Stock material or miscellaneous articles – Hollow or container type article – Glass – ceramic – or sintered – fused – fired – or calcined metal...
Reexamination Certificate
1997-04-15
2001-05-08
Cole, Elizabeth M. (Department: 1771)
Stock material or miscellaneous articles
Hollow or container type article
Glass, ceramic, or sintered, fused, fired, or calcined metal...
C428S034500, C428S034600, C428S034700, C428S036300, C442S289000, C442S291000, C442S294000
Reexamination Certificate
active
06228444
ABSTRACT:
The present invention relates to a method of making tubes out of composite material having high tribological and mechanical characteristics, in particular a low coefficient of friction, and particularly intended for manufacturing annular bearings and bearing cages capable of being used at low temperatures (e.g. 20 K to 600 K). The invention also relates to a machine for implementing the method, and to the material obtained thereby.
BACKGROUND OF THE INVENTION
At present, the materials used for making bearing cages do not give entire satisfaction, in particular in cryogenic conditions, and they also suffer from numerous drawbacks associated firstly with mechanical problems that arise at high speeds of rotation and that cause the cage to break, and secondly with the friction between the cage and the balls, rollers, or needles it contains and which are of a kind that can give rise to overheating of the bearing.
A partial solution to these difficulties is provided at present by using composite materials based on glass fiber and on PTFE which are capable, in particular, of operating at high speeds of rotation and which are manufactured mainly on the basis of two conventional methods, namely injection and winding.
The first method suffers from the major drawback of not enabling good mechanical characteristics to be obtained, but it has the advantage of making it easier to add any kind of additive suitable for imparting specific properties to the material made by the method.
The second method which consists in applying a thread to a mandrel that is rotating makes it possible to obtain mechanical characteristics which are good in a circumferential direction because the fibers are oriented, but which are nevertheless poor in a longitudinal direction, thereby having the consequence of limiting the traction strength of bearings made by this method. The weakness of this type of winding persists even when the threads are crossed (using the principle of helical winding) at an optimum angle close to 50°. In addition, the materials obtained by this method suffer from a highly random coefficient of friction that depends, in particular, on the winding directions of the various fibers and that affects both the lifetime and the stability of cages or bearings made with this material. It is also appropriate to observe that the presence of glass fibers imparts abrasive properties to this material which can give rise to certain drawbacks.
Although this simple method of winding applied to sheets of fabric makes it possible to obtain mechanical characteristics that are good in both axial and circumferential directions, it does not enable adequate tribological characteristics of friction and wear resistance to be obtained since it prevents lubricants, are not “impregnatable”, being included in significant volume.
OBJECT AND SUMMARY OF THE INVENTION
The present invention therefore proposes a novel method of manufacturing a material that possesses firstly high characteristics in both circumferential and longitudinal directions, and secondly very good tribological characteristics of friction and wear resistance, which is not possible with present methods.
This object is achieved by a method of manufacturing a composite material in the form of an annular tube by winding on a mandrel both a reinforcing fiber fabric and a sheet of matrix material obtained in known manner and available on payout rolls, the method comprising the following steps:
1) preheating the mandrel to a predetermined temperature;
2) fixing the reinforcing fiber fabric and the sheet of matrix material to the mandrel;
3) causing the mandrel to rotate at a nominal speed to wind the fabric and the sheet simultaneously, the fabric and the sheet being subjected to a nominal tension;
4) actuating heating means for heating the material and cooling means for cooling the mandrel;
5) when the tube reaches the desired diameter, stopping both the heating means and the rotation of the mandrel;
6) after a determined duration that is sufficient for bringing the temperature of the mandrel to the predetermined preheating temperature, stopping the cooling means; and
7) dismounting the mandrel.
This entirely novel and original “dual” winding method in which both a reinforcing fiber fabric and a sheet of matrix material are wound simultaneously on a common mandrel makes it possible to associate materials that cannot be mixed together by the conventional “mono” winding method. It makes it possible to obtain composite materials having a two-dimensional structure which presents high mechanical characteristics. In a particular variant implementation, the mandrel may constitute a preform for the composite material in which case it forms a part integral therewith.
The reinforcing fiber fabric comprises a woven structure of bare fibers and a polymer that is added by preimpregnation. The fibers may be constituted by fibers of carbon, of polyparaphenyleneterephthalamide known under the name “Kevlar”, of glass, or of bronze, or by a mixture of such fibers. The polymer preferably comprises PTFE or PTFCE or any other thermosetting polymer.
The sheet of matrix material comprises the polymer and at least one additive for improving the tribological and heat conductivity characteristics of the material. The additive may advantageously be constituted by a molybdenum bisulfide (MoS
2
), a silicon carbide (SiC), a graphite, silver, or lead.
The method of the invention makes it possible to obtain compositions having a wide range of reinforcement/matrix/additive ratios and thus having characteristics, and in particular tribological characteristics, that are particularly advantageous, such as excellent wear resistance and a low coefficient of friction.
Advantageously, the mandrel is cooled by air circulation and preferably, in order to avoid any transfer between the polymer and the heating means, heating is performed without contact by using infrared heating around a welding zone between the reinforcing fabric and the sheet of matrix material. Nevertheless, heating of the composite material may be reinforced by previously heating the reinforcing fiber fabric and/or the sheet of matrix material upstream from the welding zone. The welding zone preferably extends over an angle of 45°.
In order to obtain maximum adhesion between the successive strata making up the composite material, the mandrel is preheated in an oven before being used.
In a variant implementation of the method, the mandrel is preheated directly by the infrared heating means, thereby avoiding the need to use an auxiliary oven, but then requiring rotation of the mandrel to be interrupted in order to fix on the fabric and the sheet.
The present invention also provides a machine for manufacturing a composite material in the form of an annular tube by winding both a reinforcing fiber fabric and a sheet of matrix material on a mandrel, the machine comprising a load-carrying structure provided with two uprights between which the mandrel is placed to be rotated by drive means, the machine including means for combined fixing of the reinforcing fiber fabric and of the sheet of matrix material on the mandrel, tensioning means for tensioning said fabric and sheet while they are being simultaneously wound on the mandrel, and heating means for heating the composite material obtained in this way and disposed in a welding zone between the reinforcing fiber fabric and the sheet of matrix material. Advantageously, the heating means are implemented by a contact-less infrared device.
The mandrel includes a slot extending substantially along its entire length for receiving the free ends of the reinforcing fiber fabric and of the sheet of matrix material. Fixing to the mandrel then occurs naturally after one or two revolutions, after which the fabric and the sheet are subjected to their nominal operating tension. In addition, the mandrel is pierced by channels to enable a cooling fluid to circulate.
Preferably, the heating means are moved as a function of the increasing diameter of the tube of composite material by means of a pantograph
Cretegny Jean-Francois
Edeline Emmanuel
Wolki Peter
Cole Elizabeth M.
Societe Nationale d'Etude et de Construction de Moteurs d&a
Weingarten, Schurgin Gagnebin & Hayes LLP
LandOfFree
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