MXPA01002526A - Method for fabricating composite pressure vessels and products fabricated by the method - Google Patents

Abstract

A process for fabricating a composite vessel includes the steps of:A) preforming (e.g., by winding fiber and at least one thermoplastic substance onto a thermoplastic liner) a thermoplastic shell which has at least one opening for access to the interior;B) extruding a circular cross section of a fluid parison of thermoplastic material (which preferably is chosen to have a melting point lower than that of the thermoplatic shell) into the interior of the thermoplastic shell through the opening;C) in a mold, applying at least one force (such as gas under pressure) which tends to urge the fluid parison toward the interior walls of the thermoplastic shell (which may be preheated prior to introduction into the mold) such that the fluid parison imparts heat to the thermoplastic shell;D) continuing step C) until the thermoplastic shell and the fluid parison consolidate to form a composite vessel;E) cooling the vessel until it is solidified;and F) removing the vessel from the mold. For some composite vessels, prior to step C), an insert may be introduced into the interior of the parison and positioned in alignment with the opening in the thermoplastic shell such that the insert is rendered integral with the composite vessel during step D). Suitable thermoplastic materials include polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate. The resulting composite vessel exhibits superior mechanical and aesthetic properties.

Description

METHOD FOR MANUFACTURING PRESSURE TANKS COMPOUNDS AND PRODUCTS MANUFACTURED BY THE METHOD Field of the Invention This invention relates to the technique of manufacturing pressure tanks and, more particularly, to improved methods for manufacturing composite pressure tanks and composite pressure tanks made of according to the improved methods. BACKGROUND OF THE INVENTION Pressure tanks, such as hot water heaters, boilers, pressurized gas tanks and the like, have traditionally been manufactured from a metal such as steel. However, in recent years, the use of composite pressure tanks has become more frequent. These composite pressure tanks have typically been manufactured by a filament winding process that uses thermosetting plastic resins such as expoxies, polyesters and vinyl esters. Briefly, this technology is the process of impregnating dry fibers such as fiberglass filaments, with resin catalyzed before application to a core. Pre-impregnated fibers ("prepreg") can also be used. The core and the applied compound are then solidified, at room temperature or with heat, to apply the laminate and obtain a hard laminate coating of fiber and resin. This coating is either removed from the soul or the soul itself becomes part of the finished product. Although the specific application of the product determines the exact function of the resin, in any case it serves as the supporting structure to keep the continuous filaments of fiber in position. The thermosetting resins used in these processes can be classified as the low temperature product type that is characterized by its relative type of use, low cost and availability. These resins have served to meet the performance requirements of a wide range of pressure tank products. However, these resin systems have well-known disadvantages that may include their limited temperature capabilities, unsatisfactory aesthetics in the final product, lack of long duration, lack of adequacy for recycling and issues related to manufacturing such as loss of time due to cleaning and material handling costs. In addition, there are environmental concerns that arise from worker exposure to steam, overrun, emissions, etc., found during manufacturing processes. Some designed thermosetting resins improve performance through higher temperature capacity, but unacceptable material costs are associated with them. In addition, due to the materials and processes employed, composite pressure tanks prepared in accordance with prior art processes inherently have residual and significant internal stresses that, together with certain incompatibilities of material temperature sensitivity, limit the Pressure and temperature ranges in which pressure tanks find use. Thus, the increase in performance demands, environmental problems, manufacturing problems and new market opportunities have emphasized the limitations of the use of thermosetting resins in the manufacture of composite pressure tanks. Compound pressure tanks, with characteristics of greater temperature and pressure capabilities, improved appearance and greater durability and impact resistance, and that in terms of manufacturing, are environmentally more favorable, better cost effective, and present few problems of manufacturing, are according to the above highly desirable. Therefore, it will be recognized by those skilled in the art that a process for manufacturing composite pressure tanks that achieve improvements in all these areas requires a fundamentally different philosophy. It is to the provision of such a fundamentally improved process, and to pressure tanks made by such a process that the present invention is directed and by which the following characteristics are obtained: improved contact at higher temperatures between the fiber and the resin, better control over the frame / mold ratio, waste materials that can be recycled effectively, decrease in regulatory problems caused by emissions, higher processing speeds for the winding (or other form of coating) and for the solidification stages , potential savings in labor due to less material handling, reduction of floor area, adaptability to automation, a safer environment for employees, simplification of processing and storage lines and material handling, faster times of conversion, faster commissioning, lower training costs, lower energy costs, etc. Therefore, pressure tanks manufactured according to the process are substantially tension free and exhibit improved performance over pressure tanks of the prior art in which, inter alia, they can withstand higher pressures and temperatures, are more resistant to impact and they also have a significantly better finish. Objectives of the Invention It is therefore a broad object of this invention to provide an improved process for manufacturing a composite pressure tank.

