GB2123520A - Vibrating screen - Google Patents

Abstract

A vibratory screen feeder has a pair of contra-rotating motors with self-synchronising eccentric masses, the combination of motors and masses being adjustable lengthwise at least to one end of the screen so that the masses may synchronise about the feed direction which is the straight line intersecting the centre of mass M1 of the screen per se and the centre of mass M3 of the motors. <IMAGE>

Description

SPECIFICATION Vibrating screen This invention relates to vibrating screens of the kind used for de-watering, sieving and like operations on loose particulate materials.

It is conventional to provide a pair of motors each having one or more eccentric masses, arranged with parallel axes and to run in opposite directions, with their said masses synchronised, and the vibration imparted to the screen structure to which the motors are fixed is such that all forces cancel out except those in opposite directions perpendicular to a plane containing the axes of rotation, which remaining forces extend along what is herein called "the feed direction".

For many purposes, it is desired to feed material along the length of the screen. If the motor axes are vertical, the unbalanced components are equal and extend both forward and rearward. An additional feed component can be imparted to the material by any of several means including a gradient on the screen, special surfaces on the screen such as riffling, or inclination of the plane containing the motor axes so that the said unbalanced forces extend forwardly and upwardly, and downwardly and rearwardly.When the inclination is used (which is the system most relevant to this invention) the material being fed is effectively given a forward and upward movement on each appropriate part of each cycle of rotation of the eccentric masses, and some of the material is thrown clear of the screen, continuing to fall during the reverse movement part of the cycle and hence escaping reverse so that a nett forward movement of material is attained.

There are many factors affecting performance of vibratory screens of this kind. Even for a given design operating under given conditions, the material being fed may change in nature - in size range of particles, distribution across that range, shape of particles, moisture content, and feed weight for example. A change in such parameters may mean that a screen ceases to operate at maximum efficiency, and the interrelationship is so complex that the screen may even cease to operate at all.

It is known to mount the motors on a rigid beam which is arranged so that it can be angularly turned so as to vary the feed direction (as herein defined). Conventional theory is that the line of said direction should intersect the centre of mass of the complete vibrating assembly (motors, beam, and the screen, all of which is supported on springs or the like). However, the said centre of mass of the complete assembly will vary in position according to the position of the motors along the screen. The screen will have its own centre of mass, and the motor assembly its centre of mass; the centre of the assembly will lie between the two.Hence, when the beam is turned angularly, it is necessary for the beam to be movable along the screen for a limited extent in order to maintain the said intersection and because it is not readily calculable, the adjustment of position and angle of the beam has been empiric and is time wasting and leads to inefficient set-ups. Moreover, in conventional thinking, a feed direction relative to the screen of less than about 300 is rarely if ever useful and would result in material being moved back and forth because of insufficient lift.

The inventor of this application has discovered that the accepted theory is not true in practice.

Useful results can be attained without the said feed direction intersecting the said centre of mass.

The discovery is capable of industrial application, because it enables vibrating feeders to be designed with fewer limitations, and without the necessity for the beam to be rotatable, and this in turn enables machines of lower profile to be designed which are particularly advantageous when working in confined situations for example in mining.

According to the invention a vibratory feeder is provided with a pair of motors arranged for selfsynchronous rotation of eccentric masses in opposite directions and having their axes contained in a common plane and the motors are adjustable in position from at least the mid-point of the length of the screen substantially to (at least) one end of the screen. According to this aspect, the distinction between the invention and the prior art is that the adjustment can take the motors up to the end of the screen (or substantially so) which was at least unnecessary according to conventional thinking.

If desired, the motors can be mounted on a beam adjustable over the whole length of the screen (and even beyond its ends) which enables the screen to be used in either direction of feed, by appropriate beam positioning.

The motors can be arranged above or below the screen.

According to another aspect of the invention, the beam is angularly fixed in position. By omitting the conventional angular adjustment means, the low height mentioned earlier can be attained.

Hitherto this was considered to be useless, but according to the inventor's discovery and experiments made, it gives equally useful results.

However, angular adjustment may be retained in combination with the lengthwise adjustment.

The invention is now more particularly described with reference to the accompanying drawings wherein:~ Figure 1 is a fragmentary sectional elevation of a conventional (prior art) vibratory screen separator or de-watering apparatus; Figure 2 is a similar view showing apparatus to illustrate the theory of the invention; and Figure 3 is a perspective view of a practical embodiment.

