US1941672A - Brake shoe and method of making the same - Google Patents

Description

Jan. 2, 1934. F. A. FAHR'ENWALD 1,941,672

BRAKE SHOE AND METHOD OF MAKING THE SAME Filed Jan. 6, 1930 B s Exisfk i/ 1m- C IIII 'roucix-xmzsa 'loo'F 3550'? I I I l I I I I I I I I l I I 1.2 a456'1e9s xx1L1s1415m Freak g. Fabregwald I 9 o 0 19 to a: "5 77 M14 gttoszgqn Patented n 51934 I A p 1,941,672

UNITED STATES PA ENT OFFICE BRAKE SHOE AND METHOD OF MAKING I THE SAME Frankh. Fahrenwald, Chicago, Ill., assignor to The American Brake Shoe'and Foundry (loinpany, New York, N. 1., a' corporation of Dela-' ware Application January 0, 1930. Serial No. use

V This invention relates to metal brake shoes than by its wear resistance. and to hold the parts 1 and the method of making same. of a broken shoe together and prevent them from Considering as an example, but without li'mfalling away it has longbeen customary to cast. iting myself thereto, the requirements and 0011- steel reinforcements in the shoe.

5 ditions encountered in railway practice, itis It is well known that cast-iron exhibits no ducnecessary that a brakeshoe shall develop a certility whatever and that no heat treatment theretain degree of friction in contact with steel or of will render it ductile, yet a very small degree chilled-iron wheels without unduly wearing or of ductility imparted thereto would overcome aliniuring the tread or surface to which itis apmost all objections to cast-iron brakeshoes. plied or itself becoming disintegrated in the Accordingly it is the object of my invention to process. It is also necessary to"consider and produce a brakeshoe which-shall retain substanprovide for the extreme local heating produced tially the cheapness and composition and fricby the friction of the brakeshoe which very fretion-coefllcient of cast-iron combined with the quently causes the brakeshoes tobecome red hot, toughness and tensile strength and ductility of and on some occasions actually leads to melting steel; and to do all the foregoing without changat localized portionsof the working surface. This ing in any way the standard shape, size, and

' local heating produces various peculiar and unmethod of attachment of the brakes-hoes heretoexpected effects which I will shortly describe. fore adopted and standardised; it is another ob- Plenty of hard and tough alloys are known but Ject of my invention to dispense with the necesthe same are unsuitable for brakeshoe use for sity for using inserts or reinforcements; other various reasons, chief among which are that objects are the provision of amethod of making a they do not afford proper friction, or that they tough cast-iron brakeshoe without increasing unduly abrade and damage the surfaces to which its cost substantially; while further objects and they are applied; added to which they are relaadvantages will become apparent as the descriptively too expensive. The essential requisites for tion p a metal brakeshoe are that it should exhibit a It is well known that the treads of car-wheels required degree of hardness, coupled with sufare often made of what is known as chilled flcient toughness to withstand the strains and white-iron", namely a cast-iron containing such shocks incident to use, and also possess such a proportions of carbon and silicon as when cast texture as to prevent what is known as flaking against a cold metal surface shall produce what or undue flowing of the metal surface under the isknown as "white-iron", which exhibits .phe

combined'heating and abrading effect of the nomenal hardness and abrasion resistance cancompanion part. It is believed that the presence pied, however, with a very high degree of brittleof graphite in the material is of importancein ness and a deficient amount of tensile strength.

35 this connection. Ordinary gray cast-iron ex- Attempts to employ this material for brakeshoe hibits all of these requirements to a very satispurposes have proven because of its factory degree, excepting the qualities of toughunduly small frictional effect, and because of its .ness, strength, and wear resistance. The cheapbrittleness and lack of tensile strength whichunest kind of gray cast-iron, in point of coeflicient ilts it for the violent shocks and severe operation of friction and cost per pound, serves the purconditions to which brakeshoes are subjected. pose better than'almost any other metallic sub- It has also been found that when such material stance, but it has the-disadvantage of rapid wear is used for brakeshoes. the local heating at the and the liability to fracture. working surfacesets up such strains as to frac- Owing to the effect of local heating and cooling, ture the entire shoe, due to its fragility. Sand- 45 and to the inevitable formation of surface cracks cast white-iron. namely iron which casts white adjacent the heated surface due to unequal heatin sand molds owing to a reduction in the amount. ing, to the variable heating of the brakeshoe of ca'rbonand/or silicon, exhibits the same dewhich causes the same to change in shape under fectswhen applied to brakeshoe use. Attempts different conditions of service application, and to have been made to employsteel, and what-is looseness of the brake gear which known as malleable cast-iron'Z/but these at- U of the shoes to become localised at different tempts have proven chiefly because points, the brakeshoe often breaks long before of ihe iof it is worn out; which is to say that heretofore thelearto flow and to the lifeof a brakeshoe has been its disintegratrimthe form of flakes. fricbrittlenessand m1: of tensile tion'eflect g gs m gmaiid ing and flowing away of the brakeshoe material under severe conditions; and furthermore experience shows that they wear the car wheel faster than gray-iron.

