Abstract:
A hot pressing process, particularly for providing metal unions couplings for pneumatic, hydraulic and fluid-operated circuits, and a resulting metal union. The hot pressing process comprising:
       a step of preheating aluminum alloy bars,   a step of pressing the part to be obtained,   a thermal hardening treatment, and   a thermal treatment for artificial aging.       
 
     The standard cycle further provides for a step of solubilization of the pressed part, performed between the step of pressing the part to be obtained and the thermal hardening treatment. The alloy preferably comprising (weight percent): Si 0.6-1.4%, Fe 0.7%, Cu 0.2-0.5%, Mn 0.2-1%, Mg 0.6-1.2%, Cr 0.3%, Zn 0.3%, Ti 0.2%, Pb 0.4%, Bi 0.5-1.5%, balance aluminum. The process can include a solutionising step after the pressing step.

Description:
[0001]    The present invention relates to a hot pressing process, particularly for providing metal unions for pneumatic, hydraulic and fluid-operated circuits. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the field of systems and in particular in the fields of shipbuilding and rail vehicle building, the need to provide interfacing and/or connecting components with high performance among the different components of the system is now routine. 
         [0003]    More precisely, metal unions, typically made of brass and/or stainless steel alloys, are known which can be used at high operating pressures, up to ten times higher than the normal pressures used in the most widely spread systems. 
         [0004]    The choice of the material is linked substantially to the technological process used to provide the union. 
         [0005]    In fact, in order to obtain components that have a high mechanical performance and an excellent dynamic behavior, the material of the generic component that is manufactured must have a structure that is as much as possible homogeneous, uniform and free from cracks. 
         [0006]    The technological process that allows to obtain such characteristics is hot pressing, which however can be applied only to a limited range of materials, which include steel, brass, copper, et cetera. 
         [0007]    In the background art, if lighter components, for example made of aluminum, are manufactured, in view of the characteristics of aluminum such components can be provided only by means of a pressure die-casting process, which does not ensure lack of cracks and homogeneity of the material. 
       SUMMARY OF THE INVENTION 
       [0008]    The aim of the present invention is to eliminate the drawback cited above, by providing a hot pressing process, particularly for providing metal unions for pneumatic, hydraulic and fluid-operated circuits, that allows to use aluminum to obtain components that can be used in pneumatic and/or hydraulic systems with high operating pressures. 
         [0009]    Within this aim, an object of the present invention is to provide a hot pressing process that allows to obtain components with material that is structurally homogeneous and free from cracks. 
         [0010]    Another object of the present invention is to provide a hot pressing process to obtain aluminum components whose mechanical performance and dynamic behavior are comparable to those of components made of more traditional materials, such as for example brass and steel alloys. 
         [0011]    Another object of the present invention is to provide a particular aluminum alloy that allows hot pressing. 
         [0012]    This aim and these and other objects, which will become better apparent hereinafter, are achieved by a hot pressing process, particularly for providing metal unions for pneumatic, hydraulic and fluid-operated circuits, and by the resulting metal union, characterized in that it comprises:
       a step of preheating aluminum alloy bars,   a step of pressing the part,   a thermal hardening treatment, and   a thermal treatment for artificial aging.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Further characteristics and advantages of the present invention will become better apparent from the description of a preferred but not exclusive embodiment of a hot pressing process, particularly for providing metal unions for pneumatic, hydraulic and fluid-operated circuits, according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein: 
           [0018]      FIG. 1  is a block diagram of the steps of an embodiment of a hot pressing process for aluminum components according to the present invention; 
           [0019]      FIG. 2  is a partially sectional side elevation view of a first variation of a metal union that can be obtained with the hot pressing process shown in  FIG. 1 ; 
           [0020]      FIG. 3  is a partially sectional exploded view of the metal union shown in  FIG. 2 ; 
           [0021]      FIG. 4  is a partially sectional side elevation view of a second embodiment of a metal union that can be obtained with the hot pressing process shown in  FIG. 1 ; 
           [0022]      FIG. 5  is a partially sectional exploded view of the metal union shown in  FIG. 4 ; 
           [0023]      FIG. 6  is a view of the locking nut of the union shown in  FIG. 4 ; 
           [0024]      FIG. 7  is a sectional view of the locking nut shown in  FIG. 6 , taken along the line VII-VII. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    With reference to the figures, the hot pressing process, particularly for providing metal unions for pneumatic, hydraulic and fluid-operated circuits, generally designated by the reference numeral  100 , comprises a step  101  of preheating aluminum alloy bars in a first furnace at a temperature ranging substantially from 430° C. to 470° C., so that such temperature is uniform over the entire section of the bars. 
