GB2147035A - Improvements in and relating to impact-action self-propelled mechanism for driving holes in the earth - Google Patents

Abstract

A pneumatically operated impact-action self-propelled mechanism for driving holes in the earth comprising a cylindrical housing assembly (10) with an anvil member (11) located at the forward end thereof. An impact piston (12) is reciprocal in the housing to deliver successive impacts to the anvil member and shaping with the housing a forward chamber (15) of variable volume. A control assembly comprises a forwardly extending sleeve (23) which is slidably received within a rear space of said impact piston to form a rear chamber (16) of variable volume. A central passage is connected to said sleeve for continuous supply of compressed air into said rear chamber and therefrom into said forward chamber through apertures (18) in a side wall of the rear chamber of said impact piston. Means is provided for locating said sleeve longitudinally with respect to said apertures for providing forward or reverse movement of said mechanism. An elastically deformable shock-damping bush (20) is located within the rear of the housing assembly which houses an annular metallic member (21) having longitudinal apertures (22) formed therethrough, through which air is exhausted. <IMAGE>

Description

SPECIFICATION Improvements in and relating to impactaction self-propelled mechanism for driving holes in the earth The invention relates to impact-action selfpropelled mechanism for driving holes in the earth by compacting the soil about the hole being made, such mechanisms being pneumatically driven.

It is one object of the invention to provide a simplified assembly for such a mechanism.

According to the invention there is provided a pneumatically operated impact-action selfpropelled mechanism for driving holes in the earth comprising a cylindrical housing assembly with an anvil member located at the forward end thereof; and impact piston reciprocal in the housing to deliver successive impacts to the anvil member and shaping with the housing a forward chamber of variable volume and a control assembly comprising a forwardly extending sleeve which is slidably received within a rear space of said impact piston to form a rear chamber of variable volume, a central passage connected to said sleeve for continuous supply of compressed air into said rear chamber and therefrom into said forward chamber through apertures in a side wall of the rear chamber of said impact piston, means for locating said sleeve longitudinally with respect to said apertures for providing forward or reverse movement of said mechanism and an elastically deformable shock-damping bush located within the rear of the housing assembly which houses an annular metallic member having longitudinal apertures formed therethrough, through which air is exhausted.

The means for locating said sleeve longitudinally with respect to said apertures may comprise a screw thread formed on the outer surface at the rear of said sleeve which engages with a screw thread formed on the internal surface of said annular metallic member.

Said shock-damping bush may be formed with annular inwardly extending lips at each end thereof.

The outer surface of said annular metallic member may be roughened or knurled to enable a good bond with an adhesive for attachment within said shock-damping bush.

Alternatively said shock-damping bush may be moulded in site, e.g. by injection moulding.

The foregoing and further features of the invention may be more readily understood from the following description of a preferred embodiment thereof, by way of example, with reference to the accompanying drawing, which is a side sectional schematic view of pneumatically operated impact-action self-propelled mechanism.

Referring now to the drawing, the mechanism comprises a cylindrical housing 10 having an avil 11 located at the forward end.

An impact piston 1 2 engages the internal cylindrical wall of housing 10 with interrupted annular shoulder 1 3 and a continuous annular shoulder 14.

The space between the internal wall of the housing 10 and the external surface of the impact piston 1 2 constitutes a front working chamber 1 5. The rear portion of impact piston 1 2 has formed therein a cavity 1 6 which receives a forwardly extending sleeve 23 which is connected to an air supply connector 1 7. The cavity 1 6 constitutes the rear working chamber of the mechanism, responsible for forward displacement of the impact piston 1 2.

Ports 1 8 are formed through the cylindrical wall of the impact piston 1 2 in the area of the rear cavity 16, these ports 1 8 establishing communication between chambers 1 5 and 16.

A stepped annular metallic member 1 9 is screw-threadably engaged within the rear of housing 10 and an annular elastically deformable shock-damping bush 20 formed with inwardly extending lips at each end is adhered within the rear end of member 1 9.

An annular metallic member 21 with longitudinal apertures 22 formed therethrough has a roughened or knurled outer surface to enable it to be adhered within bush 20 and a screw threaded internal surface which engages with screw thread 24 formed on the exterior surface of sleeve 23.

