WO2002032209A1

WO2002032209A1 - A rotary soil engaging member and a material for use therein

Info

Publication number: WO2002032209A1
Application number: PCT/GB2001/004607
Authority: WO
Inventors: Philip Wright; Charles Creyke
Original assignee: Simba International Ltd
Current assignee: Simba International Ltd
Priority date: 2000-10-20
Filing date: 2001-10-16
Publication date: 2002-04-25
Anticipated expiration: 2003-04-20
Also published as: AU2001294058A1

Abstract

A rotary soil engaging member (20, 30) for use in treating soil comprises a soil engaging peripheral surface made of a resilient cellular material, such as microcellular polyurethane. The material has a shore hardness from 5 to 50 and a ball rebound test parameter of 30-80 %. A composite material for use in such a soil engaging member comprises a reinforcing web of, e.g. braided polypropylene and a resilient cellular material such as microcellular polyurethane surrounding the web. In another aspect a method of making such a soil engaging member comprises the steps of providing a mould, arranging a plurality of retaining members in the mould, arranging the reinforcing web around the retaining members, injecting resilient cellular material into the mould and withdrawing the retaining members from the mould.

Description

A ROTARY SOIL ENGAGING MEMBER AND A MATERIAL FOR USE THEREIN

The invention relates to a rotary soil engaging member and particularly but not exclusively limited to a rotary soil engaging member for soil tillage.

The use of rotary soil engaging means has become an important operation in the process of land management including soil tillage, crop establishment, crop growing and crop harvesting. Two modes of operation are generally practised. Firstly, when the soil is in situ a rotary soil engaging means traverses the soil carrying out its soil treatment operation. Secondly, during other soil treatment operations, for example soil cleaning and root harvesting, the rotary soil engaging means can be static and the soil passes the soil engaging means to be treated thereby.

Originally, rotary soil engaging means in the form of wooden rollers were pulled by hand or by horse. Such wooden rollers were replaced by cast iron rollers. Those rollers underwent a series of innovations including the attachment of scrapers to the rollers, the incorporation of differential rotational speeds of different parts of the roller, a profiling of the soil engaging circumferential surface of the roller to include, for example a continuous rib (such as a Cambridge roll) or sprocket-like teeth (such as a crosskill roller). Cast iron rollers have subsequently been replaced by steel rollers and rollers made in both materials and to various basic designs are available today. The use of rotary soil engaging means is now established as an accepted and beneficial way of: breaking clods to improve tilth, consolidating soil to increase seed-soil contact, levelling the soil surface to encourage accurate cutting/harvesting of crop, and pest control management. However, in moist conditions soil can adhere to the soil engaging surface of such rollers. Such adhesion destroys the effectiveness of the roller.

Roller developments in the post-war period have seen the use of rubber press wheels primarily operating singly or in pairs for consolidating soil around seeds sown in rows. It was established that a suitable material, e.g. rubber, when rotating, created a leading edge flex, a flat foot print and a trailing edge flex which effected a degree of self-cleaning of the roller surface. The use of rubber as a resilient material for the construction of rotary soil engaging means has followed specific identifiable routes, namely pressurised or unpressurised tyres and purpose built airless rubber rollers.

In designing a roller or other rotary soil engaging means it is important to provide a continuously "clean" circumferential soil engaging surface to be presented to the untreated soil, a substantially equal contact pressure both axially of the roller and longitudinally over the whole circumferential surface of the rotary soil engaging member, the ability deliberately to render the contact pressure unequal so as to enable compatibility with a desired application, differential rotational speed across the width of a rotary soil engaging member comprising multiple rotary elements, 100% efficiency in terms of soil contact across the "foot print" of the rotary soil engaging member and where multiple separate rotary elements are provided, no soil ingress between individual elements.

In the case of cast iron and steel rotary soil engaging members, although the requirement of equal spacial pressure across the width of the member, differential rotational speeds and 100% effectiveness across the width of the roller are met, such rotary soil engaging members do not self-clean, do not allow deliberate pressure differentials and do suffer from soil ingress between individual rotary elements on a rotary soil engaging member. Particularly important are the self-cleaning and soil ingress characteristics since the lack of self-cleaning requires a separate cleaning system to be provided which may not be consistently effective and the allowance of soil between rotary elements on the rotary soil-engaging member results in increased wear and tear, a higher maintenance load, possibly greater failure rate, and impaired performance in general.

