US3024912A

US3024912A - Screen structure

Info

Publication number: US3024912A
Application number: US756429A
Authority: US
Inventors: Jakobs Hans
Original assignee: Novo Industrial Corp
Current assignee: Novo Industrial Corp
Priority date: 1958-08-21
Filing date: 1958-08-21
Publication date: 1962-03-13
Anticipated expiration: 1979-03-13

Description

March 13, 1962 I JAKQBS 3,024,912

SCREEN STRUCTURE Filed Aug. 21, 1958 INVENTOR.

United States Patent 3,024,912 SCREEN STRUCTURE Hans Jakobs, Homewood, 111., assignor to Nova Indus- This invention is in the field of screening devices of the type generally in which an elastically supported screen mesh or medium, somewhat horizontally disposed, is vibrated at a high frequency, the material to be separated is fed to the upper surface of the medium, the separated material is withdrawn from below, and the oversize is disposed of over one end of the screen or deck.

A primary object of the invention is a screen structure in which individual vibrating resonant rods are connected directly to the screening medium.

Another object is a screening arrangement that is much quieter in operation as compared to previously known screens of this general type.

Another object is a high frequency vibrating mechanism for a screen which will produce or acquire the same or a greater screening effect and eificiency with less amplitude.

Another object is a screening device in which vibrations of a fundamental frequency are imparted to a screen mesh with harmonic vibrations superimposed thereon.

Another object is a screening arrangement which requires fewer vibrating units for the same area of screen deck.

Another object is a vibrating structure for use with a screening medium which employs a resonance elastomer.

Other objects will appear from time to time in the ensuing specification and drawings in which:

FIGURE 1 is a side schematic view, partly broken away, of the screen structure;

FIGURE 2 is a top view of the screen deck;

FIGURE 3 is a side view, on an enlarged scale, of a portion of the vibrating unit; and

FIGURE 4 is a side view, partly in section, of a variant form.

Referring to the drawings, it will be understood that the screen may have a suitable base with a frame above or below it, although this is not shown in detail. As shown in FIGURE 1, the frame and base support a bridge structure which may support or carry a plurality of individual driver or vibrator elements 12. Each of the vibrator elements or heads 12 is connected by rods 14 to the screening medium or mesh 16 which, as shown in FIGURE 2, may be held in a suitable frame or deck 18 to take the form of a generally rectangular deck. The heads 12 reciprocate or vibrate the rods 14 generally in an axial direction, as indicated by the arrows on FIGURE 1, with a predetermined amplitude and at a predetermined base frequency. It is preferred that each of the rods be connected directly to the screening mesh or medium 16 by a connection 20, to be explained in detail hereinafter. In FIGURE 2 it will be noted that the rods and connections may be disposed in any suitable pattern, for example in longitudinally and laterally aligned rows, one row being staggered relative to the next or aligned or otherwise arranged so that the desired vibrations will be set up in the medium.

In U.S. Patent No. 2,880,871, a method and apparatus for screening are disclosed in which a screening mesh or medium is elastically supported with a certain degree of freedom or tension such that when individual vibrations are applied directly to the medium at spaced points, concentric vibration waves Will emanate or radiate from the spaced points in all directions to set up interference vibrations in the intermediate areas between adjacent spaced points. The support or degree of tension in the screen or mesh has been referred to as elastic and it should be understood that this is not drumhead tension. Nor is the mesh slack since a certain degree of tension is necessary in all cases to properly establish or set up the concentric emanating vibrations and the interference vibrations. The present invention is advantageously used in that atmosphere and it is preferred that. the screening medium 16 in this invention be elastically supported so that interference vibrations or disturbances will be established or set up in the intermediate areas midway or approximately midway between adjacent rods or points of contact of the driving members with the screening mesh or medium. In this screening arrangement or method vibrations are applied to the mesh at a certain base frequency and harmonics on the base frequency are superimposed on the vibrating mesh so that very high frequency oscillations are set up in the mesh. In the above referred to patent, the driving heads or vibrators, such as shown at 12 in FIGURE 1 of this application, are electromagnets and are provided with single or double stops spaced apart a distance less than the natural amplitude of vibration of the armature in the head so that the vibrating armature will strike the stops to create the harmonics. But this amplitude limiting approach has the disadvantage that the armature striking the stops is quite noisy and, in certain situations and installations, has proved objectionable to personnel. In certain installations, the noise level has become prohibitive and one of the important aspects of this invention is that the same high frequency vibrations may be and are generated in or imposed on the screen ing medium without excess noise.

The heads 12 may be the same type as shown in Patent No. 2,880,871 and, for purposes of this invention, may be considered to be electromagnets which. alternately attract and release a suitable spring supported armature connected to the rods 14 so that the rods reciprocate or vibrate in an axial direction.

In FIGURE 3 such a rod is shown with a spring or elastomer 22 suitably connected by a bolt 24 or the like to the rod and at its other end by a suitable bolt 26 or the like to a connection or clamp 20 which is attached directly to the mesh or screening medium. The connection may include a stub shaft 30 which extends through opposed plates or

disks

32 and 34 held between a flange or shoulder 36 on the stub shaft and a suitable nut 33 or the like and washer 39. Suitable bushings 4t) and 41 may be provided. To properly distribute the vibrations from the connection, spring elements which may take the form of flat plates 42 or the like, graduated in size, as shown, and suitably spot welded or otherwise connected together at 44, may be provided between each clamp or disk and the screening mesh. The largest such disk may be in contact with the mesh or medium and is preferably turned up, as at 46, at its outer end so that the mesh will not be torn or broken by sharp edges.