It is a more particular object of this invention to provide an improved process having advantages that include, as opposed to prior art processes for manufacturing composite pressure tanks: better control over the frame / mold ratio, waste materials that can be recycled effectively reducing regulatory problems caused by emissions, higher processing speeds for the winding (or winding alternatives) and for the solidification stages, substantial labor savings due to less material handling, reduction of the area of floor, susceptibility to automation, a safer environment for employees, simplification of processing and storage lines and material handling, faster conversion times, faster start-up, lower training costs, lower energy costs , etc. In another aspect, it is an object of this invention to provide a process for manufacturing composite pressure tanks which, in use, enjoy long-term performance at least as good as that of traditional pressure tanks. In yet another aspect, it is an object of this invention to provide high quality composite pressure tanks manufactured according to new processes.

In yet another aspect, it is an object of this invention to provide high quality composite pressure tanks that have improved durability, impact resistance and corrosion resistance, as well as handling characteristics of higher temperature and pressure and that also have good performance attributes. machinability and can therefore be easily welded, cut, punched, threaded, stamped or the like as desired to produce a finished product of high quality. SUMMARY OF THE INVENTION Briefly, these and other objects of the invention are achieved by a process for manufacturing a composite tank that includes the steps of: A) preforming (e.g., when winding fiber, such as fiberglass, and at least one thermoplastic substance on a thermoplastic liner) a thermoplastic coating for the tank, the thermoplastic coating of which has at least one opening for access to the inside thereof; B) extruding a generally circular cross-section of a fluid parison of thermoplastic material (which is preferably selected to have a melting point that is less than that of the thermoplastic coating) within the thermoplastic coating through at least one aperture in the same; C) in a mold, apply at least one force (such as gas under pressure) that tends to drive the fluid parison towards the inner walls of the thermoplastic coating (which can be preheated before the introduction into the mold) in such a way that the fluid parison imparts heat to the thermoplastic coating; D) continuing step C) until the thermoplastic coating and fluid parison are consolidated to form a composite tank; E) cool the composite tank until it solidifies; and F) removing the formed composite tank from the mold. For some composite tanks, before stage C), it can be inserted or inserted into the interior of the parison and placed in alignment with the opening in the thermoplastic coating such that the insert is integrated with the composite tank during step D). Suitable thermoplastic materials include polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate. DESCRIPTION OF THE DRAWINGS The object of the invention is particularly pointed out and clearly claimed in the conclusion portion of the specification. However, the invention, both in terms of the organization and the method of operation, can be better understood by reference to the following description taken in conjunction with the appended claims and the accompanying drawings of which: Figure 1 is a perspective view of a liner / soul used to practice a first inventive modality; Figure 2 is a cross-sectional view taken along lines 2-2 of Figure 1; Figure 3 is a perspective view of the liner / core shown in Figures 1 and 2 being coated with a layer of a mixed thermoplastic fiber material; Figure 4 is a view of the liner after being coated with the layer of the mixed thermoplastic fiber material and includes an enlarged, fragmented transverse view; Figures 5A, 5B and 5C are cross-sectional views taken along lines 5-5 of Figure 3 illustrating three variants of a first type of material that can be wound on the thermoplastic liner to effect the coating; Figure 6 is a cross-sectional view taken along lines 6-6 of Figure 3 illustrating a second type of material, a strand of any of the three variants illustrated in Figures 5A, 5B and 5C, which can be rolled on the thermoplastic lining to effect the coating; Figure 7 is a cross-sectional view taken along lines 18-18 of Figure 3 illustrating a third type of material, a yarn of the second type of material, which can be wound onto the thermoplastic liner to effect the coating; Figure 8 is a transparency view of a mold showing the modified liner contained in a mold in which it is