Dielectric joint, particularly for metallic conduits for liquids and/gases
This is a continuation-in-part of the application Ser. No. 07/039.134 filed on Apr. 16, 1987. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an dielectric joint, particularly for metallic conduits for liquids and/or gas. 
     The use of metallic conduits for the conveyance and the transport of material, both in the liquid state and in the gaseous state, has been known for some time. 
     Such conduits, due to their length, require joints, which are the subject of particular studies aimed at their production, in order to meet the multiple characteristics required both to increase their durability with time and to cause them to resist to the stresses of various kinds to which they are subject underground, and also to comply with the norms which regulate their construction. 
     Joints are known, designed according to the abovesaid aims, which however do not perfectly meet expectations: in some cases, for example, the mechanical flexing resistance has proved to be not sufficient in said joints, compromising their seal. 
     In other cases, infiltrations of transported liquids between the elements which compose said joint have occurred, with the consequent accidental conduction of current between said component elements, which event, above all other defects, is on the contrary desirable to be absolutely avoided. 
     Together with the above, particular care must also be placed in the ability of the joint both to avoid hydraulic load losses, and to avoid altering the optimum flow of the fluids conveyed and to withstand the severe tests imposed, as mentioned, by the applicable norms. 
     SUMMARY OF THE INVENTION 
     The technical aim of the present invention is to eliminate all the disadvantages of the prior art, by providing an improved dielectric joint, particularly for metallic conduits for liquids and/or gases which ensures a complete dielectricity, associated with a high mechanical resistance and a high resistance to wear in which has an absolute seal, all in compliance with the Government norms which regulate their construction. 
     A further and not least object of the present invention is to provide an improved dielectric joint, particularly for metallic conduits for liquids and/or gases which is easy to manufacture and to install and, finally, substantially modest in cost. 
     This aim and other objects are achieved by an improved dielectric joint, particularly for metallic conduits for liquids and/or gases, of the type comprising a first cup-like shaped end portion of a first conduit length, in which a second flange-like shaped end portion of a second conduit length to be joined to said first one, is inserted, characterized in that said second end portion internally presents a precision seating recess accommodating a cylindrical element, of highly insulating material, extending flush to the inner wall of said first conduit length, the end of said cylindrical element facing towards the bottom of the cup, having a radial annular end projection for the constant separation of said flange-like portion from the bottom of said cup-like portion, said projection axially and sealingly engaging an annular gasket, and being provided with means for blocking therein, said gasket being interposed between the side of said flange-like portion facing towards the bottom of said cup-like portion and said cup and between the inner lateral walls thereof, said gasket being also provided with position blocking means between the outer walls of said flange and the inner walls of said cup there being furthermore placed electric insulation elements for electric insulation and stiffening of said joint. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and advantages of the invention will become apparent from the detailed description of an improved dielectric joint, particularly for metallic conduits for liquids and/or gases, according to the invention, illustrated only by way of non-limitative example in the accompanying drawing table, where the single FIGURE illustrates the invention in longitudinal cross section. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     More in detail, the reference numeral 1 indicates an improved dielectric joint, particularly for metallic conduits for liquids and/or gases, which comprises a first cup-like shaped end portion 2a of a first conduit length 2 to be joined, in which is inserted a second counterposed flange-like shaped end or head portion 2b of a second conduit length 2&#39; to be joined to the first length 2. As visible, the cup-like portion 2a includes an enlarged end or head portion 15 monolithic with the length 2 and a ring element 2e, welded to portion 15 at 16, which surrounds the flange-like portion 2b. Furthermore the conduit lengths 2 and 2&#39; define inner surfaces which are flush to each other, while the ring element 2e has an enlarged end portion 2g surrounding the conduit end 2&#39; and having smaller inner diameter than the outer diameter of flange 2b. The ring element 2e has a second end portion 2f countershaped and in contact with the conduit length 2. 
     The second portion 2b internally presents, for a selected portion, a precision seating recess 3 for accommodating therein a cylindrical element 4, of electrically insulating material (such as polycarbonate with a 40% of glass-wood) which, with its internal wall extends flush to the inner wall 2c of the conduit-lengths 2, 2&#39;. The cylindrical element 4, at the end directed towards the bottom 2d of the cup-like portion 2a, ends with an annular projection 5, which is directed radially outwards and extends between the flange-like portion 2b and the bottom 2d of the cup-like portion 2a. 
     The projection 5 is provided with a perimetral collar 5a which constitutes means for blocking said projection in an annular gasket 6, interposed between the side of the flange 2b facing towards the bottom 2d of the cup-like portion 2a and the ring element 2e of the cup-like portion 2a, and provided with means for blocking in position, constituted by a series of small teeth 7 which project outwards therefrom and penetrate in related complementary holes provided both in the bottom 2d of the cup 2a and in the side of the flange 2b directed towards the cup bottom. Between the outer walls of the flange 2b and the inner ones of the ring element 2e of the cup 2a, stiffening means for the joint 1 are arranged, each of which consists of a casting 8 of a material such as resin in which bars 9 of rigid and highly dielectric material (such as the one commercially available as &#34;EPOVIT&#34;) are buried; electric insulation elements are furthermore provided, also arranged between the outer walls of the flange 2b and the inner ones of the ring 2e of the cup 2a, and including a further annular gasket 10 of mixed material, also with highly insulating and rigid characteristics. 
     To close the entire joint, a casting 11 of polymerized resin is provided in the annular interspace formed between the enlarged end 2g and the conduit 2&#39;. As visible, the enlarged end portion 2g has an annular recess 12 having a transverse side 12a facing the conduit 2&#39; and defining a variable distance from the conduit 2&#39; itself. In detail, such distance increases towards the flange 2b to form a dovetail joint with the casting 11. 
     The joint is assembled as follows: first, the ring element 2e, having its end portion 2f not yet deformed and flush with the remaining part of the ring is positioned on a known machine which has the specific function of keeping all the elements of the joint 1 centered during their assembly. 
     Subsequently, the annular gasket 10 and the flange-like portion 2b are positioned coaxially with respect to the ring 2e, introducing them through the undeformed portion 2f. Above the gasket 10, the resin casting 8 is then performed between the flange-like portion 2b and the ring 2c, and the rigid and dielectric bars 9 are buried therein and interpose in direct contact between the outer walls of the flange 2b and the inner ones of the ring 2e. The cylindrical element 4 is inserted and positioned, together with the elastomeric gasket 6: the projection 5 is previsouly forced in the gasket 6, so that assembly is simplified and the connection more precise. 
     Then the head portion 15 of the conduit length 2 is inserted and the various parts are locked by plastic deforming the portion 2f of the ring 2e so that this portion is pressed against and countershaped to the head 15 to obtain a monobloc with the other components. 
     Thereafter the interspace between the end of the conduit length 2&#39; and the enlarged end portion 2g of the ring 2c is filled by the additional casting 11 of polymerized resin, which casting, at the outwards facing end, fills a recess 12 having a dovetail shaped cross section, intended to prevent an accidental leak out of said casting once it has hardened. 
     Finally, the element 2e, which constitutes the abovesaid walls of the cup 2a, is welded at 16 near the plastically deformed portion 2f to join it to the outer walls of the conduit length 2. 
     In practice, it has been observed that the invention thus described achieves the intended aims. 
     The invention thus conceived is susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept. 
     Moreover, all the details may be replaced with technically equivalent elements. 
     In practice, the materials employed, as well as the dimensions, may be any according to the requirements without thereby abandoning the scope of the following claims.