You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION 
   The present invention relates to the field of strip doors used primarily for providing a flexible barrier across entry and exit openings in commercial and industrial facilities and equipment. 
   BACKGROUND OF THE INVENTION 
   Vertically hanging plastic strips arranged side-by-side, or in an overlapping arrangement, are used in many industrial and commercial applications to provide a flexible barrier to air, insects, noise, vapors, moisture, etc. A strip door system, which provides such barrier, only minimally disrupts the passage of product, personnel or vehicles through a doorway, or the like, as the vertically hanging plastic strips are easily bent to provide an opening for entry or exit. An important application for strip door systems, which provide a significant savings in energy consumption, is on openings into freezers and coolers in warehouse facilities, food processing areas, restaurants, etc. 
   Strip door systems are typically assembled by hanging a plurality of flexible plastic strips, having a width of 8-16 inches and a thickness of 0.060 to 0.160 inches, which are produced from PVC material. The strips typically are hung to span a vertically oriented plane, such as between side jams of a doorway. The strips typically have an overlap of 25-100%, for example, for a 50% overlap, on a given strip, 25% of its width, at each edge, would be overlapped with an adjacent strip. 
   The vertically hanging strips are usually hung from a uniformity spaced series of studs disposed at or near a header of a doorway. The studs are most often fixed to a plate, or the like, to form a hanger, and the hanger is attached to the header or a wall above the doorway. Many different hangers are known for hanging the plastic strips. 
     FIG. 1  shows a known flexible strip door system for describing a general configuration of a strip door system in which a hanger of the present invention would be used. In  FIG. 1 , an opening  1  in wall  2  is provided with a flexible plastic strip door  3  having elongated flexible plastic strips  4  arranged in an overlapping pattern with areas of overlapping indicated at  5 . The strips  4  are hung from a hanger  6  having protruding studs  7  arranged in a uniform spacing along the length of the hanger. The plastic strips  4  have uniformily spaced apertures  8 , along an upper portion, which correspond in spacing with the studs  7  of the hanger. The spacing arrangement of the studs and the apertures allow for overlap of 25 to 100%, or no overlap, wherein edges of the strips are placed abutting edges of adjacent strips. 
   The system depicted in  FIG. 1  has an overlap of about 50%, that is 50% of each strip is overlapped by other strips. Although not shown, some type of retaining device is necessary to prevent the strips from sliding off the studs when the strips are encountered by personnel or equipment passing through the opening. In U.S. patent application Ser. No. 10/406,527 entitled “Flexible-Strip Hanger for a Strip Door System and Method of Making Same”, filed Apr. 3, 2003, a hinged cover prevents the plastic strips from sliding off the studs. 
   Plastic strip door systems, as described above are very durable as they can be subjected to heavy usage by personnel or equipment passing through them. In particular, fork lifts or other commercial and industrial type equipment often subject the plastic strips to harsh usage, including tearing away of the strips, if caught on such equipment or caught on the product being moved. Such harsh usage, as well as normal everyday usage, necessitates the plastic strips being replaced from time to time. Because of the typical locations of the hangers, that is at a location requiring the use of a ladder, and/or at cold or below freezing environments, replacement is often difficult and dangerous, and can require the use of more than one person to carry out the replacement. 
   One known hanger has spaced studs on a backing plate along with a strip retaining bar, which requires the use of tools to secure the bar in place. Another known hanger, although it requires no tools for installing the strips, relies solely on studs having an enlarged end to prevent the strips from sliding off. In such a system an aperture in the plastic strip, which slides over the stud, must be very accurately formed so as to fit over the stud, yet be retained by the enlarged end. In the same system, a strip having the properly sized aperture can be difficult to slide over the enlarged end, if the material of the strip is at a low temperature in a cooler or freezer application. Many retaining systems are known, however they all have undesirable features. 
   OBJECTS OF THE INVENTION 
   It is the object of the present invention to provide a hanger for plastic strips of a strip door system which is of durable construction and configured for convenient initial installation. 
   It is another object of the present invention to provide a hanger which enables easy replacement of worn or damaged plastic strips, without the use of hand tools. 
   It is still another object of the present invention to provide a hanger having a positive retaining device to prevent the plastic strips from sliding off the studs, which does not rely solely on an enlarged portion of a stud and the elasticity of the plastic strip. 
   It is yet a further object of the present invention to provide an adjustable effective stud length to better accommodate plastic strips of various thicknesses arranged to have various amounts of overlap. 