The rear internal surface of member 1 9 is screw-threaded at 25 to receive an annular metallic rear member 26 which serves as a rearwardly locating member for bush 20.

Alternatively the bush 20 may be formed by injection moulding between members 1 9 and 21, preferably with a neoprene material.

In operation of the mechanism, with the sleeve 23 in the position as shown in the drawing and with compressed air supplied to connector 1 7 such compressed air is fed to working chamber 1 5. This causes impact piston 1 2 to be driven forwardly to engage anvil 11, which impact causes the housing 10 to be driven forwardly.

At a pre-set point, immediately preceding the point at which the impact piston 1 2 strikes the anvil 11 (this pre-set point being defined by the position of the ports 1 8 in the impact piston 1 2 and by the arrangement of the head portion of the sleeve 23) the ports 1 8 establish communication between the chambers 1 5 and 16, whereby the front chamber 1 5 becomes connected with the source of compressed air via the rear chamber 16 and the connector 17.

The rebound of the impact member after an impact together with the force exerted by the compressed air on the forward face of the impact piston, due to the difference between the working (effective) areas of the impact piston 1 2 in the chambers 1 5 and 16, respectively, are responsible for the return stroke of the impact piston after it has delivered the impact upon the anvil 11.

In the course of this return stroke of the impact piston 12, the ports 1 8 become closed by the external cylindrical wall of the head portion of the sleeve 23 and during the rest of the return stroke the compressed air in the working chamber 1 5 is expanding. At this stage of its return stroke the motion of the impact piston 1 2 meets the resistance of the compressed air in chamber 16 which is continuously connected with the source of compressed air.

At the end of the return stroke of the impact piston 1 2 ports 18 thereof pass beyond the head portion of sleeve 23 and thus establish communication between the working chamber 1 5 and the ambient atmosphere through the exhaust passages 22 in member 21.

Then the above-described operating cycle repeats itself.

When it is required to reverse the mechanism out of the hole formed the air supply is turned off and the hose rotated anti-clockwise so as to move sleeve 23 rearwardly with respect to member 21. In this position the sleeve 23 is located rearwardly in chamber 1 6 and the apertures 1 8 remain open. When the air supply is turned on the impact piston 1 2 is driven rearwardly to move the mechanism rearwardly.

When it is required to drive the mechanism forwardly again the air supply is again turned off and the hose rotated in a clockwise direction to move the sleeve 23 forwardly with respect to member 21 to return the sleeve 23 to the position shown in the drawing.

The rear assembly of members 19, 20, 21 and 26 facilitates considerable ease of fabricating and assembly of the device as compared with prior art devices.

Claims (7)

1. A pneumatically operated impact-action self-propelled mechanism for driving holes in the earth comprising a cylindrical housing assembly with an anvil member located at the forward end thereof; an impact piston reciprocal in the housing to deliver successive impacts to the anvil member and shaping with the housing a forward chamber of variable volume and a control assembly comprising a forwardly extending sleeve which is slidably received within a rear space of said impact piston to form a rear chamber of variable volume, a central passage connected to said sleeve for continuous supply of compressed air into said rear chamber and therefrom into said forward chamber through apertures in a side wall of the rear cahmber of said impact piston, means for locating said sleeve longitudinally with respect to said apertures for providing forward or reverse movement of said mechanism and an elastically deformable shock-damping bush located within the rear of the housing assembly which houses an annular metallic member having longitudinal apertures formed therethrough, through which air is exhausted.

2. A mechanism as claimed in claim 1 wherein the means for locating the sleeve longitudinally with respect to said apertures comprises a screw thread formed on the outer surface at the rear of said sleeve which engages with a screw thread formed on the internal surface of said annular metallic member.

3. A mechanism as claimed in claim 1 or 2 wherein the shock damping bush is formed with annular inwardly extending lips at each end thereof.

4. A mechanism as claimed in any preceding claim wherein the outer surface of said annular metallic member is roughened or knurled to enable a good bond with an adhesive for attachment within said shock damping bush.

5. A mechanism as claimed in claim 1, 2 or 3 wherein said shock-damping bush is formed by moulding.

6. A mechanism as claimed in claim 5 wherein said shock-damping bush is formed by injection moulding.

7. A mechanism substantially as hereinbefore described with reference to the accompanying drawing.