Multistage hammer mill and a residue processing system incorporating same

A multistage hammer mill (10) has a plurality of milling stages arranged concentrically about each other. The plurality of milling stages arranged so that substantially all material in a first inner most of the milling stages passes through all subsequent adjacent milling stages. The milling stages include a first milling stage and a second milling stage. A central feed opening (12) enables material flow into a primary impact zone (14) of the first milling stage. The first milling stage has an impact mechanism (16) and a first screen arrangement (20a). The impact mechanism (16) rotates about a rotation axis (18). The first screen arrangement (20a) is disposed circumferentially about and radially spaced from the impact mechanism (16) and is provided with a plurality of apertures (22) through which impacted material of a first size range can pass. The second milling stage has a second arrangement (20b) disposed circumferentially about and radially spaced from the first screen arrangement (20a) and a circular array of impact elements (50a) disposed between the first screen arrangement (20a) and the second screen arrangement (20b).

TECHNICAL FIELD

A multistage hammer mill of a type suitable for the devitalisation of weed seeds and fragmentation of organic matter is disclosed. Also disclosed is a residue processing system which incorporates one or more multistage of the disclosed hammer mills or alternate residue processing devices.

BACKGROUND ART

Weeds and weed control are, and always have been, one of the biggest constraints and costs to grain production. Weeds are a perpetual problem that limits the food production capacity of agricultural area around the globe. Weeds compete with the cultivated crops for water, sunlight and nutrients. In the past 50 years there has been a shift from tillage being the most important method to control weeds to herbicides being the most important tool to control weeds. Herbicides in general provide much better control of weeds than tillage methods and do not have the major issues of soil erosion, moisture loss and breakdown of soil structure. The wide spread use and reliance of herbicides has resulted weeds evolving resistance to herbicides. The herbicide resistance is now widespread and presents one of the biggest threats to global food security. Strategies to provide non-chemical weed control to compliment herbicides are now paramount to reduce the selection pressure for herbicide resistance. One particular method of significant renewed interest is destroying weed seeds at harvest time to interrupt the weed cycle.

Many in crop weeds share a similar life cycle to harvested crops. Once a crop matures and is harvested, there is a broad range of weeds that have viable seeds remaining on the plant above the cutting height of the harvester. These weeds enter the harvester and their seeds either end up in a grain tank, out with straw residues, or out with chaff residues. There are a range of factors that determine where a weed seed will end up at harvest time including moisture content, maturity, and harvester setup. A major factor that determines where a seed ends up is the aerodynamic properties of the seeds or its terminal velocity. Often a weed seed is much lighter than the grain being harvested. Crop cleaning system used during harvesting employ a winnowing action to remove light chaff material from the heavier grain using airflow and mechanical sieving. The light weed seeds are caught in the wind and can exit the back of the harvester sieve. The residues and contained weed seeds are then spread on the ground to be a problem for next year. The residues also contain a proportion of grain being harvested that could not be separated by the harvester. This grain loss has the potential to become a volunteer weed after harvest. There is an opportunity to intercept and destroy weed seeds in the residues before allowing them to become a problem for next year's crop.

One method to destroy these weed seeds is to use a milling technology. Milling technology has been used for particle size reduction of a range of feedstock for over a century. Milling technology can be separated into crushing and impact technology.

The most common crushing size reduction technology is the roller mill. Roller mills have been investigated for the purpose of destroying weed seeds at harvest time. Roy and Bailey (1969) U.S. Pat. No. 3,448,933 describe a roller shear mill for destroying weed seeds out of clean grain screenings. Reyenga (1991) U.S. Pat. No. 5,059,154 describes using a separating device and roller mill to crush foreign matter such as weed seeds. A limitation of the roller mill is the ability to handle the bulk of residue material that contains the weed seeds and thus rely on a separation means to reduce the residue material.

Impact mills use high impact speeds generated by rotating elements to pulverise material. Impact mills have also been of interest for the destruction of weed seeds at harvest.

A widely used type of impact mill is a hammer mill, which uses a rotor with impact elements to pulverise material and a screen to classify the output size distribution. Hammer mills are highly versatile and are able to accept a wide range feed materials.

Plant material such as crop residues is fibrous and difficult to process. The use of hammer mills to devitalise weed seeds in crop residues has been well documented. The use of hammer mills on board a harvester to devitalise weed seeds has been subject of multiple patents (e.g. Wallis (1995) AU1996071759 Bernard (1998) FR2776468B1)).

An advantage of hammer mills is that in addition to impact, they induce crushing, shear and attrition forces that make them particularly useful for size reduction of fibrous materials. Another advantage of hammer mills is that they often have flexible impact elements that are replaceable and can handle some foreign objects without damage.

A further advantage of the hammer mill is that the screen size controls particle fineness and can then control the proportion of weed devitalisation. Control of output size distribution is particularly valuable in the processing of crop residues where material type and moisture conditions change significantly. Change in material conditions result in still similar output size distribution and weed seed devitalisation remains less dependent on material conditions than would be without the use of screens.

