US1660960A - Flexible stay bolt and method of making - Google Patents

Description

Feb. 28, 1928.

G. R. GREENSLADE FLEXIBLE STAY BOLT AND METHOD OF MAKING Filed Feb. 18, 1927 Patented Feb. 28, 1928.

J UNI ED STATES PATENT OFFICE;

GBOVER R. GREENSLADE, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOB TOFLANNERY WARE.

FLEXIBLE s'mx 3012']! AND 1111121101) or MAKING.

Application filed l'ebriiary 1a, 1927. Serial No. 169,256.

This application is a continuation part of my copending application, Serial No. 118,515, filed June 25, 1926. The present invention relates to flexible 5 staybolts and method of making, and more especially to a staybolt having a hardened head, and also to the combination of a headed staybolt and a seat therefor, one of which has an anti-friction bearing surface.

Flexible staybolts are employed in steam boilers, and more especially in locomotive boilers, in order to allow relative movement between the wrapper sheet and ,fire sheet. Referring particularly to a locomotive boiler, the fire box is formed within the boiler, the

side walls and top of the fire box being bounded by the water space of the boiler.

The sheet between the fire space and the water space of the boiler is usually called the fire sheet. The sheet around the outside of the boiler is usually called the wrapper sheet. These two sheets are tied together by staybolts. Due to unequal expansion of the parts under variations in temperature there may be a considerable movement between the wrapper sheet and fire sheet, amounting, at

' times, to perhaps one-quarter of an inch.

This movement takes place principally in V the planes of the fire and wrapper sheets. 80 In order to permit such movement without damage to the staybolts, the flexible staybolts have been employed. The usual socalled flexible staybolt consists of a bolt which is threaded into the fire sheet at one. end. 'The other end of the bolt has an enlarged head which is seated in a sleeve secured to the wrap er sheet, the head of the bolt being covered y a cap screwed or otherwise secured to the sleeve. This permits a ball-and-socket motion between the bolt head and its seat in the sleeve. The fire sheet is usually of thinner materialithan the wrapper sheet. It is also maintained at a higher temperature in service. Moreover, it would not bepracticable to have caps projecting 1 into the fire box from the fire .sheeta- For this reason the wrapper sheet end onl of the staybolt has been provided with the all and-socket joint, it being found that the thinner fire sheet has suflicient flexibility to allow the deflection of the staybolt.

' When locomotives were first constructed theboilers were small. and operated at relatively low pressures, and practically all of the staybolts were rigid. staybolts, that is, staybolts which were screwed or otherwise rigidly secured to both the wrapper and fire sheets. It was found, however, that as the size of the boilers and the steam pressure were increased, serious breakage took place with the rigid. staybolts. This breakage occurred usually at the ends of the bolts where they were screwed into the wrapper and fire sheets, and most commonly at the wrapper sheet end of the bolt. Some breakage, however, took place at the fire sheet end. In order to meet this condition, the flexible type of staybolt ,was developed, such staybolts usually being of the type shown in the Tate Patent No. 813,120 of February 20,1906.

It was found that the use of the ball-andsocket connection at the wrapper sheet not only prevented the breakage of the bolts at the wrapper sheet end, but also diminished the breakage of the bolts at the fire sheet end as well. The reason for this can be seen by an analysis of the conditions surrounding the use of therigid staybolt. The rigid staybolt is rigidly screwed into both the wrapper and the fire sheet. Therefore, upon relative movement of the two sheets the staybolt is subjected to the. stresses of a beam rigidly secured at both ends and the rigid staybolt is bent with a reverse curve. In the flexible type of staybolt, however, one end is free, so that upon relative movement of the two sheets the staybolt behaves as a beam rigidly secured at one end only, the other or loaded end being rota'tably free. Therefore, for the same relative movement be-- tween the wrapper and fire sheets, ,the amount 'of bending moment to which the flexible staybolt is subjected is only about half of that to which the rigid staybolt is subjected. I