Both pressurised and unpressurised car tyres and lorry tyres experience only partial self-cleaning. The side walls of the tyres provide a stress concentration at the edges of each tyre which means that tyres do not provide an equal spacial pressure across the width of the soil engaging surface thereof. In the light of the stress concentrations, a deliberate pressure differential cannot be incorporated. Also, the flexing of the tyre walls under load move the ground engaging (tread) parts of the tyres apart which means that there is not 100%> efficiency of soil treatment across the width of the rotary soil engaging member and also soil ingress between individual rotary elements, i.e. tyres, is possible. In the case of purpose designed airless rubber wheels or rollers, self-cleaning is possible but as with tyres there is neither equal spacial pressure or 100% effectiveness across the width of a wheel or roller. Ingress of soil and/or dust is also possible. Where multiple roller elements are provided and where the roller is unitary different rotational speeds across the width of the roller is precluded.

Increased knowledge and awareness of soil, water, crop growing and pollution has made farmers look towards the most efficient, profitable and environmentally sustainable methods of crop production. It is against that background that the use of rotary soil engaging members satisfying the above identified features can be incorporated into an agricultural system to save time, energy and detrimental soil compaction provided that spacially equal and consistent consolidation of soil to the desired amount is achieved. Spacially equal and consistent soil consolidation enables maximum infiltration of water whilst at the same time creating a soil tilth that is spacially equal and consistent so enabling seeds to have equal and consistent seed soil contact encouraging even germination of seeds. The soil surface profile created as a reflection of the profile chosen for the circumferential surface of the rotary soil engaging member has a direct effect on the capability of the soil to hold and absorb water. The aforementioned prior art systems which do not consolidate the soil spacially equally dictates that there is considerable variation of contact pressure on the soil engaging circumferential surface of the rotary soil engaging member. When used in the context of a roller, a gap may occur which is not consolidated leaving a continuous ridge. Alternatively a ridge may be created where self-cleaning has failed. Such ridges on the surface of the soil engaging circumferental means may create furrow-like channels in the soil which are conducive to swift run off of water. Such run off transports chemicals and sediment which contribute to pollution of watercourses. All of the tyre systems use a rubber generally with a shore hardness in the range 45-90 which, in order to provide the flexibility that contributes to "self-cleaning", requires a backing of void, i.e. zero air pressure or low air pressure. In order to attach such tyres to the hub "tyre walls" are required which present themselves "end on" when contacting the ground. During operation under load the tyre walls flex outwardly which precludes the assembly from working as a roller with 100% soil contact across the width thereof and prevents equal contact pressure across the width of the roller. It is an object of the present invention to provide an improved rotary soil engaging member.

According to a first aspect of the invention there is provided a rotary soil engaging member for use in treating soil comprising a soil engaging surface of a resilient cellular material having shore hardness in a range from 5-50 and a ball rebound test parameter of 30-80%.

Such a rotary soil engaging member satisfies all of the features set out above as desirable in a rotary soil engaging member. In particular, the rotary soil engaging member made from the material stated above transmits forces equally across the width of the member to the soil to and from the axis thereof, creating a transversely equal contact pressure with, in turn, a spacially equal consolidation of treated soil.

The rotary soil engaging member may comprise a plurality of rotary soil engaging elements assembled together, each made from the aforesaid material. Such an arrangement allows differential rotational speeds of the individual elements but the cellular nature of the material means that the side walls of the individual elements do not flex outwardly under load. Consequently, the individual elements can be arranged closely together and will not move apart under load thereby preventing soil ingress in-between individual elements of the rotary soil engaging member. In a preferred embodiment the individual elements of the rotary soil engaging member are compressed axially, most preferably by between 1% and 10%) of the length of the rotary soil engaging member in its uncompressed state. Such an arrangement further serves to prevent ingress of soil inbetween rotary soil engaging elements of the rotary soil engaging member. The compression also does not disturb the circumferential soil engaging surface of each rotary soil engaging element.

According to another aspect of the invention there is provided a resilient cellular material for use in a rotary soil engaging member having shore hardness in the range from 5-50 and a ball rebound test parameter of 30%-80%. Preferably the material is elastomeric. Most preferably the material is centrifugally moulded to form the rotary soil engaging member.

