GB2449901A - Auger with cutting teeth - Google Patents

Abstract

An auger adapted for cutting trenches in soil, comprises a central shaft 7, a plurality of flights 18, 19 mounted to the shaft so as to define an auger spiral having a longitudinal axis, and at least one cutting tooth 18 fixed to each flight so as to extend radially outwardly of the respective flight relative to the longitudinal axis, whereby to cut a trench in the soil as the auger is rotated about its axis and is moved laterally relative to its longitudinal axis. The teeth may be tungsten carbide. In the first group of flights, the first flight 191 terminates in cutting edges 21 and the second and third flights 192, 193 are provided with more aggressive teeth than those in a second group located on the other side of a support bearing 14 for the auger. The flight segments may be removable from the shaft of the auger.

Description

AUGER FOR CUTTING TRENCHES

Field of the Invention

This invention relates to augers, particularly but not exclusively for trenching machines, for example for use in digging drainage trenches in agricul-ture or civil engineering.

Background to the Invention

Hitherto, most trenching machines have been based on an endless chain carrying digging and lifting elements to dig out soil from a trench and lift it clear for disposal. This design suffers from significant disadvantages in that the chain involves a large number of bearings, which are continuously exposed to abra- sive particulate materials such as soil and sand, usually in the presence of wa-ter, with the result that they are subject to a high degree of wear. The cost of maintaining trenching machines is therefore very high.

An alternative configuration of trenching machine uses an auger to cut and lift the soil. This has the advantage of only requiring one bearing in contact with the soil, at the lower end of the auger. in UK Patent Application No GB 2427629, there is disclosed an auger which is disposed so as to lean backward (i.e. with the upper end of the auger behind the lower end) relative to the direc-tion of travel of the machine, so that the bottom bearing is above the floor of the trench. This arrangement is found to overcome the tendency in earlier auger-based trenching machines for the auger to lift out of the soil. In fact, the auger of the above UK Patent Application tends to be drawn downwards into the trench. Ground-engaging pads or a "skid" are therefore provided to engage the ground above the trench. The resulting trench is extremely well-defined, with smooth sides and a flat top, the auger cleanly removing spill from the trench as the trenching machine moves over the ground.

Despite these improvements to the trenching machine itself, further im-provements can be gained by an enhanced design of auger itself Augers need to perform three distinct functions: drilling (to make the first cut" into the soil); lateral cutting (to cut the trench); and lifting of the soil. These can involve con-trary technical requirements as regards (a) the need to penetrate axially into the ground and (b) the need to cut laterally into the ground as the trenching ma-chine moves sideways, i.e. to cut laterally to the axis of the auger.

The present invention therefore provides an improved auger, particularly but not exclusively, for cutting a trench in the ground

Summary of the Invention

According to the invention there is provided an auger adapted for cutting trenches in soil, comprising a central shaft, a plurality of flights mounted to the shaft so as to define an auger spiral having a longitudinal axis, and at least one cutting tooth fixed to each flight so as to extend radially outwardly of the respec-tive flight relative to the longitudinal axis, whereby to cut a trench in the soil as the auger is rotated about its axis and is moved laterally relative to its longitudi-nal axis The flights are conveniently divided into two groups, the first group com-prising a first flight having at least one cutting edge extending axially beyond the end of the shaft and substantially transverse to the longitudinal axis.

The first flight may be a multi-start spiral, each having a respective said cutting edge There may be six such cutting edges.

Second and third flights in the first group are preferably each provided with a plurality of cutting teeth.

A support bearing for the auger is suitably spaced in use above the lower end of the auger.

The support bearing for the auger is preferably located between the first group and the second group of flights.

Each flight of the second group of flights advantageously comprises a plurality of said teeth.

The teeth of the second group are preferably staggered around and along the longitudinal axis of the auger.

The teeth are preferably made of tungsten carbide.

The support bearing may consist of a bearing metal sleeve located around and secured to the central shaft of the auger and a bearing metal shell in a tubular support member surrounding the sleeve, the support member being adapted to mount the auger to a trench-cutting machine.

Flight segments forming the spiral are conveniently attachable to and removable from the shaft of the auger.

The central shaft preferably has tugs attached thereto, to which the seg-ments are secured.

The tugs may be welded to the shaft.

The segments may be secured to the lugs by means of bolts or screws The auger could alternatively be formed as one continuous flight, to be replaced in its entirety when worn out.

