GB2591077A

GB2591077A - Aggregate processing method and apparatus

Info

Publication number: GB2591077A
Application number: GB1918829.1A
Authority: GB
Inventors: Dunne John
Original assignee: Molson Washing T/a Aggregate Proc Solutions
Current assignee: Molson Washing T/a Aggregate Proc Solutions
Priority date: 2019-12-19
Filing date: 2019-12-19
Publication date: 2021-07-21
Anticipated expiration: 2039-12-19
Also published as: GB201918829D0; GB2591077B

Abstract

A grading deck / vibratory screening device 100, having a main body 102 and for grading an aggregate mixture, comprises a first screen 104 having a first plurality of apertures therethrough. A dewatering screen / second screen 106 is vertically offset / below from first screen 104, and has a second plurality of apertures therethrough. Screen 106 is disposed at an angle of less than 10 degrees relative to screen 104. Aperture of screen 104 are between 4- 10mm, and those of screen 106 between 0.1-2mm. Pressurised water is delivered to the top of screen 104 by upper spray bars 116a-d and to screen 106 via lower spray vars 118a-c. A vibrating system, utilising motors 112a-b and spring mounts 14a-b is configured to oscillate both screens 104, 106 in a lateral plane. An associated method is disclosed, as detaile din figure 4.

Description

AGGREGATE PROCESSING METHOD AND APPARATUS

TECHNICAL FIELD

The present invention relates to a method of processing aggregate, and an associated apparatus.

BACKGROUND TO THE INVENTION

Aggregate materials such as sand, gravel, crushed stone and the like must be processed and washed before they can be used in construction or for other purposes, such as producing concrete or other compound materials. In particular, it is necessary to process aggregate mixtures in order to separate the mixture into the constituent components, wherein the components are defined by the particle size. Aggregate mixtures must therefore be graded into the various particle size fractions as well as washed so that the correct aggregate mixture can be provided for any chosen application.

One commonly used grading process splits an input aggregate mixture into three different fractions, or grading bands, which are defined by reference to the diameters of the aggregate particles. These fractions are: greater than 40 mm, less than 10 mm, and between 10 mm and 40 mm. This process is particularly common at recycling sites which use the process to grade mixtures of materials which have previously been used in construction work, and/or which are the by-products of other industrial processes.

The resulting >40 mm aggregate can be sold on as coarse gravel or cobbles which may be used by customers to make concrete, for example. In some processes, this fraction is further graded to provide an aggregate mixture between 65 mm and 40 mm which can be sold as drainage or oversite material, or which can be crushed and re-washed to increase concrete aggregates. The <10 mm aggrecate may be sold on as medium gravel, which can also be used in concrete, or even as fine gravel or soil which has a number of uses, for example as backfill material.

However, the output material which is graded between 10 mm and 40 mm is difficult to reprocess to a standard which is suitable for any purpose. In particular, even after processing these mixtures are dirty and so contain a proportion of silt and sand, and conglomerated lumps with aggregate silt and clay, as well as a high proportion of organic material in addition to the aggregates. Removing the silt, sand and organic material uses a large amount of water which greatly increases the cost of processing. Often, due to the difficulty and cost of further processing, the mixtures in this grade band are not sold on but are instead sent to landfill sites for disposal.

Currently there is a need for a simple and economical processing method which uses a reduced volume of water, and which can be used to process aggregate mixtures, particularly graded at <40 mm, and where those mixtures may contain organic material, such that the output is suitable for sale and industrial use.

SUMMARY OF THE INVENTION

At its most general, the present invention provides a system and process which is suitable for processing and grading aggregate mixtures having a particle size of 65mm or less, and preferably a particle size of 40mm or less.

In a first aspect of the present invention, there is provided a grading deck for grading an aggregate mixture, the grading deck comprising: a first screen having a first plurality of apertures therethrough; a dewatering screen vertically offset from the first screen, and having a second plurality of apertures therethrough; and a vibrating system configured to oscillate the first screen and the dewatering screen in a lateral plane. P. dewatering screen is a screen which is preferably adapted to allow only water and fine silt or sand parLicles Lo pass Lhrough Lhe aperLures Lherein. In particular, the size of each aperture of the first plurality of apertures should be larger than the size of each aperture of the second plurality of apertures such that, whatever the shape of each aperture, particles which are passed through the first screen may be further graded by the second screen. By providing a grading deck in this way, the present invention is able to quickly and easily grade aggregate mixtures which were previously prohibitively expensive to deal with, for example aggregate mixtures having a particle size of 65 mm or less, or preferably 40 mm or less. In particular, the grading deck of the present invention combines two functions -the first screen is provided to separate out larger particles from an aggregate mixture, and the dewatering screen is provided to separate out finer particles from the aggregate mixture, and also to dewater these finer particles. This combination of functions has not been previously provided in a single unit. By integrating a first screen and a dewatering screen into a single grading deck in this way, water use is reduced as an aggregate mixture can be deposited directly into the grading deck for grading by each of the screens without the need to pump a mixture from a first screen output to a dewatering screen input as is the case with known arrangements, wherein pumping the mixture in this way requires a large amount of water.