The material is preferably solvent free.

The cellular nature of the material is produced by foaming. In particular, the material is "water blown". In other words, during the formation of the material water is incorporated into the process which subsequently splits into its component hydrogen and oxygen gases. Those hydrogen and oxygen gases subsequently form gas bubbles within the material to produce the cellular nature thereof. Most preferably the material is microcellular.

In a most preferred embodiment the material is an elastomeric centrifugally moulded water blown solvent free resilient cellular material. In particular, it is preferred that the material is a cellular polyurethane.

The rotary soil engaging member may be a rotary self-cleaning dibbler means. Alternatively, it may comprise a rotary self-cleaning mulch holding means arranged in conjunction with disc cutting means. Still further, the rotary soil engaging member may comprise a rotary self-cleaning disc cleaning, depth control/mulch holding means. In a further embodiment the rotary soil engaging member may comprise a rotary self-cleaning press wheel or press ring which provides spacially equal consolidation, such an arrangement replacing purpose designed airless tyres. The rotary soil engaging member could comprise a rotary self-cleaning roller having any desired profile. The rotary self-cleaning roller could be used as a levelling or cultivation means. The applicants have also found that incorporation of a matrix produces extremely advantageous characteristics.

According to a third aspect of the invention there is provided a rotary soil engaging member for use in treating soil comprising a soil engaging part of composite material, the composite material comprising a reinforcing material and a resilient cellular material surrounding the reinforcing material. According to a fourth aspect of the invention there is provided a composite material for use in a rotary soil engaging member, the material comprising a reinforcing material and a resilient cellular material surrounding the reinforcing material.

Preferably the reinforcing material comprises a webbing defining spaces therethrough. Most preferably the webbing defines a rectangular mesh, i.e. the spaces are rectangular. The rectangular spaces are preferably square, preferably having a side length of 10-30mm, most preferably 20mm. The spaces are dimensioned so as to give good reinforcement of the cellular material but still to allow the resilient material to surround the reinforcing material without leaving voids.

The reinforcing material is preferably a plastics material. In a preferred embodiment the reinforcing material is made from polypropylene.

The material may be a multistrand woven, braided or knitted material. Preferably, the weave, braiding or knitting of the strands is loose so as to allow ingress of the resilient cellular material between individual strands. The reinforcing material is preferably in the form of a hoop of material. In such a case, the reinforcing material hoop may be arranged substantially concentrically with the rotary soil engaging member within the resilient cellular material.

Most preferably two hoops of reinforcing material are arranged within the resilient cellular material of the rotary soil engaging member, one each side of circumferential centre line of the member.

The rotary soil engaging member according to the first or third aspects preferably includes a plurality of axially extending bores therethrough.

Most preferably the rotary soil engaging member comprises an annular body. In such a case the bores are preferably arranged regularly spaced around the annular body. Preferably, the rotary soil engaging member comprises an annular part having a plurality of outwardly projecting tread members extending therefrom. In that case, the bores through the body are preferably arranged at corresponding angular positions to the tread members. Most preferably, each tread member has two bores associated with it.

According to a fifth aspect of the invention there is provided a method of making a rotary soil engaging member comprising the steps of providing a mould, arranging a plurality of retaining members within the mould, arranging a reinforcing material around the retaining members so as to retain the reinforcing material within the mould, injecting a resilient cellular material into the mould so as to surround the reinforcing material then withdrawing the retaining members from the mould.

Preferably the resilient cellular material is injected then centrifugally moulded within the mould. Most preferably the resilient material is water blown, centrifugally moulded.

Examples of prior art and embodiments of the invention will now be described in detail by way of example and with reference to the accompanying drawings in which:-

FIGS. la, b and c are schematic cross-sections of prior art rotary soil engaging members,

FIG.2 is a cross-section through part of a rotary soil engaging member in accordance with the invention,

FIG.3 is an end elevation of the rotary soil engaging member of FIG.2,

FIG.4 is a schematic cross-section of the rotary soil engaging member of FIGS.2 and 3 showing the axial compression applied to the member,

FIG.5 illustrates three configurations of rotary soil engaging member in conjunction with cutting discs,

FIG.6 is a perspective view of a mould for rotary soil engaging member,

FIGJ is a view similar to FIG.6 showing the matrix arranged around the pegs,

FIG.8 is a view of the rotary member showing the matrix in place within the body of the member, and

FIG.9 is a view of the rotary member showing the bores formed by removing the pegs from the mould, with the matrix shown in broken lines. In FIGJa a roller 10 comprises a central axle 12 carrying a series of tyres, for example car tyres 14. Each tyre comprises a tread part 16 and side walls 18.