A disadvantage of current hammer mills is that the screen which controls particle size distribution determines throughput capacity. In general, to devitalise weed seeds a small screen size is required and hence throughput capacity is limited. A hammer mill with concentric screens of varying sizes has been described by Emmanouilidis (1951) U.S. Pat. No. 2,557,865. The Emmanouilidis mill has a central impact zone and additional screens are used to separate output material into different size fractions. The inner primary zone in the Emmanouilidis mill still dictates capacity and overall size reduction.

A different type of impact mill is a cage mill. A cage mill applies predominantly impact forces and level of size reduction is set through rotational speed and the number of concentric rows of bars. There is no classification of particle size with a cage mill. The impact forces in a cage mill make them suitable for friable or brittle materials and are not widely used for processing fibrous materials. However, one example is described in AU 2001/038781 (Zani) which is proposed for destruction of weed seeds. The Zani cage mill has concentric rows of impact elements supported by a ring. The mill is driven at high impact speed to destroy weed seeds. The arrangement can be neatly integrated into the harvester. The arrangement however has limited capacity and cannot process the entire chaff residue fraction exiting the harvesters sieve. Therefore, the Zani system relied on sieving to concentrate the collect weed seeds for processing.

An increased capacity cage mill is described in WO 2009/100500 (Harrington) to handle the whole chaff material fraction to destroy weed seeds. The Harrington used a large counter rotating cage mill that has fan blades similar to Tjumanok et al 1989 (U.S. Pat. No. 4,813,619) to increase airflow and capacity. This cage mill is large, heavy, requires a complex counter rotating drive and requires considerable power to operate. The system has its own power package and is towed behind the grain harvester. The size, weight and drive, limits options to integrate the cage mill into the harvester. The mill incorporates cylindrical bars that limit impact speeds because of glancing blows. The impact speed therefore has a large distribution. To get sufficient impact energy into weed seeds requires counter rotation of the cage structures.

The current state of the art for seed destroying mill technology is described in PCT/AU2014/218502 (Berry Saunders). Berry Saunders uses a rotor stator cage mill that is much simpler to integrate into a grain harvester than the counter rotation systems. The Berry Saunders mill provides an advance on the Zani cage mill by improving the throughput capacity and seed kill performance of the mill system. It achieves this by using a central distribution element (also described in Isaak (2003) DE 10203502) and angular static bars that are slanted against the rotation of the rotor. A purportedly novel aspect of Berry Saunders mill is the spacing between the angled impact bars determines if a seed will pass through to the next row of impact bars or stay within the current row of impact bars. The size of the seed does not determine if it passes through the row of impact bars or remains.

The relatively simple workings of cage mills which apply predominantly impact and do not use size classification has enabled computer modelling techniques to be used to predict mill performance. The Berry Saunders mill has been optimised using computer modelling techniques to apply the ideal requirements to devitalise weed seeds using impact alone. However, there has been little concern for the airflow component of the power consumption. The rotor bars are narrow with sharp edges resulting in high drag coefficient and turbulence generation. The stator bars are orientated to result in torque converter or water brake dynamometer like turbulence generation and wasted heat generation.

One disadvantage of this approach is that the stator impact bars take up a lot of space radially. This in turns means that adjacent rows of rotating impact bars are spaced a long way apart. For a weed seed devitalisation mill, or a particle destruction mill for that matter impact speed is crucial. When impact bars are spaced widely apart the impact speed difference between each subsequent row is significant.

The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the method and system as disclosed herein.

SUMMARY OF THE DISCLOSURE

In a first aspect there is disclosed a multistage hammer mill comprising:

a plurality of milling stages arranged concentrically about each other; the plurality of milling stages arranged so that substantially all material in a first inner most of the milling stages passes through at least one subsequent adjacent milling stage, the plurality of milling stages including a first milling stage and a second milling stage,

a central feed opening enabling material flow into a primary impact zone of the first milling stage;

the first milling stage comprising an impact mechanism and a first screen arrangement, the impact mechanism located in the primary impact zone and arranged to impact material entering the primary impact zone and accelerate the impacted material in a radial outward direction, the impact mechanism being capable of rotating about a rotation axis, the first screen arrangement disposed circumferentially about and radially spaced from the impact mechanism the first screen arrangement being provided with a plurality of apertures through which impacted material of a first size range can pass;

the second milling stage comprising a second arrangement disposed circumferentially about and radially spaced from the first screen arrangement, the second screen arrangement being provided with a plurality of apertures through impacted material of a second size range can pass, the second size range being the same as or different to the first size range, and one or more impact elements disposed between the first screen arrangement and the second screen arrangement, wherein material entering the second milling stage from the first milling stage is impacted and accelerated by the impact elements and pulverised against the screen arrangement.

