GB1603318A - Rail wheels - Google Patents

Description

(54) IMPROVEMENTS RELATING TO RAIL WHEELS (7 l) We, RAYCHE : 95 CORPORA- TION, a corporation organised according to the laws of the State of California, United States of America, of 300 Constitution Drive Menlo Park, California 94025, United States of America, do hereby dectare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement :- This invention relates to a method for applying a tire, or running rim, to a wheel and, more especially, to a method for applying a tire or running rim to a rail vehicle wheel, as well as to wheels so produced.

It has been known almost since the beginning of the railroad era that the wheel/rail adhesion of steel wheels and steel rails is somewhat poor, especially under lubricated and/or wet conditions. Whilst the adhesion has in general been tolerable in conventional railroad systems it has non thelessbeen a major limitation on the design and operation of railroad and, more recentlv, of the modern rapid mass transit rail systems now being usedfor commuters in manv urban areas. Wheel/rail adhesion affects not only the speed with which a rail vehicle can travel but also the time and distance within which the vehicle can be started and stopped. Mass transit vehicles must be reliably stopped and started quite frequently under various conditions and vehicle headway, that is the distance which must be maintained for safety reasons between consecutive trains, is, therefore, heavily dependent on acceleration and braking performance under conditions adverse to wheel/rail adhesion. Only by improving vehicle headway can service levels be increased while maintaining or increasing train speed.

In this respect, a typical rapid transit system must be designed to operate with a minimum deceleration of 2.8 miles per hour per second. To achieve this level of deceleration the minimum coefficient of adhesion between rail and wheel must lie somewhere between 0. 16 and 0.2. The term "coefficient of adhesion"is used rather than coefficient of static or dynamic friction because the contacting portions of the wheel and rail are continuously changing and some slippage between the wheel and the rail may or may not occur during braking. Unfortunately, water, oil, grease, rust and other contaminants and their various combinations all affect wheel-to-rail adhesion. For example, moisture and a small amount of rust are known to form a slurry which greatly reduces the coefficient of adhesion. Under some conditions the actual coefficient of adhesion between steel wheels and steel rails has been measured and has been found to be as low as 0.06.

Considerable research has accordingiv been conducted to obtain improved wheel/rail adhesion but, whilst it has been shown that certain materials, including titanium, give improved adhesion to steel, no practical or commercially feasible means has been found for exploiting them.

The present invention provides a wheel the tire or running rim of which consists of or comprises a member made from a memory alloy.

In an especially preferred embodiment, the present invention provides a rail vehicle wheel provided with a tire or running rim made from a binary or ternary alloy of titanium and nickel containing from 43 to 45',', by weight of titanium.

In addition, the present invention provides a method of applying a tire or running rim to a wheel which comprises applying a memory alloy member m its deformed heat-unstable configuration to the wheel and heating it to cause it to recover and either to grip the wheel and form a running rim or to secure a separate running rim member to the wheel.

In general, as will be explained in more detail hereinafter, the memory alloy member advantageously forms the running rim itself but, in certain embodiments, it may be present as an auxiliary member which is used in conjunction with and cooperates with a separate running rim member.

The present invention further provides a method of applying a tire or running rim to a wheel which comprises applying a memory alloy member in its deformed heat-unstable configuration to the wheel and heating it to cause it to recover and either to grip the wheel and form a running rim or to secure a separate running rim member to the wheel.

As is known, certain alloys, commonly called"memory alloys", can be used to make heat-recoverable articles, that is to say articles which have been deformed from an original configuration and which are capable of recovering towards that original configuration on heating. Amongst such memory alloys, there may be mentioned, for example, various alloys of titanium and nickel which are described, for example in U. S. Patents Nos. 3,174,851,3,351,463, 3, 753,700,3,759,552, British Patents Nos.

1, 327,441 and 1, 327,442 and NASA Publication SP 110,"55-Nitinol-The Alloy with a Memory, etc." (U. S. Government Printing Office, Washington D. C. 1972).

The property of heat-recoverability has not, however, been solely confined to such titanium-nickel alloys. Thus, for example, various copper base alloys have been demonstrated to exhibit this property in e. g.