Preferably, the dewatering screen is disposed at an angle relative to the plane of the first screen. Preferably the angle is less than 10 degrees, for example 5 degrees. By disposing the dewatering screen at an angle in this way, the dewatering screen can more effectively remove water from an aggregate mixture which is deposited thereon.

Optionally, a size of each aperture of the first plurality of apertures, the apertures through the first screen, is less than 10 mm. More particularly, the size of each aperture of the first plurality of apertures is greater than or equal to 4 mm. In this way, the grading deck is adapted to output, from the first screen, an aggregate fraction which is particularly suited for concrete, or any applications which require a larger particle size. The apertures may be provided in any suitable shape, for example the apertures may be generally circular, square, or elongate (e.g. recLangular or lozenge-shaped), and no dimension (e.g. a width and/or length) of the apertures should exceed 10 mm.

Preferably, a size of each aperture of the second plurality of apertures, the apertures through the dewatering screen, is less than 2 mm. In this way, the grading deck is also adapted to output, from the dewatering screen, a fine aggregate fraction which is graded as a coarse sand or grit.

More particularly, the size of each aperture of the second plurality of apertures is greater than or equal to 0.1 mm such that the grading deck is adapted to output soil, fine sand and/or silt. For example, the size of each aperture of the second plurality of apertures may be 0.3 mm, or 0.5 mm. The apertures may be provided in any suitable shape, for example the apertures may be generally circular, square, or elongate (e.g. rectangular or lozenge-shaped) ), and no dimension (e.g. a width and/or length) of the apertures should exceed 2 mm.

Any combination of aperture sizes in the grading screen and dewatering screen may be considered in the present invention, according to the purposes for which the apparatus is to be used.

Advantageously, the grading deck further comprises a nozzle for delivering pressurised water to a top surface of the first screen. Additionally or alternatively, the grading deck may comprise a second nozzle for delivering pressurised water to a top surface of the dewatering screen. For example, water may be delivered at a pressure of greater than 50 bar (5 MPa), such as up to 100 bar (10 MPa), or more. In some examples the water may be delivered with compressed air in order to provide the high water pressures, while reducing the water consumption of the apparatus. By providing a nozzle in this way, the grading deck can deliver pressurised water in order to break down and also polish aggregate mixtures which are processed. Breaking down and cleaning aggregate particles in this way may result in liberation of silt or sand from larger aggregate particles, which are then separated from the mixture by the grading deck.

Preferably, the grading deck further comprises a main body, wherein the first screen and the dewatering screen are positioned within the main body. In some examples, the main body may be mountable to a support structure having wheels or skids, or may be mountable to a vehicle, to allow the grading deck Lo be readily LransporLable Lo differenL processing sites, or easily moved around within a given processing site.

Preferably, the main body comprises spring mounts to allow the grading deck to be mounted to other apparatus, for example a vehicle, in such a way as to isolate vibrations of the grading deck from the rest of the apparatus in use. The main body may also provide mounting points for other pieces of equipment which may be used with the grading deck.

Advantageously, the vibrating system comprises a vibrating motor affixed to the main body, and configured to oscillate the main body in order to oscillate the first screen and the dewatering screen in a lateral plane. For example, the vibrating motor may be an eccentric rotating motor, or a hydraulic vibrator. Agitation of the grading deck in this way causes separation and gradinc of the aggregate material deposited therein as some particles pass through the first screen, and some particles also pass through the dewatering screen to provide different component fractions. In addition, the vibratory movement of the grading deck provides forward motion to the material deposited into the grading deck, moving the screened material to be discharged. In this way, the grading deck generally acts as a vibratory screening device.

The vibrating motor should be chosen to ensure that the oscillating motions of the main body are large enough and energetic enough to provide suitable grading by both the first screen and the dewatering screen. Furthermore, the main body and any supporting structure may be designed to cope with the larger forces such a motor may generate compared with known arrangements. In some examples, the vibrating motor may be adjustable to allow an operator to change the vibration speed, vibration magnitude and/or amplitude to suit a particular purpose.

