US 3653084 A
An inflatable structure and method of making it. The structure comprises a knitted fabric body shell, which has been impregnated with a curable elastomeric material, which material forms an outer surface coating in the structure. The fabric body shell is made up of a knitted fabric, and before impregnation is manufactured to have a shape, were the shell in an inflated condition, roughly corresponding to the shape of the finished article or structure. An inflatable, flexible-walled bladder, having substantially the same shape when inflated, is provided within the body shell to enable shaping of the body shell through inflation of the bladder. With the body shell shaped by inflation of this bladder, the elastomeric material is applied, as by spraying or brushing, to impregnate the body shell and to form a protective covering about the outside of the body shell covering any seams, etc. The bladder may remain in the structure on its completion, and for this purpose may have an elastomeric coating applied about its outer surface which cures to form a rubber-like coating on the inside of the fabric body shell.
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Description (OCR text may contain errors)
United States Patent Hartman  INFLATABLE STRUCTURE Michael G. Hartman, 11 1/2 Mile Steese Highway, Fairbanks, Ala. 99707  Filed: Apr.2,l970
 Appl.No.: 25,181
Primary Examiner-Milton Buchler Assistant Examiner-Gregory W. O'Connor At!0rneyl(0liSCh & Hartwell [4 1 Apr. 4, 1972 [5 7] ABSTRACT An inflatable structure and method of making it. The structure comprises a knitted fabric body shell, which has been impregnated with a curable elastomeric material, which material forms an outer surface coating in the structure. The fabric body shell is made up of a knitted fabric, and before impregnation is manufactured to have a shape, were the shell in an inflated condition, roughly corresponding to the shape of the finished article or structure. An inflatable, flexible-walled bladder, having substantially the same shape when inflated, is provided within the body shell to enable shaping of the body shell through inflation of the bladder. With the body shell shaped by inflation of this bladder, the elastomeric material is applied, as by spraying or brushing, to impregnate the body shell and to form a protective covering about the outside of the body shell covering any seams, etc. The bladder may remain in the structure on its completion, and for this purpose may have an elastomeric coating applied about its outer surface which cures to form a rubber-like coating on the inside of the fabric body shell.
4 Claims, 4 Drawing Figures PATENTEUAPR 4 I972 INVENTOR. MZWAEZ 1 44/97/64 BY K UQQD d NM INFLATABLE STRUCTURE BACKGROUND OF THE INVENTION The present invention concerns inflatable structures, and a method of manufacturing such structures. While the invention is not so limited, representative of the type of structure which may be manufactured according to the invention is an inflatable watercraft. Accordingly, a preferred embodiment of the invention is discussed in connection with the fabrication of such an article, although obviously the invention pertains to other types of manufacture.
Inflatable structures usually have been constructed by sewing or cementing together plural pieces of rubberized or otherwise treated fabric. Thus, a life raft could be constructed by securing together pieces of fabric coated with a rubber-like material, to produce a structure which, when inflated, has the shape desired in the raft. Using such a procedure, it is possible to produce structures of almost any desired shape, however the technique described includes a number of disadvantages. For one thing, the particular method described involves a number of individual steps which are time-consuming and costly. Furthermore, in the final structure distinct seams are present which are not covered up in any manner, making the completed structure somewhat vulnerable to leakage and collapse, due to tearing or parting of the seams under operational stresses.
SUMMARY OF THE INVENTION One general object of the invention is to provide an improved type of inflatable structure.
Another object is to provide a novel process for making such a structure.
Another object is to provide an improved process for manufacturing inflatable structures which permits a manufacturer easily and at a competitive price to manufacture specialized structures according to customer's specifications.
It is still another object of the invention to provide a continuous closed, inflatable structure having improved structural characteristics.
Yet a further object of the invention is to provide an inflatable structure having a substantially continuous surface coating of elastomer material which covers and impregnates an underlying body shell and seams provided in said shell.
BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein:
FIG. 1 is a perspective view illustrating a structure of the type that may be manufactured as contemplated herein, such structure being a life raft;
FIG. 2 is a side elevation of the life raft;
FIG. 3 is a cross-sectional view, taken generally along the line 3-3 in FIG. 2; and
FIG. 4 is a view of a sectional piece of the raft, with portions broken away to illustrate details of interior construction.
DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, illustrated in the figures is one form of inflatable structure such as may be manufactured according to the invention, the structure comprising an inflatable raft, designated generally at 9. Such raft includes an endless, inflatable tube designated at 10, forming opposed sides 11 and 12 and the bow and stem of the raft, designated at 14 and 15 respectively. A floor in the raft is shown at 17. As is brought out hereinafter, the floor is not inflatable in the particular raft shown.
The particular raft depicted has raised bow and stem sections, to inhibit the flow of water over the ends of the raft, particularly when it is operated in rough water. Perhaps as best illustrated in FIG. 3, the floor is located somewhat upwardly from the water-engaging surfaces of the endless tube in the raft, i.e., the bottoms of sides 11 and 12. As a result, a tunnellike space is formed between the floor of the raft and the surface of the supporting water. The construction contemplated reduces the water contacting surfaces of the raft, and has been found to permit easier maneuvering of the raft in rough water.
Completing the general description of the raft, inflation of the inflatable part of the raft, i.e., tube 10, is through a valve shown at 13. The valve shown at 18 in the floor of the raft is provided to permit draining of water from the interior of the raft when such collects above the floor.
Considering now in more detail the construction of the inflatable portion of the raft, and the means of manufacturing such structure, it is contemplated that as part of the process of making the raft a bladder such as that shown at 22 be prepared, having flexible, but substantially nonstretchable walls, the bladder when inflated having substantially the shape desired in the inflated structure of the raft, i.e., the tube 10. The bladder functions as a form for a fabric body shell which is assembled about the outside of the bladder, and by functioning as a form maintains such shell in proper shape during the time that an elastomeric coating is prepared about the outside of the shell.
When making a tube, such as forms the perimeter of the raft shown in FIG. 1, the bladder should have an inflated shape that generally corresponds to the shape of the tube when inflated. The bladder may be made of a film which is flexible, but preferably not substantially stretchable as is the case of the usual rubber material. Exemplifing a film which is suitable for the manufacture of such a bladder is the film marketed as Tuftane" by the B. F. Goodrich Chemical Company. Such is a polyurethane film, which is resistant to most common organic solvents, and has considerable strength (being approximately twice as strong as a polyvinylcloride film of equal thickness).
In preparing a tube or tubing about this bladder, initially a fabric body shell is prepared using a knitted fabric. A knitted fabric, whether it be produced by weft knitting or warp knitting, the latter technique corresponding to crocheting, generally can be characterized as being constructed on a loop basis, with the yarn in the fabric formed in concurrent intermeshing loops. Because of this structure, the fabric has a degree of elasticity both in a course direction, which is the direction of the row which is produced as knitting proceeds, and in a direction perpendicular to this course direction. A knitted fabric is also selected since such enables minimizing of seams in the fabric body shell, knitting accommodating certain corners and bends in the makeup of the fabric not permitted in other fabrics.
The knitted body shell is made of such a size that on its being assembled about the bladder, and on the bladder being subsequently inflated, the fabric of the body is stretched slightly in all directions. Thus, the shell without stretching is somewhat smaller than the bladder with the latter in its inflated condition. The stretching, and the consequent stresses introduced into the various courses of the fabric body shell, is the result of internal expansion of the bladder which the body shell encompasses. There is no twisting or pulling on the fabric body itself to produce a tight fit about the bladder.
In making the tube or tubing of FIG. 1, an elongated knitted sleeve may be prepared having unjoined ends. A bladder may be prepared which first takes the form of an elongated sleeve with unjoined ends, and such may be inserted into the interior of the knitted sleeve. The ends of the sleeve which forms the bladder may then be suitably sealed together to form a continuous hollow bladder. Subsequently the ends of the knitted sleeve may be joined in a suitable manner, as by knitting or other securing procedures. In FIG. 4 and in FIG. 3, the joint formed where the ends of the knitted sleeve come together is indicated at 19a, 1912.
By indicating one procedure for assembling the sleeve about the bladder, it is not intended to exclude other means of assembly. For instance, the bladder may be made as a hollow continuous structure and the fabric body shell prepared by first knitting an elongated strip of material and then laying such over the bladder. The margins of the material may then be brought together as by sewing or knitting along a line which extends circumferentially of tube or tubing 10.
