GB2244468A - Silage grab - Google Patents

Abstract

A silage grab comprises a fixed rear wall (14) for attachment to a tractor, the rear wall having forwardly-extending tines (12) attached thereto and a front cutting part (17) including a cutting blade (20) pivotably attached to the rear wall, drive means (24) being mounted between the rear wall and cutting part, in which the mounting position (16) of the drive means in relation to the pivot point (25) of the front cutting part is variable, thereby enabling the maximum opening of the cutting part to be varied. Pref. the mounting comprises a fixed, upstanding support (15) with a number of pivot holes (16). The drive is pref. a hydraulic ram. <IMAGE>

Description

SILAGE GRAB This invention relates to silage grabs for agricultural use, for example for withdrawing blocks of silage from a clamp, in particular of the type which include a fixed rear part with tines extending therefrom, for attachment to a tractor, and a pivotable front cutting part, wherein the cutting action is such as to provide a sealed face to the cut silage, thereby reducing the incidence of secondary fermentation in the silage clamp.

Silage grabs of the general type described are known and are generally manufactured in a range of sizes, thereby enabling the user to select a grab having a capacity according to his particular requirements, including the carrying capacity of his tractor together with any attachments and the maximum hydraulic pressure developed in the tractor's power system. However, from the point of view of the manufacturer, the provision of a range of grabs increases inventory costs and production time and generally adds to the manufacturing expenses.

Although, theoretically, a large-capacity grab could be used to handle a small quantity of silage or other material, merely by driving the tines into the clamp at a shallower depth, in practice the judgment of the correct depth is not easy and a tractor having a restricted load-carrying capacity may easily be over-loaded, with potentially dangerous consequences.

It is an object of the present invention to provide a silage grab which has an adjustable load-carrying capacity.

According to the invention, a silage grab comprises a fixed rear wall for attachment to a tractor, the rear wall having forwardly-extending tines attached thereto, and a front cutting part including a cutting blade pivotably attached to the rear wall, drive means connecting the rear wall and cutting part, in which the mounting position of the drive means in relation to the pivot point of the front cutting part is variable, thereby varying the maximum opening of the cutting part.

It will be understood that, for a grab of a given width and depth, the maximum load-carrying volume capacity is determined by the maximum extent of opening of the cutting part, that is, the gap between the front cutting blade and the ends of the tines when the grab is fully open. Therefore, the use of the invention enables the maximum load-carrying capacity of the silage grab to be selected according to the requirements of the user and can readily be adjusted.

The drive means is preferably constituted by a hydraulic double-acting ram powered by the hydraulic system of the tractor to which, in use, the grab is attached. In known silage grabs, either a single centrally-mounted ram, a pair of side-mounted rams, or even three rams, are used, with fixed mounting positions. In grabs according to the present invention, we have found that a single centrally-mounted ram is quicker in operation and is to be preferred, provided that the beam on the cutting part, to which the ram is attached, is sufficiently robust to distribute the cutting force evenly without distortion.

The mounting position of the drive means is preferably variable, in relation to the pivot point of the front cutting part of a silage grab according to the invention, at the position of attachment to the back wall. Where the drive means is a hydraulic ram, the cylinder part thereof is generally pivotably attached to the upper part of the rear wall and the piston thereof is pivotably attached to the cutting part, and it is preferred to vary the mounting position of the cylinder to the rear wall in a vertical direction. The variation may be infinitely adjustable, within upper and lower limits, or may be adjustable in fixed increments, for example by selecting a particular mounting position from among two or more pre-set locations.Preferably, the mounting position lies on an arc of a circle having a radius corresponding to the maximum extended length of the drive means and its centre at the point of attachment thereof to the cutting part when in the closed position. With such an arrangement, the cutting part is always in the fully-closed position when the drive means is at its maximum extent, irrespective of the actual mounting position of the drive means to the rear wall.

Preferably, the drive means comprises a hydraulic ram and the rear wall of the grab is provided with two or more, suitably three, location positions for mounting the cylinder part of the ram, the location positions all lying on an arc as described above. Preferably, the rear wall is provided with an upstanding support formation, for example a bracket member, in which are accommodated the location positions for mounting the ram.