         [0026]    A step  102  of pressing the part starting from the previously heated bars is then provided. 
         [0027]    More specifically, the generic part can consist of a metal union for pneumatic, hydraulic and fluid-operated circuits provided in a plurality of variations, which will be described hereinafter. 
         [0028]    After pressing the part, one proceeds with a step  103  known as solubilization. In this step  103 , a second preheating of the metal unions in a second furnace to a solubilization temperature ranging substantially from 515° C. to 525° C. is provided for a minimum time substantially equal to 2 hours, and then a thermal hardening treatment  104  is performed which comprises an immersion of the metal unions in a bath of water preferably at ambient temperature. 
         [0029]    With the cited solubilization temperatures, the immersion of the metal unions in the bath must be performed within 30 seconds of the solubilization step  103 , with the bath at a maximum temperature that is substantially lower than 40° C. 
         [0030]    As an alternative, immersion of the metal unions in the bath can be performed directly after the pressing step  102 . In this case, the step  101  of preheating the bars occurs at a temperature ranging substantially from 480° C. to 500° C. for a minimum time that is substantially equal to 2 hours. 
         [0031]    It must be specified that according to the invention, the standard cycle is the one that provides for the solubilization step  103 . The elimination of this step can be seen as a modification to the standard cycle and is feasible only by maintaining a higher temperature in the preheating step  101 . 
         [0032]    In any case, after the thermal hardening treatment  104 , after a waiting interval ranging from 2 to 3 hours, a thermal treatment for artificial aging  105  is provided which comprises keeping the metal unions in a third furnace at a uniform temperature ranging from 135° C. to 145° C. for substantially 8 hours. 
         [0033]    Finally, a cooling step  106  is provided after the thermal treatment  105  and can be performed according to traditional criteria. 
         [0034]    To ensure maximum resistance to corrosion caused by exposure to atmospheric agents, a treatment  107  of anode oxidation is provided on the metal unions and generates the oxidation of a thin surface layer of the metal unions, thus ensuring corrosion protection of the underlying material and determining, as a direct consequence, a considerable increase in the life of the metal union. 
         [0035]    More precisely, the anode oxidation treatment  107  provides for a first step of protective anode oxidation, which oxidizes for a thickness of approximately  15  microns the surface of the part according to the UNI4522 standard, and a second step of oxide coloring in order to give the metal union the desired color. 
         [0036]    The described hot pressing process  100  can be applied to several aluminum alloys and in particular is optimized for the use of a particular aluminum alloy known as AL2, since it is the one that ensures the best physical/mechanical quality of the pressed parts. 
         [0037]    More precisely, the chemical composition of the aluminum alloy AL2 is as follows:
       silicon, with a percentage by weight ranging substantially from 0.6% to 1.4%,   iron, with a percentage by weight substantially equal to 0.7%,   copper, with a percentage by weight ranging substantially from 0.2% to 0.5%,   manganese, with a percentage by weight ranging substantially from 0.2% to 1.0%,   magnesium, with a percentage by weight ranging substantially from 0.6% to 1.2%,   chromium, with a percentage by weight substantially equal to 0.3%,   zinc, with a percentage by weight substantially equal to 0.3%,   titanium, with a percentage by weight substantially equal to 0.2%,   lead, with a percentage by weight substantially equal to 0.4%,   bismuth, with a percentage by weight ranging substantially from 0.5% to 1.5%,   aluminum for the remainder.       
 
         [0049]    The components obtained with the AL2 alloy by means of the hot pressing process  100  have the following mechanical characteristics:
       relative density 2.7 kg/dm 3 ,   unit ultimate tensile strength 422 N/mm 2 ,   unit yield strength 410 N/mm 2 ,   Brinell hardness 110 HB.       
 
         [0054]    More precisely, the use of the AL2 alloy allows to obtain components that have a surface hardness of 60 HB after the pressing step  102  and of 110 HB or 95 HB after the thermal treatment  105  for aging, respectively with or without the solubilization step  103 . 
         [0055]    The metal unions that can be obtained from the hot pressing process of the AL2 alloy can be of several kinds. 
         [0056]    For example, two possible variations of these unions are the metal union  1   a  and the metal union  1   b.    
