DESCRIPTION TECHNICAL FIELD

This invention relates to scabblers, that is to say machines for roughening, abrading or removing projections from hard ground _. surfaces, such as roads or like concrete constructions. BACKGROUND A-RT Scabblers are known from U.S. Patent Specificati

No. 2,553,435 of Briese and British Patent Specificat

Nos. 709,904 of Metropolitan Construction Company Ltd

(Metropolitan) and 1,056,011 of John MacDonald and

Company (Pneumatic Tools) Ltd. (MacDonald) . In these previously known scabblers the scabbling tools are fo or mounted on ends of pistons that project from cylin ofthe scabblers. Each piston is caused to reciprocat by fluid pressure applied to the other end of the piston within the cylinder. In Briese, the pistons are scaling tools 33 which project downwardly from sealer heads 32, -and are supplied with motive fluid by a pneumatic line within an adjustable handle 22. Metropolitan shows drill bits on operating rods 40 passing permanently into hammers 16 to 19. MacDonald has piston rods 30 projecting from a cylinder block 1 the projecting end of each piston rod having a scabbli tool 36 mounted thereon.

The scabbier of Briese is mounted on three wheels each aligned in the front-to-rear direction, but the scabblers of Metropolitan and MacDonald are provid

with only two wheels and are therefore highly manoevrable. With the scabbier of Metropolitan the pressure of the scabbling tools on the ground surface is controlled by the operator who can raise or lower the.handles to vary the effective height of the scabbling tools above the surface being roughened. With the scabbier of MacDonald the pressure of the scabbling tools on the surface being roughened is a characteristic of the machine itself as the impacting of the scabbling tools on the ground is sufficient to raise the wheels from the ground. -

None of these prior proposed scabblers has employed pistons contained wholly within cylinders of the scabblers. Causing the pistons to project from the cylinders limits the working area of the pistons effective to move the pistons on their return strokes, which limits significantly the number of impacts per second which is attainable. Mounting or forming the scabbling tool on the pistons further Hjnits the number of impacts per second, as the motive fluid must move the entire scabbling tool and piston on both the operative and return strokes. There is also considerable tool movement which has concealed the potential advantage of keeping the machine level. This advantage is uniformity of effective scabbling

action. . Of the above three prior Specifications only

Briese has more than two ground-engaging wheels, as is necessary to attain a constant presentation of the machine to the ground. However to anoevre the machine of Briese an operator would have to manipulate the handle upwardly or downwardly to the limit of its pivotal movement and beyond so as to lift the front or rear wheels from the deck." Thereafter control of the effective height and pressure-of the scabbling tools would be as in Metropolitan. DISCLOSURE OF THE INVENTION

A scabbier according to this invention comprises a-frame, a number of cylinders mounted upon or within the frame each having a scabbling tool removably inserted into an end thereof, a piston completely received in each cylinder and reciprocable under motive fluid pressur therein for striking the scabbling tool, handle means connected to the frame, and at least three ground wheels connected to the frame, at least one being a castor wheel, for presenting the frame and scabbling tool a constant height above the ground.

The provision that one or more of the ground wheels is a castor wheel means that the machine is just as manoevrable as the previous two-wheeled machines, withou any sacrifice in the precision of the constant height presentation of the frame which is attained in the

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scabbier of this invention. Indeed if all the wheels are castor wheels the manoevrability of the machine can be increased substantially.over that of the scabbier of Metropolitan, without the loss of precision inherent in the floating action of MacDonald.

The provision of at least three ground wheels in the scabbier according to this invention ensures that the scabbl tool movement can be kep ηormal to the ground to get maximum impact. The use of a piston separate from the scabbling tool makes it possible to work at -a high number of impacts per second and a high energy per blow. The scabbling tool movement is also reduced in the scabbier of this invention by the use of a piston separate from the scabbling tool, but this reduction does not adversely affect the performance of the scabbier as the frame height above ground is maintained constant. The scabbling tool movement is much less than the piston movement, so that the tendency for dirt and grit to get drawn into the lower end of the cylinder is much less than in the above prior art machines in which the scabbling tool shank was the piston. Wear at the cylinder mouth is thus enormousl reduced. Moreover, such wear as does occur does not resul in a substantial power loss as it would if it were the ^" cylinder around the piston that were worn. Scabbling tool replacement i-s simple, as the piston and piston seals

do not have to be replaced or even disturbed. Advantageously the scabbling tool shank is received in a removable bush within the cylinder so that any wear around the cylinder mouth can be simply and speedily rectified by' renewing the bush at the same time as renewing the scabbling tool. Such a scabbling tool is preferably retained by means of a spring engaging in grooves in the exterior of the tool and of the-cylinder.

