Note: Descriptions are shown in the official language in which they were submitted.
~29~
V~CIJUM INSUI,ATED SHIPPING CONTAINER AND METHOD
BACK~Ra~ND OF l~lE I~IQ~
Field of ~h~ I~D~i~
The present invention relates to vacuum insulated
containers, and more particularly to such containers
adap~ed for use in shipping products, such as produc~s
which must be kept at very low temperatures for relatively
long periods of time~
a~çk~Q~
One of the common uses of insulated cargo containers
is for the shipment of frozen food stuff. Such containers
can be designed to produce t2mperatures below 0~.
~owever, witb age, quite commonly deterioration of the
insulation and also of the refrigeration equipment occurs,
this resulting in reduction of the ~ubzero capabilities of
such container~. Even though the operators who u~e such
Lnsulated cargo containers attempt to maintain a high
quality of service, the co t of doing so has been
continuously increasing over the years. Further, in many
instanoes, maintaining the t~nperature of food stuffs at
approximately 0F. is not optimum for food quality
mainte~nce.
It has been known for years that the fast freezin~ of
food s~uffs, such as fruits, vegetables, fish and c>ther
con~nodities, using cryogenic fluids su~h as liquid
ni~rogen can result in a superior market product. While
lthese technique~ have been used and autama~ed equiE~nent
.
lZ~5fJ4
has ~een developed to perform the freezing operation, the
problem of shipping at quite low temperatures (i.e. near
-80F.) has been a very difficult one to solve. Thus,
though the near 0F shipping temperatures are not optimum
for food quality maintenance, for the large part, shipping
containers having the capability to be used only for
shipnent at temperatures at about 0F are the current
state of the art.
It has lon~ been known tha~ excellent insulating
~apability can be obtained by pr~viding a vacuum between
two members, a common device utilizing this principle
being ~he vacuum flask Such a flask is madk up of inner
and outer walls which are spaced from one another, with a
vacuum being provided in the space between the two walls.
Quite commonly the two walls are formed as concen~ric
cylindrical side wall sections, with the ends of the
cylinders being closed by conoe ntric hemispherical
~ections. An openin~ a~ prcvided through one of the end
hemispherical sections.
~ owever, the walls of the vacuum flask are subjected
to rather ~ubstantial for oe s. With atmospheric pressurP
being approximately 15 pounds per square inch (psi) at sea
level, the out~ide wall oP a 3 inch diameter by 12 inch
long standard vacuum bottle is subjected to a total
lateral foroe of as much as 540 pounds. ffl e internal wall
of the flask does not require as heavy a wall, since the
internal force~ are directed radially outwardly~ so that
the material form ~g the inner wall is in tension, with
there being no buckling ~endency. ~owever, the outer wall
experiences wha~ can be de~cribed as a crushing force) and
the ou~er wall must be structurally stronger to withstand
the forces which would tend to buckle the outer wall~
~Z9~S6~
Because of the structural problems of providing a
vacuum insulating container, in many instances the thought
of using the evacuated area as insulation is abandoned,
and thick high quality insulation is used. Hawever, to
maintain quite low temperatures for long periods of tLme,
even the use of quite thick, high quality insulation is
not satisfactory.
Another considera~ion is that in any ~hipping
oontainer, the volume occupied by the container is ~n
important consideration. De~irably, the tGtal volume
occupied by the container should not be too much greater
than the vol~me of the pxoduct contained. Further, it is
desirable that the configuration of the ~hipping con~ainer
be such so that the loading of the containers into, for
example, a truck or a freight car, can be accomplished as
economically as possible, with the optimum use of space.
$yh~a~x QF T~E ~NVE~IO~
The present invention is closely related to U.S.
Patent application S.N. 06/821,381, filed January 21, 1986
and entitled ~VACUUM INS~LATED S~IPPING aONTAINER AND
MET~Op~, with the inventor being the ~ame as in the
present invention.
In the earlier patent appliQ tion, ~here i described
a cDntainer comprising a fluid tight outer containing
struc~ure comprising first outer wall means adapted to be
*xposed to ambient pressure, and ~lso a fluid tight inner
~ontainin~ structure defLning a product containing area
and having a second wall means spaced inwardly from the
first wall means. The first and ~econd wall means define
therebetween a substantially evacuated insulatin~ area to
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insulate the containing area from ambient heat
transfer. Each of the wall means comprises a frame on
which membrane sections are mounted.
In that earlier application, it was recognized
that due to varying temperature differentials between
the inner and outer wall means, there will be relative
movement therebetween due to thermal expansion and
contraction. To compensate for such expansion and
contraction, the forward end of the container was
arranged to permit relative longitudinal movement
between the forward perimeter frames of the inner and
outer wall means. While the structure defined in that
earlier application is fully capable of achieving the
objects of that invention, the inventor of that
original application has made further developments
; relating to the arrangement of the structure to
accommodate the thermal expansion and/or contraction
of the components. It is toward this that the present
invention is directed.