In a second aspect there is disclosed a residue processing system for an agricultural machine having a power source with a power take off rotating about a first axis, the residue processing system comprising: at least one residue processing device each having a respective first drive shaft rotatable about a respective axis perpendicular to the first axis; a transmission system coupled between the PTO and each first drive shaft to change a direction of drive from the PTO to each first drive shaft and a belt drive arrangement coupled between the transmission system and each first drive shaft to transfer torque from the PTO to each first drive shaft.

In a third aspect there is disclosed a combine harvester comprising: a power take off (PTO) rotating about a power axis perpendicular to a direction of travel of the combine harvester; least one multistage hammermills according the first aspect, each hammer mill having at least a first drive shaft for imparting rotation to the impact mechanism of the respective hammer mills about respective axes perpendicular to the power axis;

a transmission system arranged to change a direction of drive from the PTO to each first drive shaft; and a belt drive arrangement coupled between the transmission system and each first drive shaft to transfer torque from the PTO to each first drive shaft.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

FIGS. 1, 2 and 6depict an embodiment of the disclosed multistage hammer mill10(hereinafter referred to in general “hammer mill10”). The multistage hammer mill10has a central feed opening12enabling material flow into a primary impact or destruction zone14. An impact mechanism16is located in the primary impact zone14and is capable of rotating about a rotation axis18. The impact mechanism16is arranged to impact the material entering the primary impact zone14and accelerate the impacted material in a radial outward direction. The hammer mill10also has a first screen arrangement20aand at least a second screen arrangement20b. The first screen arrangement20ais disposed circumferentially about the impact mechanism16and forms a boundary of the primary impact zone14. The first screen arrangement20ahas a plurality of apertures22athrough which impacted material of a first size range can pass.

The second screen arrangement20bis disposed circumferentially about and radially spaced from the first screen arrangement20a. The second screen arrangement20bhas a plurality of apertures22bthrough which impacted material of a second size range can pass. The second size range can be the same as or different to the first size range. However in the present illustrated embodiment the second size range is different to the first size range. In particular a lower size limit of the second range is smaller than a lower size limit for the first range. The provision of the first and second screen arrangements20aand20bcharacterised the hammer mill10as being a two-stage hammer mill.

In this particular embodiment the hammer mill10is also provided with an optional third screen arrangement20c. The third screen arrangement is disposed circumferentially about and radially spaced from the second screen arrangement20b. The third screen arrangement20chas a plurality of apertures22cthrough which impacted material of a third size range can pass. The third size range can be arranged to have a lower limit that is the same or smaller than the lower limit of the second size range, although in this particular embodiment the lower limit is smaller for the third size range than the second size range.

The hammer mill10when provided with the third screen arrangement22cconstitutes a three stage hammer mill.

In the following discussion of the hammer mill10the first, second and third are screen arrangements are referred to in general as “screen arrangements20” and the apertures22a,22band22care referred to in general as “apertures22”. The apertures22are of a generally rectangular in shape with rounded corners. As described above, the apertures22are of smaller size for the screen arrangements20with increased radius.

With particular reference toFIG. 2it can be seen that the first screen arrangement20ais formed with at least one (and in this particular embodiment three) openings or gaps24a. The openings/gaps24aare dimensioned to enable the passage of impacted material that is too large to otherwise pass through the apertures22ain the screen20a. This assists in minimising the build-up of oversized material within the primary impact zone14that may otherwise reduce the throughput of material through the hammer mill10. For example this may include pieces of straw or other plant matter which is entrained in the material fed into the hammer mill10through the feed opening12.

Likewise the second and third screen arrangements20band20cmay be provided with one or more (and this embodiment three) openings or gap24band24crespectively to enable the passage of impacted material that is otherwise too large to pass through their respective apertures22. The gaps24also enable the passage of hard materials such as stones to minimise the risk of damage to the respective screen arrangements20.

The openings/gaps24of respective successive screen arrangements at least partially overlap in the circumferential direction. For example there is a circumferential overlap between the gaps24aand24b. Similarly there is a circumferential overlap between the gaps24band24c.

When a screen arrangement20is formed with a plurality of openings/gaps24the openings/gaps24are evenly spaced circumferentially about the respective screen arrangement20.

In this embodiment the arc length of the respective gaps24increases with increased radius from the rotation axis18.

Each of the screen arrangements20, at least when provided with two or more openings/gaps24, may be formed from an identical number of screen segments26. The openings24are formed by appropriately circumferentially spacing apart the respective segments26. The number, spacing and relative position of the gaps24in mutually adjacent screen arrangements20, can be varied by changing the number and arc length of the respective segments26which make up each screen arrangement20. The relative position of the gaps24can also be varied by rotating the screen arrangements20relative to each other. Varying the position of the gaps24between adjacent screen arrangements20can effectively vary the maximum rotation of material about the respective screen arrangement prior to exiting to the next screen arrangement/stage.

A plurality of axially extending supporting ribs28is provided immediately behind each of the screen arrangements20in the radial direction. The ribs28are evenly spaced circumferentially about the respective screen arrangements20. The ribs28on a trailing side of each opening24with reference to the direction of rotation of the impact mechanism16may act as impact ribs28ifor material passing from one milling stage to the next. The impact ribs28ialso assist in slowing down hard materials flowing through the openings24.