N. Nakanishi et al, Scripta Metallurgica 5, 433-440 (Pergamon Press 1971) and such materials may be doped to lower their transition temperatures to cryogenic regimes by known techniques. Similarly, 304 stainless steels have been shown to enjoy such characteristics, E. Enami et al, id at pp.

663-68. Likewise, certain alloys of titanium and niobium also exhibit memory. C. Baker, Metal Science Journal 5, 92-100 (197 1) and J. P. Morniroli et al C. R. Acd. Sci. Ser.

C 275 (16) 869-871 (1972).

In general these alloys have a transition temperature below +120 C. Particularly useful alloys have a transition temperature from-196 C to-70 C (this being well below the lowest temperature they are liable to encounter during everyday use), and may be brought into their martensitic state by immersion in liquid nitrogen. However, more recently, it has been found possible to "precondition"memory alloys so as transiently to raise their transition temperature. This enables the articles made from such alloys to be kept at room temperature prior to use, so that they can be caused to recover bv heating above room temperature to their ártificially raised initial transition temperature. After recovery, the transition temperature reverts to a value below operating temperature so that there is no danger of a reverse transformation. Such preconditioning methods, which eliminate the need for refrigeration during storage, transportation, and instaliation are described, for example, in German Offenlegungsschriften 2,603,878 and 2,603,9 U. Memory meta ! s have alreadv found certain commercial applications in which their dimensional recovery and, in some cases, high strengths have been utilised in, for example, the formation of mechanical and electrical connections.

The present invention is based on the surprising observation that memory alloys, especially binary and ternary alloys of titanium and nickel, can advantageously be used to form running rims for rail vehicle wheels, not only by virtue of their dimensional recovery properties but also by virtue of various other properties which, even if they had previously been noted, had never been fully evaluated or utilised in practical applications. As a result of this observation, the present invention is able to provide running rims which can readily be applied to the basic wheel by using the known heat-recovery properties of the alloys, but which also exhibit other surprising improvements with regard to wheel/rail adhesion and other relevant properties.

As mentioned above, the memory alloys especially preferred for use in the present invention in its application to rail vehicle wheels for rapid mass transport systems are the titanium-nickel alloys known generically in the art as the"55-Nitinol Alloys". These alloys, in general, contain from A to 48 ó by weight titanium, the remainder being comprised by nickel, and, sometimes, minor amounts of a tertiary element such as cobalt or ion which is included to control the transition temperature. Thus, for example, the transition temperature for the stoichiometric binary alloy, TiNi, is about 80 C. However, this transition temperature can be depressed towards absolute zero by adding a tertiary element such as those mentioned. The alloy used in"Crvofit" (Registered Trade Mark) parts sold by Raychem Corporation has a transition temperature of about-120 C which makes it especially suitable for use in all environmental conditions. For convenience, therefore, the present invention will now be described with reference to such allovs.

In accordance with the preferred method of the present invention an annular member of a titanium-nickel alloy is lot are in temperature to below the transition temperature of the ailoy, i. e. that in which the alloy exists in its martensitic state. The annular member is then expanded in the martensitic state so as to make it radially heat-shrinkable. In order to apply the annular member it is placed circumferentially about the bearing surface of the wheel and is then heated to, or, more usually, allowed to warm to, a temperature above the transition temperature whereby the annular member contracts towards its original diameter and thereby grips the bearing surface with compressive force, a stress of up to about 60,000 psi being developed in the alloy depending upon the amount of unresolved shrinkage.

In general the dimensions of the annular member relative to the wheel will be chosen so that a radial expansion of about 8 /ó will enable the annular member to be positioned property about the wheel and that up to 6a, e. g. from 2 to 4%, of unresolved recovery will remain when the annular member has shrunk to become firmly seated on the bearing surface.

As mentioned above, the transition temperature (or, more correctly, the transition temperature range) will depend upon the precise constitution of the titanium-nickel alloy. It will be appreciated, however, that the transition temperature should desirably be chosen to be less than the minimum temperature to which the running rim may be exposed during use and, for this reason, the transition temperature preferably lies below-60 C and, more preferably, below-115 C. Preferred alloys comprise from about 43 to 45'. by weight titanium, preferably from about 43.4 to 44. ; Ó by weight. The alloy consisting essentially of from about 43 to 45% by weight titanium, from about 2 to 5"liron, not more than 1 Ó by weight of other elements, the balance being nickel is especially suitable because it can easily be maintained in its martensitic phase prior to application by storage in liquid nitrogen (or, possibly, in dry ice), but once it has returned to its austenitic phase it can safely be used in the most extremely cold climates.

