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Патент USA US3046641

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July 31, 1962
0.. E. OLIVIER
3,046,631
APPARATUS AND METHOD FOR MAKING PRESTRESSED
CONCRETE TUBULAR MEMBERS
Filed Dec. 11, 1957
2 Sheets-Sheet 1'
1
I
lNVENTQR,
Da/mwlE,
,'
BY
'_
ATTORNEY
July 31, 1962
D. E. OLIVIER
3,046,631
APPARATUS AND METHOD FOR MAKING PRESTRESSED
CONCRETE TUBULAR MEMBERS
Filed Dec. 11. 1957
2 Sheets-Sheet 2
.
INVEN'EOR
Duruel E, (Th/two
BY
United btates Fascist
3,046,631
Mb
Patented July 31, 1962
l
,
‘
2
3,046,631
APPARATUS AND METHOD FQR MAKING PRE
STRESSED CONCRETE TUBULAR MEMBERS
Daniel E. Olivier, Bedminster, N.J., assignor to Lock
Joint Pipe Company, East Orange, N.J., a corporation
of New Jersey
Filed Dec. 11, 1957, Ser. No. 702,035
6 Claims.‘ (Cl. 25-118)
crete. A mould end is freed from the end of a completed
core when the last of the several ends of wires extending,
etherethrough has been severed by rotation of its anchor
ing device.
The break-off points of the wires are located before
the wires are stretched and assembled in a mould. The
break-off points are established by indentations which are
produced ‘by the lateral application of pressure with a tool
having rounded edges or surfaces. The pressure exerted
This invention relates to the manufacture of prestressed 10 by the tool displaces the longitudinally extending ?bers
concrete tubular bodies, such as pipes, and to apparatus
of a wire by deformation and without cutting. A deforma
and procedures for placing and embedding longitudinally
tion thus produced in a high tensile steel wire decreases
extending highly tensioned high tensile steel wires within
torsional resistance considerably as compared with only
the wall of a prestressed concrete pipe.
little less of tensile strength. This is extremely important
A concrete pressure pipe of the type with which the 15 because of the high cost of the high grade steel wires of
present invention is concerned comprises a tubular con
the character required for prestressing concrete pipes and
crete member or hollow core around which a tensioned
the desire to make economical use of them. Even though
wire is wound. The tensioned wire winding strengthens
a Wire is highly stressed in tension an end protruding
the core and enables the core to withstand high internal
from the outside of a mould end can be broken off at a
?uid pressures. At ?rst impression it would appear that 20 breal -off point simply by rotating the anchoring device.
the bursting strength and the impermeability of such a
The break-off points ‘are indented in the unstretched
core would be limited only by the contracting force which
wire at such a spacing as to locate them where ‘the wires
can be supplied by a tensioned wire winding and the
are to terminate when they are stretched and embedded in
strength of the circumferentially compressed concrete.
a ?nished pipe.
This is not the case because cracks can occur in the con
The spacing or distance between the break-oft“ points
crete during the application of the tensioned wire wind
along a tension-free wire is determinable by the formula:
ing and also during the operation of the pipe after it has
S=L—-2pd
1+5
been placed in the ground, unless the concrete is com
pressed longitudinally by sorne other reinforcing such as
longitudinally disposed tensioned rods or wires. Conse
quently, for containing higher ?uid pressures the longi
wherein:
tudinal compressive stress in the concrete which is im
L stands for the length of the pipe mould between the
parted by tensioned longitudinals as well as the circum
inside faces of the mould ends (the length of the pipe);
ferential contracting force of a tensioned wire winding
d stands for the distance of a terminal end of the wire
must be increased in proper relationship.
35 from the nearest end face of the pipe;
A high order of longitudinal compression can be ob
p stands for the tensile stress intensity to be applied to
tained by the use of prestressed wires of high tensile
the wire, and
r
steel embedded in the concrete core.
These wires are
' E stands for the modulus of elasticity of the wire.
strung through a mould for forming the core and are high
ly tensioned before the mould is ?lled with concrete. It 40 It is apparent that the spacing S is constant for all pipes
has been a practice to hold the wires in tension by anchor
having the same speci?cations.
ages located outside and beyond the ends of a mould.
