GB2067099A - Vibratory screening feeder - Google Patents

Abstract

A vibratory feeder for feeding particulate material comprises an elongate tray structure which is vibrated to cause particulate material to slide along it toward the discharge end of that structure. The tray structure includes a section comprised of a series of steps extending transversely across it at successively diminishing heights with gaps between the steps so that particles below a certain size can fall through the gaps whereas larger particles bounce across the steps towards the discharge end of the tray structure.

Description

SPECIFICATION Vibratory feeder This invention relates to vibratory feeders for feeding particulate material and more particularly it provides a vibratory feeder which has a sifting action for removal of fine particles from larger size particles in the material. The feeder of the present invention has particular, but not exclusive, application in the mining industry for sifting ores.

In the mining industry it is often necessary to remove fines from a stream of ore rocks and this is commonly achieved by passing the ore stream over a vibrating grid-like screen, often referred to as a grizzly, so that the fines fall through the screen and the larger size rocks pass to the end of the screen.

Ore rocks being fed to automatic ore sorting equip ment are commonly fed from a vibratory feeder across such a stream so as to remove fines and to present substantially clean rocks to the sorting equipment. Similar screens can also be used in grading apparatus to separate particulate material in fractions of varying sizes.

One simple form of screen commonly used in the feed systems of ore sorting equipment comprises a series of generally parallel bars projecting generally horizontally from a transverse connecting member as a series of prongs. The particulate material is fed onto the prongs and the larger size particles move along the prongs to drop from their free ends in one stream whereas small particles drop between the prongs so that they can be collected as a separate stream. Simple screens of this type are very prone to clogging, even through they may be vibrated energetically. Once a rock jams between any two of the bars, it tends to restrict the passage of succeeding material, causing further particles to become jammed and rapid clogging of the screen.This is a particularly serious problem when dealing with rocks contaminated with sand or clay which can cling to the rocks and act as a coherent binding medium which inhibits separation and bouncing movements of the rocks. In these circumstances the screen can clog up very rapidly.

The present invention provides a vibratory feeder which includes a sifting or screening section which is much less susceptible to clogging than the conventional pronged screens.

According to the invention there is provided a vibratory feeder for particulate material comprising an elongate tray structure to receive the particulate material and which in use of the feeder is vibrated to cause the particulate material to progress toward a discharge end of the tray structure, characterized in that the tray structure includes a section comprised of a series of steps extending transversely of the tray structure and spaced apart longitudinally of the tray structure at successively diminishing heights with gaps between them whereby particles of said material below a certain size can fall through the gaps whereas larger particles will progress across the steps and gaps to the discharge end of the tray structure.

Preferably, the steps are formed by a series of flat bars extending between a pair of side plates extending longitudinally along the sides of said tray section. The bars may be permanently connected to the side plates, as by welding, but preferably they are connected to the side plates by releasable connection to permit ready replacement of individual bars.

Preferably, the bars are sufficiently flexible to undergo longitudinal flexure oscillations in response to the vibration of the complete tray structure.

The connections of the bars to the side plates may be such as to provide resilient mountings for the bars so as to promote such flexure oscillations.

In order that the invention may be more fully explained one particular embodiment will be described in detail with reference to the accompanying drawings in which: Figure lisa diagrammatic illustration of the feed system for an automatic ore sorting machine, which feed system incorporates a vibratory feeder constructed in accordance with the invention; and Figure 2 is a diagrammatic perspective view showing the sifting section of the vibratory feeder.

Figure 1 illustrates a feed system for feeding ore rocks onto a rapidly moving conveyor belt 11 of an automatic ore sorting machine. The ore rocks must be presented to conveyor belt 11 as one or more steady streams of ore rocks such that the rocks drop one by one onto the conveyor belt in each stream.

The feed system comprises a feed hopper 12, a vibratory feeder 13 and a slide tray 14. The ore rocks are fed from hopper 12 onto vibratory feeder 13 which transports them as a layer to the slide plate 14. The slide plate may have longitudinal grooves or channels so as to divide the rocks into separate streams spaced laterally of the conveyor belt 11.

Vibratory feeder 13 comprises a tray structure 15 having an upstream end section 16, an intermediate rock sifting section 17 and a downstream or discharge end section 18.

The complete tray structure 15 incorporating the successive sections 16,17, is vibrated by an elec- trically operable vibrator unit 20 whereas slide plate 14 is rigidly mounted to a frame of the ore sorting machine and it is not vibrated with the feeder.

The upstream end section 16 of the tray structure comprises a metal plate floor 19 and upstanding side plates 21. The rocks fall from hopper 12 onto the tray and pass under an adjustable gate 22 to spread as a thin layer over the plate floor 19 of the tray. The floor slopes slightly downwardly from the horizontal and under the influence of the rapid vibrations imparted by the feeder 20 the rocks bounce and slide along the floor 19 to the sifting section 17 of the tray structure.

As illustrated in Figure 2 sifting section 17 is comprised of a number of flat rectangular bars 23, forming a series of steps in the tray structure. Bars 23 extend between a pair of side plates 24 extending longitudinally of the tray structure as extensions of the side plates 21 of the preceding tray section 16.