subjected to heat and at least one force tending to push the modified liner towards the shape defined by the interior surface of the mold; Figure 9 is an enlarged partial cross-sectional view of the modified liner illustrating the effects of heat and strength therein; Figure 10 is a view similar to Figure 8 showing the modified liner contained in a different type of mold; Figure 11 is a cross-sectional view of an open mold containing a preformed thermoplastic component of a pressure tank manufactured according to a second inventive embodiment; Figure 12 is a view similar to Figure 11 illustrating a step in the second inventive embodiment in which a parison of fluid thermoplastic material is introduced into the interior of the preformed component as a second component of a composite pressure tank to be formed; Figure 13 is a cross-sectional view similar to Figures 11 and 12, but with the mold closed and the components of the pressure tank subjected to a force that forms the pressure tank against the interior wall of the mold; Figure 14 is a cross-sectional view of an open mold containing a preformed thermoplastic component of a pressure tank manufactured according to a third inventive embodiment and also a thermoplastic liner component disposed within the interior of the first component; Figure 15 is a cross-sectional view similar to Figure 14, but with the mold closed and the components of the pressure tank being subjected to a force forming the pressure tank against the interior wall of the mold; Figure 16 is a cross-sectional view of the finished composite pressure tank prepared by the process shown in Figures 14 and 15; Figure 17 is a cross-sectional view of an open mold containing a preformed thermoplastic component of a pressure tank manufactured according to a fourth inventive embodiment and also a shell component positioned exterior to the first component and an interior shell component positioned in the inside of the first component; Figure 18 is a view similar to Figure 17, but with the mold closed and the force producing components coupled to the mold; Figure 19 is a view similar to Figure 18 showing the pressure tank being formed in the mold under the influence of heat and one or more forces urging the components of the pressure tank to conform to the outline of the interior wall of the mold. mold; Figure 20 is a cross-sectional view of the finished composite pressure tank prepared by the process shown in Figures 17, 18 and 19; Figure 21 is a cross-sectional view of a mold containing a preformed thermoplastic component of a pressure tank already provided with a thermoplastic liner, the pressure tank being manufactured according to a fifth inventive mode; Figure 22 is a view similar to Figure 21 showing the pressure tank being formed in the mold under the influence of heat and one or more forces urging the components of the pressure tank to conform to the contour of the inner wall of the mold; and Figure 23 is a cross-sectional view of the finished composite pressure tank prepared by the process shown in Figures 21 and 22. Description of Preferred Modality (s) Referring first to Figures 1 and 2, HE shows a thermoplastic liner / core 1 for a composite pressure tank to be manufactured according to a first inventive mode. In the exemplary embodiment, the liner / web 1 is a generally elongated preformed structure terminating at each end in a configuration of dome 2, 3 having a central axial opening 4, 5. The . ••• ^ M ^^ A ^.

The thermoplastic liner 1 can be made of, for example, polypropylene, polyethylene, polybutylene terephthalate, polyethylene terephthalate or fiber (for example, glass fiber) of impregnated polypropylene, polyethylene, polybutylene terephthalate or polyethylene terephthalate or other thermoplastic material with suitable features and can be prepared by any suitable conventional process such as molding a combination of cut fibers, directional fiber fabric, woven and / or stitched or welded bonded together in the shape of the tank and mixed with thermoplastic material. As shown in Figure 3, a fiber filament, strand, thread or ribbon 6 (eg, glass fiber, carbon fiber, boron fiber, etc.) and a material Thermoplastic materials are wound methodically onto the outer surface of the thermoplastic liner 1 to form a substantially uniform coating 7 as shown in the enlarged partial cross-section in Figure 4. This step can be carried out, for example, by mounting the thermoplastic liner 1 on the web 8 and rotating the liner as indicated by the arrow 9 while methodically feeding (n) the filament (s), strands, thread or ribbon 6 from a lateral source and reciprocally transverse as shown by double arrow 10 and continuing this procedure until the coating 7 has reached the desired thickness.

