This invention relates to a plough disc and has been devised partly as an improved form of plough disc and partly as a method of refurbishing worn plough discs.

5 It is well known to use discs in ploughing in various configurations but it is a disadvantage of such discs that they wear rapidly and consequently require frequent replacement which is expensive. Attempts have been made to build up worn discs by

10 welding annuli of steel to the periphery of the disc but it has been found that expansion of metal due to the heat in welding makesthis impracticable. It is also a disadvantage of conventional plough discs that they are only partly effective in ploughing

15 trash and straw into the soil and therefore unsuitable for modern farming methods incorporating stubble mulching.

It is therefore an object of the present invention to provide a plough disc and a method of 20 refurbishing a worn plough disc which will obviate or minimize the foregoing disadvantages in a simple yet effective manner or which will at least provide the public with a useful choice.

83.5.30 Accordingly, in one aspect the invention

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consists in a plough disc comprising a central hub adapted to be mounted on a support axle and a plurality of substantially rectangular plate-like lugs fastened to said hub and extending radially 5 outwardly therefrom in a substantially equi-spaced array, said lugs lying in a plane substantially per¬ pendicular to said axle or defining part of the surface of a shallow dish having a central axis coincident with said axle.

10 In a further aspect, the xnvention consists in a method of refurbishing a worn plough disc com¬ prising the steps of welding a plurality of sub¬ stantially rectangular plate-like lugs to the worn disc at or about the periphery thereof and extending

15 outwardly therefrom in a substantially equi-spaced array, said lugs forming a continuation of the shape of said disc.

Notwithstanding any other forms that may fall within its scope, one preferred form of the invention 20 will now be described with reference to the accompanying drawings in which:

Figure 1 is a side elevation of a plough disc according to the invention, Figure 2 is a perspective view of the 25 plough disc shown in Figure 1 with some of the lugs omitted for clarity, Figure 3 is a rear side perspective view of the plough disc shown in 30 Figure 2 ,

Figure 4 is a perspective view of one of the lugs used in the plough disc according to the invention, and Figure 5 is a reverse side perspective view 35 of the lug shown in Figure 4.

83.5.30

In the preferred form of the invention, a plough disc is constructed as follows.

The plough disc comprises a central hub 1 which may take any suitable form but which in the 5 preferred form of the invention is manufactured from steel plate of circula-r configuration having an outer circumference 10 and a central aperture 11 adapted to be mounted on the support axle of a plough. The central hub 1 may be of flat plate but in the

10 preferred form of the invention the plate is dished into a shallow dish configuration. In this manner the overall configuration of the central hub is similar to a conventional plough disc but having a reduced circumference. The central hub may be a

15 purpose manufactured hub or may alternatively be the central portion of a worn plough disc.

The plough disc according to the invention is provided _. ith a plurality of substantially rec¬ tangular plate-like lugs or "spades" 2 which are

20 fastened to the hub 1 and extend radially outwardly therefrom in a substantially equi-spaced array. Where the central hub 1 is flat the spades 2 may also be flat, lying in a plane substantially perpendicular to the axle or alternatively in the preferred form of

25 the invention where the central hub is dished then the lugs or spades 2 define part of the surface of the shallow dish having a central axis coincident with the axle.

Any desired number of lugs or spades 2 may

30 be provided depending on the size of the lugs and of the central hub but it has been found convenient for _» . example to use eight lugs as shown in Figure 1 on a 22 inch diameter disc. Similarly nine lugs could be used on a 24 inch disc and ten lugs on a 26 inch disc

35 or any other number of lugs which may be found to be effective.

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Each lug is substantially rectangular in configuration having an outer edge 3, side edges 12 and 13, and an inner edge 14. In the preferred form of the invention however the shape of each lug is modified slightly from the rectangular configuration by shaping the outer edges 3 to a convex curve and the inner edges 14 similarly to a concave curve. This method of manufacture is convenient in that a plurality of lugs may be cut from a single strip of steel plate having a width the same as the width of the lugs by making a plurality of curved cuts across the width of the strip. The corners 4 and 5 between the side edges 12 and 13 and the outer edge 3 are preferably rounded and the outer edge 3 is sharpened to a knife-like edge as shown in Figure 4.