According to a second aspect of the invention, there is provided a system for cleaning and sorting an aggregate mixture, the system comprising: a coarse material washer; and a grading deck according to the first aspect of the invention, wherein the grading deck is arranged to grade aggregate material which is output from the coarse material washer. The second aspect of the invention thereby provides a processing system which is able to wash and sort or grade aggregate mixLures which were previously prohibiLively expensive Lo deal with, for example aggregate mixtures having a particle size of 65 mm or less, or preferably 40 mm or less.

Preferably the system further comprises a belt scraper configured to remove organic material from the coarse material washer. In particular, in use the coarse material washer contains a level of water in addition to the aggregate mixture, and so organic materials will float in the coarse material washer. These organic materials may be taken out of the coarse material washer by the belt scraper, ensuring that organic material in the output aggregate fractions is minimised, and so the output aggregate fractions are suitable for use in building or other purposes. For example, the belt scraper may comprise a conveyor belt having one end which is disposed within the coarse material washer in order to remove the organic material.

Advantageously, the system may comprise a third nozzle for delivering pressurised water into the coarse material washer. In particular, as with the first nozzle and the second nozzle, water may be delivered at a pressure of greater than 30 bar (5 MPa), such as up to 100 bar (10 MPa), or more. In some examples the water may be delivered with compressed air in order to provide the high water pressures, while reducing the water consumption of the apparatus. By providing a nozzle to deliver water in this way, the system can deliver pressurised water into the coarse material washer in order to break down and also polish aggregate mixtures which are processed. In addition, the nozzle provides water which is mixed with the input aggregate mixture by the coarse material washer to form a slurry of material which is deposited into the grading deck for further processing.

Preferably, the system further comprises a water treatment system for treating water output from the dewatering screen of the grading deck. For example, the water treatment system may comprise a settling tank to allow fine sand and sediment which passes through the dewatering screen to settle out of water passing through the dewatering screen. Additionally or alternatively, the water treatment system may comprise a hydrocyclone separator to separate any fine sand and sediment from water which passes through the dewatering screen. The water treatment system helps to ensure that every fracLion of Lhe original aggregaLe mixLure is separaLed and so can be sold on.

Optionally, the system may comprise an underflow for delivering water output from the dewatering screen into the coarse material washer. In this way, the system is able to effectively recycle water, reducing water usage of the process and thereby the cost of processing aggregate materials. In addition, by recycling water it can be ensured that as much aggregate can be captured and processed as possible.

According to a third aspect of the present invention there is provided a method of processing aggregate material, particular suitable for aggregate material mixtures having a particle size of 65mm or less, such as 40mm or less, wherein the method comprises: depositing aggregate material into a coarse material washer; depositing water into the coarse material washer; forming a slurry of the aggregate material and water; depositing the slurry onto a grading deck having a first screen and a dewatering screen, the dewatering screen being positioned beneath the first screen, wherein the first screen and the dewatering screen each have a plurality of apertures therethrough; grading the aggregate material into fractions by vibrating the grading deck; depositing a first fraction of the aggregate material from a top surface of the first screen; and depositing a second fraction of the aggregate material from a top surface of the dewatering screen. In this way, the present invention provides a method able to quickly and easily grade aggregate mixtures which were previously prohibitively expensive to deal with, for example aggregate mixtures having a particle size of 65 mm or less, or preferably 40 mm or less. In particular, the method uses a small amount of water and so it is cheap to process these aggregate mixtures. Preferably, the process produces a first aggregate fraction having a particle diameter of at least 10 mm, or even a particle diameter of at least 4 mm. Preferably, the second fraction is produced having a diameter of between 0.01 mm and 10 mm, for example between 2 mm and 10 mm, or between 2 mm and 4 mm, and preferably between 0.1 mm and 4 mm, such as between 0.3 mm and 10 mm, between 0.3 mm and 4 mm, Or between 0.5 mm and 10 mm, or optionally between 0.5 mm and 4 mm. Any combination of aperture sizes in the grading screen and dewatering screen may be considered in the present invenLion, according Lo Lhe purposes for which Lhe meLhod is to be used.

Preferably, the method further comprises a step of removing organic material from the coarse material washer prior to forming a slurry of the aggregate material and water. In this way, the method may ensure that organic material in the output aggregate fractions is minimised, and so the output aggregate fractions are suitable for use in building or other purposes.

