US2846070A - Screening apparatus - Google Patents

Description

58 L. SCHLEBUSCH 2,846,070

SCREENING APPARATUS Filed NOV. 19, 1954 2 Sheets-Sheet 1 FIG'. 5.

INVENTOR LUDWIG SOI-ILEBUSOH ATTORNEYS 5, 1958 L. SCHLEBUSCH 2,84

SCREENING APPARATUS Filed Nov 19, 1954 2 Sheets-Sheet 2 F l G. 6. /Z

MIX/I now/yryr/r'yor/A 1N VENTOR LUDWIG SOHLEBUSGH 'MXM ATTORNEYS nite 2,846,070 Fatented Aug. 5, 1958 SQREENKNG APPARATUS Ludwig Schlehusch, Palenberg, Germany Application November 19, 1954, Serial No. 470,099 Qlaims priority, application Germany November 27, 1953 Elaims. (G. 209--238) The present invention relates to screening devices for the screening of comminuted material, especially nonmagnetic comminuted material, such as small pieces of coal.

lit is known that small coal is easier to screen when the screening surface is heated, so that the screen and the coal or other product in immediate contact with it are dry, and the smaller particles do not adhere to the metal cloth of the screen and cannot clog its mesh.

Such screens are known in which heating is eifected by steam, by gas, or by electric current flowing through the electric resistance of the vibrating metal cloth itself. These devices present the disadvantage that coal having a high percentage of volatile matter is subject to the possibility of explosion, and also the disadvantage of being added only with difliculty to already existing installations.

For this reason, the use of electric induction heating has been proposed. The practical application, however, of this type of heating, has been found to present dirliculties for which no practical solution has been found.

In my co-pending application, Ser. No. 431,945, filed May 24, 1954, there has been described a screening apparatus which applies electrical induction to both the heating of metal screens and to screen vibration, employing frequencies in the intermediate range ordinarily employed in practice for such mechanical vibrations, such as the range from 200 to 20,000 cycles.

The present invention is an improvement on the apparatus described in my said application, Ser. No. 431,945, and an object of the present invention is to provide an improved manner of applying the electromagnetic induction.

At the present time, experience shows that coal and other mined materials as delivered for treatment, now tend to have increasing water content, due in considerable part to the necessity of reducing to a minimum the formation of dust during handling, as a protection against silicosis and similar lung ailments. Coal may be delivered for treatment with a moisture content as high as to 18 percent. Apparatus heretofore employed for the treatment of fairly dry coal of 7-l2 mm. size, are not suitable for the treatment of such wet coal.

This difliculty of treating wet coal can be met by heating and electromagnetically inductively acting upon perforated steel sheets or screen cloths formed of relatively heavy wire mesh, by means of inductors, as described in my said application Ser. No. 431,945, but, since these pre-screening installations include, in most cases, several screen decks and a continuous closed face bottom plate, it is necessary to apply specially designed devices to heat the several screens and the bottom plate.

According to the present invention, in such apparatus, the heating of the lower screen, in apparatus using twodeck screens and a bottom plate, conveying the coal, may be eifected in considerable part by the bottom plate itself, which is made of a diamagnetic material, which is a non-conductor of electricity or a lossy insulating material.

In this diamagnetic, non-conductor bottom plate, there may be inserted a conducting element, which may be in the form of interwoven mesh, or a circular or rectangular spiral, or a ring, of metal of suitable resistivity as usually employed in electrical heating devices.

Electrical energy is not supplied by connecting wires from an external source to the bottom plate. The induetion electromagnetic field due to inductors more remote from the screens, and which inductors are supplied with current by direct connection, induces currents in the bot tom plate which generate heat therein.

The object of this inserted element is to make it possible, through the so constructed bottom plate, to heat the screening surface itself, in order to prevent clogging of the screen openings, which would stop all screening and classifying operation.

Alternatively, the bottom plate may be constituted of lossy insulating material (without a metal insert), that is, electrically poor conducting material.

The heating of the bottom plate tends to prevent, in case of materials of high moisture content, an accumulation upon the bottom plate itself of the coal or other products under treatment, which accumulation would lead to a rapid stoppage of the screening operation. Such clogging cannot occur when the measures just mentioned are employed.

By proper selection of the mesh size or of the distance between the turns of the winding constituting the element inserted in the bottom plate, and by properly selecting the material for this inserted element according to a desired value of its electrical resistance, the heating relation of the bottom plate and of the screening surfaces, can be regulated. If the inserted element consists of a winding, this relation may even be modified during the operation of the device, by the adjustment of an inserted series.

connected regulating resistance.