As seen in Figure 1, the screen per se indicated by the reference numeral 10 extends in a generally horizontal plane as the base of a channel having side members 12. The channel has an upper flange 14 and the two side flanges and the screen are connected together rigidly to form a unitary mass which is supported for example at corners on a number of springs 16 permitting the entire structure to be vibrated in a direction having at least a component extending in the directions of the arrows AA of the figure.

Mounted on the flanges 14 are a pair of carrier brackets 18 and these are bolted in appropriate positions along the length of the channel and the reference numerals 20 indicate alternative bolt holes provided to allow a degree of adjustment along the length of the feeder.

A beam 22 of square cross section is rigidly secured to end flanges 24 of circular shape, and these end flanges 24 are bolted to the brackets 18 at a plurality of positions, the bolt holes being indicated by the reference numerals 26.

Mounted on opposite and parallel faces of the beam are a pair of vibrator motors 28 each carrying eccentric weights at each end of each shaft, and these motors are arranged to be rotated in opposite directions as indicated by the arrows B, with their eccentric weights synchronised. The forces generated by the eccentric weights which are parallel to a plane containing the axes of both motors cancel out, leaving unbalanced forces which effectively reciprocate in a plane containing the line 30, called the feed direction.

The centre of mass of the channels, screen and basic vibrating structure (excluding the brackets 18, the beam, flanges and motors) is indicated by the reference Ml. For a given structure the centre Ml is fixed. The centre of mass of the lengthwise adjustable structure consisting of brackets 18 and the parts assembled thereto including the motors may be M3, approximately at the centre of the beam 22, and the centre of mass of the complete structure may typically be in the position indicated by the reference M2. It will be appreciated that M2 will shift in the direction of the length of the channels as the adjustable structure 18 is moved in the same direction.

According to accepted theory, the line 30 which is perpendicular to the plane containing the axes of the motors must intersect M2. It is for this reason that the plurality of bolt holes 26 is provided. Hence to achieve what is considered to be ideal operating conditions, the structure 18 is moved (usually empirically) in the direction AA on the flanges, and rebolted in position, and then the beam 22 is turned and rebolted in position so as to maintain the intersection of the line 30 with the usually estimated new position of the point M2. It will be clear that the angle of inclination of the line 30 increases to a maximum when the point M2 is vertically over the point Ml 1~that is when the structure 18 is in a mid-point along the length of the apparatus, but in that situation there is no feed of material along the conveyor.In normal practice the point M2 will always be displaced towards the discharge end of the conveyor, and the inclination of the line 30 will depend upon the feed speed which is required. Maximum feed speed does not necessarily mean maximum efficiency, because the de-watering or sieving effect may only be carried out when the material is in contact with the screen. A low angle for the line 30, when the point M2 is a long way away from the point Ml does not of itself mean an increased feed speed, for it may involve particles being moved back and forth rather than progressing along the screen.

Hence the necessity for empirical adjustment, even if based on experience.

Turning now to Figure 2 (which shows the beam 22 as welded, for example, directly to the brackets 18 and not adjustable), the motors are horizontally arranged, that is the plane containing their axes is parallel to the screen. In this arrangement, the axis 30 does not intersect the point M2, but it is found that satisfactory results are still attainable. It will be noted that the bracket 18 is of much smaller dimensions, particularly vertically, and (not shown) a greater array of adjustment positions is provided at least towards the discharge end of the apparatus.

The motors, in the use of the invention are essentially self-synchronising. They are found to synchronise about the feed direction which is the line 40 connecting the points M3, Ml, and the line 30 is irrelevant.

Figure 3 shows a practical embodiment using like reference numerals. The rotatable beam is retained for convenience of giving different locations for different purposes, although is not required for adjustment in normal usage.

Claims (4)

1. A vibratory feeder provided with a pair of motors arranged for self-synchronous rotation of eccentric masses in opposite directions and having their axes contained in a common plane the motors being adjustable in position from at least the mid-point of the length of the screen substantially to (at least) one end of the screen.

2. A vibratory feeder as claimed in Claim 1 wherein the motors are mounted on a beam.

3. A vibratory feeder as claimed in Claim 2 wherein the beam is angularly fixed in position.

4. A vibratory feeder substantially as described with reference to Figure 2 or 3 of the accompanying drawings.