In use, load is applied downwardly to the axle 12 and the roller 10 is pulled across the ground so that the tread parts 16 of the tyres 14 consolidate the ground.

As can be seen in FIGJa, the application of load to the axle causes the tyre walls 18 of the tyres 14 to bow outwardly which leaves a substantial gap between the respective tread parts 16 of adjacent tyres 14. Such an arrangement results in soil ingress between adjacent tyres 14 which can increase wear and tear on the roller and thus maintenance costs. Also, the fact that the side walls pass the load from the axle 12 to the tread part 16 means that stress concentrations occur at the edges of the tread part 16 of each tyre 14 where the side walls 18 bear effectively vertically into the soil. Such an arrangement produces unequal spacial distribution of consolidating force across the width of the roller 10.

Similar consequences occur in the rollers shown in FIGSJb and lc. In FIGJb the arrangement is substantially similar to that of FIGJa except the void or gas around which the body of the tyre is formed is insignificant so that under compressive stress the tyre part of the roller 10 is squeezed substantially flat. In FIGJc a larger tyre than those used in FIGJa is applied but similar problems occur with outward flexing of the side walls 18 thereof together with stress concentrations.

Referring to FIGS.2-4, a rotary soil engaging member in accordance with the invention is shown in the form of a roller 20. The roller 20 comprises a hollow cylindrical hub 22 having end flanges 24 extending radially outwardly from each end thereof. A plurality of toroidal soil engaging elements 26 are arranged around the cylindrical hub 22 between the end flanges 24. As can be seen in FIG.4, the soil engaging elements 26 are compressed axially by the end flanges 24 by 1-10% of their axial length as illustrated by the distance D in FIG.4. FIG.5 illustrates three configurations of the rotary soil engaging member in relation to a cutting disc 28. Parts corresponding to parts in FIGS.2-4 carry the same reference numerals.

In the left-hand most embodiment shown in FIG.4 a rotary soil engaging member in accordance with the invention is secured to one side of a cutting disc 28. The rotary ground engaging member acts to consolidate the soil at the side of the disc and also has a cleaning function on the disc. In the middle diagram rotary soil engaging member of the type shown in the left most embodiment is attached to either side of the cutting disc 28. In the right most version shown in FIG.5 a series of cutting discs 28 are located on a central hub 22 and two rotary soil engaging members are located between each disc 28.

The central hub 22 and end flanges 24 which may be made from steel, as all the cutting discs 28.

In all of the embodiments the toroidal soil engaging elements 26 are made from cellular elastomer. In particular, it is preferred that cellular polyurethane and most preferably microcellular polyurethane be used. The cellular polyurethane used by the applicant is manufactured by Green Tyre Ltd of Middlesborough, England and is a water blown centrifugally moulded resilient cellular elastomer having a shore hardness of 5-50 and ball rebound test parameters of 30%>-80%>. In other words, the height of rebound of a steel ball bearing dropped onto the material in accordance with the ball rebound test is 3O%>-80%> of the original height of the ball above the material.

It has been found that the specific combination of a cellular material having a shore hardness 5-50 and ball rebound test parameters 30%>-80%o provides a material which, when used in a rotary soil engaging member for agricultural purposes, produces a self-cleaning member which is compressible and which provides equal spacial load across the width of the soil engaging member. FIGS .2 and 5 illustrate schematically the load applied to the ground by the rotary soil engaging member and it can be seen that the load is substantially equal travelling axially of the soil engaging member. FIG.3 illustrates the stress concentration looking end on of the rotary soil engaging member. As one would expect, the highest concentration comes directly below the centre line of the soil engaging member with less load being applied either side of the centre line. In use, of course, the rotary soil engaging member 20 rolls across the ground so that each part of the ground receives the spectrum of stress shown in FIG.3. Consequently, the ground is treated equally.

