US2911074A - Railroad brake shoes - Google Patents

Description

Nov. 3, 1959 w. s. FRAULA ETAL 2,911,074 1 RAILROAD BRAKE SHOES Filed Aug. 10, 1956 INVENTORS.

W. SCOTT FRAULA ERWIN R. KNAUER BY RAYMOND E. SPOKES flcllaa/ul W ATTORNEIYS ,terial and the metal back structure.

United Sta es Patent O P RAILROAD BRAKE SHOES William S. Fraula, Ridgewood, and ,Erwin R. Knauer, Woodcliif Lake, N.J., and Raymond E. Spokes, Ann

Arbor, Mich., assignors to American Brake Shoe Company, New York, N.Y., a corporation of Delaware Application August 10, 1956, Serial No. 603,407 1 Claim. (Cl. 188-251) railroad industry comprises a cast iron body having a substantial thickness and having a braking surface which is curved to correspond generally to the curvature of a railroad car or locomotive wheel. A supporting plate or strip of rolled steel is frequently included in the back of the cast iron brake shoe as a reinforcement for the cast iron body and, to a certain extent, serves to hold the brake shoe body together if it becomes cracked or otherwise fractured; usually, the brake shoe body is cast around the support member to form a unitary structure. A substantially different type of brake shoe which has been considered for use on railroad cars and locomotives comprises a molded composition body which may be supported upon a steel backing plate; this steel backing structure is in some respects similar to the support member of the cast iron type of shoe, in that it lends strength and rigidity to the brake shoe body. In the composition type brake shoe, the support lugs and other elements for mounting the shoe upon a brake head are formed as a part of or are mounted upon the steel supporting back; in the cast iron type of shoe, the mounting lugs, toe guides, and the like may be cast as a part of the brake shoe body or may be formed as steel members affixed to the aforementioned steel reinforcing strip.

The composition type brake shoe provides substantially higher retarding force per unit area than the standard cast iron shoe, since it aifords aconsiderably higher coefficient of friction when brought into contact with the wheel of a car or locomotive than may be obtained with a cast iron shoe. Ingeneral, it may be stated that the cast iron shoe is a high-pressure low friction device, Whereas the composition shoe is a high-friction. low-pressure device. Accordingly, the'composition shoe may be operated at substantially lower braking pressures than the cast iron shoe and permits utilization of smaller brake cylinders. known in the art, has several serious disadvantages which have precluded widespread adoption of this type of shoe for railroad service. Among the difficulties presented with the composition shoe, a principal one has'been the tendency of the composition body toseparate from the metal back or support structure under even relatively mild braking conditions. In particular, this difliculty may be attributed to the difference in the thermal coefiicients of expansion of the brake shoe composition ma- In addition, the composition brake shoe body may be separated from its supporting metal back as a result of forces tending to flex thebrake shoe, which are frequently encountered in railroad service; these same flexural forces may also tend ;to fracture the composition brake shoebody. Moreover,

The composition type shoe, however, as

Patented Nov. 3, 1959 the relatively severe vibration frequently encountered in railroad operations often tends to crack the composition body/ or to detach the body from its metal backing struc-' ture. Q 1

One proposal which has been advanced as a means to strengthen the composition body of a railroad brake shoe contemplates the incorporation of one or more layers ofexpanded metal .into the brake shoe body as a reinforcement; the expanded metal is embedded in the composition material in a portion thereof closely adjacent the metal backing structure. Brake shoes incorporating this type of expanded metal reinforcement, however, have also exhibited certain disadvantages. --For example, the expanded metalreinforcing strip tends to create a discontinuity in the composition body and, when the body is subjected to the stresses of braking service, may cause the body to fracture or separate adjacent the reinforcement. In addition, conventional molding and processing techniques sometimes fail to fill the interstices of the expanded metal completely with composition material; as a consequence, the brake shoe body is "effectively weakened instead of being strengthened by the presence of the expanded metal.

Itis an object of the invention, therefore, to overcome or substantially minimize the'above-noted disadvantages of previously known composition-type railroad brake shoes by resort to a specific method of manufacturing a reinforced composition shoe. 7 I

A further object of the invention is the provision 'of a new and improved railroad brake shoe structure, comprising a metal back, a composition body, and a meshtype'reinforoing structure embedded in the composition body, which inherently eliminates or minimizes the disadvantages of known shoes noted above.

