GB2042640A

GB2042640A - Apparatus for Exerting Percussive Forces on Workpieces

Info

Publication number: GB2042640A
Application number: GB8003661A
Authority: GB
Original assignee: SMG Sueddeutsche Maschinenbau GmbH
Current assignee: SMG Sueddeutsche Maschinenbau GmbH
Priority date: 1979-02-06
Filing date: 1980-02-04
Publication date: 1980-09-24
Also published as: CH645824A5; GB2042640B; IT8019616A0; IT1129591B; FR2448431B1; FR2448431A1

Abstract

An apparatus for exerting percussive forces on workpieces has a cylinder 1 with pistons 3, 5 therewithin, the cylinder 1 being divided by the annular piston (5) into a gas filled chamber (7) and a working fluid chamber (6), the latter chamber (6) initially being charged with a predetermined quantity of pressurised working fluid whereafter separation of the working face (8) of the piston (3) from engagement with a cylinder and face (8) exposes the piston (3) to the working fluid to produce a working stroke of the piston (3) and its rod (2). Damping at the end of the working stroke occurs when piston (3) enters a recess (9) in the annular piston (5). The volume of the gas-filled chamber (7) increases during the working cycle since the annular piston 5 moves towards the cylinder end face 8, the increase being accompanied by a fall in the pressure of the pressurised gas. The pressurised gas in the pressurised gas chamber (7) serves to return the piston 3, 5 into their end positions shown. <IMAGE>

Description

SPECIFICATION Apparatus for Exerting Percussive Forces on Workpieces This invention relates to an apparatus of a kind suitable for exerting percussive forces on workpieces, having a pressurised-mediumoperable cylinder-and-piston unit, whose piston, forming one component of a piston-and-pistonrod assembly, is movable with clearance within the pressurised medium chamber in the cylinder thereof: the piston transmitting (in use) percussive forces via the piston rod to the workpiece; the piston being relievable of pressure, in an end position remote from the workpiece, by cooperation with a mating surface; the piston being percussively pressure loadable to leave this end position in the working stroke direction; the piston being able to cooperate (in use) with a damping space in the region of the end position nearer the workpiece; and drive means being provided for the return of the piston from the end position nearer the workpiece to the end position remote from the workpiece.

In a known apparatus of this kind (German Laid-open Specification (Offenlegungsschrift) No.

2,233,153), the distance over which the piston can travel between two non-adjustable end positions is strictly predetermined, and apart from this the piston rod can strike a workpiece, assuming that one is present, before the piston enters the damping space. Thus, for a given pressure of pressurised medium in the pressurised medium chamber, the impact energy which can be exerted on the workpiece is also nonadjustably predetermined. Furthermore, the known apparatus has at least one further cylinder-andpiston unit which acts on the piston rod and which serves, by movement in the direction of the working stroke, to make it possible for the working stroke to be initiated, and for the piston rod, when the working stroke is completed, to return to the end position remote from the workpiece.The actual initiation of the working stroke is such that the area of the mating surface is pressure-loaded initially through a throttle and afterwards is pressure-loaded more abruptly. This known apparatus has the particular disadvantages that the travel of the piston and thus the impact energy cannot be adjusted, and that, on account of the use of a further cylinderpiston unit, a complicated construction and a complicated control arrangement are required.

It is an object of the present invention to avoid these disadvantages and to provide a simple apparatus of the kind first mentioned which is versatile in use and which can be operated economically and at a high stroke rate.

According to the present invention, we provide an apparatus of the kind first mentioned characterised in that the pressurised medium chamber can be charged with a predetermined quantity of pressurised fluid, can be connected by a valve to a distribution space associated with the said mating surface, and is defined in the direction of the working stroke by an annular piston guided sealingly within the cylinder and on the pistonand-piston-rod assembly; the working surface of the annular piston which is remote from the pressurised medium chamber bounding a pressurised gas chamber situated within the cylinder; the volume of this chamber increasing (in use) during a working cycle, its increase being accompanied by a diminution of the pressure of the pressurised gas, upon movement of the annular piston in the opposite direction to that of the working stroke; and the pressurised gas in the pressurised gas chamber serving (in use) as a drive to return the first-mentioned piston and the annular piston into the end position remote from the workpiece.

