Patent Abstract:
A thermoformed reverse buckling polymer rupture disk having an unsupported raised center portion including score lines cut in the polymer disk that creates a line of weakness to control the buckling pressure of the disk and forms a predetermined burst pattern.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to polymer rupture disks and specifically to a thermoformed polymer rupture disk that can be economically manufactured and utilized in systems where no metal is desired. 
     2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98 
     Reverse buckling rupture disks are, of course, well known in the art. To applicant&#39;s knowledge, they are all formed of metal and have score lines therein that enable the disks to buckle or burst in a predetermined fashion. 
     For many, many years Teflon® film has been thermoformed as liners for metal reverse buckling rupture disks in order to separate the metal from any fluids that may be detrimentally affected by metal contact. Further, flat Teflon® rupture disks have been used for many years. Some of the flat Teflon® rupture disks develop a “domed” center section resulting from room temperature pressure applied thereto. 
     All such polymer rupture disks in the prior art have a flow area after burst that is relatively small and unpredictable. Second, the burst pressure is difficult to change when the burst pressure is controlled by the construction of the customer&#39;s rupture disk holder or flanges. 
     It would be extremely useful to have a reverse buckling, thermoformed, rupture disk with a relatively large, predictable flow area with buckling pressures controlled by score lines or thin areas or buckling points formed therein. 
     SUMMARY OF THE INVENTION 
     The present invention discloses and teaches a reverse buckling, thermoformed, polymer rupture disk with a raised center and having score lines therein, or thinned areas that are in predetermined locations and that provide a predetermined flow area after burst and enable the burst pressure to be changed even though the disk&#39;s constraining geometry is controlled by the customer&#39;s holder or flanges. 
     The present reverse buckling polymer rupture disk is thermoformed and has an annular flange and a raised center portion, both having a predetermined thickness. The raised portion may be of various shapes including dome-shaped and has an upstream convex side and a downstream concave side and buckles when pressure is applied to the upstream convex side thereof. It has at least one score line formed in the thermoformed polymer rupture disk to create a line of weakness that forms a predetermined burst pattern when rupturing under a predetermined pressure applied to the upstream convex side. 
     Note that the disk can buckle independently of the score lines. In some cases the score lines are used to influence the location of the buckling point or the magnitude of the buckling pressure. In the preferred embodiment, the buckling pressure and location are primarily defined by the thermoformed shape and thickness. The score line(s) are primarily used as a means to create a weakened and predictable rupture path. 
     The score line may be formed in several ways. One of the ways is to cause a predetermined thinning in a predetermined area of the rupture disk during thermoforming by applying a vacuum to the area where it is desired to be thinned. 
     Another method of forming a score line is to use a razor blade that can cut into the polymer material to a predetermined depth. 
     Still another method of forming the score line is to utilize a press having a relatively sharp blade extending therefrom in the shape of the score line and apply a force to the blades to force them into the surface of the polymer rupture disk to create the very narrow but deep score lines. 
     The score lines may be formed in the polymer rupture disk either before, after, or during thermoforming the polymer rupture disk. 
     The desired score line is formed in the flange of the polymer rupture disk adjacent the dome-shaped center portion and extending at least partially around the dome-shaped center portion. 
     In another embodiment, the score line is formed in the dome-shaped center portion with two score lines perpendicular to each other. 
     It is desired that the score line be preferably formed on the downstream side of the rupture disk. However, under certain circumstances, it could be formed on the upstream side thereof. 
     In addition, because some of the rupture disk holding means have centering recesses formed in the annular base thereof, the rupture disk can have a corresponding raised annual centering ring formed in the annular flange, preferably on the upstream side of the polymer rupture disk, to position the rupture disk in fluid flow line in relation to the holding means having the annular recesses. 
     Further, where first and second holding means have identical fluid flow orifice sizes, a flat rigid annular plate may be placed in the downstream side of the polymer rupture disk with an orifice therein having a diameter that is less than the fluid flow line holding means diameter to form an offset shoulder on the downstream side of the thermoformed polymer rupture disk with respect to the fluid line inside diameter to provide support to the flange area of the rupture disk and prevent bending of said flange area when pressure is applied to the convex side of the rupture disk. In some cases, the outer portion of the annular rupture disk flange can form as a skirt that extends perpendicular to the plane of the annular flange in the direction of the downstream side of the polymer rupture disk to aid in centering the polymer rupture disk in the flow line and contain the flat rigid annular plate. 