Brief Description of the Drawings

In the drawings, which illustrate an exemplary embodiment of the inven-tion Figure 1 is a perspective view of a trenching machine suitable for the au-ger of the present invention; Figure 2 is an enlarged perspective detail view showing the bearing sup-port for a lower end of a generic auger; and Figure 3 is a perspective view showing a preferred construction of the auger in accordance with the present invention.

Detailed Description of the Illustrated Embodiment

The invention consists of an auger especially adapted for trench digging.

Figure 1 illustrates a trenching machine built according to the teaching in the abovementioned earlier patent application. The trenching machine comprises a supporting framework having a generally rectangular frame 1 extending up-wardly from a ground-engaging skid 2 at an angle of approximately 30 degrees to the vertical, and support arms 3 extending forward from the frame 1. The arms 3 carry a triangular attachment frame 4 for attachment to the three-point hitch lift conventionally provided to the rear of an agricultural tractor. Additional supporting link arms 5 extend between the upper point of the triangular frame 4 and the upper end of the rectangular frame 1.

A carriage 6 is slidably mounted on the rectangular frame 1, with a hy-draulic cylinder to drive the carriage 6 relative to the frame 1. The carriage 6 in turn supports an elongate auger 7 having a hydraulic drive motor 8 at the upper end thereof. The drive motor 8 is supplied with pressurised hydraulic fluid via flexible supply pipes 9 from a pump 10 driven via a universal joint by a drive shaft lOa connectable to the tractor's power take-off shaft (PTO). The pump 10 and its associated hydraulic fluid tanks 11 are mounted between the support arms 3.

The skid 2 has a longitudinal slot 12 therein opening rearwardly, through which the auger 7 passes to cut a trench, as described hereinafter. The skid thus constitutes ground-engaging pads engaging the ground on either side of the trench, and in front of it. A hopper 13 (Figure 2) is defined by steel plates extending upwardly from the skid 2 and surrounding the part of the slot 12 through which the auger extends, receiving and deflecting the soil lifted by the auger from the trench on to a chute or conveyor (not shown) mounted to one side of the machine, and serving to deposit the soil at a desired distance from the machine as it moves forward cutting the trench.

Figure 2 shows the mouth of the hopper 13 with the auger fully raised to show the lower support for the auger. This consist of a plain metal bearing 14 surrounding the shaft 15 of the auger 7 and carried by a bar 16 extending from the carriage 6. The bearing 14 is located at a distance of approximately 100 -mm from the lower end of the auger, to ensure that it is clear of the base of the trench at all times.

In Figures 1 and 2, a relatively short flight section is shown below the bearing. In practice, a larger number of flights in this section may be advanta-geous for some circumstances.

In the machine thus far described, the auger is preferably made up from relatively short sections of the auger flight bolted onto attachment lugs welded to the shaft of the auger This construction provides a substantially continuous spiral flight but also affords the possibility of easily replacing broken or damaged sections of the flight with the minimum of downtime of the trenching machine, increasing its effectiveness and decreasing running costs significantly Figure 3 shows a schematic representation of an auger incorporating the present invention and suitable for mounting in the trenching machine thus far described. For the sake of clarity, the auger is presented in the drawings facing in the opposite direction to that in which it will be used in the trenching machine.

This should be clear from Figures 1 and 2 but, for the avoidance of doubt, the upper end of the auger as shown in Figure 3 will be facing downwards when in-stalled in a trenching machine.

In use, the operation will typically be commenced from an existing drain-age ditch or other suitable excavation. However, the drilling capability of the auger permits the auger to drill its own start hole in the ground and to be low-ered by the ram to the desired trench depth in the ditch or excavation and then rotated by the motor 8 while the machine is moved forward by the tractor. The rotation of the auger 7 tends to pull the auger downwardly into the trench. This motion is resisted by the skid bearing against the surface surrounding the trench to the front and sides, and the resultant downward pressure ensures that the sides of the trench are held firmly in place, in turn providing a very clean, stable trench structure, while also maintaining trench depth without the need for downward force on the auger and its carriage. The ram therefore serves merely to control lowering of the auger, and to lift it from the trench after use.

Returning to Figure 3, the auger comprises a central shaft 7 carrying convolutions of short sections 17 forming a spiral flight. Each section is pro-vided with a cutting edges or teeth 18. The teeth are preferable of hardened metal with tungsten carbide tips or are made entirely of tungsten carbide or other suitable hard and robust material. The bearing 14 and its mounting arm 6 support the auger at a convenient point along the length of the axis, to corre-spond with the location in the trenching machine for the mounting arm 6.

