Outer Cover for a Flexible Tank and Optimized Flexible Tank for a 40 Foot Shipping Container without a Bulkhead

Abstract

An exterior cover of a generally rectangular flexible tank for a 40 foot shipping container has longitudinal seams along the long sides of the flexible tank rather than at the ends. The exterior cover is air-tight and contains holes near the ends of the flexible tank. The exterior cover is made of a flexible vinyl material that is optimized for the flexitank. The flexible vinyl material consists of an inner scrim core of woven fibers coated with melted PVC which goes through the holes between the woven fibers.

Claims

1. A flexible tank for transporting a bulk liquid, comprising: an inner tank composed of at least one layer of a flexible water-proof material, said interior tank when filled with a liquid to be transported having a shape which is generally rectangular in shape with two ends, two sides, a bottom and a top, the length of said two sides being greater than the width of said two ends; an exterior cover covering said inner tank, said exterior cover made from a sheet of flexible polymeric material that is longer than twice the length of said two sides of said inner tank; and a valve for filling and discharging said liquid being transported into the inner tank, said valve extending through said at least one material layer of said inner tank and said flexible polymeric material of said exterior cover, wherein the sheet of flexible polymeric material of said exterior cover is formed into an enclosure enclosing said inner tank, said sheet of flexible polymeric material of said exterior cover having no seams located at the two ends of said inner tank.

2. The flexible tank of claim 1, wherein said exterior cover has two longitudinal seams along the two sides of said inner tank and one traverse seam under the bottom of said inner tank.

3. The flexible tank of claim 2, wherein said exterior cover is air-tight except for holes formed in said two longitudinal seams near the ends of said inner bladder.

4. The flexible tank of claim 1, wherein said sheet of flexible polymeric material of said exterior cover comprises PVC with an internal scrim core, said internal scrim core being constructed of woven polyester fibers.

5. The flexible tank of claim 4, wherein said flexible tank is approximately 38 feet in length and said internal scrim core is woven such that it comprises a pattern of holes, wherein said pattern has between 169 and 225 holes per square inch.

6. The flexible tank of claim 4, wherein said internal scrim core is woven such that it comprises a pattern of holes, wherein said holes have an average size of between 0.0035 and 0.0045 square inches.

7. The flexible tank of claim 4, wherein said internal scrim core is woven such that it comprises a pattern of holes, wherein said holes comprise between 70-80% of the surface area of said internal scrim core.

8. A method of manufacturing a flexible tank for the transport of bulk liquids, comprising: forming an inner tank from at least one layer of a flexible water-proof material, said interior tank when filled with a liquid to be transported having a shape which is generally rectangular in shape with two ends, two sides, a bottom and a top, the length of said two sides being greater than the width of said two ends; forming an exterior cover from a generally rectangular sheet of flexible polymeric material, said sheet having two sides, each side having a length that is greater than twice the length of said two sides of said inner tank, and having two ends, each end having a width that is greater than the width of said two ends of said inner tank; welding the two ends of said exterior cover together so as to form a continuous belt loop of said flexible polymeric material, the seam resulting from said welding traversing the entire width of said exterior cover; turning over the exterior cover so that said seam is on the bottom of said exterior cover; locating said inner tank next to said exterior cover so that one side of said inner tank is next to and parallel to said exterior cover; moving the inner tank in the direction perpendicular to said the exterior cover and toward the exterior cover until the inner tank is widthwise centered on the bottom of the exterior cover; connecting the top of the exterior cover to the bottom of exterior cover on each side of the inner tank thereby forming two longitudinal seams running the length of the sides of said internal tank and enclosing the inner tank; aligning the top of said inner tank and the top of said exterior cover; and installing a valve through the top of said inner tank and the top of said exterior cover.

9. The method of claim 8, wherein said connecting step creates an air-tight enclosure of the inner tank in the exterior cover and the method comprises the further step of putting holes in the exterior cover near the ends of said inner tank.