B

Optionally, the method further comprises a step of reintroducing water output from the dewatering screen into the coarse material washer. In this way, the system is able to effectively recycle water, reducing water usage of the process and thereby the cost of processing aggregate materials. In addition, by recycling water it can be ensured that as much aggregate can be captured and processed as possible.

Advantageously, the ratio of aggregate material to water which is deposited into the coarse material washer is no more than 60:40 by weight. This ensures that the process is able to operate at an optimal speed and cost. Of course, the ratio of aggregate to water may be dependent on application, and so may be selected by an operator.

Preferably, water is introduced into the coarse material washer at a pressure of greater than 50 bar (5 MPa), such as up to 100 bar (10 MPa), or more. In this way, the water may aid breakdown of large aggrecate particles and may also polish the aggregate material, releasing fine sediment and sand particles which may be separated through further processing.

For example, in some embodiments, water may be introduced into the coarse material washer via a nozzle, and the water may be delivered with compressed air to ensure high water pressures.

In some examples, the method may further comprise a step of treating water output from the dewatering screen to remove sand, sediment, and other fine particles. The water treatment step helps to ensure that every fraction of the original aggregate mixture is captured and so can be sold on. Optionally, the method may make use of a system according to the second aspect of the invention, and in particular may use a grading deck according to the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention is discussed below in more detail with reference to the accompanying drawings, in which: Fig. 1 is a front perspective view of a grading deck which is an embodiment of the present invention; Fig. 2 is a rear perspective view of the grading deck which is an embodiment of the present invention; Fig. 3 is a cross-sectional view of a coarse material washer which may be used in an embodiment of the invention; Fig. 4 is a flow diagram showing an aggregate processing method which is an embodiment of the present invention.

DETAILED DESCRIPTION; FURTHER OPTIONS AND PREFERENCES Fig. 1 shows a front perspective view of a grading deck, or vibratory screening device 100. Fig. 2 shows a rear perspective view of the grading deck 100, which is a vibratory screening device. The grading deck 100 comprises a main body 102 to which the other components are affixed. The main body 102 is generally cuboidal, with an open top surface to allow material to be deposited within the main body 102 and an opening at the front of the main body 102 to allow processed material to exit the device 100. The main body 102 may also have an opening in its lower surface to provide an underflow which allows water which passes through a second screen 106 to exit the device 100. For example, the underflow water may be reintroduced into the processing system or may be further processed, as will be discussed below.

Within the main body 102 are mounted a first screen 104 and a second screen 106, wherein the first screen 104 is mounted above the second screen 106. In particularly preferred embodiments, the second screen is a dewatering screen.

Preferably the first screen 104 is mounted such that it is positioned horizontally with respect to the main body 102, and the second screen 106 is positioned at an angle of 5° with respect to the main body 102 and the first screen 104 such that the second screen 106 is generally sloped upwards towards the rear face of the main body 102. Each of the first screen 104 and the second screen 106 comprise a plurality of aperLures LhereLhrough. Preferably, Lhe aper Lures are generally circular in shape, though any other shape may also be considered, for example square, or elongate (e.g. rectangular or lozenge-shaped). Generally, the first screen 104 is provided to size and clean or polish aggregate material, and the second screen 106 is provided to dewater any material passing through the first screen 104 in order to recover fine sand or silt and other fine particles from the aggregate mixture. The apertures through the first screen 104 are larger than the apertures through the second screen 106. For example, the apertures in the first screen 104 may be provided in any suitable shape and may have a diameter or maximum width of 4 mm or any other suitable size, and the apertures in the second screen 106 may also be provided in any suitable shape but may have a diameter or maximum width of 0.1 mm. In some examples, the apertures in the second screen may have a diameter of 0.3 mm or 0.5 mm, preferably less than 2mm, and the apertures in the first screen 104 may have a diameter of up to 10 mm. Any combination of aperture sizes may be considered in the present invention, according to the purposes for which the apparatus is to be used. Of course, it is envisioned that the apertures through the first screen 104 and the second screen 106 may take any appropriate shape, though it is important that the the largest dimension of each aperture in the first screen 104 (e.g. the larger of a width or a length of each aperture) is larger than the largest dimension of each aperture of the apertures in the second screen 106 such that material which passes through the first screen 104 may be further graded by the second screen 106. In some examples the second screen 106 may be a dewatering screen, such that only water and fine sand or silt particles may pass through the second screen 106. Each of the first screen 104 and the second screen 106 may comprise multiple panels which are fitted together within the main body 102 to form the generally planar screen surface. The dual screen arrangement allows the grading deck 100 to separate material which is deposited in the main body 102 into three different components or fractions -a first fraction which is passed off from the top of the first screen 104, a second fraction which passes through the first screen 104 and is passed off from the top of the second screen 106, and a third fraction which passes Lhrough Lhe second screen 106 wiLh excess waLer. A lower discharge chute 108 is fixed to the front of the main body 102 to discharge material which is passed off from the top of the second screen 106. For example, the discharge chute 108 may discharge material to a conveyor or may discharge material to ground, or directly into a container. An upper discharge chute 109 may also be provided to discharge material passed off from the top of the first screen 104. The upper discharge chute 109 is omitted from Fig. 1 for clarity.