         [0057]    Both variations  1   a  and  1   b  comprise a main hollow body  2 , which has a substantially axially symmetrical geometry and forms a cross-section  3  that is contracted radially for the abutment of a pipe  4  that can be inserted hermetically in the main body  2  and can be fixed thereto by way of retention means. 
         [0058]    More precisely, the retention means comprise a locking ring  5 , which is open and surrounds the pipe  4 . 
         [0059]    This locking ring  5  can be engaged by abutment against a compression washer  6 , which is accommodated in a circular receptacle formed internally by the pipe  4  and externally by a nut  11   a  or  11   b.    
         [0060]    Both the locking ring  5  and the compression washer  6  can be made of a white or yellow zinc coated brass alloy. For example, the P—CuZn40Pb2 UNI5705-65 alloy can be used. 
         [0061]    The tightness of the coupling between the metal union  1   a  or  1   b  and the pipe  4  is ensured by an annular gasket  7 , which is elastically deformable and is interposed between the compression washer  6  and a base  8  of the receptacle. 
         [0062]    Depending on the temperature range at which the entire metal union  1   a  or  1   b  must work, the annular gasket  7  can be made of different materials. 
         [0063]    For example, for temperatures ranging from −30° C. to +150° C. it is possible to use, as a material of the annular gasket  7 , a supernitrile mix; for temperatures ranging from −45° C. to +150° C. it is possible to use, as a material of the annular gasket  7 , an FPM mix (known commercially as Viton®); and finally, for temperatures ranging from −45° C. to +110° C. it is possible to use a nitrile mix as a material of the annular gasket  7 . 
         [0064]    The two variations  1   a  and  1   b  of the metal unions that can be obtained by means of the hot pressing process  100  of the AL2 alloy differ substantially in the means for retention with the pipe  4 . 
         [0065]    More precisely, the locking ring  5  of both variations  1   a  and  1   b  defines a substantially spherical outer surface  9 , which can engage a substantially conical inner surface  10  of the locking nut  11   a  or  11   b , depending on the variation being referenced, which can be screwed externally onto the main body  2 . 
         [0066]    In order to ensure a safe grip during fastening of the ring  5  on the pipe  4 , in both variations  1   a  and  1   b  there is a radially wider cross-section  12  of the main hollow body that has a hexagonal profile for engagement with tools. 
         [0067]    Moreover, other variations of the metal unions of the angular type can be provided. For example, the metal union can be substantially L-shaped or otherwise curvilinear, allowing the correct fastening of the ring  5  on the pipe  4  without the aid of the radially expanded cross-section  12 , since the blended or inclined portion of the union can be locked easily, allowing the screwing of the nut  11   a  or  11   b.    
         [0068]    As regards the second variation  1   b  of the metal union, the retention means of the variation  1   b  differ from those of the variation  1   a  due to the presence of a locking band  13 , which is jointly coupled to the locking nut  11   b  and forms at least two side walls  14  that can partially wrap around the pipe  4  and can be mutually closed thereon by way of screw means  15 . 
         [0069]    In practice it has been found that the hot pressing process, particularly for providing metal unions for pneumatic, hydraulic and fluid-operated circuits, according to the present invention, fully achieves the intended aim and objects, since it allows to provide aluminum unions particularly for pneumatic, hydraulic and fluid-operated use that are subjected to high pressure. 
         [0070]    Another advantage of the hot pressing process according to the present invention consists in that the aluminum unions that can be obtained have mechanical strength properties that can be compared to unions made of brass. 
         [0071]    A further advantage of the hot pressing process according to the present invention consists in that the aluminum unions that can be obtained have a better corrosion resistance than white zinc-coated brass. 
         [0072]    Another advantage of the hot pressing process according to the present invention consists in that the aluminum unions that can be obtained are distinctly lighter than unions made of steel and those made of brass. 
         [0073]    The hot pressing process, particularly for providing metal unions for pneumatic, hydraulic and fluid-operated circuits, and the metal unions and the composition of the aluminum alloy known as AL2, thus conceived, are susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept. 
         [0074]    Moreover, all the details may be replaced with other technically equivalent elements. 
         [0075]    In practice, the materials used, so long as they are compatible with the specific use, as well as the contingent shapes and dimensions, may be any according to requirements and to the state of the art. 
         [0076]    The disclosures in EPA No. 08425525 from which this application claims priority are incorporated herein by reference.