In other embodiments of the present invention the running rim may be made from any material possessing the desired adhesion and other properties relevant to the problems discussed above and one or more memory a) ! oy members may be used to retain the running rim in position (including the case where the memory alloy member (s) forms at least part of the running surface). For example, the running rim may be retained in position by two flanged heatshrinkable alloy rings provided at each side thereof. In another embodiment a heatshrinkable memory alloy hoop may act to retain a separate annular running rim in position by the force which it generates when its thickness increases on recovery, the hoop being positioned as an intermediate member between the rim and the wheel bearing surface. In addition, in preferred embodiments of the present invention, the wheel and/or the tire is provided with means to assist proper location between said components. Other variations will, of course, be apparent to those skilled in the art.

In all embodiments, it will in general be preferred for the rail-contacting annular rim member to be formed as an integral part.

However, in certain applications, the annular rim may be split at one or more points around its circumference, preferably at an angle, so as to facilitate installation and subsequent removal for repair, etc.

Whilst in many embodiments it will be preferable to provide the running rim as a simple annular member it may in other embodiments be advantageous to provide the rim with an annular flange extending radially outward from one of its edges. Such a flange, which may or may not be in contact with a flange on the wheel itself, may further enhance wheel to rail adhesion and also help further to eliminate noise.

One advantage of these embodiments of the present invention is that the rim members and assemblies may readily be removed and repaired or replace without unnecessary damage to themselves or to other components of the wheel. For example, a heat-shrunk Nitinol running rim may be caused to expand to an extent which will allow its removal from the wheel simply by cooling it below the transition temperature, for example by spraying it with liquid nitrogen, see U. S. Patent No.

4,035,007. Yet another advantage is that the radial contraction of the annular member is accompanied by an increase in its width which may be used to locate the running rim tightly within a groove in the wheel by virtue of the lateral recovery forces.

It will be seen, therefore, that the dimensional recovery properties of memory metals can readilv be used to advantage in securing the running rim to the wheel. It has further been found, however, that various other very important advantages can be obtained by their use. Perhaps the most surprising and significant of these is the greatly improved adhesion shown by a Nitinol running rim as compared with steel.

The following Table summarises the average dynamic coefficients of friction obtained under different conditions by using Nitinol and steel running rims.

Nitinol wheel Steel Wheel Test condition on steel rail on steel rail Dry. 5)).2)6 Grease. 341. 130 Hydraulic fluid. 529. 167 Grease & Hydraulic fluid & water mist. 452. 172 It will be seen from the Table that, on average, the Nitinol to steel ratio is about 2.8 to I which is obviously a very important improvement. To some extent the improvement may be attributed to the fact that the relatively low modulus of elasticity of Nitinol, from 12 to 14x 106 psi (which is less than half that of steel), results in a larger area of contact with the rail and, in turn, leads to greater adhesion, the NitinoUsteel : steeVsteel contact area ratio being about 1. 4 : 1. A residual benefit of this greater contact area and a more complant wheel is noise reduction as exemplified by a significant decrease in the roar caused by microsurface imperfections.

In a conventional experimental testing method it was found that the wear exhibited by the rail when a Nitinol wheel was used was only 40% of that shown when a steel wheel was used. In addition, the wear exhibited by the Nitinol wheel was on) y 70% of that shown by the steel wheel.

