Note: Descriptions are shown in the official language in which they were submitted.
CA 02472402 2004-06-23
1'iUo: BOOT fOR STREETCAR ftAIL~
(0011 Typioatly, atreetoar freaks are embedded down below the surface of the
toed material
IoonGrete, eaphelt, etcl, over e~ long distonce. As compared with a raadlreil
crossing, where the
track is embedded in the road for a distance of no more than, say, ten metros,
streetcar traok$ can
be embedded in the road for distances of hundreds of metres, and more.
[0021 The requirement often arises, with streetcar tracks, for the metal rail
to be insulated
eleotrioally from the road material in which it is embedded. Although the rail
and the road are
nominally both at the same tground) voltage. it i all too common for stray
voltages and currents to
be present, which can lead to (electrolytic) corrosion and other problems aver
a long period of
service. The problem is exacerbated in cold-winter areas, where salt is likely
to be present.
(0031 In addition to providing electrical insulation, a boot of an elastomeric
material can also
provide some mechanical Isolation from vibrations and shock loading. This can
be beneficial both to
streetcar traffio, and to the tracks and roadway.
[004] It is known to provide an insulating rubber or plastic boat or shroud,
which envelops the rail,
in order to address this rail corrosion problem. To be effective, the
insulating boot must ba
complete, in that it should fully envelop the rail, with no gaps - except, of
course, that the top
surface of the head of the rail must be clear, and one side-face of the head
of the rail li.a the gauae-
slde of the rail, which recaSves the wheel-flonges of the passing streetcera)
must also be clear.
(005] Fhe boot passes underneath the rail profile, i.e between the rail and
the cross-tie. Where
the rail is secured to the cross~ties by means of clips, e.g pandrol clips,
the components are
arranged to ensure that the boot is not interrupted or broken at the clip
locations.
(0081 Being all-enveloping, the boot is applied to the rail befvra the rail is
lowered down onto the
cross-ties; then the booted rail is plaoed on the ties; then the clips are
applied; and then concrete or
other road filler material is poured in, and made up to the level of the road.
[0071 Boots are not only applied to rails in ca3es where the rails rest on
Conventional cross-ties.
Various prpcedures exist where a concrete bad is poured, then the rails are
tightly supported, and
concrete is poured around the rails, up to the road level; or the rails may be
Laid upon a prQ-made
concrete pad or deck, and only the final layer of concrete is poured char the
rails are in place.
(0081 Often, the rails are continuous-welded, for streetcar applications. In
some cases, the rails
are finished as to length, fitment, etc, and the rails are lifted to enable
the boots to be nssomblsd,
before being finally lowered into position. Typically, the boots are extruded
in e.g five-meter
Sengths. At the joints between adjacent boat-lengths, the joints may be seated
using a sealing cuff.
[0091 A difficulty that oan arise is that the boot is not secured firmly to
the rail. Thus, during
installation, the sides of the boot can flop down, and become displaced. One
common approach is
to use adhesive tape, which is applied to the upper portions of the sides of
the boot, the tape
passing over the top of the rail to hold those portions together until the
Conprete la poured In. The
idea has been that, after installation, the oonerete finally holds the boot
against becoming displaced.
However, concrete often shrinks as it sets, which can cause a gap to appear-
the gap might be
between the boot and the rail, ar between the boot and the conorete. Either
can be troubiosomr~.
[0010] The invention provides a boot that fits around the profile of the rail,
except for the top and
gauge-side of the raSl head. The invention is aimed at providing a boot that
is Self-Supporting, onto
fitted around the tall, with respect to the rail, whereby the boot holds
itself in position on the rail
with enough tenacity to ensure that the boot remains in its proper place
during placement of the
rail, and during pouring and setting of the concrete- Furthermore, it is an
aim of the invention that
CA 02472402 2004-06-23
the boot can maintain a seal against the rail, not only during assembly and
concreting, but
throughout the service life of the roadlrail installation,
THE PRIO~t AIiT
[x0111 Patent publication US-5,898,379 iBruyn et ai, May 1999) discloses an
interface strip for a
road/rail Crossing, in which the (extruded rubber) Strip is designed to hold
itself in place against tlza
side of the rail. The profile of the rubber strip is designed such that, when
the strip is hammered
into contact with the side of the rail, the profile wedges itself between the
underface of the head
and the overface of the base of the rail.