According to the present invention, there is
provided a vacuum insulated container, defining a
containing area and having a longitudinal axis, a
front end and a rear end, said container comprising:
a. a first fluid tight outer side wall structure
adapted to be exposed to ambient pressure;
b. a second fluid tight inner side wall structure
spaced inwardly from said outer side wall
structur~ and defining a said containing area;
c. said first and second outer side wall
structure defining therebetween a
substantially evacuated insulating area to
insulate said containing area from ambient
; heat transfer;
12~
d. said outer side wall structure comprising a
plurality of side wall sections, each of said
side wall sections comprising:
i. a perimeter frame defining a side wall
section area;
ii. a generally planar membrane section
extendiny across said side wall section
area and having a main central portion
and a perimeter portion attached to said
perimeter frame;
iii. the main central portion of the membrane
section having a configuration, relative
to said perim~ter frame, of an inwardly
curved plane, such that amhient pressure
acting against an outer surface of said
membrane section causes said membrane
section to react substantially entirely
in tension to withstand said ambient
pressure; and
e. a fluid tight rear end wall section comprising
a rear outer wall section and a rear inner
wall section which define thereb~tween a
second substantially evacuated area, at least
said rear inner wall section being connected
to a rear end of the second inner sidewall
structure so as to be movable therewith, said
rear end of the second inner side wall
structure and the rear inner wall section
~ being mounted so as to be movable along said
: longitudinal axis relative to said outer side
wall structure, in a manner that differential
thermal expansion and contraction of the first
outer side wall structure and the second inner
: : wall structure is permitted through movement
:
.
.
of the rear end of the second sidewall
structure and the rear inner wall section
relative to the first outer side wall
struc~ure.
According to a furthsr aspect of the invention,
there is provided a vacuum insulated container,
defining a containing area and having a front Pnd, a
rear end, a longitudinal axis, a vertical axis, and a
transverse axis:
a. a first fluid tight outer side wall structure
adapted to be exposed to ambient pressure;
b. a second ~luid tight inner side wall structure
spaced inwardly from said first outer side
wall structure and defining said containing
area;
c. said first and second structure defining
therebetween a substantially evacuated
insulating area to insulate said containing
area from ambient heat transfer;
d. said outer containing structure comprising a
first support frame, said first support ~rame
comprising:
i. a plurality of first longitudinally
extending corner beams located at edge
corner locations of said container;
ii. a plurality of first cross beams
extending transversely between adjacent
pairs of said first corner beams, with
each adjacent pair of first cross beams
forming with portions of their said
related corner beams a first perimeter
frama section;
~ e. said outer side wall structure further
: comprising a first membrane means mounted to
-- 7
said first support frame, each first perimeter
frame section defining a first related wall
SeCtiQn area, with said first membrane means
defining a plurality of generally planar first
membrane sections, each extending across a
related one of said first wall section areas,
with each first membxane section having a main
centxal portion and a perimeter portion
attached to its said related first perimeter
frame section, the main central portion of
each first membrane section having a
configuration~ relative to its said related
perimeter frame, of an inwardly curved plane
in a manner that ambient pressure acting
against an outer surface of said first
membrane section causes said first membrane
section to react substantially entirely in
tension to withstand said ambient pressure;
f~ said inner containing structure comprising a
second support frame said second support frame
comprlslng:
i. a plurality of second longitudinally
extending corner beams located at edge
corner locations of said container;
ii. a plurality of second cross beams
extending transversely between adjacent
: pairs of said first corner beams, with
~: each adjacent pair of second cross beams
forming with portions of their said
related corner beams a second perimeter
: frame section;
~: : g. said inner side wall container structure
further comprising a second membrane means
~: : mounted to said second support frame, each
,:.
: :
~ ,
~L29~6~
- 7A -
second perimeter frame section defining a
second related wall section area, with said
second membrane means defining a plurality of
generally planar second membrane sections,
each extending across a related one of said
second wall section areas, with each second
membrane section having a main central portion
and a perimeter portion attaching to its said
related second perimeter frame, the main
central portion of each second membrane
section having a configuration, relative to
its said related perimeter frame section, of
an outwardly curved plane in a manner that
pressure within said container acting against
an inner surface of said second membrane
section causes said second membrane section to
react substantially ~ntirely in tension to
withstand said ambient pressure; and
h. a fluid tight rear end wall section comprising
a rear outer wall section and a rear inner
wall section which define therebetween a
second substantially evacuated area, at least
said rear inner wall section being connected
to a rear end of the second inner sidewall
structure so as to be movable therewith, said
rear end of the second inner side wall
structure and the rear inner wall section
being mounted so as to be movable along said
longitudinal ax.is relative to said outer side
wall structure, in a manner that differential
thermal expansion and contraction of the first
outer side wall structure and the second inner
wall structure is permitted through movement
of the rear end of the second side wall
8~
- 7B -
structure and the rear inner wall section
relative to the first outer side wall
structure.
According to yet a further aspect of the
invention, there is provided a vacuum insulated
container, defining a containing area and having a
longitudinal axis, a ~ront end and a rear end, said
container comprising:
a. a ~irst fluid tight outer side wall structure
adapted to be exposed to ambient pressure,
b. a second tight inner side wall structure
spaced inwardly from said outer side wall
structure and defining said containing area;
c. said first and second outer side wall
structures defining therebetween a
substantially evacuated insulating area to
insulate said containing area from ambient
heat transfer;
d. a fluid tight rear end wall section comprising
a rear outer wall section and a rear inner
wall section which define therebetween a
second substantially evacuated area, said rear
inner wall section and said rear outer wall
section being connected to a rear end of the
seaond inner side wall structure so as to be
movable therewith, the rear end of the second
inner side wall structure and the rear inner
and outer wall sections being mounted so as to
be movable along said longitudinal axis
relative to said outer side wall structure, in`
a manner that differential thermal expansion
and contraction o~ the first outer side wall
structure and the second inner side wall
structure is permitted through movement of the
c ;,~
, ~
.
