Patent Publication Number: US-2010109250-A1

Title: Dynamic sealing element

Description:
The present invention relates to a dynamic sealing element, intended in particular for a steam head gasket, with a base body having a contact face, whereby the contact face is in surface contact with a surface to be sealed after breaking in. Furthermore, the invention relates to a method for forming a contact face of a dynamic sealing element which develops out of a base body and is in surface contact with a surface to be sealed after breaking in. 
     DE-C-482 546 discloses a coupling for a steam line having a loose sealing ring between the opposing end faces of one-half of the coupling which is stationary and another half of the coupling which is rotating. The coupling ring is provided with a sealing face perpendicular to the axis of rotation and with a curved sealing face and is made at least in part of carbon or pressed graphite. 
     The subject matter of DE-C-332 831 is a sealing disk for sealing the bearing of a crankshaft with respect to a crankcase. The sealing disk has ring-shaped sealing strips which become wider in terms of their basic area and which rapidly wear up to a certain limit in breaking in the machines. The sealing strips then ensure a tight contact with the housing wall. 
     A sealing element for a bearing according to DE-A-1 750 294 comprises two ring-shaped pressed parts that are rotatable relative to one another and have oppositely directed contact sealing faces. 
     DE-A-197 09 369 discloses a machine for making paper webs or cardboard webs in which a heatable roller is supported over a loose bearing. 
     To seal rotating systems such as rollers or drums with respect to pressurized lines carrying hot or cold water or heating medium oils, for example, steam head gaskets or feed head gaskets are used. The construction of such gaskets must be designed so that in addition to a rotating movement, vibrational movements, pendulum movements and tumbling movements are also made possible, all of which may occur in sealing the corresponding systems. This is done by using primarily carbon sealing rings having a convex or concave contact surface. Sealing elements in this regard must run without interruption and without maintenance for long periods of time, e.g., in the paper and pulp industry. 
     To achieve the desired sealing effect, complex manufacturing steps are necessary because surface contact of the sealing element with a surface to be sealed must be ensured to prevent liquids or gases from escaping. Usually the sealing elements are inserted into a steel mold after processing by cutting and then are rotated to check on the extent to which there is point contact or surface contact. If point contact is observed, follow-up processing is required. 
     The object of the present invention is to further improve upon a sealing element, intended in particular for a steam head gasket, of the type defined according to the invention such that the manufacturing process is simplified without having to accept any sacrifices in terms of the sealing effect. 
     According to the invention, this object is achieved essentially by the fact that the contact surface of the unused sealing element has at least one protrusion supportable on the surface to be sealed, functioning as a breaking-in aid. 
     More than one protrusion may also extend away from the contact surface. 
     Based on the inventive teaching, after production of the sealing element, no further machining, e.g., by lapping or polishing, is necessary. Instead, because of the at least one protrusion forming a breaking-in aid, a greater sealing effect is achieved with a shorter breaking-in time. The protrusion wears rapidly, so that then surface contact with the opposing running surface to be sealed is achieved, with the result that the desired sealing effect prevails. 
     According to the invention, in an area of rapid wear on the sealing face, a change in geometry is implemented to ensure at least a linear seal after insertion of the sealing element, developing into a surface seal after a short period of time, this in turn offering the desired sealing effect without requiring expensive reworking or insertion in a gauge and checking the sealing surface after production of the sealing element itself. 
     In particular this provides for the breaking-in element to be designed to be integral with the base body. However, there is also the possibility of the breaking-in element being designed by adhesive bonding, spraying or as an insert to be introduced into a recess in the base body. 
     The sealing element should be made of at least one material from the group of carbon graphite, graphite, metals, thermoset plastics, filled thermoset plastics, elastomers, filled elastomers. 
     The material of the breaking-in element may be the same as that of the sealing element but it may also deviate from the latter. 
     A method for forming a contact surface of a dynamic sealing element which proceeds from a base body and is in flat contact with a surface to be sealed after breaking-in is characterized in that a dynamic sealing element is used; in the unused state this sealing element has at least one protrusion extending away from the surface to be sealed and supported by the base body, serving as the breaking-in element which is worn to the required extent, in particular completely or almost completely during the breaking-in of the sealing element for surface contact of the contact surface with the surface to be sealed. 
    