DETAILED i7ESCRIPTiON OF PREFERREb EMBdf7]MENTS
[00121 gy way of further explanation Of the invention, exemplary embodiments
of the invontion will
now be described with reference to the accompanying drawings, in which:
Fig 1 is cross-sectional profile of an extruded rubber boot that embodies the
invention.
Fig 2 is a cross-sectional profile of a rail.
Ftg 3 shows the boot of Fig 1 in an intermediate stags of assembly to the rail
of Flg 2.
Fig 4 shows the boot of Fig 1 finally assembled around the rail of Fig 2.
Fig 6 shows a rnished streetcar installErtion, with rails and boots, in
oross,sectlon at a cross-tie.
Fig 6 shows the streetcar installation of Fig 5, in arose-section between
cross-ties.
Fig 7 shows a modificati4n to a portion of the boot of FIg 1.
Fig 8 is a cross-sectional profile, corresponding to that of Fig 4, of an
alternative boot.
[00131 The apparatuses shown In the accompanying drawings and described below
arc examples
which embody the Invention. (t should be noted that the scope of the invention
is defined by the
accompanying claims, and not neoessnrily by specific features of exemplary
embodiments.
[00141 Fig T shows the proille of the boot 20, by itself, in I2s as-extruded
condition. Fig 2 shawl
the profile of the rail 23 around which the boot 20 is to be fitted. The boot
20 comprises an
extrusion in rubber. The rubber of the profile is of uniform thickness, except
that there are
thickened pads 24 along the under-rail-portion 26 of the profile of the boot.
[0015] The boot 20 is flexible, to the extent that the portions 26,28 can be
spread apart
sufficiently for the boot to be fitted around the base of the rail. Being made
of relatively thin
rubber, the boot is flexible enough to do this.
[001 B] ft will be understood that it would not be practical to build enough
residual springiness into
the boot such as would enabte the sides of the boot to press tightly against
the sides of tho rail, to
the extent that the sides of the boot would inharen2ty hold themselves against
the sides of the rail.
it will be understood that, in a practical boot, the tendency, rather, is for
the side portions 26,2ii of
the boot to flop sideways, away from the sides of the rail, after the boot has
been fitted around the
rail. The sides of the boot have no inherent tendency to press against the
sides of the rail, It would
not be practical to provide a boot of such profile that the sides of the boot
would be self-supporting
by building an inherent springiness into the boot.
[fj0171 The distance 32 as measured over the gauge portion 26 of the boot, is
made slightly larger
than the corresponding distance 34 as measured on the rail 23. Thus, the gauge
portion 26 of the
boot can be made to wedge itself botween tho underface 35 of the head 29 of
the rail and the
overfiacv 3a of the base $0 of the rail. The same is true as regards the field
portion 28 of the boot,
with respect to the other side of the rail.
CA 02472402 2004-06-23
(001 t3] The portions 26.2$ of the boat err: double-walled, as shown, with
spacer-bars 37 at
appropriate intervals. The wails are thin. being preferably between three
rrtfllimetras and six
millimetres in thickness. The sides of the boot need to by stiff, in the sense
that an upright calurnn
is stiff, in order for the sides to become tightly jammed or wedged between
the head and the br~sv
of the rail. On the other hand, the sides should not be so stiff, ss columns,
that it would be hard to
drive sham into the rail,
[001 tJ) It is recognised that this Condition is mat when the wall thickness
of the extruded rubber is
within the above limits. It is hardly practical that the walls could be lass
than three mm and st ill
have the stiffness needed to bald tightly when wedged into the rail. On the
other hand, thicknesses
rnare than six mrn might be favoured with the softer formulations of rubber. A
wall-thickness limit
might be set at ten mm. tt Is not so much that a thicker wall would be too
stiff, but rather: the
boat profile is one 3ingte unitary exin.~sion, and it is good extruding
practise far the wall ttuokness of
the profile to be reasonably uniform Over the whole extruded section;
therefore, given that the
profile of tho boat has to be flexible enough to be wrapped around the rail,
thick chunky saetians on
the extruded profile are contra-indicated.
