Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a radiation shielding door having a fire rating, and more particularly, to a radiation shielding door having a high fire rating and method for making same. 
     2. Description of the Related Art 
     Building codes require that doors to be installed in certain building positions need to have a particular fire rating that is measured in time, such as a 20 minute door, a 45 minute door, a one-hour door, a one and one-half hour door, etc. Doors are given a fire rating in accordance with a standard test specification. There are a number of national testing laboratories performing these tests, all of which lead to a “listing” or certification of conformance. Three such listing agencies in the United States are Factory Mutual, Intertek Testing Services, and Underwriters Laboratories. 
     In conducting such tests, doors are mounted in an opening of a fireproof wall and then exposed on one side to a predetermined time-temperature rise function. The time that a door can withstand the heat before it is penetrated by burning determines its fire rating. A component of the test is a high pressure water stream applied to the door for a set period of time immediately after the door is removed from the test furnace. 
     An example of a door that provides such a fire rating is disclosed in U.S. Pat. No. 4,104,828, the disclosure of which is incorporated by reference in its entirety. U.S. Pat. No. 4,104,828 discloses a solid fire door having three basic components: a mineral core, wood edges attached around the core (the vertical edges being referred to as stiles and the horizontal edges as rails), and thin facing material covering both sides of the door for its appearance. 
     SUMMARY OF THE INVENTION 
     It is a technical advantage of the present invention that a door for radiation shielding purposes with a fire rating of forty-five minutes or one hour is provided. It is another technical advantage of the present invention that a method of manufacturing a radiation shielding door having a fire rating is provided. It is another technical advantage of the present invention that a method of making a multi-layer material comprising a layer of radiation shield and a layer of a non-combustible material is disclosed. 
     It is another technical advantage that a door for radiation shielding purposes with a fire rating of forty-five minutes or one hour is provided. It is another technical advantage of the present invention that a non-combustible core is used. It is yet another technical advantage of the present invention that lead sheets are used as a component of the door to shield from radiation. 
     According to one embodiment of the present invention, a radiation shielding door having a fire rating is disclosed. The radiation shielding door comprises a non-combustible core having a first face, a second face. A supporting material is in contact with the non-combustible core. A first radiation shield is in contact with the first face of the non-combustible core. An intumescent material is in contact with the supporting material. 
     A second radiation shield may be provided in contact with the second face of the non-combustible core. A first cover and a second cover may be provided in contact with the first and second radiation shields, respectively. 
     The non-combustible core may comprise a mineral core, and may further comprise calcium silicate. The radiation shield may comprise lead. The supporting material may comprise Tectonite™. The radiation shielding door may have a fire rating of at least 45 minutes, and may have a fire rating of at least one hour. 
     According to another embodiment of the present invention, a method of manufacturing a radiation shielding door having a fire rating is disclosed. The method includes the steps of providing an non-combustible core having a first face, a second face; securing a supporting material to the non-combustible core; adhering a first radiation shield to the first face of the non-combustible core; and providing an intumescent material to the supporting material. 
     The method may further include the step of adhering a second radiation shield to the second face of the non-combustible core; adhering a first cover to the first radiation shield; and adhering a second cover to the second radiation shield. 
     The non-combustible core may comprise a mineral core, and may further comprise calcium silicate. The radiation shield may comprise lead. The supporting material may comprise Tectonite™. The radiation shielding door may have a fire rating of at least 45 minutes, and may have a fire rating of at least one hour. 
     According to yet another embodiment of the present invention, a method of making a multi-layer material comprising a layer of radiation shield and a layer of a non-combustible material is disclosed. The method includes providing a layer of a cross linking polyvinyl acetate emulsion adhesive between the radiation shield layer and the non-combustible material layer. The adhesive may be Multibond 2000. The multi-layer material may include a cover layer in contact with the side of the radiation shield layer opposite to that which is in contact with the non-combustible material layer. A layer of adhesive may be provided between the cover layer and the radiation shield layer. 
