GB2046653A

GB2046653A - Impact Tool Holder

Info

Publication number: GB2046653A
Application number: GB8007073A
Authority: GB
Original assignee: Fosroc International Ltd
Current assignee: Fosroc International Ltd
Priority date: 1979-03-03
Filing date: 1980-03-03
Publication date: 1980-11-19

Abstract

The head assembly (2) of a substrate breaker, coal pick, chipping hammer or the like is made of a metal casting (3) which does not need broaching, and a tool (7) is releasably received in the casting socket (6) held there by a resilient insert (9). The insert preferably comprises an elastomeric inner bush (12) and a steel outer bush (13), and at each end has hardened steel tool guides 14a, 14b. <IMAGE>

Description

SPECIFICATION Head Assembly for an Apparatus Such as a Substrate Breaker The invention relates to a head assembly for an apparatus such as a substrate breaker, a coal pick, a hammer drill, a chipping hammer, a demolition pick or a clay digger.

A known type of head assembly for a substrate breaker or like apparatus comprises a metal casting having a socket which receives a reciprocable impact tool of polygonal, usually hexagonal, cross-sectional shape. The tool is a free-siiding fit within the socket and the crosssectional shape of the socket corresponds to that of the tool. In order that the tool be prevented from rotating in the socket it is necessary that there be only a small clearance between the tool and the wall of the socket. The socket is formed by a technique known as broaching which involves drilling a circular hole in the casting and then driving a broaching tool of suitable cross-sectional size and shape into the hole to cut the wall of the hole to the required shape.This technique is unsuitable for use with castings of poorer quality but cheaper material as the broaching tool tends to bind on the hole wall when these materials are used, thus forming a socket of irregular shape. This requires the use of a high quality ferrous casting to prevent the broaching tool from binding. Therefore, with the known type of head assembly, not only must the casting be shaped in an expensive way, but the casting must also be formed of a high quality and expensive material. Another problem with this type of head assembly is that in use, the wall of the socket is prone to wear despite the high quality of the material, such that the clearance between the tool and the wall of the socket increases and the assembly becomes noisy. In Europe, and in other parts of the world, there are strict regulations governing the noise output from substrate breakers.Worn castings must therefore be replaced frequently to keep the noise.level within the prescribed limits.

It is among the objects of the invention to provide an improved form of head assembly for a substrate breaker or like apparatus, which is cheaper to manufacture, which has an increased working life, which is easily adaptable to receive tools of different cross-sectional size or shape, and which is substantially quieter than known head assemblies.

According to the invention there is provided a head assembly for an apparatus such as a substrate breaker comprising a metal body having a socket therein, an impact tool being reciprocably movable within the socket, and releaseable means to retain the tool within the socket, the tool and the socket being dimensioned relative to each other such that an annular clearance to restrain the tool against lateral wall of the socket, an insert being present in the clearance to restrain the tool agianst lateral' movement within the socket.

The impact tool may be conventional tool having say a chisel-shaped, a pointed or a hammering tip.

The means to hold the tool within the socket may be a conventional arrangement such as a latch or stirrup arrangement or a retaining nose which is screw-threaded on to the metal body.

Preferably the tool is of polygonal crosssectional shape and the wall of the socket is of generally circular cross-sectional shape, and the insert has correspondingly shaped inner and outer walls and is dimensioned such that the insert is a tight fit in the socket and the tool is a sliding fit in the bore of the insert. The wall of the socket may to advantage be recessed to receive the insert.

Preferably at least a portion of the bore of the insert is of a resilient material. The resilient material may be an elastomeric or a plastics material. Most preferably a longitudinal mid portion of the bore is of the resilient material. The two end walls of the insert are preferably formed of high-strength metal to serve as guides for the tool. Each end wall may be formed in one piece, but for ease of manufacture each end wall is preferably formed in two or more pieces. The end walls may be radially divided, or they may be divided transversely into a stack of pieces.

It is especially preferred that the outer portion of the insert which is disposed adjacent the wall of the socket is of high-strength metal.

The insert is preferably located remote from the working end of the tool.

Preferably the metal body is a relatively low quality ferrous casting or is a lightweight metal casting such as aluminium.