    
     
       Additional details, advantages and features of the invention are derived not only from the claims, the features to be derived from the claims—either alone and/or in combination—but also from the following description of an exemplary embodiment based on the drawings. 
         FIG. 1  shows a detail of a housing with a sealing element, 
         FIG. 2  shows a detail from  FIG. 1  in an enlarged diagram. 
     
    
    
       FIG. 1  shows a detail of a housing  10  in which a shaft (not shown), e.g., of a roller or a drum, is mounted and is sealed with respect to the housing  10  by a dynamic sealing element  12 . The sealing element is intended for a steam head gasket or a feeder head gasket in particular to allow sealing with respect to the hot or cold water or heating medium oils. The sealing element  12  has a base body  13  in the form of a ring body in the exemplary embodiment, said ring body being acted upon by force applied by means of a spring arrangement  16  in the direction of a surface  14  of the housing  10  to be sealed, e.g., by means of a spring arrangement  16 . 
     In supplying steam, hot and cold water and heat exchanger oils in revolving drums and rollers, in addition to the rotational movement, vibrational movements, pendulum movements and tumbling movements may also occur. The design of the gasket  12  must thus allow a certain angular movement. This is achieved by the fact that the gasket  12  has a crowned contact surface  18  that has a convex curvature in the present exemplary embodiment. However, the present invention is not limited in this regard. Instead, a concave contact surface may also be used. However, the inventive teaching still applies even to contact surfaces that are designed to be flat, i.e., having neither a convex nor a concave curvature. 
     To simplify the production of the sealing element  12  without having to accept sacrifices in the sealing effect, it is provided according to the present invention that at least one protrusion  20  extends from the contact surface  18  and consequently protrudes over the contact surface  18 . According to the diagram in  FIG. 2 , the protrusion  20  may be provided in the area of the largest diameter of the sealing element  12 . The protrusion  20  may have the geometry of a section of a circle in cross section and may have a height between 0.01 mm and 2 mm, in particular 0.02 mm and 0.5 mm, for example, although these numerical values are not to be interpreted as restrictive. The protrusion  20  may also have the same dimensions in width. Widths between 0.02 mm and 1 mm are to be preferred, however. 
     In the case of a sealing element having an outside diameter of 100 mm intended for a steam head gasket, the height of the protrusion should be between 0.02 mm and 0.1 mm. 
     Due to the presence of the protrusion  20 , this ensures that when the sealing element  12  is inserted, a sealing effect occurs immediately with respect to the surface  14  to be sealed or the opposing surface. At the same time, there is rapid wear, resulting in a high sealing effect being achieved after only a short breaking-in time. The breaking-in time typically amounts to a few seconds and depends on the material. In particular the breaking-in time amounts to between 1 second and 10 minutes, preferably between 1 second and 60 seconds. 
     The protrusion  20 , which is present only in the unused sealing element  12 , consequently serves as a breaking-in aid which is worn off after only a short period of use. 
     Due to the protrusion  20  that produces the sealing effect already at the beginning of use, it is not necessary after production of the sealing ring  12  to first have to place the sealing ring in a gauge such as a steel mold to ascertain by turning the sealing ring whether the contact surface has a shape within the defined tolerance, i.e., there is surface contact rather than linear contact with the steel mold. If linear contact occurs, then reworking is necessary, e.g. by lapping and polishing. 
     The dynamic sealing element  12  is made of a material from the group of carbon graphite, graphite, metals, thermoset plastics, filled thermoset plastics, elastomers, filled elastomers. The at least one protrusion  20  protruding above the contact surface  18  of the sealing element  12  prior to use likewise consists of a material of the group mentioned above. However, this does not mean that the protrusion  12  and the base body  13  of the sealing elements  12  must be made of the same material. 
     It also does not go beyond the scope of the present invention if the at least one protrusion  20  is not produced as an integral part with the base body  13 . Instead there is the possibility of manufacturing the at least one protrusion  20  separately and then adhesively bonding it to the contact face  18 , for example. Spraying of a material that forms the protrusion  20  is also possible. 
     According to another proposed approach, one or more receptacles are formed in the contact face, an element forming the protrusion  20  being inserted into these receptacles, exerting the function of the breaking-in aid. 
     Furthermore, the inventive teaching is not limited to sealing elements which execute a rotational movement. The inventive teaching can also be applied to sealing elements which execute a translational movement.