When the wires have been strung through the mould
Before the hardener core could be removed from the
cavity one end of each Wire is anchored to the mould end
mould, the wires had to be cut ‘betwen their anchorages
by the individual anchoring devices with an indentation
and the mould ends in order to enable the removal of 45 or breakdo? point located at the desired distance from the
the mould ends from the moulded core. After the ends
inside face ‘of the mould end. Tension is then applied to
of the mould had been removed, it was necessary again
the other end of the wire until the wire is stretched suf~
to cut the wires to remove the ends of the wires protruding
?ciently to locate the secondv indentation or break-01f
from each end of the core. In carrying out the second
point at the same distance from the inside facev of the
cutting operation, manufacturers have usually been con 50 mould end at the other end of the mould, or until the
tent with cutting the wires close to or flush with the end
desired predetermined tension in the wire has been at~
faces of a concrete core and with giving the exposed ends
tained, and then said other end of the wire is anchored
of the wires a modicum of protection by brushing them
to said other end of the mould. The wires may be ten
with a bi-tumastic paint or similar protective material.
sioned one or more at a time. The lengths of the tensioned
The present invention reduces the number of cutting
Wires within the mould are wholly embedded in concrete
operations previously required to free the mould ends
as the concrete is placed and the pipe is moulded. A.
from the compressed core and to leave the core free of
protruding wires. It also results in leaving but a short
cylindrical bore in the end of the concrete of approxi
mately the same diameter as that of the wire and which
is more suited for receiving and holding a solid plug of
a durable material capable of protecting the wire for a
dense concrete in bonded relationship with the wires is
obtained by rotating the mould in a roller suspension
machine or in a centrifugal machine as is well under
stood.
'
'
'
'
'
.
Although the novel features which are believed to be
characteristic of this invention will be particularly pointed
considerable time.
out in the claims appended hereto, the invention itself,‘ as
to its objects and advantages, and the manner in which
mould of the present invention secure the ends of the 65 it may be carried out, may be better understood by re
tensioned wires and hold them in place in the mould. The
ferring to the following description taken in connection
anchoring devices press on the mould ends and the thrusts
with the accompanying drawing forming a part hereof, in
of the mould ends are counteracted by the intervening
which:
shell or main casing which forms the exterior of the core.
FIG. 1 is a general outside view of a rotatable mould
Each anchoring device is constructed and supported in
with one end partially cut away and showing tensioned
Individually manipulatable anchoring devices of the
a manner to enable its rotation about the axis of a gripped
wire so that the wires can be broken off within the con
wires extending longitudinally through the moulding
space;
3,046,631
4
FIGS. 2 and 3 are representative of prepared lengths
of a high tensile steel wire in an unstrained or tension
less condition and‘illustrating, respectively, the wire as
viewed in planes at right angles to one another;
FIG. 4 diagrammatically illustrates the relationship of
a strained and tensioned wire in reference to the length
4)
tortion the cumulative pull of all of the tensioned wires
27 connecting between them.
The wires 27 are equally spaced circumferentially
around the mould in such number and at such intervals
as to uniformly distribute the longitudinal compression
around the concrete core to be cast in the mould. The
of the moulding space or of a concrete pipe;
‘ FIG. 5 is a longitudinal section“ through the wall of
wire size, with accompanying stress intensity, and the
a mould and showing a placed wire before tensioning;
the longitudinal compressive stress desired to be attained
FIG. 6 illustrates the tensioning and anchoring of one
end of a wire;
in a particular concrete core.
FIG. 7 illustrates an anchored end of a wire prior to
the placement of concrete;
FIG. 8 is illustrative of the moulding and hardening
stages;
FIG. 9 shows the mould shell removed and the stage
preceding severance of the wire and the freeing of the
mould end from an end of the formed core of concrete;
FIG. 10 is an end view of part of a mould end and
number and spacing of wires are determined to develop
The ends of the wires are similarly anchored to the
mould end rings 12 and 13. Each of the mould end rings
is drilled as at 29 (FIG. 5) at proper intervals for the
passage of the several wires. The outer side of each ring
is provided with a bore 30 concentric with each drilled
hole for receiving a washer 31 and the cylindrical nose
32 of an anchoring device 33. The anchoring device
acts as a clamp which can be slid along a wire for bring
ing the device into abutting engagement with the washer
showing means for rotating an, anchoring device to twist 20 against the end ring.
