Abstract:
The invention relates to a seal for medium-conducting components, whereby the components ( 12, 13 ) comprise sealing surfaces ( 20, 25 ), which are exactly complementary to each other and which are directly pressed together to form a gap-free seal. The contact surfaces ( 44 ) between the sealing surfaces is limited to a narrow region directly adjacent to the medium cavity ( 19 ). Said gap-free and dead-volume-free seal can be used, for example in germfree, or sterile processes.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a sealing system for media-carrying parts according to the preamble of claim  1 . 
     In order to meet the increased demands made as regards hygiene and product quality, such as e.g. the reduction in the quantity of preservatives in cosmetic products and foods, the increase in the keeping quality of dairy products and beverages, as well as in the pharmaceutical and other industries, where GMP (Good Manufacturing Practice) is a prerequisite, corresponding installations, components and parts are required, which satisfy the requirements as regards low germ content and sterility. 
     It has been found that in particular the sealing system of the components or the like is a key aspect of such processes. As a result of ageing phenomena, external influences such as temperature, attacks by aggressive media, the seals are often damaged to such an extent that at the seal zone between the components dead volumes, clearances, etc. form, which are potential contamination sources, so that it is possible for germs, bacteria or the like to be deposited there. Thus, the nature of the seal is particularly critical. Whereas on the one hand a profile seal has been discussed, other users favour a sealing system using an O-ring. 
     BRIEF SUMMARY OF THE INVENTION 
     The problem of the invention is to provide a detachable sealing system for media-carrying parts, which differs from conventional seals in that it has a better sealing action and consequently satisfies the constantly increasing demands made in low-germ or sterile processes. 
     This problem is solved by the features of claim  1 . Further developments of the invention form the subject matter of the subclaims. 
     The invention proposes that the media-carrying parts have precisely complimentary sealing surfaces to one another and which are directly pressed against one another for forming a clearance-free seal. The contact surface between the sealing surfaces is limited to a narrow area directly adjacent to the media area. Unlike in the case of conventional seals, the sealing system according to the invention has no additional sealing element, such as a sealing ring or the like. Preferably it is a purely “metal on metal seal” made from the same basic material and whose sealing action is brought about by the characteristically formed sealing surfaces on both parts, when the latter are braced against one another. A surface treatment or coating is possible, but not absolutely necessary. The complimentary sealing surfaces act in the manner of a plug and a die, which engage in one another. As opposed to conventional seals, where as a result of the material thickness of the sealing element a clearance always forms towards the media area, the seal in the present case is free from clearances. In particular the sealing clearances on conventional seals constitute potential contamination sources, because the sealing element can deform through the clearance into the media area, where a bead-like projection forms, on which residues in the form of puddles can e.g. form on emptying media-carrying pipelines and which constitute an ideal nutrient medium for bacteria or germs. This problem is obviated by the clearance-free seal of the connection according to the invention. In general, the sealing elements of conventional seals are foreign bodies, which behave quite differently to the remaining media-carrying parts. They are e.g. permanently exposed to the medium, e.g. gases or liquids and can consequently be attacked or swell, which leads to a reduction in the sealing action. They are also exposed to constant temperature changes, e.g. if the installation is steam-sterilized. For example, conventional sealing rings are only allowed up to approximately 135° C. in low-germ or sterile processes. However, in the process according to the invention the seal is formed by the media-carrying parts, so that a swelling or the like is impossible. 
     Another advantage of the sealing system requiring no elastomeric seals is that in the case of thermal sterilization the seal does not act as an insulator and the sterilization heat in the minimum time reaches all necessary areas by heat conduction. 
     Media-carrying parts in the sense of the present application are understood to be all devices in contact with or conveying media, such as liquids or gases and which can be devices in the form of pipes, containers, fittings, valves, etc. The connections for media-carrying parts are understood to mean connections between the pipes, containers, etc. The sealing system can be a joint connection between two pipes, a pipe and a container, etc. Such connections can be screw, flange, clamp or clip connections or the like. However, it is also possible to use the sealing system for valves or the like, e.g. as a valve housing seal and/or as a spindle seal. 
     The contact surface between the sealing surfaces of the parts is limited to an area, whose size is very small compared with the nominal width of the sealing system. The nominal width is the internal diameter of the medium area of the sealing system in millimeters and which is bounded by the medium area wall. The width of the contact surface can be a {fraction (1/5,000)} to {fraction (1/50)}, preferably {fraction (1/1,000)} to {fraction (1/250)} of the nominal width of the sealing system, e.g. 0.01 to 1 mm, preferably 0.05 to 0.2 mm. This area is directly adjacent to the media area and the sealing action of the seal consequently starts directly at the transition between the contact surface and the media area. 
