GB2061687A - Grass cutting machines and improved blade therefor - Google Patents

Abstract

A pasture topper or other agricultural machine for cutting grass etc. having cutting rotors 12 turning about vertical shafts 17 and suspended from above, has blades 24 each with a cutting part 30 carried by a downwardly descending web 32 (to increase ground clearance) which tapers in the direction of the cutting part 30, so as to reduce the mass of the lower parts of the blade relative to the stiffness of its upper parts and thereby resist radially outward distortion during rotation. The upper bend 36 is reinforced by deformation of the material to give a bracing part 38, 40 cater-cornered across the included angle. <IMAGE>

Description

SPECIFICATION Grass cutting machines and improved blade therefor The present invention relates to agricultural machines for cutting grass and the like. It is concerned with their cutting blades. It relates especially, but not exclusively, to pasture toppers, which are machines for cutting off rough growth, thistles, nettles or other unwanted taller vegatation from a field of grass. Since this operation is not totally essential, it is important that the machine is inexpensive- although nevertheless efficient.

One example of this type of machine has a supporting structure carrying a plurality of belt-driven motor arms arranged to rotate about upright axes.

Each arm has cutting blades at its ends.

The machine can be carried on the linkage arms of a tractor and the supporting structure is mounted on skids which rest on the ground when the machine is in use. These skids are adjustable to vary the height between the rotor arms and the ground, and so vary the cutting height.

Adjacent rotor arms may rotate in opposite directions. An arrangement as above is disclosed in, for example, my copending UK Patent Application 80.27101 and South African Application 80.4749.

It is possible for the cutting blades to be formed in one piece with the rotor arm but it is preferable to have a separate cutting blade pivotally mounted at each end of the rotor arm and which may be removed from the rotor arm for sharpening or replacement. The pivotal mounting enables a cutting blade to swing out of the way should it encounter a solid obstruction such as a tree root or a large stone.

Whether the blades are fixed or pivotted, the part of the blade carrying the cutting edges should desirably be below the level of the rotor arm so that the rotor may clear an obstruction such as a stone on the ground. To achieve this the blade may be shaped so as to have a connecting part which extends downwardly from the rotor arm, say at 70 or so to the horizontal and a cutting part which projects outwardly at the lower end of the descending connecting part. (The cutting part is customarily inclined slightly downwards towards its distal end, say at 10 to 15"to the horizontal).

In this way the cutting part is spaced vertically from the support part, enabling the rotor arm to clear obstructions.

This arrangement has, however, the problem that, if the descending part is long thereby to make the vertical spacing between the cutting part and the rotor arm large, then during rotation a large turning moment is set up on the blade tending to distort the descending part radially outward.

The extent of this distortion varies in dependence upon the speed of rotation of each rotor arm. Such variable distortion can make it impossible to design a machine so that the blades of adjacent rotors pass close to each other (which is necessary to avoid leaving a "wisp", that is to say a thin strip of uncut grass). It can also entail a risk of the blades fouling the sides of the machine.

The present invention seeks to provide a blade construction, and machines in which it is incorporated, which reduces the extent of distortion and yet can be economical to produce.

According to one aspect of the present invention, there is provided an agricultural cutting machine comprising at least one cutting rotor rotatable about a generally upright axis, and support means by which said rotor is mounted, the or each rotor having at least one blade with a connecting part extending downwardiy from the rotor and a cutting part angled outwardly from the lower region of the connecting part wherein the connecting part tapers in the direction from the rotor to the cutting part.

The taper could be formed by making the blade of uniform width but with a thickness that decreases towards the cutting part. It is preferable, however, to form the blade from a piece of metal of uniform thickness the taper then being a decreasing width of the connecting part, which may then be in the form of a regular trapezium. This allows the blade to be formed by cutting to shape a piece of metal plate bending the result to the desired angles, and providing at least one sharpened edge on the cutting part.

By this construction, the mass of the part of the blade furthest from the rotor arm is reduced, so reducing the turning moment on the upper parts of the blade. Also, the junction of the support part and the connecting part is strengthened relative to the mass of the lower parts of the blade because of the greater width given to it. The cutting part may also be tapered to reduce further the moment on the upper parts of the blade.