The material 6 can be rolled "cold" onto the thermoplastic liner 1 or it can be passed through a heater 12 which, in some applications, results in a more uniform coating 7 (Figure 4) with better functional characteristics and / or aesthetics. The resulting structure 11 is further processed then as will be described in detail below. It has been found desirable to suitably vary the feed ratio in the regions of the domes and end pieces, so that a substantially uniform thickness of the coating is obtained through the length of the liner 1. Alternative winding techniques to achieve a satisfactory coating uniform are well known in the prior art, and reference may be made, for example, to US Pat. 3,282,757 entitled METHOD OF MAKING A FILAMENT REINFORCED PRESSURE VESSEL, (METHOD OF ELABORATING A REINFORCED FILAMENT PRESSURE TANK) by Richard C. Brussee, incorporated herein by reference and which describes various winding techniques that can be employed in the practice of present invention. However, the shape, and especially the type of the fiber and the thermoplastic material 6 is of significant importance for the practice of the invention so that attention is briefly directed to Figures 5A, 5B, 5C, 6A, 6B and 7 which illustrate suitable variants of the material 6 that can be employed in the practice of the invention. In Figure 5A separate yarns of the thermoplastic material 13A and the fiber 12A are wound together or separately, but more or less contiguously, as indicated in 6A, on the liner / core 1. The types of suitable thermoplastic material 13A which can be used in the practice of the invention for this purpose include, but are not limited to, polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate. Figure 5B shows a cross section of a second variant 6B for the material 6 in which the fiber filament 12B is coated with the thermoplastic material 13B by, for example, double extrusion or by any other suitable preliminary process. Similarly, Figure 5C shows a cross section of a third variant 6B for the material 6 in which the fiber filament 12C is coated with a powder of the thermoplastic material 13C. However, preferably the fiber 12 and the thermoplastic material 13 (in any of the forms shown in Figures 5A, 5B, 5C), before being wound on the liner / web 1, are first mixed in a 6D strand as shown in Figure 6A or in a wire 6E of such strands as shown in Figure 6B. Another preferred configuration for the material 6 is shown in Figure 7 as a 6F ribbon of mixed fiber and thermoplastic material. Mixed fiber strands, yarns and tapes, for example, glass fiber, and thermoplastic material are commercially available, and a family of products that has been found to be very suitable for use in the present invention is distributed under the Twintex brand. ® by Vetrotex. Twintex is prepared by a proprietary process involving mixed filaments of fiberglass (eg, 17 micrometers in diameter) with filaments (eg, 20 micrometers in diameter) of thermoplastic (eg, polyethylene or polypropylene) during production continuous of threads, threads and ribbons that are available as such and also in the form of fabrics. Thus, only by way of example, the thermoplastic liner / core 1 can, itself, be fabricated from Twintex fabric "which is sewn or welded together and is properly treated with heat, for example, in a mold to obtain the preform that is subsequently wound with the fiber and the thermoplastic material 6 to obtain the intermediate structure 11. Referring now to Figure 8, after the intermediate structure 11 has been prepared as described or in any suitable manner, it is placed in a mold 13 (two pieces in the example). The mold is then heated, for example, by built-in resistance heaters represented by the heater 15B controlled in a controllable manner from an E 15A source and / or by circulating hot oil, heated by an H 14A source, through coils 14B and / or any other suitable convenient conventional mold heating. In addition, at least a force is applied to the mold 13 and / or to the interior of the intermediate structure 11 which tends to cause the outer surface of the intermediate structure to conform to the inner surface 13A (Figure 9) of the mold when the heat Q applied causes the thermoplastic liner 1 and the rolled-up liner 7 to melt together and flow against the mold. The force or forces can be generated by applying external compression to the mold halves to propel them together as indicated by the arrows designated "F" and / or by pressurizing the interior of the thermoplastic liner 1, for example, using a gas pressure from a suitable source 16 conveyed within the liner 1 through a conduit 18. If pressurization is employed, the lids 19 (threaded or permanent) serve to seal the ends of the intermediate structure 11. Then, the heat is removed from the mold 13 allowing the now formed composite pressure tank to harden and be removed by opening the mold in a conventional manner.

In practice, two important optional considerations can be taken into account. First, it has been found that the mold must be vented, as represented by the peripherally distributed ventilation holes 17 shown in Figure 8, to allow the retained air to escape while the pressure tank is formed against the inner wall of the mold and thus achieve a particularly fine finish on the outer surface of the pressure tank which requires, if at all, little additional finishing of the surface. Second, in order to ensure complete fusion between the thermoplastic liner 1 and the rolled overlay 7, it has been found preferable to select respective materials with somewhat different melting temperatures for the liner and the coating. More particularly, the best results are obtained if the heat ratio is controlled and it is selected that the melting point of the liner is above that of the coating so that the thermoplastic material effectively melts around the fiber while the Lining softens, but does not fully melt during the molding process. For example, as is well known in the art, the melting point range of polypropylene is 300 ° F to 330 ° F while that of polyethylene is 120 ° F to 140 ° F. As shown in Figure 10, the composite pressure tank can be manufactured according to a process . . . -,. . . .. . r- and. . . A similar one in which a two-piece mold 20 is used, provided with coupling flanges 21, 22 which interlock together thereby completely defining a predetermined three-dimensional configuration for the inner surface of the assembled mold. In this configuration, the intermediate structure 11 is placed inside the mold that is assembled. Then, heat Q is applied as described above while the interior of the intermediate structure is pressurized to form the tank of compound pressure. In this variant, there is no need to apply external compression forces to the mold. Preferably, ventilation holes 17 are provided for the reasons noted above. Figures 11, 12 and 13 illustrate a process different but related, to manufacture a composite pressure tank. For clarity, these Figures are shown in cross section. With reference to Figure 11, a preform 31 is placed in a two-piece mold 30A 30B. The preform 31, which will serve as the outer covering for the The composite pressure tank to be manufactured can be prepared in the manner previously described for the thermoplastic liner 1, but alternatively can be prepared in the manner previously described for the intermediate structure 11; that is, the thermoplastic liner 1 wound with the fiber covering 7 and a thermoplastic material.

