Metal working – Method of mechanical manufacture – Process for making bearing or component thereof
Reexamination Certificate
2001-06-04
2003-03-18
Vidovich, Gregory M. (Department: 3726)
Metal working
Method of mechanical manufacture
Process for making bearing or component thereof
C029S898047, C029S898056, C029S898059, C029S898070, C384S111000, C384S118000
Reexamination Certificate
active
06532663
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of cellular hydrostatic fluid bearings for supporting rotary shafts, in particular in rocket engine turbopumps for pressurizing fluid.
PRIOR ART
Cellular hydrostatic fluid bearings are in widespread use in numerous industrial applications, in particular where high loads are involved or which require high speed, or great precision, or long lifetime. Nevertheless, they are still relatively little used in rocket engine turbopumps.
FIG. 4
shows the structure of a conventional hydrostatic bearing
40
comprising an annular bearing stator
41
in which a rotor
42
constituting the shaft of a turbopump is received. When the turbopump is in operation, the rotor
42
is held in suspension by a thin layer of fluid introduced under pressure through orifices
44
in cells
43
of the bearing stator
41
. The cells
43
are machined directly in the material of the stator
41
. Since the inside surface of the stator is cylindrical, it is quite difficult to machine such cells. Machining is particularly difficult when the diameter of the stator is small.
An auxiliary tank for pressurizing fluid to keep the shaft in levitation from the first instants can be used during transient stages so as to avoid any shaft-bearing contacts that could damage the pump drive system. Such an auxiliary device contributes to making the pump apparatus as a whole heavier and increases the risk of failure. Thus, in rocket engine turbopumps, the pressure used for introducing fluid into the bearing stator is usually taken directly from the outlet of the pump. Consequently, during a portion of the transient stages (starting, stopping, . . . ) that occur during the operation of such pumps, the fluid pressure feed to the bearings as taken from the outlet of the pump is not yet or is no longer at a level which is sufficient to ensure that the rotor is levitated.
In order to reduce the risk of failure during shaft-bearing contacts, the inside surface of the stator can be subjected to special surface treatment or a thin lubricating layer can be deposited thereon. Unfortunately, such treatment of the inside surface of the bearing presents various difficulties, in particular concerning the thickness of such a coating layer, which thickness is generally less than 50 micrometers (&mgr;m), and also concerning its uniformity.
The small thicknesses contained do not make it possible to accommodate a large number of transient stages without damaging the shaft and the bearings.
OBJECT AND BRIEF DESCRIPTION OF THE INVENTION
The present invention seeks to remedy the above-mentioned drawbacks and to provide a cellular hydrostatic fluid bearing in more convenient manner and minimizing the risks of failure in the event of shaft-bearing contacts.
These objects are achieved by a hydrostatic fluid bearing comprising a cylindrical stator having orifices for introducing fluid under pressure, wherein said stator has on its inside surface a ring constituted by an assembly of a metal plate including orifices which co-operate with the orifices for introducing fluid and of a layer of self-lubricating composite material which includes cells disposed around said orifices.
Thus, the fluid bearing of the invention presents a thickness of a layer of composite material on its inside surface that can accommodate a large amount of wear therein without running the risk of irremediable damage to the shaft or the bearing in the event of shaft-bearing contacts, which also makes it possible to pass through transient stages without auxiliary means for providing pressure.
More particularly, the ring is an open ring held in compression inside the stator.
Specifically, the thickness of the layer of composite material is greater than 50 &mgr;m and less than 2 millimeters (mm).
The invention also provides a method of manufacturing a cellular hydrostatic fluid bearing, the method comprising the following steps: assembling a layer of self-lubricating composite material on a surface of a plane metal plate; cutting the assembly comprising the metal plate and the composite material to dimensions that correspond to the development of an inside surface of a stator; machining cells in the thickness of the layer of composite material of said assembly; curving said assembly to form a split ring; inserting said assembly in the form of a split ring against the inside surface of the stator; and machining orifices through the thickness of the stator and through said cells of the inserted assembly.
The method of the invention for manufacturing a hydrostatic bearing thus makes it possible to make the inner portion of the stator that is to receive a rotary shaft from a plane metal structure that enables a thick layer of self-lubricating composite material to be formed and that makes it easier to machine the cells.
More specifically, the thickness of the layer of composite material is greater than 50 &mgr;m and less than 2 mm.
In a particular aspect of the invention, the step in which said assembly is inserted as an interference fit is performed either by means of a press, or by thermally expanding the stator, or by thermally shrinking the ring-shaped assembly, or indeed by a combination of two or three of these techniques.
In another aspect of the invention, the method of manufacture further comprises a final step of re-boring the inside surface of the stator in the composite material.
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Brune Claude
Fayolle Patrice
Frechon Gilles
Moello Régis
Compton Eric
Snecma Moteurs
Vidovich Gregory M.
Weingarten Schurgin, Gagnebin & Lebovici LLP
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