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- 7C -
rear end of the second side wall structure and
the rear inner and outer wall sections
relative to the first outer side wall
structure;
e. said rear outer wall section comprising a rear
outer perimeter frame which is mounted
adjacent to a rear perim~ter frame of the
first outer side wall structure and which is
connected to the perimeter frame of the first
outer side wall structure through a fluid
tight seal which permits movement of the rear
outer perimeter frame of the rear outer wall
section relative to the rear perimeker frame
of the first outer side wall structure, said
rear outer perimeter ~rame, o~ an inwardly
curved plane, such that ambient pressure
acting against an outer surface of said rear
outer membrane section causes said rear outer
membrane section to react substantially
entirely in tension to withstand said ambient
pressure; and
. a rear inner wall section comprising:
i. a rear inner perimeter frame defining a
rear inner wall section area;
ii. a generally planar rear inner membrane
section extending across said rear inner
perimeter frame area and having a main
central portion and perimeter portion
attached to said rear inner perimeter
frame;
iii. the main central portion of the rear
: inner membrane section having a
configuration, relative to the rear inner
perimeter frame, of an outwardly curved
~ ~'
: `
- 7D -
plane in a manner that pressure within
said container acting against an inner
surface of said rear inner frame section
causes said rear inner membrane sections
to react substantially entirely in
tension to withstand said pressure inside
the container,
Other features of the present invention will
become apparent from the following detailed
description.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a side elevational view of a first
embodiment of a container embodying teachings of the
present invention;
Figure lA is a schematic drawing illustrating the
manner in which pressure forces are reacted into the
membrane section and frame portion of the container of
the present invention;
Figure 2 is an end view of the container of
Figure 1, looking at a rear closure portion of the
container;
Figure 3 is a transverse sectional view taken
along line 3-3 of Figure 1;
Figure 4 is a sectional view taken along line 4-4
of Figure l;
Figure 5 is a sectional view taken along line 5-5
of Figure 1, and illustrating the configuration of the
front end cover;
Figure 6 is a highly schematic view illustrating
a~Curved membrane section mounted ~o a pair of beams,
indicating certain dimensional relationships which are
utilized in an analysis of the effects created by
varying the deflection of the membrane section;
.
.
,
:
.
,.
lZ9t~5~i~
Figure 7 is a graph illustrating certain relationships
resulting frcm varying the deflection of a membrane
section;
Figure 8 is a view similar to Figure 5 showing a
second embodiment of the present invention.
pESCRIPTION OF THE PREF~RR~p ~M~QEI~N~
Much of the basic structure o~ the present invention
is disclosed in my pending U.S. patent application Serial
No. B21,381, filed January 21, 19~6, and the benefit of
the filing date is claimed for the subject fihown in that
application~ In the first part of this text there will be
a description of the components of the present invention
which are the same ~s, or closely ~imilar to~ those fihown
in V.5. application Serial Mo. 821,381, after which the
features which are newly disclosed in this ~ppiication
will ke discussed.
A first embodi~ent of the present invention is
illustrated in Figures 1-5, which show a container 10
shaped as a rectangular prism having a ~quare
cross-~ectional area, and having a longitudinal oe nter
axis 11. In tenms of conf iguration, the container 10
compri~es a top wall 12, a bottom wall 14, two side
walls 1~, an end wall 18, and a removable end cover 20
positioned at an end of the container 10 opposite to the
location of the end wall 18. me end of the container 10
adjacent the cover 20 shall be considered the forward end
of the conta~ner 10, while the location proximate to the
end wall 18 will be considered the rear of the
cont~iner 10.
In terms of structure, the container 10 can be
considered as having an inner side wall structure 22 and
an outer side wall structure 24 substantially surrounding
tbe inner side wall structure 22 and spaced a ~hort
distance outwardly ~herefrGm ~o as to defLne with the
inner side wall structure 22 an evacuated insulating area,
generally designa~ed 260
~2~
--10--
The outer side wall structure 24 comprises a skeletal
f rame 28 which is covered by a plurality of sheet sections
or membrane ~ections 30 . In the p~rticular ~ nfiguration
shown herein, the frame 28 comprises two upper
longitudinal beams 32, located at the juncture lines of
the side walls 16 and the top wall 12 and two lower
longitudinal beams 34 located at the juncture lines of the
two side walls 16 with the bottam wall 14. In addition,
there ~re four rear end beams 36 located adja oe nt to the
edges of the end wall 18, and a second se~ of front end
beams 38 interconnected in a sguare configuration at the
location o~ the cover 20, so that two of the~e ~econd end
b2ams 38 are positioned at the front edges of ~be ~ide
walls 16, while the other two second end beams 38 are
positioned at the front edges of the top wall 12 and
bottom wall 14, respectively.
Extending between each upper longitudinal beam 32 and
a related lower longitudinal beam 34 positioned
immediately below, there are a plurality of evenly spaced
vertical intermediate beams 40~ In like manner, there are
a plurality of upper intermediate beams ~2 e~tending
horizontally between the two upFer beams 32, and a
plurality of lower intermediate beams 44 extending
horizontally between ~he two lower longitudinal beams 34.
Thus, it can be seen that the beams 32-44 collectively
define a plurality of interconnected rectangular fr~me
sections 46. For example, a pair of adjacent vertical
intermediate ~eams 40 form with those portions of the
upper and lower longitudinal beams 32 and 34 that extend
thereb@tween a rectangular frame section.
Each of the frame æctions 46 has a related membrane
~ection 30 h~ving two edges 52 which join to the
1~9~S6~
longitudinal beams 32 and/or 34, and two second edges 54
which join to ~he in~ermediate beams 40 or the beams 36 or
38. Ihe membrane sections 30 are made fluid tight so as
to be impervious to the passage of air, and the membrane
edges 52 and 54 are joined to their respective beam
memkers to make a fluid tigh~ connection.
As indicated earlier, the area ~6 between the outer
and inner side wall structures 22 and 24 is evacua~ed.