The flexible staybolts such as shown in the Tate patent solved the staybolt problem for.

the time being. However, in recentyears the size of the locomotive boilers and the steam pressures have been greatly increased so that the staybolts have not only been subjected to greater relative lateral movements of the fire and wrapper sheets, but also the tension .on the bolts hasbeen greatly increased. The staybolt breakage again be an to be serious. It was found that the ate and wrapper sheets.

flexible staybolts whichwere practically unbreakable in locomotive boilers in; vogue when the Tate bolts were first introduced, were subject to breakage in the more modern 5 large locomotives. I havefoundthat the breakage appears to have been due to two factors, namely, the increased tension on the bolts and theincreased relative movement between the fire The tension on the parts of the boilers has been increased to a point where the staybolt head has been drawn against its sleeve so tightly as to reduce and even prevent the ball-andsocket slippage between the head and its seat in the sleeve. This'increase in tension has practically defeated the object of the flexible staybolt, because a bolt which hasits head frictionally locked against its seat acts as a rigid bolt, and the shank of the bolt is subjected to the same amounts of stress as a rigid bolt. This has resulted in breakage of, the flexible staybolts, par- *ticularly at the neck just belowwthe head of the bolt, and also near the fire sheet end of the bolt, these two points being the points of maximum bending to which the'rigidly locked bolts have been subjected.

ll have found that this breakage may be prevented by making one or both of the contacting surfaces between the bolt member and the sleeve member of the assemblage of a very hard metal. If one or both members are made of a hard metal, I have found that staybolts at certain 3 the locking which took place between the relatively soft metal surfaces of the bolt head and sleeve may be prevented for boiler pressures now encountered. This condition is preferably secured by locally hardening 40 the head of the bolt where it contacts with the sleeve. This condition could not be remedied by using a bolt wholly of a hard material, as will be apparent from the following considerations. Tn practice in the United States, staybolts have been practically universally made of wrought iron because of its ductility and resistance to corrosion. Some roads, particularly the Canadian railroads, have used avery low carbon mild ductile steel for staybolts. These materials are necessary because a considerable amount of ductility is required in the staybolt. The yield point of the material should not be too high. The staybolt, particularly at the fire sheet end, is subjected to deformation which I may exceed the elastic limit of the material, and therefore to minimize or prevent breakage from fatigue a mild ductile metal should be used. Also, it is practically impossible in applying the staybolts to the cold boiler to screw them in so that when the boiler is heated up and the tension isapplied to the bolts, that the tension is uniformly distributed over all of the staybolts. Some of t5 the staybolts will inevitably be put under greater tension and the staybolt metal should workmen strike the caps with hammers to loosen them, thus subjecting the sleeves to severe treatment, so that the sleeves should be made of material which will not readily fracture. For this reason it is preferred to have the body of the bolt and the body of the sleeve of the milder metals now used, and .to surface harden the bearing surfaces between the bolt head and sleeve.

Another weakness, in flexible staybolts as usually heretofore made has been brought out by the increased demands on staybolts by modern locomotive practice. This weakness has been the tendency of the bolts to crack just under the heads. In making the flexible staybolts, according to the usual practice, a round bar of staybolt iron (or steel) of the proper length has several inches of one end heated. The bar is then clamped in a machine, leaving projecting suflicient metal to form the head. A die is then brought against the heated end and gathers or mashes the metal into a generally spherically shaped ball or bunch on the end of the bar. The roughly formed upset head'is then finished by a forging operation usually carried out by placing the head in hammer dies which strike forming blows on the head to shape it to spherical form. The head, however, may be entirely forged by forming dies. The dies of the hammer or forging machine are cold and the metal has been cooling from the time upset, so that the finishof the forming operation is often carried out on metal, particularly at the surface, which may have dropped in temperature below the best forging temperature. Since the forging is a and operation, it is practically impossible to see that the workmen always carry out the forging at the best forging temperature. The result has been that the metal, particuthe-head was first larly at the surface of the head and of the neck where the head joins the shank of the bolt, has in many cases had its grain structure seriously impaired. Photo-micrographs have shown that while the iron at the interior of the head has the normal grain structure with bands of slag running longitudinally of the bolt, at the thegrains seem to be distorted and broken up. The slag bands are also somewhat broken up. The result has been that the sur-' face metal has been weakened so that cracks forged surfacescould start in it and penetrate into the metal atthe interior of the bolt. As is well known, a crack tends to continue from weakened metal into normal metal.

