US1921837A - Brake shoe - Google Patents

Description

R. B. POGUE BRAKE SH Original Filed May 51, 1930 I? a W 1 Z 7 m Patented Aug. 8, 1933 UNlTED STATES PATENT OFFICE BRAKE SHOE Application May 31, 1930, Serial No. 457,813 Renewed June 28, 1932 6 Claims.

This invention relates to brake shoes and it has for its object, broadly, to prolong the life of the shoe until it is completely worn out under ordinary conditions or" service.

It has been the practice for many years to en bed a ductile metal reenforcement in the back of the cast iron body of a shoe to hold the parts of the body together in case of fracture so that the shoe may continue in service. These reenforcements have been made usually of ductile metal and are commonly called steel backs. The backs comprise rods, bars or plates, and the plates have been perforated, slotted or cut out in a variety of skeleton forms. It has been proposed also to make the backs of expanded metal and other mesh material. When a shoe is pressed against the tread of a wheel under the usual application of braking pressure, intense heat is quickly developed and before this heat has a 90 chance to travel back into the body of the shoe it causes the face portion of the shoe to expand rapidly, thereby producing ununiform expansion in the metal of the body. While the face portion of the shoe is thus highly heated and expanded it wears to a fit to the wheel tread and when the braking pressure is released the shoe cools and contracts out of fit to the tread. On the next application of braking pressure the end portions of the shoe face engage the wheel tread while the intermediate portion of the shoe face is spaced from the wheel tread and forms a truss effect, and as the braking pressure exceeds the strength of the truss the body of the shoe will fracture. A shoe takes a different set at each brake application and this produces what has been called a weaving action in the shoe which is, in fact, a bending of the back. The cast iron body of a shoe is liable to fracture at any time in service, but fractures usually occur early in service. Long experience has proven that so long as the parts of the body are held together by the steel back the efiiciency of the shoe as a braking element is not materially if at all reduced, and it is not uncommon for fractured shoes to continue in efficient service until worn down to and even beyond the predetermined limit of wear. This has added importance when it is considered that the average life of reenforced cast iron freight car shoes is between four and five years. When the steel back breaks and an end portion, for example, of the shoe falls away, the shoe must be replaced. In recent years freight cars have been made heavier, have been more heavily loaded, have been made up in longer trains and have been run at higher rates of speed,

and braking pressures have been increased and more often applied. Allof these things make the life of a brake shoe harder and increase the tendency oi the body to fracture and the back to break.

It has been assumed that the back has sufiicient strength to withstand all conditions of service because it has been made or" a material and with a cross sectional area much greater than necessary to withstand the tangential strains to which the back is subjected in service. The conditions which cause the body to break have been well understood but the conditions which cause the back to break have not been understood. As a result of my investigations I have found that 7 after the body or a shoe is fractured the steel back will, sooner or later according to varying conditions, crystalize and break at the point next to the fracture in the body where the back is held rigidly in the body. In the manufacture of brake shoes the steel back, with the lug strap assembled therewith, is suspended in the mold cavity and the cast iron is poured into the mold cavity to form the shoe body. The steel back has a protective coating applied thereto to prevent the back from burning during the casting operation. If the back is not protected it may burn or carbonize under the heat or" the hot metal and partially unite with the cast iron. This makes the back brittle so that it is liable to break when 5 the shoe fractures, and at the point of fracture. When the back is protected it does not become united in this way with the cast iron body but it is firmly held by the cast iron body throughout its length, and under this condition it will break 9 at the fracture in the body. The back breaks because of fatigue of metal which causes crystalization, and this fatigue, I have found, is the result of at least four major conditions, compression, tension, bending and vibration of the steel back. Compression, tension and bending result from brake application. Bending also results from impact of the shoe against the wheel when the brake rigging is caused to swing which mostly occurs in switching service but also occurs in train operation. 'Vibration occurs in the loose end of the shoe whenever the car is in motion and this vibration varies in intensity according totrack conditions and is transmitted to the steel back. The effect of the compression, tension, bending and vibration is concentrated in the steel back at the fracture of the body if the steel back is rigidly held in the body at this fracture, and it is supposed under present conditions to be rigidly held at this point.