     The radiation shield layer may comprise lead. The non-combustible material layer may comprise a mineral core, and may further comprise calcium silicate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, the objects and advantages thereof, reference is now made to the following descriptions taken in connection with the accompanying drawings in which: 
         FIG. 1  is a front view of a radiation shielding fire rated door according to one embodiment of the present invention showing pertinent interior components with dotted lines; 
         FIG. 2  is a sectional view along line  2 ′- 2 ′ of a radiation shielding fire rated door according to one embodiment of the present invention; 
         FIG. 3  is a sectional view along line  3 ′- 3 ′ of a radiation shielding fire rated door according to one embodiment of the present invention; 
         FIG. 4  is a schematic of the radiation shielding fire rated door according to another embodiment of the present invention; 
         FIG. 5  is a front view of a half scale radiation shielding fire rated door according to another embodiment of the present invention; 
         FIG. 6   a  is a section view of the door of  FIG. 5  taken along line  6   a ′- 6   a′;    
         FIG. 6   b  is a section view of the door of  FIG. 5  taken along line  6   b ′- 6   b′;    
         FIG. 6   c  is view of the top of the door of  FIG. 5 ; 
         FIG. 7  is a front view of a pair of radiation shielding fire rated doors according to another embodiment of the present invention; and 
         FIG. 8  is a front view of a radiation shielding fire rated door according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention and their advantages may be understood by referring to  FIGS. 1-8 , wherein like reference numerals refer to like elements. 
     As used herein, the term “stiles” refers to the vertical edges of the door, or it can be used to refer to a laminate that constitutes the vertical edges of the door. The term “rails” refers to the horizontal edges of the door, or it can be used to refer to a laminate that constitutes the horizontal edges of the door. 
     Referring to  FIG. 1 , a view of a core of fire door  100  is provided.  FIG. 2  depicts a view of the core of door  100  along section  2 ′- 2 ′.  FIG. 3  depicts a view of the core of door  100  along section line  3 ′- 3 ′. Generally, fire door  100  includes non-combustible core  110  and supporting structure  120 . Intumescent material  130  is provided on the outer surfaces of supporting structure  120 . Intumescent material  130  may also include graphite. 
     In one embodiment, non-combustible core  110  may comprise a mineral core. For example, a calcium silicate mineral block may be used, and is available from Marshfield Door Systems, Inc., Marshfield, Wis. 54449. Although two slabs of non-combustible core  110  are illustrated in  FIG. 1 , a single, larger slab may also be used. Non-combustible core  110  has a thickness necessary to provide the desired fire rating, e.g., about 1¼ inch to about 1¾ inch for a fire rating of about one hour. In one embodiment, non-combustible core  110  has a thickness from about 1.458 inch to about 1.500 inch. 
     Supporting structure  120  provides the necessary support for non-combustible core  110 . In one embodiment, supporting structure  120  is in contact with the edges of non-combustible core  110 . 
     A strip of supporting structure  120  may be provided near the center of door  100  in order to facilitate the installation of door locks and other hardware. 
     In one embodiment, supporting structure  120  has a width that is suitable to provide sufficient support for non-combustible core  110 . This may be due to the characteristics of non-combustible core  110 , such as its weight, dimensions, malleability, etc. In one embodiment, supporting structure has a width of at least 5 inches. In other words, approximately at least the outermost 5 inches of door  100  is comprised by supporting structure  120 . Depending on the type and weight of non-combustible core  110 , other amounts and/or widths for supporting structure  120  may be used. 
     In one embodiment, Tectonite™, a strong, low heat transferring, light mineral based material available from Warm Springs Composites, Warm Springs, Oreg. may be used to form the supporting structure. Tectonite™ is a non-combustible artificial material, and may surround non-combustible core  110 . Additional Tectonite™ may be provided as necessary or required. In addition, Tectonite™ has excellent tooling qualities, and allows for door hardware, such as hinges, locks, etc. to be attached to door  100 . Any other suitable material may be used to form the supporting structure. 
