AU661607B2 - Sorting particulate material - Google Patents

Description

-1- P/00/011 6 6 1 6 0 7 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: SORTING PARTICULATE MATERIAL i..

*i.

*i The following statement is a full description of this inventicn, including the best method of performing it known to us: GH&CO REF: P15885

I

2 TECHNICAL FIELD This invention relates to the sorting of particulate material. It has particular but not exclusive application to the sorting of tree bark particles in the production of potting mixes or other plant growing media.

In the nursery industry, tree bark, most commonly pine bark, is used as a raw material in the preparation of plant growing media. Pine bark is milled and shredded into the form of a particulate material which may be screened into different size classes providing appropriate starting material for different types and sizes of the plants. A representative set of size classes may comprise fine (3-5 mm), medium (5-10 mm), coarse (8-18 mm) and extra coarse (18-30 mm). The sized bark pieces may be mixed with extra ingredients and chemically stabilised to produce a final growing medium product.

Certain plants, in particular orchids, require a very loose growing medium with large air pockets so that the roots of the plant remain substantially exposed to air. Growing media produced from bark particles which have been sized by mechanical screening generally retain too much water and do not have sufficient air pockets.

This is because the bark particles passed by a screen will range in size and shape from generally chunky and hard particles to more attenuated particles of soft fibrous composition and a significant proportion of fine particles. The soft fibrous material and fine particles tend to fill the gaps between the chunkier particles to 30 produce a closely packed medium which retains water and has poor aeration. In order to produce a good orchid growing medium it has previously been necessary to sort particulate bark material by hand to pick out the hard material either prior to a pulverising and screening process or after an initial pulverising and screening process. The present invention provides a technique which enables satisfactory sorting to be carried out mechanically to produce a high quality growing medium for PL4379/700 3growing orchids and other plants requiring good root aeration.

DISCLOSURE OF THE INVENTION According to the invention, there is provided a method of sorting particulate material comprising projecting the particulate material in a stream generally downwardly onto an upwardly inclined and upwardly moving conveyor surface such that a first fraction of the particles in the stream moves downwardly along the conveyor surface to a bottom end of the conveyor surface whereas a second fraction of the particles in the stream is transported by the conveyor surface to an upper end of the conveyor surface, the particles of the first fraction being generally more chunky than the particles of the second fraction and the second fraction comprising generally more attenuated particles and generally lighter particles than the particles of the first fraction.

Preferably said stream is projected downwardly so as to impinge on an upper part of the upwardly inclined conveyor surface at an acLte angle to that surface and in a downwards direction relative to that surface so that the particles of the first fraction tend to bounce and eeo.

Stumble from the upper part of the conveyor surface to the lower end of that surface.

Preferably further the conveyor surface is a flat surface inclined at an acute angle to the horizontal in the range 200 to 600 and the stream of particulate material is projected onto that surface at an acute angle to that surface in the range 100 to 700.

30 Said stream may be projected onto the conveyor surface by deflection from a deflector means disposed above the upper part of the conveyor surface.

The method of the invention may further comprise directing a flow of gas upwardly along the conveyor surface to assist the upward transport of the particles of the second fraction. Said gas may be air.

PL4379/700 4- The invention also provides apparatus for sorting particulate material into fractions of differing particle characteristics, comprising a belt conveyor having a run defining an upwardly inclined conveyor surface;.

O\sposeAd conveyor drive meais A to drive the conveyor so as to move said conveyor surface in an upward direction; disposed material feed means to feed particulate material to be sorted to the belt conveyor and to project that material in a stream onto said conveyor surface; first particle collection means to collect a first fraction of the particles from the bottom end of said conveyor run; and second particle collection means4to collect a second fraction of the particles from the upper end of said conveyor run.

The particle feed means may comprise a feed conveyor operable to feed the particulate material onto a deflector plate disposed above an upper part of said belt conveyor surface such that the parLiculate material will in use of the apparatus be deflected from said deflector plate in said stream at an acute angle to that conveyor surface and in a downwards direction relative to that surface.

The apparatus may further comprise means to direct a flow of gas upwardly along the belt conveyor surface.

That means may comprise a fan or blower operable to blow air along the belt conveyor surface.

The belt conveyor surface may be ribbed or textured 30 to promote collection and transport of the paicticles thereon.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more fully explained one particular embodiment will be described in some detail with reference to the accompanying drawings, in which:- Pa37&/700 Figure 1 is a side elevation of an apparatus constructed and operated in accordance with the present invention; Figure 2 is an enlarged vertical cross-section through an upper prt of the apparatus; and Figure 3 is a cross-section on the line 3-3 in Figure 2.

BEST MODE OF CARRYING OUT THE INVENTION The illustrated apparatus has been designed to sort pulverised .and screened pine bark to separate out relatively hard and chunky particles from a residue of more attenuated and fibrous particles and generally fine material. The relatively hard chunky partiJles are to be used in an orchid growing medium and are therefore generally referred to as "orchid bark" whereas the residue material may be used in growing media for plants which do not require such a high degree of root a:eration and Fre not so sensitive to waterlogging.