IiiflMUTffif Yf * As shown in Figure 12, a parison 32 of molten thermoplastic material, such as polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate, is extruded as an elongated tube through an axial opening 37 in the upper end of the preform 31. The material of the parison 32 is selected to form a good bond with a given preform 31. An insert 33, which can be threaded or permanent, is juxtaposed with respect to the axial opening 37 and inside the parison 32. Thus Similarly, if the preform 31 includes a second axial opening 38, another insert 34 is juxtaposed in the second opening. It will be understood by those skilled in the art that the melted parison 32 stores a large amount of latent heat. Thus, with reference now to Figure 13, the mold halves 30A, 30B are closed, and the interior of the parison is pressurized from a source 35 of pressurized gas by means of a conduit 36 such that the thermoplastic material 32A in the parison not only flows against the inner surface of the 31A preform, but also imparts sufficient heat to the preform 31A in order to render it fluid. Accordingly, the outer surface of the preform 31A flows to conform to the internal surface of the mold, the inserts 33A, 34A fuse with the rest of the structure or define removable inserts as may be proposed. 25 If, in a given configuration, there is sufficient ~ *. ~. ~~ tii **? a * ~ *? -M-. ...

Latent heat in the parison to cause complete consolidation of the preform and thermoplastic material and the proposed conformity of the outer surface of the preform to the inner surface of the mold, then the additional heat Q can be applied to the mold to complete the formation of the tank pressure 37. The mold can then be allowed to cool (or be conventionally forced to cool) and opened in such a manner that the completed pressure tank can be removed. Figures 14, 15 and 16 (shown in cross section) illustrate another molding process for forming a preform 41 in a pressure tank 41A. Referring first to Figure 14, the preform 41 can be prepared according to any of the corresponding processes previously described including the process described in connection with Figures 1-10 which includes the winding of mixed fiber and a thermoplastic material on a thermoplastic liner that it can, in itself, have been prepared by components of mixed fiber and thermoplastic material welded or sewn together. 0, the preform 41 can be coarsely molded from a suitable thermoplastic material such as polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate. The preform 41, which in the example has axial openings 44, 46, is inserted into a two-piece mold 40A, 40B. Then, the threaded inserts 43, 45 are juxtaposed in the openings 44, 46. (Of course, the inserts 33.34 employed in the process illustrated in Figures 11-13 or some other type of insert could be used alternatively depending on the configuration precise pressure tank that is sought). If threaded inserts are used, their material is selected to have a melting point that is well above the melting point of the preform 41. At least one of the inserts includes an opening for admitting an inflatable bag 42 of silicone rubber. in the interior of the preform 48. In addition, a heater 48 is placed inside the inflatable bag 42 that is selected to have heat handling capabilities greater than the melting point of the preform 41. A silicone rubber suitable for the bag Inflatable 42 is Mosites 1453D supplied by Mosites Rubber in the United States and by Aerovac Systems (Keighley) Ltd, in the United Kingdom. The heater 48 can be of any suitable type such as an electric resistance heater, the energy is also supplied by conductors (not shown) which extend through the opening in the threaded insert 43 and are coupled to a controllable energy source adequate (not shown). In addition, provision may be made, if necessary or desirable, to separately preheat the preform 41, such as by providing a set of heaters, represented by the electric resistance heaters 47A, 47B, close to the walls of the preform. The energy for the heaters 47A, 47B can be supplied by conductors (not shown) extending through one or the other or both of the axial openings 44, 46 in the preform 41 and coupled to a controllable energy source adequate (not shown). The mold 40A, 40B, by itself can be conventionally preheated and / or heated during the molding process. If the preform 41 is to be preheated (typically to increase the performance of the process), this step is carried out to melt the preform almost to fluid and the heaters 47A, 47B are removed from the mold 40A, 40B which is then closed. With reference now to Figure 15, the inflatable silicone rubber bag 42 is inflated by a source 49 of gas under pressure by means of a conduit 50 while the heater 48 heats the preform 41 to a fluid state through the bag, so that the bag exerts forces directed outwardly on the preform which consequently flows to conform to the inner surface of the mold 40A, 40B to form the pressure tank 41A. It will be noted that in the example, the axial opening regions of the preform flow to conform to the threads of the inserts 43, 45. The application of heat then ceases, and when the mold 40A, 40B and the pressure tank 41A formed are they have cooled sufficiently, the mold is opened, the inserts 43, 45 are unscrewed and the silicone rubber bag 42 and the heater 48 are removed leaving the pressure tank 5 formed. It will be noted that, as shown at 51, the internal threads have been formed, as proposed in the example, at the axial openings of the composite pressure tank formed. In the preparation of some pressure tanks compounds, such as domestic water heaters, the color of