In some apparatus, the material which passes through the lowest screen does not fall upon a bottom plate, but through the screen openings, directly into a hopper. In such cases, the lowest screen is heated and inductively acted upon, by arranging the inductors in a linear array under the lowest screen, and providing these inductors with inclined covers or housings in the shape of a triangular gable.

In most cases, the top screen does not require to be heated or to be acted upon electromagnetically by induction, since in most cases the mesh or openings of the top screen are generally large enough to prevent any clogging. Should, however, such heating or inductive action on the top screen become necessary, the inductors therefor would be mounted above the upper screening surface, as in my said application, Ser. No. 431,945.

My invention will be understood by the following description taken with the accompanying drawings showing several embodiments of apparatus to heat and inductively act upon the lower screens of multiple deck screening apparatus, and wherein:

Fig. l is a diagrammatic side elevation of an inclined classifying screening apparatus with electrical conductor units placed therebelow and using a closed bottom plate;

Fig. 2 is a vertical cross section of a laminated bottom plate with intermediate electrical conducting element consisting of a woven mesh screen cloth of metal;

Fig. 3 is a plan view with top sheet removed of the bottom plate of Fig. 2;

Fig. 4 is a vertical cross section of a laminated bottom plate with intermediate electrical conducting element consisting of a spiral winding;

Fig. is a plan view with top sheet removed of the bottom plate of Fig. 4;

Fig. 6 is a vertical cross section of a bottom plate consisting simply of a single homogeneous sheet of diagrammatic material which is of lossy electrical insulating material; V

Fig. 7 is a plan view of the sheet of Fig. 6; and

Fig. 8 shows a screening apparatus working above a hopper and having individual inductor units below the lowest screen and employing no closed bottom plate.

Referring to the drawings in detail, in Fig. 1, there is shown a two-deck screening apparatus having a continuous closed-face bottom plate 6. The vibratable screening assembly as a whole is shown at 1 consisting of the two superposed screens 3 and 5 and the bottom plate 6, underneath both superposed screens, and to this assembly are applied mechanical substantially horizontal vibrations in conventional manner as from a conventional reciprocating eccentric drive device 20 21, at a frequency of which a representative value 19400 cycles per minute. Screen 5 is of finer mesh than screen 3. l V

In Fig. 1, the incoming coal or other product to be treated is shown at 2 as it falls from intake trough 2:: onto the upper screen 3, over which the larger pieces 4, for example those larger than 30 mm, traveland are discharged therefrom at the left end. The smaller pieces of coal fall through upper screen 3 upon the lower screen 5. The smallest pieces of coal fall through screen 5 onto closed bottom plate 6, along which they pass and are discharged to the left. Since the openings of lower screen 5 are smaller than the openings of upper screen 3, they are more likely to clog when wet coal is being handled. To heat and magnetically act upon this lower screen 5, an inductor 7 is mounted directly below bottom plate6, which bottom plate is constructed as hereinafter described. Inductor 7 is mounted on the fixed frame or base of the whole apparatus and not on the vibratable screen assembly, This inductor 7 is supplied with electrical energy from an external source by suitable wiring connections and produces an electromagnetic field of considerable magnitude which acts upon screen 5 and bottom plate 6, including the metal insert as in the bottom plate 6, and thereby generates heat in bottom plate 6 and heats and magnetically applies vibrations to screen 5.

One embodiment of laminated bottom plate 6 is shown in Figs. 2 and 3, in section, and in plan, respectively. Between an upper sheet 8 and a lower sheet 9, there is inserted an electrically conducting woven metal mesh cloth 10, of metal of suitably high resistivity as usually employed in electrical heating devices. The sheets 8 and 9 are preferably in this case of hard-pressed paperboard or asbestos which are diamagnetic and electrically non-conducting, and these sheets may be coated with a synthetic resin which will resist heat, such as secaphene.

The elementary filar members of woven metal mesh cloth 10 may be of the shape of a flat ribbon to facilitate heating of sheet 8.