At a rear side of the main body 102, two mesh panels 110a, 110b are provided as an overflow exit, allowing excess water to drain out from the rear side of the main body 102 above the second screen 106 if necessary.

At the top of the main body 102 are mounted two vibratory motors 112a, 112b. The vibratory motors 112a, 112b may be eccentric rotating motors configured to rotate at around 10000 RPM or less. Other motor types or vibrators may be considered, such as hydraulic vibrators. The vibratory motors 112a, 112b thereby vibrate the main body 102 in horizontal and vertical planes causing corresponding movement of the first screen 104 and the second screen 106. Agitating the first screen 104 and the second screen 104 causes separation and grading of the aggregate material deposited within the main body 102 as some particles pass through the first screen 104, and some particles also pass through the second screen 106 to provide the three component fractions discussed above. In addition, the vibratory movement of the first screen 104 and the second screen 106 provides forward motion to the material deposited into the main body 102, moving the screened material to the front end of the main body 162 where it is discharged. For example screened material is discharged onto respective conveyors which carry the material fractions onwards.

As vibrations can be particularly damaging to other pieces of apparatus which are used with the grading deck 100, the grading deck 100 comprises front spring mounts 114a and rear spring mounts 114b. The spring mounts 114a, 114b each comprise compression springs to ensure that the vibrations of the screen device 100 are sufficiently isolated from the rest of the apparatus, such as a coarse material washer as discussed below. The spring mounts 114a, 114b also act to return the main body 102 to a rest position in response to the agiLaLing moLion provided by Lhe vibraLory moLors 112a, 112b, damping vibrations of the main body 102. Spring mounts 114a, 114b may be provided on each side of the main body 102, and also provide the mounting point at which the grading deck 100 is connected to a support structure (not shown) when the grading deck 100 is in use. In some examples, the support structure may allow the grading deck 100 to be portable. For example, the support structure may be provided with wheels, or may be directly connected to a vehicle such as a lorry or truck so that the grading deck 100 can be easily moved to a location where it is needed.

The mounting points provided by the spring mounts 114a, 114b are arranged such that when the device 100 is in use, the first screen 104 are set at an angle of approximately 5 degrees with respect to a horizontal level, and the second screen 106 is at an angle of approximately 10 degrees with respect to a horizontal level, though this may be adjusted by a user dependent on application. In some embodiments, the spring mounts 114a, 114b may be movably mounted to the main body 102 to allow the angle of the main body 102 to be adjusted by a user. Additionally or alternatively, the spring mounts 114a, 114b may comprise means of adjusting the height of the mounted points to achieve a similar effect. In some examples, it is envisaged that the first screen 104 may be positioned horizontally, and the second screen 106 may be set at an angle of 5 degrees with respect to the horizontal, as the angle of the second screen 106 allows solids to move towards a discharge chute 106 while water is separated.

A plurality of upper spray bars 116a, 116b, 116c, 116d are connected to an upper portion of the main body 102, and are provided to spray material deposited therein with high-pressure water. The spray bars may each be provided with a number of nozzles through which water is delivered. The jets of water from the upper spray bars 116a, 116b, 116c, 116d are directed at the upper surface of the upper screen 104. For example, water at a pressure of around 100 bar (10 mFa) may be supplied to each spray bar 116a, 116b, 116c, 116d. Spraying the material deposited into the main body 102 provides a number of advantages. For example, the high pressure water spray may break down clumped material into constituent particles, and may also clean and polish the aggregate par Licles which pass Lhro ugh Lhe waLer spray. In order Lo achieve the high water pressure, and also to reduce the amount of water which is used in processing the aggregate mixtures, the water may be delivered with compressed air.

