Abstract:
The neck of a container has a smooth seal surface engaged by the inner skirt or plug of a cap. Such surface is free of trim and parting line flaws which are characteristic of blow-molded jars because the surface is formed in such a way that the seal surface is not in contact with mold parting lines and further the trim (excess plastic) of the neck is located away from the sealing surface. In one form of the disclosure, above the sealing surface the neck wall slants outward and then bends upward-inward in a short, tapered stretch which engages the underside of the cap disk to compress against the disk or a liner or foil. Other forms of seal surfaces are disclosed. The exterior of the neck is formed with screw threads which engage threads on the interior of the outer skirt of the cap. Caps suitable for combination with the neck, methods of forming the neck and mold apparatus for forming the neck are also disclosed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application No. 08/894,189 filed Jul. 29, 1997, now U.S. Pat. No. 6,003,699, which is a continuation-in-part of U.S. patent application Ser. No. 08/385,808 filed Feb. 9, 1995, now abandoned. This application is also a continuation-in-part of U.S. patent application Ser. No. 08/847,928, filed Apr. 28, 1997 now U.S. Pat. No. 5,964,362, which is a continuation of U.S. patent application Ser. No. 08/385,808 filed Feb. 9, 1995, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a new and improved blow molded neck construction for a bottle or other container, a cap therefor, a method of forming said neck and molds for forming said neck. More particularly, it relates to the neck finish for a blow molded plastic bottle characterized by the fact that when used with a cap having a plug (i.e., inner skirt) the surface of the neck against which the plug seals is a seal surface without parting lines and no portion has a diameter less than that of the seal surface. Hence, the plug seals against a smooth surface and leakage is prevented. 
     2. Description of Related Art 
     An exemplar of the prior art is U.S. Pat. No. 4,691,834 which shows an upward inward directed flexible flange sealing against the corner of the intersection of the outer wall of the plug and the underside of the top of the cap. The neck sealing surface is, inherently, somewhat uneven and ragged since the neck is cut or sheared adjacent this sealing surface. In the present invention, however, the neck is trimmed on the edge above the seal surface but such edge is not the portion of the neck which seals against the cap plug. 
     The references cited against said U.S. Pat. No. 4,691,834 are likewise distinguishable. 
     U.S. Pat. Nos. 4,625,876 and 4,798,301 show curved plug contacting surfaces but these are of substantially the same diameters as the inner edge of the flanges which engage the underside of the top of the cap. 
     SUMMARY OF THE INVENTION 
     The bottle of the present invention is blow molded in a split mold by techniques well known in the art. The surfaces of the mold which define the neck structure cause the neck shape hereinafter described. An upper portion of the parison above the neck is trimmed or cut from the neck according to conventional practice (e.g. pull-up trim, spin trim, ram-down, etc.). In one neck structure the circle at which the upper portion of the parison is severed from the neck is the inner edge of an inward-upward slanted flange. The other end of the flange merges into a curved surface which extends inward a greater distance than the aforesaid edge to merge with an internal sealing surface of lesser diameter than said edge. The neck structure above the neck sealing surface may have rapidly changing diameters which form a flexible membrane due to parison stretching in the blow molding process. In one form of the invention, below the sealing surface the exterior of the neck structure slants downward-outward to a horizontal shoulder and then extends downwardly and then outwardly to a second or lower shoulder. Other cap engaging means may be used. Most of the modifications of the invention shown in U.S. application Ser. No. 08/385,808 disclose neck finishes and caps of the “snap-on” variety. In accordance with the present invention, however, screw caps wherein the neck and cap skirt have complementary threads are illustrated. The fact that the same upper neck structure may be used either with a snap-on or a screw-on cap thus becomes apparent. 
     A cap with which the neck is used has a top having a depending central plug or inner skirt, the outer surface of which seals tightly against the sealing surface of the neck. The cap also has an outer skirt having internal sealing beads which engage the upper and lower shoulders of the neck to hold the cap in place. Alternatively, the neck may have threads which are engaged by threads on the cap skirt. The lower portion of the outer cap skirt may be removed by the user engaging and pulling a pull tab which causes the lower part of the skirt to disengage at a circumferential score line. Until such lower skirt is removed, the cap and neck are tamper-evident. Other types of neck engaging means may be employed. 
     Several different ways may be employed to form the neck finishes of the present invention in blow molding operations. One such means employs a conventional blow mold wherein a blow dome is formed above the neck finish with several abrupt bends in the parison between the blow dome and the neck sealing surface. The blow dome is trimmed from the neck in a conventional trimming operation. 