     As a result of the small dimensions of the contact surface the specific sealing pressure on pressing together the parts, is preferably in the elastic deformation range of the material of the parts. It can be close to the yield point (0.2% yield strength) of the material of the parts, e.g. 20 to 80% of the yield point value. The sealing pressure value can be approximately 30 to 140 Newton/mm 2 . There is no cold welding of the parts, even under a high contact pressure. However, certain plastic deformations, e.g. in parts of the surfaces are possible. 
     According to a further development of the invention the sealing surfaces can have a guide, which acts transversely to the media area, e.g. in the radial direction. As a guide, particularly in the radial direction, are preferably provided the profiled sealing surfaces of the parts. For this purpose the cross-sections of the sealing surfaces preferably have a complimentary curved profile. The profiles can e.g. be in the form of a bead and groove. However, preferably these sealing surfaces have two complimentary S-shaped profiles engaging in one another on bracing the parts. It is also possible to use interengaging trapezoidal profiles. The sealing surfaces can consequently form a type of ring spherical seal. 
     In a further development of the invention the sealing surfaces can be designed in such a way that the specific sealing pressure decreases from the intersection line of the sealing gap with the wall of the media area. This makes it possible to prevent the sealing gap “beaking” at said intersection line leading to the formation of a clearance in which germs or bacteria could collect. As a result of the adjustable contour of the sealing surfaces it is possible to interchange parts without leaks occurring. In particular, an addition of tolerances in the dimensions of the sealing surfaces does not give rise to leaks. The sealing gap is always directly tight at its intersection line with the media area. The sealing surfaces are constructed as a type of sealing lip with a complimentary half-recess. 
     Adjacent to the contact surface formed by the two sealing surfaces can be surface portions of both parts cut free from the contact surface, which i.e. are not in stop form on bracing the parts. However, these can serve as reserve contact surfaces, if the contact surface is enlarged away from the media area under the sealing pressure. Therefore the free-cut away from the contact surface should gradually increase. These surface portions are also preferably constructed complimentary to one another. They can pass into two plane-parallel surfaces, but preferably are also curved and preferably form an annular clearance. The width of the annular clearance can e.g. be {fraction (1/5,000)} to {fraction (1/500)}, particularly {fraction (3/5,000)} to {fraction (7/5,000)} of the nominal width of the sealing system. 
     In a further development of the invention guide portions can be provided transversely and spaced from the sealing surfaces for the precentring of the two parts. The guide portions can e.g. be axially directed guide surfaces. At the two guide portions, particularly at the transition of the guide portions into the surface areas forming the reserve contact surfaces and at an end opposite the same, said guide portions can have insertion bevels, which are used for bringing together the two parts. The insertion bevels can e.g. be formed by chamfers. Between the two guide portions there is preferably a guide clearance, e.g. an axial separating gap, which makes it possible to orient the two parts in accurately fitting manner with respect to one another on pressing together the sealing surfaces. 
     In particularly preferred manner the dimension of the contact surface, particularly the sealing lip adjacent to the media area with its complimentary half-recess is dimensioned in such a way that the sealing chamfer at the transition to the media area wall is aligned in projection-free manner therewith. As a result of the clearance-free seal between aligned wall portions a detachable connection is possible, whose sealing gap is scarcely visible or tangible in the media area. Apart from ideal conditions for a low line resistance, a residue-free cleaning and emptying are possible. 
     According to a further development of the invention a clearance is formed between the parts in the bracing direction. The clearance is in particular so large that on bracing the sealing system up to the closing of the clearance, the sealing pressure is built up by the elastic deformation of the parts. The clearance width can be approximately {fraction (1/5,000)} to {fraction (1/100)}, preferably {fraction (1/100)} to {fraction (3/100)} of the nominal width of the sealing system. For this purpose between the sealing surface and a bracing or clamping device bringing about the bracing of the parts, e.g. tightening screws, clamps, etc. can be provided a portion of the parts, e.g. a ring or tube-like projection, which is elastically deformable. Therefore the presetting of the contact pressure is essentially determined by the size of the clearance, the length of the projection, the modulus of elasticity of the material and the flexibility of the parts. 