the finished product may be of importance. It is, of course, possible to prepare a preform according to any of the processes previously described using material (s) that already have color. However, there are two potential objections to this direct approach viz .: pre-colored raw materials are more expensive, and a limited number of colors are available in pre-colored raw materials. However, using the principles of the present invention, color can be imparted to a tank of pressure finished in a different and highly satisfactory way. Similarly, there are applications for pressure tanks, such as ultra pure water storage, gas storage (eg, propane, butane, natural gas, etc.) and food storage, in It is desirable to provide a waterproof integral inner liner within a composite pressure tank. Again, a process for providing such an integral waterproof inner liner according to the present invention can be developed. For convenience, an example, shown in Figures 17-20, deals so much, the provision of a desired external color for a composite pressure tank as the provision of an integral integral waterproof liner. It will be understood that each feature can be provided individually. Thus, with reference to Figure 17, an assembly including a preform 63 (manufactured according to any of the previously described methods), surrounded by a film 67 of desired colored thermoplastic material of the product, is introduced into a mold 60A, 60B of two pieces. If a waterproof integral inner liner is to be implemented, a thermoplastic film 66 having the desired characteristics is introduced into the interior of the preform 63 before the inserts 64, 65 are suitably juxtaposed. The mold 60A, 60B includes respective recessed face sections 61A, 61B and 62A, 62B, which when the mold is closed, provide passages inside the mold. Now with reference to Figure 18, the mold 60A, 60B is closed, and the interior of the mold is coupled to a vacuum source 68 by means of a duct 69. Alternatively, or additionally, the interior of the inner liner 66 ( or the inside of the preform 63 if no inner liner is to be incorporated) is coupled to a source 70 of gas under pressure by a duct 71. As shown in Figure 19, the heat Q is applied to the mold in order to of carrying all the components of the composite pressure tank to be formed in a fluid state while the interior of the mold is evacuated as represented by the arrows 72 and the inside of the inner liner 66 (or of the preform 63 if there is no inner liner) is pressurized as represented by the arrows 73. Accordingly, the three (or two) components are consolidated and the outer surface of the colored film 67 conforms to the configuration of inside the mold 60A, 60B. After the mold has been allowed to cool (or is forced to cool) and has been opened, the resulting composite pressure tank 74, shown in Figure 20 (as a cut in cross section), is ready for any subsequent process. As noted Preferably, of course, the inserts 64, 65 can be threaded for subsequent removal by leaving one or two axial openings as appropriate for the proposed purpose of the composite pressure tank. A similar process to manufacture a tank of The pressure is illustrated in Figures 21-23. Figure 21 shows a two-piece mold 80A, 80B which can be, for example, a simple sheet metal mold so that a number of pressure tanks can be formed simultaneously. The shown mold placed in a suitable furnace 81 has been loaded with a preform 82 made according to any of the methods and any of the materials and / or combinations of materials previously described above and having at least one opening for access to the inside of it. A bag 83 of thermoplastic film, which is intended to function as an integral liner in the finished pressure tank, is introduced into the interior of the preform 82 before the mold 80A, 80B is closed. Referring now to Figure 22, while the heat Q is transferred from the furnace 81 to the mold 80A, 80B, the gas pressure P (coming from any suitable source, not shown) is applied to the interior of the bag 83 of thermoplastic film, by which it is deflected towards the inner surface of the preform 82. In addition, the vacuum V (coming from any suitable source, not shown) is extracted from the interior of the mold 80A, 80B and thus outside the preform 82. continuous state until the plastic materials of the preform 82 and the plastic film bag are consolidated and the outer surface of the composite structure assumes the shape of the interior of the mold. Then, the mold is taken out of the furnace 81, allowed to cool and opened to remove the finished composite pressure tank 85 which is shown in Figure 23 as a composite of the integral structure including the molded preform 82A and the film liner 83A plastic that has melted into the composite pressure tank. Compound pressure tanks manufactured in accordance with all the processes described above have significantly improved performance and aesthetics characteristics over those manufactured with prior art processes. More particularly, they can withstand higher pressures and temperatures, are more resistant to impact and exhibit a significantly better finish. They also have good machinability attributes and can therefore easily be welded, cut, punched, tapped, stamped or the like as desired to produce a high quality finished product. Thus, while the principles of the invention have now been clarified in the illustrative embodiments, many modifications of structure and components used in the practice of the invention that are particularly suited for environments and operating requirements will be immediately obvious to those skilled in the art. without departing from those principles.