It is contemplated that the bladder prepared have means for introducing fluid under pressure, such as air, thereinto, to inflate the same. For instance, a football-type valve may be provided in some region of the bladder which receives a needle utilized to inflate the bladder. Such needle is easily inserted through one of the loops of the knitted structure and into the valve for the purpose of inflation.
In a preferred embodiment of the invention, the bladder, prior to consolidating the knitted fabric body shell about the bladder, is coated with a curable coating composition which cures to form an elastomeric covering about the bladder. For this purpose, the same coating composition may be utilized which is utilized to impregnate and form an outer covering over the fabric body shell to be described hereinafter. The advantage of such a coating on the bladder is that when such is inflated, the coating is pressed against the inside of the fabric body shell to form a fluid-tight barrier on the inside of the shell. This covering also may bond to some extent to the coating composition applied to the fabric body shell to impregnate the shell, to produce a unitized structure of the bladder and the shell.
In the manufacture of floor l7, and for the purpose of securing web 21 in place which forms part of the floor, a flange is formed which extends about the inner perimeter of tube or tubing 10. As probably best shown in FIG. 3, such may be prepared by flattening the body shell along a portion thereof extending about the inner perimeter of the shell, and sewing a seam to maintain this portion flattened. The material between this seam and the outer edge of the flattened portion of the sleeve is utilized as the flange. By indicating a particular procedure for forming a flange, however, it is not intended to preclude other means of preparing the flange, such as by sewing a piece of material onto the inner periphery of the tube. Furthermore, of course, in articles where a floor is not a requirement the flange may be omitted. As shown in FIG. 3, knitted web or sheet 21 is secured, as by sewing, to flange 20.
In the completed life raft, the fabric part of the construction has a minimum number of seams. Those seams that are present are covered and further made more secure by the application of a coating composition to the outside of the fabric body shell, which impregnates such shell and forms a protective covering over the outside thereof, as now will be described.
The coating composition which is utilized is one which on curing forms an elastomeric covering impregnating the knitted structure of the body shell and preferably forming a protective, continuous and fluid-tight covering about the outside of the structure. Various coating compositions will suggest themselves to those skilled in the art. I have found that the so-called Hypalon coatings (Hypalon" being a registered trademark of E. l. du Pont de Nemours & Company, Inc.), which are coating compositions containing chlorosulfonated polyethylene polymers in solution, are highly effective. Such chlorosulfonated polyethlene polymers are more fully disclosed in US. Pat. No. 2,586,363, issued Feb. 19, i952, and coatings from such polymers are described in detail in US. Pat. No. 2,854,425, issued Sept. 30, 1958, and in a publication entitled Coatings of Hypalon 20 Synthetic Rubber prepared by lrvan D. Roche, dated Nov. 1956 in a report of E. I. du Pont de Nemours & Company numbered 56-10. In general terms, the coating composition may be applied by spray, brush, or dipping techniques, to the fabric body shell prepared as described above, with such subsequentially curing to form a tough, flexible, elastomeric protective coating extending about the exterior of the fabric body shell.
The coating composition is applied with such then impregnating the fabric body shell with the interior bladder inflated. With inflation of the bladder, the knit material of the fabric body shell becomes fully and evenly tensioned, both in the direction of its course and in the warp direction. The
material lies flush against the surface of the bladder at all points about the structure. With application of the coating composition, such impregnates the evenly tensioned fabric body shell to fill the interstices thereof, and also to come against the internal bladder, and if such has been covered with an elastomeric covering, to bond with such covering. With a number of coatings prepared over the fabric body shell, ultimately a protective covering of cured elastomeric material is produced forming a tough protective outer covering about the inflatable structure which is fluid-tight.
Illustrating the manufacture of an inflatable structure as contemplated by the invention, a curable coating composition is prepared by first preparing a so-called grind composition from the following constituents, with the ratios indicated:
Toluene 50 arts Butanol 2 5 parts Mineral spirits 35 parts Tribasic lead maleate 40 parts Super multifex (Calcium carbonate from Diamond Alkali Company) 50 parts Phthalic acid 2 parts Thiuram E (tetraethylthiuram disulfide) 1.5 parts The composition is ground in a pebble mill to obtain dispersion of the various ingredients.