tO0~0) Fig 3 shows a stage during assembly, in which the boots 20 have been
wrapped around the
rails 23. Tho sides of the boots are touching tightly against the sides of the
head of the rail. Now.
the sides of the boot are ready to be hammered or kicked into place, whereby
the sides become
wedged tightly between the head and the base of the rail in the position as
shown in Fig 4.
(00211 it will be understood that the boot iS assembled or wrapped around the
raN prior to the rail
boing embedded in the ground. Once the boot is in place, the wrapped rail is
placed on the chairs
39 on the crass-ties (Fig 5), and pandrol clips 38 era assembled in the usual
way. It may ba noted
that plastic pads 38 are located between the clip 38 and the rubber boot
material. The pads 39
provide mechanical protection for the boot, by preventing direct contact with
the metal of the clip
38. The portion 28,28 of the boot remain wedged against the sides of the rail
during fitmant of the
eNps 38. Fig B is a section of the track structure, taken between cross-ties.
(00223 in Figs 5,8, the roadway has bean filled with concrete, or asphalt etc.
The concrote
contacts the cross-ties 40, the slips 38, the ballast 43, and presses against
the boots 20. The
concrete does not touch the metal rails 23. As shown at 45 in Fig 8, it is to
be expected that tho
concrete wiN not penetrate into the space underneath the (wrapped? rails,
between the cross-ties.
A suitably-profiled moulding bar is used to form the cut-out 46 for the wheel
flanges, on the gauge
sides of the rails,
(0023] The manner of embedding the rails in the roadway as shown in Fies 5.6
is common for
strestcar$. However, many installations use means other than spaced cross-ties
for mounting the
rails. The sppllcability of the invention Is not limited to the spaced Gross-
ties type of installation.
[00241 Fi9s 5,8 show the finished Installation, in which the installation is
now ready for cars,
trucks, bicycles, and other road vehicles to pass both along and across the
tracks, and for
streetcars to pass along the tracks.
10025) Wlth the boat having the extruded form as shown in Fig 1, it has been
found, wtoan the
boat is pressed against the sides of the rail with the kind of force easily
applied by a worker kicking
or hammering the boot, that the boot will remain wedged firmly enough against
the sides of the rail
as to remain in place during assembly, installation, concreting, etc. It has
been found that, oftEn. a
tool is required in order to remove the hoot from the rail, once it has been
pressed against the rail.
As will be explained, the configuration of the boot is such that 1t i9 as if
ihB boot were barbed; that
is to say, the force needed to putt the boot out is greater than the farce
needed to press it in. This
barb-like effect is not guaranteed in every case, but it is the aimed-for
generality.
CA 02472402 2004-06-23
t442B1 It should be noted that the task of installing streetcar rails is
carried out with the emphasis,
not on careful attention to detsil, but on speed and simplicity. Not only do
the Components have to
be robust enough to stand up to the inevitable abuses, but the oomponents
should be of such
design fihet an Inspector can readily determine, at a glance, that the
components are indeed properly
placed, and can do this at a time when remediation, if required, can and wit!
ba carried out. !t may
be noted that, with a batch of concrete ready and waiting to be poured, the
tendency is to proceed
With pouring anyway, and oover up the mistakes. The!'sfore, it is important
that the boot be of
such design that it has very little tendency not to become misatigned during
theca operations. 'fhe
boot as shown may be expected to be successful in this regard.
(00271 It has been found that the boot of Fig 1 fits tightly enough against
the side of the refit to
make a watertight neat. It may be expected that the seal will remain over a
long service life. fn this
regard, the designer should tailor-fit the boot to the rail. The boot should
not tit so tightly between
the base and the head that the thin welts might tend to buckle, as that might
effect the boot-raft
seaiability: rather, the aim should be that the thin walls tie under a slight
compression, after 'fitting.