Claims (40)

1. CLAIMS 1. A process for manufacturing a composite tank comprising the steps of: A) preforming a thermoplastic coating for the tank, the thermoplastic coating of which has at least one opening for access to the inside thereof; B) Extrude a generally circular cross section of a fluid fluid parison 10 thermoplastic inside the thermoplastic coating through at least one opening therein; C) in a mold, apply at least one force that tends to drive the fluid parison towards the 15 inner walls of the thermoplastic coating in such a way that the fluid parison imparts heat to the thermoplastic coating; D) continue stage C) until the thermoplastic coating and fluid parison 20 are consolidated to form a composite tank; E) cool the composite tank until it solidifies; and F) removing the formed composite tank from the mold.
2. 2. The process of claim 1, wherein, 25 before step C), the thermoplastic coating is It is preheated to ensure consolidation of the thermoplastic coating and fluid parison during step D).
3. The process of claim 1, wherein, prior to step C), an insert is introduced into the interior of the parison and placed in alignment with the opening in the thermoplastic coating such that the insert becomes integral with the composite tank during stage D).
4. The process of claim 2, wherein, prior to step C), an insert is introduced into the interior of the parison and placed in alignment with the opening in the thermoplastic coating such that the insert becomes integral with the composite tank during stage D).
5. A process for manufacturing a composite tank comprising the steps of: A) preforming a thermoplastic coating for the tank, which thermoplastic coating has at least one opening for access to the interior thereof upon winding fiber and at least one thermoplastic substance on a thermoplastic liner; B) extruding a generally circular cross-section of a fluid parison of thermoplastic material into the interior of the thermoplastic coating through at least one opening therein; C) in a mold, apply at least one force that tends to drive the fluid parison towards the inner walls of the thermoplastic coating in such a way that the fluid parison imparts heat to the thermoplastic coating; D) continuing step C) until the thermoplastic coating and the fluid parison are consolidated to form a composite tank; E) cool the composite tank until it solidifies; and F) removing the formed composite tank from the mold.
6. The process of claim 5, wherein, before step C), the thermoplastic coating is preheated to ensure consolidation of the thermoplastic coating and fluid parison during step D).
7. The process of claim 6, wherein, prior to step C), an insert is inserted into the interior of the parison and placed in alignment with the opening in the thermoplastic coating such that the insert becomes integral with the composite tank during stage D).
8. The process of claim 7, wherein, during steps C) and D), the at least one force comprises gas pressure introduced into the interior of the parison.
9. 9. The process of claim 7, wherein the thermoplastic material is selected to have a melting point that is lower than that of the thermoplastic coating.
10. 10. The process of claim 8, wherein the thermoplastic material is selected to have a melting point that is lower than that of the thermoplastic coating.
11. The process of claim 1, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
12. 12. The process of claim 2, wherein the thermoplastic material is selected from the group that 15 comprises polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
13. The process of claim 3, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, terephthalate 20 polybutylene and polyethylene terephthalate.