Accordingly, in one aspect the invention is directed to a railroad brake shoe of the type comprising a composition body having a predetermined length, width, and longitudinal curvature supported upon a metal back. In accordance with the inventive method, a metal brake shoe backing structure is fabricated with a predetermined length, width, and longitudinal curvature approximately corresponding to the length, width, and curvature of a composition brake shoe body. This metal backing structure is deposited in a mold with the concave surface of the backingstructure facing inwardly in that mold. A sheet of expanded metal, preferably having approximately the same length, width, and longitudinal curvature as the backing structure, is packed or otherwise coated with an uncured composition material and is then deposited within the brake shoe mold adjacent theconcave surface of the metal backing structure. The composition-packed expanded metal may be deposited directly on the backing structure surface or an additional layer of uncured composition material may be interposed between the expanded metal layer and the backing structure. Subsequently, the mold is filled with an uncured composition material, after which all of the composition material is subjected to a curing treatment to harden the composition material.

In another aspect, the invention is directed to a railroad brake shoe comprising a metal back structure having a predetermined length, width, thickness, and longitudinal curvature; this metal back structure is bonded on its concave surface to a brake shoe formed from a first composition material and having corresponding-dimensions but with a thickness substantially greater .than the thickness of the back structure. A reinforcing member, comprising a metal mesh having a length, width, and curvature approximately corresponding to the back structure is embedded in the composition brake body at a position closely adjacent the metal back structure. A

bond coating, which comprises a second composition material, completely covers this reinforcing member and is utilized to bond the reinforcing mesh to the brake body.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawing which, by way of illustration, shows a preferred embodiment of a brake shoe construction in accordance with the method of the invention. The principles of the invention are set forth fully in the description and claim; other embodiments of the invention embodying the same and equivalent principles may be used and structural changes in the devices to whichthe inventive method is applied may be made as desired by those skilled in the art without departing from the invention and the purview of the appended claim.

In the drawings:

Fig. 1 is an elevation view, partly in cross section, of a composition-type railroad brake shoe including an expanded metal reinforcing element;

Fig. 2 is a plan view of the brake shoe illustrated in Fig. 1;

Fig. 3 is a plan view of an expanded metal reinforcing member incorporated in the brake shoe of Fig. 1;

Fig. 4 is a cross sectional view taken along line 4-4 in Fig. 3, illustrating the expanded metal reinforcing element at an intermediate stage in the inventive process;

Fig. 5 is a cross sectional view, taken along line 5-5 in Fig. 2, showing the location of the expanded metal reinforcing element in the brake shoe body;

Fig. 6 is a cross sectional view of the brake shoe taken along line 66 in Fig. 1; and

Fig. 7 is a detail sectional view taken along line 7-7 in Fig. 2. e I

The brake shoe 20 illustrated in Fig. 1 comprises a metal back structure including a support member 21 which is utilized to support a molded composition body 22 and to mount brake shoe 20 upon a brake head (not shown). Composition body 22 has a predetermined length, width, and thickness and further has a predetermined curvature along its length approximately corresponding to the curvature of the railroad car or locomotive wheel with which it is to be employed. The length and width of metal support equal to the corresponding overall dimensions of composition body 22 and the metal support member has essentially the same longitudinal curvature as the composition brake shoe body. It should be understood that the dimensional correspondence between support member 21 and composition body 22 need not be exact, although major variations are not desirable; for example, in some applications it may be necessary or desirable to extend the length of composition body 22 somewhat beyond the end of metal support member 21 or to make it somewhat wider than the metal back structure.