Because of the reduced tool movement it may be desirable according ^" to this invention to provide an air stream directed at the scabbling tools to blow away chippings produced by the working action of the scabbier. Where the motive fluid for the pistons is compressed air, exhaust air from the cylinders may advantageously be used to provide such an air stream.

The frame is preferably a casting which may have formed therein each of a motive fluid inlet, a motive fluid outlet, one or more lubricators and one or more lubricating oil reservoirs. The cylinders are preferably received substantially completely in,recesses in the frame between a forward 'pair of the ground wheels.

Preferably the frame is a single casting extending backwards, incorporating a lubricator and carrying a rear castor wheel. This makes for simplicity and robustness of construction, and easy serviceability.

Another modification is the mounting of two of the wheels mounted on stub-axles projecting from the sides of the frame. These larger wheels pass more readily over uneven ground, and together with the rear castor wheel

provide accurate manoeuvrability in use. DRAWINGS

This invention is illustrated by way of example, in the drawings of which:

Figures 1, 2 and 3 are respectively a side eleva a rear elevation and a plan view of a scabbier according this invention;

Figure 4 is a vertical section through a lubrica assembly of one half only of the scabbier of Figure 1, t section being taken along the line A-A of Figure 5; Figure 5 is a staggered section taken along the

B-B of Figure 4;

Figure 6 is an ^' axial section through a cylinder assembly, piston and scabbling tool of Figure 5;

Figure 7 is a side elevation of a modified scabb and

Figure 8 is a plan thereof. BEST MODE OF CARRYING OUT THE INVENTION

Referring first to Figures 1 to 3, the scabbier comprises a frame 1 to which is secured a handle 2 and t ground-engaging castor wheels 3, 4 and 5. The castor wh 3 and 4 are arranged near the front of the frame 1, and about vertical axes that are in alignment with a row of scabbling tools 6. The rear castor wheel 5 is mounted o rearward extension 7 of the frame 1 that is bolted betwe opposite side portions of the handle 2. The mounting of each of the castor wheels 3, 4 a is such that when the scabbier is on a flat surface the scabbling tools 6 are presented normally to the surface

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and the height of the frame 1 above tha.t surface is constant.

A pneumatic air line (not shown} is in use connected to the scabbier to provide the motive fluid for the - scabbling tools 6, ^• The air line is connected to an on/off control valve 8 secured at the top of the handle 2, and an air pipe 9 leads the air from the control valve 8 to an inlet 10 in the frame 1.

The inlet 10 leads to an air dividing chamber 11 0 from which it is passed to identical pneumatic air passages in opposite sides of the frame each side of ^• the frame 1 having air passages therein for controlling two of the four scabbling tools 6. For convenience only the left hand side of the machine is illustrated in 5 ^: . Figure 4 and described below..

From Figure 4 it can be seen that the air passes from the dividing chamber 11 into a passage 12 formed in the frame 1. The opening 13 from the dividing chamber 11 into the passage 12 is shown _' dotted in Figure 4 even 0 ^{^} though this opening would be above the plane of the paper. The left-hand end of the passage 12 is closed by a plug 14, so that air is forced to pass through a venturi tube 15 into which oil is allowed to seep through a filter 16 from a reservoir 17. The venturi 25. tube 15 and filter- 16 together form a lubricator 18 by

eans of which a,n oil mi.st is generated andj≥ntrained in the motive air. Replenishment of--the oil in the reservoir is through a filler cap 19^ - A pressure equalization tube 20 extends from _^ the passage 12, before the venturi tube 15, . ±nt r-t e reservoir 17,

From the venturi tube 15 the motive air, with its entrained lubricating oil mist, passes upwardly to an inlet chamber 21 for an operating cylinder of the inner one of the left hand pair of scabbling tools 6 and through a passage 22 (Figure 5} to an inlet chamber 23 for an operating cylinder of the outer one of the left hand pair of scabbling tools.