     In another modification of the invention, the shear steel located above the neck finish insert has a projecting extension which is engaged by an outward projection on the blow pin so that when the blow pin is withdrawn, the two extensions shear the parison above the sealing surface of the neck. 
     In still another form of the invention, the shear steel is formed with an outward projection and the blow pin is formed with an outward projection below the level of the shear steel. When the blow pin is raised, the two projections shear the excess parison. In this form of the invention the neck finish is approximately vertical. 
     The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a neck portion of a jar in accordance with the present invention partially broken away to reveal structure. 
     FIG. 2 is an enlarged sectional view of the neck structure and a portion of a blow dome superimposed thereabove. 
     FIG. 3 is a side elevational view of a snap-on type cap with which the neck of FIG. 1 is used, the cap being partially broken away in section to reveal internal construction. 
     FIG. 4 is an enlarged sectional view of a portion of FIG.  3 . 
     FIG. 5 is a further enlarged fragmentary bottom plan view of a portion of the cap showing a top view of the pull tab. 
     FIG. 6 is a fragmentary sectional view taken substantially along the line  6 — 6  of FIG.  5 . 
     FIG. 7 is an enlarged sectional view showing schematically the seating of the cap on the neck. 
     FIG. 8 is a view similar to FIG. 7 of a prior art device. 
     FIG. 9 is an enlarged view of the neck structure showing an alternate seal area. 
     FIG. 10 is a view similar to FIG. 2 of a modification wherein screw threads are formed on the exterior of the neck. 
     FIG. 11 is a view similar to FIG. 7 showing the neck of FIG. 10 with a cap applied thereto. 
     FIG. 12 is a vertical sectional view through a modified container neck and portions of the mold and blow pin forming same. 
     FIG. 13 is a view similar to FIG. 12, showing the blow pin in raised position. 
     FIG. 14 is a fragmentary vertical sectional view through a portion of a neck similar to that of FIG. 13 with the snap-on features replaced by screw threads. 
     FIG. 15 is an enlarged view of the structure of FIG.  14 . 
     FIG. 16 is a fragmentary sectional view of a further modified mold, blow pin and parison. 
     FIG. 17 is a fragmentary sectional view of a neck formed in accordance with FIG. 16 and a cap seated thereon. 
     FIG. 18 is a view similar to FIG. 16 of another modified mold, blow pin and parison showing the blow pin in raised position. 
     FIG. 19 is a view similar to FIG. 18 showing the blow pin in lowered position. 
     FIG. 20 is a view similar to FIG. 7 showing a neck similar to FIG. 19 with a cap seated thereon. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to those embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. 
     As shown in FIGS. 1-7, neck  11  is formed on a thin-walled jar or other container and has a curved primary seal surface  12  which is very smooth and is distinguished by the absence of parting lines inasmuch as it is formed by air pressure or other mechanical means during the blow molding process and is not formed by the mold halves and thus does not have a mold parting line formed therein. As shown in FIG. 12, seal surface  12  may be vertical or it may be curved, as shown in FIG.  2 . Further, the primary sealing surface has minimal ovality, by reason of the way it is formed. Above surface  12  the neck structure extends outwardly in a outward stretch  13  which terminates in an upward bend  14 . Above bend  14  is a thin, tapered upward-inward extending flange  16 , the inner edge of which is of greater diameter than the diameter of surface  12 . Below surface  12  the neck extends downwardly-outwardly in a slanted stretch  17  which terminates in a short vertical stretch  18 , there being an inward directed substantially horizontal upper shoulder  19  below surface  18 . Vertical stretch  21  extends downwardly from the inner edge of shoulder  19  terminating in an inwardly curved portion  22  which merges with an outward-downward stretch  23 . An approximately vertical short surface  24  (of greater diameter than surface  18 ) terminates in a second or lower horizontal inward directed shoulder  26 . Vertical stretch  27  depends from the inner edge of shoulder  26 , merging with an outward stretch  30  which merges with an outward-downward stretch  29 . The lower end of stretch  29  merges with an inward-downward stretch  31 . 
     In accordance with one form of standard blow molding practice, a parison of the plastic material from which the container is to be formed is deposited in the split mold. Air is blown into the parison to expand it to fill the mold. In this form of the present invention, the mold has an insert which shapes the finish of the neck of the container heretofore described and above the neck insert the mold widens out to establish what is known as a blow dome of excess material. The blow dome is severed from the neck finish by well-known means. In accordance with one form of the present invention, as distinguished from prior neck finishes, the blow mold is severed at the inner edge of flange  16 , as by trimming. Severing the edge of the neck from the blow dome may cause a rough surface. One of the advantages of the present invention is that the edge at which the blow dome is severed is not the primary sealing surface  12 . Thus, directing attention to FIG. 2, blow dome  33  has an outward-upward slanted stretch  34  merging into a curved stretch  36  which has an inward slanted stretch  37 . The cut line  38  is a circle wherein the stretch  34  is severed from the inner edge of flange  16 . By reason of the almost 180° bend  14  and the rapid diameter changes within a relatively short vertical distance flange,  16  is thin and flexible. 