Although, in a straightforward arrangement, fixed locations may be provided, which may constitute journals formed in the support formation for pivotably receiving the ram, thereby providing for incremental adjustment of the mounting position by removal of the ram from one location and re-attaching it at another, infinitely-variable adjustment may be provided by means of a further hydraulic ram, a screw adjuster or the like, which may be optionally controlled from the driving position of the tractor.

It is desirable for the resolved movement of the arcuate path followed by the cutting blade during the cutting stroke to be close to vertical, to avoid imparting substantial thrust forces against the cut face of the clamp on the one hand, or pulling forces on the cut block on the other, both of which impair the cutting efficiency. To achieve this, it is preferred that the fully-open position of the cutting blade with the grab set in the position of maximum-capacity should be substantially vertically above its position when closed, whereby the straight line joining the two positions defines a chord which is substantially vertical, that is, substantially orthogonal to the plane containing the tines of the grab.With the grab set for a lower capacity, the arcuate path followed by the cutting blade will then create a slight withdrawing or pulling force on the cut block towards the rear wall, since the fully-open position of the blade will be somewhat in front of the line of the chord as defined above, but this is to be preferred in comparison with the generation of thrust forces, which would cause increasing pressure between the front of the cutting part of the grab and the cut face of the clamp, as the cutting part neared the end of its movement.

We also prefer that the pivot point of the front part on the rear wall should be at a vertical height above the tines which approximates to half the chord, as defined above, in order to optimise the mechanical advantage, irrespective of the selected load-carrying capacity.

The geometry of silage grabs, in relation to the mounting points for the drive means and the stroke thereof and the pivot position of the cutting part, may within limits be selected according to desired operating parameters such as maximum cutter part opening, cutting force and the like and indeed the final choice with any given size of silage grab is generally a compromise in that, for example, the lower is the mounting position of the cylinder part of a hydraulic ram on the rear wall of the grab, the greater is the maximum jaw opening but the lower is the initial cutting force, that is, the net downward force exerted by the ram on the cutting part of the grab at the beginning of the cutting stroke. Nevertheless, we have found using grabs according to the present invention that the cutting force exerted at the start of the cutting stroke, with the grab set for its maximum load-carrying capacity, is considerably greater than a typical small-capacity grab of the type currently commercially available.

According to further preferred features of the invention, the cutting part may include side members which may have side cutting blades at their lower edges; the side blades may include angled rear portions which cooperate with side frame members of the rear wall to provide a shearing cutting action; the tines may be adapted to facilitate withdrawal of the tractor and grab, leaving a cut block of silage on the ground, for example by being angled slightly forwardly and downwardly or by being cranked; the end tines may be more robust than the central-section tines and may be mounted slightly higher in the rear wall; the cutting blade or blades of the front part, optionally including the side blades, may be either integrally formed or detachably secured thereto; and the front cutting blade may have a tail portion angled to urge the cut face of the silage clamp away from the front part during the cutting movement.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which Figure 1 is an exploded view of a silage grab and Figure 2 is a side elevational diagram to show the effect of altering the mounting position of the drive means.

Referring to Figure 1, a silage grab has a rear wall 10 constituted by a fabricated frame including a lower cross member 11 carrying tines 12, side members 13 in which are formed journal holes 13a, an upper cross member 14 in the form of a horizontally-disposed plate, and various intermediate strengthening and reinforcing members. A bracket member which includes a pair of spaced-apart parallel plates 15 is mounted vertically and formed as an integral part of the frame; the upper portion of the plates extend upwardly and include three reinforced journal holes 16, positioned on an arc (see the description with reference to Figure 2).

A front cutting part 17 of the grab includes a beam member 18, arcuate support members 19 and a cutting blade 20. The front part also includes side wall members 21 having side cutting blades 22 terminating rearwardly in angled cutter portions 23. The front part is pivotably attachable to the rear wall by means of pins (not shown) carried in journals 21a formed in the side walls and journal holes 13a.

A hydraulic double-acting ram 24 is mounted between front support lugs 25 on the beam member 18 and one of the three journal holes 16 formed in the rear wall, in either position I, II or III.