     Thus, it is an object of the present invention to form the reverse buckling polymer rupture disk by thermoforming the disk. 
     It is another object of the present invention to use Teflon® as the polymer material forming the rupture disk. 
     It is yet another object of the present invention to provide a reverse buckling, thermoformed, polymer rupture disk with a relatively large, predictable flow area after rupture and that has a buckling pressure that is controlled by score lines or thinned areas or buckling points created in the thermoforming process. 
     It is still another object of the present invention to provide a thermoformed reverse buckling polymer rupture disk having a score line therein that penetrates through at least 60% of the polymer rupture disk thickness. 
     It is yet another object of the present invention to provide a rupture disk wherein the score line is thermoformed into the flange of the polymer rupture disk adjacent its dome-shaped center portion and extending at least partially around the dome-shaped center portion. 
     It is also an object of the present invention to provide a reverse buckling, thermoformed, polymer rupture disk having a score line that is cut into the annular flange of the polymer rupture disk adjacent the dome-shaped center portion and extending at least partially around the dome-shaped center portion. 
     It is still another object of the present invention to provide a reverse buckling, thermoformed, polymer rupture disk having a score line mechanically pressed into the annular flange of the polymer rupture disk adjacent the dome-shaped center portion and extending at least partially around the dome-shaped center portion. 
     It is yet another object of the present invention to provide a reverse buckling, thermoformed, polymer rupture disk wherein the score line is formed in the dome-shaped center portion of the polymer rupture disk. 
     It is also an object of the present invention to provide a reverse buckling polymer rupture disk having a score line preferably formed on the downstream side of the rupture disk. 
     It is yet another object of the present invention to provide a reverse buckling, thermoformed, polymer rupture disk that has a raised annular centering ring formed in the annular flange on the upstream side thereof and a skirt formed on the outer portion of the annular flange that extends perpendicular to the plane of the annular flange in the direction of the downstream side of the polymer rupture disk to center a flat, rigid, annular plate placed on the downstream side of the polymer rupture disk. An orifice in the annular plate has a diameter less than the fluid flow line inside diameter and forms an offset shoulder on the downstream side of the thermoformed polymer rupture disk with respect to the fluid line inside diameter to provide support to the flange area of the rupture disk and prevent bending of said flange area when pressure is applied to the convex side of the rupture disk. 
     Thus, the present invention relates to a reverse buckling polymer rupture disk for mounting in a fluid flow line fixture having a predetermined inside diameter and comprising a thermoformed polymer rupture disk having an annular flange and a dome-shaped center portion, both having a predetermined thickness; the dome-shaped portion having an upstream convex side and a downstream concave side and being reverse buckling when pressure is applied to the upstream convex side thereof. At least one score line is formed in the thermoformed polymer rupture disk, either in the annular flange or in the dome-shaped center portion, to create a line of weakness that forms a predetermined burst pattern when rupturing under a predetermined pressure applied to the upstream convex side. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the present invention will be more filly disclosed when taken in conjunction with the following Detailed Description of the Invention in which like numerals represent like elements and in which: 
     FIG. 1 is a side view of the novel thermoformed polymer rupture disk showing the state of the disk in its unstressed condition, an intermediate condition and the final “ruptured” condition; 
     FIG. 2 is a bottom plan view of the novel thermoformed polymer rupture disk shown in FIG. 1; 
     FIG. 3 is a bottom plan view of a thermoformed polymer rupture disk in which score lines are formed in the domed center portion thereof; 
     FIG. 4 is a partial view of a flange and portion of the domed center of the thermoformed polymer rupture disk illustrating the score line cut in the downstream side thereof; 
     FIGS. 5A and 5B illustrate first and second adapters that are used to contain the novel thermoformed rupture disk therebetween in a fluid line; 