     The sealing system can also be a flange connection, in which the contact pressure is produced by screwing the flanges. Sealing systems constructed as joint connections are preferably welded in a pipeline or to a container, orbital welding being particularly suitable. The weld point is preferably approximately 35 to 50 mm from the sealing surfaces of the sealing system. This is sufficient to prevent a temperature-deformation at the sealing surfaces. In addition, the relatively large diameter and the relatively high thermal capacitance inhibits heat conduction to the sealing surface. Particularly for high-grade sealing systems the heat conduction from the weld point in the direction of the sealing surfaces is low, because the high-grade steel acts as an insulator. 
     The clearance-free seal can be used for the connection of two pipe or container parts. However, it can also be used for sealing valve components, e.g. for sealing a metal valve bellows. 
     The parts forming the sealing system and the sealing surfaces can be made from a hard material, e.g. stainless steel. However, other materials are also suitable from which all the parts can be produced, e.g. ceramic or plastics materials. 
     The invention also covers a process for the production of a sealing system according to one of the claims  1  to  12 . The process is characterized in that the sealing surfaces can be produced by precision profile turning by means of complimentary profile cutting edges or bits. The reserve sealing surfaces can be produced at the same time using the same profile bits. The turning method can e.g. be face-turning, in which a surface located perpendicular to the workpiece rotation axis can be worked. 
     Plastic sealing systems are preferably produced by injection moulding. The relatively small sealing surfaces can either be moulded at the same time through the use of precision injection moulding processes or can be made subsequently by precision working. 
     These and further features can be gathered from the claims, description and drawings and the individual features, both singly and in subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions, for which protection is claimed here. The subdivision of the application into individual sections and the subheadings in no way restrict the general validity of the statements made thereunder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the invention is described hereinafter relative to the attached drawings, wherein show: 
     FIG. 1 A part sectional view through the connection. 
     FIG. 2 A longitudinal section through a first part of the connection. 
     FIG. 3 A larger scale representation of detail X of FIG.  2 . 
     FIG. 4 A longitudinal section through a second part of the connection. 
     FIG. 5 A larger scale representation of detail Z in FIG.  4 . 
     FIG. 6 A part sectional representation of details X of FIG. 1 and Z of FIG. 3 with the connection parts joined together. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The sealing system according to the invention is to be illustrated in exemplified manner by means of a screw coupling  11 . However other sealing system types are possible, e.g. flange, clamp or clip seals. 
     FIG. 1 shows a screw coupling  11  such as is in particular used for the detachable connection of two pipes. The screw coupling  11  comprises three parts, namely a threaded connector  12 , a collar connector  13  and a clamping device  50  in the form of a box nut  14 . The threaded connector  12 , collar connector  13  and box nut  14  are preferably made from stainless steel, e.g. a chrome-nickel-molybdenum steel. It is e.g. possible to use austenitic chrome-nickel-molybdenum steels of material numbers 1.4404 or 1.4435 with a 0.2% yield strength (Rp 0.2 ) at 50° C. of 182 mm 2 . The standard nominal widths of such sealing systems are 6 to 100 mm (DN 6 to 100). The sealing systems are conventionally designed for operating pressures up to 60 bar. As a function of the diameters, they can also be designed for much higher pressures. The surfaces of the sealing systems are suitable for cleaning-in-place (CIP) cleaning and sterilization-in-place (SIP) sterilization. 
     The threaded connector  12  comprises a pipe section  15 , to which is connected a larger diameter threaded section  16 . The pipe section  15  is welded to a not shown pipe. Orbital welding has proved to be a suitable welding process for sterile or low-germ processes. The transition between the threaded section  16  and pipe section  15  is conically rounded. The threaded section  16  has an external thread  17 , which extends from the transition between the pipe section  15  and threaded section  16  to the end of the latter. At the threaded section-side end of the threaded connector  12  is formed a radially circumferential slit  18 , which is directed towards the media area  19 , i.e. towards the pipe interior. At the foot of the slit  18  are formed the sealing surfaces  20  and reserve sealing surfaces  21  of the threaded connector (FIG.  6 ). 
     The collar connector  13  also has a pipe section  22 , as well as a flange section  23 . The pipe section  23  of the collar connector is also welded to a not shown pipe. The flange section  23  is a step-like widening on the outer surface of the pipe section  22 . At the flange-side end of the collar connector, the flange section  23  has a radially circumferential, annular projection  24 . At the face of the projection  24  are formed the sealing surface  25  and the reserve sealing surface  26  of the collar connector. 