10. The method of claim 8, wherein said sheet of flexible polymeric material of said exterior cover comprises PVC with an internal scrim core, said internal scrim core being constructed of woven polyester fibers.

11. The method of claim 8, wherein said internal scrim core is woven such that it comprises a pattern of holes, wherein said holes comprise between 70-80% of the surface area of said internal scrim core.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIGS. 1-3 show a prior art method of assembling a flexible tank.

[0011] FIGS. 4(a) and 4(b) illustrate the end seam of a prior art flexible tank.

[0012] FIG. 5 shows the inner tank 110 and the outer cover sheet being formed into a belt loop according to a preferred embodiment of the invention.

[0013] FIG. 6 shows the inner tank 110 being inserted in the outer cover 120 according to the preferred embodiment of the invention.

[0014] FIG. 7 shows a side view of the outer cover 120 after enclosing the inner tank therein according to the preferred embodiment of the invention.

[0015] FIG. 8 shows the arrangement of the inner scrim and PVC layers in the material of the outer cover 120 according to a preferred embodiment of the invention.

[0016] FIG. 9 is a cross-section view of the arrangement in FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A preferred embodiment of a freestanding flexitank 100 for a 40 foot shipping container and a method of manufacturing the same is shown in the accompanying figures. Flexitank 100 consists of a liquid containing inner bladder 110, which may be a conventional bladder or an improved bladder, and a unique outer cover 120. The inner bladder 110 has a generally rectangular shape when empty, and is, in the example of a 40 foot shipping container, approximately 37 feet long and 9½ feet wide. It may consist of a single layer or of several layers. As in conventional flexitanks, the outer cover 120 supports and provides additional strength along the length of the flexitanks that will help absorb and control the internal liquid dynamics during transport, and it also reinforces inner bladder 110, particularly at the ends thereof.

[0018] A main feature of the preferred embodiment is that outer cover 120, and thus flexitank 100, is uniquely manufactured and configured. In the preferred embodiment, the outer cover 120 is not formed into a tube. Furthermore, the material sheet used for outer cover 120 is not close to the lngth of the inner bladder 110 and is at least twice the length of the inner bladder 110, for example 74 feet. The inner bladder 110 is laid on top of outer cover 120 while it is spread out and measurements are taken of its position and marked. The inner bladder 110 is set aside and ends of outer cover 120 are brought together and joined at a single lateral seam 125. The result resembles a belt shaped loop or “envelope”. See FIG. 5. Before the inner layer is put in place, the outer cover 120 is turned over so that the lateral seam 125 is on the bottom. The inner bladder 110 is moved into place from the side rather than from an end and positioned on the marks. Consequently, it only moves a small distance (about 10 feet) in the preferred embodiment of the invention compared to movement from the end in the conventional flexitank (about 40 feet). See FIG. 6. A reinforced opening is made at the appropriate location in the top of outer cover 120 for the valve to be positioned and secured in place with a clamp or other suitable mechanism. The top and bottom portions of outer cover 120 are then joined to each other by two longitudinal seams 130 on the sides. See FIG. 7.

[0019] Lateral seam 125 is preferably a welded “overlap” joint cross seam. When the outer cover 120 material is as specified, the overlap is preferably about 2 inches. The longitudinal side seams 126 are not the prior art seams shown in FIGS. 4(a) and 4(b). They are preferably overlapped “prayer” joints where the material is folded over and back again and welded in place. Other types of seams may also be used for side seams 130. FIG. 7 shows the longitudinal side seams larger than they actually are for emphasis. Preferably, only 2 to 3 inches of material are used for the seam.