     FIG. 6 is a partial cross-sectional view of the novel thermoformed rupture disk to be mounted between the first and second flanges shown in FIG.  5 A and FIG.  5 B and having a flat, rigid, annular plate placed on the downstream side thereof for providing an offset shoulder to create proper buckling of the thermoformed polymer rupture disk; 
     FIG. 7 is a cross-sectional view of a gasket holding the novel thermoformed polymer rupture disk and the flat annular plate for forming the offset shoulder such that a single package (gasket plus disk plus flat annular plate) can be inserted between two standard flanges in a fluid flow line; 
     FIG. 8 is a cross-sectional view of one type of the mounting device for holding a thermoformed polymer rupture disk therein in a fluid flow line; 
     FIG. 9 is a cross-sectional view of a second type of holder illustrating that, in this particular holder, the skirt from the outer edge of the novel thermoformed polymer rupture disk extends perpendicular to the plane of the flange and in the direction of the upstream side of the fixture; and 
     FIG. 10 is a diagrammatic representation of a scoring die device that includes a cutting edge for forming score lines therein. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a side view of a novel thermoformed polymer rupture disk  10  of the present invention. The polymer material is preferably Teflon® but could be other polymers. It has a flange portion  12  and a raised center portion  14  in the shape of a dome that has a convex side  16  in the direction of the operating pressure or upstream side, all shown in phantom lines to the left of flange  12 . A transition area  13  joins the raised center portion  14  and the flange  12 . For illustration purposes and as will be discussed in more detail later, there is also shown an irregular area  17  representing the start of buckling in dome  14 . To the right of flange portion  12  and also in phantom lines, there is shown an intermediate condition where the original convex side  16  of the dome has inverted and is now concave and the dome portion  14  has partially separated from flange  12 . The solid lines represent the final position and condition of disk  10  after rupture is complete. 
     FIG. 2 is a bottom view of the novel thermoformed polymer rupture disk of FIG. 1 illustrating the concave side  18  of the raised portion, which, in the present embodiment, is shown as the center domed portion  14  and the score line  20  that extends at least partially around the dome-shaped center portion  14 . It should be understood that although a raised dome or hemispherical shape is illustrated in the figures as the raised portion, many other raised shapes including but not limited to cylindrical, conical, non-spherical domes, and even combinations of these and other shapes are also intended to be included in the scope of this invention. The score line  20  in the particular case having a dome as shown in FIG. 2 is on the downstream side of the novel thermoformed polymer rupture disk. However, under certain circumstances, as desired, it could be on the upstream side. When pressure is applied to the convex side  16  of the novel thermoformed polymer rupture disk  10  and a predetermined pressure is reached, the disk first buckles in the dome section  14  or in the transition section  13 . The pressure continues to reverse the dome of the disk until the dome becomes taut. The force of reversal then exceeds the strength of the material in the score lines and the disk ruptures along the score lines creating a flow area that is large and predictable. The score line may be formed in a number of ways as will be shown hereafter. One way is to cut it into the flange material  12 . It can be cut to a depth of at least 60% of the thickness of the polymer disk material and preferably 80%. The groove  20  may also be formed by pressing a sharp edge in the shape of the desired groove into the surface of the novel thermoformed polymer rupture disk to a desired depth. Finally, the score line  20  may be formed by the thermoforming process by applying a vacuum in the thermoforming device to the area in which the score line is to be formed, thus thinning the material. 
     Thus, with the knife or the pressure-formed score line, the score line may be formed either before, after, or during thermoforming. However, the score line formed by thinning the material is formed during the thermoforming process itself. 
     FIG. 3 is a plan view of a thermoformed polymer rupture disk having the score line  20  formed of score lines  24  and  26  formed perpendicular to each other in the dome of the disk  22 . 
     FIG. 4 is a partial cross-sectional view of the novel thermoformed polymer rupture disk  10  showing the outer flange  12 , the domed center portion  14  with its convex side  16 , transition portion  13 , and concave side  18 , and the score line  20  formed in the annular flange  12  on the downstream side thereof extending at least partially around the dome-shaped center portion  14 . Note that score line  20  is narrow and deep. 