Optionally for the third screen arrangement20cat least one rib28gis placed in each of the gaps24c. The ribs28ghave the same shape and configuration as ribs28but acts as an impact bar for particles travelling through the opening24c. The spacing of the rib28gcan increase with each outward screen arrangement and still provide effective impact for fragmenting material passing through the gaps24cdue to the increase in the tangential component of velocity relative to the radial component with increased radial distance from the rotation axis18. Evenly spacing the ribs28gin the gaps24cminimises the chance of material missing the ribs28g. In addition to improving efficiency of fragmentation of the material, when the screen arrangements20are stationary, the ribs28gassist in decelerating hard materials that may be entrained in the flow. This further reduces the likelihood of damage to the mill10. Also, in this regard the ribs28gmay be sacrificial to the extent that they are damaged in preference to the screen arrangement20.

With particular reference toFIG. 3the axially opposite ends of the screen segments26of screen arrangement20aare attached to the upper and lower rings30a. The axially opposite ends of the screen segments26for screen arrangement20bare attached to the upper and lower rings30b. The axially opposite ends of the screen segments26for screen arrangement20care attached to the upper and lower rings30c.

The screen arrangements20are fixed relative to each other by coupling to a common upper annular plate32shown inFIGS. 1 and 4. This forms a screen structure33. The annular plate32is formed with a central opening which constitutes the feed opening12.

The radius of the feed opening12is smaller than the radius of the first (i.e. inner most) screen arrangement20a. This dimensional relationship facilitates acceleration of air and material in the radial outward direction as it enters the primary impact zone14.

Referring particular toFIGS. 2 and 5athe impact mechanism16is provided with a plurality (in this instance six) radially extending flails or hammers34. Each hammer34is coupled to a common central hub36which rotates about the rotation axis18. The hammers34are provided with bifurcated arms38which are pivotally coupled about respective bolts or pins40to the hub36. This enables the hammers34to swing if impacted by a hard foreign object which enters the impact zone14to minimise the likelihood of major damage. A hard foreign object, if not fragmented into pieces small enough to pass through the apertures22, will eventually exit through the gaps24.

Each hammer34has an outer axial edge40which extends for a length marginally smaller than the depth of the impact zone14. This enables the provision of a small clearance between the upper and lower radial edges of the hammers34and the annular plate32and bottom surface of the impact zone14.

The axial edge40is formed with a plurality of spaced apart grooves of flutes44the purpose of which is to assist in fragmenting elongated material such as straw that may enter the feed opening12as well as reduce smearing of material on the screen arrangement20a. An impact side46of the hammers34is substantially planar and lies in the axial plane. A trailing face48of the hammers is scalloped. The purpose of this is to balance the impact mechanism16any radial plane. In this regard the hammers34extend in an axial direction higher than the hub36. In the absence of the scalloping the centre of gravity of the impact hammers34would be axially offset from the centre of gravity of the hub36which may lead to instability together with increased bearing wear and heat generation.

The combination of the impact mechanism16and the screen arrangement20aforms a first milling stage of the multistage hammer mill10.

As can be seen fromFIGS. 2 and 5aembodiments of the hammer mill10are provided with a first plurality of impact elements50adisposed between the screen arrangements20aand20b. The combination of the first plurality of impact elements50aand the second screen arrangement20bforms a second milling stage of the multistage hammer10.

A second plurality of impact elements50bis disposed between the screen arrangements20band20c. The combination of the second plurality of impact elements50band the third screen arrangement20cforms a third milling stage of the multistage hammer10.

The impact elements50a,50b(hereinafter referred to in general as “impact elements50”) between mutually adjacent screen arrangements are evenly spaced apart in the circumferential direction thus forming corresponding circular arrays of impacts elements.

A lower end of each of the impact elements50is fixed a base plate42. An upper end of each of the impact elements50ais attached to a ring52a, while the upper end of each of the impact elements50bis attached to a concentric ring52b. The base plate42also forms the bottom surface of the impact zone14.

As shown onFIGS. 2 and 5b, each impact element50has a first flat surface54that lies parallel to the radial direction of the mill10. However in other embodiments the first flat face54may lie within 20 degrees to a radial direction of the multistage hammermill. Each impact element50also has on its radial inner side a second flat face56that joins, and forms an acute included angle with, the flat surface54. A curved (i.e. non-linear) surface58extends between the flat faces54and56.

The hub36and thus the central impact mechanism16are fixed to the base plate42. Thus the impact mechanism16and the impact elements50a driven together. When the impact elements are rotating about the rotation axis18the first flat face54is a leading face of the impact element50and provides for improved impact speeds. The curved surface58is a trailing surface and assists in reducing drag and turbulence. The second flat face56being at the acute angle relative to the first flat face54minimises sidewall impact of material moving radially outward's. This assists in improving airflow and chaff flow capacity.