I can overcomethis weakness by restoring the grain structure without surface hardening the metal ofthe bolt head, although I prefer to combine the surface hardening and grain restoration in the same operation.

The preferred process of making sta bolts in accordance with my invention Wlll now be described, reference bein had to the accompanying drawings, in which- Figure 1 is an elevation partly in section showin a 'staybolt assemblage applied to I the boi er; and

Figure 2 is a detailed sectional-view of a sleeve showing a modification.

Referrin sheet 1 and fire sheet 2 are shown as being which comprises the usual bolt member 3, sleeve 4 and cap ,5. The bolt 3 is threaded at 6 into the fire sheet 2, the end 7 being riveted over in the usual manner. The sleeve 4 is threaded at 8 into the wrapper sheet 1. The. bolt 3has the. usual enlarged spherical head 9 which engages the seat 10 of the sleeve 4. I

The parts as above described are those of the well known .Tate bolt employing a threaded sleeve. The invention, however, is not limited to the Tate bolt but may beembodied in various other t pes 6f flexible staybolts, such, for examp e, as the so-called fbutton head or the taper head type of flexible crownstay in which a spherically surfaced nut is screwed on the wrapper sheet end of the bolt to make contact -with the sleeve, or may be embodied in the so-called welded ty e of staybolt assemblages in whichthe s eeves, instead of being threaded to the wrapper sheet, are welded to the wrapper sheet.

.While the bearing seat for the staybolt head is usually provlded in a sleeve attached to the boiler sheet as shown for example in the Tate Patent No. 813,120, of February 20, 1906, the bearing seat maybe otherwise formed, for example, as shown in the Mennie Reissue No. 14,796, of January 27, 1920, in which the bearing seat is formed directly in the outer boiler sheet.

In my improved staybolt assemblage. one or, both of the contacting surfaces of the bolt member 3 and sleeve or'seat member 4 are hardened so as to prevent the frictional sticking under heavy tensions on the bolt. The motion of the parts is not suflicient so that the surface hardening is neoessa'r to resist wear. The surface hardening is one forithe pur ose of reventing the parts from binding, w ich I ave found to take place with metal surfaces having the ductility and 'mildness demanded for the. body of the stayof the staybolt has its surface carburized,

as indicated by the shading 11. This sur to the drawings, the wrapper face carburization is usually applied over the entire head of the bolt and a short distance along the neck 12. The sleeve 4: is shown as having its surface hardened by carburization, as indicated at 13.

While both the head and sleeve are shown as having their contact bearing surfaces carburized, one only need be carburized, preferably the bolt head.

In Figure 2 is illustrated a: modification in which the sleeve body, instead of having a hardened seat formed by surface carburizing, has a hardened seat formed by an inset 14 of hard steel or of other suitable hard metal or alloy.

The preferred process of making the stay- -bolts is as follows:

connected by a flexible stay-bolt assemblage A bar of staybolt iron of the proper. length has its end heated for several inches to a forging heat and the end is then upset to r form a roughly spherical head. This upset ting operation, if properly carried out, should not destroy what is commonly called the fibrous constitution of the iron. Staybolt iron is made from wrought iron con taining a certain amount of slag. It is found that the presence of the slag gives the iron greater resistance to corrosion and also a more fibrous nature than that of the so called dry wrought iron from which the slag is ractically eliminated. In' making the stay olt' iron bars, a number of muck bars are either box piled or slab piled and slag, The iron is stronger lengthwise of the so-called fibers. If the upsetting operation is properly carried out, the fibrous condition then re-rolled so as to give the staybolt iron of the iron will persist in the head, the socalled fibers in the head being bulged out somewhat like the layers of'an OlllOIl but still preserving the general longitudinal direction. I

After the metal is upset to form the rough head, the head is forged to finished s herical form in the usualway by finishing ies.

