WHEEL TREAD CONDITIONING BRAKE SHOE

SEMELLE DE FREIN SERVANT AU REPROFILAGE A LA SURFACE DE ROULEMENT DE ROUES

English Abstract

A brake shoe for engagement with the tread of a
railway car wheel having a tread conditioning agent
incorporated in the composition friction brake shoe
material of the brake shoe block for altering the adhesion
between the wheel and rail on which the railway car is
guidably supported. The tread conditioning agent is a
material that is dissimilar from the composition friction
material of the brake shoe block, being chosen in
accordance with a lubricating quality or an abrasive
quality depending upon whether the brake shoe use is
intended to reduce or increase wheel/rail adhesion. In
either case, the chosen conditioning material has a wear
rate that exceeds that of the composition friction material
so that the degree of conditioning is controlled by the
wear rate of the composition friction material and the
percentage of brake surface of the brake shoe block
occupied by the conditioning material.

Claims

We claim:
1. A brake shoe adapted to engage the tread of a
railroad car wheel via which the railroad car is guidably
supported on a railed track, said brake shoe comprising:
a) a backing plate; and
b) a brake lining affixed to said backing plate and
having a braking surface engageable with said wheel
tread, said brake lining comprising:
i) a first and a second segment disposed on
opposite sides of a midpoint of a key bridge of
said backing plate;
ii) a first material in the form of a friction
composition suitable for braking said railroad car
wheel, said first material formed on each of said
first and said second segments and having at least
one recess formed in said braking surface of said
first material; and
iii) a second material dissimilar from said first
material, said second material disposed as an at
least one discrete insert in said first material,
said second material conditioning said railroad car
wheel tread so as to affect adhesion between said
wheel tread and said railed track, said second
material having a wear rate dissimilar to that of
said first material.
8

2. A brake shoe, according to claim 1, wherein said
second material is a lubricant, said railroad car wheel tread
being conditioned thereby to reduce the adhesion between said
wheel tread and said railed track.
3. A brake shoe, according to claim 2, wherein said
lubricant is molybdenum disulfide.
4. A brake shoe, according to claim 1, wherein said
second material is an abrasive, said car wheel tread being
conditioned thereby to increase the adhesion between said
wheel tread and said railed track.
5. A brake shoe, according to claim 4, wherein said
abrasive is cast iron.
6. A brake shoe, according to claim 1, wherein said
second material is a solidified mixture of about 95%
molybdenum disulfide and about 5% resin.
7. A brake shoe, according to claim 6, wherein said
solidified mixture corresponds in shape to said at least one
recess.
9

8. A brake shoe, according to claim 1, wherein said at
least one discrete insert in said first material is
cylindrical in shape.
9. A brake shoe, according to claim 8, wherein the
total area of said at least one discrete insert in said first
material is in the range of between about 5% and about 15% of
the total area of said braking surface.
10. A brake shoe, according to claim 8, wherein said
cylindrically shaped said at least one discrete insert
is molybdenum disulfide.
11. A brake shoe, according to claim 1, wherein said at
least one discrete insert in said first material is
rectangular in shape.
12. A brake shoe, according to claim 11, wherein the
total area of said at least one discrete insert in said first
material is in the range of between about 5% and about 25% of
the total area of said braking surface.
13. A brake shoe, according to claim 11, wherein said
rectangular shaped said at least one discrete insert
is cast iron.

14. A brake shoe, according to claim 1, wherein said at
least one discrete insert in said first material is preformed
and said at least one recess of said first material having a
shape conforming thereto so as to provide an interference fit
therewith.
15. A brake shoe, according to claim 1, wherein said at
least one discrete insert in said first material is two.
16. A brake shoe, according to claim 15, wherein said
two inserts are disposed as a first insert in a first segment
of said first material and a second insert disposed in said
second segment of said first material.
11