According to much preferred embodiment of the invention, a head assembly for an apparatus such as a substrate breaker, comprises a relatively low quality metal casting having a socket of generally circular cross-sectional shape therein, an impact tool of polygonal cross-sectional shape being reciprocably movable within the socket, releasable means to retain the tool within the socket, an insert being interposed between the wall of the socket and the wall of the tool and being received within a recess in'the wall of the socket remote from the working end of the tool, the insert being a tight fit within the recess so as to prevent rotation of the inset within the socket, the insert comprising an outer portion of high strength metal adjacent the wall of the socket, two metal end portions bf the insert each having a central bore of the same general cross-sectional shape as that of the tool and being dimensioned such that the tool is reciprocable within the bores but is substantially unable to rotate therein, the portion of the insert intermediate the end portions being of a resilient material and being dimensioned to restrain the tool against lateral movement within the bore of the insert during reciprocation therein.

Head assemblies according to the invention are suitable for use with most conventional hydraulic or pneumatically driven substrate breakers or like apparatus. Such apparatus may typically contain a reciprocating piston to drive the tool when the head assembly is attached to the body of the apparatus.

The invention includes a substrate breaker or like apparatus having a head assembly as described. The invention further includes an insert for use in a head assembly as described, comprising an annular element having an outer wall shaped to correspond to the shape of the socket wall and an inner wall shaped to correspond to the cross-sectional shape of the tool, and having at each end an end wall formed of high strength metal and an intermediate portion formed of resilient material.

It will be understood that although the term 'head assembly' is often used for an assembly such as that described above, the assembly may be attached to the lower end of the apparatus in use.

The invention will now be further described by way of example, with reference to the accompanying diagrammatic drawings in which Figure 1 is a partial longitudinal section through part of a substrate breaker having a downwardly directed head assembly according to the invention, and Figure 2 is a partial plan view of the head assembly of Figure 1.

The head assembly 1 is attached to the body 2 of a hydraulically operated substrate breaker, only a part of the body being shown for convenience.

The head assembly 1 comprises an aluminium casting 3, the upper end of which has four bolt holes 4, Figure 2, by which the head is attached to the body 2 by boits 5. A drilled socket 6 of generally circular cross-sectional shape extends through the casting 3 and receives an end portion of a tipped breaking tool 7 of hexagonal crosssection. At the upper end of the socket 6 is an annular recess 8 to receive an insert 9 as a tight fit within the recess. The recess 8 forms a shoulder 10 at the junction with the lower part of the socket, on which the insert 9 is seated.

The insert 9 has a central bore 11, Figure 2, to receive the tool 7. As shown in Figure 1, the bore 11 comprises three portions 1 a, 1 b and 11 c, and these will be described in more detail below.

The insert comprises an elastomeric inner bush 12 and a steel outer bush 13 and at each end of the insert there is a hardened steel tool guide 1 4a, 1 4b. The tool guides 1 4a and 1 4b are both formed in two halves, as shown for the upper tool guide 1 4a in Figure 2. Each tool guide 1 4a, 1 4b, has a central hexagonal bore portion 1 a, 1 c respectively which receives the tool 7 as a sliding fit.The bore portions 11 a, 11 c, are dimensioned such that the tool 7 is unable to rotate within the bore 1 The bore portion 1 b is defined by the elastomeric inner bush 12 and is smaller in crosssection than the bore portions 1 a, 1 c of the tool guides, and abuts the sides of the tool 7 to prevent lateral movement of the tool within the bore 11.

The tool 7 is retained within the socket 6 by a conventional pivoted latch assembly 1 5 which is dimensioned to abut an annular flange 16 on the tool 7 when the tool 7 moves downwards within, the socket. The tool 7 is reciprocable between a lower position in which the flange 1 6 abuts the latch 1 5 and an upper position in which the upper end of the tool abuts a piston 17 which is contained within the body 2. The piston 1 7 is reciprocably driven by conventional hydraulic means, not shown.

