The present invention relates to a belt cleaner assembly for cleaning a conveyor belt.

The majority of materials transported by conveyor belts in Australia are granular bulk solids with a particle size distribution typically ranging from a few centimetres to a few microns.

In any given situation, a portion of a granular bulk material that is conveyed by a section of a belt is retained on the belt after the section reaches the head pulley and discharges the remainder of the material from the section of the belt. In addition, a further portion, typically referred to as "carry back", of the retained portion continues to adhere to the section of the belt after the remainder of the retained portion is dislodged by the combined effect of gravity, vibration, air friction and centrifugal forces as the section of the belt moves around the head pulley and along the return path.

There are a number of factors that influence the amount of carry-back and these include:

(a) the characteristics of the transported material, such as the particle size distribution and the moisture content of the material;

(b) the conveyer belt design parameters, such as the size of the head pulley, the belt speed, and the magnitude of centrifugal force generated by movement of the belt around the head pulley; and

(c) the condition of the surface of the conveyor belt.

In order to optimise conveyor belt performance it is important to remove carry back from conveyor belts, and there has been developed a range of belt cleaners for this purpose.

The most widely used type of belt cleaner is a scraper blade assembly that relies on direct contact with the belts. A major disadvantage of scraper blade assemblies is that the reliance on direct contact with a belt produces -friction between a scraper blade assembly and the belt which causes wear to the scraper blade assembly and can cause wear to the belt and thereby reduces the life of the belt/scraper blade assembly and increases maintenance costs. Moreover, in some situations, an abrasive paste of granular material can form on the scraper blade assembly and accelerate considerably the wear of the belt/scraper blade assembly.

An object of the present invention is to provide a belt cleaner assembly that alleviates the disadvantage of the known scraper blade assemblies described in the preceding paragraph.

According to the present invention there is provided a belt cleaner assembly comprising, an elongate

nozzle for delivering air under pressure across the width of a conveyer belt to remove carry back from the belt and to form an air cushion between the belt and the nozzle to minimise friction between the belt and the nozzle.

It is preferred that the belt cleaner assembly further comprises, a means to bias the nozzle towards the belt.

It is preferred that the nozzle comprises, a pair of opposed plates clamped or otherwise resiliently held together so that the plates are in contact when there is no air supplied to the belt cleaner assembly and the plates separate to form an elongate air supply channel when pressurised air is supplied to the belt cleaner assembly.

It can readily be appreciated that, with such an arrangement, when there is no air supplied to the belt cleaner assembly the biasing means forces the closed plates of the nozzle against the belt and the belt cleaner assembly thereby functions as a conventional scraper blade assembly that relies on direct contact with the belt.

It is preferred that the air pressure be at least 100 psi.

It is preferred that the belt cleaner assembly comprises a plurality of said nozzles mounted side by side to extend across the'width of the belt.

It is preferred that the belt cleaner assembly comprises a means for supporting the or each nozzle in relation to the conveyor belt and for delivering compresse air from a compressed air source to the or each nozzle.

It is preferred that the support and compressed air delivery means comprises, a shaft for supporting the or each nozzle, and the shaft comprises an air passage along the length thereof which is adapted to be coupled to a supply of compressed air, and the shaft further comprises a plurality of radial openings along the length thereof for allowing pressurised air to flow from the passage to the or each nozzle.

It is preferred that the shaft be adapted to be mounted for rotation about its longitudinal axis and that the biasing means be adapted to be positioned to rotate the shaft and thereby the or each nozzle towards the belt.

According to the present invention there is also provided, in combination, a conveyor belt, and the conveyor belt cleaner described in the preceding paragraph.

It is preferred that the belt cleaner assembly be located at a discharge end of the belt with the or each nozzle angled with respect to the belt so that carry back removed by the or each nozzle is projected in the same direction as the material otherwise discharged from the discharge end of the belt.

The present invention is described further with reference to the accompanying drawings in which:

Figure 1 illustrates schematically the basic principle of operation of the belt cleaner assembly of the present invention;

Figure 2 is a perspective view of a preferred

embodiment of a belt cleaner assembly formed in accordance with the present invention located at a discharge end of a conveyer belt;

Figure 3 is a front view of a preferred embodiment of a modular cleaner element of the belt cleaner assembly shown in Figure 2;

Figure 4 is a section along the line 4-4 in Figure 3;

Figure 5 is a front view of another preferred embodiment of a modular cleaner element of the belt cleaner assembly shown in Figure 2; and

Figure 6 is a section along the line 6-6 in Figure 5.

