Tool driving or impacting – Impacting devices – Impact transmitting anvil
Reexamination Certificate
2000-05-26
2003-01-28
Smith, Scott A. (Department: 3721)
Tool driving or impacting
Impacting devices
Impact transmitting anvil
C173S128000, C173S210000
Reexamination Certificate
active
06510904
ABSTRACT:
FILED OF THE INVENTION
This invention relates to an improved bushing engaging the tool in an impact hammer and more particularly to a low friction bushing protected from foreign objects in use.
BACKGROUND OF THE INVENTION
Hydraulic impact hammers are heavy equipment used in mining, construction, demolition, roadwork, quarrying, and similar applications. Such hammers range in size from units weighing less than 200 lbs. to units weighing more than 15,000 lbs. These hammers are used to break up concrete, rock, ore, and the like. They are also sometimes used to remove surface portions from an underlying substrate.
Hydraulic impact hammers generally comprise a housing having a central cylinder. A piston is contained within the cylinder. The top end of the cylinder communicates with or forms part of a gas chamber. The bottom end of the cylinder communicates with a bore in a tool holder which is connected to the housing. The tool holder contains a tool, such as a chisel point, which will strike a workpiece. A valve is attached to the housing and controls the flow of hydraulic fluid into the cylinder. The hydraulic fluid forces the piston up compressing the gas in the gas chamber. When the piston reaches a certain height, the hydraulic fluid is allowed to exit the portion of the cylinder below a piston seal and the piston is brought down forcefully to strike the tool. The tool is thus sharply hammered and in turn impacts upon the substrate desired to be broken or modified. The operation of the valve causing the piston to travel upward and allowing it to travel downward is automatic. The piston reciprocates rapidly resulting in numerous forceful blows of the tool against the substrate. The impact frequency, the number of impacts per minute, of a hydraulic impact hammer ranges from about 200 to over 2000 impacts per minute. Each impact involves significant amounts of energy. At high impact rates, large amounts of energy are used and/or dissipated. Because of the large amounts of force and energy involved, hydraulic impact hammers must be built robustly.
Hydraulic impact hammers create dust, debris and obstructions by their operation. Breaking-up of concrete results in dust, flying stones and particles of concrete and exposed reinforcing rod (rebar). The dust is created at the working end of the hammer as are the flying stones and other particles. The dust and flying particles can be moving quickly and can penetrate between working parts causing wear and interfering with operation. Rebar is often encountered in breaking up concrete. As it is long, often relatively slim, and tough, it can cause damage. The environments in which hydraulic impact hammers are used are often difficult environments.
One mechanism developed to compensate for the difficult environment described and the intrusion of particles into the lower end of the hammer is the use of bushings. The tool holder, holding the tool in place at the bottom of the hammer does not bear directly against the tool. Rather, a cylindrical bushing is fitted into a recess in the bottom end of the tool holder and surrounds the tool. Such bushings are sometimes made of steel and sometimes made of nylon or another polymer. The bushings do not move with respect to the tool holder. Therefore, there is no wear or very little wear around the bushing. The tool moves within the bushing. Wear occurs between the tool and the tool bushing. This wear is aggravated by the intrusion of dust and particles of concrete. Moreover, impacts from standing rebars and the like often damage the bushing. The bushing is replaceable. Thus, while the bushing and tool wear the tool holder and rest of the hydraulic impact hammer are protected.
Additionally, when one uses a steel bushing and a steel tool, frictional forces generate significant heat where the tool rubs against the tool bushing. This heat can interfere with lubrication and aggravate wear on the tool and tool bushing.
This arrangement requires that the operator check the tool and tool bushing for wear periodically. When the tool bushing is worn excessively, the hammer must be taken out of service, the tool removed and the tool bushing removed from the tool housing. After the tool bushing and tool are replaced, the hammer can be placed back in service. Significant maintenance costs and down time are thereby incurred.
Plastic, often nylon, bushings have been used in place of steel bushings. Such bushings fail frequently. One mechanism of failure is cracking of the bushings. Once the bushing starts to crack, it quickly deteriorates and must be replaced.
SUMMARY OF THE INVENTION
The present invention provides an improved bushing and tool housing structure which overcomes many of the above referred to problems, minimizes wear, extends bushing life, and is easy to maintain. In accordance with the present invention, there is provided a tool holder assembly for a hydraulic impact hammer in which the lower end of the central bore contains a polymeric or plastic bushing adapted to surround a tool and a metallic bushing protector below the bushing having an inside diameter slightly larger than the inside diameter of the bushing.
Further in accordance with the invention, a recess is provided in the lower end of the tool holder of a hydraulic impact hammer and a cylindrical polymeric bushing is contained in the recess. The polymeric bushing has an inside diameter slightly larger than the outside diameter of the tool being supported. A robust steel ring is pressed into the recess below the polymeric bushing. This steel ring has an inside diameter slightly larger than the bushing so it does not engage against a tool but protects the bushing from impact by flying debris, upstanding rebar or the like.
Still further in accordance with one aspect of the invention, the bushing protector is an add-on device for existing hammer designs in which a steel ring is pressed into the tool holder and is held in place by an interference fit.
Further in accordance with another aspect of the invention, the bushing protector is part of an original design in which the bushing protector is machined from the same workpiece as the tool holder and is integral with the tool holder.
Yet further in accordance with the invention, the polymeric bushing is generally cylindrical in shape and is retained in the tool holder by the bushing protector. Still further in accordance with the invention, a cylindrical polymeric bushing is provided with a generally axial gap which allows the bushing to be compressed to have a smaller outside diameter, inserted through the bushing protector and expanded within a recess in the tool holder where it will engage a tool.
Still further in accordance with the invention, the gap in the cylindrical tool is skewed with respect to the axis of the tool.
Still further in accordance with the invention, the diameter of the opening through the bushing protector is at least one-quarter (¼) inch larger than the diameter of the polymeric bushing central opening.
Yet further in accordance with the invention, the diameter of the bushing protector central opening is between about one-eighth (⅛) inch (2 millimeters) and one-half (½) inch (12 millimeters) larger than the diameter of the central opening of the polymeric bushing.
Still further in accordance with the invention, the bushing protector is at least one-half (½) inch (12 millimeters) long in the axial direction.
Yet further in accordance with the invention, the bushing protector is between one-half (½) inch (12 millimeters) and three (3) inches (75 millimeters) long in the axial direction.
It is the principal object of the present invention to provide a tool holder assembly for a hydraulic impact hammer in which the components last longer, are less prone to failure, produce less heat, and are reasonably maintained.
It is another object of the present invention to provide a polymeric tool bushing for an impact hammer which is protected from impact and abrasion by foreign bodies.
It is still another object of the present invention to provide a to
Fay Sharpe Fagan Minnich & McKee
Nathaniel Chukwurah
Nippon Pneumatic Mfg. Co. Ltd.
Smith Scott A.
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