~ith the outer surface 56 of each o~ the m~mbrane
sections 30 being exposed to ambient atmosphere, and with
the inside surface 58 of each membrane 30 facing a vacuum,
it is readily apparent that atmo~pheric pressure acting
upon the membrane 30 creates a substanti?l foroe tending
to pu~h the membxane 30 inwardly toward the interior of
the container 10. As will be discussed more fully
hereina~ter, each of the membranes 30 is arranged so that
these rather substantial force loads are reacted
fiubstantially entirely in tension along lines of force
parallel to the curved plane of the membrane 30. This
causes the outer surface 56 of each membrane 30 to assume
a moderately concave curvature.
Each membrane 30 can, for purposes of de~cription, be
considered as having a lo Q ting plane which is coinciden~
with the perlmeter ~f the membrane (i.eO the edges 52
and 54) where the membrane 30 joins to its related
perimeter frame. Then the membrane can be considered as
actually being positioned in a curvPd plane which mæets
the locating plane at the edge locations 52 and 54~ bu
whicb curves aw~y from the lo~ating plane~
It i~ believed that a better understandin~ of the
description which is to follow will ~e achieved by at this
time providing a æimple analysis of the nature and effec
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~2~
-12-
of the tension loads exerted on each membrane 30, and
reference is n~w made to Figure lA, which is a rather
simplified diagram showin~ two beams 60 of theoretically
infinite length, with a membrane 62 extendiny between the
two beams 60, with this membrane 62 also being of infinite
length. In this example, we shall assume that the
beams 60 will not deflect under loading, and that the
membrane 62 does not elongate under tension loads.
In this example, the width dimen~ion of the membrane
~i.e. the distance between the two beams 60) is
designated ~wn. me atmospheric pressure exerted agaLnst
the outer surface of the membrane 62 is indicated by a
multiplicity of ~all arrows ~pnr and the resultant force
of this pressure is indicated at ~Fr~. It is assumed that
the membrane 62 is constructed, relative to the spacing of
the beams 60, so that the middle portion of the
membrane 62 will deflect a distance ~d~ from the plane
extending between the beam~ 60 at the juncture point of
the membrane 62.
This force Fr is reacted totally in tension in the
membrane 62. To calculate the tension foroe exerted on
the m~mbrane 62, a line i8 drawn tangent to the
membrane 62 at the juncture point 66 where the membrane 62
joins to the beam 60, this tangent lisle being
designated 68. ~rhe angle being made by the line 68 with
the line or plan~ 64 is designated by ~, and the tension
force at the point of t~slgency 66 is designated "E'tn. The
force Ft can be divided into two force components, namely
~Fan, directed oppositely to the force Fr, and a second
force component designated ~Fbr, ext:ending perpendicular
to the for~e conponent Fa. It can readily be appreeiated
that as the angle ~ decreases, the resultant tension
~29~6~
force Ft on the membrane 62 will increase. As an example,
let it be assumed that the angle ~ was 10. The tension
force Ft would be equal to Fa (which would be equal to Fr
times the cosecant of ~). With the cosecant of 10 being
approximately 5.7, the ~ension force Ft would be 5.7 tLmes
the resultant force Fr.
Another consideration is the amount ~f deflection
which the membrane undergoes~ For a given width w, the
amount of deflection d can be calculated accoxding to the
following fo~mula:
d = w~2 (csc ~ - cot ~)
For an angle a of 10, this deflection d will be about
O .O9w.
For relatively small angles of B i.e. 10 or less),
the tension force exerted on the membrane 62 would be
nearly directly inversely proportion21 to the magnitudb of
the angle ~. On the other hand, the deflection d of the
membrane 62 would be substantially directly proportional
to the angle ~. It is, of course, desirable to keep the
amount of deflection d as ~mall as possible to keep the
oontaining volume of the container 10 as great as po~sible
relative to the total volume occupied by the container 10.
On the other hand, there is a practical lower limit to
which the de~lection d can be lowered, before the stress
on the membrane 62 and the beams 60 becomes so excessive
~hat the bulk and weight of the beams 60 and m~branes 62
are unrealistically high.
With the foregoing in mind, we will naw continue
~ith a description of the structure o~ ~he ~ontainer 10
m e skeletal frame of the inner structure corresponds
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-14-
almost exactly ~o that of the outer structure.
Accordingly, for ease of description, the beams of the
inner ~tructure which correspond to beams of the outer
structure will be given like numerical designations, with
an ~a" 8uffix dlstinguishing the beams of the inner
structure 24. Thus, ~he inner structure 24 has a ~keletal
frame 28a made up of the upper and lower longitudinal
beams 32a and 34a, beams 36a and 38a, and also
intermediate beams 40a-44a.
Likewise, there are a plurality of membrane
sections 30a extending between the variou~ frame
sections 46a provided by the interior skeletal frame 28a.
~owever~ while the interior membrane sections 30a are also
placed in tensionr the pressure is exer~ed again~t the
membrane sections 30a from the interior of the
container 10 thus causing the membrane ~ections 30a to
curve outwardly toward their corresponding outer m~mbrane
sections 30. m e analysis presented above relative to the
membrane 30 applies as well to the ~embranes 30a.
It is necessary to provide interconnecting support
members between the outer and inner skeletal frames 28
and 28a. ~owever, ~hese interconnecting supports should
be made in a manner to mimimize the heat conductive path
made by such interconnecting structures. m is can be done
in three ways. First, the interconnecting structure
should be made of a material whicb has low heat
~onductivityO Second, the structure should be arranged so
th~t its conductive path ls as long as possible. l~ird,
the in~erconnecting ~tructures should have a
cros~sectional area along the heat conductive path to be
aæ ~anall as possible~ Further, it should be recognized
that ~hile each ~ the ~keletal ætructure~ 28 and 28a arP
~29~564
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subjected ~o very high loads due to the pressures exer~ed
by the ambient atmosphere and the atmosphere or liquid
contained within the container 10, the intercsnnecting
structure between the frames 28 and 28a need only be
strong enough to support the weight of the inner
structure 24 plus the contained material, and al~o to
withstand any Lmpact loads to which the container 10 might
be subjected~ Further, as will be discussed more fully
later herein, the interconnecting structure ~hould be such
as to permit lLmited relative movement between fr~mes 28
and 28a to allaw for thermal expansion and contraction,
and particularly along the leng~hwi axis 11.