There is a type of iron, intermediate between the gray-ironand the white-iron, which I herein call mottled-iron" since it exhibits a kind of mottled apearance due to the coexistence in the same article of regions of white-iron and regions of grayiron. My tests have shown that brakeshoes made of this mottled-iron" retain substantially all the high friction of the gray-iron, together with one advantage of white-iron, namely, increased wear-resistance although, when made by direct casting methods, they still retain the brittleness and fragile nature of the ordinary cast-iron. The one advantage of such mottlediron is longer wear, but it has been impossible heretofore to produce 'brakeshoes of this mottled-iron by usual casting methods owing to the accurate control of composition and temperature necessary to be exercised and, furthermore, the mottled-iron as produced by casting methods has little, if any, superiority in strength over gray or white-iron. However, I have discovered a mode of producing brakeshoes of castiron which shall combine the friction qualities of gray-iron, the wear-resisting qualities of mottled-iron, and the toughness and ductility of steel, and this at a cost as low or even lower than is required in the production of ordinary gray-iron brakeshoes.

To effect this I first cast the brakeshoes at least in part of chilled-white iron, and then by maintaining the castings at the proper tempera- .ture for the necessary period of time I cause such a controlled decomposition of the primary cementite thereof with liberation of secondary graphite as shall afford the graphite material desirable for the service of the brakeshoes as above described while retaining such a proportion of the cementite as to afford the desired increase in resistance to wear; and I also anneal or temper the steel'matrix in such wise as to decrease its brittleness and render it tough and strong. The results of this treatment and the temperatures and times required to perform the .same vary with the composition of the iron and the method of casting employed, although in one respect the result is largely independent of either the composition or the foundry practice, namely: the usual gray cast-iron has very little tensile strength and. practically no elongation, due to the shape and arrangement of the graphite particles, while: due to the rounded or nodular shape of the graphite masses resulting from my process the strength is much increased.

The customary brakeshoe composition at the present day is approximately:

Carbon 2.80 to 3.10% Silicon .60 to 1.20% Phosphorus Up to .'l0% Sulphur Up to 25% Manganese Less than 1% Balance iron According to my improvements I cast these brakeshoes in white-iron, for example, by employing essentially the same composition of melt, the same raw materials, the same cupola practice as at present, but using molds which are made of metal, at least in part, such for 'example as a mechanical casting machine. After casting I subject the shoes to a temperature of about 1700 Fahrenheit for a period of time of from one to six hours, and afterwards cool them slowly through the *critical range, after which the remaining cooling can be at any convenient speed. The result of this first heat treatment at the time and temperature mentioned is to break down the combined carbon partly into graphite, retaining a substantial proportion of the hardness and wear resistance of the whitelron while overcoming sufiicient of the brittleness to avoid the objections heretofore made to whiteiron,-and producing a degree ofv friction coefficient substantially the same as that of mottlediron. Y

The breaking strength of a gray-iron or a mottled-iron brakeshoe of the above dimensions as heretofore made has seldom been as high as 20,000 pounds even when new and is more frequently around 17,000 pounds. A similar brakeshoe made according to my process and tested in the same manner ordinarily shows a breaking strength of from 23,000 to 26,000 pounds with an increase of useful life of 100 percent or more. It may be stated, in another way, that these shoes can be so made as to exhibit the wearresistance of white-iron coupled with the friction 'coeilicient of gray-iron and a type of toughness heretofore not possessed by either type of iron, so that their useful life is not, as heretofore, terminated by premature fracture.