A further surprising and significant point is that Nitinol/steel static adhesion appears to be lower than the corresponding slipping adhesion so that adhesion increases slightly with increasing slip. On the other hand, steel/steel static adhesion appears to be higher than slipping adhesion and thus decreases with increasing slip. tus it follows that the use of a Nitinol running rim may enhance a typical braking slip-spin control system and thus improve the braking performance under emergency conditions. Putting it more simply, with a steel wheel on a steel rail a braking control system of this type faces an inherently unstable condition as slip begins to occur and this has led to the need for very sensitive and responsive slip-spin control systems. Using a Nitinol running rim, however, the system may be inherently stable and self-correcting. If so, this will reduce the requirement for sensitive slipspin systems or else enhance the slip-spin performance in existing systems. It is believed that the frictional characteristics of Nitinol alloys have never been studied before and it follows, therefore, that these surprising advantages could not have been foreseen. Other properties of Nitinol alloys which are advantageous in this application are their fatigue and corrosion resistance, which give them a long and reliable life, and their relative insensitivity to commonly encountered adhesion reducing contaminants. These properties also give rise to reliable low electrical impedance at the wheel-to-rail interface, which is important for the efficient working of the control and detection methods used in modern rail systems.

It will also be appreciated that the improved adhesion coefficient and other properties shown by the Nitinol alloys may, in some applications, be utilised without at the same time using the memory characteristics of the alloy. In such applications it will be sufficient to affix the annular member to the wheel by conventional methods. Alternatively, the entire wheel may be fabricated from such alloys, if so desired.

Whilst the present invention has been particularly described with reference to titanium-nickel alloys it will be appreciated that similar advantages may be obtained by using other memory alloys, and, in particular, titanium memory alloys, which exhibit a coefficient of adhesion with steel rail of at least 0. 16, preferably at least 0.2, and, in any case, that those and other memory alloys may have application to other rail systems, e. g. freight rail systems, where noise reduction is especially important.

It will be appreciated that the present invention is applicable, in principe, to any type of wheel and that the wheels may themselves be provided with other features intended to improve their performance, including, for example, those designed to reduce or eliminate impact loading of vehicle chassis components and unwanted noise such as squeal, impact and roar.

Various embodiments according to the present invention will now be described in more detail, by way of examples only, with reference to the accompanying drawings, in which: Figure I is an isometric flow diagram showing the steps in a method for securing a memory alloy running rim to a rail vehicle wheel ; Figure 2 is a schematic stress/strain diagram showing the shape memory process in a titanium-nickel alloy ; and Figures 3 to 11 are partial sectional views illustrating different rail vehicle wheels in accordance with the present invention.

Referring now to Figure 1, there is shown a rail vehicle wheel 11 having a bearing groove 12 positioned between an inside flange 13, which is provided to prevent lateral motion of the wheel relative to a track rail, and a keeper flange 14. In accordance with the present invention the bearing groove 12 is provided with a running rim 16 made of a memory alloy, preferably a 55-Nitinol alloy.

Running rim 16 may be made, for example, by a rolling process so as to have an inside diameter which is less than the diameter of the cylindrical bearing surface of groove 12. The degree of difference between the inside diameter of the running rim and the bearing surface diameter will depend upon the amount of internal stress it is desired to develop within the memory alloy when the rim compressively grips the bearing surface. Generally, however, satisfactory results are obtained when the running rim 16 has an inside diameter which is from about 2 to 4% less than the diameter of the bearing surface.

After running rim 16 is formed with such an original diameter it is cooled to a temperature below the transition temperature zone or at least between the austenitic and martensitic phases of the memory metal, for example by immersion in liquid nitrogen. It is then expanded by using, for example, a radially expanded collet so that its inside diameter becomes greater than the diameter of the bearing surface. Of course, when a keeper flange 14 is provided, as shown, the expanded inside diameter of running rim 16 must be sufficient to allow the rim to clear the flange. In general, it will be appreciated that the dimensions of the flange 14 and the groove 12 should preferably be such that with about 8% ring expansion the flange 14 may be cleared in the expanded state and yet that from 2 to 4 of unresolved recovery will remain when the running rim is firmly seated in groove 12.

However, the relatively large diameter of the wheel, i. e. about 30 inches, ensures that such design requirements may be met.

Once it is expanded the running rim 16 is maintained in its martensitic phase until it is desired that the rim be applied to the wheel 11. The rim 16 will remain in the martensitic phase as long as it is kept below its transition temperature, e. g. by being stored in liquid nitrogen.

