Tool driving or impacting – Impacting devices – Impact transmitting anvil
Patent
1997-02-10
1999-08-31
Vo, Peter
Tool driving or impacting
Impacting devices
Impact transmitting anvil
173212, 173135, 173DIG2, B25D 904
Patent
active
059441186
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a pneumatic impact breaker of the type comprising a housing with a cylinder bore, a hammer piston reciprocable in the cylinder bore, a rear cylinder head with an air distributing valve for directing motive pressure air to alternative ends of the hammer piston to reciprocate the latter in the cylinder bore, a front portion attached to the housing and forming a guide and support means for a working implement, and a forwardly directed cylinder bore extension coaxial with and having a smaller diameter than the cylinder bore. The cylinder bore extension is separated from the cylinder bore by an annular shoulder, and an anvil is sealingly guided in the cylinder bore extension. The anvil has a forward end normally abutting the rear end of the working implement and a rear end normally located within said cylinder bore extension. The hammer piston is formed with a piston head for sealing and guiding cooperation with the cylinder bore, and a forwardly extending stem portion for cyclical penetration into the cylinder bore extension to deliver repeated impacts to the anvil at reciprocation of the hammer piston, whereby the stem portion and the piston head form together with the cylinder bore and the annular shoulder an annular energy absorbing air cushion chamber.
BACKGROUND OF THE INVENTION
Pneumatic impact breakers of the above type provide an effective breaking by a high impact energy but generate at the same time external vibrations and internal blows which have a detrimental influence on the operator as well as on the mechanical parts. Detrimental blows or so called bottom blows of the hammer piston occur as the application or feeding force on the breaker is very low, nill or negative. A negative feeding force is accomplished as the breaker is lifted up, for instance when the working implement has become jammed.
In previous impact breakers of the above type, these bottom blows have been difficult to dampen out fully, and, in order to make the parts withstand the stress forces and to ensure a safe assemblage of the breaker, the parts thereof, including the housing itself, have to be oversized. It has also been necessary to use extra strong tie bolts and/or threaded joints to keep the parts safely together. An example thereon is shown in U.S. Pat. No. 3,179,185, FIG. 4, in which the damping means for absorbing the hammer piston energy at bottom strokes comprises an annular elastomer element. In practice, this known arrangement has no ability to absorb the kinetic energy of the hammer piston, and moreover, the service life of this impact damping elastomer element will be very short.
Another example is shown in U.S. Pat. No. 3,451,492. The impact breaker illustrated therein comprises a hammer piston which has a comparatively long impact delivering stem portion in relation to the length of the piston head. This means that, due to the inevitable tilting of the piston occurring when the stem portion is out of guiding engagement with the forward small diameter cylinder bore extension, there must be provided a relatively large play between the stem portion and the bore to avoid too a violent metallic contact therebetween. This results in a relatively wide leak gap around the stem portion, and, accordingly, a rather ineffective damping volume entrapped between the hammer piston, the cylinder bore and the forward shoulder in the cylinder bore. Despite a rather large play between the piston stem and the cylinder bore extension and a following poor air volume energy absorption, there is an undesirably severe wear of the piston stem and the cylinder bore extension due to metallic contact therebetween.
OBJECT OF THE INVENTION
The main object of the invention is to accomplish a pneumatic impact breaker having an improved air cushion energy absorption at noload or bottom strokes of the hammer piston by means of an improved, more accurate rectilinear movement of the hammer piston stem portion.
Another object of the invention is to reduce the detrimental energy absorbing air volume entrapped between
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Johansson Ingemar Sven
Nilsson Ake Lennart
Atlas Copco Berema AB
Calve James P.
Vo Peter
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