The entire assembly of the base plate42, impact elements50and impact mechanism16may form a replaceable unit. Additionally the flails34can be individually replaced by decoupling from the central hub36. Also individual impact elements50or separate complete arrays of arrays of impact elements50may be replaceable.

The combination of the impact mechanism16and the impact elements50which are both attached to the base plate42forms a rotor structure60. The screen structure33inter-fits with the rotor structure60in a manner so that the annular plate32overlies the rings52a,50band the base plate42; the first screen arrangement20alocates between the hammers34and impact elements50a; the second screen arrangement20binterposes between the impact elements50aand50b; and the third screen arrangement20csurrounds the impact elements50b. A housing (shown inFIG. 13b) extends about the outer most screen arrangement20and is used to convert the pressure generated by the rotor into velocity at the exit. A discharge opening is formed in the housing. Material exits the multistage hammer mill through the discharge opening and is spread by the air flow generated initially by rotor structure60in particular the impact mechanism16.

If desired the screen structure33can also be driven to rotate about the rotation axis18. The screen structure33can be rotated in the same direction or in an opposite direction to the impact mechanism16/rotor structure60.

The general operation of the multistage hammer mill10is as follows. Material enters through the feed opening12and flows in the radial direction by airflow generated by the impact mechanism16. While in the primary impact zone14the material is accelerated by the hammers34and undergoes sheer, crushing, impact and attrition forces between the screen arrangement20aand the hammers34multiple times. If the material is small enough to pass through the apertures22ait passes to the next (second) milling stage constituted by the impact elements50aand the second screen arrangement20b. However, if the material isn't small enough, it has a maximum of approximately ⅓ rotation of the mill to reach an opening24awhere it subsequently passes to the second milling stage. In this way, over processing of material is prevented in an application where capacity is very important. As previously described above the number and/or relative position of the openings24can be adjusted to vary the maximum rotation.

Material in the second milling stage is impacted and accelerated by the impact elements50aand pulverised against the screen arrangement20b. Material that is small enough to pass through the apertures22benters the next (third) milling stage constituted by the impact elements50band the third screen arrangement20c. Material that is not small enough passes into the third stage through an opening24b.

Material in the third stage is impacted and accelerated by the impact elements50band pulverised against the screen arrangement20c. Material that is small enough to pass through the apertures22centers a discharge chamber formed between the housing and the third screen arrangement20c. Airflow in the discharge chamber exits together with entrained milled material through the discharge opening.

Embodiments of the disclosed multistage hammer mill have an advantage over traditional hammermills because reducing the screen size with each row allows smaller particles passing through quickly to the next stage. This reduces the amount of over pulverising on each row to improve the overall capacity of the mill for a given size.

Embodiments of the disclosed hammermill approach are believed to have an advantage over the Berry Saunders mill by virtue of the screen arrangements20enabling control over particle size. In particular screen arrangements20of different aperture22sizes can be interchanged to facilitate adjustment to target different weed species. Additionally, the screen arrangements20are radially narrow and therefore rotating impact elements50can be close together radially and operate at similar tip speeds. It is believed that the impact elements operating at similar tip speeds improve seed kill effectiveness and energy efficiency. Additionally, the multistage hammer mill is able to provide shear, crushing and attrition to material for more effective processing of fibrous crop materials.

In one embodiment the output airflow and chaff material can be used to assist the spread of a straw chopper by directing onto the chopper tailboard, which has either stationary vanes or rotating spinners or otherwise to spread the residue material.

In another embodiment the output of the material from the disclosed mill can be directed into a straw chopper itself. By combining chopper and the multistage hammermill air flows the overall performance can be improved. For example the chopper and multistage hammermills will require a certain amount of air flow operating individually to process and distribute residue material. By operating in series, this amount of air flow pumping could be reduced and still be able to process and distribute material effectively. This could be achieved by reducing the air flow effect of either or both of the chopper and impact mill.

FIGS. 7aand 7billustrates a part of a residue processing system80which comprises at least one but in this case two multistage hammer mills10aand10bin a side-by-side juxtaposition. The residue destruction system80may also include a chopper (not shown) arranged relative to the hammer mills as described above. The hammer mills10aand10b(hereinafter referred to in general as “hammer mills10”) in this embodiment are of the same structure and design as the hammer mill10.

The residue processing system80includes a drive system82for driving the hammer mills10. The drive system82has a main pulley84for driving a first belt86and a second belt88. The first belt86runs about an idler90, a drive pulley92aand a drive pulley92b. An outer surface of the belt86drives the pulley92awhile an inner side of the belt86drives the pulley92b. As a consequence the pulleys92aand92brotate in mutually opposite directions. The pulley92aimparts torque to a drive shaft93aof the impact mechanism16and the corresponding rotor structure60of the mill10a. The pulley92bimparts torque to a drive shaft93bthe impact mechanism16and the corresponding rotor structure60of the mill10b.