Referring to FIGS. 12 and 13, each of the anchoring
the end of an embedded wire;
'
devices has a nut portion 35 whereby the device can be
FIG. 11 shows the concrete core after the mould end
rotated with a wrench for twisting an end of a wire.
has been removed;
The hollow interior of the device has a smooth tapered
FIG. 12 is a longitudinal section of a combined an
surface 36 which narrows towards the free end of the
choring and twisting-off device; and
'
FIG. 13 is a cross-section on line 13-13 of FIG. 12.
nose 32 and opens at its larger end into a chamber 37
which houses a coiled spring 39. A retaining ring 40,
In the drawing, certain speci?c disclosure of the inven
which is buttressed by a plurality of lugs 41, engages one
tion is made for purposes of explanation, but it will be
'end of the spring. The other end of the spring presses
understood that the details may be modi?ed in various
respects without departure from the broad aspect of the 30 upon the larger ends of a nest of three similar jaws 42.
Each jaw 42 is in the form of a segment of a trim‘
invention.
cated cone having exterior surfaces 43 corresponding in
In the following description and in the claims, various
details will be identi?ed by- speci?c names for conven
ience, but they are intended to be as generic in their ap
plication as the art will permit.
The mould illustrated in the accompanying drawing in
cludes 'a shell formed of two semi-circular shell plates 10
'and711 to which mould ends 12 and 13 are ?tted. The
mould ends are in ‘the form of rings. The longitudinal
edges of each shell plate are provided with ?anges 14 and
15 by which the shell plates are bolted together to form
the outer periphery of a tubular moulding cavity. A
flange‘ 14 welded to the shell plate 10 and a ?ange 15
welded to the shell plate 11 are shown in FIG. 1 and a
similar set of ?anges are located oppositely across the
curvature to the tapered surface 36 on the interior of the
anchoring device and a serrated interior providing teeth
44 for gripping a wire. The three jaws are individually
interengaged with a ring 45 in a manner to limit axial
displacement of the jaws with respect to one another with
out interfering with their adjustability. The construction
is such that the teeth on the jaws bite into a wire and
prevent relaxation of tension on the wire when the device
is held against movement as by a mould end. The teeth
e?ect such a solid grip on the wire as to enable the
gripped portion of the wire to be twisted notwithstanding
a very high tensile stress on the wire.
In preparing the mould for casting one of the anchor
mould. _ Removable devices such as a series of bolts 16
ing devices 33 and a washer are slipped over a wire as '
secure the shell plates together. Ears 17 provide means
whereby attachment to the mould may be made for carry
shown at the left of FIG. 5 and the wire is threaded
ing purposes.
through aligned drilled holes 29 in the end rings 12 and
13. Another anchoring device and washer are then
‘ The semi-circular segments 18 and 19 attached to the 50 slipped onto the end of the wire as shown at the right
of FIG. 5, preferably with the end of the wire ?ush with
the outer end of the device.
.
stiffen the curvature of the plates and are adapted for
In order to provide twist-off points of lower torsional
use as a rolling ring. A similar pair of segments 20 and
strength with the least loss of tensional strength the wires
21 are located at the other end of the mould.
The mould end ring 12 is centered and supported with 55 are provided with rounded indentations at their twist
oif points. As illustrated in FIG. 2, these may be pro
_ respect to the shell within a socket formed by lips 22 and
respective shell plates adjacent one end of the mould
duced by applying pressure to the wire from opposite
sides by a pair of parallel carbide tipped jaws 47, 48
which compact the steel ?bers and leave rounded indenta
a similarly sloped surface adjacent the end of the shell
when the mould is assembled and ready for use. The 60 tions 49, 50. Highly stressed high tensile steel wires
are critical to secondary stress concentrations and caution
inner surface 25 of the mould end ring moulds the end
23 which extend from the respective shell plates. The
mould end ring 12 has a bevelled surface 24 which abuts
face of a- concrete core or pipe and its remaining interior
is taken to prevent scratches or nicks occurring in the
wires. In practice, a radial reduction in a Wire of slightly
less than twenty-?ve percent of its diameter and the use
to the end of any particular tubular body of concrete.