[0020] When the preferred embodiment is constructed, the outer cover 120 does not have two end seams. Instead, there is only one lateral seam 125 on the bottom (not located at either end), and two longitudinal seams 126. The lateral seam 125 is supported by the floor of the container and is not significantly stressed by the movement of liquid like the end seams. Preferably, the lateral seam 125 is preferably located 16-18 feet from the rear of the flexitank and the valve is approximately 33 inches from the rear of the flexitank and, consequently, near the rear open end of the container. Even when the end seams of a conventional flexitank are reinforced or strengthened, the preferred embodiment has advantages because the seams are not located at the point of the greatest amount of stress. Prior attempts to improve flexitanks have focused on strengthening the end seams. The preferred embodiments contain a more radical improvement by rethinking the manufacture of the flexitank so as to eliminate the end seams and to do so in a manner that does not introduce other undesireable effects. The preferred embodiments are also have the additional benefit that less fabric is used for the outer cover 120.

[0021] Unlike a conventional flexitank, the seams 125 and 126 in the outer cover 120 in the preferred embodiments cause the outer layer to be air tight. In addition to the above construction, the end portions of each one of the two side longitudinal seams 126 may be reinforced such as with a heavy duty fabric tape 127 and air vent holes 128 punched therethrough. There may be one, two, or three holes 128 on each side. The holes 128 are not as large as they may appear in FIG. 7 and, for example, may be % inch diameter circles. Although the reinforcing tape 127 and holes can be placed elsewhere, it is preferred that the holes 128 are punched out at the side seams 126 since the side seams 126 are thicker than the rest of the outer cover 120 and help to prevent tearing of the holes 128 causing them to become larger. The air vent holes 128 and reinforcing tape 127 are preferably located near, for example, approximately 1 foot from, the front and/or rear of the flexitank. The air vent holes 128 help to equalize air pressure within outer cover 120 as the liquid in the flexitank shifts back and forth and also allows the flexitank to be folded and rolled into a highly compressed form so that it has a small volume while it is transported prior to use.

[0022] In the preferred embodiment, cover 120 is made from a single sheet of material rather than two pieces sewn together at the ends. Moreover, the outer cover 120 is not formed into a tube shape and does not have any end seams. The flexitank is shorter than the internal length of the shipping container and its ends fall short of the end walls of the container.

[0023] The cover 120 for the flexitank is preferably constructed from layers of a 610 gram per square meter vinyl fabric on a base reinforcing scrim of either a 14×14 or 20×20 per centimeter polyester thread. Such a relatively high thread count of the scrim provides added strength for the carriage of liquids with a specific gravity higher than water. The diameter of the cover is customized when the flexitank is used in a 40 foot container depending on the amount and viscosity of the liquid material.

[0024] As mentioned previously, the primary function of the inner bladder 110 is to keep intact the liquid contents therein. Specifically, the inner bladder 110 is made of a material that will not chemically interact with the liquid. Moreover, the inner bladder 110 will not physically interact with the liquid, such as by shedding particles of itself into the liquid, or leaching chemical components of the inner bladder 110 into the liquid. It is essential that the inner bladder 110 does not in any way compromise the liquid, as that would ruin or diminish the value of the liquid.

[0025] It is the primary function of the outer cover 120 to offer physical reinforcement and protection to the inner bladder 110 and the entire flexitank, and thus protect the liquid during shipment in a 40 foot container. As described herein, the construction and selection of durable and flexible materials that comprise the outer cover 120 is important to this function. In one preferred embodiment, the outer cover 120 is constructed of a polymeric material or PVC plastic.

[0026] In a particular embodiment for a 40 foot shipping container with no bulkhead, the outer cover 120 is preferably constructed of a PVC plastic that has incorporated within it a flexible woven scrim 121 comprised of a polymeric material so that outer cover 120 has sufficient strength and flexibility to safely contain the liquid contents during all phases of transport without introducing any other unnecessary disadvantages. The scrim 121 is made of polymeric, polyester or nylon fibers densely woven in a manner, such as an orthogonal criss-cross pattern, to maintain its integrity during production of outer cover 120 and use in a flexitank. The weave of fibers creates a corresponding pattern of holes between the fibers, and the weave of fibers and holes being important aspects of the preferred embodiments of outer cover 120.