' be made of rods or bars or Under these conditions the back will break relatively quick and my invention has for its object to control these causes of break in the steel back and to distribute the effect thereof over a considerable area of the back so that the shoe will have a chance to wear out in service before the back breaks. As I have said, the back will break at the point where it is held firmly by the body and this point will be at the fracture in the body because the back is intended to be rigidly held throughout its length under present conditions of manufacture. I have found that if the point where the back is held firmly in the body is spaced from the fracture in the body the effect of these breaking causes is relieved to the extent that breaking of the back is delayed, and this delay is in direct proportion to the distance of the rigid point from the point of fracture. From this I have determined that it is not desirable to hold the back rigid in the body except at its end portions. This will take care of any usual fractures in the body and enable the shoe to be worn out in service before the back breaks.

In the accompanying drawing I have illustrated the invention in a plain car shoe in Which Fig. l is a plan view showing the body of a plain cast iron shoe in broken lines and the steel back and lug strap in full lines.

Fig. 2 is a bottom plan view of the back and lug strap which are usually assembled and inserted in the mold for casting the body metal thereon.

Fig. 3 is an edge View of the back and lug h: strap shown in Fig. 2.

Fig. 4 shows a brake shoe suspended in a brake head and illustrating features of my invention.

Fig. 5 is a sectional view on the line 5-5 of Fig. 4.

Fig. 6 is a sectional view on the line 66 of Fig. 2.

' Fig. 7 is a sectional view on the line 7-7 of Fig, 2.

The shoe selected for illustration comprises a cast iron body '7, a ductile metal plate back 8, and a ductile metal lug strap 9. The body may be made in any desired form and provided with the usual end stops 10 and guide lugs 11. The back shown is of the slotted plate variety but it may be perforated instead of slotted or it may in other form of back.