     As shown in FIGS. 12 and 13, another way to achieve the neck structure of the present invention is to employ what is commonly referred to as “pull-up” trim. In this case the cut line  38  is achieved by having a close diametrical fitting of a blow pin positioned internally within the parison and sets of shear steels mounted on the split mold. Diameters of the blow pin are typically 0.001 inch to 0.004 inch smaller than that diameter defined by the shear steels in closed position. After blowing of the neck and container, the portion of the parison above cut line  38  is severed from the neck portion below cut line  38  by upward movement of the blow pin relative to the shear steels. 
     It will be understood that the type plastic used to mold neck  11  may be any suitable relatively hard plastic such as polyethylene. 
     One form of closure or cap used with the present invention is shown in FIGS. 3-7. The closure of FIGS. 3-7 comprises an indented circular top  42  having a short peripheral cylindrical upward extending member  43  from which extends outwardly a stack rim  44 . The outer edge of rim  44  has a depending downward stretch  46  which merges into vertical, substantially cylindrical upper outer skirt  48 . The lower end of skirt  48  merges into an outward-downward slanted stretch  55 . Below stretch  55  is the lower substantially cylindrical outer skirt  49 . An internal scoreline  51  separates stretch  55  from lower skirt  49 . Below lower skirt  49  the cap has an outward-downward slanted flange  52  which, for practical purposes, rests against the surface  30  of neck  11 . Interrupted upper inner bead sections  53  engage under the shoulder  19 . Lower inner bead  54  at the lower end of skirt portion  49  engages under the shoulder  26 . When the cap is attached, the beads  53  and  54  prevent cap  41  from being removed from neck  11 . In order to enable the user to grip cap  41 , ribs  50  extend outwardly from member  48  as best shown in FIG.  7 . Ribs  50  also impart columnar strength to the closure to transfer vertical force and prevent closure collapse during axial application of the closure to the finish. 
     At one portion of the circumference of lower skirt  49  (as best shown in FIGS.  5  and  6 ), and spaced downwardly therefrom is a horizontal pull tab  57  having a curved connection  58  to skirt  49 . The interior of skirt  49  is formed with a notch  59  where tab  57  joins lower skirt  49 . Notch  59  forms a vertical line of weakness through skirt  49 . Enlargement  61  is formed on the distal edge of pull tab  57 . The flange  52  is formed thinner than the rest of flange  52  in the thin area  62  adjacent tab  57 . 
     As a downward extension of cylindrical member  43  the cap  41  is formed with a depending skirt extension  66 , the lower outer edge of which is formed with a radius  67 . The inner surface of member  43  seals against primary seal surface  12 . The vertical position of cap top  42  can be adjusted to provide for compression of surface  12  against the adjacent surface of member  43 . 
     Directing attention to FIG. 7 it will be seen that the surface  12  is the primary sealing surface against the member  43 . As has been noted, the surface  12  is very smooth and hence forms a very effective seal against the member  43 . 
     When the cap is applied, the beads  53  and  54  lock under the shoulders  19  and  26  to prevent removal of the cap and hence are tamper evidencing. When the user wishes to open the container, the user grips the enlargement  61  and bends the pull tab  57  outwardly and then pulls circumferentially, tearing the lower skirt  49  from the upper cap portion. The user may then grip under the surface  55  which, as shown in FIG. 7, is spaced from the bottle finish by a considerable gap, and pull upwardly causing the interrupted upper bead segments  53  to disengage from shoulder  19  so that the cap may be removed. The ribs  50  rigidify the upper portion of the cap to allow the forces necessary to push the cap onto the bottle from causing the cap to buckle. The portion of the cap above line  51  constitutes a reclosure cap and may be pressed back on the neck after portions of the contents of the jar are dispensed as frequently as required. 
     Comparison of FIG. 7 with prior art structure shown in FIG. 8 shows that in the present invention the very smooth surface  12  causes a tight seal against the member  43  and the flange  16  need not seal at all, whereas in the prior art the cut inner edge of the flange is a primary seal. The primary seal surface  12  has minimum deviation from ovality as compared to FIG. 8 where the primary seal is coincident with a trim surface. Bottles of the type of this invention and the prior art were molded. The ovality of the two types was measured. The unexpected result of these experiments was that the current invention produced a significantly more circular primary seal area. Refer to Table A. for tabulated results. The stretch occurring on both sides of the primary seal  12  is primarily contributing to the superior ovality and differentiate it from prior art. 
     
