Patent Application
20070189649
Bearing cartridges typically have an outer retaining member that defines a concave spherical or cylindrical surface, or race, that forms a sliding surface and an inner member that defines a convex spherical or cylindrical surface. The outer and inner members typically may be a ring and a ball, or a ball and pin, or a bushing and a pin, all respectively.
In order to decrease sliding friction, the sliding surface of the outer member may be lined with a lubricating liner, such as a polytetrafluoroethylene (PTFE)-based liner like TEFLON® or the like. When the sliding surface is lined with such a liner, the inner member should be made of a material with high hardness and good wear characteristics.
However, materials with high hardness and good wear characteristics currently in use, such as steel, are not lightweight. In certain applications, such as aerospace applications, it is desirable to use lightweight materials.
Titanium is a lightweight material that is widely used in many applications, such as aerospace applications, in which saving weight is a desirable objective. For example, weight of titanium is typically about 0.57 times the weight of steel. However, titanium does not have a surface hardness that provides good wear characteristics.
It would be desirable to fabricate a bearing cartridge using lightweight materials that have good wear characteristics. To that end, attempts have been made to provide titanium with a surface hardness that provides good wear characteristics. These attempts have involved mechanically bonding a surface coating onto the convex spherical surface.
However, a mechanically-bonded surface coating can spall and/or chip. Dislodged particles can then serve as an abrasive, which in turn can tear up the lubricating liner on the concave spherical or cylindrical surface of the outer retaining member, thereby accelerating wear.
It would therefore be desirable to provide a bearing cartridge using lightweight materials that have good wear characteristics without use of mechanically-bonded surface coatings.
The foregoing examples of related art and limitations associated therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.
The following embodiments and aspects thereof are described and illustrated in conjunction with systems and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the problems described above in the Background have been reduced or eliminated, while other embodiments are directed to other improvements.
In a non-limiting, exemplary bearing cartridge, an outer retaining member defines a first curved surface that is lined with a lubricant, and an inner member that is made of carburized titanium is received by the outer retaining member. The inner member defines a second curved surface that is in sliding contact with the first curved surface of the outer retaining member.
According to an aspect, the outer retaining member may include a ring and the first curved surface may be a concave spherical surface that may include a race, and the inner member may include a ball and the second curved surface may include a convex spherical surface. In such an arrangement, the cartridge may be swaged in a housing with end walls such that the ball is laterally spaced apart from the end walls. In this case, the ball may serve as the outer retaining member and define a bore that defines a concave cylindrical surface that is lined with a lubricant, and a carburized titanium pin or bolt may serve as the inner member and define a convex cylindrical surface that is received by the ball in sliding contact with the concave cylindrical surface of the bore of the ball. Alternately, the cartridge may be swaged in a housing with end walls such that the ball abuts the end walls. In this latter case, the bore of the ball need not be lined with a lubricant.
According to another aspect, the outer retaining member may include a bushing and the first curved surface may be a concave cylindrical surface, and the inner member may include a pin or bolt, such as without limitation a shoulder bolt, and the second curved surface may be a convex cylindrical surface.
According to further aspects, the titanium may include an alloy such as Ti-6Al-4V alloy. Also, the inner member defines a carburized case that extends a predetermined distance from the second curved surface into the inner member. Further, the outer retaining member may be made of one of 15-5 PH CRES, 17-4 PH CRES, and titanium. Moreover, the lubricant may include a polytetrafluroethylene-based lubricant, such as without limitation TEFLON®.
In addition to the exemplary embodiments and aspects described above, further embodiments and aspects will become apparent by reference to the drawings and by study of the following detailed description.
Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.
By way of overview and referring to
In some embodiments, and as shown in
In some embodiments, and as shown in
Advantageously, the inner member 16 is made of carburized titanium. Use of carburized titanium for the inner member 16 imparts lightweight titanium with a surface hardness that provides good wear characteristics. Moreover, such desirable surface hardness is provided without use of a mechanically-bonded surface coating.