The interconnectin~ elements are ~hown only
schematically herein, and these are simply given the
numerical designation 70, it being understood that the
interconnecting structure could be structural components
already kncwn in the prior art. These interconnecting
elements 70 are located at ~paced locations along the
length of the various pairs of adjacent beams 40-40a,
42-42a and 44-44a. Since the opposed side bea~s are
subjected to bending moments which tend to move the beams
together, the elements 70 tend to cancel these bendin~
moments out. Also the elem~nts 70 ~hould be such as to
permit ~ome relative movement between the frame~ 28
and ~8a due to thermal expan~ion and contraction.
In ~he particular configuration as shown herein, ~he
upper and lower longitudinal beams 32 and 34 are
substantially identical, and the~e comprise a pair of
pl~te6 72 which meet at a right angle corner 74~ with the
opposite ends of the plate~ curving inwardly, as at 76.
Reinforcing webs 78 can be pr~vided~ me membrane
~ections 30 can be ~oined to the beams 32 and 34 ~y u~e of
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conventional bonding techniques, and the edges 5~ of the
membrane sections 30 can be joined to the beams 32 or 34
at the location of the curve 76 to minimize any localized
stresses.
It is to be ~nderstood that outer and inner floor
and/or wall ~tructures can be pr~vided for the
container 10. Such an inner structure is shown at 79 in
Figu~e 3.
The components described above are ~he same as, or
clo~ely similar to, ~hose shown in the above-nentioned
U.S. Patent application Serial No. 821,381. The
components which are aescribed hereafter will differ in
various respects from corre~ponding components shown in
the prior patent application.
The cover 20 .is made in a manner to incorporte the
same structural principles as those of the outer and inner
structures 22 and 24 of the main container 10. AS shown
herein, the cover 20 has an outer skeletal frame 82 of a
square conf$guration supporting an outer m~mbrane
section 84 which, as described previously, is loaded in
tension, so a~ to have a generally concave configuration.
m ere is an inner frame 86 having an inner membrane
~ection 88. The cover m~mber 20 and the forward edge
portion of the container 10 are formed with suitable seals
~hich are or may be conventional Ln the art. Ascordingly,
this seal structure is simply indicated somewhat
schematically and generally designated 90. Further, when
the cover 20 is in place at the end of container 10,
suit~ble fas~ening devices, such as shown at 92 in FIG. 1
can be provided to hold the cover 20 in place. me t~o
frames 82 and 86 are rigidly connected to one another
through a ~uitable fluid tight insulating ~onnecting
~z~
device which is simply indicated schematically at 94. As
indicated previously, it is to be understood that the
connecting device 94 could take a variety of forms, and
could be similar to the connecting devices or spacers
indicated schematically at 70.
With regard to the front edge portion of the main
container 10, ~he two front end frames sections 38 and 38a
are connected rigidly to one another by means of a
~uitable fluid tight insulating connection, indicated
schmatically at 96. This is done in a manner that the two
front end frame m~m~ers 38 and 38a are rigidly
interconnected with one another.
The configuration of the rear end wall 18 is
considered to be significant in the present invention, and
this will be described with referen oe to Figure 4. There
is an outer perimeter frame 98 having a square
configuration, and an inner perim~ter frame 100 spaced a
~hort distance forwardly of the frame 98. There is a
suitable insulating connecting device 102 by which the two
frame~ 98 and 100 can be fixedly connected to one anoth~r.
As indicated previously, this insulating connector 102 is
~imply ~hown schematically hereLn, and various such
~onnecting devices ~ould be used.
: There are outer and inner membranQs 104 and 106,
respectively, and these are connected tol respectively,
the outer and inner frames 98 and 100. The same
structural principals as those utilized in the outer and
i~ner stru~tures 22 and 24 and those used in the door 20
are utilized în the rear w~ll 18, in that the membranes
104 and 106 define therebetween an insulated evacuated
area, and the membranes 104 and 106 withstand the pressure
loads from ambient a~mosphere a~d the fluid medium (i.e.
~9~
-18
air or 5Cme other medium) within the container by react~ng
substantially in tension.
The outer frame 98 is connected to the rear end frame
36 of ~he outer structure 22 by means of a fluid tight
flexible seal 108 which permits relative movement between
the rear wall 18 and the frame 3~ forwardly and
rearwardly. Also, it is ~o be recognized ~hat the
seal 108 provides sufficient structural support between
the fr~mes 36 and 98 so that the rear wall 18 is properly
centered relative to the frame 36. Alternatively,
suitable ~pacers could be placed be~ween the frames 36 and
either or both ~f frames 98 and 100, with a non load
bearing seal. To describe the operation of the present
invention, let it be assumed that the container 10 is to
be used to ship a product, such as a frozen food product,
at very low temperatures (e.g. -80 F). me product can
be brought to the desired low temperature by use of
conventional means, 8uch as exposure to a cryogenic fluid,
and the product then placed in the container 10. In some
instances, a quantity of cryogenic fluid (e.g. liquid
nitrogen) can be placed in~ide the ~ontainer 10 for
e~tending its low temperature ~ondition, with the
evap~rated fluid being vented from time to time to prevent
an undue buildup of pressure~
AS indicated previouslyr the area 26 between the outer
and inner structures 22 and 24 is evacuated, with the
res~ t that the outer membrane sections 30 are expo&ed to
ambient pressure (14.7 psi at sea lPvel)~ while the inner
membrane ~ections 30a can be expec~ed to be subjected to
pressures at l~ast a~ high as ambient atmDspheric
pressure, and possibly some~hat greater if a cryoyenic
fluid within the container 10 is evapora~ing. AlfiO, the
~ 3S~
--lg--
area between the membrane sections 84 and 88 of the
cover 20 and the area between the membranes 104 and 106 of
the rear wall 18 are likewise evacuated.
