Abstract:
The present invention relates to a method for manufacturing a tank ( 1 ) comprising a main body ( 4 ) with several compartments ( 7 ), a base ( 6 ) closing the lower part of the main body ( 4 ), and a cover ( 5 ) closing the upper part of the main body ( 4 ), said method comprising the following steps:
       shaping sheets to produce the parts making up the tank ( 1 );   assembling each of the component parts by butt welding in order to produce the tank ( 1 ).

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This patent application claims priority to European Patent Application No. 13169374.9, filed May 27, 2013, the entire teachings and disclosure of which are incorporated herein by reference thereto. 
         [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method for manufacturing a tank. The present invention also relates to a fluid tank designed more particularly to be positioned in an environment of reduced size. Preferably, the tank is an oil tank designed to be positioned in a so-called “slim” airplane nacelle. 
         [0004]    2. Background of the Invention 
         [0005]    The oil tank is a component of the lubrication/cooling system of an airplane engine allowing to recover and store oil from the lubrication system. 
         [0006]    In a bypass turbojet engine, the oil tank is positioned between the nacelle and the intermediate casing that delimits the primary flow path and the secondary flow path. 
         [0007]    New so-called “slim” nacelles with a profile that is optimized in order to reduce drag have been created. In these nacelles, the space between nacelle and intermediate casing is reduced, with the result that the shape of the tank must be adapted. Currently, the tanks in so-called “slim” nacelles are flat, i.e., they are wider than they are deep. They are either made from aluminum and obtained by foundry, or from mechanically-welded steel. In both cases, the main faces, i.e., the flat faces of the tank, are maintained by a multitude of tie rods or baffles. 
         [0008]    This geometry is not favorable to the mechanical strength of the tank and consequently requires the thicknesses of the tank and/or the number of tie rods/baffles to be increased in order to ensure the integrity of the parts. This results in drastically increasing the mass and cost of the tank in so-called “slim nacelle” environments. 
         [0009]    Geometries close to a cylinder are the most favorable, after spheres, to withstand the pressure and vibrations that are specific to aeronautics. However, confined environments do not always allow the integration of a cylindrical tank in a single piece. 
         [0010]    It is thus proposed in the state of the art to produce tanks for “slim nacelles” that comprise two cylindrical bodies. The proposed tanks have the drawback of being closed at their ends by domes manufactured by foundry, resulting in an increased mass and cost associated to the production of the parts by foundry. 
       AIMS OF THE INVENTION 
       [0011]    The present invention aims to provide a tank specially adapted for reduced spaces and having very good mechanical strength given its design and method of assembly. 
         [0012]    The present invention further aims to produce a tank with a reduced mass and obtained using an inexpensive method. 
         [0013]    The present invention also aims to produce a tank that is easy to control with non-destructive tests. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0014]    The present invention relates to a method for manufacturing a tank comprising a main body with several compartments, a base closing the lower part of the main body, and a cover closing the upper part of the main body, said method comprising the following steps:
       shaping sheets to produce the parts making up the tank;   assembling each of the component parts by butt welding to produce the tank.       
 
         [0017]    According to specific embodiments of the invention, the method comprises at least one or a suitable combination of the following features:
       the assembly is exclusively achieved by butt welding each of the component parts to produce the tank;   the tank is formed by the assembly of two or more component parts;   said component parts respectively comprise the cover, each of the compartments and the base;   said component parts respectively comprise the cover and two half-shells each incorporating half of the base and half of the main body;   said component parts respectively comprise two half-shells each incorporating half of the cover, half of the base and half of the main body;   said component parts respectively comprise the base, the cover and a plurality of pieces of the main body;   each compartment comprises, at each of its ends, at least one flange allowing an end-to-end assembly between the compartments.       
 
         [0025]    The present invention also relates to a fluid tank for a turbojet engine, said tank comprising a main body with several compartments, a base closing the lower part of the main body, and a cover closing the upper part of the main body, characterized in that the main body, the base and the cover are essentially made from sheets. 
         [0026]    According to specific embodiments of the invention, the tank comprises at least one or a suitable combination of the following features:
       said tank comprises butt welds and is free of fillet welds;   each compartment comprises, at each of its ends, at least one flange that extends in a direction substantially perpendicular to the longitudinal axis of the compartment and connects the compartments to each other;   each compartment comprises a portion with a cylindrical, nearly cylindrical or ovoid shape;   the section of the compartment is not constant along the longitudinal axis of the compartment;   said sheets are made from steel, stainless steel, copper, brass, aluminum or an aluminum or copper-based alloy;   said tank is designed to be positioned between a nacelle and an intermediate casing of the turbojet engine.       
 
         [0033]    Lastly, the present invention relates to a turbojet engine comprising a fluid tank as described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]      FIG. 1  shows diagrammatic views from different angles of the tank as in the invention positioned in a turbojet engine between the nacelle and the intermediate casing. 
           [0035]      FIG. 2  shows two planar views of the tank as in the invention respectively comprising two or three substantially cylindrical compartments. 
           [0036]      FIG. 3  shows a three-dimensional view of the tank as in the invention comprising two compartments. 
           [0037]      FIG. 4  shows a three-dimensional view of the upper part of a tank compartment as in the invention. The compartment is designed to be positioned at one of the side ends of the tank. 
           [0038]      FIG. 5  shows a three-dimensional view of the upper part of the tank compartment as in the invention. The compartment is designed to be positioned in an intermediate position between the compartments of  FIG. 4 . 
           [0039]      FIG. 6  shows a three-dimensional view of the different component elements of the tank made as in a first embodiment of the invention. 
           [0040]      FIG. 7  shows a three-dimensional view of the different component elements of the tank made as in a second embodiment of the invention. 
           [0041]      FIG. 8  shows a three-dimensional view of the different component elements of the tank made as in a third embodiment of the invention. 
           [0042]      FIG. 9  shows a three-dimensional view of the different component elements of the tank made as in a fourth embodiment of the invention. 
           [0043]      FIG. 10  shows a three-dimensional view of the different component elements of the tank made as in a fifth embodiment of the invention. 
       