The axial compression of the soil engaging elements 26 shown in FIG.4 does not distort the outer circumferential surface thereof unlike the prior art rollers shown in FIGSJa, lb and lc. Likewise, the transmission of load from the hub to the outer circumferential surface of the soil engaging elements 26 is uniform across the axial length thereof, also unlike the embodiments shown in FIGSJa-ac where the load is transmitted via the side walls 18 of the tyre 14. Consequently, stress concentrations acting on the soil are eliminated.

The present invention provides a rotary soil engaging member which is self-cleaning, which provides spacially equal contact pressure across the width thereof, the axial compressibility of the material prevents soil ingress in-between individual elements of a rotary soil engaging member without distortion of the outer circumferential (and ground engaging) surface thereof. The fact that the material is axially compressible without radial distortion also allows differential rotational speed of individual elements of the rotary soil engaging member. Such differential rotational speed is not possible where a single unitary rubber roller is provided. Such a characteristic is particularly useful in applications where the rotary soil engaging member has not just a self-cleaning function but a disc cleaning function as shown in FIG.5. The rotary soil engaging member is compressed axially against the discs 28 and so would tend to wipe the discs 28 clean as they rotated relative to the rotary soil engaging member. In FIG.5 it will be noted that a compression of the cellular material tends to expose more of the cutting disc into the ground and so as the cutting disc emerges from the ground and the resilient cellular material resiles into its natural position any contaminants adhering to the opposite faces of the cutting disc will tend to be wiped off the disc by the wiping action of the returning cellular material. Any resilient cellular material having a shore hardness of 5-50 and bounce parameters of 30%-80% will suffice to perform the functions recited above of the rotary soil engaging member.

FIGS.6-9 illustrate an alternative rotary soil engaging member in accordance with the invention and its method of manufacture.

The completed rotary soil engaging member is shown in FIG.9. In FIG.9, the rotary soil engaging member 30 comprises an annular body 32 having six tread members 34 regularly spaced about the periphery thereof protruding raidally outwardly from the outer peripheral surface of the annular body 32. The annular body 32 is substantially non-hollow. The inner peripheral wall of the annular body 32 may include small inwardly projecting annular lip formations at the top and bottom edge thereof so as to facilitate axial location of the rotary soil engaging member 30 along a hub (not shown).

The annular body 32 is made from a composite material comprising a polypropylene webbing material and polyurethane foam as a continuous phase material. The webbing 36 extends around the circumference of the annular body at a point approximately midway between the inner and outer peripheral walls of the annular body 32. The webbing 36 is shown in broken lines on FIG.9. Six pairs of axial bores are arranged substantially regularly spaced around the annular body so as to extend substantially right the way through the body. Each of the bores 38 is located between the mesh 36 and the inner peripheral surface of the annular body 32. The tread members 34 are substantially triangular in cross-section extending from a wide base adjacent the outer peripheral wall of the annular member 32 to an edge which curves in complementary fashion to the outer peripheral surface of the annular body 32.

As stated above, the mesh is preferably polypropylene mesh. The applicant has found that a light duty cargo netting comprising a square polypropylene mesh with 20mm squares woven into a tube is particularly suitable for the present invention. Such material can be obtained at Union Industries Ltd of Hunslet, Leeds. Preferably the polypropylene has a break strength of 0.8kN. The rotary soil engaging member 30 in accordance with the third aspect of the invention includes the reinforcing material to reinforce the base material. The applicants have found that that improves resistance to splitting and allows the use of one basic flexible specification to apply to the majority of applications including extremes of weight and in the context of use with soils including sharp stones and flints. The applicants have also found that by using the composite material, the requirement of material performance mentioned in the first aspect is not essential.

The bores 38 have also been found to impart additional advantageous characteristics to the rotary soil engaging member. In particular, as the rotary soil engaging member rotates and progressive tread members 34 come into contact with the ground, the weight of the machine comprises the rotary soil engaging member. As shown above in relation to the earlier embodiments of the invention the choice of the resilient cellular material prevents the rotary engaging member from bowing at the side walls when the tread parts are compressed. The compression of the tread member applies a force to the annular body 32 and the bores 38 which are closest to the ground tend to close up slightly. As the weight of the machine is moved off the relevant bores as the rotary soil engaging member rotates, the bores expand again.

