Abstract:
An explosion retaining housing includes a sheet metal member or outer skin which at least in part forms an interior region of the housing. At least one structural element provides additional strength to the member to retain the explosion in the region. The structural element can be inside of, or, outside of the region. The structural element can have a plurality of components which cooperate together to resist the force of an explosion in the interior region.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of and claims priority benefit under 35 U.S.C. §121 to co-pending U.S. patent application Ser. No. 12/813,667, filed on Jun. 11, 2010, and entitled “Sheet Metal Explosion-Proof, and Flame-Proof Enclosures”, which is hereby incorporated by reference for all purposes as if reproduced in its entirety. 
     
    
     FIELD 
       [0002]    The invention pertains to explosion-proof, dust-ignition proof and flame-proof enclosures. More particularly, the invention pertains to such enclosures implemented, at least in part, with sheet metal-type housings. 
       BACKGROUND 
       [0003]    Traditional explosion and flameproof enclosures are constructed using cast metal components. These enclosures are typically expensive, and heavy. Further, manufacture and assembly are time consuming. 
         [0004]    Cast metal enclosures often suffer from porosity caused by blowholes and fissures leading to thick wall constructions, welded repairs and additional pressure testing requirements of the enclosure to ensure it can be operated safely within explosive gas and dust atmospheres. In summary, known explosion resistant enclosures resist the explosion pressure by use of a load bearing skin, for example a cast housing. 
         [0005]    There is a continuing need for enclosures for housing electrical equipment intended for use in explosive gas and dust atmospheres. Such enclosures could be used to house various types of gas detectors. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a diagram of an embodiment of the invention; 
           [0007]      FIG. 2  is a diagram of another embodiment of the invention; and 
           [0008]      FIG. 3  is yet another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    While embodiments of this invention can take many different forms, specific embodiments thereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention, as well as the best mode of practicing same, and is not intended to limit the invention to the specific embodiment illustrated. 
         [0010]    In embodiments of the invention, a thin walled explosion, dust-ignition proof and flameproof enclosure can withstand the pressure developed during an internal explosion of an explosive mixture, without damage. This containment prevents the transmission of the explosion to the explosive gas and dust atmospheres surrounding the enclosure. In such embodiments, a thin walled sheet metal structure, which is difficult to assemble using traditional fasteners while maintaining the requirements of a flame-proof joint, can advantageously be utilized. 
         [0011]    Structural members can be incorporated which are separate from the enclosure itself. Such members can be internal or external of the respective housing. While the external housing needs to withstand and retain the pressure of an internal explosion, the addition of one or more additional, structural components which can provide some of the structural integrity of the overall housing results in this requirement being met with a much lighter housing. For example, drawn sheet metal can be used. 
         [0012]    In one aspect of the invention, such housings can incorporate a thin sheet metal enclosure. Two metal end covers and are assembled using a threaded nut. Such sheet metal enclosures do not suffer from the same porosity issues as a cast enclosure. As a result, a lighter gauge material can be used 
         [0013]    In one embodiment, a clamped cylindrical design can be used to realize the benefits previously described of a sheet metal enclosure. In a disclosed implementation, the sheet metal enclosure is formed in a cylindrical form with openings at either end and clamped onto a cylindrical ‘chassis’ securely with a clamping nut. The clamping nut is a structural member which withstands the pressure developed during an internal explosion of an explosive mixture and prevents the enclosure from separating. 
         [0014]    The cylindrical ‘chassis’ can include front and rear housings clamped together using one or more tie rods. The tie rods represent structural members which can withstand the pressure developed during an internal explosion of an explosive mixture and prevent the enclosure from separating. Flameproof joints can he incorporated at the interface between the front and rear housing and the cylindrical sheet metal enclosure. Such joints prevent the transmission of an internal explosion to the explosive gas atmosphere surrounding the enclosure. 
         [0015]      FIG. 1  illustrates an embodiment of the invention. An explosion resistant enclosure  10  includes a relatively thin sheet metal-like member  12  which could have a variety of cross-sectional shapes such as circular, oval, rectangular, or square all without limitation. Characteristic of the present invention, the member  12  would not itself be of a type which would be expected to contain an internal explosion in the internal region V defined in part by the member  12 . Rather, that additional strength is provided to the enclosure  10  by one of an internal framework  16 , illustrated in phantom in  FIG. 1 , or an external framework, such as external framework  14  illustrated in  FIG. 1 , in combination with a separate outer skin or member  12 . Those of skill will understand that the framework  14  provides explosion resisting strength and need not completely enclose the outer skin  14 , as discussed below. 
         [0016]    The framework  14  could for example be of unitary construction with a first portion  14   a  joined to a second portion  14   b  by a central portion  14   c.  The portions  14   a,b,c  can be rod-like and form a frame that can in part surround the outer skin  12 . The outer, skin or, member  12  is sandwiched therebetween. As appropriate, and known to those of skill in the art, flame-proof joints could be incorporated into the enclosure  10 . 