The annular piston may encircle the piston rod, whereby, during return to the end position remote from the workpiece, the piston-a nd-piston-rod assembly can be carried back by the annular piston. Instead, however, the annular piston may encircle the first-mentioned piston, whereby, during return to the end position remote from the workpiece, the pressure of the pressurised gas in the pressurised gas chamber acts directly not only on the annular piston but also on the firstmentioned piston.

The travel of the first-mentioned piston, and thus the percussive energy which is to be exerted, are adjustable, a predetermined quantity of pressurised fluid being introduced into the pressurised medium chamber, whereby, although the first-mentioned piston remains in its end position remote from the workpiece, the annular piston is displaced in the direction of the workpiece, against the pressure of the pressurised gas in the pressurised gas chamber, over a certain distance determined by the introduced quantity of pressurised fluid. In this connection, it should be appreciated that, during the subsequent working stroke, which is initiated by connection of the pressurised medium chamber to the distribution space associated with the mating surface, the annular piston is displaced through a certain distance in the direction opposite to the direction of the working stroke.

Displacement of the annular piston in the direction opposite to the direction of the working stroke occurs, in the case of an annular piston which encircles the piston rod, by reason of the fact that, when the first-mentioned piston is in the end position remote from the workpiece, the pressurised fluid occupies a composite space comprising an annular space surrounding the first-mentioned piston and an annular space surrounding the piston rod; whereas, in the end position of the first-mentioned piston which is nearer the workpiece, the pressurised fluid occupies a composite space comprising an annular space surrounding the piston and a cylindrical space adjacent the mating surface.By reason of the constancy of the quantity of pressurised fluid, these two composite spaces must be of the same volume, but the lattermentioned composite space has, in the direction of the working stroke, a shorter length than the first-mentioned composite space.

The displacement of the annular piston in the direction opposite to the direction of the working stroke occurs, in the case of an annular piston encircling the first-mentioned piston, by reason of the fact that the constant quantity of pressurised fluid present in the pressurised medium chamber is displaced, out of an annular space which surrounds the first-mentioned piston and which is occupied by the pressurised fluid when the firstmentioned piston is in the end position remote from the work-piece, into a cylindrical space which is adjacent the mating surface and which is occupied by the pressurised fluid when the firstmentioned piston is in the end position which is nearer the workpiece.This cylindrical space is a uniformly cylindrical space having a diameter equal to the inside diameter of the annular piston if the annular piston during the working stroke is fully displaced into the furthest possible position from the workpiece; or a stepped cylindrical space, having in one portion a diameter equal to the inside diameter of the first-mentioned cylinder and having in another portion a diameter equal to the inside diameter of the annular piston, if, during the working stroke, the annular piston is not fully displaced into the furthest possible position from the workpiece. (The "firstmentioned cylinder" is that of the pressurisedmedium-operable cylinder-and-piston unit).

The movements of the first-mentioned piston together with its piston rod and of the annular piston in opposite directions has the result that there is an at least partial equalisation of the moving masses. At the end of the travel of the first-mentioned piston in the direction of the working stroke, if the piston rod with a tool mounted thereon has not previously struck a workpiece, then the first-mentioned piston will move into the damping space.

In the case of an annular piston encircling the piston rod, the damping space can be provided in the operative face of the annular piston which is remote from the pressurised gas chamber, so that it is impossible for the first-mentioned piston to strike hard on the annular piston. By relieving the pressure in the pressurised medium chamber, it is possible, after the end position nearer the workpiece has been reached, to return the firstmentioned piston together with its piston rod, and also the annular piston, without delay, into the end position remote from the workpiece, the pressure of the pressurised gas in the pressurised gas chamber permitting this rapid return.