The main body 102 also comprises a plurality of lower spray bars 118a, 118b, 118c which are mounted beneath the first screen 104 and above the second screen 106. The lower spray bars 118a, 118b, 118c provide a plurality of jets, e.g. through nozzles, of water which are directed onto the upper surface of the lower screen 106. For example, water at a pressure of around 100 bar (10 MPa) may be supplied to each spray bar 118a, 118b, 118c. In some embodiments, the water may be delivered via the spray bars 118a, 118b, 118c using compressed air, which may lower water use and also increase the pressure of water which is delivered. The lower spray bars 118a, 118b, 118c may further aid breakdown of material which passes through the first screen 104, as well as cleaning and polishing any material which is passed to the discharge chute 108.

As mentioned above, the main body 102 may have an opening in its lower surface to provide an underflow. Water and any particles which pass through the second screen 106 may flow through this opening to be reintroduced to the apparatus to reduce water consumption of the aggregate processing operation. For example, the underflow may be introduced into a coarse material washer such as coarse material washer 200 discussed below. Additionally or alternatively, the water passing through the second screen 106 may be directed to settling pools or other water treatment apparatus to separate out fine sand or silt particles from the water and so provide a third fraction separated out from the initial aggregate mixture.

Fig. 3 shows a cross-sectional view of a coarse material washer 200 which may be used with an embodiment of the present invention. For example, the coarse material washer 200 may supply a slurry material which is deposited into a vibratory grading deck, such as the grading deck 100 shown in Figs. 1 and 2.

The coarse material washer 200 comprises a tub 202 which is configured to hold a mixture of water and the aggregate material which is to be processed. A top side of the tub 202 is open Lo allow aggregaLe maLerial and waLer Lo be deposiLed therein. A rotatable shaft 204 is supported within the tub 202, wherein the rotatable shaft 204 comprises a screw thread 206 which is provided to mix water and aggregate material to form a slurry, break down large pieces of aggregate material and conglomerated lumps, and also to move the slurry along the tub 202 to an outlet 208 when the shaft 204 is rotated. In some examples, the rotatable shaft 204 may instead be provided with a plurality of paddles which perform the same task as the screw thread 206. The paddles may be provided in addition to one or more screw threads which are also present on the rotatable shaft 204.

In some embodiments, the coarse material washer 200 may comprise multiple shafts 204, each comprising screw threads and/or paddles. For example, the coarse material washer 200 may comprise two rotatable shafts 200 which are laterally offset from one another, which may provide the capability to process additional aggregate material.

The outlet 208 is provided towards a distal end of the tub 202, and is located in the lower face of the tub. In this way, aggregate material which is moved towards the distal end of the tub 202 under action of the rotating shaft 204 and screw thread 206 may be pushed by the screen thread 206 out of the outlet 208. For example, the outlet 208 may be positioned above a vibratory screening device, such as the grading deck 100 shown in Figs. 1 and 2.

A motor 210 is provided to rotate the shaft 204, and in the depicted embodiment the motor 210 rotates the shaft 204 via a drive belt 212. The motor 210 may be configured to rotate the shaft 204 at between 25 and 30 revolutions per minute (RPM), for example. Of course, the motor 210 may be configured to rotate the shaft 204 at any suitable speed. The motor 210 may also be configured to allow the shaft 204 rotation direction to be reversed as required, which may be useful to prevent blockages. In some examples, the motor 210 may be configured to allow the speed at which the shaft is rotated to be adjusted by a user. The motor 210 is preferably configured to provide a high torque output to ensure that the rotatable shaft 204 and screw thread 206 is able to form a slurry and break aggregate material down. A high torque motor 210 may also be preferable to allow large volumes of aggregate maLerial Lo be processed. For example, iL is envisaged LhaL the coarse material washer 200 is suitable to process aggregate material at a rate of at least 50 tons per hour, and preferably up to 100 tons per hour.

At the proximal end of the tub 202, a belt scraper 214 is provided. The belt scraper 214, in this example, takes the form of a short conveyor belt which is positioned such that a first end of the conveyor belt is within the tub 202, at or slightly below the level of water within the tub 202 when the coarse material washer is in use. A second end of the conveyor belt is located away from the rear edge of the tub, such that the longitudinal axis of the conveyor belt is aligned with the longitudinal axis of the rotatable shaft 204 and the tub 202.