The thickness of the wall of concrete is determined by 65 of jaws having compacting surfaces rounded on a radius
of one-sixteenth of an inch have worked out satisfactorily,
the diameter of the inner surface 26 of the mould end
but these proportions may be varied to suit different sizes
ring.
of wires and other conditions prevailing in the manufac
‘ For forming a tubular core for a straight-walled pipe
ture of pipes of different sizes and strengths.
or for a pipe having spigot ends at both ends the two
70 ‘ In a ?nished pipe the twist-off points are located a
ends of the shell and the rings at either end of the mould
distance d (FIG. 4) inward from the ends of a concrete
are constituted alike. In the embodiment of the mould
core, say within a range of about 1A" to 1/2" from an end
illustrated in FIG. 1, the ends of the mould are mirror
of the mould, for example, although the actual location
selected will vary depending upon the size of the wires
likenesses of one another (FIG. 5). Each mould end
ring is "solid and sui?ciently stout to sustain without dis 75 and the length and diameter of a core. Once the ultimate
may be shaped to provide the shape desired to begiven
5
3,046,631
locations of the twist-oft‘ points are settled, the interval
S along a longitudinally unstressed wire may be calcu
lated as hereinabove explained and the indenting jaws 47,
48 and 51, 52 are positioned for impressing the notches.
All of the wires needed can ‘be indented Without chang
ing the spacing between the two pairs of jaws.
After the wires have been placed in the mould, FIG.
5, the predetermined stress intensity p is applied to the
wire by a tensioning machine 53 (FIG. 6). The right
end of the wire remains anchored with respect to the
mould end 13, as shown in FIG. 5, as the wire is stretched.
When the desired stress is attained the washer 31 and the
second anchoring device ‘33 are moved into engagement
with the mould end 12, FIG. 6. The stretched Wire is
6
properties are required. Hard drawn steel spring wire
is highly suited for the purpose.
The manner of employing the invention will be appar
ent to those skilledin the art in view of the foregoing
disclosure. While the described apparatus illustrates a
manner and means for carrying out the invention, it is
understood that some of the various features and elements
thereof may be altered and others omitted without depart
ing from the general results outlined and the invention
within the scope of the appended claims.
What is claimed is:
1. In apparatus for making a prestressed concrete pipe
with tensioned wires embedded in the Wall of the pipe
and maintaining the pipe longitudinally compressed, the
?rmly anchored as the tensioning machine is removed, 15 combination comprising a tubular mould casing, a mould
FIG. 7, and then the unused Wire is cut to release it from
end axially abutting one end'of said casing and formed to
the mould.
mould ‘one end of said concrete pipe, a mould end axially
After all of the wires have been tensioned and an
abutting the other end of said casing and formed to mould
chored in like fashion the mould is rotated and ?lled
the other end of said concrete pipe, a plurality of highly
with a relatively dry and rich concrete mix 54, FIG. 8. 20 tensioned high tensile steel wires extending generally longi
In view of the quality of the concrete and the moulding
tudinally through the moulding cavity within said tubular
method employed the concrete is 'bonded to the wires
casing and through openings in said mould ends to beyond
throughout their lengths.
the outer sides of said mould ends, each of said tensioned
When the placement of the concrete is completed, the
wires having a section of reduced cross-sectional area ad
?lled mould is removed from the rotating machine and
jacent the inner side of the respective mould ends which
the concrete is cured for adequate strength. Upon com
provides break~oit points for said tensioned wires within
pleting the curing the shell plates 10 and 11 are stripped
the wall of a hardened concrete pipe contained in said
from the hardened core 55, FIG. 9, thereby transferring
moulding cavity, and a plurality of wire-anchoring de
to the solid concrete and mould ends the reaction to the
vices supported ‘by said mould ends at the outer sides of
tensioned wires which was previously provided by the 30 said mould ends whereby the mould ends are pressed
against the tubular casing by the pull of said wires, each
shell.
The end rings are then freed from the tension of the
wires by removing the anchoring devices. As shown in
FIG. 10, the anchoring devices may be removed by the
of. said devices having ‘jaws frictionally gripping one of '
said tensioned wires, said jaws positionable laterally to
the axis of a tensioned wire, and means acting on said
use of a wrench 55 whereby the end of a wire is broken 35 jaws for forcing the jaws in gripping engagement with a‘
off at the adjacent twist~off point simply by rotating the
wire while the Wire gripped thereby is maintained in
tension by said devices and said mould ends, each of said
more or less. The removal of the loosed wire ends
devices rotatable about the axis of a gripped tensioned
leaves a relatively small cylindrical bore adapted to be
wire with said jaws in gripping engagement with the
solidly plugged with cement mortar 57 to protect the wire 40 gripped tensioned wire so that all of the gripped tensioned
end from rusting.
