Fatigue and impact resistant railway brake shoe

A bonded composition type railroad brake shoe is disclosed in which the keybridge cavity of the brake shoe backing plate is filled with composition brake lining material for reinforcement and dampening of the keybridge. An insert located in the keybridge cavity comprises a pair of spaced-apart ribs that are upturned from a base plate such that the insert partitions the keybridge cavity. The insert is bonded in place by the composition brake lining material, which is formed with a keyway by the insert. The insert further serves to reinforce the keybridge in conjunction with the composition brake lining material therein.

BACKGROUND OF THE INVENTION 
The present invention relates to brake shoes and particularly to 
composition lined brake shoes for railroad car brakes having a metal 
backing plate to which the composition brake shoe material is bonded. 
Brake shoes of the aforementioned type are typically attached to a carrier 
member known as a brake head that may be mounted on the ends of a movable 
brake beam adjacent the wheel treads associated with a given axle of a 
railroad car truck. An opening in the brake head is adapted to receive a 
U-shaped keybridge that protrudes from the convex surface of the backing 
plate at its mid-section. Openings are provided in the keybridge via which 
a spring-type locking key is directed via a keyway in the brake head to 
affix the brake shoe to the brake head under spring tension of the locking 
key. 
During braking, severe vibration forces and shock impacts due to irregular 
track and/or damaged wheel treads can occur at the interface between the 
brake head and backing plate, particularly when the brake shoe/brake head 
connection is not as tight as desired. Brake shoe failures have been 
attributed to deformation and collapse of the keybridge and, in extreme 
cases, fracture of the backing plate at the keybridge. Because of the 
keyholes provided in the keybridge, this is the weakest area of the 
backing plate and thus the area prone to collapse and/or fracture due to 
repetitive flexure of the backing plate incident to vibration and shock 
impacts. Should fracture occur across the width of the backing plate at 
this critical keyhole location, one-half of the brake shoe could become 
separated from the brake head. This seriously degrades brake effectiveness 
and unless serviced relatively soon, results in the brake head contacting 
the wheel with consequent damage to these parts. 
Heretofore, backing plates have been strengthened in the keybridge area by 
welding a reinforcing plate A to the backing plate across the mouth of the 
keybridge, as shown in FIGS. 1 and 2 of the drawings. In this manner, 
backing plate flexure at the keybridge of a brake shoe having such 
reinforcing plate is reduced, making such brake shoes less susceptible to 
breakage. However, the welded connection of the reinforcing plate to the 
backing plate is not only expensive, but is prone to failure. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to prevent deformation 
and collapse of the backing plate keybridge of a brake shoe having a 
molded composition brake lining in a low-cost, yet effective manner. 
It is an extension of the foregoing objective to strengthen the backing 
plate keybridge by bonding the composition material from which the brake 
shoe lining is molded to the backing plate within the keybridge area. 
It is a further object of the invention to employ a metal insert in the 
keybridge cavity to form a keyway in the composition material with which 
the keybridge cavity is filled and to further strengthen the keybridge 
against deformation and collapse. 
It is a still further object of the invention to provide a low-cost metal 
insert in accordance with the foregoing that can be affixed to the backing 
plate without welding. 
In accordance with the present invention, there is provided a composition 
type brake shoe including a continuous metal braking plate to which a 
composition brake lining is bonded. The backing plate is formed with an 
upraised keybridge having keyholes to receive a locking key for affixing 
the brake shoe to a brake head. A composition brake lining is bonded to 
the backing plate, and the area within the keybridge cavity is filled with 
the composition brake lining material. This composition brake lining 
material substantially fills the keybridge cavity except for a keyway 
through which the locking key is inserted and thereby serves to dampen 
vibrations transmitted to the keybridge, and to further reinforce the 
keybridge against deformation and collapse.

