Patent Publication Number: US-2010107414-A1

Title: Method and apparatus for manufacturing grating

Description:
TECHNICAL FIELD 
     The present invention relates, in general, to gratings and, more particularly, to a method and an apparatus for manufacturing a grating having a lattice shape. 
     BACKGROUND ART 
     In general industrial fields, gratings are lattice-shaped covers and are used for various purposes, for example, as covers for manholes, covers for subway vents provided in footways, stairs, footboards, etc.  FIG. 1  illustrates a representative example of such conventional gratings. 
     As shown in the drawing, a grating  100  includes an outer frame  102 , and lateral members  104  and longitudinal members  106 , which are arranged inside the outer frame  102  at relatively close intervals in lateral directions and longitudinal directions to have a lattice shape. A linear steel bar having a twisted shape to increase the tensile strength thereof is used as each lateral member  104 . Each longitudinal member  106  typically has a longitudinal plate shape, which has an I-shaped cross-section. Each longitudinal member  106  has in the upper edge thereof insert notches, which are formed at positions spaced apart from each other in the longitudinal direction at predetermined intervals, and into each of which a corresponding lateral member  104  is fitted. 
     Typically, the lateral members  104  and the longitudinal members  106  are perpendicular to each other, and they are fixed to each other by welding at the junctions therebetween. Gratings made of stainless steel can be mass-produced using an automatic resistance welding method. However, in the case of nonferrous metals such as aluminum and copper, it is difficult to use the resistance welding method. Thus, in the case where nonferrous metals are used as the material for a grating, a welding process must be separately conducted for every junction. This is not easy. Even though the grating is completed through such welding processes, if a relatively large load is applied to the grating, or, after it is used for a long period time, welded portions may be separated from each other, thus deteriorating the external appearance of the grating and causing noise. In addition, the separated portions may be potentially dangerous to pedestrians. 
     In an effort to overcome the above problems, as shown in the sectional view of  FIG. 2 , a grating, in which rod-shaped lateral members  104  are fitted into corresponding coupling holes  106   a  formed through longitudinal members  106 , was proposed. A spacer  108  having a pipe shape is interposed between adjacent longitudinal members  106  to maintain the gap between the adjacent longitudinal members  106  constant. This grating has an advantage in that a welding process is unnecessary. However, there is a disadvantage in that it is inconvenient to alternately fit the large number of spacers  108  and the longitudinal members  106  over the lateral members  104 , and the cost of manufacturing the grating increases due to the addition of elements. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method and an apparatus for manufacturing a grating, having a plurality of lateral members and a plurality of longitudinal members which are coupled to each other in a lattice shape, the method and the apparatus being able to solve the problem of separation of the lateral members and the longitudinal members at junctions and making the coupling between the elements easy, thus reducing the cost of manufacturing the grating. 
     Technical Solution 
     In order to accomplish the above object, in an aspect, the present invention provides a method of manufacturing a grating, including: fitting a plastic deformable lateral member having a hollow pipe shape into coupling holes, formed through respective longitudinal members, in a lateral direction of the longitudinal members; holding the lateral member and the longitudinal members; and passing a forming weight through the lateral member from a first end of the lateral member to a second end thereof using external force, the forming weight having a predetermined size suitable for passing through the lateral member to expand a cross-sectional area of the lateral member such that the lateral member is plastic-deformed, so that the lateral member is force-fitted to inner surfaces of the coupling holes of the longitudinal members, thus fixing the lateral member to the longitudinal members. Preferably, each of the lateral members and the longitudinal members may be made of aluminum or an aluminum alloy. 
     In another aspect, the present invention provides an apparatus for manufacturing a grating, including: a holding means for maintaining a state in which plastic deformable lateral members, each having a hollow pipe shape, and longitudinal members having coupling holes, into which the lateral members are fitted in directions of the longitudinal members, are assembled with each other in a lattice shape; forming weights, each having a size suitable for passing through the corresponding lateral member to expand a cross-sectional area of the lateral member such that the lateral member is plastic-deformed; a tensioning device to pull the forming weights using tensile force; and tension rods placed through the respective lateral members, the tension rods being removably coupled at first ends thereof to the tensioning device and being coupled at second ends thereof to the respective forming weights. Here, each of the lateral members and the longitudinal members may be made of aluminum or an aluminum alloy. 
     Preferably, the tensioning device may comprise one selected from between a hydraulic cylinder and a pneumatic cylinder, which generates linear motion and is easily controlled. 