' The stayboltsare then 'treated to restore the grain structure and to surface harden mersin'g the heads of the sta bolts in a molten bath ofpotassium cyani e at a temperature of about 800 C. for about ten minutes. This brings the heads quickly to a bright red heat which serves to normalize the metal,

the heads. This is preferably done by imv.

that is to say, it restores to a normal condition the grain structure which may have been damaged by the forging operation. The

. particularly at the neck, at which place fail-.

cyanide treatment also serves to carburize.

the surface of. the staybolt headbut without carburizing theinter'ior of the head or themetal in the shank,

During this c'arbu-rizingoperation only the heads of the bolts are dipped into the molten cyanide bath. Assoon as the bolts are removed from the cyanide bath they are immediately quenched in water. This serves to increase the yield point and ultimate tensile strength of the metal throughout the head,

ure frequently takes place. Since the hardened surface prevents thehead of the staybolt from binding in the sleeve, the metal in tl1e head and neck is not subjected to distortion due to bending moments, and hence can,

be made harder and stiffer than the metal in the shank and at the fire sheet end of the bolt body, where the metal is subjected to bending. This treatment, therefore, re-

' sults in localizing the hardness and the increased yield point and ultimate tensile strength where they are most desired, leaving the original ductility of the metal local ized in the shank andfire sheet end.

While for practical shop operation: the heating of the metal in the cyanide bath is grain structure, the process may be modified, if desired, by heating the staybolt heads to a somewhat higher temperature, say, about 900 centigrade, and thereafter either immediately immersing them in the molten cyanide bath or quenching and then immersing them in the molten cyanide bath. Such preliminary treatment to a higher temperature can more completely restore a badly damaged grain structure.

I have found that with staybolt iron there is practically no objectionable grain growth encountered in heating the heads of the bolts in accordance with the ordinary shop practice of my a method and without, any extraordinary precaution. Staybolt iron in this respect difiers somewhat from steels, and particularly the higher carbon steels.

For general purposes it is usually sufficient to harden the bolt heads only. However, if desired, the seating surface of the sleeves maybe hardened, in which'case the hardening of the bolt heads may be omitted or both the bolt heads and sleevesmay be hardened. The sleeves are preferably -,hardened by a local cyanide carburizing treatment, leavin thebody of the sleeve of the usual mil tough sleeve steel stock. However, the hardened surface of the sleeve may be provided in other ways, as, for example, by the inset 14 shown in Figure 2, or the entire sleeve may be made of a hardened alloy steel, as contrasted with the practice heretofore of using a mild steel for the sleeves, Such hard alloy steels will give an excellent'bearusually sufficient to restore any damaged as above described fracture, but they are, however, relatively expensive.

While a cyanide carburizing treatment is preferred for hardening the contact surfaces, other hardening treatments might be employed, such, for example, as carburlzing by other processes such as the pack process, or by plating, such as with chromium, or chromium alloys, or other plating metals.

The bearing surface of the bolt head or the bearing surface of the sleeve should be much harder than-the metal of the main body of the bolt proper. By the expression fmuch harder, I mean a degree of hardness comparable to that obtained by carburizing and quenching, by the use of hard steels, or by chromium plating or the like, as distinguished from such differences in hardness as may have existed between the usual un hardened or mild steel sleeves and the Wrought iron staybolts as heretofore made.