DESCRIPTION AND OPERATION 
Referring to FIGS. 3 and 4, there is disclosed a first embodiment of the 
invention in which a brake shoe 10 is shown comprising a continuous metal 
backing plate 12 to which a composition brake lining 14 is bonded. At its 
midsection, backing plate 12 forms an upraised keybridge 16 that is 
generally U-shaped. Each side of the keybridge 16 has a keyhole 18 to 
receive a spring type locking key (not shown) for securing the brake shoe 
to a brake head (not shown) under spring tension of the locking key. Being 
U-shaped, keybridge 16 has opposed legs 19 and a bight portion between 
which is formed a concavity 20 on the underside of backing plate 12 that 
extends the entire width of backing plate 12 and is open at the lateral 
ends thereof. 
Located in keybridge concavity 20 and between legs 19 of keybridge 16 is a 
metal insert 22. As best viewed in FIG. 5, insert 22 comprises a generally 
rectangular base plate 24 and a pair of spaced-apart ribs 26 that are 
upturned from opposite sides of base plate 24. These ribs 26 are 
preferably integral with base plate 24, and may be formed by bending 
arcuate-shaped ends of a piece of sheet metal substantially 90.degree.. 
The arcuate shape of each rib 26 conforms to the contour of the keybridge 
concavity 20 with which ribs 26 are thus contiguous. Insert 22 is located 
within concavity 20 so that the respective ribs 26 are disposed on 
opposite sides of the respective keyholes 18 and base plate 24 traverses 
the mouth of concavity 20 at a location in proximity with the bottom of 
keyholes 18, as viewed in FIG. 3. 
During molding of brake shoe 10, the composition material forming brake 
lining 14 fills concavity 20 in surrounding relationship with insert 22 
and is bonded thereto, as well as to the backing plate, as shown in FIG. 
6. It will be appreciated, therefore, that insert 22 is molded in place, 
while at the same time preventing brake lining material from entering the 
area of concavity 20 between ribs 26. Consequently, a keyway 28 is 
partitioned off by ribs 26 within concavity 20, such keyway 28 being 
formed in alignment with keyholes 18 in keybridge 16 to receive a brake 
shoe locking key. 
In filling keybridge concavity 20 with composition brake lining material on 
opposite sides of ribs 26, and at the underside of base plate 24, as 
explained, it will be further appreciated that vibrations normally 
transmitted to the brake shoe backing plate 12, and more particularly to 
keybridge 16, are dampened. Moreover, the composition brake lining 
material within concavity 20 serves as a primary component in 
strengthening the keybridge 16. This primary component in the 
strengthening of keybridge 16 is reinforced by engagement of the ribs 26 
and base plate 24 with the underside of backing plate 12 within the 
concavity of keybridge 16, specifically adjacent keyholes 18 therein, such 
keyholes 18 being the weakest area of backing plate 12 and thus the 
location most prone to deform, collapse and fracture. 
It is well known in the molding of composition type brake shoes to employ a 
composition binder material for bending to the metal backing plate and to 
which a friction composition material is bonded. Is it therefore 
preferable in the present invention, as shown in FIG. 4, to utilize a 
composition binder material 30 adjacent the backing plate 12, including 
the area within concavity 20 but outside of ribs 26 of inset 22, such 
binder material being known to have high impact resistance, as well as a 
high bonding characteristic, which assures stability of metal insert 22 
and effectively prevents flexing of the backing plate 12 in the vicinity 
of keyholes 18. The friction composition material 32 is molded to the 
binder material and forms a braking face 34 with which brake shoe 10 
engages a railroad car wheel tread (not shown). 
It is also within the scope of the present invention to bond the friction 
composition brake lining material 32 directly to backing plate 12 without 
utilizing composition binder material 30, in which case the friction 
composition material is also bonded directly to the metal insert 22 and 
provides the strengthening component for keybridge 16, which the metal 
insert reinforces. 
In an alternate embodiment of the invention, as shown in FIGS. 7-10, a 
metal insert 22A similar to insert 22, is employed. Insert 22A comprises a 
generally rectangular base plate 24A, a pair of spaced-apart ribs 26A that 
are upturned from opposite sides of base plate 24A, as in the embodiment 
of FIG. 5, and a pair of elongated arms 36 that extend generally 
longitudinally from the sides of base plate 24A opposite the sides from 
which ribs 26A are upturned. 
As with the insert 22, it is preferred that this insert 22A also be formed 
by appropriate bending of a generally flat sheet of stamped metal into the 
desired shape shown in FIG. 9. In addition to the ribs 26A being upturned 
and having a shape corresponding to the contour of backing plate 12 within 
concavity 20, longitudinal arms 36 are shaped to conform to the radius 
where keybridge 16 converges with backing plate 12. Although not a 
requirement, it is preferred that the width of arms 36 be less than the 
width of backing plate 12. Insert 22A is located in concavity 20 similar 
to insert 22 with respect to keyholes 18. In addition, arms 36 engage the 
backing plate 12 beyond the area of concavity 20 to thus afford a greater 
surface area for bonding and further to permit welding the insert to the 
main structure of the metal backing plate in order to supplement the 
holding integrity of the chemical bond. 
This insert 22A serves the same purpose as insert 22 in partitioning 
concavity 20 to provide a keyway therein and to reinforce the 
strengthening component of brake lining material that fills concavity 20.