I have described heat treatment of from one hour to six hours at 1700 Fahrenheit, but these are approximately the extreme time limits at this temperature with the composition described. It is important in my estimation to stop the heat treatment before all of the white-iron condition has been broken down because if carried too far it will produce the customary inferior qualities of malleable-iron brakeshoes, while if not carried far enough it will exhibit the unsatisfactory conditions of white-iron brakeshoes; Preferably, with the composition described, I employ a heat treatment of from three to four hours at 1700 Fahrenheit. The same amount of reaction can be produced by subjecting the brakeshoes to lower temperatures for a longer time or to higher temperatures for a shorter time. However, the time necessary for treatment varies very greatly with the temperature. Maintaining a brakeshoe of this composition at a temperature of 1800 Fahrenheit one hour is excessive for the best results with iron of this specification, and fifteen to twenty minutes seems to be about right, depending of course upon the rapidity of heating and cooling, but such severe conditions are diilicult to control or arrest at the desired point. subjection of this composition to temperature of 1600. Fahrenheit for eight hours yields a material of high wear resistance but somewhat deflcient in friction coemcient, and I therefore consider this temperature less desirable because of the long processing required, although it can be used with the right composition of melt, and is sometimes desirable in case it is possible to remove the shoes from the molds at a sufficiently high temperature so that they can be heattreated by their own retained heat, being placed the previous heat treatment.

in a thermally insulated receptacle inlarge numbers to soak in their mutual heat.

It will be understood that the time and temperature required will vary with the composition of metal employed. Thus if the amount of silicon be increased (or fortified by other ingredients having the same general eflect as silicon e. g. nickel, copper, or aluminum) the temperature and/or time of treatment can be decreased somewhat; while if the amount of silicon be decreased relative to the carbon, or if ingredients be introduced havingv an opposite effect to that of silicon (e. g. chromium, vanadium, or manganese) it may be necessary to increase the time or temperature or both.

In the practical performance of my improved process I preferably employ a casting machine because of the economy of labor and the uniformity of speed and temperature control obtainable thereby. For purposes of speed and heat economy the casting machine is preferably located in such proximity to the heat-treating furnace as to cause the castings to be delivered into that furnace substantially at the desired temperature. Preferably they are discharged directly onto a traveling conveyor whose speed of movement is so adjusted as to remove them from the heated chamberafter the lapse of the desired heating interval and carry them through subsequent chambers decreasing in temperature at a predetermined rate, whereby they are cooled through the critical temperature at the desired speed for the structure and toughness desired.

It should be noted that the mere subjection of the castings to the first or high temperature heat treatment, while sufficient for the development of some qualities, exhibits its full advantages only when followed by a controlled cooling through and adjacent to the critical range. The treatment at the high temperature fixes the pro-' portions of cementite and graphite; the cooling from this higher temperature down through the critical rangedetermines the relation of hardness to toughness in the matrix metal.

The secondary graphite liberated during the high temperature treatment appears in the form of compact nodules of irregular outline embraced by a steel-like matrix; the extent of the graphitizing depends on the temperature and time and should not be carried to completion but only until the desired friction-coefficient is attained and before the matrix metal has become decom-' posed, which is rather early. If suddenly quenched after this first treatment the matrix metal would be unduly hard and brittle and hence I prefer to cool the castings through the critical range at such a speed as to secure toughness rather than hardness, since toughness has always been the absent feature in brakeshoes and hardness can always be secured by shortening It is especially important that the high-temperature treatment be not too long continued, since it is important that the brakeshoes should not show the conditions characteristic of malleable iron. It is important that the brakeshoes possess a considerable proportion of combined carbon.

In the drawing accompanying and forming a part of this application Fig. 1 is a side elevation and Fig. 2 is a longitudinal section through a brakeshoe in which my improvements are or may be embodied; Fig. 3 is a cross sectional view on the line 3-3 of Fig. 1; Fig. 4 is a longitudinal sectional view of a brakeshoe containing a modifled form of my invention; Fig. 5 illustrates a third form of my invention before heat treating and Fig. 6 the same after heat treatment; Fig. 'lshowstherelationoftoughnesstotimeof treatment in the case of the same composition of unstable or chilled white-iron subjected to diiferenttemperatures; andl'ig.8showssimilardata in respect of stable white-iron.

While my invention is applicable to any kind or shape of deceleration element acting frictiona11y I have here chosen for illustration a common freight-car type comprising a cast-iron body 1 cast on an arcuate steel back 2 and attaching lug 3. While my improvements may enable the omission of these steel members the same can be used without detriment and will still be demanded in any event for many years, even though I consider them unnecessary. When the entire article is cast in a cold metal mold from an iron alloy containing iron, silicon andcarbon of the proper relative proportions as above set forth,all the carbon will be retained in combined form; and it should be noted that primarygraphite, that is graphite which has originally separated out in flake form at the outset, cannot be modified; and it will also be noted that castings wherein the absence of primary graphite is caused by the essential stability of the mixture are impracticable for the p p se in view.