The applicant has discovered that such a flexing open and closed of bores in the present invention results in advantageous characteristics of the rotary soil engaging member. In particular, the principle advantage of arranging the peg holes at the angular position of the tread members 34 is that the holes by flexing inwardly tend to reduce the wearing stress on the depression between the treads. Also, the closing and opening action of the holes draws in and expels air which cools the wheels. FIGS.6-9 illustrate the method of manufacture of the rotary soil engaging member 30. In FIG.6 a mould 40 is shown schematically. The mould 40 is in two parts and splits in half along a line around the mid point of the periphery shown in dotted form and indicated generally at A. A series of pegs 42 are arranged in pairs regularly spaced about the mould. The pegs 42 extend through the base and part of the mould into the body of the mould and abut the upper face of the mould. When manufacturing the rotary soil engaging member 30 the mould halves are initially split so that the base part is exposed with the pegs 42 protruding upwardly. The polypropylene mesh 36 is then arranged around the pegs so as to be stretched taut in the mould. The pegs 42 are positioned so that the mesh is located approximately halfway between the inner and outer peripheral surfaces of the completed rotary soil engaging member 30. That can best be seen in FIGJ in which the base part of the mould 40 is shown schematically. In FIG.8 the pegs 42 have been removed from the view of FIGJ for clarity. Once the mesh 36 is arranged around the pegs 42, the top part of the mould 40 is arranged in place and the mould is sealed. A resilient cellular material, such as polyurethane foam is then injected into the mould 40 so as to fill the mould. The section of the mesh with apertures therethrough allows the cellular material to penetrate through the mesh so as to surround it and completely fill the mould. The applicants have discovered that a mesh having an aperture size of 20mm on a side is particularly preferred from the point of view of allowing rapid penetration of the cellular material through the mesh into the mould 40. The cellular material surrounds the mesh completely and fully fills the mould 40 in such a way as to resist delamination of the material on either side of the mesh. After the resilient cellular material has been injected into the mould and has solidified sufficiently, the pegs 42 are withdrawn from the base of the mould and the mould 40 is opened and the moulded product removed. The presence of the pegs 42 during injection of the cellular material results in the formation of axial bores 38 which impart the advantageous characteristics described above.

The rotary soil engaging member 30 made as described above has all of the advantages described in relation to the first and section aspects of the invention. However, the provision of the strengthening mesh material within the rotary soil engaging member means that a lower grade of material can be used without the requirement to meet the material parameter set out in those aspects. It is simply necessary that the continuous phase material which forms the bulk of the rotary soil engaging member be a resilient cellular material so as to provide the self-cleaning facility without the problems associated with rubber tyres including bowing of the side walls of the soil engaging member 30.

In another embodiment, two loops of mesh 36 are arranged around the pegs 42. One loop of mesh is arranged on each side of the centreline of the wheel. In another embodiment, the pegs 42 each comprise two peg halves, one on each side of the mould which, when the mould halves are brought together, are colinear and almost contact each other, with a small space defined between the tips of the peg halves.

Claims

1. A rotary soil engaging member for use in treating soil comprising a soil engaging surface of a resilient cellular material having shore hardness in a range from 5-50 and a ball rebound test parameter of 30-80%.

2. A rotary soil engaging member according to claim 1 in which the rotary soil engaging member comprises a plurality of rotary soil engaging elements assembled together, each made from the resilient cellular material.

3. A rotary soil engaging member according to claim 2 in which the individual elements of the rotary soil engaging member are compressed axially.

4. A rotary soil engaging member according to claim 3 in which the axial compression of the elements is between 1 and 10%) of the length thereof.

5. A rotary soil engaging member according to any preceding claim in which the rotary soil engaging member is a rotary self-cleaning dibbler means.

6. A rotary soil engaging member according to any of claims 1 to 4 in which the member comprises a rotary self-cleaning mulch holding means arranged in conjunction with disc cutting means.

7. A rotary soil engaging member according to any of claims 1 to 4 in which the rotary soil engaging member comprises a rotary self-cleaning disc cleaning, depth control/mulch holding means.

8. A rotary soil engaging member according to any of claims 1 to 4 in which the rotary soil engaging member comprises a rotary self-cleaning press wheel or press ring.