With reference to Figure 2, the preferred embodiment of the belt cleaner assembly of the present invention, generally identified by the numeral 3, is shown positioned at a discharge end 5 of a conveyor belt assembly, generally identified by the numeral 7.

The conveyor belt assembly 7 comprises a conveyor belt 13 arranged to extend around a head pulley 9 that is supported for rotation about a horizontal axis X-X by means of a support frame 11. The conveyer belt assembly 7 is arranged to carry granular bulk solids or any other material on the belt 13 and to project the material from the belt 13 in the direction of the arrows A.

The belt cleaner assembly 3 comprises a plurality of separate cleaner elements 15, each having an air

delivery nozzle 31, positioned side by side to extend across the width of the conveyor belt 13. It is noted that only one cleaner element 15 is shown in Figure 2 to simplify the drawing. It is also noted that, whilst a single cleaner element extending across the width of the belt 13 is within the scope of the present invention, a plurality of smaller-width cleaner elements 15 is preferred to allow the belt cleaner assembly 3 to be more responsive to localised discontinuities in the belt 13, such as variations in belt thickness or curvature, across the width of the belt 13.

The belt cleaner assembly 3 further comprises a means for supporting each cleaner element 15 in relation to the conveyor belt 13 and for delivering compressed air from a compressed air source (not shown) to each nozzle 31.

Specifically, each cleaner element 15 is mounted on a shaft 17-that extends across the width of the belt 13 and is supported for rotation about a horizontal axis by mounting plates 19 fixed to the support frame 11 of the conveyor belt assembly 7. A tensioner, generally identified by the numeral 27, applies a moment to the shaft 17 that rotates the cleaner element 15, and in particular the nozzles 31, towards the belt 13. The tensioner comprises a compression spring 21 of a predetermined spring force mounted at one end to an arm 23 that is fixed to and therefore rotates with the shaft 17 and at the other end to a mounting bracket 25 that is fixed relative to the shaft 17. The shaft 17 is hollow and is formed with a fitting 29 at one end to allow the shaft 17 to be coupled to a source of compressed air (not shown) . As is described hereinafter in more detail, the shaft 17 comprises a plurality of radial openings (not shown) at spaced intervals along the

length thereof to allow compressed air to flow from the hollow core to the nozzles 31.

With reference to Figure 2, the scraper blade assembly 3 further comprises a wiper arm 55 positioned for reciprocating movement across the upstream face of each nozzle 31 to remove carry back that tends to build-up on the face. Each wiper arm 55 is mounted to a shaft 57 that is supported by the mounting plate 19 and the hollow shaft 17 for reciprocating movement by means of a piston assembly 59.

The construction of a preferred embodiment of the cleaner elements 15 is shown in detail in Figures 3 and 4. With reference to the figures, each nozzle 31 is formed from two plates 33 mounted at one end of a holder 35. The other end 37 of the holder 35 is bulbous and has a central hollow core dimensioned to fit snugly around the shaft 17. The main body 53 of the holder 35 comprises a central passage 39 extending from the hollow core in the bulbous end 37 and terminating in a plenum chamber 41 at the nozzle end of the holder 35. The air passage 39 is formed so that, when it is aligned with one of the radial openings i the shaft 17, compressed air can flow through the central passage 39 into the plenum chamber 41. The purpose of the plenum chamber 41 is to ensure that there is an even pressure of air across the nozzle 31. The holder 35 further comprises a pair of clamps 43 positioned at the nozzle end of the holder 35 and held together and to the main body 53 of the holder 35 by cap head screws 45. The pair of clamps 43 is formed to define a seat for the nozzl plates 33 and to bias the nozzle plates 33 together, as is shown in Figure 4. The seat and the tip 51 of the nozzle 31 are formed so that the nozzle 31 presents an angle to

the belt 13 at which carry back removed by cleaner element 15 is projected in the direction of the arrows A in Figure 1 along with the stream of material being discharged from the belt 13. In addition, the clamping force of the pair of clamps 43 is selected so that a prescribed operating pressure, typically 100 psi, of compressed air from the source of compressed air is sufficient to separate the nozzle plates 33 and allow compressed air to escape from the nozzle 31. The tension in the cap head screws 45 allows control of the air flow rate through the nozzle 31 over a small range to allow matching of sets of cleaner elements 15.