   SUMMARY OF THE INVENTION 
   The present invention is a hanger for use in a strip door system for supporting vertically hanging flexible plastic strips, wherein each strip has a row of uniformily spaced apertures along an upper end portion. The hanger has an elongated backing plate portion for attaching the hanger to a structure above an opening, a plurality of uniformily spaced studs fixed along the length of the backing plate, for supporting the plastic strips by engagement through the strip apertures, and an elongated retaining plate for locking with the studs to prevent the engaged strips from sliding off the studs. Each stud has a plurality of locking grooves along its length for locking the retaining plate with the studs so as to provide an adjustable effective stud length between the backing plate and the retaining plate . 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will become more readily apparent from the following description of preferred embodiments thereof, shown, by way of example only, in the accompanying drawings, wherein: 
       FIG. 1  is a prior-art strip door system wherein flexible plastic strips having uniformily spaced apertures are supported on a hanger having uniformily spaced protruding studs; 
       FIGS. 2A and 2B  are respectively, a front view and an end view of a backing plate of a first embodiment of the invention; 
       FIGS. 3A and 3B  are respectively, a front view and an end view of a retaining plate of the invention; 
       FIGS. 4A and 4B  are respectively, a front view and an end view of the backing plate of  FIGS. 2A and 2B , having the retaining plate of  FIGS. 3A and 3B  in an engaged position; 
       FIGS. 5A and 5B  are respectively, a front view and an end view of the retaining plate of  FIGS. 3A and 3B  as disposed when sliding the retaining plate onto studs of the backing plate; 
       FIGS. 6A and 6B  are respectively, a front view and an end view of the hanger of the first embodiment of the invention having flexible plastic strips in place on the hanger; 
       FIGS. 7A and 7B  are respectively, a front view and an edge view of a retaining disc of the invention; 
       FIGS. 8A and 8B  are respectively a front view and an end view of the hanger of the first embodiment of the invention having the flexible plastic strip in place on the hanger and retaining discs in place on studs of the hanger. 
       FIGS. 9A and 9B  are respectively, a front view and an end view of a backing plate of a second embodiment of the invention, for use when mounting the hanger on a header; 
       FIGS. 10A and 10B  are respectively, a front view and an end view of a universal backing plate of a third embodiment of the invention, for either wall or header mounting of the hanger. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 2A and 2B  show a front view and an end view, respectively, of an elongated backing plate of the first embodiment of the invention. The three embodiments of the invention, discussed below, are distinct only in the shape of the backing plate which is provided for mounting: 1) on a vertically oriented wall above an opening, 2) on a horizontally oriented header of an opening, and 3) on either a vertically oriented wall or a header of an opening. 
   The first embodiment, shown in  FIGS. 2A and 2B , is for use in mounting on a wall above an opening which is to be provided with a strip door system. Shown is an elongated backing plate  9  of the hanger having apertures  10  for attaching the hanger to a vertically oriented wall above an opening to which the strip door is to be installed. Protruding from a front face  11  of the backing plate are a plurality of uniformily spaced studs  12  for supporting the flexible plastic strips of the strip door system. Apertures provided along a top portion of each strip are slid over the uniformily spaced studs to install the strips on the hanger. The studs, which preferably have a cylindrical shape, feature annularly shaped grooves  13  spaced along the length of each stud. The grooves have a major diameter D which corresponds to the surface of the stud, and a minor diameter d as measured at the base of a groove. To insure a tight attachment to the backing plate, the studs preferably extend through the backing plate  9  and have a head portion  14  which rests against back face  15  of the backing plate. Any known method, such as a press fit, brazing, or the like, can be used to maintain a tight attachment of the studs to the backing plate. Preferably the backing plate includes bent portions, such as at  16  and  17  to give rigidity to the backing plate and to provide a spacing for the head portions  14  of the studs. The hanger can be of any length required to span the opening being addressed. 
     FIGS. 3A and 3B  show an elongated retaining plate  18  of the hanger which prevents the installed flexible plastic strips from sliding off studs  12 . Retaining plate  18  features apertures  19 , having a minor portion  20 , and a major portion  21  which communicate with each other. Apertures  19  have centerlines  22  which correspond in spacing with center lines  23  of the studs of backing plate  9 . The apertures  19  of retaining plate  18  are configured such that the major portion of the aperture is slideable along the length of the studs, and the minor portion is slideable into one of the grooves  13 , but not slideable along the length of the stud. Thus the grooves of the studs act as a locking mechanism for the retaining plate  18 . 
     FIGS. 4A and 4B  show the retaining plate  18  in an engaged position, that is minor portions  20  of the apertures are seated in the grooves  13  of the studs  12 .  FIGS. 5A and 5B  show retaining plate  18  in a state whereat the major portion  21  of the aperture is being slid over the stud  12  to a position at which the retaining plate  18  is aligned with a groove  13  of the stud, and whereat by solely the force of gravity, the retaining plate  18  becomes locked on the stud  12  by engagement of the minor portion  20  of the aperture with the groove  13  as shown in  FIGS. 4A and 4B . 