A polymer solution is then introduced to the grind solution, with continued grinding in the pebble mill. Such polymer solution has the following formulation:
Toluene Hypalon 20 25 parts 5 parts Grinding is continued to complete the dispersion of the various ingredients of the compounded mixture.
The product of the pebble mill is then let down with stirring into this additional polymer solution to mix all the ingredients and obtain a curable coating composition which may be applied with spray techniques.
An assembly comprising a bladder encompassed by a knitted fabric body shell is prepared as described above. Prior to assembly of the body shell and bladder, the bladder has an elastomeric covering prepared about the outside thereof, by spraying onto the bladder the coating composition described above. With the assembly prepared the bladder, equipped with a football-type valve, is inflated, using a needle inserted through the fabric of the body shell, to produce slight stretching and equalized tensioning of the body shell in warp and course directions.
Subsequently, an outer covering is prepared using a coating composition which impregnates the interstices of the fabric body shell and builds up on the outer side of said fabric body shell. Such may be prepared by spraying the coating composition, preferably in multiple applications, against the fabric body shell. With the bladder earlier having been coated with the coating composition used to prepare the outer covering, the elastomeric covering which results adheres to the covering of the bladder to produce a unitized structure from the assembly. Where a web like web 21 is present, coating composition is applied to opposite sides of this web.
A valve is mounted on the resulting tube, to be used for general inflation and deflation purposes, by cutting a hole where desired in the tube, and mounting therein a conventional commercially available valve which is secured in place by members in the valve which clamp against inner and outer surfaces of the tube adjacent margins of such hole.
The structure which results is highly resistant to tearing, ripping, and other damage because of the knitted composition of the fabric body shell, the latter having a degree of stretch in all directions. The elastomeric coating produced from the tough abrasion resistant coating composition is water-tight, and protects the cord structure of the fabric body shell.
Summarizing some of the features of applicant's invention, it will be noted that the fabric body shell is made initially to a shape which generally corresponds to the final shape which the shell is to have in the completed structure as supported by the bladder. The bladder itself includes walls which are flexible but not substantially stretchable, and the bladder also is made to have a shape when inflated which corresponds to the shape of the final inflated structure. Thus, when the bladder is inflated it serves to fill out within the fabric body shell and produce a tensioning of the material thereof, in both a warp and a course direction, which is substantially uniform. Absent in the method is any twisting or pulling of portions of the fabric body shell which results in uneven tension applied to parts thereof. Tension which is produced in the body shell is the result of an internal expansion of the bladder.
The coating composition which is applied forms a covering which impregnates and extends about the outside of the fabric body shell. The bladder initially used to shape the fabric body shell may become an integral part of the final assembly.
The method described can be used to fabricate other structures than rafts, for example the fabrication of inflatable mattresses of a variety of shapes is possible, as is the fabrication of collapsible tanks for the transportation of food and materials. Further, it should be noted that the inflatable structures may comprise multiple compartments where such is desired.
It is claimed and desired to secure by Letters Patent:
1. A method of fabricating an inflatable structure compris- 6 ing preparing an inflatable bladder which has a shape when inflated that generally corresponds to the shape of the final structure,
preparing about said bladder an enveloping knitted fabric body shell which envelops the bladder and which has a generally corresponding inflated shape, said shell absent any stretching therein being of a smaller size than the bladder with the latter in its inflated condition,
with the body shell prepared inflating the bladder to enlarge it and to produce from the bladder an internal support for the body shell, and simultaneously stretching the body shell in both warp and course directions of the knitted fabric in the shell thus to evenly tension it where it extends about the inflated bladder, and
with the body shell so supported and tensioned then preparing a cured elastomeric coating which forms a protective covering over the outside of the body shell and which also permeates the interstices of the body shell.
2. The method of claim 1, wherein the body shell is prepared about the bladder by placing a knitted piece on the bladder and joining end margins of such piece to have the piece extend continuously about the bladder, and the coating composition is applied over such end margins where they are joined to form a coating over such location of joinder.
3. The method of claim 1, wherein an elastomeric layer is prepared about the outside of said bladder prior to preparing said fabric body shell about the bladder, and the curable coating composition is applied with such permeating the fabric body shell and on curing bonding to said elastomeric layer where the coating composition has permeated through the body shell.
4. The method of claim 1 wherein the bladder has flexible walls of limited stretchability whereby on inflation it assumes a predetermined inflated size.