To assemble the head, the insert 9 is gently tapped into the annular recess 8 from the upper end of the socket 6, until the upper end face of the insert is flush with the upper end face of the casting 3 and the lower end face of the insert is seated on the shoulder 10. The head 1 is then bolted to the body 2 by the bolts 5. The latch 1 5 is rotated anti-clockwise and the tool 7 is inserted from below into the socket 6 and into the bore 11 of the insert 9 until the upper end of the tool abuts the piston 1 7. The latch 1 5 is then rotated clockwise until it reaches the position shown in Figure 1 when the latch serves to retain the tool within the socket.

When the substrate breaker is operated, the piston 17 7 rapidly moves downwards and urges the tool 7 to move downwards within the socket, enabling the point of the tool to strike a substrate to be broken. The downward movement of the tool 7 is limited by the flange 1 6 abutting the latch 1 5. The piston then moves upwards and the tool 7 is then free to move upwards. The upward stroke of the tool is caused partly by the tool rebounding from the substrate and partly by the weight of the breaker which slides down over the tool.

When it is desired to use a tool of different cross-sectional shape, or when the tool guides 1 4a, 1 4b, become worn, the insert 9 may be easily replaced by tapping the insert out of the socket and inserting a new insert into the socket as described above.

The head assembly is quiet in operation and wear of the head assembly is considerably reduced compared with conventional head assemblies. The insert is easily replaced when the tool guides become worn or when a different tool is to be used. The cost of the head assembly is substantially reduced because of lower machining cost and because cheaper materials may be used for the casting. Longitudinal guide rods, not shown, may be present in the insert 9, to hold the end walls 14a, 14b together.

Claims

1. Head assembly for an apparatus such as a substrate breaker, comprising a metal body having a socket therein, an impact tool being reciprocably movable within the socket, and releaseable means to retain the tool within the socket, the tool and the socket being dimensioned relative to each other such that an annular clearance is present between the tool and the wall of the socket, an insert being present in the clearance to restrain the tool against lateral movement within the socket.

2. An assembly according to Claim 1, in which the tool is of polygonal cross-sectional shape and the wall of the socket is of generally circular cross-sectional shape, and the insert has correspondingly shaped inner and outer walls.

3. An assembly according to Claim 1 or 2, in which the wall of the socket is recessed to receive the insert.

4. An assembly according to any preceding Claim in which a portion of the bore of the insert is of a resilient material.

5. An assembly according to Claim 4, in which a longitudinal mid-portion of the bore is of the resilient material.

6. An assembly according to Claim 5, in which the two end walls of the insert are formed of highstrength metal.

7. An assembly according to Claim 6, in which each end wall is formed in two or more pieces.

8. An assembly according to any preceding Claim, in which the outer portion of the insert which is disposed adjacent the wall of the socket, is of high-strength metal.

9. An assembly according to any preceding Claim, in which the insert is located remote from the working end of the tool.

10. An assembly according to any preceding Claim, in which the metal body is a relatively low quality ferrous casting or is a lightweight metal casting.

11. A head assembly for an apparatus such as a substrate breaker, comprising a relatively low quality metal casting having a socket of generally circular cross-sectional shape therein, an impact tool of polygonal cross-sectional shape being reciprocably movable within the socket, releasable means to retain the tool within the socket, an insert being interposed between the wall of the socket and the wall of the tool and being received within a recess in the wall of the socket remote from the working end of the tool, the insert being a tight fit within the recess so as to prevent rotation of the insert within the socket, the insert comprising an outer portion at high strength metal adjacent the wall of the socket, two metal end portions of the insert each having a central bore of the same general cross-sectional shape as that of the tool and being dimensioned such that the tool is reciprocable within the bores but is substantially unable to rotate therein, the portion of the insert intermediate the end portions being of resilient material and being dimensioned to restrain the tool against lateral movement within the bore of the insert during reciprocation therein.

12. A head assembly substantially as described with reference to the drawings.

13. A substrate breaker or like apparatus incorporating a head assembly according to any preceding Claim.

14. An insert for use in a head assembly according to any preceding Claim and comprising an annular element having an outer wall shaped to correspond to the shape of the socket wall and an inner wall shaped to correspond to the crosssectional shape of the tool, and having at each end an end wall formed of high strength metal and an intermediate portion formed of resilient material.

1 5. An insert substantially as described with reference to the drawings.