         [0017]    The member  12  can carry in the internal region V (which might be closed in part by the framework  14 ) a detector  18  having a sensor  18   a,  and control circuits  18   b . An explosion in the region V would be contained by the framework  14 , in combination with the member  12 . It will also be understood that the type of detector  18  is not a limitation of the invention. A variety of gas sensors can be used and come within the spirit and scope of the invention. The detector  18  can be in wired or wireless communication  20  with a displaced alarm system. 
         [0018]    The chassis type construction of the enclosure  10  of  FIG. 1  makes it possible to use a much thinner member, or outer skin, than would otherwise be possible and still retain internal explosions in the region V. The configuration  10  of  FIG. 1  results in a lower cost solution when compared to traditional explosion retaining enclosures which use prior art cast members. 
         [0019]    Those of skill will understand that the location of the framework  14  is not a limitation of the invention. It can he located in the internal region V or outside thereof as illustrated in  FIG. 1 . Further members of framework  14  need not be directly or integrally coupled together. Variations and permutations thereof come within the spirit and scope of the invention. 
         [0020]      FIG. 2  illustrates an alternate embodiment  30  of the invention. In the embodiment  30  of  FIG. 2 , strength adding elements are located in the explosion-proof enclosed volume, region, V 1 . The assembly  30  includes a sheet metal enclosure  32  which can be cylindrical, without imitation. 
         [0021]    The enclosure  32  can be formed with openings  32   a,b  and can bound in part the internal volume or region V 1 . A gas detector which includes a sensor S 1  and associated control circuits CI can be carried on a printed circuit board B 1  in the internal volume V 1 . 
         [0022]    Enclosure  32  is clamped onto a chassis  34 , having elements  34   a,b  of a comparable shape, for example if the enclosure  32  is cylindrical, the chassis  34  most conveniently could also be cylindrical, A clamping nut  36  can be used to clamp the housing, or enclosure  32  to the chassis  34 . The end  32   a  of the enclosure  32  and a portion of the element  34   a  can provide a cable feed through. 
         [0023]    The clamping nut  36  is a structural member which withstands the pressure developed during an explosion in the internal region V 1  due to an internal explosive mixture. The nut  36  works to prevent the enclosure  32  from separating due to the explosive pressures developed in the region V 1 . 
         [0024]    The cylindrical chassis  34  includes first and second elements  34   a,b  which are clamped together using tie rods and screws  38   a,b . It will be understood that the number of tie rods is not a limitation of the invention. In selected configurations, one or three or more tie rods could be used instead of two as in  FIG. 2  without departing from the spirit and scope of the invention. 
         [0025]    The tie rods  38   a,b  are internal structural members which withstand the pressure developed during an explosion in the internal region V 1  and also contribute to preventing the enclosure  32  from separating. 
         [0026]    Flameproof joints  40   a,b  can be incorporated at the interfaces between elements  34   a,b  and the sheet metal enclosure  32 . The joints  40   a,b  prevent the transmission of an internal explosion to an explosive gas atmosphere surrounding the assembly  30 . 
         [0027]    In summary, as illustrated in  FIG. 2 , the load bearing chassis, or, structure of the assemblage  30  is separate and apart from the outer skin  32 . The load bearing chassis, for example, the nut  36  and first and second elements  34   a,b  in combination with the internal tie rods  38   a,b  form a structure which can withstand the explosive pressure of an explosion in the region V 1  and keep the outer skin  32  from separating in response to that pressure. 
         [0028]      FIG. 3  illustrates an alternate embodiment  60  of the invention. In the embodiment  60  of  FIG. 3 , strength adding elements are located outside of the explosion-proof enclosed volume, region, V 2 . The assembly  60  includes a sheet metal enclosure  62  which can he cylindrical, without limitation. 
         [0029]    The enclosure  62  can be formed with openings  62   a,b  and can bound in part the internal volume or region V 2 . A gas detector which includes a sensor S 2  and associated control circuits C 2  can be carried on a printed circuit board B 2  in the internal volume V 2 . 
         [0030]    Enclosure  62  is clamped between first and second elements  64   a,b  which are clamped together using external tie rods  68   a,b . It will be understood that the number of tie rods is not a limitation of the invention. In selected configurations, one or three or more tie rods could be used instead of two as in  FIG. 3  without departing from the spirit and scope of the invention. 
         [0031]    The tie rods  68   a,b  are external structural members which withstand the pressure developed during an explosion in the internal region V 2  and also contribute to preventing the relatively thin walled enclosure  62  from separating. 
         [0032]    Flameproof joints  70   a,b  can be incorporated at the interfaces between elements  34   a,b  and the sheet metal enclosure  32 . The joints  70   a,b  prevent the transmission of an internal explosion to an explosive gas atmosphere surrounding the assembly  60 . 
         [0033]    In summary, as illustrated in  FIG. 3 , the load bearing structure of the assemblage  60  is separate and apart from the outer skin  62 . The load bearing external tie rods  68   a, b  form and ends  64   a, b  form a structure which can withstand the explosive pressure of an explosion in the region V 2  and keep the outer skin  62  from separating in response to that pressure. 
         [0034]    From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.