The lug strap is of well-known form and the body metal is run up in a known manner at the sides of the strap. The side edges 12 of the back are beveled and the slot edges 13 are also generally beveled to anchor the body and back together. The shoe so far described is of wellknown commercial manufacture. My invention consists in securing the back to the body at its end portions and leaving the intermediate portion of the back free from the body but anchored thereto. I accomplish this in the manufacture of the shoe without adding any parts and without materially changing the method of manufacture. I apply to the intermediate portions of the back between the end portions which are to be rigidly and firmly secured to the body in the casting operation, a sufiicient coating of refractory material to keep the back free from the body at this coated portion. I may use a coating of oil and silica or othercoating suitable for the purpose, and I have indicated the coated intermediate part 14 of the back by a heavy line in Figs. 2 and 4 to 7. It is not necessary although it may be convenient to coat the entire outer face of the intermediate portion of the back but the edges of the intermediate portion of the back and the edges of the openings therein and that portion of the outer face of the back which lie beneath the cast iron of the attaching lug as well as the inner face of the back should be coated. lhe coating does not extend to the end portions of the back which are intended to be rigidly secured to the body. It is desirable to apply a light coating to these end portions in accordan e with present practice. Such coating should not be sufficient to prevent the end portions of the back from becoming rigidly secured to the body in the casting operation, whereas the coating of the intermediate portion of the back between the end portions should be sufficiently heavy to ensure that this intermediate portion will not become rigidly secured to the body. It will understood that the body is anchored to the intermediate portion of the back as well as to the end portions of the back by the engagement of interlocking edges on the back and body, and. while the intermediate portion of the back is free from the body in the sense that it is not secured rigidly tiereto the body is at all times anchored to this intemediate portion so that if the body is fractured in several places the fractured portions would be held in place by the back. I have indicated the intermediate portion of the back as extending to or about the guide lugs but the size of the intermediate and end portions may be varied as found desirable. I prefer to make the intermediate free portion as long as possible consistent with the provision of end portions of sufficient length to secure the back at the end portions rigid with the body. When the shoe is suspended in upright position in the head 15 and the body is fractured, at a 4, the part of the body below the fracture will be held in place by the back and the shoe will continue giving efiicient service, but the part of the body below the fracture will be subjected to vibration which varies in consistency and intensity according to service conditions. If the back were rigidly secured to the body throughout its length, the vibrations would affect the back opposite the fracture in the body and cause fatigue of the metal and breakingof the back, allowing the unattached portion of the shoe to fall away and rendering the shoe unfit for further service. Also, the back would be subjected at the fracture to compression, tension and bending. Under such conditions the back would break opposite the fracture relatively soon because it is held rigid in the back at the fracture. My invention overcomes this because the effect of compression, tension, bending and vibration will be distributed through the back to the straight or irregular line indicated at b Fig. 4, where the back is rigidly secured in the body. This line is so far away from the fracture that the fatigue of the metal of the back is very materially retarded and so much retarded that the body of the shoe will wear down to the limit of wear before the back breaks. This is due to the fact that the point at which the back is held rigid in the body is remote from the fracture, compression and tension and bending are distributed over a considerable area of the back instead of being concentrated at the fracture, and the period of vibration is interrupted by en agement of the back with the body. It will be understood, of course, that both end portions of the body are rigidly secured to the end portions of the back and that the intermediate portion of the body is anchored or interlocked with the back by the beveled edges so that even though the back is free from the body at this intermediate portion no part of the body will fall away from the back if the body is fractured. The construction makes it possible for a limited relative movement of the back and body at the intermediate portion of the back and body. My invention is particularly useful in plain cast iron shoes with or without inserts in the wearing face, and of any size, form or construction. It is not found that the steel backs of flanged shoes break to any material extent, and this is for various reasons and particularly because the back is arched for the flanged portion of the body and is thus stiffened and less likely to be affected by the conditions which cause other backs to break. However, the invention may be used with flanged shoes and any other kind of shoes whenever it is found desirable.

I appreciate the fact that my invention is a material departure from the past and present practice of manufacturing brake shoes wherein it is attempted to secure the back rigidly in the body throughout the length of the back, but my invention has the advantage of prolonging the life of the shoe until it has been worn to a predetermined wear limit; and in addition thereto I believe my invention improves the general quality of the shoe by enabling whatever degree of relative movement may be desirable or required between the back and the body throughout that area of the back which is free from the body. I do not aim to define the limits of the intermediate part or the end portions because I believe it is desirable to make the free intermediate part as long as possible and the proportions of these parts may be varied to suit many conditions as will be readily understood by those skilled in the art.

I claim:

1. A brake shoe comprising a body and a reenforce back embedded therein, said back having its end portions independent of but rigidly secured in the end portions of the body and its intermediate portion free from but anchored to the body.

2. A brake shoe comprising a body and a reenforce back embedded therein, said back having a portion thereof independent of but secured in the body against relative movement and another portion secured in the body to permit relative movement.

3. A brake shoe comprising a body and a reenforce back embedded therein, said back having both end portions independent of but secured in the body against relative movement and an intermediate portion secured in the body to permit relative movement.

4. A brake shoe comprising a body and a reenforce back embedded therein, said back having both end portions independent of but secured in the body against relative movement and its entire intermediate portion between said end portions secured in the body to permit relative movement.

5. A brake shoe comprising a body and a reenforce back embedded therein, said back having both end portions independent of but secured in the body against relative movement and an intermediate portion secured in the body to permit relative movement, said intermediate portion of the back being interlocked with the body.

6. A brake shoe comprising a body and a reenforce back embedded therein, said back having alternate portions independent of but secured rigidly to the body and movable relative thereto.

. ROBERT B. POGUE.

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