9. A rotary soil engaging member according to any of claims 1 to 4 in which the rotary soil engaging member comprises a rotary self-cleaning roller having any desired profile.

10. A rotary soil engaging member according to claim 9 in which the rotary self-cleaning roller is used as a levelling or cultivation means.

11. A resilient cellular material for use in a rotary soil engaging member having shore hardness in the range from 5-50 and a ball rebound test parameter of 30%>-80%.

12. A resilient cellular material for use in a rotary soil engaging member according to claim 11 in which the material is elastomeric.

13. A resilient cellular material for use in a rotary soil engaging member according to claim 11 or 12 in which the material is centrifugally moulded to form the rotary soil engaging member.

14. A resilient cellular material for use in a rotary soil engaging member according to claims 11, 12 or 13 in which the material is solvent free.

15. A resilient cellular material for use in a rotary soil engaging member according to any of claims 1 1 to 14 in which the cellular material is produced by foaming.

16. A resilient cellular material for use in a rotary soil engaging member according to any of claims 11 to 15 in which the material is water blown.

17. A resilient cellular material for use in a rotary soil engaging member according to any of claims 11 to 16 in which the material is an elastomeric centrifugally moulded water blown solvent free resilient cellular material.

18. A resilient cellular material for use in a rotary soil engaging member according to any of claims 11 to 17 in which the material is cellular polyurethane.

19. A composite material for use in a rotary soil engaging member, the material comprising a reinforcing material and a resilient cellular material surrounding the reinforcing material.

20. A composite material according to claim 19 in which the reinforcing material comprises a webbing defining spaces therethrough.

21. A composite material according to claim 19 or 20 in which the webbing defines a rectangular mesh.

22. A composite material according to claims 19, 20 or 21 in which the rectangular spaces are square.

23. A composite material according to claim 22 in which the square spaces have a side length of 10-30mm.

24. A composite material according to claim 22 in which the square spaces have a side length of 20mm.

25. A composite material according to any of claims 19-25 in which the reinforcing material is a plastics material.

26. A composite material according to any of claims 19-25 in which the reinforcing material is made from polypropylene.

27. A composite material according to any of claims 19-26 in which the material is a multistrand woven, braided or knitted material.

28. A composite material according to claim 27 in which the weave, braiding or knitting of the strands is loose so as to allow ingress of the resilient cellular material between individual strands.

29. A composite material according to any of claims 19 to 28 in which the reinforcing material is in the form of a hoop of material.

30. A composite material according to claim 29 in which the reinforcing material hoop is arranged substantially concentrically with the rotary soil engaging member within the resilient cellular material.

31. A composite material according to claim 30 in which two hoops of reinforcing material are arranged with the resilient cellular material of the rotary soil engaging member, one each side of circumferential centre line of the member.

32. A rotary soil engaging member according to any of claims 1 to 10 or 19 to 31 in which the member includes a plurality of axially extending bores therethrough.

33. A rotary soil engaging member according to claim 32 in which the rotary soil engaging member comprises an annular body.

34. A rotary soil engaging member according to claim 33 in which the bores are arranged regularly spaced around the annular body.

35. A rotary soil engaging member according to claim 33 in which the rotary soil engaging member comprises an annular part having a plurality of outwardly projecting tread members extending therefrom.

36. A rotary y/ /eennggaaging member according to claim 35 in which the bores through the body are arranged at corresponding angular positions to the tread members.

37. A member according to claim 36 in which each tread member has two

bores associated with it.

38. A method of making a rotary soil engaging member comprising the steps of providing a mould, arranging a plurality of retaining members within the mould, arranging a reinforcing material around the retaining members so as to retain the reinforcing material within the mould, injecting a resilient cellular material into the mould so as to surround the reinforcing material then withdrawing the retaining members from the mould.

39. A method according to claim 38 in which the resilient cellular material is injected then centrigually moulded within the mould.

40. A method according to claim 39 in which the resilient material is water blown, centrifugally moulded.

41. A rotary soil engaging member substantially as described herein and with reference to the accompanying drawings.

42. A resilient cellular material substantially as described herein.

43. A composite material for use in a soil engaging member substantially as described herein and with reference to the accompanying drawings.

44. A method of making a rotary soil engaging member substantially as described herein and with reference to the accompanying drawings.