Description

~ 2141720
WHEEL TREAD CONDITIONING BRAKE SHOE
Background of the Invention
The present invention is related to brake shoes for
railway cars and particularly to an improved railway car
brake shoe that is adapted to influence the adhesion
between the railway car wheel and the rail on which the
wheel runs.
Railroad locomotives and cars have historically
provided braking effort through wheel tread braking. Brake
shoe engagement with the wheel tread produces friction that
dissipates the energy of momentum in the form of heat. In
order for such braking to be effective, wheel rotation is
required. The adhesion due to the friction between the
wheel tread and rail tends to maintain such wheel rotation,
as the wheel is braked.
Excessive wheel wear and brake shoe changeouts have
been found to be cyclically high during the winter season
One theory attributes this, at least in part, to the more
pronounced cleaning effect that the brake shoe has on the
wheel as a result of the higher moisture contact during
wintertime. In that such cleaning action tends to increase
the contact friction or adhesion between the wheel and
rail, increased contact stresses are created in the wheel,
such contact stresses being particularly high during the
guiding and steering action of the wheel set, particularly
when encountering track curvature.
The combination of braking effort through friction
between the brake shoe and wheel tread surface and the

214172~
adhesion between the wheel and rail translates into thermal
and contact stresses of the wheel, which often result in
wheel damage. High thermal and contact stresses are known
to contribute to minute failure of the wheel tread due to
the condition known as spalling.
Another related problem encountered by some railroads
where high levels of retardation are required is wheel
sliding, which results in wheel tread flat spots. Such
flat spots have a deleterious effect on equipment, lading,
and passengers due to the high vibration and noise produced
by the flat spots. Repairing such a damaged wheel requires
removal of the wheel and subsequent machining of the wheel
tread to remove the flat spot.
Summar of the Invention
y
The object of the present invention, therefore, is to
provide a friction composition brake shoe capable of
altering the adhesion between the wheel of a railway car
and the track rail without adversely affecting the wheel
braking force;
Another object of the invention is to incorporate a
conditioning agent in the brake shoe composition friction
material to decrease the wheel/rail adhesion;
Another obj ect of the invention is to incorporate a
conditioning agent in the brake shoe composition friction
material to increase the wheel/rail adhesion;
Another object of the invention is control the rate of
application of a brake shoe conditioninq agent to a railway

21~1720
car wheel tread.
Briefly, these objectives are achieved in a brake shoe
comprising a brake block having a braking surface adapted
to engage the tread of a railroad car wheel, the brake
block being a molded friction composition material to which
is added a different material that conditions the railroad
car wheel tread in such sense as to affect the adhesion
level between the car wheel and rail in response to braking
engagement between the brake shoe and wheel tread.
Brief DescriPtion of the Drawinqs
The foregoing objects and other objects and advantages
of the present il~vention will be understood from the
following more detailed explanation of the invention when
taken in conjunction with the accompanying drawings in
which:
Fig. 1 is a plan view showing the braking surface of
a brake shoe block in accordance with one embodiment of the
invention;
Fig. 2 is a section view taken along the lines 2-2 of
2 0 Fig . l;
Fig. 3 is a plan view showing the braking surface of
brake shoe block in accordance with another embodiment of
the invention; and
Fig. 4 is a section view taken along the lines 4-4 of
2 ~ Fig . 3 .
Descri~tion and O~eration
Referring now to Figs. 1 and 2, there is shown a brake

21~1720
shoe 10 comprlsing a backing plate 12 having a key bridge
14 for affixing the brake shoe to a bake head (not shown)
by conventional means such as a brake shoe key (also not
shown). Affixed to kacking plate 12 is a molded brake shoe
block 16, which is preferably segmented so as to be
separated along a centerline of the krake shoe bridge. The
molded brake shoe block is formed from a composition
friction material, such as is typically employed in
railroad type brake shoes, and is preferably affixed to the
backing plate by being bonded thereto during the process of
molding the friction brake block.
Each segment of brake block 16 is formed with a recess
20 that is preferably cylindrical in shape and in which
recess is received an insert 22 having a shape
corres~Qnding generally to recess 20. Insert 22 is a
material dissimilar from the composition friction material
of brake block 16 and in this embodiment of the invention
constitutes a lubricant, such as molybdenum disulfide.
Being normally available in powder form, the molybdenum
disulfide is envisioned as being combined with a suitable
resin, preferably in the proportion of about 95 percent to
5 percent, and hardened into a preformed insert 22 that
corresponds to the shape of recess 20. In one aspect of
the invention, insert 22 may be incorporated with brake
block 16 during the aforementioned molding process, such
that recess 20 is actually formed by and thus conforms to
the shape of the insert, which is accordingly secured