It will generally be convenient and indeed desirable for the connecting part to be in one piece with and extend downwardly from, a support part which is angled inwardly from the connecting part.

In preferred forms of the invention the blade has at least one bracing part extending cater-cornered across the angle included between such a support part and the connecting part. Such a bracing part may be formed by a depression of the material of the blade intermediately between the edges of the blade at the junction of the support part and the connecting part. One fairly substantial bracing member may be provided centrally between the side edges of the blade or more than one bracing member could be provided by several smaller deformations of the material so as to give the same total reinforcement.

Alternatively, a bracing part cater-cornered across the included angle may be formed by folding down the material of the blade at an edge thereof at the junction of the support and connecting parts. In this case it is suitable for each edge to be folded down, thus forming two such bracing parts.

It would be possible for two cutting blades to be joined by, and integral with, a common support part.

The support part would then constitute a rotor arm of the pasture topper or other agricultural cutting machine and would have a connecting portion of a blade descending from each end of it. However, it is preferred for individual blades to be detachable from a rotor arm which is a more-or-less permanent part of a pasture topper. This facilitates the replacement of blades and additionally, it is preferable for the blades to be pivotally attached to the rotor arm so as to be able to swing around a generally upright axis as mentioned previously.

In a second aspect the invention provides blades for agricultural machines in accordance with the first aspect of this invention.

Embodiments of the present invention will now be described in detail, by way of example, with reference to the accompanying drawing, in which: Fig. 1 shows a diagrammatic plan view of a pasture topper; Fig. 2 is a side view of one of the rotors of the machine shown in Fig. 1; Fig. 3 is a plan view of a blade on the rotor shown in Fig. 2; Fig. 4 is a diagrammatic view of a blade on the rotor shown in Fig. 2, the three parts all being viewed directly on, as shown by the arrows A in Fig. 2; Fig. 5 is a section on the line X-X in Fig. 3 and Fig.

4; Fig. 6 is a view analogous to Fig. 4 of an alternative blade; Fig. 7 is a section on the line Y-Y in Fig. 6; Referring first to Fig. 1, the machine has supporting structure carrying three rotors with arms 12 (Fig.

2) carrying blades whose tips describe circles 13. The rotors are supported from above and are driven by a belt drive (not shown) to rotate in the direction of arrows 14 about axes 16. The pasture topper has skids 18 at either side which are adjustable within practical farming limits to vary the height of the rotors above the ground and hence vary the cutting heighth. The machine is connected for use to the linkage arms 20 of a tractor (not otherwise shown) and is towed in the direction of arrow 22. The belt drive is powered from the tractor. A suitable belt drive is described in my copending applications referred to earlier.

Fig. 2 shows the arm 12 of one rotor fast with the end of a shaft 17 on the rotor's axis 16 with blades 24 constructed in accordance with the present invention. Each blade 24 has a support part 26 which is pivotally mounted on the respective end of the rotor arm 12 by means of a bolt 28 through hole 29. The cutting part of the blade is spaced downwards from the rotor arm 12 and is connected to the support part 26 by a connecting web 32. The web 32 is steeply inclined to the horizontal, for example by 700. The cutting part 30 is also inclined to the horizontal, but only by a small angle, e.g. 100 to 150.This inclination reduces the friction between the cutting part 30 and the stubble on grass beneath the blades which remains uncut as most of the cutting is done by the tip 34 of the blade, and the radially inner portion of the cutting part is somewhat higher offthe ground.

Thus the blade forms a "lazy Z" shape with obtuse angles included between the support part 26 and the connecting web 32, and between the connecting web 32 and the cutting part 30, creating a vertical distanceH between the tip 34 of the blade 24 and the rotor arm 12. The maximum clearance between th rotor arm 12 and the ground is thus the distanceH plus the cutting heighth between the tip 34 of the blade 24 and the nominal ground surface.