On the other hand, in the case of an annular piston encircling the first-mentioned piston, the damping space can be provided in the end face of the cylinder which bounds the pressurised gas chamber, so that a hard impact of the firstmentioned piston on the said end face cannot occur. In order to enhance the effect of the damping space, it is possible, where the relevant end face of the cylinder is its lower end face, to provide in the damping space a small quantity of fluid of low compressibility. This is an alternative to providing a damping space having such a depth, for penetration by the first-mentioned piston, as will permit adequate damping by compression of the pressurised gas.To prevent the annular piston from striking that end face of the cylinder which bounds the pressurised medium chamber, moreover, there may be provided in this end face, in a position annularly surrounding the distribution space, an annular damping space into which the annular piston can penetrate, in the end position which is remote from the workpiece. By relieving the pressure in the pressurised medium chamber, it is possible, after the end position nearer the workpiece has been reached, to initiate the return of the firstmentioned piston together with its piston rod, and also (as appropriate) of the annular piston, without delay, into the end position remote from the workpiece, the pressure of the pressurised gas in the pressurised gas chamber permitting this rapid return.The pressurised gas acts here on the annular end face of the first-mentioned piston which encircles the piston rod and which is nearer the workpiece, and on that annular end face of the annular piston which is nearer the workpiece.

In order to feed the predetermined quantity of pressurised fluid to the pressurised medium chamber, it is possible for the latter to be connected valvelessly to the cylinder chamber of a metering cylinder-and-piston unit. The said quantity can be adjusted by adjusting the means determining the stroke of the piston of the metering cylinder-and-piston unit.

Alternatively, the predetermined quantity of pressurised fluid may be fed to the pressurised medium chamber through a valve from a pressurised medium source at an adjustable pressure; in this case a predetermined value can be established for the pressure of the pressurised gas in the pressurised gas chamber whereby, upon the predetermined quantity of pressurised fluid being charged into the pressurised medium chamber, the pressure in the pressurised medium chamber is balanced through the annular piston, the latter being in the appropriate position for equilibrium. Upon this pressure balance being attained, the charging in of the pressurised fluid is terminated by the actuation of a valve.

Inasmuch as it is desirable to avoid a situation wherein, in the case of the annular piston encircling the piston rod, the first-mentioned piston and its piston rod move together with the annular piston in the direction of the working stroke during charging of pressurised fluid to the pressurised medium chamber, it is possible to provide, on the first-mentioned piston, an additional pressurised-medium-operable surface which can be pressured against the direction of the working stroke, so that the first-mentioned piston and its piston rod can be depended upon to remain in the end position remote from the workpiece.This additional pressurised-mediumoperable surface can for example be disposed opposite the bottom of the damping space, slots being provided in the peripheral surface and in the bottom of the damping space through which pressurised fluid can act on the relevant pressurised-medium-operable surface on the piston.

In the case of the annular piston encircling the first-mentioned piston, the pressure of the pressurised gas acts on that annular end face of the first-mentioned piston, encircling the piston rod, which is nearer the workpiece, ensuring that, when the pressurised fluid is fed to the pressurised medium chamber, there is no undesirable movement of the first-mentioned piston and its piston rod, together with the annular piston, in the direction of the working stroke.

In the accompanying diagrammatic drawings, Figs. 1 to 3,4to 6, 7 to 9 and lotto 12 showfour embodiments of the invention, each embodiment being shown in three different positions, as follows: Figs. 1, 4, 7 and 10 show the positions prior to feeding of pressurised fluid; Figs. 2, 5, 8 and 11 show the positions upon completion of feeding of pressurised fluid; and Figs. 3, 6, 9 and 12 show the positions at the end of the working stroke.