Apair of longitudinal flanges 23 and 24, which are best shown in Figs. 1, 5 and 6, may be aflixed to the edges of metal support member 21 and extend from the support member into engagement With the sides of the composition body. These flanges are preferably formed as an integral part of the metal support member in order to achieve maximum strength and manufacturing economy in the back structure. The efiective height of flanges 23 and 24 is preferably made substantially smaller than the thickness of composition body 22 in order to prevent the metal backing structure from contacting the wheel or other surface to which the brake is applied, since the steel from which support member 21 and flanges 23 and 24 are preferably fabricated could score the wheel or might become welded to the wheel at the-extreme temperatures encountered in railroad braking service. As shown in Figs. 1 and 2, a pair of end stops 25 and 26 are formed at one end of support member 21 and extend above theconcave surface 27 of the support member to engage a brake head; an additional pair of end stops 28 member 21 are approximately and 29 are provided at the opposite end of support member 21. A pair of toe guides 30 and 31 are formed at opposite ends of the support member; the end stops and toe guides are most economically fabricated as an integral part of support member 21 by punching or similar manufacturing techniques. A center attaching lug 32 is mounted on support member21 by clinching or any other suitable method; the usual keyway 33 is formed in the center attaching lug as indicated in Fig. 6.

Individual portions of support member 21 are punched out at distributed locations on the support member to form a plurality of individual metal anchor elements 35 extending from the concave surface 34 of support member 21 into composition body 22, as best indicated in Figs. 5 and 6. These projections or anchor elements serve to interlock the composition body and metal backing structure of the brake shoe to each other. As in the case of flanges 23 and 24, anchor. elements 35 should have an effective height. substantially smaller than the thickness of composition body 22 to prevent the metal anchor elements from contacting the wheel during braking service. In addition, composition body 22 may be further interlocked with support member 21 by means of a plurality of openings 37 in support member 21 immediately adjacent and extending into a portion of flanges 23 and 24 (see Fig. 7); portions of the composition body extend into openings 37 to provide further anchorage points with support member 21.

The metal backing structure of brake shoe 20 comprising support member 21, the end stops, the toe guides, and the longitudinal flanges, along with anchor elements 35, is preferably formed from steel, either hot-rolled or cold-rolled; hot-rolled steel is.usually preferred. The construction of brake shoe 20, as thus far described, provides substantially improved characteristics with respect to adherence of the composition body to the steel backing structure when compared with previously known devices and is also substantially more resistant to fracture; this construction is described and claimed in the copending application of E. E. Caton et al., Serial No. 606,869, filed concurrently herewith and assigned to the same assignee as the present invention. In some applications, however, it is desirable to strengthen the brake shoe further and to provide even greater adherence between the metal backing structure and composition body. For this purpose, and in accordance with the invention, a mesh-type reinforcing strip or. sheet 40 is incorporated in the brake shoe, as indicated in Figs. 1,5 and 6, being embedded in composition body 22 at a position closely adjacent support member 21. Reinforcing strip 40 is preferably formed from expanded metal and is shaped to conform to the dimensions and curvature of metal back 21. The present invention is based upon the discovery that a particular method of incorporating expanded metal reinforcing member 40 in the brake shoe is highly advantageous and effectively avoids the disadvantages encountered in previously known composition type brake shoes incorporating reinforcing elements of this general yp In manufacturing brake shoe 20, and in accordance with the'invention, the following method is followed: the metal back structure comprising support member 21, the toe guides, end stops, flanges, center lug, and the like is first fabricated as a complete unit having a predetermined length, width, and longitudinal curvature approximately corresponding to the length, width, and curvature desired for the composition brake shoe body. This metal backing structure is then deposited in a suitable brake shoe mold with the concave surface 34 of the backing structure facing inwardly in the mold. A sheet of expanded metal 40, illustrated in Fig. 3, is shaped to conform in curvature to the curvature of backing member 21, as indicated in Fig. 4; preferably, expanded metal sheet 40 has a length and width closely approximating the 4 length andwidth of the brake shoe support member.

, Expanded metal member 40 isthen coated with an uncured composition material; in some instances the reinforcing strip may be filled and packed completely with the composition as indicated at 41 in Fig. 4. Composition material 11 may be packed into the expanded metal under pressure in order to avoid any air pockets or discontinuities in the composition material filling the expanded metal. In other instances, as set forth in detail hereinafter, the composition material may be applied to reinforcing mesh 40 by spraying, painting, or similar techniques. i 1 v Expanded metal reinforcement 40, after coating or packing with composition material 41, is then deposited within the brake shoe mold adjacent concave surface 34 of support member 21. It may be desirable to first deposit a layer of composition material upon surface 34 before the packed expanded metal is inserted in the mold, depending upon the thickness of the coating or packing layer 41. The brake shoe mold is then .filled with uncured composition material, which may be of different constituency from coating 41, after which all of the composition material is subjected to a curing treatment to harden the composition material. This curing treatment entails the application of heat and pressure to the mold to solidify and harden the composition material, as described in greater detail hereinafter.