The second belt88runs about an idler94and drive pulleys96aand96b. An outer surface of the belt88drives the pulley96bwhile an inner side of belt88drives the pulley96a. Accordingly the pulleys96aand96brotate in mutually opposite directions. The pulley96aimparts torque to a drive shaft95aof the screen structure33of the mill10awhile the pulley92bimparts torque to a drive shaft95bthe screen structure33of the mill10b.

It should be recognised that the pulleys92aand96arotate in mutually opposite directions; as do the pulleys92band96b. Thus the drive system82operates to drive the rotor structures60and screen structures33for each hammer mill10in mutually opposite directions.

The main pulley84is coupled to a transmission system98. In the present illustrated embodiment the transmission system98comprises a pulley100which is coupled by shaft102to a gearbox104which has an output shaft106that drives the pulley84. The pulley100is driven by a belt108which receives power from a power source (not shown) that drives the belt108about a power axis that is perpendicular to the shaft106and to the rotation axes of the shafts93a,93b,95aand95b. The use of drive belts86and88to impart torque to the hammer mills10assists in reducing shock loads on the gearbox104.

The residue processing system80may be part of an agricultural machine such as but not limited to a combine harvester.FIGS. 8aand 8bare schematic representations of a rear portion of a combine harvester120depicting a chopper122with radial chopper blades123, a tailboard124and fitted with two multistage hammer mills10aand10b(hereinafter referred to in general as “hammer mills10”). The chopper122is driven to rotate about an axis126which is parallel to a power take off shaft (not shown) of the combine harvester120. The power take off shaft extends in a direction perpendicular to the direction of travel of the combine harvester120.

The hammer mills10are driven by the drive system82which is also powered by the power take off shaft of the combine harvester120. Specifically the belt108is engaged with a pulley (not shown) mounted on the power take off shaft. It should be appreciated here that the hammer mills10are mounted in a manner so that their respective impact mechanisms16are rotated about axes that are perpendicular to the power take off shaft and the axis126. In the arrangement shown inFIGS. 8aand 8bmills10are arranged so that their discharge flow is directed or otherwise fed into the chopper122. Thus the airflow of the hammer mills10is added to the airflow of the chopper122which may provide a synergistic effect. More particularly the airflow from the hammer mills10may be added to the respective axial end regions of the chopper122. This may assist in providing greater sideways or lateral spreading of the material from the chopper122. This effect may be further enhanced by installing curved blades or fins125in an outlet chute127of the chopper122at least near or adjacent its axial end regions.

In the arrangement shown inFIG. 9the discharge flow from the hammer mills10is directed onto the tailboard124of the chopper122to assist in spreading their respective discharged processed materials.

FIGS. 10aand 10bshow an alternative form of drive system82afor transferring drive from a power take off shaft130of the combine harvester120to the hammer mills10aand10b. In these Figures the same reference numbers are used to denote the same features as described for the system82shown inFIGS. 7aand7b.

The drive system82ahas many similarities to the drive system82shown inFIGS. 7aand 7bin that it includes the gearbox104driven by the PTO130via the belt108and pulley100; and the gear box104rotates a pulley84that drives the hammer mills10aand10b. However the drive system82aalso includes a PTO shaft132connected between the gear box driveshaft106and the drive pulley84. The drive pulley84drives to belts86and88. The belt86engages the pulley92ato drive the driveshaft93afor the impact mechanism of the mill10a. The drive belt88engages the pulley92bto drive the driveshaft93bfor the impact mechanism16of the mill10b. An idler pulley90is provided to enable tension variation in the belt88. By this arrangement the shafts93aand93bare driven in the same direction but the screen arrangements20of the mills10are not driven, rather they remain stationary.

FIGS. 11aand 11bshow yet a further variation of the drive system82b, in which the same reference numbers are used to denote the same features of the drive system82shown inFIG. 10aand 10b. In the system82bthe impact mechanisms16of the hammer mills10are driven by a single belt89which engages the pulley84, the idler pulley90and pulleys92aand92b. The gearbox104receives power from the harvester PTO130by a two belts108aand108band an intervening jack shaft134.

FIG. 12shows a further drive system82cwhich is somewhat of a hybrid between the system shown inFIGS. 10aand 11a. In the system82cdrivers received from a belt108b(fromFIG. 11a) to drive pulley100coupled to a gearbox (not visible inFIG. 12). The gearbox drives the pulley84to rotate about an axis perpendicular to that of the pulley100. The pulley84drives belts86and88. These belts engage with pulleys92aand92bof corresponding hammer mills10. Due to the drive arrangement the hammer mills10are driven in the same direction as each other. Idler pullies91are provided for tensioning the belts86and88.

In the drive system82ca fan140is optionally incorporated in the pulley84. The pulley84is formed with a belt engaging ring142, a central hub144and a plurality of pitched fan blades146emanating from the hub144to the inside of the ring142. In this way the pulley84acts as a cooling system for the gearbox to which it is connected. It should be appreciated that other pulleys described in earlier drive systems may also incorporate a similar fan to provide cooling to gearboxes or indeed other parts and components including the hammer mills10themselves. For example the pulleys100shown inFIGS. 7aand 10acan be formed with fans100.