In each of the four illustrated embodiments, there is a cylinder 1 accommodating a piston 3 which is mounted.on a piston rod 2 and which is guided with clearance in respect of the inside wall of the cylinder 1 between an upper extreme position in which it is remote from a workpiece 4 and a lower extreme position in which it abuts against the workpiece 4. An annular piston 5 sealingly surrounds the piston rod 2 in the first and second embodiments (Figs. 1 to 3 and 4 to 6) or the piston 3 on the third and fourth embodiments (Figs. 7 to 9 and 10 to 12). The annular piston 5 slides sealingly on the inside wall of the cylinder 1, subdividing the interior of the cylinder 1 into a pressurised medium chamber 6 and a pressurised gas chamber 7.The upper end face of the piston 3, and the upper inner end face of the cylinder 1, which is opposite the end face of the piston 3 and serves as a mating surface therefor, each have a flat recess, and the two recesses jointly form a distribution space 8.

Surrounding the space 8 there is, on one of the two end faces, a seal which can bear sealingly against the opposite end face.

In the first and second embodiments (Figs. 1 to 3 and 4 to 6), there is provided, in the end face of the annular piston 5 which faces towards the pressurised medium chamber 6, an annular recess serving as a damping space, 9, into which the piston 3 can descend, in its bottom extreme position. In the third and fourth embodiments (Figs. 7 to 9 and 10 to 12), there is provided, in the end face of the cylinder 1 which bounds the pressurised gas chamber 7, an annular recess serving as a damping space, 9, into which the piston 3 can descend, in its lower extreme position.

In the first and third embodiments (Figs. 1 to 3 and 7 to 9), a pipe line 10 has its two ends connected to the pressurised medium chamber 6, one of its ends being connected in the region of the recess affording one portion of the space 8, and the other of these ends being connected in an upper end zone of the wall of the cylinder 1; in the line 10 there is a first valve 1 whereby one can select, as desired, either a through-connection of the line 10, or a connection permitting its branch leading to the space 8 to be relieved of pressure.

The other branch of the line 10 is connected to a cylindrical chamber 12 of a metering cylinderand-piston unit in the cylinder 13 of which a piston 14 together with a piston rod 1 5 is movably accommodated. The piston rod 15 carries an adjustable stroke limiter 1 6 by means of which one can adjust the predetermined quantity of pressurised fluid which is to be metered by the unit. To a cylinder space 1 7 remote from the cylinder chamber 12, there is connected, via a second valve 18, a source of pressurised medium 1 9. The latter serves to feed pressurised medium to the pressurised medium chamber 6 by displacement of the piston 14.

In the second and fourth embodiments (Figs. 4 to 6 and 10 to 12), there is a line 10 which is connected at its two ends to the pressurised medium chamber 6, one of its ends being connected in the region of the recess affording one portion of the space 8, and the other of these ends being connected in an upper end zone of the wall of the cylinder 1. The line 10 has a first valve 11 whereby one can select, as desired, either a through-connection of the line 10 or a connection permitting its branch leading to the space 8 to be relieved of pressure.The other branch of the line 10 is connected to a feed line 20 for pressurised fluid, and the branch of line 20 nearer the pressurised medium chamber 6 can, as desired, by means of a second valve 21, be relieved of pressure (Figs. 4 and 10), connected to a source of pressurised medium 19 (Figs. 5 and 11), or shut off (Figs. 6 and 12). The branch of the feed line 20 which leads to the pressurised medium source 1 9 is connected to an adjustable pressure limiting valve 22. Furthermore, the branch of the feed line 20 which is nearer the pressurised medium chamber 6 is connected to a pressure indicating device 23. Another pressure indicating device 24 is connected to the pressurised gas chamber 7. It is intended that the user should calculate beforehand and an appropriate value of the pressure of the pressurised gas which is to be obtained in the pressurised gas chamber 7 prior to commencement of introduction of pressurised fluid into the pressurised medium chamber 6, and that the user should also calculate beforehand an appropriate value of the pressure which is to be set at the pressure limiting valve 22 and which is to be operative during introduction of pressurised fluid into the pressurised medium chamber 6; it is thus possible to preselect an appropriate value of the quantity of pressurised fluid which is to be introduced into the pressurised medium chamber 6. Introduction of pressurised fluid into the pressurised medium chamber 6 ends upon the attainment of equilibrium of the forces acting on the two operative faces of the annular piston 5.