The illustrated apparatus comprises a bulk storage hopper 11 to receive pulverised bark which has been screened to an appropriate size so that it will have a significant proportion of relatively hard chunky particles of the proper size for orchid propagation.

More particularly, the particulate pine bark material may be screened to a particle size in the range of 3 mm to mm.

RIM

The bottom of bulk storage hopper 11 is provided with a slat bed feed conveyor 12 driven by a conveyor drive 13. Particulate bark material can thus be fed from r 30 bulk storage hopper 11ii onto the bottom end of a belt elevator denoted generally as 14. The belt elevator 14 comprises an endless conveyor belt 15 having an upper run supported in a troughed configuration by troughed idler roll sets 16 spaced along an elevator frame 17 supported on stands 18, 19. The conveyor belt has a flat return run disposed within the confines of the support frame 17.

The belt is driven by an elevator drive 21 to raise the particulate bark material to the top of the elevator and PL4379/700 6 to project it in a stream 22 onto a deflector plate or chute 23 which deflects it onto a bark separating belt conveyor denoted generally as 24.

Bark separator conveyor 24 is hung from the elevator frame by suspension mountings 25. It comprises a flat conveyor belt wrapped around an upper drive roller 26 and a lower idler roller 27 so as to have a flat upper run 28 which is inclined upwardly at an acute angle to the horizontal and a lower return run 29. Conveyor 24 has an elonga-e frame 30 connected to the mountings 25 and carrying the rollers 26,27. Frame 30 also drives a motor and belt drive 31 which drives roller 26 so that the upper span of the conveyor belt moves in the upward direction. Frame 24 also carries a pair of upstanding side wing plates disposed one to each side of the upper belt run 28 and extending throughout a major part of the length of that run. These act to prevent spillage of material from the belt run 28.

Deflector plate 23 is supported from the upper part of elevator frame 17 by supports 32 so that it is downwardly inclined at a location above the upper part of the separator conveyor belt run 28. The plate has upstanding wings or flanges 33 along its sides to confine the particulate material so that it is deflected into a stream 34 which impinges on the upper part separator belt conveyor run 28 at an acute angle to the belt surface and in the downwards direction. The material is thus projected onto the conveyor belt run such that it tends to move downwardly along that run. However the upwardly 30 moving belt conveyor surface tends to collect the particles and transport them to the upper end of the separator belt conveyor run. The reaction of the particles to these competing tendencies depends very much on the physical characteristics of the individual 3T particles. Relatively chunky and hard particles will bounce and tumble on the belt conveyor to maintain their downward impetus under gravity such that they quickly move to the bottom end of the separator conveyor belt PL4379/700 I I CII 7 run. On the other hand, particles of more attenuated shape, soft fibrous particles and fine particles will not bounce and tumble to the same extent and will tend to settle on the conveyor surface so as to be captured and be transported to the upper end of the separator conveyor run. This difference in the behaviour of the different kind of particles can be enhanced by providing a flow of gas along the conveyor surface tending to move the particles toward the upper end of the separator conveyor.

To this end a fan or blower 35 is hung by suspension members J from the elevator frame 17 so as to be operable to direct a flow of air onto the bottom parc of the separator conveyor which will then flow upwardly along that conveyor.

The airflow provided by blower 35 helps to arrest the downward movement of fine particles and those particles of attenuated shape which will have a relatively large surface area exposed to the upward airflow as compared with chunky particles. The balance 20 between the downward movement of particles ulder gravity and the tendency for upward movement promoted by the conveyor and the airflow can be adjusted by controlling the airflow and appropriate choice of the angles of inclination of the separator conveyor and the deflector plate. To ,his end the suspension mountings 25 for the separator conveyor 24 and the support 32 for deflector *plate 23 may be designed to permit adjustment of the slopes of that conveyor and the deflector plate.

The separator conveyor belt surface may be provided 30 with ribs or a textured pattern to promote capture of the particles which are not capable of bouncing and tumbling.

It is has been found that a textured belt available commercially under the name UNITEX INCLINED CONVEYOR BELTING is particularly suitable in operation.

It has also been found in practice that particularly satisfactory results can be achieved if the separator Sbelt conveyor run is set at an angle to the horizontal in the r--ge 200 to 600 and the deflector plate 23 is set at PL4379/700 -a- 8 an angle to the horizontal in the range 400 to Air flows of the order of 1100 cubic feet per minute have been found to improve the sorting of bark particles of more than 5 mm size. For smaller size particles, however, the apparatus may be operated without any airflow. The airflow can be varied according to the particle size of the material to be sorted. For particles in the size range 5 mm to 30 mm, airflows may be selected in the range of 650 c.f.m. to 1500 c.f.m.