(40281 In Fig 4, the face ~.7 of the boot is designed to lie flush with the
flange-side A~8 of the head
of the rail. This makes it easy for the inspector to check that the gauge
portion of the boot has
bean assembled properly, in that the inspector can simply sight len~thwise
along the rail, rnd ct~n
very quitkly see if and where the boot is bulging out from the rail. if (t is,
a worker can very
quickly place a board against the face 47 of the boot, and tap It with a
hammer, until the face 47 of
the boot lies flush with the face 48 of the head of the rail.
(00291 ft may be noted that in those installations where the sides of the boot
have been secured
during assembly by adhesive laps wrapped around the boot (and running across
the top of the rail!,
the inspector connot take a comparable quick sighting to determine that the
boot was oorrectly in
place, nor can a worker quiokly and simply correct any misalignments that
might be present.
[00301 Fig 7 shows a variation of the boot of Fig T, in which a lip 27 is
provided on the gauge-
portion of the boot. Such a lip may ba preferred in some cases, to assist in
properly locating the
boot on the rail, and in ensuring that the gauge side of the boot is not
driven too far under the rail
head, in case that might cause the thin ma:aria! to buckle.
[003'll Tire top surface of the head of a streetcar rail of course is subject
to wear, over time. The
rust of the rail, and the boot. ere not subject to wear. However, even the
buried components can
ba subject to odd movements duo to the passage of road and rail traffic over a
long period of time.
'fhe boot as illustrated, assuming it is tight against the rail at
installation, pan be expected to remain
tight against the rail over a tong service period, despite such odd movements
of the rail,
(0031 As t4 the material of the boot. the elastomeric material should have
good electrical
insulative properties, whereby it is preferred to use non-conductive materials
far reiniarcemenc and
filling, in place of the usual Carbon, Also, the material should have good
weathering
charaeteristios, as to e.g temperature end tllV resistance, resistance to
becoming brittle, etc. EPDM
may be expected to perform well. The rubber should preferably be in the region
of 75~$0
durometer shore-A hardness, for the required degree of flexibii'tty. Also, the
compression set of thr~
material should be such as to ensure that the material will retain enough
resllienrre to remain finrly
wedged into the rail throughout its service life.
(00331 Sorne of the terms used in defining and explaining the invention wilt
now be examined in
more detail. Referring to Fig 2, an upper-mid-point is determined, which is
the mid-point between
the head-gauge-extremity of the head of the rail, and the web-gauss-extremity
of the web of the
rail; fhet is to say, the upper-mid-point is halfway between those two point3
in vertical projection.
The lower-mid-point is the point on the rail-base-gauge-overface that tiers
vertically below the upper-
mid-point. The rail-gauge-vertical-tine 34 is the line joining the upper-mid-
point to the lower-rnid-
CA 02472402 2004-06-23
p8lnt.
(0034) The boot-gauge-verticat~line 32 IFig 1] is the same tine as the rail-
gauge-vertical-line 34 (Fiq
2?. but is measured over the wedged-in gauge-portion of the boot. That is to
say, if the boot were
removed from the rail. whereby the boot were no longer compressed, the boor-
gaugo-vertical-line
32 would expand. (The rail-gauge-vertioal-line 34 remains the same len8th, Of
course.) 'The
designer should arrange that this amount of expansion, which of Course is
equated to the amount of
compression that has bean forced into the wedged-in column of the hoot, Is
preferably around four
or five millimetres. If the amount of compression were less than about two or
three mm. the boot
would not be wedged in tightly enough; if the compression were more than about
six or seven mm,
the boot would be Close to outer-buckling under the compressive loading.
(00351 It Is important, in order for the boot to become wedged into the rail,
that the vertical colurnn
of rubber be enginsgred properly. In Fig 4, the column 49 comprises the outer
strut 50, together
with the web-side wall 62 and the upper portion &3. The outer strut 60 and the
web-side wall 62
arc convex with respect to the web of the rail. As a result, i.e because of
the convex curvature,
when the centre of the Column, in the region of the spacer-bar 37, is pressed
inwards towards the
web, that action Inherently draws the upper 54 and lower 56 ends of the column
49 together.