14. The process of claim 4, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
15. 15. The process of claim 5, wherein, lft-ja-a * lfcM "" - t the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
16. 16. The process of claim 6, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
17. The process of claim 7, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
18. 18. The process of claim 8, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
19. 19. The process of claim 9, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
20. The process of claim 10, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
21. 21. A composite tank manufactured by the process of: A) preforming a thermoplastic coating for the tank, the thermoplastic coating of which has at least one opening for access to the interior thereof; B) extruding a generally circular cross-section of a fluid parison of thermoplastic material into the interior of the thermoplastic coating through at least one opening therein; C) in a mold, apply at least one force that tends to drive the fluid parison towards the inner walls of the thermoplastic coating in such a way that the fluid parison imparts heat to the thermoplastic coating; D) continuing step C) until the thermoplastic coating and fluid parison are consolidated to form a composite tank; E) cool the composite tank until it solidifies; and F) removing the formed composite tank from the mold.
22. 22. The composite tank of claim 21, wherein, prior to step C), the thermoplastic coating is preheated to ensure consolidation of the thermoplastic coating and fluid parison during step D).
23. 23. The composite tank of claim 25, wherein, prior to step C), an insert is introduced into the interior of the parison and placed in alignment with the opening in the thermoplastic coating in such a way that 5 the insert becomes integral with the composite tank during step D).
24. 24. The composite tank of claim 26, wherein, prior to step C), an insert is inserted into the interior of the parison and placed in alignment with the 10 opening in the thermoplastic coating such that the insert becomes integral with the composite tank during step D).
25. 25. A composite tank manufactured by the process of: 15 A) preforming a thermoplastic coating for the tank, which thermoplastic coating has at least one opening for access to the interior thereof upon winding fiber and at least one thermoplastic substance on a liner 20 thermoplastic; B) extruding a generally circular cross-section of a fluid parison of thermoplastic material into the interior of the thermoplastic coating through at least one opening in 25 the same; C) in a mold, apply at least one force that tends to drive the fluid parison towards the inner walls of the thermoplastic coating in such a way that the fluid parison imparts heat to the thermoplastic coating; D) continuing step C) until the thermoplastic coating and the fluid parison are consolidated to form a composite tank; E) cool the composite tank until it solidifies; and F) removing the formed composite tank from the mold.
26. 26. The composite tank of claim 25, wherein, prior to step C), the thermoplastic coating is preheated to ensure consolidation of the thermoplastic coating and fluid parison during step D).
27. 27. The composite tank of claim 26, wherein, prior to step C), an insert is inserted into the interior of the parison and placed in alignment with the opening in the thermoplastic coating such that the insert becomes integral with the composite tank during stage D).
28. 28. The composite tank of claim 27, wherein, during stages C) and D), the at least one force comprises gas pressure introduced into the interior of the parison.
29. 29. The composite tank of claim 27, wherein the thermoplastic material is selected to have a melting point that is lower than that of the thermoplastic coating.
30. 30. The composite tank of claim 28, wherein the thermoplastic material is selected to have a melting point that is lower than that of the thermoplastic coating.
31. 31. The composite tank of claim 21, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
32. 32. The composite tank of claim 22, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
33. 33. The composite tank of claim 23, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
34. 34. The composite tank of claim 24, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate. * * - 4-
35. 35. The composite tank of claim 25, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
36. 36. The composite tank of claim 26, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
37. 37. The composite tank of claim 27, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
38. 38. The composite tank of claim 28, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
39. 39. The composite tank of claim 29, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate.
40. 40. The composite tank of claim 30, wherein the thermoplastic material is selected from the group comprising polyethylene, polypropylene, polybutylene terephthalate and polyethylene terephthalate. SUMMARY A process for manufacturing a composite tank includes the steps of A) preforming (for example, by winding fiber and at least one thermoplastic substance on a thermoplastic liner) a thermoplastic coating having at least one opening for access to the interior; B) extruding a circular cross-section of a fluid parison of thermoplastic material (which is preferably selected to have a melting point lower than that of the thermoplastic coating) inside the thermoplastic coating through the opening; C) in a mold, apply at least one force (such as a gas under pressure) that tends to drive the fluid parison towards the inner walls of the thermoplastic coating (which can be preheated before the introduction into the mold) in such a way that the fluid parison imparts heat to the thermoplastic coating; D) continuing step C) until the thermoplastic coating and fluid parison are consolidated to form a composite tank; E) cool the tank until it solidifies; and F) removing the tank from the mold. For some composite tanks, before stage C), an insert can be inserted into the interior of the parison and placed in alignment with the opening in the thermoplastic sheath in such a way that the insert becomes integral with the composite tank during stage D ). The materials Suitable thermoplastics include polyethylene, polypropylene, polybutylene terephthalate, and polyethylene terephthalate. The resulting composite tank exhibits superior mechanical and aesthetic properties. ° < / ¿¿S?