On the other side of the bearing 14 there is another set of convolutions l9, 192 and 193. These form the leading end of the auger. The first flight con- sists of a convolution terminating in a cutting edge 21. This extends a little be-yond a cone-shaped termination 22 for the auger shaft 7 and also extending substantially transverse to the longitudinal axis. The first flight l9 functions more as a drill than a slot cutter and, for that reason, the first flight may be con- structed with a double-start by adding an additional convolution or part convolu-tion 23 at the leading end of the shaft. This too will have a cutting edge like that 21 provided on the opposite side of the shaft. The second and third flights 192 and 193 are aggressive, with many teeth It should be noted here that the draw-ings, for the sake of simplicity and clarity, indicate that only three or four teeth are provided per convolution. This need not be the case and any number of teeth can be provided. Where the teeth are expensive items, the cost of provid-ing many teeth will need to be balanced against the time saving in achieving faster trench cutting. Also, the drawings indicate that the teeth are aligned axi-ally. This is again for the sake of clarity and simplicity and, in most cases, it would be expected that the teeth will be radially spaced from one convolution to the next in order to even out the cutting effort and to distribute the load more evenly on the motive force for the auger and the towing vehicle.

The first flight 19 preferably has tungsten carbide teeth of grade B1OG, which is the same as for road planing. The number of convolutions 17 on the other side of the bearing 14 may be varied to suit the nature of the ground being worked. Clearly, the more convolutions, the more spill can be removed at any one time but there is an adverse effect on the load presented to the motive force and the tractor vehicle.

In a practical implementation of the invention, and for illustrative pur-poses only, the auger was provided with tungsten carbide teeth brazed to the flights. There were six such teeth fixed to the first flight along its bottom edge In this way, the first flight was able more effectively to drill into the soil. The third flight was aggressive in that it was provided with eight teeth, which were set to extend 8-10mm radially beyond the circumference of the flights. This en-sured that the teeth did the cutting and not the edges of the flights.

At a rotational speed for the auger of 500rpm, a trench 150mm wide and 1000mm deep and 10 to 18 metres long can be cut in one minute, depending on the rotational speed of the auger and the nature of the soil. With typical di-mensions of a 1000mm shaft length, 10mm flight thickness, 50mm screw pitch, 25mm flight radius and 10 flights, approximately 2.3 to 4.2 tonnes of soil can be removed in the same time.

While the invention is illustrated and described in relation to a forward- facing auger, it will be appreciated that it is equally applicable to a rearward-facing auger.

Claims (16)

1. An auger adapted for cutting trenches in soil, corn prising a central shaft, a plurality of flights mounted to the shaft so as to define an auger spiral having a longitudinal axis, and at least one cutting tooth fixed to each flight so as to extend radially outwardly of the respective flight relative to the longitudinal axis, whereby to cut a trench in the soil as the auger is rotated about its axis and is moved laterally relative to its longitudinal axis.

2. An auger as claimed in Claim 1, wherein the flights are divided into two groups, the first group comprising a first flight having at least one cut- ting edge extending axially beyond the end of the shaft and substantially trans-verse to the longitudinal axis.

3. An auger as claimed in Claim 2, wherein the first flight is a multi-start spiral, each having a respective said cutting edge.

4. An auger as claimed in Claim 3, wherein the first flight has six said cutting edges.

5. An auger as claimed in Claim 3 or 4, wherein second and third flights in the first group are each provided with a plurality of cutting teeth.

6 An auger according to any of Claims 1 to 5, further comprising a support bearing for the auger spaced in use above the lower end of the auger.

7. An auger according to 6 when dependent from claim 2, wherein the support bearing for the auger is located between the first group and the second group of flights.

8. An auger as claimed in Claim 7, wherein each flight of the second group of flights comprises a plurality of said teeth.

9. An auger as claimed in Claim 8, wherein the teeth of the second group are staggered around and along the longitudinal axis of the auger.

10. An auger as claimed in any of Claims 1 to 9, wherein the teeth are made of tungsten carbide.

11. An auger according to Claim 6, wherein the support bearing con-sists of a bearing metal sleeve located around and secured to the central shaft of the auger and a bearing metal shell in a tubular support member surrounding the sleeve, the support member being adapted to mount the auger to a trench-cutting machine.

12. An auger according to any of claims 1 to 11, wherein flight seg-ments forming the spiral are attachable to and removable from the shaft of the auger

13. An auger according to Claim 12, wherein the central shaft has lugs attached thereto, to which the segments are secured.

14 An auger according to Claim 13, wherein the lugs are welded to the shaft.

15. An auger according to Claim 13 or 14, wherein the segments are secured to the lugs by means of bolts or screws.

16. An auger, substantially as described with reference to, and/or as shown in, the drawings.