However, while primary graphite cannot be modified and while stable carbides cannot be broken down within my process, the casting may contain portions either of gray-iron or of stable white-iron (or both) without detriment so long as essential parts of the casting consist of the unstable white-iron. The shoe of Fig. 2 is supposed to have been cast in an all-metal mold and to have become chilled throughout. The shoe of Fig. 4 represents the condition which exists when the same is cast in a mold having metal surfaces ,for the back and ends and a non-chilling surface for the face, the composition of the melt being such as to be chilled only part way through. The back and ends hence show no primary graphite and in heat treatment become toughened without changing the gray-iron in any observable way. This produces a gray-iron wearing surface 5 with an integral toughened back 6 which takes the place of the steel insert, and enablesv an integral lug So also to be cast without reinforcement although I do not consider its use as incompatible with my invention.

InFig'.5 the shoeiscastwithagrayfaceportion 7, a chilled white back portion 8 and an intermediate mottled portion 9. Heat treatment of this kind of shoe, as I have described, produces a tough back portion 10 as shown in Fig. 6 and leaves the gray face portion 7 and intermediate portion 9 practically unchanged. This I esteem to be due to the fact that the carbide content quickly passed, at 1650" Fahrenheit it is lower and unduly long in attainment. The maximum strength is obtained by about 4 to 5 hours at about 1700 Fahrenheit, though I do not limit myself to this temperature. The curves of Fig.1

8 were taken from the behavior of a stable whiteiron which showed little or no primary graphite even when cast in a sand mold. This is the composition used for making malleable iron which when completely malleableized consists only of a ferrite matrix with graphite inclusions.

It is important, however, after the termination of this heat treatment to cool the brakeshoe at a proper rate. The result of quick heat treatment of the unstable carbides isto produce a substance characterized by a continuous phase of a steellike composition having rounded or nodular inclusions of graphite therein. If cooled too quickly the matrix metal will be quenched to a condition of undue hardness and brittleness; if cooled too slowly (as in the usual malleableizing process) it may be converted to ferrite by the migration of its carbon to the nodules already formed.

Other procedures than the continuous process v furnace can be employed; for example, the castings immediately after solidifying may be piled on cars "and introduced successively into chambers of the desired temperature; or with a proper control of composition they may be introduced into heat insulated pits and allowed to cool gradually therein by slow dissipation of their own heat content, until they have reached a temperature around l100 Fahrenheit. To do this successfully requires such a composition as shall cast white in the first step, and shall during this prolonged cooling period break down only part way into free carbon.

I do not limit myself to the composition above specified. I have used:

A B C soomazs 3.25to3.50

.80tol.00 .70to

' Balance. Balance.

Upto .20 Upto .20 Up to;.60 Up to .60 Uptolfl Uptol.00

I have also used other alloying constituents such as are called hardeners and .softeners".

Such hardeners as chromium, vanadium, manganese or molybdenum render the cementite harder to break down and increase the time and temperature required. They also tend to neu-. tralize the effect of the silicon and enable more silicon to be used (and also more carbon) without producing initial gray iron. Such softeners as nickel or aluminum may reduce the amount of silicon (or carbon) permissible or reduce the time or temperature of treatment. Any cast iron As a result of this toughness and strength it becomes possible to wear these shoes almost through prior to their breaking, and to dispense with all j known inclusions can still be employed if desired.

I do not limit myself to continuous production method or to the chill-cast method. It is possible to allow the articles to cool to seasonal temperatures and subsequently reheat them to the graphitizing temperature, and this indeed may be indispensible to some plants not equipped with continuous-production mechanism.

I have referred herein to railway brakeshoes in describing the invention but it is not limited to such shoes and may be used wherever a braking eifect is desired, although the special advantages of the invention in an arcuate shoe and in one subjected to the severe service conditions of railway brakeshoes'will be apparent.

In general I do not limit myself in any wise excepting as recited in my several claims which I desire may be construed broadly each independently of limitations contained in other claims.

I claim:

1. A heat-treated brake shoe of integral section and consisting of gray cast iron containing flake graphite in the wearing portion and cast iron containing nodular graphite in the other portions whereinnot more than a substantially negligible proportion of graphite occm's in flake 1 form.

2. A heat-treated brake shoeof integral section and made of cast iron, the body of theshoe graphite in flake form, and'the back and ends of 1 the shoe being characterized by the occurrence of substantially all of the graphite in nodular form.

3. A heat-treated cast iron brake shoe of integral section wherein substantially allof the carbon in the wearing portion occurs in the form 1 of flake graphite and wherein a part of the carbon in the portions other than the wearing portion occurs in the form of cementite and part in the form of nodular graphite and substantiallynone in the form of flake graphite. 1

4. A heat-treated brake shoe ofintegral section and made of cast iron containing from 2.20% to 3.50% carbon and from 1.25% to silicon and'wherein substantially all the graphite in the portions other than the wearing portion occurs in 1 nodular form.