The construction of another preferred embodiment of the cleaner elements 15 is shown in detail in Figures 5 and 6. The embodiment is similar in construction to that shown in Figures 3 and 4 and like numerals are used to denote like parts. The main difference between the embodiments is that the main body 53 of the holder 35 is split, as indicated by the numeral 71, in the embodiment shown in Figures 5 and 6 and does not comprise the continuous bulbous end 37 of the embodiment shown in Figures 3 and 4. With reference to Figures 5 and 6, the split main body 53 comprises a pair of legs 73 having openings 75 for bolts (not shown) to hold the bulbous portion of the split main body 53 to the shaft 17. The arrangement is such that by deflecting the legs 73 it is possible to position the cleaner element 15 onto the shaft 17 or to remove the cleaner element 15 from the shaft 17. The advantages of the split main body 53 are that it

^• enables the shaft 17 to be installed without the cleaner elements 15 mounted to the shaft 17 and individual cleaner elements 15 may be exchanged in situ, thereby reducing maintenance down-time.

The basic principle of operation of the belt cleaner assembly 3 is shown schematically in Figure la. With reference to the figure, compressed air expands between the nozzle tip 51 and the belt 13 and then flows outwardly from the nozzle 31 in the direction of the arrows shown in the figure and dislodges carry back from the belt 13. In addition, compressed air generates an air cushion between the nozzle tip 51 and the belt 13 which is sufficient to maintain a small clearance between the nozzle tip 51 and the belt 13 against the biasing force of the tensioner 27 so that there is minimal friction between the belt cleaner assembly 3 and the belt 13.

With reference to Figure lb, in situations where there is no compressed air delivered to the belt cleaner assembly 3, the pair of clamps 43 hold the nozzle plate 33 in close contact to prevent any damage to the air delivery passages, and/the tensioner 27 biases the nozzle tip 51 against the belt 13 so that the belt cleaner assembly 3 functions as a conventional scraper blade that relies on direct belt contact.

A series of laboratory bench tests was carried out to investigate the effectiveness of the present invention. A 100 mm wide cleaner element 15 in accordance with Figures 3 and 4 was machined out of SC 25 steel and hardened to 65 RC (Rockwell hardness) . The performance of the cleaner element 1E> was measured against that of a conventional direct contact Hosch scraper blade having a 100 mm wide, 11 cm high, tungsten carbide tip. Both the scraper blade and the cleaner element 15 were subjected simultaneously to 10 hour duration wear tests cleaning iron ore pellet rejects at 2 m/s belt speed on a new belt and on

a worn belt. For the duration of the tests, constant supervision was maintained to ensure uniform carry back levels and moisture content of the material. At the end of each run, performance was checked and the progress monitored. A summary of the results is set out in the Table below.

(a) NEW BELT

(b) WORN BELT

With reference to the table, the cleaning

efficiency of the cleaner element 15 was significantly higher than for the Hosch scraper blade on both new and worn belts.

Furthermore, the wear rate of the cleaner element

15 was marginally higher than that of the Hosch scraper blade, although, given the higher hardness of tungsten carbide compared to hardened SC25 steel, the results suggest that the life of the cleaner element 15 could be extended significantly by the use of harder materials such as tungsten carbides and ceramics.

A series of trials of the belt cleaner assembly 3 was carried out at the pellet plant of BHP Steel Long Products Division (LPD) and at the Hay Point Coal loader managed by BHP Australia Coal.

The results of the trial at LPD on a conveyor moving iron ore fines with a high moisture content indicate a reduction in clean-up from 20 kg/hr to 1.5 kg/hr with lower rates of cleaner wear and lower belt wear with the belt cleaner assembly 3. The preliminary results of the trail at Hay Point on a coal conveyor indicate a five-fold reduction in the amount of carry-back with the belt cleaner assembly compared with the two types of conventional scraper blade assemblies previously installed.

The belt cleaner assembly 3 has a number of advantages over conventional scraper blade assemblies including, substantially frictionless cleaning, low wear rates even when cleaning abrasive materials, excellent performance on belts that are in relatively poor condition, and little or no adjustment required over the life of the belt cleaner assembly 3.

Many modi ications may be made to the preferred embodiment described above without departing from the spirit and scope of the invention.