Referring now to Figure 2, the silage grab of Figure 1 is shown in the fully-open position at the maximum load-carrying capacity (solid outline) and at the minimum load-carrying capacity (dashed line). As shown, the maximum capacity is attained with the ram attached at position I to the rear wall, whereas the minimum capacity is attained by attachment at position III. Position II is for an intermediate load-carrying capacity.

It will also be seen that positions I, II and III lie on an arc of a circle centred at the axis of lugs 25 with the ram fully extended and the front part of the grab fully closed (chain-dotted line), the radius R of the circle (distance from 24 to any of positions I, II or III) corresponding to the length between centres of the ram 24 when fully extended.

By way of example, the following Table sets out the cutting forces which may be attained at various load-carrying capacities with a silage grab having the following dimensions, compared with a typical small-capacity grab of the type currently available, having a ram of stroke 250mm: Width of grab: 1.25m Stroke of ram: 400mm

Position Position Position Current I II III type Cut block size (est) 0.85m 0.63m 0.53m 0.52m Total loaded weight (est) 1250kg 1030kg 930kg Cutting force: start 5T 7.95T 10.38T 2.33T Cutting force: mid 7.431 8.43T 10.6T 5.23T Width of blade opening 900mm 710mm 590mm 800mm A width df l-.-25m is little or no wider than an average tractor and therefore still enables blocks of silage to be taken cleanly from right up to a side wall of a store, and yet the maximum capacity of 0.85m3 is almost as much as a current large-capacity grab (0.93m3) of considerably greater width but reduced manoeuverability.

Claims (17)

1. A silage grab comprising a fixed rear wall for attachment to a tractor, the rear wall having forwardly-extending tines attached thereto and a front cutting part including a cutting blade pivotably attached to the rear wall, drive means being mounted between the rear wall and cutting part, in which the mounting position of the drive means in relation to the pivot point of the front cutting part is variable, thereby enabling the maximum opening of the cutting part to be varied.

2. A silage grab according to Claim 1, in which the drive means comprises a double-acting hydraulic ram.

3. A silage grab according to Claim 1 or Claim 2, in which the drive means is constituted by a single centrally-mounted ram.

4. A silage grab according to any preceding claim, in which the drive means is variably positioned at its attachment to the rear wall.

5. A silage grab according to any preceding claim, in which the mounting position of the drive means to the rear wall lies on an arc of a circle having a radius corresponding to the maximum extended length of the drive means and its centre at the point of attachment thereof to the cutting part when in the closed position.

6. A silage grab according to Claim 5, in which the drive means comprises a hydraulic ram and the rear wall of the grab is provided with two or more location positions for mounting the cylinder part of the ram, the location position lying on said arc.

7. A silage grab according to any preceding claim, in which the rear wall is provided with an upstanding support formation in which are accommodated the mounting positions for the drive means.

8. A silage grab according to any preceding claim, in which the cutting blade when in the fully-open position and with the grab set in the position of maximum capacity is substantially vertically above its position when closed, whereby the notional straight line joining the two positions defines a chord which is substantially orthogonal to the plane containing the tines.

9. A silage grab according to Claim 8, in which the pivot point of the cutting part on the rear wall is at a vertical height above the tines which is approximately half of the said chord.

10. A silage grab according to any preceding claim, in which the cutting part includes side members which may have cutting blades at their lower edges.

11. A silage grab according to Claim 10, in which the side members include blades, the blades including angled rear portions to cooperate with side frame members of the rear wall to provide a shearing cutting action.

12. A silage grab according to any preceding claim, in which the tines are angled slightly downwardly in a forward direction.

13. A silage grab according to any preceding claim, in which at least some of the tines are cranked.

14. A silage grab according to any preceding claim, in which the tines at each end are more robust than the remainder of the tines and may be mounted at a higher position in the end wall.

15. A silage grab according to any preceding claim in which the cutting blade or blades are detachably secured to the front part.

16. A silage grab according to any preceding claim, in which the front cutting blade has a tail portion angled so as to urge the cut face of the silage clamp away from the front part during the cutting movement in use.

17. A silage grab substantially as hereinbefore described with reference to and as illustrated in the accompnaying drawings.