     The clamping or bracing device  50  for joining the parts is a box nut  14  in the present embodiment. It is used for bracing the threaded and collar connectors  12 ,  13 . It has a threaded section  27  with an internal thread  28 , as well as a stop collar  29  for fixing the box nut  14  to the collar connector  13 . The internal thread  28  has a hard metal coating in order to prevent corrosion on screwing the box nut  14  to the threaded connector  12 . In place of a threaded bracing device it is also possible to use flanges with clamping bolts, bracing clips, hydraulic clamping devices, etc. 
     FIGS. 2 and 5 show the collar connector  13  separately. The projection  24  of the collar connector  13  has a profiled face, on which are formed the sealing surface  25  and reserve sealing surface of the collar connector  13  (FIG.  3 ). 
     The sealing surface  25  has a curved profile in the form of a S-shape. Adjacent to the media area wall  30  is a half-recess  31 , which passes into a bead-like protuberance  32 . In turn, the protuberance  32  passes at its side remote form the media area  19  into a groove-like depression  33  to which is adjacent the reserve sealing surface  26 . The reserve sealing surface  26  is a semicircular protuberance which, at its end remote from the media area  19 , passes into a planar insertion bevel  34 . The dimension of the reserve sealing surface  26  is approximately 5 to 10 times larger than the dimension of the sealing surface  25 . Adjacent to the insertion bevel  34  is provided a guide section  36  of projection  24  positioned axially to the media area wall  35  and passing into a radial section  37  of the flange section  23  of the collar connector  13 . 
     FIG. 4 separately shows the threaded connector  12 . At the foot of the slit  18  are formed sealing or reserve sealing surfaces  20 ,  21  of the threaded connector  12  complimentary to the sealing surface  25  or reserve sealing surface  26  of the collar connector  13  (FIG.  5 ). The sealing surface  20  also has a S-shaped profile. Adjacent to the media area wall  30  is a sealing lip  37  complimentary to the half-recess  31  of the collar connector  13  and which passes into a groove-like depression  38 , which is complimentary to the bead-like protuberance  32  of the collar connector. The groove-like depression  38  at its end remote from the media area  19  passes into a bead-like protuberance  39  complimentary to the groove-like depression  33  on the collar connector. The reserve sealing surface  21  is adjacent to the bead-like protuberance  39 . The reserve sealing surface  21  is a semicircular depression, which at its end remote from the media area passes into a planar insertion bevel  40 . The dimension of the reserve sealing surface  21  at the threaded connector  12  is also approximately 5 to 10 times larger than the dimension of the sealing surface  20  at the threaded connector  12 . Adjacent to the insertion bevel  40  is a guide section  41  of slit  18  positioned axially to the media area wall  30 . At its end facing the reserve sealing surface  21 , the guide section  41  passes through a further insertion bevel  42  into a radial section  43  of the threaded section  16  of the threaded connector  12 . 
     The sealing surfaces  20 ,  25  and the reserve sealing surfaces  21 ,  26  on the collar or threaded connectors  12 ,  13  are produced by a precision turning process, e.g. by precision face-turning. The cutting tool used can be in the form of a small flip or turnover plate, e.g. made from hard metal, which has cutting edges with the contour of the S-shaped sealing surface  20 ,  25  and semicircular reserve sealing surface  21 ,  26  and which cuts said contour into the face of the projection  24  of the collar connector  13  and to the foot of the slit  18  of the threaded connector  12 . The complimentary profiled tool bits are shaped by profile grinding wheels. 
     FIG. 6 shows the projection  24  of the collar connector  13  engaging in the slit  18  of the threaded connector  12 , when the collar connector  13  and threaded connector  12  are brought together. A contact surface  44  immediately adjacent to the media area wall  30  is formed between the sealing surfaces  20 ,  24  of the threaded and collar connector  13 . The contact surface  44  begins directly at the intersection line between the sealing gap  45  formed by the two sealing surfaces  20 ,  25  with the media area wall  30 . The sealing lip  37  of the threaded connector  12  with the complimentary half-recess  31  of the collar connector  13  engages in stop manner. The bead-like protuberance  32  of the collar connector  13  and the complimentary groove-like depression  38  of the threaded connector  12  also engage in stop manner and consequently form the second portion of the contact surface  44 . The groove-like depression  33  of the collar connector  13  and the bead-like protuberance  39  of the threaded connector  12  are not completely in stop engagement, but are instead increasingly spaced from the media area  19  on their media-side, remote flanks and consequently also form reserve sealing surfaces. For a nominal width of 50 mm, the size of the contact surface  44  is e.g. approximately 0.1 mm. 