The composition material employed in manufacturing brake shoe 20 may be of any type suitable for railway braking service, but preferably comprises a comminuted friction material, selected from the sillimanite group and related aluminum silicates, distributed in a heat-stable rubber binder. The friction material, which may include kyanite, sillimanite, andalusite, mullite, topaz, and/ or dumortierite, preferably comprises about ten parts by weight of the composition. The binder may comprise any heat-stable synthetic or natural rubber; for example, Buna-S synthetic rubber either with or without an additional liquid polymer has been found quite satisfactory for this purpose. The'invention may also be applied to a brake shoe composition employing phenolic or other resin binders, although an elastomer-base composition of the type noted above, which is described and claimed in the copending application of R. E. Spokes et al., Ser. No. 491,510, filedMarch l, 1955 and assigned to the same assignee as the present inventio is much preferred because of its superior characteristics with respect to heat and shock resistance. Moreover, the Spokes et al. composition affords a favorable ratio of wet to dry coefficients of friction, a highly desirable characteristic in railroad service. In addition to the mineral friction material, the composition may include further friction material in the form of cast iron particles or other suitable material.

Several different specific processes incorporating the inventive concept have been found to be most advantageous, as compared with previously known techniques; the particular examples set forth hereinafter are intended primarily as an illustration of individual applications of the invention and are not to be construed as limiting the invention to the specific coating compositions set forth.

therein. For convenience, and to assist in understanding the application of the invention, the various steps of the processes set forth in the specific examples are separately designated as Steps A, B, etc.;, nevertheless, as will bequite apparent from a consideration of the examples themselves, the sequence of steps in the examples is not particularly critical in most instances and may be subject to wide variation without in any way departing from the invention.

Example I Step A.A metal brake shoe backing structure is fabricated with a predetermined length, width, and longitudinal ing, painting,

tially similar to that described above in connection with Figs. 1 and 2 and may include suitable mounting lugs.

Step B.A mesh-type reinforcing strip is cut to a size approximately corresponding to the length andwidth of the metal backing structure and is shaped to have a longitudinal curvature corresponding to that of the meta l backing structure; the shaping operation may be readily performed in a punch press or similar apparatus. The reinforcing strip is preferably fabricated; from expanded metal as illustrated in Fig. 3; I

Step C.-The expanded metal or other mesh reinforcing strip is coated with a rubber-resin cement possessing superior bonding qualities with respect to the metal. This cement, which comprises an uncured coating composition,

preferably includes a combination of a rubber, a thermosetting resin, and a suitable solvent. A preferred composition which afiords excellent results is as follows:

'Solids: Parts by weight Buna-N 50 Phenol aldehyde 50 The rubber and resin solids are dissolved in a suitable solvent; methyl ethyl ketone has been found quite suitable for this purpose, although other organic solvents may alsobe employed. The relative weights of the Buna-N butadiene-acrylonitrile) rubber and the thermosetting resin are not particularly critical and may be varied within relatively broad limits. The ratio of solids to solvent I may be adjusted as desired to suit the particular technique selected for applying the uncured composition to the reinforcing mesh; thismay be accomplished by spraydipping, or by any other method adapted to coat the entire mesh with the composition. It will be appreciated that the cementing phenomenon involved is physical in nature and that other cements having similar properties may be employed.

Step D.The concave or under surface of the metal back structure is coated with the cement set forth in Step C or With a similar uncured composition by spraying, painting, etc. It should be noted that although this step in the inventive process is highly desirable and improves adherence of the brake shoe body to the metal backing structure, the major benefits of the invention may be obtained without its use.

Step E.The metal backing structure is deposited in a mold with the concave surface thereof facing inwardly in the mold and the composition-coated mesh reinforcing element is located adjacent the concave surface of the metal back. It may be desirable to fill the metal backing structure with a relatively thin layer of the composition material to be employed as the brake shoe body before the expanded metal reinforcing element is placed within the mold.