It has further been found in practice that the impingement of the stream of particulate material 22 on the deflector plate 23 also contributes to the separation of the chunkier particles from the residue since the chunkier particles tend to bounce from the plate 23 and be projected further down the separator belt surface than the attenuated and fine particles. This initial separation may be further enhanced by turning the bottom edge of deflector plate 23 outwards to form an upturned lip which will act to deflect the harder and chunkier 20 particles further than the soft and fine particles.

In the illustrated apparatus the relatively chunky orchid bark particles fall from the bottom end of the separator conveyor into a first collection bin 37 and the residue particles are collected in a second collection bin 38 disposed beneath the upper end of the separator conveyor. However, it will be appreciated that other kinds of collection means may be used to collect the separated bark fractions. They could for example, be continuously transported away from the respective ends of 30 the separator conveyor by appropriate transport too.m conveyors.

Although the invention has arisen from a need to sort tree bark particles in the production of plant growing media, it could be applied in other fields where it is desired to sort particulate materials so as to separate out relatively hard and chunky particles from a residue of attenuated and/or fine particles. Moreover the illustrated apparatus has been advanced by way of PL4379/700 i 9 example only and it may be modified considerably according to the material being handled. It is accordingly to be understood that the invention is in no way limited to details of the illustrated apparatus and that many modifications and variations will fall within the scope of the appended claims.

a.

*oo PL4379/700

Claims (3)

1. 2. A method as claimed in claim 1, wherein said stream is projected downwardly so as to impinge on an upper part of the upwardly inclined conveyor surface at an acute angle to that surface and in a downwards 20 direction relative to that surface so that the particles of the first fraction tend to bounce and tumble from the upper part of the conveyor surface to the lower end of that surface.
2. 3. A method as claimed in claim 1 or claim 2, 25 wherein the conveyor surface is a flat surface inclined at an acute angle to the horizontal in the range 200 to
3. 600. 4. A method as claimed in claim 3, wherein the stream of particulate material is projected onto that surface at an acute angle to that surface in the range 100 to 700. A method as claimed in any one of the preceding claims, wherein said stream is projected onto the conveyor surface by deflection from a deflector means disposed above the upper part of the conveyor surface. 6. A method. as claimed in claim 5, wherein the deflector means comprise a deflector plate set at an angle to the horizontal in the range 400 to 800. 4 9 S 5 ,r 4 9 9 *r .5 S S. SS PL4379/700 11 7. A method as claimed in any one of the preceding claims, which further comprises directing a flow of gas upwardly along the conveyor surface to assist the upward transport of the particles of the second fraction. 8. A method as claimed in claim 7, wherein said gas is air. 9. A method as claimed in claim 7 or claim 8, wherein said flow of gas has a flow rate in the range of 650 c.f.m. to 1500 c.f.m. 10. A method as claimed in any one of the preceding claims wherein said particulate material comprises tree bark particles. 11. A method as claimed in claim 10, wherein the tree bark particles are produced by milling tree bark and mechanically screening the milled bark to separate said particles. 12. A method as claimed in any one of the preceding claims, wherein the particles are in the size range to 13. Apparatus for sorting particulate material into fractions of differing particle characteristics, comprising a belt conveyor having a run defining an upwardly inclined conveyor surface; ns sosc& 25 conveyor drive meansAto drive the conveyor so as to move said conveyor surface in an upward direction; material feed meansito feed particulate material to be sorted to the belt conveyor and to project that material in a stream onto said conveyor surface; first particle collection meansito collect a first fraction of the particles from the bottom end of said conveyor run; and S second particle collection meansto collect a second fraction of the particles from the upper end of said conveyor run. 14. Apparatus as claimed in claim 13, wherein the particle feed means comprises a feed conveyor operable to Q feed the particulate material onto a deflector plate 0379/700 i 12 disposed above an upper part of said belt conveyor surface such that the particulate material will in use of the apparatus be deflected from said deflector plate in said stream at an acute angle to that conveyor surface and in a downwards direction relative to that surface. Apparatus as claimed in claim 13, wherein said belt conveyor surface is set at an angle to the horizontal in the range 20° to 60° and the deflector plate is set at an angle to the horizontal in the range 40° to 16. Apparatus as claimed in.any one of claims 13 to pose.A. which further comprises meansAto direct a flow of gas upwardly along the belt conveyor surface. 17. Apparatus as claimed in any one of claims 13 to 16, wherein the belt conveyor surface is ribbed or textured to promote Collection and transport of the particles thereon. DATED this 13th day of August 1993 DEBCO PTY LIMITED By their Patent Attorneys GRIFFITH HACK CO. *o 0 0" PL4379/700 ABSTRACT Method and apparatus for sorting particulate material such as tree bark particles. A stream 22 of the particulate material is projected onto deflector plate 23 5 which deflects it onto an upwardly moving inclined conveyor belt run 28. Relatively chunky particles bounce and tumble to the bottom of the belt run 28 whereas particles of more attenuated shape, soft fibrous particles and fine particles settle on conveyor run 28 .4 10 and are transported to the top of that run. Separation of the particles may be enhanced by blowing air from blower 35 upwardly along conveyor belt run 28. o* p PL4379/700