A second embodiment of laminated bottom plate 6 is shown in Figs. 4 and 5, which has a spiral shaped closed winding 11 located between non-conducting sheets 8 and 9, instead of metal cloth 10, of Fig. 2. Winding 11 may be composed of a fiat ribbon to facilitate heating of sheet 8. The winding 11 may be opened at one point, and at the so opened point may be inserted a variable resistor 11a to adjust the action of winding 11. The heating relation between screen 5 and bottom plate 6 is definitely fixed, after Wire sizes and dimensions have been selected, by the resistance of the windings and their number, in the insertion as 11 in bottom plate 6, unless an adjusting resistance 11a is used.

In the embodiments of Figs. 2 and 4, the metal inserts 1t) and 11 may be molded into an integral molded piece instead of constituting an intermediate layer of a laminated sheet.

Figs. 6 and 7 show an embodiment of the bottom plate 6 which is a single homogeneous sheet 12 composed of el ctrically lossy diamagnetic insulating material without a metallic insert, that is a sheet material which is electrically a poor conductor but passes enough electrical current to generate heat therein. Comminuted carbon may be dispersed through this sheet during manufacture. It is necessary to avoid selecting a material which is such a good electrical conductor that no induction field can pass through it to screen 5. The induction field due to inductor 7 generates considerable heat in the lossy material of sheet 12.

Fig. 8 shows a two-screen apparatus working above a hopper 18 into which the smallest pieces of screened material drop directly from the lowest and finest screen 15. This arrangement of Fig. 8 does not use a bottom plate as 6. The coal 13 is delivered to the coarse upper screen 14 from a bin through intake trough 13a, and the larger pieces are delivered from the left end of upper screen 1d. The smaller pieces drop through upper screen 14 onto the finer-mesh lower screen 15. Of these, the larger pieces pass along to the left and drop off screen 15, while the smallest pieces pass through screen 15 and drop directly into hopper 18. In this case, the electromagnetic field is applied from a plurality of inductors 16 arrayed linearly below screen 15 and above hopper 18. Each of these inductors has external connecting wires by which electrical energy is supplied to them, and on their upper surface they are individually provided with a housing 17 of triangular gable shape, over which dropping pieces of coal pass easily and do not accumulate. These inductors 16 are supported fixedly by the frame of the apparatus and do not vibrate with the displaceable screen assembly 19. The housings 17 are of electrically nonconducting diamagnetic material so that they do not intercept the field transmitted from inductor 16 to screen 15. The housings 17 may be additionally heated separately, if necessary, to facilitate sliding off of particularly wet material, but usually the heat produced by inductors 16 themselves is sufficient.

The apparatus of the present invention provides for a substantial improvement in systems for the screening of coal and other materials. It will be apparent to those skilled in the art that the apparatus of my invention is susceptible of modifications to adapt the same to particular applications, and all such modifications which are within the scope of the appended claims I consider to be comprehended within the spirit of my invention.

What is claimed is:

1. In screening apparatus for wet comminuted materials, a metal screen, means for feeding comminuted material onto said screen, and electromagnetic induction means placed beneath said screen for applying heat to said screen and to said comminuted material thereon, said electro-magnetic induction means including at least one electro-magnetic inductor mounted near said screen and adapted to generate an induction field in the vicinity of said screen for heating the screen by induced electric current therein, and a member made of diamagnetic material interposed between said inductor and said screen and extending over said inductor.

2. Apparatus according to claim 1, wherein said member made of diamagnetic material is in the form of a bottom plate mounted beneath and near said screen, and said electro-magnetic induction means are placed beneath and near said bottom plate and adapted to generate an induction field of considerable magnitude, and wherein said bottom plate includes electrical means adapted to generate heat under the application of theinduction field due to said induction means.

3. Apparatus according to claim 2, wherein said electrical means in said bottom plate comprises a woven metal mesh cloth.

4. Apparatus according to claim 2, wherein said elec trical means in said bottom plate comprises a spiralshaped closed winding.

5. In screening apparatus for wet comminuted materials, a metal screen; means for feeding comminuted material onto said screen; a hopper beneath said screen; a plurality of individual electromagnetic inductors mounted beneath and near said screen and adapted to generate an induction field of considerable magnitude in the vicinity of said screen, whereby said screen will be heated by induced electric current; and an individual housing for each said conductor mounted thereover and being of triangular gable shape on the upper side of each said inductor and adapted to shed downwardly all comminuted material falling thereon from said screen.

References Cited in the file of this patent UNITED STATES PATENTS 2,338,904 Cowles Jan. 11, 1944 2,468,472 Townsend Apr. 26, 1949 FOREIGN PATENTS 1,010,522 France Mar. 26, 1952

Images