Patent Publication Number: US-2015069057-A1

Title: Liner and Composite Tank Assembly Method

Description:
This utility patent application is based upon and claims the priority filing date of U.S. provisional patent application (application Ser. No. 61/815,651) filed on Apr. 24, 2013, 
    
    
     Notice is given that the following patent document contains original material subject to copyright protection. The copyright owner has no objection to the facsimile or digital download reproduction of all or part of the patent document, but otherwise reserves all copyrights. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains to liners for storage containers and more particular, to such liners that are more durable than liners used in the prior art and can be used to manufacture the outer container in which the liner is placed. 
     2. Description of the Related Art 
     Above ground and underground storage tanks are commonly used to store different 
     Above ground and underground storage tanks are commonly used to store different gases, liquids and fine solids. Such storage tanks are manufactured in different shapes adn sizes and usually made of metal or composite materials. They often include valves, ports, and internal conduits. 
     Two problems with large tanks made of metal are: (1) the outside surfaces and tank&#39;s support framework deteriorates when exposed to weather, and (2) material stored inside the tank may react with the tank&#39;s interior metal surfaces. Eventually, leaks or cracks are created that require repair or replacement of the entire tank. Sometimes, liners made of composite material that does not react with the stored material are placed inside the tanks to prevent deterioration of the tank&#39;s inside metal surfaces. 
     Tanks made of composite materials are commonly used an alternatives to metal tanks. The tanks are hollow with uniform wall thickness. The most common method to manufacture composite tanks with inside hollow cavities and with uniform side walls is to use a process known as roto-molding. One problem with large tanks made of composite materials is that composite material itself has relatively high co-efficiency of expansion. Because the container and tanks are used outdoors and exposed to different weather conditions, creaks often occur. Like metal tanks, liners made of composite material that does not react to the stored material may be placed inside the composite tanks to prevent leakage through the cracks. 
     What is also needed is an improved liner that can be used inside both metallic and composite tanks that is less susceptible to cracking and leaking. What is also needed is a method of manufacturing a tank made of composite material with pre-manufactured liner placed inside the mold so that the composite tank may be manufactured around the liner. 
     SUMMARY OF THE INVENTION 
     An improved liner for a container in which gases, liquids, or powders are stored. The liner is a multi-layer structure that includes an outer layer made of metallocene polyethylene, an intermediate gas and liquid impermeable layer, and one or more inner layers made of thermoplastic material. The metallocene polyethylene layer provides rigidity and has no or very low coefficient of expansion properties making the liner less susceptible to cracking and useful as a layup structure for molding an outer structure around it. The inner most layer is made of composite material compatible with the material stored inside a storage container in which the liner is installed. During the molding process, the inner three layers are sequentially manufactures and then fused together to form a uniform composite layer. The liner may be made by blow molding or roto molding processes. 
     In one embodiment, the liner is a separate structure that can be inserted into an existing container or tank made of metal or composites. In a second embodiment, the liner is used as a layup structure located inside the cavity of a mold used to make a composite container or tank in which the liner will be placed. Because the liner is semi-rigid and has little or zero co-efficiency of expansion, it may be uses as a lay-up structure for either roto-molding or blow molding process. In one embodiment, the liner&#39;s outer layer which is made of composite material may become fused and integral with the container&#39;s or tanks side walls. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional side elevational view of a mold with the outer container made of composite material with the improved liner formed therein. 
         FIG. 2  is a sectional side elevational view of an upper section of the mold shown in  FIG. 1 . 
         FIG. 3  is a sectional side elevational view of a lower section of the mold shown in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
       FIG. 1  is a sectional side elevational view of a mold  10  used to manufacuture a composite tank  12  made of composite material with the improved liner  20  formed therein. An improved liner  20  is specifically designed to be used with composite tanks  12  in which gases, liquids, or powders will be stored. 
     The liner  20  is a multi-layer structure that includes an outer layer made of metallocene polyethylene  22 , an intermediate gas and liquid impermeable layer  24 , and one or more inner layer  26  made of thermoplastic material. The metallocene polyethylene layer  22  provides rigidity and has relatively low coefficient of expansion properties making the liner  20  less susceptible to cracking and useful as a layup structure for molding. The two inner layers  24 ,  26  are made of composite material compatible with the material stored inside a storage container in which the liner is installed. The thickness of each inner layer  24 ,  26  and the number of inner layers  24 ,  26  may be selectively controlled for use with different stored materials. During the molding process, the inner three layers  22 ,  24 ,  26  are bonded and fused together to form a composite tank  12  with a durable, protective liner  20 . 
     It should be understood, however the liner  20  described above is not limited to composite tanks or only used to make in situ tanks. It may be made separately and used with metal containers or tanks. 
     The liner  20  is manufactured by a roto-molding process that uses a roto-molding machine. The linear  20  is fabricated one layer at a time with allows the thickness of each layer to be precisely controlled. During fabrication, each layer  22 ,  24 ,  26  is allowed to cure and cool and the adjacent layers are then formed over the adjacent layer. The temperature and vacuum pressure is controlled so that the adjacent layers are fused together. When all of the layers have been fabricated, the entire liner  20  is then inspected using ultrasound testing procedures. 
     The raw material powders used to fabricate each inner layer  24 ,  26  are selected based on the stored material inside the tank  12 . 
     More specifically, each layer is roto molded and formed by introducing powder resin that includes metallocene polyethylene and composite fibers into the mold cavity to create the first layer (called the inner layer  26 ) of the liner  20 . The powder is heated to a very specific temperature so that it becomes a liquid. The mold is then rotated  360  degrees to form a layer with the desired dimensions. The above steps are repeated each time for each additional intermediate layer  24 . In the preferred embodiment, the second layer  24  is made of gas and liquid impermeable material. The outside layer  22  is made of material compatible with the material exposed to the liner  20 . When completed, a multi-layer liner  20  is produced that has zero coefficient of expansion, and leak resistant. Minimum thickness of each layer  22 ,  24 ,  26  should be not less then 1 mm and not thicker than 4 mm. 
     As shown in  FIG. 3 , optional metallic&#39;s inserts  90  can be in-bedded in the liner  20  to server as supports fort pipe connections. 
     Bow molding liner is another technology who could used to make the multi layer liner  20 . The bow molding process is similar to the process used to fabricate plastic bottles. It is possible to coextruded two, three materials together like a big tube in continuous mode. Very special machinery and equipments must be used to make liners. This technology is used to produce millions of parts. 
     Also disclosed is a method for fabricating a composite tank  12  using the liner  20  as a build up structure that becomes permanently installed inside the tank  12 .  FIG. 2  is a sectional side elevational view of an upper section of the mold shown in  FIG. 1 .  FIG. 3  is a sectional side elevational view of a lower section of the mold shown in  FIG. 1 . During fabrication, the liner  20  is separately manufactured and placed into the mold  10  used to manufacture the tank  10  Fiber plies (not shown) are then built-up around the liner  20 . As stated above, because the liner  20  is made of material that has zero coefficient of expansion, is it ideal for use as a layup structure. The number of plies are used determine the thickness of the sidewalls of the tank  10 . As stated above, during the lay-up step optional inserts  90  can be added in the structure. 
     In compliance with the statute, the invention described has been described in language more or less specific as to structural features. It should be understood however, that the invention is not limited to the specific features shown, since the means and construction shown, comprises the preferred embodiments for putting the invention into effect. The invention is therefore claimed in its forms or modifications within the legitimate and valid scope of the amended claims, appropriately interpreted under the doctrine of equivalents.