Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a bulk container, and
more particularly, to a flexible bulk container made of fabric
adapted to discharge static electricity.
Flexible bulk containers have been utilized for a
number of years to transport anddeliver finely divided solids
such as cement, fertilizers, salt, sugar, and barite, among
others. Such bulk containers can in fact be utilized for
transporting almost any type of finely divided solid. The
fabric from which they are constructed is a weave of a polyolefin,
specifically, polypropylene or polyethylene, which may or
may not receive a coating of a similar polyolefin. If such a
coating is applied the fabric will be non-porous, while fabric
without such coating will be porous. The usual configuration of
such flexible bulk containers involves a rectilinear or
cylindrical body having a wall, base, cover, and a closable
spout secured to extend from the base or the cover or both. As
shown in British Patent No. 1,129,917 and U.S. Patent
No. 3,961,655, it is also known to place a surrounding flap
or skirt around the spout extending from the base of the
container.
Such containers are handled by placing the forks of
forklift hoist means through loops attached to the container.
The weight of such bulk container when loaded is usually between
500 pounds and 4,000 pounds, depending upon the density of the
material being transported.
It has been found that the shifting of specific materials
within the bulk container as well as friction created between
the material and the container during loading and unloading
of the container creates localized pockets of built-up static
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electricity in the container.
The sub~ect invention is a bulk container of
rectilinear shape which is capable of dissipating static
electricity from its surface so as to reduce the possibility
of an explosion when discharge occurs near volatile gases or
materials. The fabric utilized in the bulk container of the
subject invention has parallel strands of conductive yarn
extending therethrough, the strands being connected by grounded
conductive connection means such that localized static
electricity on the container is discharged. The fabric may
be a weave of polyolefin filaments and carbon fibre, the
carbon fibre acting as conductive yarn, the weave optionally
being coated with polypropylene or polyethylene. The polyolefin
filaments are preferably formed from polypropylene or poly-
ethylene. The bulk container is constructed such that a pair
of its opposite walls and the strands of conductive yarn in
those walls are integral with the base, with a conductive
collector strip extending around the line of joinder between
those walls, the other two walls, and the cover. The strands of
conductive yarn in spouts that connect to the base and cover of
the container extend parallel to the longitudinal symmetric
axis of the spouts. If the container has an outer flap or
skirt extending around the spout connected to the base of
the container, the flap or skirt is constructed such that
the strands of conductive yarn extend longitudinally there-
through and parallel to the strands of conductive yarn in the
concentric spout. A conductive collector strip extends along
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the line o~ joinder between the base of the container and the
spout that connects thereto as well as the outer flap or skirt
that may also connect thereto. A grounding connection is
attached to each of the conductive collector strips.
A preferred embodiment of the bulk container of the
subject invention will next be described utilizing the
accompanying drawings, in which:
Figure 1 is a perspective view of the bulk container
of the subject invention, illustrating the components of the
Container.
Figure 2 is a side view of the bulk container of
the subject invention illustrating the position of the
conductive fibre yarns in the fabric of the container.
Sections A, B, and C relate to details of the container
construction which are amplified in Figures 7, 8, and 9,
respectively.
Figure 3 is an end view of the bottom portion of the
container illustrating the closable discharge spout of the
container and the skirt surrounding that spout.
Figure 4 is an end view of the bottom of the container,
as in Figure 3, but illustrating the discharge spout in the
closed position with the skirt closed therearound.
Figure 5 is a side view of the bulk container of the
subject invention while empty.
Figure 6 is a side view of the bulk container of the
subject invention while loaded.
Figure 7 amplifies Section A of Figure 2 to illustrate
the connection between the wall of the container and each
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of the four lifting loop straps.
Figure 8 amplifies Section B of Figure 2 to illustrate
the relative placement of the strands of conductive yarn in the
weave of the container fabric.
Figure 9 amplifies Section C of Figure 2 to illustrate
the conductive collector strips that extend along the joinder
line between the wall and the cover of the container and the
joinder line between the base of the container and the spout
that connects thereto, and to illustrate the grounding loop
connected to each such conductive collector strip.