Thus, the action of pushing the convexly-curved centre of the column inwards,
towards the web,
draws the ends of the column together, and makes it easier to drive the column
further inwards
towards the web, into the wedge angle. By contrast, if tho column had a
concave Curvature with
respect to the web, pressing the centre of the column towards the web would
make the column
expand.
1003fi] Ths upper end of the column includes a lateral wall 57, whereby the
upper-portion 53 ha$
the form of a cell or pocket. This form is important in the design, in that
the form enables tho
column loading to be spread over the underface 35 more evenly and resiliently
then it would be if
the column extended, as a compressive strut, over the whote distnnc~ 32. One
effect of the sell or
packet form of the upper-portion 53 between the top of the outer strut 80 and
the underface 36 is
that the wedging force Is relatively unaffected by manufacturing errors in the
dimension 32 of the
boot land Crrors in the dimension 34 of the r8ilt.
[0037] Th~ cell-tike upper-portion 53 es described on the gauge-side may be
present also on the
bold-side. tn fact, the designer may prefer to include a vertical bar in the
extruded profile, an the
field-side, which would be symmetrloal to the wall 47 on the gauge~side
(003131 it has been found, with the column arrangement as illustrated ir! Fig
4, that it takes very
little skill and care on the part of the worker to hammer or kick the boot
into its correct place,
wedged into the side of the rail. Once the boot is in place, as mentioned, it
has been found that
usually a tool is required to pry it out of the rail. This applies equally to
both the gauge side and the
field side of the rail; the field Side differs from the gauge side by the
provision, on the field aide, of
the porxton 58 of the boot that extends up the field side of the rail head.
Mowever, the column
portion of the boot, being then portion under the rail head, can be the same
bath sides.
(0035] In Fig 8, the column 68 is of a single-wall construction. Again, as in
Flg 4, the column IS
c4nvex with respect to the web of the rail. Therefore, the action of pressing
the centre of the
cohtmn 69 inwards towards the Web again eases the upper and lower ends of the
column more
doapty into thQ wedge angle. To Install the boat, the gauge and field portions
of the boot ore
pressed (kicked, hammered) inwards against the web. until the nose 60 touches
the web of tho rail.
Then, when the pressing force is withdrawn, the column 59 tries to straighten
itself, wedging t(ea)t
tightly between the base and the head of the rail.
[OOq.Q] ball profiles are set by official standards. However, the standards do
permit some
variations: for example, while the wedge angle is usually constant through
different manufacturers'
CA 02472402 2004-06-23
varsinns of tile standard rail, the radius between the underface of the head
and the web, for
instance, can vary with different manufacturers. The present design
ooncentrates the contact areas
at tYte upper and lower ends of the column, where the rubber settles against
the prediotably~flat
head-underface and the predictably-flat base-overface of the rail, and away
from the not-so-
predictable radfused areas.
(00411 In the designs as illustrated, it can be expected that the amount of
springback, Le in Fig 8
the distance separating the nose 80 from the web of the rail after the
installation force hss bean
rer»oved. will be of the order of about three millimetres or so. There is no
corresponding springbnck
movement at the upper and lower ends of the column, of course. The upper and
lower ends of the
column lock to the underfaoe and ovarface of the rail more tightly as the
centre of the Column
springs back and the oolumn straightens out. The springback movement of the
centre of the
column however does cause a rotation to take place at the ands of the oolumns.
Thus, fn Fig 8, the
rotation of the upper end of the gauge side of the boot profile causes the
outer area 82 to press n
little more tightly against the underface 3S of the head. This extra pressure
serves to enhance the
seal of the boat against the rail, which is advantageous because it aids in
preventing moisture from
seeping down between the rail and the boot,
10042) On the other hand, when the Concrete or other road material Is poured
against the sides of
thp boot, and consolidated, it is likely that the web portions of the boot
wilt then be pressed
inwards, and possibly back into actual contact with the web. So the designer
should not place too
much reliance on the spring-back effect to actually make the seal.