    
    
     KEY 
       [0044]    ( 1 ) Tank 
         [0045]    ( 2 ) Nacelle 
         [0046]    ( 3 ) Casing 
         [0047]    ( 4 ) Main body 
         [0048]    ( 5 ) Dome, also called cover 
         [0049]    ( 6 ) Base 
         [0050]    ( 7 ) Compartment 
         [0051]    ( 8 ) Protruding part, also called flange, over the end of the compartment 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0052]    The present invention relates to a fluid tank more particularly designed to be arranged in an environment of reduced size, and to its manufacturing method. Preferably, the tank  1  as in the invention is an oil tank designed to be positioned in a turbojet engine between the so-called “slim” nacelle  2  and the intermediate casing  3  as diagrammed in  FIG. 1 . 
         [0053]    The tank  1  illustrated in  FIGS. 2 and 3  comprises a main body  4  closed at its respective ends by a base  6  and by a cover  5 . The main body  4  comprises cylindrical or nearly cylindrical, or ovoid, compartments  7 . According to the invention, the section of the compartment may vary along the longitudinal axis of the compartment. In this case, reference will be made to a “nearly cylindrical” shape rather than a “cylindrical shape”. 
         [0054]    The main body  4  comprises at least two compartments  7 . It may comprise two, three or more compartments (not shown), depending on the available space and required contents. The ends of the compartments comprise a flange  8 , which can be seen in  FIGS. 4 and 5  among others, that extends in a direction substantially perpendicular to the longitudinal axis of the compartment and connects the compartments after assembly. The flange may assume any shape allowing an end-to-end assembly between the compartments of the tank. In a configuration with two compartments, each end comprises a single flange as shown in  FIG. 4 . In a configuration with more than two compartments, the compartment(s) in the intermediate position comprise(s) two flanges at each end, as shown in  FIG. 5 . 
         [0055]    According to the invention, the assembly of the tank is made from stamped sheets, or more generally shaped and/or cut sheets, without using single-piece foundry or machined parts. The component elements of the tank are shaped and/or cut so that they can be assembled together from the inside with butt welds, which facilitates welding and ensures that the latter can be tested. Preferably, the assembly is exclusively achieved by butt welding. 
         [0056]    Still preferably, the tank is entirely made from sheets, for example steel or aluminum alloys. It will, however, be specified that the tank may be provided with means (valves, etc.) for supplying and/or recovering oil, and that the latter may be made from materials other than metal sheets. It is more accurate, in that case, to mention that the tank is essentially made up of sheets. 
         [0057]    The tank may be assembled from a variable number of component elements. As one non-limiting example, the assembly method is described below for a tank comprising two compartments. 
         [0058]      FIG. 6  shows one embodiment of the invention where the tank is assembled from four component elements, namely the cover  5 , the base  6  and the two compartments  7 . The end of the compartments has a particular geometry in the form of a flange  8  as already mentioned, which allows to assemble the two compartments end-to-end by welding. 
         [0059]      FIG. 7  shows another embodiment of the invention where the tank is assembled from three component elements. The assembly is made up of the cover  5  and two shells each comprising half of the base  6  and of the main body  4 . Alternatively, the two shells may also incorporate the cover (namely one half thereof per shell), the assembly then being achieved from two component elements (not shown). 
         [0060]    According to still another embodiment of the tank as in the invention, the assembly is achieved from six component elements. The assembly is made up of the cover  5 , the base  6  and four pieces of compartments  7 , as shown in  FIGS. 8 and 9 . 
         [0061]    This is a non-exhaustive list of examples. It will generally be noted that the tank may be made from any number of component elements and that the object of the invention is to shape/cut the component elements made from the sheet such that they can be assembled by butt welding. 
         [0062]    The present invention is illustrated for a turbojet-engine tank, but it extends to any application where a tank must be positioned in a confined space potentially subjected to vibrations. 
       ADVANTAGES OF THE INVENTION 
       [0063]    The design of the component elements allows to produce a tank entirely from shaped/cut sheets. The elimination of cast parts thus allows to reduce manufacturing difficulties as well as the foundry-related mass. 
         [0064]    The tanks as in the invention comprising substantially cylindrical or ovoid compartments offer better mechanical strength than the flat tanks as in the state of the art. Consequently, the thickness of the walls and therefore the total mass may be reduced, with an equivalent strength. In this respect, making the tank from steel sheets allows to achieve very low thicknesses without significantly increasing cost relative to parts obtained by foundry that have much higher manufacturing tolerances. It will also be noted that the tank as in the invention no longer requires the use of tie rods or baffles. 
         [0065]    The assembly of the component elements of the tank with butt welds has many advantages relative to assemblies with fillet welds. First of all, butt welding is easier to achieve. Next, the butt welds are 100% controllable using non-destructive tests, which is not the case for fillet welds. The latter in fact have material discontinuities. Thus, during non-destructive testing, it is not possible to detect whether the detected defect comes from the weld or from the assembly. A better assembly and testing of the butt welds thus leads to a decrease in defects and discard rates. Lastly, butt welds are stronger than fillet welds and eliminate the risks of cracks spreading at the root of the weld. 
         [0066]    Due to its shape and butt-welded assembly, the tank as in the invention is particularly suitable for confined spaces subjected to vibrations, such as airplane engines. 
         [0067]    The use of steel, which intrinsically has good fire resistance, has the advantage that it is not necessary to provide additional fire protection.