It will be also recognised that in each of the described residue processing systems80, drive/torque from the PTO130is transmitted through 90° to rotate shafts92,93. The shafts92and93are shown extend in a vertical plane when mounted on a harvester120, but could be slanted towards the front of the harvester or towards the rear of the harvester.

FIGS. 13aand 13bdepict a possible orientation and juxtaposition of two hammer mills10when rotated in the same direction and mounted on a combine harvester.FIG. 13ashows the hammer mills10with their respective covers148on, whileFIG. 13bshows the same arrangement but with the covers148off. Here both of the hammer mills10, and more particularly the impact mechanisms16are rotated in a clockwise direction as indicated by the arrows drawn on the respective upper annular plates32. The hammer mills10are mounted on a common base plate150. Each base plate has a substantially circular portion152and an outlet portion154. The hammer mills10are eccentrically mounted on the respective circular portions152so that a radial distance156between the outer peripheral radius of the hammer mills10and the edges of the circular portions152increases in the direction of rotation toward the outlet portion is154. This assists in airflow through the hammer mills10.

Whilst a number of specific embodiments of the mill and residue processing system have been described, it should be appreciated that the mill and system may be embodied in many other forms. For example the illustrated embodiment shows a three stage hammer mill with respective screen arrangements20each having apertures22of progressively smaller dimension with distance away from the rotation axis18. However in one embodiment the size of the apertures22can be the same for all of the screen arrangements20. Alternately the size the apertures22can be arranged so that the size stays the same or decreases with increased radius from the rotation axis18relative to the aperture size of a radially inward adjacent screen arrangement20. In yet a further variation the orientation of the apertures may vary between respective screen arrangements. For example the apertures22amay be of a rectangular shape having a major axis parallel to the rotation axis, while the apertures22bmay be of the same size and shape of apertures22abut orientated so that their major axis is +45° to the rotation axis18, and apertures22cagain of the same size and shape but orientated so that their major axis is −45° to the rotation axis18.

In other variations the mill10may be formed with screen arrangements20that have either: no gaps24; or one or more gaps in the inner most screen arrangement20aand either no or one or more gaps in radially outer screen arrangements. Also, while the illustrated embodiment shows gaps24in successive screen arrangements20having some degree of overlap, in other embodiments the gaps in respective screen arrangements may be offset from each other so as to not overlap.

In each of the illustrated embodiments of the hammer mill10the first screen arrangement20ais radially adjacent the central impact mechanism16and associated flails/hammers34. However this is not an essential requirement. One or more circumferential arrays of impact elements (for example similar to the impact elements50) may be interposed between the impact mechanism16and the first screen arrangement20a. This is exemplified inFIG. 14which shows embodiment of the multistage hammer mill10chaving: an impact mechanism16with flails/hammers34rotatable about a rotation axis18; a first screen arrangement20a; a second screen arrangement20b; and a first plurality of impact elements50ais disposed between the screen arrangements20aand20b; as per each of the earlier described embodiments of the hammer mill10. However the hammer mill10calso includes two circumferential arrays A1and A2of impact elements50. The radially inner array A1of impact elements50may be: stationary; arranged to rotate in the same direction as the impact mechanism16; or, arranged to rotate in an opposite direction to the impact mechanism16. The radially outer array A2of elements50may be arranged to rotate with the impact mechanism16. In a modified form of the hammer mill10c, the radial inner array A1of impact elements50may be dispensed with so that the modified hammer mill10cincludes only the rotating array A2interposed between the impact element16and the first screen arrangement20a. In these embodiment the impact mechanism18, the arrays of impact elements A1, A2and the first screen arrangement20amake up the first hammer mill stage.

FIGS. 15aand 15bshow further possible modification to the screen segments26which make up the respective screen arrangements20. Here a plurality of ribs28fis fixed to a radial inner side of the screen segments26. The ribs28fextend in the axial direction and are circumferentially spaced apart. Conveniently respective ribs28fare located in the space between mutually adjacent columns of apertures22. The addition of ribs28fslow the material traveling around the screen arrangements20, keeping the material in the impact zone for longer and thereby increasing the shear and impact forces on the material. Any one of the screen arrangements20can be provided with one or more of the ribs28f.

FIG. 16illustrates a modified or alternate form of the screen arrangements20a′,20b′ and20c′ (hereinafter referred to in general as screen arrangements20′). The substantive differences between the screen arrangements20′ and the screen arrangements20are as follows. In the screen arrangements20′ upper rings30au,30bufor the screen arrangements20a′,20b′ extend laterally from a radial outer side of the respective screen arrangements to a location close to (but not touching) a radial inner side of the screen arrangements20b′ and20c′ respectively. This avoids the creation of a substantial gap between the upper surface of the rings52and the inside surface of the annular plate32. By way of comparison phantom line F in this Figure shows the location of the radial outer side of the upper rings30band30c.