Each of the inlet chambers 21 and 23 leads to a control valve assembly 24 of its associated cylinder. The control valve assemblies 24 and cylinders are identical, and the construction of each is illustrated in Figure 6.

The control valve assembly 24 is a conventional clack valve for supplying the motive air intermittently to an upper working face of a piston to cause the piston to reciprocate. The piston is numbered 25 in Figure 6, and is completely received in a cylinder 26 which is mount in the frame 1. It is clear from Figure 5 that the cylinder 26 is inserted downwardly.into the frame 1, the control valve assembly 24 inserted over it and the whole retained in position by a top plate 27. The

cylinder 26 is further secured in position by a bolt 28 in the rame 1.

From Figure 6 it can be seen that motive air is directed by the control valve assembly 24 intermittently to a pneumatic working chamber 29 above the piston 25 to drive the piston downwardly. Towards the bottom of its downward stroke the leading edge of the piston 25 passes and closes a radial, exhaust port 30 that communicates, via a vertical bore 31- in the ^' cylinder wall, with an exhaust chamber 32. A pneumatic chamber 33 below the piston 25 is thus shut off from exhaust, and further downward movement of the piston causes the pressure in the pneumatic chamber 33 to rise. This pressure increase in the chamber 33 is transmitted as a pilot pressure to the control valve assembly 24 via a radial port 34 and a vertical bore 35 in the cylinder wall and causes the control valve assembly to interrupt the supply of motive air to the pneumatic working chamber 29. This action coincides with both the uncovering of an exhaust port 36 of the pneumatic working chamber 29 and the impacting of the piston 25 against the scabbling tool 6. The rebound of the piston 25 from the scabbling tool 6, together with the upward impulse from the air compressed in the chamber 33, causes the piston to bounce back until the exhaust port 36 is closed and the air in the

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chamber 29 is compressed. At this stage pilot pressure again causes actuation of the control valve assembly 24 so that the cycle is repeated.

The exhaust air is passed, at the end of each power stroke of the piston 25, to the exhaust chamber 32 formed between the cylinder 26 and frame 1, whence it may be directed to a silencer Cnot shown) or to jets Cnot shown) arranged to clear away the chippi gs produced by the machine in use .. ^' At the downward limit of its travel when the piston

25 has cleared the exhaust passage 36, it impacts a stem 37 of the scabbling tool 6 associated with that cylinder. The stem 37 is slidably received in a bush 38 in the cylinder 26, and the scabbling tool 6 is retained in the cylinder by means of a beehive spring 39 (not shown in

Figure 6) engaging annular grooves 40 and 41 in the cylin

26 and the scabbling tool 6 respectively.

By removal of the beehive springs 39 the scabbling tools 6 can easily be removed from the cylinders 26, for example for replacement when tungsten carbide teeth 42 thereon become worn.

In use the motive air is applied intermittently to the pneumatic chamber 29 so that reciprocation of the pistons 25 is very rapid. At the limit of each downstro of the pistons 25 a high energy impact is delivered ^" to

the associated scabbling tool 6, so that an efficient scabbling action is achieved. The various pistons and cylinders operate in a random manner.

Because each impact is followed immediately by a rapid upward movement of the piston that has caused the impact there is no great tendency for the wheels 3, 4 and 5 to be lifted off the ground as there would be if the pistons carried the scabbling tools at their ends. Accordingly the provision of the three ground-engaging castor wheels 3, 4 and 5 is effective to provide a constant and optimum presentation of the scabbling tools to the ground in use, without any sacrifice in the manoeuvrability of the machine.

In Figures 7 and 8, the main frame comprises a single casting mounting cylinders 26 and the lubricator 18, and having the rearward extension 7 carrying the rear castor wheel 5. The air inlet 10 is above the lubricator 18, but the air passes through the divider chamber 11 and down through the Venturi tube 15 and inner inlet chamber 21 to the control valve assemblies 24.

The rearward extension 7 of the main frame meets a lower extension, and the rear castor wheel 5 is bolted ^' thereto. The side wheels 3, 4 are mounted directly on the main frame.