     Intumescent material  130  is provided to door  100  to provide additional fire protection. In one embodiment, intumescent material  130  is provided in the door stiles and the door rails. In one embodiment, intumescent material  130  may be provided in the door stiles and only in the top door rail. Intumescent material  130  may be provided in a channel in supporting structure  120  or in a channel formed between supporting structure  120  and cover  150 . This will be illustrated in  FIG. 6   b , below. Preferably, intumescent material  130  is covered by cover  150 , as will be discussed below. 
     An example of a suitable intumescent material  130  is Palusol®, available from BASF, which is essentially sodium silicate encapsulated in a rigid, thermoplastic profile. Other suitable intumescent materials may be used, such as Intumet™, available from Zero International. Intumet™ is a rubber-matrix material that begins intumescing at the relatively low temperatures where organic materials begin to emit combustible and noxious gases. It expands gradually with low force and forms a firm char. 
     When exposed to heat, intumescent material  130  preferably expands to seal door  100  to a door frame (not shown). In one embodiment, cover  150  will preferably disintegrate due to the heat, allowing intumescent material  130  to expand to seal the edges of door  100 . 
     Radiation shield  140  is provided to door  100 . In one embodiment, radiation shield  140  is provided on both sides of non-combustible core  110 . In another embodiment, radiation shield may be provided on only one side of non-combustible core  110 . 
     Preferably, radiation shield  140  comprises a sheet of substantially pure lead. In one embodiment, the lead meets Federal Specification QQ-L-201F, Grade C, and is at least 99.97 percent pure. 
     The thickness of radiation shield  140  may vary depending on various factors, including the proximity to the source of radiation and the type of radiation. If two lead sheets are used, each preferably has at least half the specified thickness for the door. For example, if a total of ¼ inch thickness is required, each lead sheet would have a thickness of at least ⅛ inch. In other embodiments, if radiation shield  140  is provided on only one side of non-combustible core  110 , a ¼ inch thick sheet of lead may be provided on only one side of non-combustible core  110 . 
     In one embodiment, the radiation shield  140  is provided on both sides of core  110 , and each shield  140  has a thickness of between about 1/64 of an inch to about ¼ inch, for a total thickness (both shields combined) of between about 1/32 inch to about ½ inch. Other thicknesses may be used which may be dictated by a particular environment in which the door is used. 
     Cover  150  may be provided over intumescent material  130  and over radiation shield  140 . Cover  150  provides “door skins” to the front and back surfaces of the door, as well as a cover around the door stiles and door rails. In one embodiment, cover  150  may be a hardwood veneer or plastic laminate that is aesthetically pleasing. Cover  150  has a thickness of about 0.100 inch to about 0.110 inch before trimming. For example, a suitable cover is a hardwood wood veneer, available from Birchwood Inc., Birchwood, Wis. Other materials may be used. 
     The edges of door  100  may be chamfered or beveled as necessary. 
     A window (not shown) with radiation shielding may be provided in door  100  as required. 
     Doors may be secured to a frame in a manner known to those of ordinary skill in the art. 
       FIG. 4  depicts an arrangement of non-combustible core  412  and  414 , supporting structure  422 ,  424 , and  426 , and  430  in door  400  according to another embodiment of the invention. According to one embodiment, door  400  has a height of 8 feet 0 inches, and a width of 4 feet and 1/16 inch. In this embodiment, supporting structure  422  may have a width of between 1 and ⅜ inch and 8 inches, and preferably has a width of 5 and ½ inches. Supporting structure  424  has a height of between 4 and 6 inches, and preferably a height of 5 inches. Supporting structure  426  has a height between 5 and 12 inches, and preferably a height of 10 inches, or it may not be provided. 
     Note that, in this embodiment, non-combustible core  412  and  414  have different dimensions. This is so that a doorknob can be located at an appropriate position. Thus, supporting structure  426  may be positioned in door  400  accordingly. For example, structure  426  may be positioned with its centerline at 41″ from the bottom of the door, but this may vary as needed. 