Without limitation, titanium or a titanium alloy such as Ti-6Al-4V is made into a part having the desired shape of the inner member 16. The titanium part is carburized in a known manner. A diffused, carburizing treatment for titanium that has been found to be especially well suited for treating the inner member 16 is plasma carburizing treatment (PCT). Details of the PCT process are described in U.S. Pat. No. 5,466,305 entitled “Method of Treating the Surface of Titanium” and assigned to Tanaka Limited of Osaka, Japan, the entire contents of which are incorporated by reference.
Using the PCT process, the curved surface 18 of the titanium part for the inner member 16 is treated to reduce the friction coefficient and wear loss without sacrificing its corrosion resistance. The titanium part is subjected to plasma-carburizing in an atmosphere containing hydrocarbon gas at a pressure between 0.5 Torr and 15 Torr and a temperature between 700 degrees Centigrade and 1,100 degrees Centigrade. In an especially advantageous process, the titanium part is plasma-carburized at a temperature that is low enough so strength of the titanium is not detrimentally affected. That is, any aluminum (Al) or vanadium (V) that may be present in a titanium alloy will not be put into solution at such temperatures.
As a result of diffused carburizing, a diffused carburized case 20 of desired hardness extends a depth d from the curved surface 18 into the inner member 16. The case 20 includes carbon in the form of carbon and/or carbides. Average Vickers hardness exhibited on the curved surface 18 and in the case 20 suitably is 420 HV0.1, 0.98N and 499 HV0.025, 0.24N. The depth d suitably is in a range between around 0.0002 inch (0.2 mil) to around 0.0005 inch (0.5 mil), as desired for a particular application. In one exemplary application, the depth d is around 0.2 mil. The depth d is thus shallow enough so deflections do not damage the case 20, thereby providing some flexibility.
The bearing cartridge 10 may be swaged in various housings as desired to provide exemplary bearings. For example and referring now to
The ring 112 and the ball 116 are swaged into a housing that includes a lug 122 and a clevis 124. End walls of the clevis 124 are laterally spaced apart from ball 116. A carburized, titanium pin or bolt 126 is received inside the bore of the ball 116. Thus, a convex cylindrical surface of the carburized titanium pin or bolt 126 slides against the lubricant liner on the concave cylindrical surface 119. In such an arrangement, the ball 116 may be considered the outer retaining member and the pin or bolt 126 may be considered the inner member. The pin or bolt 126 is secured against an exterior of the clevis 124 with a nut 128.
The bearing 100 allows joint misalignment from a plane perpendicular to an axis of rotation of the ball 116 in an unclamped application that allows movement of the carburized titanium pin or bolt 126 in the bore of the ball 116. Relative motion may occur between the ring 112 and the ball 116 and between the ball 116 and the pin or bolt 126. In the exemplary bearing 100, the load-carrying capability is limited by the lubricant liner on the bore of the ball 116. The bearing 100 can carry the same load and can withstand a temperature of 320 degrees Fahrenheit as can a conventional spherical, lined bearing with a ball made of 440C CRES. However, the bearing 100 provides substantial weight savings over a conventional spherical, lined bearing with a ball made of 440C CRES. The bearing 100 thus is well-suited for lightweight applications that are not exposed to contamination such as dirt, sand, and debris. Examples of suitable applications include, but are not limited to, aerospace interior applications, such as supporting aircraft interior components such as stow bins.
Referring now to
Referring now to
The bearing 200 (along with conventional bearings) was wear tested, and advantageously showed no appreciable wear after being subjected to a radial stress of 40 ksi for 100,000 cycles of +/−25 degrees oscillation. Results of the wear testing are shown in Table 1.
While a number of exemplary embodiments and aspects have been illustrated and discussed above, those of skill in the art will recognize certain modifications, permutations, additions, and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, and sub-combinations as are within their true spirit and scope.