In FIGURE 4 an alternate or modified form has been shown in which the lower end of the rod 14 has been provided with a housing or cage 48. A stub shaft 56 extends up into the housing 48 and is provided with a washer or disk 52 of any suitable type secured or integrally formed at the upper end. Springs 54 are provided on each side of the disk and the lower end of the housing is closed by a washer 56 which allows reciprocation of the stub shaft. The connection 53 may be the same as in FIGURE 3.

The use, operation and function of the invention are as follows:

It is desirable to impose high frequency vibrations on the screening medium and this is preferably done by connecting a source of vibration at individual points, suitably spaced and arranged, on the screening medium and imparting vibrations individually to such points. The thus imposed vibrations should have a fundamental frequency on which is superimposed a higher harmonic vibration.

In the various forms shown and suggested, the spring or elastic member is tuned to be in resonance with the weight of the attachment to the screen. The spring may be chosen with particular characteristics, regardless of its shape, size and disposition, so that a resonant condition or vibration will be set up when the base frequency is applied to the rod 14. The condition need not necessarily be right on resonance, but it should be close or approximate. The Spring is chosen or proportioned in accordance with the weight of the connection 24, since this will affect the harmonic or resonant condition. The elastic member, be it a spring or otherwise, could be arranged in any suitable manner, and it is preferred that the weight of the connection to the screen be as small as possible so that resonance may be more easily, simply, and cheaply acquired or effected.

While the driver or head has been referred to as an electromagnet, it should be understood that it may be any suitable means for creating reciprocations or vibrations at a suitable base frequency. For example, it might be a mechanical eccentric. A coil spring has been shown in the drawings for the elastic member, but it should be understood that it might be a suitable combination of leaf springs, Bellvilles or otherwise. At the same time, the elastomer or elastic member is not necessarily restricted to being a spring as it might be a suitably arranged and proportioned rubber element or an air cylinder and piston. The important point is that the elastomer should be tuned to a resonant condition in accordance with the weight supported by it which is the weight of the attachment to the screen.

It will thus be seen that a base frequency with superimposed harmonics will be applied to the screening medium without excess noise. Additionally, it has been found in test that the structure of this invention will allow the vibrating rods to be more widely spaced which means that fewer heads or vibrating elements are required, thereby substantially reducing the cost of the over-all unit. The same screening efliciency may be acquired with the base frequency at half the amplitude of previously known units whichmay allow for a smaller unit and an according saving in cost.

While the rods have been shown connected to the screen from above, it should be understood that the screening medium may be on top with the rods extending up from below. The invention is not restricted to any particular frequency of vibration or any particular driver or vibrating element, but it is preferred that electromagnets be used to supply the base frequency.

Whereas the preferred form and several variations of the invention havebeen shown and suggested, it should be understood that suitable additional modifications, changes, substitutions and alterations may be made without departing from the inventions fundamental theme. For example, the particular weave or make up of the mesh or screen itself is not important. The angle of disposition of the screening medium, such as diagrammatically shown in FIGURE 1, is not important. With these and other modifications in mind, it is therefore wished that the invention be unrestricted, except as by the appended claims.

I claim:

1. In a screening device, a frame, a screening medium on the frame and means for vibrating the medium including a plurality of rods opposite the medium at spaced localized points and disposed generally at right angles to the general plane of the medium, a connection to the screening medium for each rod, means for vibrating each rod at a predetermined base frequency in a direction generally at right angles to the plane of the medium, and a resonant element in each rod tuned to the base frequency of vibration of the rod and the weight of the connection between the rod and the medium such that harmonic vibrations will be superposed on the medium when it is vibrated at the base frequency.

2. The structure of claim 1 further characterized in that the resonant element includes a spring.

3. The structure of claim 1 further characterized in that the resonant element includes a spring disposed and connected between the rod and the connection to the screening medium, the spring being approximately tuned in resonance to the weight of the connection to the screening medium.

4. In a screening device, a frame, an elastically supported screening medium in the frame, means for vibrating the medium including at least one rod, a connection to the screening medium for the rod, means for vibrating the rod at a base frequency to vibrate the medium, and a harmonic inducing elastomer in the rod in resonance with the weight of the connection to the screening medium to produce harmonic vibrations in the screening medium superposed on the base frequency.

5. The structure of claim 4 in which the elastomer is a spring connecting the rod and screening medium connection.

6. In a screening device, a frame, an elastically held screening medium on the frame and means for vibrating the medium including a plurality of rods opposite the medium at spaced localized points and disposed generally at right angles to the plane of the medium, a connection to the screening medium for each rod, means for creating relative vibratory movement between the rods and the medium at a predetermined base frequency and in a direction generally at right angles to the plane of the medium, and a resonant element in each rod tuned to the base frequency of vibration and the weight of the connection between the rod and the medium such that harmonic vibrations will be created on the medium when it is vibrated at the base frequency.

7. The structure of claim 6 in which the rods are disposed above the screen.

8. In a screening device, a frame, an elastically supported screening medium in the frame, means for vibrating the medium including at least one rod, a connection to the screening medium for the rod, means for vibrating the rod at a base frequency to vibrate the medium, and a harmonic inducing elastomer in the rod for establishing a resonant condition in the screening medium to impose harmonic vibrations on the base frequency.

References Cited in the file of this patent UNITED STATES PATENTS 2,570,035 Lauglin Oct. 2, 1951 2,575,143 Strain Nov. 13, 1951 2,865,505 Bruninghaus Dec. 23, 1958 2,880,871 Bruninghaus Apr. 7, 1959