     The semicircular reserve sealing surfaces  21 ,  26  are not in stop engagement, but instead form between them an annular clearance  46 . The width of the annular clearance  46  is approximately 0.05 mm in the embodiment described. 
     To the annular clearance  46  is axially towards the media area wall  30 , a separating gap  47 , which is formed by the two guide sections  35 ,  41  of the threaded or collar connector  12 ,  13 . The width of the separating gap  47  is about the same or slightly less than that of the annular clearance  46 . 
     Adjacent to the separating gap  47  is a clearance  48  perpendicular to the media area wall  30  or radial to the pipe and which is used for bracing the threaded and collar connectors  12 ,  13 . The width of this clearance  48  is e.g. approximately 0.1 mm for the nominal width DN50. The widths of the projection  24  of the collar connector  13  and the slit  18  of the threaded connector  12  are approximately 3 mm, e.g. with a nominal width of 50 mm. 
     Hereinafter is described a further embodiment, which is not shown in the drawings. The sealing system according to the invention can e.g. be used for sealing valves. In sterile technology, e.g. the rods of piston valves are sealed in substantially dead volume-free manner with respect to the reaction vessel by a bellows. Materials for such bellows can be metals or also Teflon (PTFE). The bellows is in turn sealed at a seat towards the piston valve rod and at the housing to the environment. In the case of metal bellows the sealing system at the seat and housing can be implemented by the sealing system according to the invention using two complimentary sealing surfaces, i.e. a profiled sealing surface on the piston valve rod or a profiled sealing surface on the housing cover. The sealing system of the valve body in the valve seat can also take place according to the invention and a pipeline system made entirely from one material, e.g. stainless steel can be formed. 
     FUNCTIONAL DESCRIPTION 
     In the case of the screw coupling  11  shown in FIGS. 1 to  5 , firstly the collar connector  13  is mounted on the threaded connector  12 . The guide section  35  of the projection  24  is guided by the guide section  41  of the threaded connector  12  and is radially precentred. On further bringing together the collar and threaded connectors  12 ,  13 , the complimentary constructed, profiled sealing surfaces  20 ,  25  engage in one another, which brings about a further radial centring, thereby preventing damage to the precision worked sealing surfaces. The collar and threaded connectors  12 ,  13  are brought together until the sealing surfaces  20 ,  25  stop-engage on the end face of the projection  24  of the collar connector  13  and on the foot of the slit  18  of the threaded connector  12 . The sealing surfaces  20 ,  25  form a contact surface  44  bringing about a seal towards the media area  19 . As a result of the separating gap  47  between the guide sections  35 ,  41 , the two sealing surfaces  20 ,  25  can be mutually oriented in accurate fitting manner. In the case of damage or deformations in the front area of the sealing gap  45 , the contact surface  44  can migrate radially away from the media area  19  and can consequently be subject to automatic adjustment. This is helped if the sealing surfaces are profiled in such a way that they initially contact in the area adjacent to the media area, i.e. where the pressing action is greatest. 
     Thus, a contact surface can form between the reserve sealing surfaces  21 ,  26 . If the sealing surfaces  20 ,  25  are stop-engaged and have been oriented, the bracing of the parts can commence. For this purpose the internal thread  28  of the box nut  14  is screwed onto the external thread  17  of the threaded connector  12 . The pretension is set in that the clearance  28  between the radial sections  36 ,  43  of the collar and threaded connectors  13 ,  12  is closed and the projection  24  can elastically deform. The sealing surfaces  20 ,  25  are so mutually oriented that the maximum contact pressure occurs at the contact area between the sealing lip  37  and the half-recess  31 , i.e. directly at the transition to the media area wall  30 . In the described embodiment the contact pressure is approximately 140 N/mm 2 . Due to the high contact or sealing pressure and the high precision working of the sealing surfaces with respect to the surface and radial orientation, particularly in the area of the sealing gap adjacent to the media area a clearance-free, i.e. gapless connection is formed. With respect to the roundness of the parts, a certain automatic adjustment can take place as a result of the profiling of the sealing surfaces.