       
         
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
             
           
               
                 TABLE A 
               
             
             
               
                   
               
               
                 STD BOTTLE STYLE 
                   
               
             
          
           
               
                 Run 
                   
                   
                   
                 PRESENT INVENTION 
               
             
          
           
               
                 A 
                 Run B 
                 Run C 
                 Run D 
                 Run A 
                 Run B 
                 Run C 
                 Run D 
               
               
                   
               
               
                 0.055 
                 0.020 
                 0.048 
                 0.028 
                 0.024 
                 0.058 
                 0.002 
                 0.015 
               
               
                 0.053 
                 0.002 
                 0.056 
                 0.015 
                 0.006 
                 0.010 
                 0.106 
                 0.030 
               
               
                 0.062 
                 0.000 
                 0.044 
                 0.010 
                 0.017 
                 0.002 
                 0.013 
                 0.010 
               
               
                 0.043 
                 0.010 
                 0.058 
                 0.003 
                 0.016 
                 0.004 
                 0.005 
                 0.027 
               
               
                 0.058 
                 0.029 
                 0.025 
                 0.009 
                 0.014 
                 0.013 
                 0.005 
                 0.034 
               
               
                 0.064 
                 0.016 
                 0.055 
                 0.003 
                 0.011 
                 0.060 
                 0.017 
                 0.017 
               
               
                 0.011 
                 0.005 
                 0.059 
                 0.002 
                 0.004 
                   
                 0.003 
                 0.017 
               
               
                 0.019 
                 0.013 
                 0.049 
                 0.005 
                 0.007 
               
               
                 0.042 
                 0.006 
                 0.045 
                 0.002 
                 0.013 
               
             
          
           
               
                 Average 0.028 
                 Average 0.016 
               
               
                   
               
             
          
         
       
     