Additionally in screen arrangements20′ the apertures22include an uppermost row apertures22u, for at least the second and third milling stages, that extend in the axial direction to at least an under surface of the upper rings30auand30bu. A benefit of this arrangement is that material located in a region R between the inside of the annular plate32and the rings52can pass through the apertures22uto the next milling stage. This minimises the risk of material building up in the region R.

FIG. 17illustrates further possible variations of the disclosed hammer mill10in which axial and radial scrapers51and53respectively, are associated with the impact members50. This association is by way of the scrappers being provided on the rings52aand52bof the corresponding circular array of impact members. The axial scrapers51are formed on the upper surfaces54aand54bof the corresponding rings. The scrapers51act to clear material in the regions R and assist in directing that material to pass through the apertures22u. The scrapers53are formed on a radial outer circumferential edge of the rings52aand52band extended to a location close to but not touching the adjacent screen arrangements20,20′. The purpose of the scrapers53is to also assist in directing material to pass through the apertures22u. Moreover the scrapers53assist in preventing a build-up of material between the rings52a,52band the adjacent screen arrangements.

FIG. 18shows another modification where a screen segment26adjacent one of the openings24of a screen arrangement20is replaced with a pulverising block160. The pulverising block160has a solid front face formed with a sawtooth like profile. The block160provides an additional grinding and crushing zone within a milling stage. More than one block160can be incorporated in each milling stage. For example one screen segment26immediately adjacent an opening24could be replaced with a block160. For a screen arrangement having three openings24there would then be three blocks160. Ideally each block160would be on a leading side of the opening24with reference to the direction of rotation of the corresponding impact elements50.

FIG. 19shows is a further slight modification or variation in which the ribs28that would otherwise be on adjacent sides of an openings24are replaced with plates28pthat are angled in the direction of rotation of the impact mechanism16and impact elements50. This would serve to increase the velocity of material and air exiting the screen arrangement for increased capacity. This may be particularly beneficial for the outermost milling zone/screen arrangement20.

In a further variation the cross sectional shape of the impact elements50may be varied for that specifically shown inFIGS. 2 and 5aand5b. For example the impact elements50may have a simple circular cross-sectional shape.

Embodiments of the disclosed multistage hammer mill10have a minimum of two milling stages. The embodiment described and illustrated in the present drawings is provided with an optional third milling stage. It should be understood however that additional milling stages can be sequentially added with increased radius from the rotation axis18, each additional milling stage comprising a screen arrangement and an array of impact elements50. It is also possible in one embodiment for the milling stages to be arranged so that material milled in the first milling stage passes through at least one subsequent adjacent milling stage, or alternately through all of subsequent milling stages.

As previously described the provision of the openings24in the screen arrangements20is an optional feature. In one variation an embodiment of the hammer mill10may be formed in which the first milling stage is formed with no openings24in the first screen arrangement20a. In this way hard materials are prevented from passing through sequential milling stages and into possible other mechanisms in a harvester such as a chopper. In such a variation the hammer mill10may also be provided with one or more sensors and an alarm to notify an operator of the existence of hard materials circulating within the first milling stage.

Weed seeds and crop residue material have varying properties. The amount of destruction (i.e. crushing, shearing, impact and attrition) needed depends on the seeds being targeted and the residue material that is being processed. Embodiments of the disclosed multistage hammer mill10enable the degree of destruction of residue material to be increased by:

1) increasing the relative rotational speed to increase impact and shear forces;

2) reducing the size of the screen openings22to keep larger material in the impact zone for longer;

3) increasing the circumferential spacing of the openings24allowing larger material to be processed for longer before passing through;

4) providing the inner ribs28fto increase residence time in the impact zones.

In a variation to the above described drive system82the main drive98may be in the form of a hydraulic pump powered by the PTO130which provides hydraulic fluid to a hydraulic motor coupled which drives the shaft106. This avoids the need for the gearbox100. A potential benefit in using the hydraulic motor is better speed control and the inherent ability to provide a soft start. This method is believed to be more efficient than directly driving two mills individually as it requires only one hydraulic motor which can be operated at optimum speed (slower) and pressure.

It should also be understood that when the residue processing system80or the combine harvester120has only a single residue processing device the corresponding drive system82is simplified by requiring: only a single drive belt drive and a single shaft in the event that the residue processing system has only one rotary component. In the event that the single residue processing device has counter rotating components then two belts will be required however the number of pulleys required to be driven is reduced in comparison to the above described processing systems and combine harvesters having two or more side-by-side residue processing devices.

Also in the above-described residue processing systems80the residue processing devices are exemplified by embodiments of the disclosed hammer mill10. However the residue processing system80may use different types of residue processing devices such as but not limited to, pin mills, cage mills single stage hammermills, chaff spreaders and straw choppers. That is, the residue processing system80and the associated drive system82is independent of the specific type of residue processing device.

In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word “comprise” and variations such as “comprises” or “comprising” are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the hammer mill and residue processing system as disclosed herein.