[0027] There are two alternative methods of coating scrim 121 to produce outer cover 120. In the first method, the scrim 121 is sandwiched by, or placed between, two layers of PVC 122, 123. A layer of PVC 122 is covered by scrim 121, and that is covered by a second layer of PVC 123. See FIGS. 8 and 9. The sandwich of 122-121-123 is then heated and pressed together such that the two PVC layers 122, 123 melt and are forced through the holes in the woven scrim 121, and meld with one another, thereby creating an integral outer cover 120 that is a single piece of melded PVC with an inner core of scrim 121. In the second alternative method, scrim 121 is coated on one side by a layer of molten PVC polymer 122. Once completed, the scrim 121 is turned over and the reverse side is coated with a second layer of molten PVC polymer 123. In either of these alternative methods, a strong yet still light outer cover 120 is created that can handle the physical pressures and protect the flexitank 100.

[0028] The weave of of fibers and the size of the holes in scrim 121 is an important feature of the preferred embodiments for flexitanks used in 40 foot shipping containers. If the holes of scrim 121 are too small, not enough bonding occurs between the two layers of PVC 122, 123, and the outer cover 120 will lack integrity. If the holes are too large, outer cover 120 will not have sufficient strength to fulfill its protective function or will have a disadvantageous strength-to-weight ratio. In a flexitank having a typical capacity for a 40 foot shipping container, the scrim 121 is preferably woven such that there are between 144 and 289 holes per square inch. This corresponds to a weave pattern that provides between 12 to 17 holes per linear inch, and a pattern of between 12×12 and 17×17 holes per square inch. In a more preferred embodiment, the scrim is woven such that there are between 169 and 225 holes per square inch. This corresponds to a weave pattern that provides between 13 to 15 holes per linear inch, and a pattern of between 13×13 and 15×15 holes per square inch. In a most preferred embodiment, the scrim is woven such that there are 196 holes per square inch. This corresponds to a weave pattern that is 14 holes per linear inch, and a pattern of 14×14 holes per square inch.

[0029] While the number of holes per square inch is important, it is also important that the size of the holes be large enough, yet not too large. Preferably, the holes are between 0.0030 square inches per hole and 0.0055 square inches per hole. In a more preferred embodiment, the holes are between 0.0035 and 0.0045 square inches per hole. In an even more preferred embodiment, the holes are between 0.0037 and 0.0040 square inches per hole. Related to this is the portion of the total surface area of the scrim 121 that consists of the woven fibers, and the portion of the total surface area that consists of holes within the woven fibers, and through which the PVC layers 122, 123 can meld together. In a preferred embodiment, the holes within the woven fibers comprise between 65-85% of the total surface area. In a more preferred embodiment, the holes comprise between 70-80% of the total surface area. In an even more preferred embodiment, the holes comprise between 74-78% of the total surface area.

[0030] A flexitank having an outer cover 120 according to the preferred embodiments operates much like conventional flexitanks but is superior in several respects. In particular, it is optimized for use in 40 foot shipping containers having no bulkhead. If a flexitank sized for a 40 foot shipping container is produced by simply taking an existing flexitank design for a 20 foot shipping container flexitank and modifying its dimensions to fit the 40 foot shipping container, it will fail due to the increased capacity and increased dynamic forces created when liquid travels 40 feet instead of 20 feet. If the existing flexitank design for a 20 foot shipping container is additionally modified by strengthening the materials, it will be too heavy to be useful for shipping in a 40 foot containers. Flexitanks have to be moved around and manipulated when empty. The flexitanks of the preferred embodiments should be used with other shipping precautions. There may be non-stick floor mats placed under the flexitank to prevent sliding of the flexitank on the floor of the 40 foot shipping container. Also, capacity bands can be used around the flexitank as a simple and modest way of suppressing wave action inside the flexitank. Preferably, there are a plurality of different length capacity bands made available with the flexitank according to the preferred embodiments, a particular one of the capacity bands being chosen and used in a particular shipment according to the volume of liquid in the flexitank and/or the viscosity of the liquid in the flexitank.