When separating fragments of magnetic material from a mixture of such fragments and fragments of non-magnetic material, conventional magnet separators are usually utilised, in which the fragment mixture is conveyed on a conveyor belt to a station, where powerful magnets lift out the fragments of magnetic material from the conveyor belt, thus separating them from the rest of the mixture.

This separation functions in a satisfactory manner when fragments of magnetic material and fragments of non- magnetic material are free from each other. When frag- ments of magnetic material and fragments of non-magnetic material are hooked into each other and interconnected, which is the case in particular when the fragments are turning chips or milling chips, the problem of the above- described separation by means of a conventional magnet separator is that such fragments of non-magnetic material which are connected to fragments of magnetic material are entrained by the latter in the separation process, which naturally results in an unsatisfactory separation.

Therefore, the object of the present invention is to provide a method and a device, which eliminate this prob- lem and thus make it possible to separate chips of mag- netic material from chips of non-magnetic material even if these chips are interconnected.

As concerns the method, this object is achieved by a method, in which the chip mixture is supplied to one side of a plane run of an endless conveyor belt, which in this run passes over a fixed magnetic plate, which is arranged

at the side of the plane run opposite to said one side close to the plane run and supports a plurality of per- manent magnets, which are adapted to retain the chips of magnetic material on the conveyor belt and have such alternating polarity and are positioned in such a manner on the magnetic plate that, as the conveyor belt moves over the magnetic plate, flinging motions are imparted to the chips of magnetic material to release chips of non-magnetic material connected to these chips, and the plane run of the endless conveyor belt is oriented in such a manner that the major part of the chips of non- magnetic material, which are released from the chips of agnetic material as the conveyor belt moves over the magnetic plate, fall freely from said one side of the plane run without falling back on the conveyor belt.

As concerns the device, this object is achieved by a device, which is characterised in that an endless con- veyor belt, which has a plane run, which is intended to receive the chip mixture at one side thereof, and a mag- netic plate, which is arranged at the side of the plane run opposite to said one side close to the plane run and supports a plurality of permanent magnets, which are adapted to retain the chips of magnetic material on the conveyor belt and have such alternating polarity and are positioned in such a manner on the magnetic plate that, as the conveyor belt moves over the magnetic plate, flinging motions are imparted to the chips of magnetic material to release chips of non-magnetic material con- nected to these chips, the plane run being oriented such that the major part of the chips of non-magnetic mate- rial, which are released from the chips of magnetic material as the conveyor belt moves over the magnetic plate, fall freely from said one side of the plane run without falling back on the conveyor belt.

The conveyor belt is preferably provided with drivers, which extend transversely of the conveyor belt and are adapted to remove chips of magnetic material

which gather at the front end of the magnetic plate, seen in the direction of motion of the conveyor belt.

The direction of motion of the conveyor belt suit- ably forms an angle of 30°-60° with the horizontal plane.

The plane of the plane run is advantageously in- clined in relation to the vertical plane in the direction of said one side.

The invention will now be described in more detail with reference to the accompanying drawings.

Fig. 1 is a side view schematically showing a device according to the invention.

Fig. 2 shows the device in the direction of the arrow II in Fig. 1.

Fig. 3 is a top plan view showing on a larger scale a magnetic plate arranged in the device according to Figs 1 and 2.

The device shown in Figs 1 and 2 has a frame (not shown), which supports an upper cylinder 1 and a parallel lower cylinder 2. A motor (not shown) is arranged to ro- tate the upper cylinder 1. An endless conveyor belt 3 in the form of a rubber sheeting having a profiled outside extends over the two cylinders 1 and 2. When using the device, the conveyor belt 3 is driven in the direction of the arrow P by the upper cylinder 1 driven by the motor. The conveyor belt 3 has a first plane run 3a and a parallel second plane run 3b between the two cylinders 1 and 2. On its outside, the conveyor belt 3 has a plu- rality of ribs 4, which extend transversely of the con- veyor belt along its entire width. The ribs 4 function as drivers in a manner described in more detail below.

A magnetic plate 5, which supports a plurality of permanent magnets, is arranged between and parallel with the two plane runs 3a and 3b. The magnetic plate 5 is ar- ranged close to the first plane run 3a and extends along the major part of its width and length (see Fig. 1).

The conveyor belt 3 is inclined such that its direc- tion of motion P forms an angle a with the horizontal

plane (see Fig. 1). In the shown embodiment, this angle a is about 40° but can vary within a range of suitably 30°- 60°. The plane of the first run 3a is inclined in the di- rection of the outside of the first run at an angle ß to the vertical plane (see Fig. 2). In the shown embodiment, this angle P is about 10° but can vary within a range of suitably 0°-90°.