Of course, the belt scraper 214 may also be positioned at an angle to the longitudinal axis of the rotatable shaft 204 and the tub 202. The belt scraper 214 is provided to remove organic material and any other floating debris from within the tub 202, as the organic material tends to float and so generally collects at the top surface of the water within the tub 202. For example, the belt scraper 214 picks up organic materials from within the tub 202 and passes them along the conveyor belt where they are deposited outside of the tub 202. The organic materials may be collected by another apparatus, or may be discharged to ground. As the rotatable shaft 204 is rotated in use, the screw thread 206 breaks up aggregate material which allows pieces of organic material to float to the proximal end of the tub 202 where they are collected and discharged by the belt scraper 214.

Towards the distal end of the tub 202 is provided a spray bar 216, having a number of nozzles, which is located above the rotatable shaft 204, and positioned to subject the slurry produced by the screw thread to a spray of high pressure water before exiting the tub at the outlet 208. The jet of water from the spray bar 216 may help to further break down and clean or polish pieces of aggregate in the slurry. For example, water at a pressure of around 100 bar (10 mFa), and the water may be delivered under pressure using compressed air, which also reduces the amount of water which is used. In particular, water should be introduced into the tub 202 to maintain a constant water level so that the removal of organic material and other floating debris can be maintained.

In use, Lhe coarse maLerial washer 200 may be posiLioned such that the opening 208 is located above the rear end of a vibratory screening device, such as grading deck 100 discussed above. In particular, the coarse material washer 200 is positioned such that the aggregate slurry which is discharged through the opening 208 is deposited onto an upper screen of the grading deck, such as the first screen 104. In this way, the coarse material washer 200 and grading deck 100 may be operated to perform an aggregate processing method substantially as described below. The coarse material washer 200 is preferably positioned such that the tub is inclined towards the distal end (that is, the end having the discharge opening 208) at an angle of around 5°, though this angle may be adjustable by a user, for example by adjusting the mounting points of the coarse material washer 200.

Fig. 4 is a flow diagram showing an aggregate processing method 300 which is an embodiment of the present invention. Preferably, the aggregate processing method 300 uses a grading deck 100 and a coarse material washer 200 as described above with respect to Figs. 1-3. The method 300 is particularly suited for processing aggregate mixtures having an aggregate size of 65 mm or less, such as 40 mm or less.

In a first step 302, the aggregate mixture which is to be processed is introduced into a coarse material washer, for example coarse material washer 200 described above with respect to Fig. 3. Following this, water is also introduced into the coarse material washer (step 304). In some examples, at least a portion of this water is introduced into the coarse material washer at a high pressure via spray bar and/or nozzle. For example, water may be delivered at 100 bar (10 MPa) to clean the aggregate material, as well as breaking up some parts of the aggregate to liberate sand, soil or other fine particles.

By introducing water into the coarse material washer, any organic material which is present in the aggregate mixture is encourage to float. The organic material may then be easily removed at step 306. In some examples, as described in Fig. 3, the organic material may be removed by a belt scraper 214 which continuously operates to remove the organic material from within the coarse material washer 200. Removing the organic material helps to ensure that the aggregate fractions which are provided by We process are clean and suiLable for use, e.g. in building, such as for use in concrete or as backfill, or in other uses.

After the organic material has been removed, the aggregate mixture and water is formed into a slurry (step 308). For example, this is performed by a screw or auger within the coarse material washer 308. It is particularly preferred that the slurry is comprise of a ratio of 60:40 aggregate material to water, by weight, as this provides an optimal ratio of aggregate material to water for further processing by the grading deck, as will be described below. After the slurry has been formed, it is deposited into a grading deck (step 310). Preferably the grading deck is a grading deck 100 as described above with respect to Figs. 1 and 2. The grading deck is a vibratory sorting apparatus which is able to sort the aggregate material into different fractions. In particular, the grading deck comprises a first screen and a dewatering screen such that the first screen is able to remove a first aggregate fraction from the aggregate mixture (step 312) and the dewatering screen is able to remove a second aggregate fraction from the aggregate mixture (314). Preferably, the first screen has a first plurality of apertures therethrough having a size of 4mm, such that the first aggregate fraction comprises particles having a diameter of 4mm or more. Preferably, the dewatering screen has a second plurality of apertures therethrough having a size of 0.1 mm, such that the second aggregate fraction comprises particles having a diameter of between 0.1 mm and 4 mm.

In addition to the second aggregate fraction, the dewatering screen also outputs water containing fine silt and/or sand particles. At least a portion of this water may be recycled, and re-introduced into the coarse material washer (step 316a). Additionally or alternatively, at least a portion of this water may be sent for further processing (step 316b).