Step F .The mold is filled with an uncured composition material suitable for braking service, preferably the composition described and claimed in the aforementioned Spokes et a1. application. 1

Step G.All of the composition material is subjected to heat and pressure to cure and harden the material and form the completed brake shoe. It should be noted that the cement or coating composition is cured in this stage of the process along with the composition which forms the braking surface of the shoe and that the resin included in the cement is advanced'or cured to a relatively hard unflexible state and is bonded to both the composition body of the shoe and the metal reinforcing strip. The rubber in the coating composition imparts a certain degree of flexibility to the coating composition so that it is able to withstand the flexural stresses to which the shoe is subjected during braking service.

Example II Steps A and B, in this example, are essentially similar to thecorrespondingly designated steps of Example I. Step C'.-The metal reinforcing mesh is coated or "7 packed with an uncured composition of the following constituency:

Constituents: Parts by weight i Rubber cement 6.00 Sulphur 0.21 Liquid phenol aldehyde resin 13.00 Barytes 6.55 Petroleum 'solvent (naphtha) 2.00 Asbestos (Canadian Std. 7D) 26.70 Asbestos (Canadian Std. R) 20.90 Methyl or ethyl alcohol 1.00

The rubber cement included in this particular composition may comprise one part Buna S rubber, three and one half parts reclaimed rubber, and four parts petroleum solvent by Weight. The composition, after meshing, is extruded, and excess solvent is removed by oven drying at 150 F. for twenty hours before using.

jfStep D.,The concave surface of the metal backing structure is filled with a relatively. thin layer of the uncured composition set forth above in connection with Step C.

The last three Steps E, F, and G in this example are essentially similar to those setforth above in connection with Example I.

It must be understood that the two examples set forth above are ,not mutually exclusive. For example, the metal backing structure and the reinforcing mesh of the :brake shoe may be coated with the composition described in Example I by spraying, painting, etc. and may also be further coated or packed in accordance with the technique set forth in Example II in fabricating the shoe. On the other hand, it may be desirable to fill the backing structure with a special composition as in Step D of Example III and to coat the reinforcement with a cement as described in Step C of Example I without recourse to Steps C and D of the example. Other combinations of the 'two'examples are also possible. It must be borne in mind, however, that in every instance the mesh must be pre-coated or pre-packed with an uncured composition material before it is inserted into the mold and before the mold is filled with the composition which is to afford the braking surface.

Composition-type shoes constructed in accordance with the above-described inventive methods exhibit markedly better resistance to fracture from either the flexural or vibrational forces encountered in railway braking service.

The pre-coating or packing technique avoids the serious disadvantages of expanded metal reinforcements as previously applied to composition type shoes and assuresa substantially uniform composition body free of weakness along the plane of expanded metal. In addition, brake shoes constructed in accordance With the inventive technique exhibit substantially better adherence of the composition body to the metal backing structure than is obtained in unreinforced shoes.

Hence, while we have illustrated and described the preferred embodiments of our invention, it is to be understood that these are capable of variation and modification, and we therefore do not wish to be limited to the precise details set forth, but desire to avail ourselves of such changes and alterations as fall within the purview of the following claim.

We claim:

A railroad brake shoe comprising: a metal back-structure having a predetermined length, width, thickness, and longitudinal curvature; a first bond coating, comprising a first composition material covering the internal surface of said back structure; a brake body, formed from a second composition material different from said first composition material; bonded to the concave surface of said metal back structure by said first bond coating and having a length, width and curvature approximately correspond.- ing to said metal back structure and a thickness substantially greater than said back structure; a reinforcing member, comprising a metal mesh having a length, Width and curvature approximately corresponding to said back structure, embedded in said composition brake body at a position closely adjacent said metal back structure and spaced therefrom by a layer of said second composition material; and a second bond coating, comprising said first composition material, completely covering said reinforcing member, for bonding said reinforcing member to said brake body.

References Cited in the file of this patent UNITED STATES PATENTS 1,830,341 Smith Nov. 3, 1931 2,052,808 Spokes Sept. 1, 1936 2,431,393 Franklin Nov. 25, 1947 2,702,770 Steck Feb. 22, 1955 2,728,701 Wirth Dec. 27, 1955 2,746,090 Hoover May 22, 1956

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