As shown in Figure 1, the preferred embodiment of the
bulk container is generally square in cross-section. One of
the opposite pair of wall sections of the container and the
base of the container are formed by a single main panel 20
to which are attached a pair of lateral panels 21, defining the
opposite pair of wall sections of the container, and a top
panel 22 defining the cover of the container. A filling spout 23
having a closure tie tape 24 extending therearound is connected
at a central position to top panel 22.
As shown in Figures 2 and 7, a loop strap 25 is sewn
into each upper corner of the bulk container, the two ends of
each loop strap being stitched to adjacent upper corners of
adjacent wall sections of the container. Webbing 26 extends
along the line of joinder between the wall of the container
and the cover panel of the container. At the upper corners of
the container webbing 26 is also stitched to the loops 25
to provide improved strength to the container. A copper
conductive braid 27 extends through webbing 26.
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The bulk container is constructed of a woven fabric
of polypropylene filaments and carbon fibres; in Figure 8, which
represents Detail B of Figure 2, the polypropylene filaments
are shown as thin intersecting lines and the carbon fibres
are shown as heavy dashed lines. The carbon fibres extend
longitudinally in the walls of the container such that one end of
each carbon fibre in those walls contacts the copper conductive
braid 27 in webbing 26, that braid also contacting the carbon fibres
in top panel 22. One pair of opposite wall sections are integrally
connected to the base section of the container to form main
panel 20; carbon fibres extend longitudinally through main
panel 20, i.e. down one wall section, through the base section,
and up the opposite wall section. Filling spout 23 has
carbon fibres woven therethrough so as to extend parallel to
the symmetric longitudinal axis of spout 23. Although the line
of joinder between filling spout 23 and top panel 22 does not have
a copper conductive braid extending therealong, static electricity
discharges from the carbon fibres of filler spout 23 into the
carbon fibres in top panel 22 and then into the copper braid
surrounding the outer perimeter of top panel 22. A tinned
braided copper grounding loop 28 is connected to copper braid
27 such that a grounding cable connected to grounding loop 28
will remove static charge from the copper braid 27. The Detail
of Figure 2, which is shown in Figure 9, illustrates the
connection of copper grounding loop 28 to copper braid 27.
A furthPr length of copper braid 27 e~tends along the line
of-joinder between the base of the container and a discharge spout
29 which extends therefrom. A skirt 30 may also be connected to
the latter line of joinder~ The discharge spout 29 and the skirt
30 each have carbon fibres extending therethrough parallel to
the symmetrical longitudinal axis of the spout and skirt; this
allows discharge of static electricity through another grounding
loop 28 which is connected to the further length of copper
braid 27. The orientation of the carbon fibres in the woven
polypropylene fabric is illustrated in Figure 2.
Discharge spout 29 and skirt 30 have closure tie tapes
31 extending therearound, each tietapa being fitted with a
self-locking quick-release tension device 32. Figures 3 and 4
illustrate open and closed positions, respectively, of discharge
spout 29 and skirt 30; in particular, Figure 4 illustrates a
closed discharge spout 29 positioned inside of a closed
skirt 30.
Figures 5 and 6 illustrate generally the side profile
of the bulk container while empty and during discharge,
respectively; "X" indicates the sling effect of the bulk
container which ensures a constant-flow, total discharge of
the materials from the container. This sling effect results
because one of the pair of opposite wall sections of the \
container and the base of the container are formed from a
continuous length of the woven fabric, i.e. main panel 20
in Figure 1.
Electrical discharge tests have been conducted on the
type of bulk container herein describad. It has been found
that when the subject container is properly grounded static
electrical charges in the container were reduced to less than
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500 volts, whereas prior to grounding voltages in excess of
1,000 volts were registered. Powdery material is thus more
safely handled by~ the bulk container of the subject invention
in gaseous and volatile environments than by conventional
bulk cOntainers which do not have static electricity discharge
capability.