I am aware of the suggestion of the use of copper liners or washers between staybolt heads and sleeves to prevent corrosion and reduce friction. I have found, however, that with the enormous tensiles to pressures. I have found, however, that when one or both of the contacting surfaces are hardened, this interlocking is prevented, at least to such an extent that the heads are free to turn in the sleeves with the staybolt tensiles even greater than those encountered in modern locomotive practice. This has been demonstrated by tests in which the ordinary staybolts have been compared with my improved staybolts. In such tests a eavy tension, equal or exceedin that to which the staybolts are subjected in modern locomotive practice, is applied to a staybolt. The headed end of the staybolt is held in a sleeve which is rigidly mounted. The lower end of the staybolt to whch tension 'is' applied is given a continued slight oscillatory movement at right angles to the axis of the bolt. It has been found that while the ordinary staybolts may stand, say, from 150,000 to 250,000 oscillations before break-z of locking under heavy :pressure effected by the hardened contact surfaces, by the restoring of any damaged grain structure, particularly at the point where the head joins the neck, and by the increased strength given to the neck and head by quenching.

While all three of these factors are apparently necessary for the best results, it is obvious that not all of them need be present. For example, the performance of the staybolts may be greatly improved by restoring the damaged grain structure without quenching and without surface hardening, or the surface may be hardened without quenching, as, for example, by electroplating, or the heads and necks may have their hardness and strength increased by quenching without carburizing or plating.

While I have described the problems encountered'and the preferred embodiments of my invention, at considerable length, it is to be understood that the invention is not limited to its preferred embodiments but may be otherwise embodied within the scope of the following claims. 1

I claim:

1. The combination of a headed staybolt and a seat therefor having cooperating bearing surfaces", at least one of which is much harder than the metal of the main body of the bolt member.

2. The combination of a headed staybolt and a seat therefor having cooperating hearing surfaces, at least one of which is formed by a carburized hardened surface.

3. The combination of a headed staybolt and a seat therefor having cooperatin bearing surfaces, the bearing surface of t e bolt head being much harder than the metal of the main bod of the bolt.

4. The com ination of a headed staybolt and a seat therefor having cooperating hearing surfaces, the bearing surface of the'bolthead bein carburized to a surface hardness much har er than that of the metal of the body of the bolt.

5. A staybolt assemblage comprising a headed bolt member and a sleeve member having cooperating bearing surfaces, and a cap secured to the sleeve member and covering the bolt head, at least one of the cooperating bearing surfaces of the bolt and sleeve member being much harder than the metal of the main body of the bolt member.

6. A staybolt having an enlarged forged head, the bolt head being normalized, surface carburized and quenched, whereby there is imparted to the head .a normal grain structure having a greater strength than that of the shank of the bolt and hardened hearing surface.

7. A staybolt having an enlarged head and a neck of much greater surface hardness and strength than the shank of the bolt.

8. The process of making staybolts which comprises upsetting and forging an enlarged head on the bolt body, heating the bolt'head in contact with a carburizing agent for a sufficient time to restore grain structure damaged by the forging operation and to carburize the surface of the bolt head which contacts with the sleeve, and thereafter quenching, leaving the metal of the bolt shank substantially unaffected.

9. The process of making a staybolt which comprises upsetting and forging an enlarged head on the bolt body, immersing the head in a heated cyanide bath for a suflicient time to carburize the surface and restore damaged grain structure, and thereafter quenching to harden the carburized surfaces and locally increase the strength of the body of the head and neck, leaving the metal of the bolt shank substantially unaffected.

10. The process of making staybolts which comprises upsetting and forging an enlarged head on the bolt body, carburizing the surface of the bolt head which contacts with the sleeve in the staybolt assemblage, and quenching, whereby such surface is rendered much harder than the metal of the main body of the bolt.

11. A staybolt having an enlarged head which is forged, normalized and surface hardened.

12. A staybolt having an enlarged head provided with a bearing surface much hardgr than the metal of the main body of the olt.

In testimony whereof I have hereunto set

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