     Intumescent material  430  has a thickness of between 1/16 inch and ½ inch, and, in one embodiment, ⅛ inch. Cover  450 , such as a hardwood veneer or plastic laminate, covers intumescent material  430  in the stiles of door  400 , and preferably has a thickness of 5/16 inch before trimming. After door  400  is trimmed to finished size, cover  450  may have a thickness of less than ¼ inch. 
     Door  100  may be manufactured as follows. Non-combustible core  110  is provided with supporting material  120  as necessary and desired. The specified amount of radiation shield  140  is then provided. In one embodiment, radiation shield  140  is attached (or bonded) to non-combustible core  110  and supporting material  120  with an adhesive (or glue). Any suitable adhesive may be used. For example, glues known as a shelf stable, one-component (pre-catalyzed), cross linking polyvinyl acetate emulsion adhesive may be used. An example of such a glue is Multibond 2000, available from Franklin International, Columbus, Ohio. During the bonding process, pressure must be applied to radiation shield  140  and non-combustible core  110 , and to cover  150 . 
     In one embodiment, it may be necessary to pre-treat the lead sheets in order to insure proper bonding of the lead sheets to non-combustible core  110  and cover  150 . This treatment process involves flattening the lead surfaces and then thoroughly cleaning the lead surfaces. In one embodiment, the surfaces of the lead sheets are flattened by any suitable mechanical means, such as a hammer and a block. Other suitable mechanical means may also be used. 
     Once the surfaces of the lead sheets are flattened, surface impurities are removed. In one embodiment, a non-abrasive cloth that has been soaked with certain chemical products, such as denatured alcohol, may be used to remove surface impurities on the lead. 
     In conjunction with the bonding of radiation shield  140  to non-combustible core  110 , cover  150  for the front and rear of door  100  may be bonded to radiation shield  140 . Any suitable glue may be used, such as a shelf-stable, one-component (pre-catalyzed), cross-linking polyvinyl acetate emulsion adhesive. An example of such a glue is Multibond 2000, available from Franklin International, Columbus, Ohio. 
     Intumescent material  130  is then provided to the door stiles and door rails. In one embodiment, intumescent material  130  is provided to the door stiles and the top door rail. Intumescent material  130  is then covered with cover  150 . In one embodiment, Palusol® is provided in the stiles, and Intument™ is provided in the top rails. 
     In one embodiment, cover  150  is only provided over intumescent material  130  in the door stiles, but not in the door rails. Cover  150  for the door stiles are usually made of a suitable hard wood veneer or plastic laminate and have a thickness of about 0.1 to about 0.25 inch. 
     The radiation shielding door of this invention withstands the industry standard minimum 45 minute and up to 60 minute fire test as administered by Intertek Testing Services. 
       FIG. 5  depicts a half-scale door according to another embodiment of the present invention, and  FIGS. 6   a - 6   c  depict sectional views of door  500 . Door  500  is provided in frame  580 , and includes non-combustible core  510 , supporting material  520 , intumescent material  530 , radiation shield  540 , and covering  550 . Note that  FIG. 6   c  illustrates a top view of door  500  that has cover  550  removed from its top rail. 
       FIG. 7  depicts a pair of doors according to another embodiment of the present invention. Doors  700  are constructed in a similar manner as door  100 . 
       FIG. 8  depicts a door including a window according to another embodiment of the present invention. Door  800  is constructed in a similar manner as door  100  and is provided in frame  880 . Door  800  includes window  860 . Window  860  may include lead shielding, as is apparent to one of ordinary skill in the art. Additional supporting structure may be provided in the area of window  860  to ease in its installation. 
     It will be apparent to those skilled in the art that doors of all embodiments of the invention can be manufactured in a manner similar to that used to manufacture door  100 , as described herein. 
     Other embodiments, uses, and advantages of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The specification and examples should be considered exemplary only.

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