When it is desired to apply the running rim 16 to the wheel 11, the rim 16 may be removed from its cold storage and placed circumferentially over the bearing groove 12 under ambient conditions at which time it will attempt to recover to its original diameter. However, it is only able to contract to the point when its inner surface engages the bearing surface of groove 12 with the result that the running rim 16 grips the bearing surface with compressive force.

Figure 2 is a typical stress/strain diagram showing the relationship of such parameters in the memory alloy of a running rim subjected to the method of the invention.

The relationship of stress to strain within the metal of the rim when such metal is in its austenitic phase is defined by curve 17 whereas when it is in its martensitic phase such relationship is defined by the curve 18.

When the diameter of the rim is enlarged while the rim is in its martensitic phase, such rim will be stressed along curve 18 to the point indicated at 19. Upon the stress causing the diameter enlargement being removed, the strain will recover to the point 21. Upon the rim later being subjected to a temperature above the transition zone between the martensitic and austenitic phases thereof at the time it is applied to a wheel, the strain will recover along the abscissa axis to the point indicated at 22 at which the rim engages the wheel bearing surface and can no longer contract. Because the material will be reverting to its austenitic phase, internal stress will be developed within the rim consistent with the amount of strain required to maintain the rim at the same diameter as the diameter of the bearing surface. That is, the internal stress developed within the rim will reach the relatively high value on the curve 17 indicated by the point 23.

Figure 3 is a partial sectional view illustrating a portion of a rail vehicle wheel 31 having a circumferential running rim 36 secured compressively to the bearing surface thereof by the internal stress developed within the rim when it is applied in accordance with the method of the invention. It will be recognised that the question of whether or not the keeper flange 34 is required in order to assure that the running rim 36 will not slip axially off the wheel 31 is governed by the amount of compressive force with which the running rim 36 is designed to grip the wheel 31. It is, however, preferably provided for safety.

Turning now to Figure 4, it is not unusual for the surface of the inside flange 43 of a rail vehicle wheel 41 also to experience wear. The method of the invention not on) y enables a running rim 46 to be applied to the bearing groove 42 of such a rail vehicle wheel, but also enables a replaceable rail engaging surface to be applied to the inside flange. Such an inside flange surface can be provided merely by constructing the metal running rim 46 with an annular flange 47 extending radially outward from one peripheral edge thereof. Such annular nange 47 will be expanded together with the remainder of the rim 46 and will recover to engage the inside flange 43 of the wheel 41.

Figure 5 illustrates an alternate embodiment of a rail vehicle wheel which has a circumferential running rim 52 secured thereto by retaining rings 53 and 54 made from a memory alloy. The rings 53 and 54 are provided with flanges 55 and 56, respectively, which overlap the circumferentiat edges of the running rim 52.

In this embodiment the running rim 52 which is made from any suitable material having the necessary adhesion and hardness, etc., is split. That is it is made to be discontinuous at one location around its circumference so that it can easily be expanded for installation. The split is preferably diagonal of the axis of the rim so that the vehicle load stress is concentrated at any one time on long a portion of the split.

The retaining rings 53 and 54 may be expanded as described above, and on application, they are positioned together with the running rim 52 over the bearing surface 55 of the wheel 51. As the rings 53 and 54 attempt to recover to their original inside diameters they contract and compressively engage the circumferential edges of the rim 52 and force it against the bearing surface 58.

Figure 6 illustrates another form of wheel 61 in accordance with the present invention which is again provided with a running rim 66 which need not be made from a memory alloy. In this embodiment the running rim 66 is secured about the bearing surface 62 of wheel 61 by means of an intermediate hoop 63 made from a memory alloy. As in the previous embodiments the hoop 63 is stretched uniformly parallel to the axis of rotation whilst in the martensitic state so as to have an inner diameter which is slightly greater than that of bearing surface 62 and an outer diameter slightly less than the inner diameter of running rim 66, and so that the thickness of the hoop is reduced. On installation it is positioned about bearing surface 62 and the running rim 66 is itself positioned about hoop 63. As hoop 63 recovers to shrink down over bearing surface 62, so also does its thickness increase and thus the hoop exerts an outward compressive force on running rim 66 so that, in effect, the hoop grips both the bearing surface and the running rim to secure the assembly. It will be appreciated that the hoop 63 need not be continuous.

