IMPROVEMENTS IN PAVING BREAKERS

Abstract: There is described a paving breaker (1) comprising a han­ dle (10), a cylinder (20) and a front end (30) wherein the handle is attached to one end of the cylinder by means of spring pins (21) and wherein the other end of the cylinder is attached to the front end also by spring pins (32). A novel design of cylin­ der is also disclosed wherein the cylinder is formed of a rolled steel tube. There is described also a muffler for use with paving breakers, the muffler being formed by two identical parts.

Description: "Paving Breakers" This invention relates to improvements in paving breakers. Conventional paving breakers comprise a handle which includes an air supply control valve, a cylinder in which the operating piston reciprocates, and a front end which incorporates a chuck bushing and means for retaining the tool bit. Hitherto, bolts, studs or set pins have been used to attach the handle to the cylinder and the cylinder to the front end. Such arrangements suffer from the disadvantage that assembly and dismantling of the breaker involve complicated procedures. It is an object of the present invention to provide an improved paving breaker and to obviate or mitigate some of the disadvantages of known breaker designs. According to one aspect of the present invention there is provided a paving breaker comprising a handle, a cylinder and a front end, wherein the handle is attached to the cylinder by means of spring pins and wherein the cylinder is attached to the front end also by means of spring pins. In accordance with a second aspect of the present invention, the cylinder is formed of a rolled steel tube. In accordance with a third aspect of the present invention, the chuck bushing is retained within the front end of the breaker in such a manner as to be replaceable without the need for a hydraulic press. In accordance with a fourth aspect of the present invention, the lower end of the cylinder.is connected to the air supply control valve in the handle by means of external ducting. Still further, the invention provides a muffler for use with paving breakers and like machines wherein the muffler is formed to two identical parts. Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a sectional view of one embodiment of a paving breaker made in accordance with the present invention; Fig. 2 is a sectional view of an alternative embodiment of a paving breaker made in accordance with the present invention; Fig. 3 is an elevational view of a paving breaker of the present invention having a novel handle design; and Fig. 4 is a part-sectional view of a muffler made in accordance with the present invention. Referring to Fig. 1 of the drawings, a paving breaker, shown generally at 1, comprises a handle 10, a cylinder 20 and a front end 30. The handle 10 has an inlet 11 for compressed air which is fed, under the control of a hand operated valve (not shown), alternately to the top of the cylinder 20 and to the bottom of the cylinder 20 via a valve assembly, for example, of the type illustrated in our co-pending U.S. Patent Application No. 241,856. Alternatively, the valve assembly may be of any conventional type and, as is known in the art, is located in the handle 10 within a valve assembly chamber 12. The valve assembly serves to pass automatically compressed air to the top of the cylinder 20 and to the bottom of the cylinder through a port 13 which communicates with an oiler port 14. The cylinder 20 is attached to the handle 10 by means of a pair of spring pins 21 received in and co-operating with semi-circular apertures 22 drilled in the handle 10 and corresponding semi-circular apertures 23 drilled in the cylinder 20. The apertures 22 and 23 are offset by an interference amount so that when the pins 21 are inserted, the cylinder 20 is held tightly against the handle 10. The cylinder 20 is provided with a piston 24 for reciprocating movement therein and at the lower end of its stroke engages an anvil 35 located in the front end 30. The cylinder 20 is also provided with a transfer port 26 which communicates with the port 13 in the handle 10 via an external pipe 80 (Fig. 3). In a similar manner, the cylinder 20 is attached to an outer part 31 of the front end 30 by means of a spring pins 32 which engage respective semicircular apertures 36, 37 in the cylinder 20 and in the outer part 31. Within the outer part 31 there is provided a chuck bushing 33 which is fixed within the outer part 31 by means of a spring pins 34 which engage respective semicircular apertures 38, 39 in the outer part 31 and in the chuck bushing 33. At the front end larger diameter spring pins 32 and 34 are used and the tolerances employed are such that whilst the pins hold the chuck bushing tightly against the cylinder, if a shock load is applied there is enough flexibility and resilience left in the springs to allow slight movement and thereby absorb the shock. At the lower end of the outer part 31 of the front end 30 there is provided a tool 41 fixed in place by a tool retaining mechanism 40 in the form of a spring loaded cam 42. Referring now to Fig. 2, there is shown a paving breaker similar to that illustrated in Fig. 1 having a handle 50 and a front end 70. The cylinder 50 has a smaller bore and may be formed of a rolled steel tube. To reduce weight, the outer part of the cylinder 50 is machined away to leave a thin wall portion 50a. In this way, the bore to weight ratio of the paving breaker is kept within a desired range. As described with reference to Fig. 1, the handl 60 is attached to the cylinder 50 by spring pins 51 and the cylinder is attached to the front end 70 by spring pins 52. The front end 70 has an outer part 71 and a chuck bushing 72 carrying an anvil 74. The chuck bushing 72 is held against the cylinder 50 by virtue of an annular portion 77 engaging a ledge portion 71a of the outer part 71. A tool 76 is located by a tool retaining device 78 fixed to the chuck bushing 72 by a thumb screw 75, the tool 76 being held in the device 78 by a spring loaded locking mechanism 73. The use of the spring pins 52 permits replacement of the chuck bushing 72 without the need for special tools. As is shown in Fig. 3, the connection between the bottom of the cylinder and the handle is effected by external ducting 80. In this way the need for intricate castings is avoided. The ducting is connected to the cylinder and to the handle by standard fittings. In this embodiment the handle is formed of a steel tube 85 to which the inlet control valve 86 is fitted, the valve 86 being operated by a control handle 87 through a plunger 89. The tool 84 is retained in place by a pivotal retaining bar 88. To comply with noise regulations, the paving breaker of the present invention is provided with a muffler 90 as illustrated in Fig. 4. The muffler serves also to protect the external ducting 80 and is provided with exhaust opening 91. The muffler 90 is preferably formed of two identical halves which are suitably sloped internally to receive the cylinder and the external ducting 80. Each half of the muffler is symmetrical about a horizontal axis so that a complete shape may be formed from two identical parts simply by inverting one of them. When a sound absorbing muffler is not required a protective cover may be fitted to protect the external ducting. Modifications and improvements may be incorporated without departing from the scope of the invention.

Claims: CLAIMS 1. A paving breaker comprising a handle, a cylinder and a front end wherein the handle is attached to the cylinder by means of spring pins and wherein the cylinder is attached to the front end also by means of spring pins. 2. A paving breaker as claimed in claim 1 wherein the cylinder is formed of a rolled steel tube. 3. A paving breaker as claimed in claim 1 wherein the lower end of the cylinder is connected to an air supply contrc-l valve in the handle by means of external ducting. 4. A muffler for use with paving breakers and like machines wherein the muffler is formed to two identical parts. 5. A paving breaker substantially as hereinbefore described with reference to the accompanying drawings.

Inventors: ALLAN, DAVID THOMSON
Applicants: ALLAN, DAVID THOMSON, JOHN MACDONALD & COMPANY (PNEUMATIC TOOLS) LIMITED
Application year: 1982
Main classification: B25D17
IPC codes: B25D9, B25D17