     FIGS. 5A and 5B illustrate two mating adapters  28  and  42  that can be used to mount one of the novel thermoformed polymer rupture disks therebetween. Note, in FIG. 5A, that a first adapter or body portion  28 , well known in the art, has a first orifice  30  extending axially therethrough in fluid engagement with the fluid flow line with fluid flow being in the direction shown by the arrow. 
     A first end  32  on the first adapter  28  provides for attachment to the fluid flow line and a second end  34  has an annular flange  36  with a flat face  38  thereon and extending outwardly from first end  32  diameter for mating with one flange side of the thermoformed polymer rupture disk as will be shown hereafter. A first annular recess  40 , preferably semicylindrical in shape, is formed in flat face  38  for engaging at least a portion of the flange of the polymer rupture disk to center it. 
     A second adapter or body portion  42  is shown in FIG.  5 B and is substantially identical to the first adapter  28  so that an essentially universal adapter is obtained and either adapter  28  or  42  may be used in place of the other. It has a first end  44  for mating with the other flange side of the thermoformed polymer rupture disk as will be seen in relation to FIG. 6 and a second end  46  that is vented to atmosphere. A second orifice  48  extends through the second body portion  42  in axial alignment with, and having the same diameter as, the first orifice  30 . A second annular recess  50 , similar to annular recess  40 , is formed in the flat face  52  of the annular flange  54  that extends outwardly from the outer diameter of the second end  46 . Flat face  52  is used for mating with the other flange side of the thermoformed polymer rupture disk. 
     A reverse buckling polymer rupture disk holding device  56 , shown in FIG. 6, is mounted in the fluid line. It includes novel thermoformed polymer rupture disk  58  and annular plate support  60 . Because the first and second orifices  30  and  48  of the first and second adapters  28  and  42  have the same diameter, the annular plate support  60  in the form of a flat, rigid washer, has an orifice  62  therein that has a smaller diameter than the adapter orifices  30  and  48 . Thus, support  60  forms an offset shoulder  61  with respect to the flat faces  38  and  52  of the first and second adapters  28  and  42 . The offset shoulder  61  is on the downstream side of rupture disk  58  and therefore the rupture disk  58  first buckles in the dome section  14  or in the transition section  13 . The pressure continues to reverse the dome of the disk until the dome becomes taut. The force of reversal then exceeds the strength of the material in the score lines and the disk ruptures along the score lines creating a flow area that is large and predictable. 
     It will be noted that in FIG. 6 rupture disk  58  has an annular skirt  68  formed on the outer edge  64  of the flange  70  that extends generally perpendicular to the flange  70  in the direction of fluid flow. This skirt is not always needed but when placed in a fixture such as illustrated in FIG. 6 where the annular support  60  is required, the skirt  68  assists in holding the annular support  60  in proper relationship with the rupture disk  58 . In some installations that will be shown later, the skirt  68  could extend in the opposite direction perpendicular to the flange  70 . 
     It will also be noted that rupture disk  58  has an annular centering ring  72  extending outwardly from flange  70  on the upstream side of the rupture disk  58 . This annular centering ring  72  is sized for mating with the annular grooves or recesses  40  or  50  in the flat faces  38  and  52  of the first and second adapters  28  and  42  to enable proper centering of the rupture disk  58  with respect to the first and second adapters  28  and  42 . 
     After the rupture disk  58  and the annular support  60  are placed between the first and second adapters  28  and  42  as shown in FIG. 6, a clamp  74 , well known in the art, is placed around the adapter flanges  36  and  54  and tightened in a well-known manner to maintain the assembly in a fluid-tight relationship. 
     FIG. 7 illustrates a unitary package  76  for mounting between two adapters such as those shown in FIG.  5 A and FIG.  5 B. It includes a rubber or otherwise flexible material  78  that is annular in shape and has an annular recess  79  on the inside center thereof for receiving the thermoformed polymer rupture disk  80  and the support plate  82 . The thermoformed polymer rupture disk  80  has an annular score line  84  in the outer flange thereof that extends at least partially around the center domed portion thereof. The flexible gasket  78  has annular projections  86  and  88  on the sides thereof that extend into the annular recesses  40  and  50  in the adapter faces shown in FIGS. 5A and 5B thus holding the unit  76  tightly between the adapters. A fastener, well known in the art, can then be placed around the adapter flanges shown in FIG. 6 to hold the entire package  76  therebetween. 