As can be seen from Fig. 2, each blade has a uniform thickness to it in the direction of the arrows A. However, as best seen from the diagrammatic view in Fig. 4, the width b across the connecting web 32 between the side edges 35 of the blade (in the direction which is approximately circumferentially of the rotor) decreases progressively between the upper bend 36 and the lower bend 37. Thus the connecting web 32 has a uniform taper in the direction towards the cutting part 30. In consequence of this the mass of the lower parts of the blade, which principally contributes to the turning moment distorting it during rotation, is less relative to the width across its upper parts, which resistsuch distortion, than if the taper of the connecting web were absent.The cutting part 30 also tapers towards it tip 34 thus further reducing the mass of the lower parts of the blade.

To strengthen the top bend 36 between the support part 26 and the web 32, each blade has a depression of its material so as to provide a part 38 extending cater-cornered across the included angle. The depression is provided mid-way along this bend 36, that is to say centrally between the side edges 37. As best seen from Fig. 4, the depression has an outline which is a rhombus. The bracing provided by this depression of material provides added stiffness at the bend 36.

An alternative arrangement is shown in Figs. 6 and 7 in which both side edges of the blade are folded over at portions 40 adjacent the bend 36. This provides two bracing parts extending cater-cornered across the included angle.

In each of the above cases the side edges of the blades' cutting parts 30 are sharpened at distal regions 42 to give cutting edges. Cutting is performed by the leading sharpened edges only. When an edge becomes blunt the blade can be transferred to a rotor which turns in the opposite sense, to use the other sharpened edge.

The blades described above can be formed by guillotining flat blanks from sheet steel of appropriate grade and thickness and bending itto form the upper bend 36 and lower bend 37 in conventional manner. After the bends have been formed the depressed part 38 or folded over portions 40 are formed by a swaging process in which the blade is placed on a supporting block with the upper bend 36 uppermost and a blunt tool or tools are driven down against the appropriate point or points on the upper bend to depress the part 38 or fold down the edge portions 40 into a suitable recess or recesses provided in the supporting block. This can be done either hot or cold before hardening of the steel, or if a prehardened steel is used then it must be carried out as a hot process.

The blades described above enable high ground clearance to be achieved and are of a construction ' which minimises outward distortion during rotation, any enhancing the stiffness of the upper parts of the blade relative to the mass of the lower parts, yet can be produced easily and economically.

Claims (12)

1. An agricultural cutting machine comprising at least one cutting rotor rotatable about a generally upright axis, and support means by which said rotor is mounted, the or each rotor having at least one blade with a connecting part extending downwardly from the rotor and a cutting part angled outwardly from the lower region of the connecting part wherein the connecting part tapers in the direction from the rotor to the cutting part.

2. A machine according to claim 1, wherein the connecting part is in one piece with, and extends from, a supportwhich is angled inwardly from the connecting part.

3. An agricultural machine according to claim 2, wherein the blade has a bracing part extending cater-cornered across the angle included between the support part and the connecting part.

4. An agricultural machine according to claim 3, wherein the bracing part is formed by a depression of the material of the blade at the junction of the support part and the connecting part, and intermediately between the edges of the blade.

5. An agricultural machine according to claim 3, wherein the bracing part is formed by a fold of the material of the blade at an edge of the blade.

6. An agricultural machine according to any one of the preceding claims, wherein the or each blade is pivotally mounted on to respective rotor.

7. An agricultural machine according to any one of the preceding claims, wherein the web part is inclined at an angle between 60 and 80 to the horizontal.

8. An agricultural machine according to any one of the preceding claims, wherein the cutting part is inclined to the horizontal at an angle of not more than 20 .

9. An agricultural machine substantially as herein described with reference to Figs. 1 to 4 or Figs. 1,2,5 and 6.

10. A one-piece blade for a power driven agricultural grass cutting machine, comprising a cutting part, a support part, and a connecting part extending between the support part and the cutting part and being tapered in a direction from the support part to the cutting part, the support part and the cutting part being angled outwardly from opposite side faces of the connecting part, with an inclined angle of at least 90" and less than 1800 in each case, the cutting part being sharpened along at least a distal portion of at least one of the cutting part's side edges extending from the connecting part.

11. A blade according to claim 10, wherein the support part has a hole through it for pivotally mounting the blade on a rotor of the machine.

12. A one-piece cutting blade substantially as herein described with reference to Figs. 2, 3 and 4 or Figs. 2,5 and 6.