In Figure 7 there is shown a rail vehicle wheel 71 which is provided with a running rim 76 located in a bearing groove 72. In this embodiment the dimensions of the running rim 76 in its expanded form have been chosen so that after shrinkage it lies flush with the surface of the upper shoulder of the wheel 71. In addition its dimensions can be chosen so that during radial shrinkage the accompanying increase in its width causes it to exert lateral compressive forces on walls 73 and 74 of the bearing groove 72 so as further to ensure that it remains in position during operation of the wheel. Further, if so desired, the running rim 76 can be so dimensioned that when installed all stresses in the rim are compressive.

Figure 8 shows a further wheel 81 in which the running rim 86 is somewhat thicker than the running rims previously shown. As is known to those in the art some systems require a heavier tire and Figure 8 shows how one may readily be provided by using a memory alloy in accordance with the present invention.

Figure 9 shows yet another wheel 91 provided with a heavy tire 92 in accordance with the present invention. In this instance the tire 92 provides both a running rim 96 and an inner flange 97. It will be appreciated that such a tire will be especially suitable to applications where there will be a heavy load on the rim and the flange and, furthermore, that the tire may readily be removed and replace without the necessity of reprofiling the wheel 91.

Figure 10 shows a somewhat similar wheel 101 provided with a heavy tire 102. In this arrangement the wheel 101 is provided with a protrusion 103 on its outer peripheral surface and the tire 102is contoured to cooperate with this protrusion 103 to facilitate proper location and further to enhance the secure grip of the tire on the wheel. It will be appreciated, in this respect, that other arrangements may be employed for this purpose.

Finally, in Figure 11 there is shown a wheel 111 which is similar to the wheel shown in Figure 4. However, in this arrangement the retaining rim 112 is provided with an inner flange 113 which extends over the inner edge of the wheel 111 which is suitablv contoured to ensure that the thickness of the memory alloy running rim remains substantially constant.

The terms"tire"and"running rim"as used in this specification generally include all members having a running surface thereon which contacts the rail. Thus whilst some members may more commonly be regarded as tires by those skilled in the art and other members as running rims, each of said terms in the present specification is meant to include the other.

It will be appreciated that the present invention provides a wheel and a method of fabricating such a wheel which is especially suited to the modern rapid mass transit systems. However, it may also be advantageously utilised in other railroad systems and may be used, for example, on freight trains and trucks and other railroad vehicles. In this respect, one further significant advantage of the present invention is that it provides a lighter wheel assembly than has hitherto been possible using steel tires and running rims. This leads to a significant improvement in wheel dynamics because the lower unsprung mass constituted by the wheel may more readily be forced back on to the rail by the springs of the vehicle when an imperfection in the rail surface causes the wheel to jump upwards.

Other modifications and variations in accordance with the present invention will be apparent to those skilled in the art.

Claims (33)