   As indicated earlier, a plurality of grooves are disposed along the length of each stud. Such arrangement enables the use of various thicknesses of plastic strips in either an overlapping or non-overlapping side-by-side hanging pattern.  FIGS. 6A and 6B  show the hanger of the invention having plastic strips  23  hanging from the studs  12  in an overlapping arrangement. As shown in  FIG. 6B , having retaining plate  18  in a selected groove  13  of the stud provides an effective stud length, as measured between the backing plate  9  and the retaining plate  18 , such that the strips are prevented from moving backward and forward along the length of the stud. The spacing of the grooves need not be uniform along the length of the stud, however all of the studs of a hanger must have the same groove pattern. As can be seen in  FIG. 6B , if thinner or thicker plastic strips are desired, or if no overlap is desired, the various grooves provide for flexibility by enabling an adjustment of the effective length of each stud. The grooves preferably have side walls which are perpendicular to the central axis of the stud, so as to more securely hold the retaining plate. As in the backing plate  9 , a bend  25  is provided in the retaining plate  18  in order to provide rigidity. When the retaining plate is engaged in the grooves  13  of the studs along the length of the hanger, normal passage through the strip door will not cause disengagement. 
   As an added safety feature, a retaining disc,  26 , as shown in  FIGS. 7A and 7B  can be used with the backing plate  9  and the retaining plate  18 . Referring to  FIGS. 8A and 8B , the retaining disc  26  is shown as disposed on stud  12 . The retaining disc  26  is fabricated of a material having elasticity, yet some stiffness, in order that an aperture  27  formed in the retaining disc can be slid over a stud and be retained by elastic forces in a groove of the stud, that is one of the same grooves used for the retaining plate  18 . Preferably the aperture  27  is formed to have a diameter corresponding to the diameter d of the base of the groove. The disc is positioned on the stud, extending downward to contact a ridge  29  along a bottom portion of the retaining plate as shown in  FIGS. 8A and 8B . Preferably the disc  26  has a thickness approximately equal to a width of the grooves to assure that the disc hangs vertically downward without a clearance between the disc and the groove with would enable easy movement of the disc away from its preferred vertical orientation. The disc  26  is placed in the groove which is adjacent to the groove occupied by the retaining plate. Also, in order to facilitate use of the retaining disc, a tab  28  extending from the body of the disc, is provided. In use of the invention, at least one of the retaining discs is used to assure that the retaining plate, due to an occurrence other than normal use of the strip door, does not move upwardly so as to become disengaged from the studs. The elimination of upwardly movement is assured by the disc  26  making contact with the ridge  29 . 
     FIGS. 9A and 9B  show a front view and an end view respectively of a second embodiment of the invention for use in mounting a hanger to a horizontally oriented header of a doorway, for example. Shown in  FIGS. 9A and 9B  is backing plate  30  having a portion  31 , which is oriented horizontally when installed, which can be attached to a horizontally oriented surface for installation. Apertures  32  are provided to facilitate the installation. In the second embodiment, shown in  FIGS. 9A and 9B  all remaining features and operation are as described in the description of the first embodiment. 
     FIGS. 10A and 10B  show a front view and an end view respectively of a third embodiment of the invention, which can be used for mounting the backing plate  33  to either a horizontally or vertically oriented surface. The backing plate  33  provides apertures  34  in portion  35  and web  36  of the backing plate  33 . In the third embodiment, shown in  FIGS. 10A and 10B , all remaining features and operation are as described in the description of the first embodiment. 
   In all of the embodiments of the invention, because of the typically moist environment of the installation, galvanized steel or stainless steel is the preferred material for the components, however other materials are available in practice of the invention. The backing plate and retaining plate are preferably formed of 10 to 20 gauge sheet material. The studs preferably have a diameter of ¼-⅜ inches and a length of ¾-1¼ inches. The depth of the grooves is preferably about 0.07 inch. 
   While specific materials, dimensional data, etc. have been set forth for purposes of describing embodiments of the invention, various modifications can be resorted to, in light of the above teachings, without departing from Applicant&#39;s novel contributions; therefore in determining the scope of the present invention, reference shall be made to the appended claims.

Summary:
A hanger for plastic strips having uniformity spaced apertures along an end portion thereof, to form a strip door across an opening. Uniformily spaced studs are provided on a mountable backing plate to support the plastic strips. A retaining plate retains the strips on the studs which have locking means along the length thereof, so as to provide an adjustable effective length for each of the studs.