5. A brake shoe of integral section and.consisting of graycast iron containing flake graphite in the wearing portion and cast iron in the being characterized by the occurrence of primary other portions wherein substantially all of the graphite occurs in nodular form, the shoe hav= ing been heated to a temperature'between 1600" Fahrenheit and 1800" Fahrenheit and slowly cooled through the critical range.

sisting of gray cast iron containing flake graphite in the wearing portion and cast iron in the other portions wherein substantially all of the graphite occurs in nodular form, the shoe hav- 6. A brake shoe of'iritegral. section and con- 139 Y ing been heated to a temperature between 1800 Fahrenheit and 1800 Fahrenheit for a period of from fifteen minutes to eight hours and slowlycooled through the critical range.

'1. A brake shoe of integral section and consisting of gray cast ironcontaining flake graph- 1 ite in the wearing portion and cast iron contain-' ing from 2.20% to 3.50% carbon and from 1.25% to .70% silicon inthe other portions wherein substantially all 01' the. graphite occurs in nodular form, the shoe having been heated to a tem- 1 perature between 1660 Fahrenheit and 1800' Fahrenheitand slowly. cooled through the critical e. BJA brake shoe ofv integral section and consisting of gray cast iron containing iiakegraph- 1 ite in the wearing portion and cast iron containing from 2.20% to 3.50% carbon and from 1.25%

to 310% silicon in the other portions wherein substantially all 01 the graphite occurs in nodular form, the shoe having been heated to a temperature between 1600 Fahrenheit and 1800" Fahrenheit for a period of from fifteen minutes to eight hours and slowly cooled through the critical range.

9. A brake shoe of integral section and consisting ofg cast iron containing from 2.20% to 3.50% carbon and from 1.25% to 170% silicon. the cast iron in the wearing portion of the shoe containing flake graphite, the cast iron in the ends, back and lug portion or the shoe having substantially all of the graphite occurring in nodular form, the shoe having been heated to a temperature of approximately 1700" Fahrenheit ior about four or five hours and slowly cooled through the critical range.

10. The process of making a brake shoe which contains the steps of first casting an unstable mixture of iron, carbon and silicon under conditions which shall restrict the formation of primary graphite in the portions of the shoe. other than the wearing portion, and heating the casting a period of approximately one to six hours at a temperature between 1600 and 1800 Fahr nheit to decompose the cementite in said portions at least in part graphite. V

11. The process of making a brake shoe which contains the steps of first casting an unstable mixture of iron, carbon and silicon under conditions which shall restrict the formation of primary graphite in the portions of the shoe other than the wearing portion, heating the casting a period of approximately one to six hours at a temperature between 1600 and 1800 Fahrenheit to decompose the cementite in said portions at least in part with ite and, finally cooling at such a rate as to produce pearlitic cementite in the matrix metal.

12. The process of making a brake shoe which with liberation of secondary liberation of secondary graph consists in the steps 0! first casting the same in white iron containing from 2.20% to 3.50% carbon, from 1.25% to .'10% silicon, and iron under conditions which restrict the formation of primary graphite in the portions of the shoe other than the wearing portion and which permit the formation of primary graphite in the wearing portion, subsequently heating the casting for a period or approximately four to five hours at a temperature about 1700 Fahrenheit to decompose the cementite in the portions oi! the shoe other than the wearing portion at least in part with the liberation of secondary graphite in the form or compact nodules of irregular outline embraced by a matrix, and finally cooling at such a rate as to produce pearlitic cementite in the matrix without materially affecting the wearing white iron containing from 2.20% to 3.50% carbon and from. 1.25% to 310% silicon and in chilling the portions of the shoe other than the wearing portion, subsequently maintaining the shoe at a temperature between 1600 Fahrenheit and 1800 Fahrenheit for a period of time to decomthe cementite in said portions at least in part with the liberation of secondary graphite in nodular form, and in finally cooling the shoe through the critical range.

14. The process of making a brake shoe which consists in the steps of first casting the same in white iron containing from 2.20% to 3.50% carbon and from 1.25% to 310% silicon and in chilling the portions or the shoe other than the wearing portion, subsequently maintaining the shoe at a temperature between 1600 Fahrenheit and 1800 Fahrenheit for a period 01 time of from to eight hours to decompose the in part with secondary graphite in nodular the liberation of form, and in finally cooling the shoe through the FRANK a. mnmmwam.

critical range.

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