10043) the Fig 8 design is less preferred, however. Ahhough the extrusion die
for Fig 8 is easier to
make, having no cavities, again these boots are hammered or kicked into place.
end the F1g 8 profile
is more likely to be abusively distorted than is the Fg 4 profile under the
same treatment. The
double wall shape of Fig 4 also means that the euler load of the Fig 4 column
is greater, i.e the
compressive force needed to cause the column to actually buckle is greater in
Fig 4 than in Fig 8.
(00441 Attention is drawn to the following further points regarding the
convexity of the column.
Tha column should be almost straight, upon installation. That is to say,
although the column should
be convex in shape rather than concav~, the Column should not be too convex.
The boot should
not be so profiled that the upper and lower ends of the column become engaged
with the rail while
the centre of the column is still a Ion$ way from touching the web. If it were
too convex, the
column would be less able to support compressive forces acting vertically
along its length. The
designer should see to it that the wedged-in column is stressed in
compres9lon, not in bending or
buckling. The column should not be so convex that, upon relaxation or
springback, after the press-
in force has been removed, should return the column to an almost-straight
condition, rather than to
a still-very-convex condition. The almost-straight condition preferably should
not include an actually
straight condition, sinoe that would carry with it the possibility that the
column might go slightly
concave. Concavity of the column is contra-indicated, as that would reverse
the barb-like effect, i.e
thc~ effect (of convexity) that the boot is easier to push in than to pull
out.
f00A.51 The convexity may also be defined as follows. Upon installation, note
the IEU point 64,
being the point of innermost extremity of the contact between the upper end of
the column 69 avd
the underface 35 of the rail head; also, note the IEL point 66, being the
point of innermost
oxtrerrtity of the contact between the lower end of the Column 59 and the
ovarfaco 36 of the rail
base: then, draw a line between the IEtJ point and the IFL point. Preferably,
the whole length of
this line should pass through rubber: or rather, preferably there should be
rubber on both sides of
the line, being rubber that is stressed by the compressive farces in the
column. The column is
convex if, in the vertical centre region of the column, there is compression-
stressed rubber on 'the
inside (i.e on the rail side) of the 16U-18L line.
(0048) It also follows that the column is convex if the vertical compressive
stresses in the column
CA 02472402 2004-06-23
fond to bend the centre of th~ column towards the web at the rail; and tho
column la concave if the
vertical compressive stresses in the column tend to bend the centre of the
column away from the
wob of the rail. The amount of convexity would be too much If there wero no
stressod rubber do
tho outside of the I>;U-IEt. lute, in the centre regions of the column, i-a if
alt the stressed rubber were
inside the IEU-IEL lins. The IEU-I~L line may be an the web side of the rail-
vertical-tine (Fig ?.l, or
may be outside the rail-vertical-line.
[OOA~7] The boot may be designed to the same profile as the rail in the
overfece, underfaco, and
web areas. However, because the rail profile might vary, the boot should be so
praflled that,
whatever the actual shape of the actual rail, the boot cannot touch against
the raft in any manner
that might interfere with the wedging action. Thus, for exempla, the web-to-
underiace or web-to-
overface radius should not be smatter in the boot than in the rail. The
designer should make sure
the ends of the column era free to touch, and engage tightly With, the
underface and overface of
the rail, which means making sure no other parts of the boot prafite touch the
rail, including tho
radiuses between the web and the underface and between the web and the
averface.
fi?04~il 1t is common for railway rails to be angled slightly Inwards: thus
the chairs 31 in Fig 5 have
sloping upper faces. The term vertical as used herein refers td the axis of
symmetry of the rail
(assuming the rail is symmetrical -- which sometimes they are noti, and this
axis lies at a slight
angle to the absolute vertical if the rail is tilted.
[pp~l9~ There3 is s rail standard in which the profile includes a rolled-in
flangeway. Such a rail loftan
termed a girder rail) is hugely non-symmetrical. The invention can stilt bo
used with such rail
profiles; the invention can ba used sa long as the rail profile is Such that
the profile includes both a
rail..field-wedge-angle and a rail-gauge-wCdge-angle.