21~1~20
therein. Other means of securing the insert 22, such as a
press fit with a molded-in recess 20 for example, may also
be viable.
In addition, such other methods of incorporating the
molybdenum disulfide in brake block 16 include that of
blending the powder-like lubricant with the composition
friction material prior to molding, whereby a substantially
homogenous dispersion of the molybdenum disulfide
throughout the composition friction material is realized
following molding of the brake block 16; and pelletizing
the molybdenum disulfide and interspersing such pellets in
the composition friction material prior to molding into
brake block 16, such that a distinctly non-homogenous
distribution of the lubricating material is realized when
the molding process is complete.
In all cases, the rate of wear of the lubricating
material is greater than that of the composition friction
material, so that the latter controls the rate of
application of the lubricating material to the wheel tread.
In addition, the total surface area of the lubricating
inserts 22 is generally in the range of 5 to 15 percent of
the surface area of brake shoe block 16, being chosen in
accordance with their respective wear rates so that when
brake shoe 10 is brought into braking engagement with the
tread of a railroad car wheel, a light film of lubricant is
deposited on the wheel tread. In thus applying such a
desired film of lubricant, the friction level between the

. ` 21~172Q
.
wheel tread and rail can be reduced sufficiently to allow
for a partial slip condition to exist, particularly on
track curvature, thereby lowering wheel/rail contact
stresses. By controlling the rate of application of the
lubricant, reduced wheel stress can be achieved, while
still providing wheel/rail adhesion levels as reguired to
support such brake force as necessary to achieve a desired
rate of retardation.
Referring now to Figs. 3 and 4, there is shown a brake
shoe 10 having a backing plate 12, a key bridge 14 and a
molded composition friction brake block 16.
Each segment of brake block 16 is formed with a recess
21 that is preferably rectangular in shape and in which
recess is received an insert 23 having a shape
corresponding generally to recess 21. Insert 22 is a
material dissimilar from the composition friction material
of brake block 16 and in this embodiment of the invention
constitutes an abrasive, such as cast iron. Of course
other suitable abrasives are also within the scope of the
invention. In one aspect of the invention, as shown in
Fig. 3 and 4, the cast iron insert is incorporated with
brake block 16 during the process of molding the
composition friction brake block, such that recess 21
conforms to the shape of the insert, which is accordingly
secured therein.
In addition, such other methods of incorporating the
cast iron with the friction composition brake block 16

21~17 2D
include homogenous dispersion of a suitable abrasive and
non-homogenous blending of the abrasive and friction
composition material prior to molding thereof.
In all such cases, the rate of wear of the abrasive
material i6 greater than that of the composition friction
material. Rectangular inserts 23 traverse a major portion
of the width of brake block 16, so that in response to
engagement of brake block 16 with the wheel tread during a
brake application, the wheel tread is abraded. Cast iron
has been found to satisfactorily produce a desired micro
level of wheel tread abrasion when having a surface area
that is generally in the range of 5-25 percent of the
surface area of the brake shoe block. Such conditioning of
the wheel tread with successive brake applications
establishes and maintains an optimum level of adhesion to
prevent break-away of rolling contact between the wheel and
rails. In this manner, not only is wheel rotation
maintained to assure that vehicle retardation can be
achieved through on-tread braking, but such wheel rotation
decreases the occasion of slid flat spots on the wheel
tread .
In accordance with both of the foregoing aspects of
the invention, the wheel tread conditioning provides
significantly increased wheel life and decreased
maintenance costs, a reduced vibration environment for the
rail car equipment, lading and passengers, and reduced
noise levels.

Representative Drawing