Let us turn our attention first to the forces exerted
by the outer membrane sections 30 on ~he outer skeletal
frame 28. First, with regard to the upper and lower
longitudinal beams 32 and 34, the side membran
sections 30 would exert a force on its related upper
longitudinal beam 32 which is parallel to that portion of
the curved plane of the membrane at the point where it
joins to the beam 32. This force would have an inward
componentt but the main force oompQnent would be directed
vertically. In like manner, each of the top membrane
sections 30 would be exerting primarily a laterally inward
force on the two beams 32. me net foroe exerted on each
of the upper beams 32 would be the resultant o~ the
vertical and lateral forces exerted by the side and upper
membrane sections 30, and with the upper and side membrane
sections 30 being of substantially the same area, the
resultant would be a downward and laterally inward force
at about 45 from the horizontalO Similar forces would
react on the lower longitudinal beams 34. These force~
would be resisted by the i~termediate beams 40t 42 and 44,
whicb would be loaded in compression.
e membrane sections 30 would also be placing
substantial tension forces on each of the intermediate
beams 40, 42 and 44O However, it will be noted that the
lateral force components of two adjacent m2mbranes would
essentially cancel each o~her out, so that the
intermediate beams 40~ 42 and 44 ~ould be resi~ting
prL~arily only the inwardly directed resultant force
component. However, even this inward force component
2~8~
-23-
could be substantial. For example, if one of the membrane
sections 30 had a height dimension of four feet and a
width dimension of three feet, the ~o~al inwardly directed
force componen~ by ambient pressure at sea level would be
approx~mately 150,0~ pounds. This loading would be
shared by a pair of adjacent intermediate beams 40, 42
or 44 and the Eection~ of the longi~udinal beams 32
and/or 34 extending therebetween. Further as indicated
earlier herein, the spacing members 70 provide ~upport
between the inner and ou~er beans 40-44a, 42-42~ and
44~44a.
m e force~ exerted on the four end beams 36 w~uld be
omewhat differenk than those exerted on the longitudinal
beams 32, in tbat theæe end beams 36 would resist the
forces exerted by membrane sections 30 by providing a
resisting force opposite to the tension forces exerted by
the adjaoent membrane 30, which tension forces would be
generally parallel to the plane of the membrane where it
connects to the beam 36.
As indicated previously, from a standpoint of
maximizing the effective ~torage space within the
container 10, relative to the total volume occupied b~ the
container, the deflection of the membranes 30-30a (which
is related to the curvature) should be kept to a minimum.
~owever, the stress on the membranes 30-30a and the beams
supporting these membranes increases as the curvature and
deflection of the membranes 30-30a decreas~.
To illustrate these relationships, reference is made
to Figures 6 and 77
Figure 6 illustrates a somewhat idealized and highly
schematic illustration of a configuration of a single
outer frame sæction. The dimension ~W" is the total
1~9~5~;~
lateral dimension of the con~ainer, which is presumed to
be 90 inches. It is assumed that the corner beams ~such
as described previously and indicated at 32 and 34) would
occupy a certain amount of space, ~nd it is assumed that
the dimension "RA" is equivalent to the corner beam width,
which is presumed to be 8 inches for each ~eam~ Thus, the
lateral dimension of the curYed portion of the m~nbrane
(identified at "L" in Figure 6) is 74 inches. The radius
o~ curvature (indicated at ~RM" of the membrane) will vary
in accordance with the amount of deflection of the
membrane (indicated at ~D~). In this idealized example,
it is assumed that the defle~tion aD" varies between 1 to
10 inches. For these defleetions, the tensile force
resulting from the force of atmospheric pressure on a
single one inch width of the membrane has been calculated.
A table presenting the various information and the
calculations is presented at the end of the text of this
specif lcation~
To illustrate these relationships, reference is now
made to the graph of Figure 7. On the horizontal axis,
there is presented the deflection ~D~ in inches, and there
is also presented the values of ~D/Ln. On the vertical
axis, there i~ presented the tensile force on each one
inch strip of the membrane for the various deflections,
and there i5 also presented the ratio of the outside
volume of the container to the inside volume of the
container (Ao/Ai). In this idealized example, it is
assumed that the thickness dimension of the membranes is
zero, and that the spacing ~etween each pair of inner and
outer membranes at the maximum point of deflection i also
zero Also, it is assumed tha~ the length of the
container is infinite, so that no allowan~es would have ~o
:~29~3564
~22-
be made for loss of volume by the presen oe of an end wall.
Also, to simplify calculations, it was assumed that the
inside area would be a square area.
As can be seen in Figure 7, as the deflections become
quite small (in the order of one to two inches, which is
D/L of 0.014 ts 0~027, ~he force exerted on the membranes
(and consequently the total force exerted on the frame
structure) increases dramatically. On the other handr for
greater deflections (from 5-10 inches, which is D/L of
0.068 to 0.135~, the decrease in the tensile force on the
membranes relative to the increase of deflection is
substantially les~. Also, it ~an be seen that for very
sm~ll deflectionsr the Ao~Ai ratio does not increase
significantly. Howeverr as the deflection~ become
greater, this area ratio (which is directly related to the
volume ratio of the container for this theoretical
oontainer of infinite length) increases at a much greater
rate for each increment of deflection.