     FIG. 9 illustrates a shape wherein seal surface  12   d  is cylindrical rather than curved. 
     Directing attention to FIGS. 10 and 11, the neck finish  11   b  and the portion above the neck finish formed in the blow dome  33   k  resembles that of FIG. 2 except that screw threads  127   b  are formed on the exterior of upper neck surface  126   k . Below threads  127   b  the neck has an outward curved portion  128   k  which merges with horizontal shoulder  129   b  against which shoulder  141   k  on the bottom edge of cap lower skirt  148   b  rests. Depending from shoulder  129   b  are lower ratchet teeth  131   b  and below teeth  131   b  is the remainder  132   b  of the neck  11   b.    
     The vertical stretch  137   b  of cap  11   b  is formed with internal threads  138   b  which mesh with threads  127   b . On the exterior of upper cap skirt  48   b  are vertical ribs  138   b  and on the lower end of stretch  137   b  is outward directed shoulder  141   b  from which depend ratchet teeth  146   b  which mesh with ratchet teeth  147   b . Lower skirt  149   b  is joined to shoulder  141   b  at juncture  148   b . Juncture  148   b  is frangible so that the lower skirt  146   b  and the internal ratchet teeth  146   b  thereof may be removed to permit the cap to be unscrewed from the neck. Fracture of juncture  148   b  indicates tampering with the contents of the container. Below lower skirt  146   b  is a downward-outward directed flange  149   b  which is in close proximity to the remainder  132   b  of the neck so as to prevent foreign matter from entering between the ratchet teeth. 
     Directing attention to the modification shown in FIGS. 12 and 13, formation of a modified container neck is shown. Such a neck may resemble that shown in FIGS. 1 and 2 of U.S. Pat. No. 4,699,287, with an important modification, as hereinafter explained. In FIG. 12 the parison forming the neck is shown between a blow pin  86  and shear steel  76  and neck insert  21  as molding is being completed. 
     Shear steel  76  has an inward projection  77  terminating in a vertical inward extending shearing edge  78 . Blow pin  86  has a lower portion  87  having an outward extending shearing edge  88  with a groove  89  thereabove. 
     As shown in FIG. 12, blow molding of the parison to the shape of shear steel  76  and neck insert  81  has just been completed. The shape of the parison generally resembles the neck shown in said U.S. Pat. No. 4,699,287. Edge  88  is located below edge  78 . Air blowing through hole  91  has formed vertical stretch  101  and flange  102 . The smooth, vertical, lower cylindrical portion  87  has formed internal primary seal surface  12   f.    
     The blow pin  86  then moves from the position of FIG. 12 to the position of FIG. 13 The neck structure is sheared between edges  78  and  88 . Flange inner edge  96  is formed where the edges  78 ,  88  have sheared the same and the parison sheared-off portion  94  thereabove is discarded. 
     It is noted that edge  96  is of a larger diameter than primary seal surface  12   f . hence the hollow plug or inner skirt such as that shown in U.S. Pat. No. 4,699,287 seated on the container neck seals against surface  12   f  instead of surface  96 . Since blow pin  86  has no parting line, surface  12   f  has no flash. Surface  12   f  is smooth and its diameter is always the same during repetitive molds and hence makes a superior seal with the cap plug. 
     FIGS. 14 and 15 illustrate a neck finish  11   g  similar to that shown in FIG. 13 modified in that external screw threads  127   g  are formed on the neck structure to replace the snap-on structure shown in FIG.  13 . FIG. 15 is an enlarged view of a portion of FIG. 14 showing the positioning of ratchet teeth  121   g  which are interengaged by internal ratchet teeth on the lower portion of a cap skirt similar to that shown in FIG.  11 . 
     Directing attention now to FIG. 16, a different shape neck is produced by the mold parts therein illustrated. Blow pin  86   h  has a lower tapered portion  111  at the upper end of which is a vertical cylindrical surface  115  which is smooth and terminates at its upper end in a shear corner  114 . Above corner  114  is a cut-away  116 . Blow pin  86   h  may be made of two parts in order to facilitate fabrication. As shown in FIG. 16 the lower portion  86   h  is attached to upper blow pin  116  and radial grooves or channels  112  are cut in the top surface of  86   h , being connected to vertical air holes  91   h . Thus when air is blown into the blow pin  86   h  air travels up holes  91   g  and out channels  112 . The lower corner of upper blow pin  113  is formed with a cut-away  117  which merges with cut-away  116  to clear the inward shearing edge  78   h  of inward extension  77   h  of shear steel  76   h . The upper end of neck insert  81   h  is formed with seal forming projection  106   h  which presses the parison against surface  115 . The neck formed in neck insert  81   h  has external threads and hence grooves  118  for such threads are formed therein. Below the threaded portion of the neck, the bottle may assume any desired shape and hence the details of the neck insert  81   h  which form the same are not specifically set forth. 
