Abstract:
A method of forming a tension resistant O-ring is formed by extruding a length of precured elastomer with a coextensive central aperture; longitudinally dividing the elastomer; winding a strand of nonelastic synthetic material to form an endless ring having a predetermined toric axis diameter and a toric diameter less than the diameter of the elastomer aperture; assembling the endless ring and elastomer halves in a rubber mold; and, heating the mold to cure the elastomer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to O-ring seals and more particularly to an apparatus and method of forming a tension resistant O-ring. 
     1. Field of Invention 
     O-ring seals are well known and are generally formed from elastomeric material of a predetermined diameter. These seals are used for preventing fluid leaking in many applications and in particular in valves in the oil industry. These seals are effective in maintaining the instrument fluid tight under pressures for example, to 2000 psi, however when the pressure against the seal exceeds these pressures and is in the range of, for example, 68,950 KPA (10,000 psi) and a relief valve opens due to such pressure this high pressure dislodges the O-ring seal from its groove. Another O-ring must be installed in its place which requires disassembly of the relief valve in order to return the apparatus to operating condition. 
     This invention obviates this problem by forming an O-ring seal which is tension resistant and remains in place. 
     2. Description of the Prior Art 
     Conventional O-ring seals presently available in the market place may usually be expanded diametrically, beyond their diameter of repose, through a certain limit without exceeding the yield point of the O-ring material. 
     I am not aware of any prior patent that provides an O-ring seal in which its manufactured diameter cannot be exceeded by either manually or mechanically applied force. 
     BRIEF SUMMARY OF THE INVENTION 
     A continuous length of procured elastomer is extruded in elliptical configuration having a central aperture. A selected length of this tube is longitudinally and divided on its minor axis to form first and second halves. The first half is placed in a circular groove of predetermined diameter in a rubber mold with ends abutted and the semicircular opening facing upwardly. A high tensile cord of nonelastic syntectic material is wound in a groove on a cylinder equal in diameter with the toric axis of an O-ring to be formed and heat sealed to form a single endless strand. This strand is placed in the upwardly open semicircular elastomer groove. The second elastomer half is cooperatively superposed on the first elastometer half with the butted ends of the second half mismatched with the abutted ends of the first half. A companion section of the rubber mold overlies the elastomer and strand assembly and is heated to cure the elastomer, resulting in a tension resistant endless O-ring. 
     The principal object of this invention is to provide an apparatus and method for forming tension resistant O-rings for controlling fluid under high pressure without material damage to the O-ring sealing such pressure. Another purpose is to prevent the O-ring from being blown out of its groove when an O-ring sealed piston leaves its seat. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a vertical cross-sectional view of a typical buckling pin type pressure relief valve, illustrating the valve in open position by dotted lines; 
     FIG. 2 is a transverse cross-section of extruded elastomer; 
     FIG. 3 is a top view of a length of the material of FIG. 2 in place in an upwardly open grove; 
     FIG. 4 is a vertical cross-section taken substantially along the lie  4 — 4  of Fig.3; 
     FIG. 5 is a fragmentary longitudinal cross-section of a cylindrical form; 
     FIG. 6 is a top view of an endless ring formed by nonelastic material; 
     FIG. 7 is a vertical cross-section view of a rubber mold containing the tension resistant O-ring assembly; and, 
     FIG. 8 is a fragmentary cross-section view, to a smaller scale, illustrating installation of a tension resistant O-ring on the perimeter of a valve piston. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Like characters of reference designate like parts in those figures of the drawings in which they occur. 
     In the drawings: 
     The reference numeral  10  indicates a right angle relief valve body  12  having an inlet port  14  and an outlet  15 . The end of the valve body opposite inlet port is closed by a centrally bored bonnet  16  which slidably receives a rod  18  of a valve piston  20  normally sealing with the wall  21  forming the inlet port. An O-ring,  22  insures a fluid tight fit. The piston  20  is held on seat by a slender column  24 , axially interposed between the end of the rod  18  opposite the piston and a plate  26 , supported in spaced relation with respect to the bonnet  16  by a plurality of posts  28 . Excess pressure beyond a preset value for the slender column  24  against the piston  20 , results in the slender column  24  collapsing or bending, in accordance with Euler&#39;s law for slender columns, which suddenly releases the fluid pressure at the inlet port to the atmospheric pressure of the outlet port  15 . This sudden pressure differential between the inlet and outlet ports, particularly when such pressure is on the order of 68,950 KPA (10,000 psi), results in the O-ring  20  leaving its groove. This necessitates shutting down the system and removing the valve body  12 , from the line being monitored, in order to replace the O-ring  22  and reseat the piston  20  after the problem, if any, has been corrected. If this O-ring  22  can be caused to remain in place all that is necessary for placing the valve  10  back in operation is manually closing the piston with its sealing wall  21  and installing a new slender column. 