To draw a comparison between these relationships and a
cylindrical vacuum container, let it be assumed that there
is a cylindrical vacuum container of infinite length, and
that it~ wall thicknesses are ~ero, with ~he space between
these wall8 also being zero. Further, since most cargo is
oontained in square containers, and ~ince there must be a
floor within the cylindrical vacuum container, we shall
assume tha~ the containing area is a square fitting within
the limits of the circle defined by the cylindrical vacuum
container. Fur~her~ sinoe the~ various cylindrical
vacuum container~ mu~t be contained in a larger shipping
container of rectangular con~iguration (e.g. a trailer or
a freight car), we shall con~ider the effective outside
area of the cylindri~al oontainer to be equal to a square,
"
i6~
-23-
where each side of the square is equal to the diameter of
a cylindrical container. ~nder these idealized
conditions, it can be seen that the Ao/Ai ratio of ~his
idealized cylindrical container is ~wo- ThU5, by plotting
this value on the graph of Figure 7, it can be seen that
where the deflection of ~he container of the example of
Figure 6 is six inches or less, the Ao/Ai ratio of the
container of the present invention is less than (and
therefore better than) that ratio for the cylindrical
container. On the other hand, for a deflection of seven
inches or greatPr, the Ao/Ai ratio of the container of the
present invention iæ greater than (and thus poorer than~
~he ratio for the cylindrical container).
; It is to be emphasized that the~e relationships are
presented in a rather theoretical fashion, primarily to
illustrate the r~lationships. In actually designing the
container of the present invention, consideration must be
given to the volume occupied by the ~tructural components,
tolerances for spacing the components, membrane thickness,
etc. E`urther, the analysis of the cylindrical vacuum
c~ntainer i8 higbly idealized, and no consideration has
been given to the structural aspectx, particularly the
structure of the outside shell of the cylindrical
container which must be made sufficiently strong to avoid
the buckling loads that would be imparted thereto~
To discuss other facets of the present invention, it
will ke noted, with reference to Figure 3, that ~he
related pair of corner beams 32-32a and 34-34a are aligned
with one another at an angle of 45 to the vertical and
horizontal axes. It will also ~e noted that, as discussed
previously~ the force component~ exerted on these corner
beams 32-32a and 34-34a are also along a line which is
~298~
-24-
approxLmately 45 to the horizontal and vertical axes.
Since the alignment component is at 451 the spacing
between the outenmvst corner of an outer beam 32 or 34 to
the innermos~ corner point o~ the inner beam 32a or 34a is
at a maximum. Thus, for every unit of the total thickness
~imension of a pair of outer and inner panel ~ections, ~he
maximum spacing from the beam surfaces spaced further from
one another is approximately 1.4 times grea~er. This
permits the depth of these beams 32-32a and 34-34a to ~e
maximized in the direction where the greatest force is
exerted, thus penmitting the structure of the beams to be
optimiz~d to withstand these forces.
It will also be noted that where each of the
membranes 30 or 30a joins to a related beam, at the
juncture point, the alignment of the membrane 30 or 30a,
relative to the beam, is such that the surface of the beam
i5 tangent to the curvature of the membrane, with the
membrane bein~ in a uniform curve. For example, it can be
seen that at the juncture point 5~ of the membrane 30 to
the beam 32 (see Figure 3) the curved surface portion of
the beam 32 is tangen~ to the membrane 30O ffle tangent
line drawn at the point of contact ~ould make an a~gle
with the general plane occupying ~e panel aection which
would be equal to the angle as illustrated in ~igure lA.
Thus, substantially no bending moments axe imparted ~o the
membranes 30 or 30a at the location where ~hese membranes
joint to a related ~eam.
The various analyses presented above apply generally
~o the aforementioned U.S~ Patent app~ication Serial No.
821,381 as well as to the pre~ent invention. The analysis
which follows deals more particularly with oertain novel
aspects resulting particularly from the no~el features of
lZ9~564
the present application.
~ nder circumstances where the ambient atmosphere is
quite warm and the contained product is at a very low
temperature (and also where the opposite condition
exists), ~he probl~m of thermal expansion exists. It can
easily be seen with referen oe to Figure 4 ~hat the
flexible seal 108 readily permits such thermal expansion.
With further reference to Figure 4, let us now examine how
the force loads are reacted in the tructure. It can be
seen ~ha~ the pressure of the gaseous medium inside of the
container 10 acts upon the rear inner membrane 106 to
produce a net rearward force which is reacted into the
perimeter frame 100. In like manner, the ambient air
pressure against the outer rear m~mbrane 104 produ oe s an
opposite force to that exerted on the membrane 106, and
this is reacted into the frame 98. The net effect is that
the æ two forces cancel each other out.
To recognize the significance of this, referenoe is
made a~ain to Figure la. It was previously discussed that
the tension on the membrane, shown schematically at 62 in
Figure la produces a substantial hori~on~al force which
tends to draw the two beams (shown schemat~cally at 60 in
Figure la) together. To apply this æam2 principal ~o the
container 10, the m2mbranes 30 act between each set o
cross-beams 40-44 to pull these cross-beams ward one
another. These tension forces are counteracted by the
sections of the longitudinal beams 32 and 34, and also 32a
and 34a which are placed in compression.
To continue ~his aralysis fur~her, reference is made
back to Figure 4. As indi~ated previouslyy the gaseous
pressure forces against the membranes 104 and 106 ~ancel
each other out. There is ~ net forwardly directed force
.
