Expansible chamber devices – With removal conduit for liquid seepage from expansible chamber
Reexamination Certificate
1999-08-09
2001-07-10
Ryznic, John E. (Department: 3745)
Expansible chamber devices
With removal conduit for liquid seepage from expansible chamber
C092S106000, C092S110000, C279S004010
Reexamination Certificate
active
06257122
ABSTRACT:
The invention relates to a clamping cylinder for operating the chuck of a machine tool, particularly a turning machine, comprising a cylinder casing including a cover plate fixed to its face side, a piston axially shiftable in a work chamber of the cylinder casing for generating a clamping force, the piston rod of the cylinder being capable of being coupled with the chuck, and a distributor fixed to the other face side of the cylinder casing and having ports for introducing and removing the hydraulic pressure means into and from the work chamber.
In cutting workpieces, chucks are generally used for clamping the tool or the workpiece, a rotationally symmetric component of the tool, e.g. its shaft, or of the workpiece being clamped in the chuck. Particularly in turning machines such chucks of clamping cylinders formed as hollow clamping cylinders or solid clamping cylinders are operated. Hollow clamping cylinders serve to hold rod or pipe shaped workpieces, the rod material protruding through the chuck and also the clamping cylinder. Solid clamping cylinders are used in connection with correspondingly formed collet chucks for holding short workpieces.
In cutting workpieces, an undesirable heating of the clamping cylinders occurs which has to be limited by appropriate measures such as heat dissipation, air cooling or the like. These thermal problems are connected with a possibly insufficient lubrication of the highly loaded components of the clamping cylinder which increasingly occurs particularly during a long-duration machining of workpieces, i.e. in continuous duty. The lubrication of conventional clamping cylinders and their distributors is effected by the hydraulic pressure means which is introduced into the conduit system provided in the distributor under a high pressure and is separately guided to the one or the other work chamber in the cylinder casing within the same. From the snap ring grove in the pressure carrying branch of the conduit system, a small amount of the pressure means gets into the gap between the circumferential surface of the rotating piston rod and the inner wall of the distributor housing. Since no elastically deformable sealing rings can be used in the distributor due to the high pressures and speeds, the sealing is effected by the dimensions of the narrow sealing gap itself, the necessarily occurring leakage being removed in a pressureless manner via separate bores and conduits. The leaking oil flowing off through the sealing gap serves as a lubrication and heat dissipation means. A too narrow sealing gap causes a high heat development due to an insufficient cooling effect and a low lubrication effect. Since both work chambers in the cylinder housing are alternatively provided with pressure means via two separate snap ring groves in the distributor housing as well as two separate conduits with parallel axes provided in the rotating piston rod and the two snap ring groves necessarily have a certain axial distance to each other, further an irregular distribution of the leaking oil along the axial length of the sealing gap may be caused, which in turn will give rise to an increased one-sided heating of the respective components.
In the case of clamping cylinders and their collet chucks, the aspect of the inertia occurring is also of considerable importance, particularly when those clamping elements are to be used in modern turning machines operating at high speeds. This particularly applies to hollow clamping cylinders which, due to the inner bore required for receiving the rod material, must have a correspondingly larger outer diameter and on which extremely high circumferential speeds act. To reduce the inertia of the clamping cylinders, it has been proposed to produce the important components, such as the cylinder casing and its lid, of aluminium. It has, however, been found that these embodiments undergo too much wear due to the relative softness of the Al material.
It is the object of the invention to provide a clamping cylinder for operating chucks in which the drawbacks of the state of the art are considerably reduced and which is particularly suitable for the use at high speeds due to its enhanced operation behaviour, particularly with respect to the inertia moment, the lubrication and the heat dissipation.
According to the invention, this object is achieved by forming the cylinder casing and its lid as well as the distributor from a light metal, the sliding surfaces thereof being at least partly hard coated, by forming the piston of tool steel with hard coated sliding surfaces, and by introducing the pressure means into the sealing gap between the piston rod and the distributor walls via separate bores.
The formation of the cylinder casing and its lid of a light metal enables a reduction of the weight of these components in connection with largely the same dimensions, which leads to a considerable reduction of the inertia moments occurring in the operation. The use of hard coated sliding surfaces according to the invention, particularly on the inner walls of the through bore in the distributor housing, in connection with the hard coated sliding surfaces of the piston rods results in an extreme reduction of wear, which leads to considerably enhanced operation properties, particularly continuous duty, to a more effective pressure oil in the sealing gap which is practically constant along its length, and finally to an enhanced cooling effect. An optimisation of the lubrication and cooling effects is accomplished also in that in every operating state of the clamping cylinder pressure oil is introduced into the sealing gap at two positions, respectively, i.e. on the one hand, in the conventional way, via the snap ring grove, and on the other hand via the radial bore additionally provided according to the invention and disposed in a sufficiently large axial distance to the respectively associated snap ring grove. This additional introduction of pressure oil into the sealing gap ensures a largely uniform distribution of the pressure oil along the full axial length of the sealing gap and thus excellent lubrication and cooling effects.
According to an advantageous embodiment of the invention, the heat dissipation is further intensified by a specially formed air conduction system which preferably comprises an air conduction sheet fixed to the distributor housing and partly overlapping the cylinder casing as well as outer axial groves in the distributor housing generating an intensive directed flow of cooling air.
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patent: 3924514 (1975-12-01), Parsons et al.
patent: 4040338 (1977-08-01), Wilson et al.
patent: 4621568 (1986-11-01), Gailey
patent: 4945819 (1990-08-01), Rohm
patent: 36 37 823 (1987-05-01), None
Gulde Siegfried
Michler Gerhard
Heinz-Dieter Schunk GmbH. & Co., Spanntecknik KG
Ryznic John E.
The Maxham Firm
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