     The above description forms no part of the present invention other than to set forth a typical buckling pin relief valve problem illustrating the desirability of a new improved tension resistant O-ring as disclosed hereinbelow. 
     Referring to FIGS. 2-7, the reference numeral  30  indicates a grooved block for preparing the material for a tension resistant O-ring. The block  30  comprises a rectangular section of material  32  having a planer top surface provided with an annular upwardly open groove formed on a diameter equal with the toric axis of the O-ring to be formed. The radius of the upwardly open semicircular groove is equal with the radius of the O-ring to be formed. 
     A second form, indicated by the numeral  40  (FIG. 5.) is for preparing the tension strand for an O-ring to be formed. The form  40  comprises two cylindrical parts  42  and  44  each having a right circular end surface in contiguous contact when the two parts are arranged in axial aligned relation. The axial relation is maintained by guide pins  46  cooperatively projecting into respective bore holes in the interface  47  formed by the end surfaces. The assembled form is provided with a circumferential semicircular groove  48  centrally intersecting the interface  46  at the perimeter of the two members  42  and  44 . The semicircular groove is formed on a radius, substantially equal with the radius of the O-ring to be formed and on a diameter substantially equal to the toric axis of the O-ring to be formed. 
     A third unit indicated by the reference numeral  50  (FIG.  5 ), comprises a rubber mold having two parts  52  and  54  each substantially rectangular in overall configuration having a common edge surface which when abutted in contiguous contact relation forms an interface  56 . This interface is intersected by an angular, circular in transverse cross-section, opening  58 , formed on a diameter equal with the toric axis of an O-ring to be formed. At least one of the blocks  52  or  54  is provided with weep holes  60  communicating with the opening  58  at one end and exposed to the atmosphere at the opposite end for draining or releasing excess material during the curing of an O-ring as presently explained. 
     In carrying out the invention a continuous length of recurred elastomer  70  is extruded in elliptical transverse cross-section with a central coextensive opening  72  having a diameter substantially one-third the minor diameter of the elastomer. The diameter of the extrusion  70  along its minor axis is 0.9525 cm (⅜ inch), by way of example. The major axis of the ovate extrusion  70  is preferably substantially one-third greater than its minor axis. A length of the extrusion  70  is placed within the groove  36  of the form  30  with the respective ends of the elastometer in abutted relation. In this position the minor axis of the extrusion  70  is aligned with the top surface  34  of the block  30 . The extrusion  70  is then divided along its minor axis, while in the groove  36  as a guide by using a sharp instrument, resulting in two elongated semiovate sections of the elastomer, as indicated in  74  and  76 . A thread of a nonelastic synthetic material presently marketed by DuPont Corp. under the trademark Kevlar, or another suitable yarn, is wound around the form  40  within its circumferental groove  48  to form a strand of the material having a diameter approximately ¾ the diameter of the elastomer opening  72 . This wound strand of wraps is bonded together, as by heating or cementing in the form  40 , forming an endless ring of the material, as indicated at  78 . The semiovate half  76  of the elastomer is placed in the semicircular groove of rubber mold  50  with the divided opening  72  disposed upwardly. The ring of the synthetic material  78  is then placed within the half of the opening in the elastomer half  76 . The other or opposite half of the elastomer of  74  is placed in registration with the half  76  and the top section of the rubber mold  50  is then position as illustrated by FIG.  7 . The mold is heated with the assembled elastomer parts and ring  78  to a desired temperature, for example, 148.9° C. (300° F.) to 315.5° C. (600° F.) depending upon the elastomer for curing the elastometer and forming a tension resistant O-ring  80  to be used in place of the O-ring  22  in the valve disclosed by FIG.  1 . 
     Referring also to FIG. 8, since the tension O-ring  80  may not be expanded beyond the diameter of its toric axis to install the O-ring on the piston valve  20 ′ it is necessary to modify the piston valve as indicated at  20 ″. The piston valve is transversely divided at the position of the groove, normally nesting the O-ring  22  allowing the O-ring  20  to be seated in the rabbited edge defining the O-ring receiving groove in the perimeter of the remainder of the piston valve  20 ′ as by a bolt or screw  82 . 
     Obviously the invention is susceptible to changes or alterations without defeating its practicability. Therefore, I do not wish to be confined to the preferred embodiment(s) shown in the drawing(s) and described herein.