-26-
resulting from ambient air pressure pushing against that
perimeter portion of the frame 36, the seal 108 and the
frame 98 where there is not a counteracting force exerted
from within the container 10. In effect, there is an
area, which i~ approximately proportional to the
difference in the area defined by the frame 36 and that
defined by the interior part o~ the frame 100 expo~ed ts
pressure within the container 10, and the ambient air
pressure exerted on tha~ perLmeter ar~a results in a net
forward force. This net fonward force is rasis~ed by ~he
longitudinal beams 32, and 34.
H~waver, even though the.total forces exerted on th~
beams 32, 32a, 34 and 34a ~an be substantial, it should
also ~e recognized that this particular arr~ngement of the
rear wall 18 does not create any unwanted additional loads
on ~hese beams.
A second embodiment of the present invention is
illustrated in Figure 8. m e basic structure of this
second embodiment is substantially the same as in the
first embodimant, except that the rear end portion of the
container is modified. Components o~ this second
embodiment which are substantially similar to
corresponding components of the first embodiment will be
given ~ike numerical designations with a prime (')
designation dlstinguishing ~hose of the second embodiment.
Thus, there is a container lO' having a rear end wall 18'
comprising an outer membrane 104' and an inner membrane
106'.
m ere is a rear ou~er perimeter frame 110, havLng an
overall square configuration, and the outer me~brane 104'
is mounted to his frame 110 in the manner described
p~eviously herein. There is an inner rear perimeter
--27--
frame 112, also having an overall K~uare configuration,
and ~ itting within the f rame 110 . The cross-sectional
configuration of the frame 110 is somewhat sLmilar to that
of the beams 32 and 34, and the cross-sectional
configuration of the frame 112 is rather similar to the
cross-sec~ional configuration of the beams 32a and 34a.
Elawever, the cross-sectional configuration of these beams
could, of course, be modified.
m ere are m sulated spacing el~ments 114 sep2rating
the frames 110 and 112. These spacing elements are shown
rather schematically, and each spacing element 114 could,
if desired, be similar to the spacing elements 70. The
spacing elements 114 are such as to allaw limited forward
to rear m~vement of the inner frame 112 relative to the
outer frame 110. This permit~ relatiave movement of the
inner and outer structural components due to thermal
expansion and contraction~
With regard to the manner in which the ~tructural
loads are imparted into the frame, it will be noted that
the pressure of the ambient air against the outer membrane
104 will produce a resultant forward force against the
outer fr~me 11OD mis force will h~ve to ke reacted into
the longitudinal beams of the outer structure 24'. ~hus,
in oomparison with the first embodiment, for a structure
of comparable size, the outer longitudinal beams (numbered
32 and 34 in the first embodiment, but not shown in the
second embodiment) will be placed under greater
compression loads in the second embodiment~
On the other hand, with the gaæou~ medium Lnside the
c~ntainer 10' pressing again~t the inner rear membrane
106', there i~ a re~ultant rearward foræ exerted on the
rear inner frame 112. Thi8 in turn is reacted into the
129~564
.
-28-
inner longitudinal beams (numbered 32a and 34a in the
first embodiment, but not shown in the second embodiment)
as tension loads. This tension loading would tend to
counterac~ the compression loading which is caused by the
tension forces exerted by ~he inner membranes 39a'. Thust
in oomparison with the fir~t embodiment, he second
~mbodiment for containers of comparable size and
configuration) results in lower net compression loads in
the inner longitudinal beams 32a and 34a.
It is to be recognized that various modifications
could be made without departing from the ba~ic teachings
of the present invention.
Z~85~i~
--2 9 -
T~EI E OF ~ P~TIOS T0 ~LECTIONS OF .s!Eq9~E
D I 1 2 3 4 5 6 7 ~ 9 10 6.S92
L 74 7~ 7~ 74 7~ 7~ 74 74 74 7~ 74 74
IS 15 15 IS 15 15 15 15 ~5 lS 15 15
9 ~ a ~ 8 8 ~ 9 a o 8 B
T~ET~liL/i2*RM)))~190/~Dl 3.dg66.;g9 9.27'12.34d15.39~ 1~.4æ21.42624.40127.34330.248 20.204
RY114~DA2~+~`2)/18~D)~5 343 230 173 139 117 101 90 al 73 10?
F tp~ 102?5 5149 3~5 2597 2091 1756 1519 1343 120a 1102 1607
U ~ 90 ~ YO 90 ~ g 50 90 90
+~IA2 9100 ~10013100 9100 9100 B100 9100 B100 B100 BIC0 alO0
1~4~DlA2 7396 6724 60~4 5476 43~0 ~356 38~ 33~;4 2916 ~S00 404g
~0/al +~0/al 1.095 1.2051.33~ 79 1.653 I.B60 2.107 2.4~9 ~.77~ 3.2~0 2.040
DJL +D/L 0.01~ 0.0270.0410.05~ 0.06D 0.061 0.0~5 0.108 o.læ 0.135 0.099
C2RCLE
R~ClalC t~0C/RIC I .571
~O~alC ~AO/aIC 2
~OC ePI-~h/2)A2 6361.72
alC ~K~eCOS(ePI/O)A2WJO
DEFINITIONS
D DFLECTloN OF YE~DR~NE - INCHES
L ~TH C~ aRC OF ~R~ - INCHES
P PQE~
M WRtER BEa~ IDTH - II~ES
wa aN6LE QF INCIDB~CE
atl RaDIus ~ aTuRE - INl:HES
F tEliSlLE FOM:E - Pa~S PER INa~ OF lllDTH
11 OYERJ~LL IIIDTH - INCIES
PO ~TSlDE a~ SQ IN
RI INSIDE ~ SC IN
~O/AI RatlO
D/L PATIO
aoc oursloE aN~a CIR~E - SC 11~ -
: ' ,