The bars are connected to the side plates by releasable end clamps 30 so that the steps extend transversely of the tray structure and are spaced apart longitudinally of the tray structure at successively diminishing height with gaps 25 formed between them. The rocks arriving at the sifting section of the tray structure tumble down these steps and onto the discharge end section 18 of the tray structure which has a flat plate floor 26 and side plates 27.

Large size rocks will progress across the sifting section 17 and onto the discharge section 18 of the vibratory feeder whence they are delivered to slide plate 14. Fine material and rocks below a certain size will fall through the gaps 25 between the steps and can be collected from a chute or hopper (not shown) for waste disposal or for separate processing.

It has been found that the illustrated sifting section of the vibratory feeder is most effective in separating out fine material and small size rocks from a main rock stream and it is very resistant to clogging even when handling ores contaminated with sand or clay.

The rocks progress down the steps with a pronounced bouncing action and they also tend to tilt or sway which helps to dislodge any fine material from the tops of the rocks.

It has been found that the sifting section is virtually self-clearing. If a rock does jam in one of the gaps between two steps a following rock, (often a larger one), will strike it to either force it through the gap or to dislodge it so that it continues across the sifting sections. Moreover the bars 23 are sufficiently resilient to flex longitudinally in response to the vibrations of the complete feeder structure and the resulting oscillations of the bars become out of phase with one another so that there is relative movement between adjacent bars producing a self-clearing action.

Such oscillation of the bars is enhanced if they are clamped to side plates 24 via resilient mounting pads. This can alter the mode and frequency of flexure of the bias and itis possible to obtain complex vibrational modes ensuring there is relative movement between successive bars at all times. Mounting of the bars through releasable clamps also has the advantagethat individual bars can be rapidly replaced when worn. The bars can be simply cut from strip steel stock and replacement is therefore quite cheap.

It has been found in practice that the bars do not wear as rapidly as the cylindrical bars used in conventional screens because they tend to become covered by a build-up of mud, clay or other fine material which protects the underlying material from abrasion by the rocks.

The sifting section in the illustrated construction is also effective as a water barrier since water cannot run across the transverse gaps between the steps.

With conventional screens water can run along the longitudinal prongs and pass into the ore sorting equipment and sometimes affect the operation of that equipment.

The number and size of bars 23, the vertical drops between the bars and the horizontal gaps between them are critical to effective operation of the sifting section and must be chosen according to the size of rocks being handled and the amplitude of vibration of the feeder but the optimum design can readily be determined empirically. In one installation now in commercial production, optimum performance has been achieved with a sifting section comprising 5 mild steel bars each 51 inches long, 3 inches wide and a inch deep set with a 1 inch drop or vertical gap and a 1 inch horizontal gap between successive bars.

The amplitude of vibration is inch in a direction 30 from the horizontal and the frequency of vibration is 1000 cycles per minute. This feeder is successfully removing sand, clay and rock chips from rocks which vary in size from about 14 inches maximum dimn- sion to 6 inches maximum dimension. Although the material feed is heavily contaminated with sand and clay which would rapidly clog a screen of the cost- ventional type, no clogging problems have been encountered and the feeder produces a very clean feed of rocks to theore sorting equipment.

The illustrated embodiment of the invention has been advanced by way of example only and it could be modified considerably. For example, the number of transverse bars in the sifting section could bevaried and the vertical drops between successive bars could vary along the length of the vibrator. In some circumstances it may be preferable to provide at least one significantly larger vertical drop part-way along the sifting section to impart a rolling or tuning movement to the rocks. At least some of the steps could be inclined to the horizontal from their leading to their trailing edge for the same purpose. It is accordingly to be understood that the invention is in no way limited to the details ofthe illustrated construction and that many modifications and variations will fall within the scope of the appended claims.

Claims (8)

1. A vibratory feeder for particulate material comprising an elongate tray structure to receive the particulate material and which in use of the feeder is vibrated to cause the particulate material to progress toward a discharge end of the tray structure, characterized in that the tray structure includes a section comprised of a series of steps extending transversely of the tray structure and spaced apart longitudinally of the tray structure at successively diminishing heights with gaps between them whereby particles of said material below a certain size can fall through the gaps whereas larger particlews will progress across the steps and gaps to the discharge end of the tray structure.

2. Vibratory feeder as claimed in claim 1, wherein the steps are formed by a series of flat bars extending between a pair of side plates extending longitudinally along the sides of said tray section.

3. Avibratory feeder as claimed in claim 2, wherein the bars are permanently connected to the side plates.

4. Avibratory feeder as claimed in claim 2, wherein the bars are connected to the side plates by releasable connections.

5. Avibratory feeder as claimed in anyone of the preceding claims wherein the bars are sufficiently flexible to undergo longitudinal flexure oscillations in response the vibration of the complete tray structure.

6. A vibratory feeder as claimed in claimS, wherein the connections of the bars to the side plates are such as to provide resilient mountings for the bars so as to promote said flexure oscillations.

7. A vibratory feeder as claimed in claim 4, wherein the bars are clamped to the side plates via resilient mounting pads to promote longitudinal flexure oscillations of the bars in response to the vibration of the complete tray structure.

8. A vibratory feeder substantially as hereinbefore described with reference to the accompanying drawings.