For example, the water which is output from the dewatering screen may be sent to a hydrocyclone, and/or a settling pool or tank in order to remove the fine silt and/or sand particles from the water, thereby removing a third aggregate fraction (step 318) which may also be sold on as a product of the process.

Although a few preferred embodiments have been shown and described, IL will be appreciaLed by bhose skilled in Lhe art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purposes, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclose is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS1. A grading deck for grading an aggregate mixture, the grading deck comprising: a first screen having a first plurality of apertures therethrough; a dewatering screen vertically offset from the first screen, and having a second plurality of apertures therethrough; and a vibrating system configured to oscillate the first screen and the dewatering screen in a lateral plane.
2. A grading deck according to claim 1, wherein the dewatering screen is disposed at an angle relative to the plane of the first screen.
3. A grading deck according to claim 2, wherein the angle is less than 10 degrees.
4. A grading deck according to claim 2 or claim 3, wherein the angle is 5 degrees.
3. A grading deck according to any one of the preceding claims, wherein a size of each aperture of the first plurality of apertures is less than 10 mm.
6. A grading deck according to claim 5, wherein the size of each aperture of the first plurality of apertures is greater than or equal to 4 mm.
7. A grading deck according to any one of the preceding claims, wherein a site of each aperLure of Lhe second plurality of apertures is less than 2 mm.
8. A grading deck according to claim 7, wherein the size of each aperture of the second plurality of apertures is greater than or equal to 0.1 mm.
9. A grading deck according to any one of the preceding claims, further comprising a nozzle for delivering pressurised water to a top surface of the first screen.
10. A grading deck according to any one of the preceding claims, further comprising a second nozzle for delivering pressurised water to a top surface of the dewatering screen.
11. A grading deck according to any one of the preceding claims, further comprising a main body, wherein the first screen and the dewatering screen are positioned within the main body.
12. A grading deck according to any claim 11, wherein the vibrating system comprises a vibrating motor affixed to the main body, and configured to oscillate the main body in order to oscillate the first screen and the dewatering screen in a lateral plane.
13. A system for cleaning and sorting an aggregate mixture, the system comprising: a coarse material washer; and a grading deck according to any one of claims 1 to 12, wherein the grading deck is arranged to grade aggregate material output from the coarse material washer.
14. A system according to claim 13, further comprising a belt scraper configured to remove organic material from the coarse material washer.
15. A system according to claim 13 or claim 14, further comprising a third nozzle for delivering pressurised water inLo Lhe coarse maLerial washer.
16. A system according to any one of claims 13 to 15, further comprising a water treatment system for treating water output from the dewatering screen of the grading deck.
17. A system according to any one of claims 13 to 15, further comprising an underflow for delivering water output from the dewatering screen into the coarse material washer.
18. A method of processing aggregate material, the method comprising: depositing aggregate material into a coarse material washer; depositing water into the coarse material washer; forming a slurry of the aggregate material and water; depositing the slurry onto a grading deck having a first screen and a dewatering screen, the dewatering screen being positioned beneath the first screen, wherein the first screen and the dewatering screen each have a plurality of apertures therethrough; grading the aggregate material into fractions by vibrating the grading deck; depositing a first fraction of the aggregate material from a top surface of the first screen; and depositing a second fraction of the aggregate material from a top surface of the dewatering screen.
19. PI method according to claim 18, further comprising a step of removing organic material from the coarse material washer prior to forming a slurry of the aggregate material and water.
20. A method according to claim 18 or claim 19, further comprising a step of reintroducing water output from the dewatering screen into the coarse material washer.
21. A method according to any one of claims 18 to 20, wherein the ratio of aggregate material to water deposited into the coarse material washer is no more than 60:40 by weight.
22. A method according to any one of claims 18 to 21, wherein waLer is inLroduced inLo Lhe coarse maLerial washer aL a pressure of at least 5 MPa.
23. A method according to any one of claims 18 to 22, further comprising a step of treating water output from the dewatering screen to remove sediment.
24. A method according to any one of claims 18 to 23, wherein the aggregate material deposited into the coarse material washer has a particle diameter of 65 mm or less.
25. A method according to any one of claims 18 to 24, wherein the first fraction of aggregate material has a particle diameter of at least 4 mm.
26. A method according to claim 25, wherein the second fraction of aggregate material has a particle diameter of between 0.1 mm and 4 mm.
27. A method according to any one of claims 18 to 26, wherein the grading deck is a grading deck according to any one of claims 1 to 12.