Some typical pressure values which may be adopted for the second embodiment in its three illustrated positions are listed below.

Position According to Fig. 4 Bars Pressure limiting valve 22 120 Pressure indicating device 23 0 Pressure indicating device 24 100 Position According to Fig. 5 Bars Pressure limiting valve 22 120 Pressure indicating device 23 1 20 Pressure indicating device 24 120 Position According to Fig. 6 Bars Pressure limiting valve 22 120 Pressure indicating device 23 110 Pressure indicating device 24 110 It is to be understood that the illustrated embodiments incorporate such further control means, lines and so forth, e.g. pressurised gas feed means, pressure relief valves and electrical circuitry, as are required to operate the apparatus, even though these are not shown in the drawings.

Claims

1. An apparatus for exerting percussive forces on workpleces, having a pressurised-mediumoperable cylinder-and-piston unit, whose piston, forming one component of a piston-and-pistonrod assembly, is movable with clearance within the pressurised medium chamber in the cylinder thereof; the piston transmitting (in use) percussive force via the piston rod to the workpiece; the piston being relievable of pressure in an end position remote from the workpiece, by cooperation with a mating surface; the piston being percussively pressure loadable to leave this end position in the working stroke direction; the piston being able to cooperate (in use) with a damping space in the region of the end position nearer the workpiece; and drive means being provided for the return of the piston from the end position nearer the workpiece to the end-position remote from the workpiece; characterised in that the pressurised medium chamber (6) can be charged with a predetermined quantity of pressurised fluid, can be connected by a valve (11) to a distribution space (8) associated with the said mating surface, and is defined in the direction of the working stroke by an annular piston (5) guided sealingly within the cylinder (1) and on the piston-and-piston-rod assembly (2, 3); the working surface of the annular piston (5) which is remote from the pressurised medium chamber (6) bounding a pressurised gas chamber (7) situated within the cylinder (1); the volume of this chamber (7) increasing (in use) during a working cycle, its increase being accompanied by a diminution of the pressure of the pressurised gas, upon movement of the annular piston (5) in the opposite direction to that of the working stroke; and the pressurised gas in the pressurised gas chamber serving (in use) as a drive to return the first-mentioned piston (3) and the annular piston (5) into the end position remote from the workpiece (4).

2. An apparatus according to Claim 1, characterised in that the annular piston (5) encircles the piston rod (2), whereby, during return to the end position remote from the workpiece (4), the piston-and-piston-rod assembly (2, 3) can be carried back by the annular piston (5).

3. An apparatus according to Claim 1, characterised in that the annular piston (5) encircles the first-mentioned piston (3).

4. An apparatus according to Claim 1,2 or 3, characterised in that the said predetermined quantity of pressurised fluid can be fed to the pressurised medium chamber (6) by means of a cylinder chamber (12) of a metering cylinder-andpiston unit (13, 14, 15) which is valvelessly connected to the pressurised medium chamber (6).

5. An apparatus according to Claim 1,2 2 or 3, characterised in that the said predetermined quantity of pressurised fluid can be fed to the pressurised medium chamber (6) through a valve (21) from a pressurised medium source (19) at an adjustable pressure; and in that a predetermined value can be established for the pressure of the pressurised gas in the pressurised gas chamber (7) whereby, upon the said predetermined quantity of pressurised fluid being charged into the pressurised medium chamber (6), the pressure in the pressurised medium chamber (6) is balanced through the annular piston (5), the latter being in the appropriate position for equilibrium.

6. An apparatus according to Claim 2, substantially as described with reference to Figs.

1-3 or Figs. 4-6 of the accompanying drawings.

7. An apparatus according to Claim 3, substantially as described with reference to Figs.

7-9 or Figs. 10-12 of the accompanying drawings.