1. WHAT WE CLAIM IS : 1. A wheel, the tire or running rim of which consists of or comprises a member made from a memory alloy.
2. 2. A wheel as claimed in claim I which is a rail vehicle wheel.
3. 3. A wheel as claimed in claim I or claim 2, wherein the tire or running rim is made from a memory alloy.
4. 4. A wheel as claimed in claim 3, wherein the tire or running rim has been applied by expanding it diametrically whilst the memory alloy was in its martensitic state, positioning it about a bearing surface of the wheel, and causing it to warm to the austenitic state so that it contracted and gripped the wheel with compressive force.
5. 5. A wheel as claimed in any one of claims 2 to 4, wherein the running rim is provided with an annular flange made from the memory alloy which flange abuts the inner flange of the wheel to provide a railengaging surface thereon.
6. 6. A wheel as claimed in any one of claims 2 to 4, wherein the tire is formed so as to provide an inner flange for engaging a rail.
7. 7. A wheel as claimed in claim I or claim 2, wherein one or more memory alloy members act to retain a separate running rim or tire in position on the wheel.
8. 8. A wheel as claimed in claim 7, wherein a separate running rim is secured in position by two memory alloy retaining rings provided with annular flanges which engage the upper circumferential edges of the rim.
9. 9. A wheel as claimed in claim 7, wherein a separate tire or running rim is held in position by the compressive forces which were exerted on it by a memory alloy hoop positioned between said tire or rim and the wheel as the hoop increased in thickness during radial shrinkage about said wheel.
10. 10. A wheel as claimed in any one of claims t to 9, wherein the wheel is provided with a groove in which the retaining rim or tire is located.
11. 11. A wheel as claimed in any one of claims I to 10, wherein the memory alloy is a titanium alloy.
12. 12. A wheel as claimed in claim 11, wherein the memory alloy is a binary or ternary alloy of titanium and nickel containing from about 43 to about 45"/o by weight titanium.
13. 13. A wheel as claimed in claim 12, wherein the alloy consists essentially of from 43 to 45 , a by weight titanium, 2 to 5% by weight iron, not more than 1% by weight of other elements, the balance being nickel.
14. 14. A wheel as claimed in claim 12 or claim 13, wherein the alloy contains from about 43.4 to about 44. 4 ú by weight titanium.
15. 15. A wheel as claimed in any one of claims I to 14, wherein the memory alloy has a coefficient of adhesion on a steel rail of not less than 0. 16.
16. 16. A wheel as claimed in claim 15, wherein the memory alloy has a coefficient of adhesion on a steel rail of not less than 0.2.
17. 17. A rail vehicle wheel provided with a tire or running rim made from a binary or ternary alloy of titanium and nickel containing from 43 to 45 o by weight of titanium.
18. 18. A rail vehicle wheel as claimed in claim 17, wherein the alloy consists essentially of from 43 to 45 ; o by weight titanium, 2 to 5 O by weight iron, not more than lobby weight of other elements, the balance being nickel.
19. 19. A rail vehicle wheel as claimed in claim 17 or claim 18, wherein the alloy contains from about 43.4 to about 44.4 ; o by weight titanium.
20. 20. A method of applying a tire or running rim to a wheel which comprises applying a memory alloy member in its deformed heat unstable configuration to the wheel and heating it to cause it to recover and either to grip the wheel and form a running rim or to secure a separate running rim member to the wheel.
21. 21. A method as claimed in claim 20 wherein an annular memory alloy member is expanded, whilst the alloy is in its martensitic state, from a diameter less than that of the bearing surface of the wheel to one which allows it to be positioned about said bearing surface and when so positioned is caused to warm to a temperature at which the alloy exists in the austenitic state so that it shrinks radially and contacts the bearing surface.
22. 22. A method as claimed in claim'0 wherein two retaining rings made from the memory alloy provided with annular flanges recover to secure a separate running rim to the wheel by the forces exerted by said flanges on the circumferential edges of the rim.
23. 23. A method as claimed in claim 20, wherein a memory alloy hoop is positioned in an expanded heat-unstable condition between a tire or running rim and the wheel and on recovery exerts compressive forces on the wheel by its radial shrinkage and on the tire or running rim by the increase in its thickness on recovery.
24. 24. A method as claimed in any one of claims 20 to 23, wherein the wheel and/or the tire is provided with means to assist proper location between said components.
25. 25. A method as claimed in claim 24, wherein the wheel is provided with a groove to locate the tire or running rim.
26. 26. A method as claimed in claim 25, wherein the memory alloy member exerts a compressive force on the sides of said groove by the increase in its width during recovery.
27. 27. A wheel whenever made by a method as claimed in any one of claims 20 to 26.
28. 28. A wheel as claimed in claim 27, wherein the memory alloy is a binary or ternary alloy of titanium and nickel containing from about 43 to 45% by weight of titanium.
29. 29. A wheel as claimed in claim 28, wherein the alloy consists essentially of from 43 to 45"o by weight titanium, 2 to 5, ' by weight iron, not more than l, Ó bv weight of other elements, the balance being nickel.
30. 30. A wheel as claimed in claim'9 wherein the alloy contains from about 43.4 to about 44. O by weight titanium.
31. 31. A rail vehicle provided with a wheel as claimed in any one of claims 2 to 19 or 27 to 30.
32. 32. A wheel as claimed in claim 1, substantially as described herein, with reference to, and as illustrated in the accompanying drawings.
33. 33. A method as claimed in claim 16, substantially as described herein, with reference to, and as illustrated in the accompanying drawings.