     FIG. 8 illustrates another embodiment of a holder for the present invention wherein the holder  90  includes a first body portion  92  and a second body portion  94 . The first body portion  92  has an inside diameter D 0  and the second body portion  94  has an inside diameter D 1  that is greater than D 0 . The novel thermoformed polymer rupture disk  98  is placed between the shoulder  100  of body portion  94  and shoulder  102  of body portion  92  to hold the flanges thereof securely in place. The difference in the diameters D 1 −D 0  forms an offset shoulder for properly positioning the thermoformed polymer rupture disk with respect to the D 0  of the first body portion  92  without the need for any annular support plate. A lock pin  104  can be used if desired to lock the first and second body portions  92  and  94  together. 
     FIG. 9 illustrates a holder for a second embodiment of the novel polymer rupture disk. Note, in FIG. 9, that the unit  106  has the polymer rupture disk  108  with its outer flange  109  being held securely between opposing surfaces  114  and  116 . Note, that the score line  112  is on the downstream side thereof. Also note that the skirt  110  on the outer edge of the flange of the thermoformed polymer rupture disk extends generally in the vertical direction with respect to the plane of the flange but extends in the upstream side direction rather than the downstream side direction as shown previously. Therefore, orifice  118  is coupled to fluid pressure and orifice  120  is coupled to the atmosphere. 
     The novel polymer rupture disks are formed with a thermoforming device such as that disclosed in commonly assigned copending application Ser. No. 09/512,486 filed Feb. 24, 2000 and entitled “Tension Loaded, Thermoformed, Polymer Rupture Disk”, incorporated herein by reference in its entirety. 
     FIG. 10 is a generalized diagram for a scoring die. 
     One method of forming the score line therein is to use a razor blade  140  either in the arcuate shape of the score line to be formed or as a single blade that could be rotated by rotating the upper portion  142  of the die to cause the score line to be cut into the downstream side of the flange of the polymer rupture disk. 
     If the knife blade  140  is a single arcuate blade, then the die  142  can be pressed downwardly to form the score line in the flange  138  of the polymer rupture disk. Shims  144  can be placed between the die  142  and the spacer  126  to set the cut depth and enable the razor blade or knife to cut preferably at least 60% into the polymer rupture disk material. 
     If desired to form the score line in the dome  132  of the polymer rupture disk, crossed knife blades, two blades perpendicular to each other, and arcuate in shape, would be attached to the lower end of screw  146  in a well-known manner such that, when it is pressed downwardly, it would press the knife blades into the inner side of domed center portion  132 . In such case, an anvil  154  (shown in phantom lines) could be placed in the chamber  152  to provide a support for the dome-shaped portion  132  of the polymer disk while the cutting is taking place. 
     Of course, the cuts could be made in either side of the polymer rupture disk, either the flange or the dome, and could be made either before, during, or after the thermoforming takes place. 
     When the score line is deformed by thinning the material in the area of the score line using the thermoforming process, then at the point where the score line is to be formed, a vacuum is applied, as shown in commonly assigned copending application Ser. No. 00/512,486 entitled “Tension Loaded, Thermoformed, Polymer Rupture Disk” incorporated herein in its entirety, to thin a particular area and form the score line. 
     Thermoforming processes are well known in the art and need not be described in any further detail here. 
     Thus, the novel invention disclosed herein teaches that a polymer rupture disk, preferably Teflon®, can be thermoformed into the proper shape and a score line provided therein to provide a polymer rupture disk that can be used in pressure lines where it is desired that no metal exist. The novel thermoformed polymer rupture disk has a score line that extends preferably through at least 60% of the flange or dome surface thereby enabling a controlled burst pressure and burst pressure area to be formed. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed.

Technology Classification (CPC): 8