'
wires may ‘be broken adjacent the inner sides of the
The wires used may be plainor lightly dirnpled at
mould ends upon rotation of said devices and the mould
intervals along their lengths, When plain wires are em
ends freed from the lengths of said wires embedded in
ployed, it is desirable that they be provided with ?at
said pipe.
‘
tened portions d1 (FIGS. 2, 3 and 4) to the sides of 45
2. In apparatus for making a prestressed concrete pipe
the notches which are the more remote from the ends
with tensioned wires embedded in the Wall of the pipe,
of the mould. The ?attened portions prevent rotation
the combination comprising a cylindrical mould having
of the ends or" the wires which remain in the core. These
an outer shell and a mould end ring in abutting relation
wrench through a moderate angle of the order of 70°
can be applied by dies at the same that the bre< -off
notches are indented.
’
ship with each end of said mould shell, and means for ‘ I
50 axially constraining said end rings on said shell, said
Though popularly regarded as a rigid material con
means including a plurality of highly tensioned high ten
sile steel wires spaced at substantially equal distances
tain degree of plasticity aside from drying shrinkage.
around the space within said mould shell and extending
Inelastic strains including creep strain due to plastic
through openings in said mould end rings, and individual
55
?ow develop under continuous load over a prolonged
anchors having jaws in gripping engagement with the re
period of time and these strains are related to theamount
spective ends of the wires extending through said open
of compression applied to the concrete.
,
ings in said rings and supported against the pull of said
The prestressing technique requires that only wires of
wires at the outside of said mould end rings, said anchors
very high tensile stress the used. Since the crack-proof
having cylindrical noses extending within bores in the
quality of a prestressed concrete pipe is a function of
outer surface of said end rings and transaxially disposed
the amount or" pre-compression the concrete is subjected
bearing surfaces for supporting said anchors in opposition
crete which is subjected to a sustained load has ,a cer
to, the initial tensile stress in each wide should be above
to the tension in the gripped'wires, said anchors provided
100,000 pounds per square inch to make sure that the
with tool engageable portions extending outwardly be
subsequent inelastic losses or strain in the concrete will
yond the outer surfaces of said end rings whereby the
become a small percentage of the total strain induced 65 anchors are rotatable with respect to the mould end rings .
to rotate the gripped portion of a wire while stressed in ‘
in the wire. Unless this is done, the ultimate inelastic
tension, each of said tensioned wires having a notch ad
strain of the concrete may completely counteract or nega
tive the effect of the initially induced compression with
jacent the inside moulding surfaces of said end rings
adapted to be broken through upon rotation of said
little or nor resulting prestressing improvement. For ex
ample, a wire having a tensile strength of approximately 70 anchors.
, 3. A method for making prestressed pipes or similar
200,000 pounds per square inch may be required to be
tubular bodies of concrete having highly tensioned high
used in order to produce a resultant tensile stress intensity
tensile steel wires extending longitudinally and in bonded
in the wire of approximately 100,000 pounds per square
relationship with the concrete wall of the pipe, said
inch. Quality wires with uniform chemical and physical 75 method comprising the steps of establishing break-off
3,046,631
7
8
points of reduced torsional resistance in each high tensile
wherein L stands for the inside length of the mould be
tween mould ends, a’ stands for the distance of the loca
tion of a break-off point from an adjacent end of the
mould after the wires are stretched under said predeter
mined tension, p stands for the intensity of tensile stress
in the wires, and E is the modulus of elasticity of the
steel wire to be embedded in the wall of the pipe'at such
spaced-apart distance as -to ‘locate said break-oh“: points
within the pipe wall adjacent to each end of the pipe
when the wire is stretched under a predetermined tension,
mounting the wires in a pipe mould having ends which
wires.
determine the length of a pipe to be moulded with the
6. In the forming of a concrete pipe having highly
wires passing through openings in the opposite ends of
tensioned high tensile steel wires extending longitudinally
the mould, stretching the wires under said predetermined
tension and so locating said break-cit points adjacent to 10 and in bonded relationship with the concrete wall of the
but removed inwardly of the mould from the moulding
sides of the mould ends, ?lling the mould with a concrete
mix while holding said wires in tension and thereby em
pipe, the method which comprises reducing the cross
bedding said tensioned wires in concrete between the
mould ends, curing the concrete mix while the wires are
pressing notches spaced apart at such a distance as to
locate the reduced cross-sectional areas of each wire ad
strained under said predetermined tension, and after the
concrete is cured, breaking said tensioned wires in the
concrete adjacent to the inner sides of said mould ends
jacent to, but inside of the respective mould ends of a
pipe mould for moulding a given length of a concrete pipe
when the wireis stretched under a predetermined tension
of a magnitude su?’iciently high to result in holding the
by individually twisting the portions of said wires outside
of said mould ends while the wires are stretched in tension,
and then removing the mould ends from the hardened
concrete pipe.