It is a further feature of the invention that the side edges 12 and 13 are left square or blunt as shown in Figures 4 and 5 as this has been found to be particularly effective for stubble mulching as will be described further below.

It has also been found particularly advantageous to provide the inner edges 14 of each lug with a concave configuration as this provides two "ears" 15 at each inner corner of the lug which distributes the loading from each lug in use more evenly into the central hub 1 and reduces the tendency for the central hub to crack at the weld-line 16 as might otherwise happen if the inner edges of each lug are square rather than concave. Each lug is preferably welded to the central hub 1 by welds 16 and may also be welded on the rear edges 17 as shown in Figure 3.

It is an advantage of the plough disc according to the invention that the lugs or spades 2

can be hardened to a substantial extent. In this respect, lugs manufactured from Broken Hill Proprietary Limited (B.H.P.) steel to specification No. S1070 and of size 4 inches by 6 inches can be hardened to three times the minimum hardness for S1070 whereas a larger piece of similar steel 14 inches by 10 inches could only be increased to twice the minimum hardness of S1070. When lugs of B.H.P. specification XK5155 of 4 inches by 6 inches size were used they could be hardened to four times the minimum hardness of XK5155 whereas a large body could have its hardness increased only by 50 per cent. It is therefore a feature of the invention that because the lugs 2 are manufactured separately from the central hub 1 they are able to be separately hardened before being welded to the central hub to a hardness which could not be achieved by treatment of a single plough disc of the prior art type. It is a further feature of the invention that the central hub 1 can be made of mild steel plate to a thickness greater than that which would normally be used for a conventional plough disc and which therefore may be used as a base suitable for re-use after the original set of lugs or spades have become worn. In this manner a plough disc according to the invention may be used until the lugs or spades 2 become unacceptabl worn whereupon the lugs may be removed from the central hub and replaced by a new set of lugs. This operation is considerably cheaper than replacing an entire plough disc. In tests using a plough disc made in accordance with the invention it has been found that the hardened lugs 2 have at least twice the life of a new conventional plough disc and that the plough disc according to the invention ploughed 1 to 1 inches deeper without extra drawbar pressure, produced smaller

sods than conventional plough discs, exposed weed roots well, covered mulch well and left pyramid shaped domes on the bed under the ploughed soil which should be of help in aerating and restricting soil erosion.

It has also been found particularly advantageous that the square or blunt side edges 12 and 13 on each lug act to shatter and splinter straw and trash during ploughing allowing complete break-down of the straw and trash in a typical period of approximately six weeks. .iThis- rapid break-down allows a further crop to be sown the same year that the trash has been ploughed down and once the break¬ down begins the soil is able to absorb 100 to 150 mm. of rain in 1 hour compared to an absorption rate of

25 mm. per hour without trash break-down. This allows the ploughed soil to resist soil erosion to a far greater degree than has hitherto been possible with conventional disc ploughs. Although the invention described above uses a custom-made central hub 1, it is of course a feature of the invention that it is possible to utilize worn plough discs for the central hub. The above method of manufacture of plough discs can be applied both to the repair of worn plough discs, in which case the central portion 1 will be the central portion or remainder of a worn plough disc, and to the manufacture of new plough discs in which case the hub portion 1 will be made for the purpose. It is to be noted that in the manufacture of new discs it would be possible and in some instances desirable that the hub portion 1 should be made of thicker steel than that conventionally used in plough discs. For instance, it is common that plough discs

be made from metal from 5 mm. to 7 mm. thick but it has been found that the use of a central hub of 9 mm. to 12 mm, thick is desirable as such a thick plate has good stability and life and could expect to have several sets of lugs 2 welded thereto during its lifetime.

In this manner a plough disc is provided which is comparatively cheap and simple to manufacture and which can be readily refurbished when worn as well as providing advantages in use over conventional plough discs.

Although the lugs have been described as being welded to the hub, in some situations, e.g. in lightweight or domestic applications, the lugs may be fastened by other means such as bolting or rivetting.

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