     After the neck has been blown, as shown in FIG. 16, the blow pin  86   h  is raised and hence the shear corner  114  shears off the parison by shearing action against edge  78   h . Thus the neck has a straight upward section  122  which is a smooth sealing surface characterized by the absence of mold parting lines and also characterized by the absence of rough edges. 
     Directing attention to FIG. 17, the neck  11   h  formed in the mold parts shown in FIG. 16 is illustrated with a cap  41   h  snapped thereon. Thus neck  11   h  has an upper lip  121  below which is a vertical, smooth, seamless seal surface  122 . On the outside of the neck  11   h  there is an upper, vertical, straight surface  126  below which are external threads  127 . Below the threads is an outward curved portion  128  which merges with an horizontal shoulder  129 . Below the shoulder  129  are outward extending vertical ratchet teeth  131 , and below the teeth  131  is the remainder of the neck  132 . 
     Cap  41   h  has a top  42   h  with a vertical outer skirt  135  depending from the outer edge thereof. Upper skirt  135  is connected to lower skirt  146  as hereinafter appears. The upper edge of skirt  135  is connected to top  42   h  by corner  136 , and below corner  136  is a substantially vertical stretch  137 , the inner surface of which is formed with internal threads  138  which mate with the external threads  127  of neck  11   h . On the exterior of upper skirt  135  are vertical ribs  139  which assist the user in unscrewing the cap. An inner projection from the interior of the cap skirt wall shown in the embodiment of FIG. 17 as filet  140  is provided. The purpose of filet  14   o  is to increase the compressive force between the seal surface  122  and plug  210 . The inner surface of lower skirt  146  is formed with ratchet teeth  147  which mate with the teeth  131 . The upper inner corners of teeth  147  are joined to shoulder  141  on the lower end of upper skirt  135  at frangible juncture points  148 . Below lower skirt  146  is an outward, downward slanted flange  144  which engages the outside of skirt portion  132 . 
     Depending from top  42   h  is a plug or inner skirt  210  having a radius  67   h  at its lower, outer corner. Compression of the neck surface between plug  210  and projection  140  forms a liquid tight seal. 
     It will be seen that the cap shown in FIG. 17 is tamper-evidencing. When the cap  41   h  is unscrewed, the junctures  148  fracture, permitting the cap to be unscrewed but so long as the junctures  148  are intact, evidence that the cap has not been opened appears. 
     Directing attention to FIGS. 18-19 a neck similar to that of FIG. 17 is produced. The molding process used is generally known as “ram down” molding in that the blow pin  86   j  is forced down on striker plate  156 . Blow pin  86   j  has an upper cylindrical portion  104   j , a reduced diameter portion  87   j  below portion  104   j , and a curved portion  157  intermediate portions  87   j  and  104   j . A corner  88   j  at the juncture of curved portion  157  and upper portion  104   j  comprises a cutting edge. Neck insert  81   j  resembles that of FIG.  16 . Above neck insert  81   j  is a striker plate  156  having a rounded point  158  which is opposite curved portion  157  when blow pin  86   j  is in down position (FIG.  19 ). The spacing between point  158  and curved portion  157  is slightly less than the thickness of parison  93   j . As shown in FIG. 19, when pin  81   j  is in down position, cutting edge  88   j  engages striker plate point  158  thereby cutting off parison portion  94   j . The parison  93   j  is squeezed between point  158  and curved portion  157 , thereby creating primary seal surface  12   j.    
     FIG. 20 shows the neck structure  11   k  of FIG. 19 with a cap  41   k  seated thereon. 
     It will be understood that different neck shapes are shown formed by the various types of molds and molding methods illustrated in the drawings and described herein. However the neck shapes and molding techniques may be interchangeable, as will occur to one skilled in the art. 
     In FIGS. 8,  9 ,  10 - 11 ,  12 - 13 ,  14 - 15 ,  16 - 17 ,  18 - 19  and  20  the same reference numerals are used for parts corresponding to those elsewhere mentioned followed by subscripts a, d, b, f, g, h, j, and k respectively. 
     The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use con- templated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.