4. In the making of a concrete pipe with pretensioned
high tensile steel wires extending longitudinally in the
concrete wall of the pipe and maintaining the wall longi
tudinally compressed, the method which comprises estab
lishing break-off points in high tensile steel wires by local
ly reducing the torsional strength of each wire, prior to
its stretching, at two locations along the wire disposed
apart at such a distance as to locate said points within
the concrete of the pipe adjacent to, but inside of, the
respective ends of the pipe when the wire is stretched
under a predetermined tension for holding the concrete
wall of the pipe compressed, said predetermined tension
exceeding a stress of about 100,000 pounds per square
inch, arranging the unstretched wires in a pipe mould
having end walls which determine the length of a con
crete pipe to be moulded with the ends of the wires pro
truding from the opposite end walls of the mould, grip
ping the ends of the wires outside of the mould, subject 40
the wires to said predetermined tension by applying
forces to the gripped ends and concomitantly locating said
break-oh.’ points adjacent to the end walls of the mould
but between the end walls when the wires are stretched,
placing a quantity of a concrete mix into the mould sut? 45
cient to form a concrete pipe of a’ length determined by
the walls of the mould and thus embedding the lengths of
said tensioned wires between the end walls of the mould
in the concrete mix, allowing the concrete to harden while
maintaining the wires tensioned by the continued appli~
cation of said forces to the gripped ends of the tensioned
wires, ‘and discontinuing the application of said vforces by
twisting the gripped ends of the tensioned Wires while they
are still tensioned and until they break at the break-0E
points and thereby transferring the reaction of the ten 55
sioned wires to the hardened concrete.
5. In a method according to claim 4 wherein said
break-off points are spaced apart along the tension-free
wires a distance S approximately equal to
60
L-2d
1+5
E
sectional area of each of a plurality of tension-free high
tensile steel wires at two points along each wire by im
concrete wall of the pipe compressed, threading the ends
of a plurality of similarly notched wires through openings
in said mould ends, anchoring the wires to one of said
mould ends with one of the notches of each wire spaced
a short distance inwardly from the inside moulding sur
face of said mould end, stretching each of the wires by
applying forces to the ends of each wire of su?icient mag
nitude to stress each wire in excess of about 100,000
pounds per square inch and thereby locating the second
of said notches of a wire a short distance inwardly from
the inside moulding surface of the other mould end,
anchoring the stretched wires against said other mould
end, ?lling the mould space between said mould ends with
a concrete mix and thereby embedding the stretched wires
between the mould ends, curing the concrete, and trans
ferring the reaction to the tension in each wires from the
mould .ends to the hardened concrete by twisting oil the
anchored ends of the tensioned wires at said notches.
References Cited in the ?le of this patent
UNITED STATES PATENTS
1,624,191
1,990,234
2,153,741
2,216,896
2,370,174
2,571,578
2,580,330
Venzie ______________ .... Apr. 12,
Kemper ______________ __ Feb. 5,
Cobi ________________ __ Apr. 11,
Trickey _______________ __ Oct. 8,
Kinninger ____________ __ Feb. 27,
Van der Maelen _______ __ Oct. 16,
Symons ______________ __ Dec. 25,
1927
1935
1939
1940
1945
1951
1951
2,639,731
Whiting ______________ __ May 26, 1953
2,686,951
2,747,249
Seaman _____________ __ Aug. 24, 1954
Chiverton ____________ __ May 29, 1956
338,864
375,161
692,354
555,510
1,087,848
1,116,458
Great Britain _________ __ Nov. 18,
Italy ________________ __ Sept. 25,
Great Britain __________ __ June 3,
Great Britain _________ .. Aug. 26,
France ______________ _. Sept. 1,
France _______________ __ Feb. 6,
FOREIGN PATENTS
1930
1939
1953
1943
1954
1956
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