A substantially horizontal vibrator conveyor 6 is adapted to convey a mixture 7 of turning and/or milling chips 8 of magnetic material, such as steel, and turning and/or milling chips 9 of non-magnetic material, such as aluminium, to the first run 3a of the conveyor belt 3.

These chips 8,9 are supplied from a chip crusher (not shown), in which chips originating from turning and milling operations have been crushed into a size of about 1 mm-20 mm. The vibrator conveyor 6 ends at a distance from the first run 3a of the conveyor belt 3, but since it is located, seen from the side as shown in Fig. 1, within the area of the magnetic plate 5, the chips 8 of magnetic material and the chips 9 of non-magnetic mate- rial connected thereto are supplied, by magnetic effect, to the first run 3a. The chips 9 of non-magnetic material which are not connected to any chip or chips 8 of mag- netic material fall down into a first container 10, which is placed under the conveyor belt 3 and which is intended for chips 9 of non-magnetic material. A second container 11, which is intended for chips 8 of magnetic material, is placed under the conveyor belt 3, seen in the direc- tion of motion P, in front of the first container 10. As should appear from Fig. 1, a certain degree of inclina- tion a is required to utilise at least part of the width of the conveyor belt 3 when transferring the mixture 7 from the vibrator conveyor 6. If a was 0°, i. e. the di- rection of motion P was horizontal, naturally only a limited part of the width of the conveyor belt 3 would be utilised, at least initially, that is the part corre-

sponding to the height of the mixture 7 of chips 8,9 which is present on the vibrator conveyor 6.

On its side facing away from the first run 3a, the magnetic plate 5 has a steel plate 5a, on which the per- manent magnets are positioned, and on its side facing the first run 3a a plate 5b of stainless steel. The permanent magnets are positioned between these plates 5a and 5b. The permanent magnets are blocks, which have a right-angled parallelepipedic shape and which are arranged in parallel rows 12 that extend in the transverse direction of the conveyor belt 3 at a distance from each other in its longitudinal direction and are distributed over the en- tire surface of the magnetic plate 5. The magnets are of the kind which are sometimes referred to as"super mag- nets"and, in this case, they are magnets marketed under the trade name Neodymium. The magnets are retained on the magnetic plate 5 by their powerful magnetic effect.

In the shown embodiment, the permanent magnets are arranged in three groups distributed along the magnetic plate 5, that is a first group I, a second group II lo- cated downstream of said first group and a third group III located downstream of said second group. In the first and the second group I and II, respectively, the magnet blocks are arranged adjacent to each other to form rows 12 with alternating polarity (N and S). The distance between the rows 12 in the first group I, which is some- what smaller than the distance between the rows 12 in the second group II, is adjusted to the size of the smaller chips 8 of magnetic material in the mixture 7 which are to be separated, whereas the distance between the rows 12 in the second group II is adjusted to the size of the larger chips 8 of magnetic material in the mixture 7 which are to be separated. When the chips 8 and 9 have been treated in a chip crusher before being supplied via the vibrator conveyor 6 to the inventive device, they have, as already mentioned, a size of about 1 mm-20 mm.

In the shown embodiment, the distance between the rows 12

of the first group I and between the rows 12 of the sec- ond group II is 3 mm and 10 mm, respectively, whereas the extension of the magnet blocks in the longitudinal direc- tion of the conveyor belt 3 is about 30 mm. In the third group III, the distance between the rows 12 is the same as in the second group II, but the blocks in each row are not arranged adjacent to each other but at a distance from each other, which is substantially the same as the distance between the rows 12. The blocks in one and the same row 12 have alternating polarity (N and S). Blocks located opposite to each other in the different rows 12 of the third group III also have alternating polarity (N and S).

When chips 8 and 9 have been supplied to the first plane run 3a of the conveyor belt 3, they are conveyed in the direction of motion P. Owing to the fact that the permanent magnets are positioned in the above-described manner and have the above-described alternating polarity, flinging motions are imparted to the chips 8 of magnetic material as the conveyor belt 3 moves over the magnetic plate 5, such that chips 9 of non-magnetic material con- nected to these chips 8 are released. The chips 9 of non- magnetic material which have been released in this manner fall down into the container 10. The major part of these released chips 9 of non-magnetic material fall freely from the first plane run 3a of the conveyor belt 3 with- out falling back on the conveyor belt thanks to the above-described inclination of the first run 3a defined by the angles a and P.

Chips 8 of magnetic material successively gather at the upstream edge of the magnetic plate 5, i. e. they do not pass said edge of the conveyor belt 3. When these chips 8 of magnetic material are hit by a rib 4, they are thrown away batchwise from the conveyor belt 3 and gath- ered in the container 11.