanent magnets mounted in a ferro-magnetic housing and arranged in alternating, polar sequence between a base of the housing and a cover plate of ferromagnetic material seating directly on pole surface of the permanent magnets and pres

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. plate. The permanent magnet system of Figure 1 consists, in a manner known from the prior art, of a clamping plate unit having a ferro-magnetic base plate 1, individual barlike permanent magnets 2 arranged thereon in alternating polar sequence, a cover plate 3, likewise of ferro-magnetic material, and lateral parts 4, 5, 6, 7. The lateral parts 4, 5, 6, 7 which seal the magnetic system box or housing-like construction consist of ferromagnetic material, for example, iron. The cover plate 3, which acts as a magnetic retention surface, is provided with holes 8 distributed substantially over its entire surface or in spaced sections or arrangements, as described hereafter, and seats directly on pole surfaces of the permanent magnets. These holes are drilled continuously from the top side to the bottom side of the cover plate 3, or they can be formed in any other suitable manner, for example by a Laser beam. The magnetic lines of force, thus, flow only through the bridges 9, Figures 2 to 5, between the perforations and thus radiate with corresponding reinforcement at the externally disposed edges of the holes 8. Depending on the number and the distribution of the holes 8 in the cover plate 3, a strong external magnetic retention field exists on the surface of the plate, this field being composed of a multiplicity of individual external magnetic retention fields. The cross-section of the holes 8 can take different configurations. Thus, as shown in Figure 2, the holes 8 have a cylindrical cross-section. In Figure 3, the holes 8 have a tapered configuration. In case of holes 8 with a tapered cross-section configuration, the tapering may extend from the top side of the cover late 3 toward the bottom side as in Figure ), or in the opposite direction as in Figure 4. With the selected cross-section, it is possible to determine the thicknesses of the bridges 9 between the perforations 8 in a differential manner, and this also applies to the prevailing strength of radiation of the magnetic lines of force at the surface of the cover plate 3. Independently of the selection of the cross-section for the perforations 8, it is advisable to fill them with a nonmangentic conductive material 10, in order to restore a uniform surface on the cover plate 3. There is nothing critical about such non-magnetic materials and they may comprise non-magnetic metals or alloys such as brass, or synthetic or natural non-magnetic materials. Instead of having a cylindrical or tapered cross-section, the perforations 3 can be made to have a cross-section different from the above, for example, a triangular, quadrangular or a stellate cross-section. For achieving the desired effect according to the present invention thsre exists practically no limitation on the cross-section configuration which the perforations 8 can have. Depending on whether there is a regular or irregular distribution of the holes 8 on the surface of the cover plate 3, the forces of magnetic retention may differ. With a close arrangement of the holes 8 the magnetic saturation of the cover plate is reduced and the external magnetic retention field, originating from the bridges 9 between the perforations 8, is increased. Conversely, the external magnetic retention field is reduced when the distance of the perforations 8 from each other is increased. It also may be desirable in certain instances, as shown in Figure 6, to reduce the number of holes 8 in the area above the poles of the magnets 2, and/or to arrange them in these areas at larger distances from each other than the holes in the areas between the poles so as to limit the intensity of the magnetic retention field in the areas above the poles where the magnetic flux induced by the magnets in the plate is strongest. This increases the magnetic flux in the areas of the plate between the poles to the extent necessary to develop an external magnetic retention field of uniform intensity over the entire surface of the cover plate 3. Figure 7 shows a further embodiment of the system of the invention in which a uniform retention field intensity over the entire surface of the cover plate is obtained by providing perforations 8 only in he area between the poles of the magnets 2. In regard to the thickness of the cover plate 3, there is a relationship therebetween and the distance of the holes 8 from each other. Thus, for an optimal magnetic force of retention, the thicker the cover plate 3 the closer together should be the holes 8; and, conversely, if the thickness of the cover plate 3 is reduced, the distance from each other of the holes 8 must be increased for optimal results. The thickness is so dimensioned in relation to the magnetic flux of force of the permanent magnets that it provides a magnetic retention field exceeding the magnetic saturation. The magnetic system of the present invention can be provided with means known per se for suppressing the magnetic retention field in order, for example, to facilitate removal of ferromagnetic articles from the cover plate. WHAT I CLAIM IS:

1. A permanent magnet system for the magnetic retention of ferromagnetic articles, comprising a plurality of individual bar-like permanent magnets mounted in a ferro-magnetic housing and arranged in alternating, polar sequence between a base of the housing and a cover plate of ferromagnetic material seating directly on pole surface of the permanent magnets and pres

enting a magnetic retention surface, said cover plate being provided with holes or perforations and having a thickness so dimensioned in relation to the magnetic flux induced therein by the permanent magnets that an external magnetic retention field exceeding the magnetic saturation in the plate is developed.

2. The permanent magnet system of claim 1, wherein the holes are drilled through the one side of he surface of the cover plate to the other one.

3. The permanent magnet system of claim 1 or claim 2, wherein the holes or perforations are cylindrical.

4. The permanent magnet system of claim 1 or claim 2, wherein the holes or perforations are conical.

5. The permanent magnet system of claim 4, wherein the holes or perforations taper from the top surface to the bottom surface of the cover plate.

6. The permanent magnet system of claim 4, wherein the holes or perforations taper from the bottom surface to the top surface of the cover plate.

7. The permanent magnet system as defined in any one of claims 1 to 6, wherein the holes or perforations are filled with a non-magnetic conductive material.

8. The permanent magnet system of any one of claims 1 to 7, wherein the holes or perforations are distributed substantially irregularly over the surface of the cover plate.

9. The permanent magnet system of claim 8, wherein the number of holes or perforations is reduced in the area above the poles of the magnets.

10. The permanent magnet system of claim 8 or claim 9 wherein said holes or perforations is the areas above the poles of the magnets are arranged at larger distances from each other than are the holes or perforations which are in the areas between the poles.

11. The permanent magnet system of claim 8, wherein the holes or perforations are positioned only between the poles of the magnets.

12. A permanent magnet system substantially as hereinbefore described with reference to and as shown in Figures 1 and 2, or Figures 3 or Figure 4 or Figure 5 or Figure 6 or Figure 7 of the accompanying drawings.