     Advantageous Effects 
     A method and an apparatus for manufacturing a grating according to the present invention can markedly enhance productivity through the elimination of an operation of welding a large number of junctions between lateral members and longitudinal members. In addition, the method and apparatus of the present invention can solve a problem of separation of the lateral members from the longitudinal members, ensure a superior appearance of the grating, and reduce the cost of manufacturing the grating. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a conventional grating; 
         FIG. 2  is a sectional view of another conventional grating; 
         FIG. 3  is sectional views illustrating steps of a process of manufacturing a grating, according to an embodiment of the present invention; 
         FIG. 4  is a perspective view illustrating a step of coupling an outer frame to an assembly body of lateral members and longitudinal members according to the present invention; 
         FIG. 5  is a sectional view showing the coupling between a lateral member and longitudinal members, according to another embodiment of the present invention; 
         FIG. 6  is a side view showing an apparatus for manufacturing a grating, according to an embodiment of the present invention; and 
         FIG. 7  is a perspective view of the grating manufacturing apparatus of  FIG. 6 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.  FIG. 3  is views illustrating steps of a process of manufacturing a grating, according to an embodiment of the present invention. 
     In the embodiment, each lateral member  2  has a hollow pipe shape. Each longitudinal member  4  has a longitudinal plate shape having an I-shaped cross-section. Several coupling holes  10  are formed through the longitudinal member  4  at positions spaced apart from each other in a longitudinal direction at regular intervals. Each of the lateral members  2  and the longitudinal members  4  is made of aluminum, an aluminum alloy or stainless steel. 
     The lateral member  2  preferably has a circular shape when viewed in cross-section, but is not necessarily limited to this. The cross-section of the lateral member  2  has the same shape as the coupling hole  10 . The lateral member  2  has a diameter corresponding to the size of the corresponding coupling hole  10  to have an appropriate clearance such that the lateral member  2  can be inserted into the coupling hole  2  without large resistance. The lateral member  2  is firmly friction-coupled to the coupling hole  10  by expanding the cross-section of the lateral member  2 , and this will be explained in detail later herein. 
     As shown in  FIG. 3   a , each lateral member  2  is inserted into the corresponding coupling holes  10  in the longitudinal members  4 . That is, the longitudinal members  4  are fitted over the lateral members  2  such that the longitudinal members  4  maintain regular intervals therebetween, thus forming a lattice shape, as shown in  FIG. 3   b.    
     The lateral members  2  and the longitudinal members  4  are fixed to each other in the state of  FIG. 3   b . Thus, a jig or a holding means for this purpose must be provided. 
     To achieve the above purpose, a forming weight  12 , which has a size appropriate to pass through each lateral member  2  and expand the cross-sectional area of the lateral member  2  such that the lateral member  2  having the pipe shape is plastic-deformed, is coupled to an end of a wire  14  having high tension resistance. It is preferable that the forming weight  12  have a tapered shape, the cross-section of which is increased from one end thereof to the other end thereof, as shown in the drawing. The cross-section of the forming weight  12  has the same shape as that of the coupling hole  10  and the lateral member  2 , and the maximum cross-sectional area thereof is larger than the cross-sectional area defined by the inner diameter of the lateral member. For example, in the case where the lateral member  2  and the forming weight  12  have square cross-sections, one side of the forming weight  12  (in the case where they have circular cross-sections, the diameter of the forming weight  12 ) is from 0.5 mm to 2 mm longer than that of the lateral member  2 . 
     The forming weight  12  and the wire  14  are coupled to each other by inserting the wire  14  into a hole, which is formed through the center of the forming weight  12 , and by knotting a first end of the wire  14 . A second end of the wire  14  is coupled to a tensioning device (see  FIGS. 6 and 7 ). In the state of  FIG. 3   c , when the wire  14  is strongly pulled to the right, the forming weight  12  passes through the lateral member  2  and expands the inner diameter, that is, the cross-section area, of the lateral member  2 .  FIG. 3   d  shows the state in which the lateral member  2  and the longitudinal members  4  are coupled to each other by frictional force after the forming weight  12  passes through the lateral member  2 . If necessary, the forming weight  12  and the wire  14  may be integrated with each other into a single body. In this case, an inflexible tension rod ( 56 , see  FIG. 6  or  7 ) may be used as the wire  14 . 
     As such, while the forming weight  12  forcibly passes through the lateral member  2 , the sidewall of the lateral member  2  is brought into close contact with and is fixed to the corresponding coupling holes  10  in the longitudinal members. 
     In the grating of the present invention, most of the load transmitted to the upper surface of the grating in a downward direction is applied to the longitudinal members  4 . The lateral members  2  mainly serve to maintain regular intervals between the longitudinal members  4 . Therefore, the lateral members  2  have little relation to the load. However, because the possibility of application of a very large load to the upper surface of the grating cannot be excluded, a reinforcing member (not shown) may be selectively inserted into each hollow lateral member  2  to reinforce the grating. A twisted linear steel rod, used in the conventional technique, a simple rod or pipe may be used as each reinforcing member. 
       FIG. 4  is a perspective view illustrating a step of coupling an outer frame  20  to a lattice assembly body of the lateral members  2  and the longitudinal members  22 . According to the intended purpose of a product, the installation of the outer frame  20  may be a selective item. The outer frame  20  has a longitudinal plate shape and includes longitudinal frames  22 , which are coupled to the lateral members  2 , and lateral frames  24 , which are coupled to longitudinal members  4 . In this embodiment, each longitudinal frame  22  may be coupled to the lateral members  2  by a welding or a bolt coupling method (the method shown in  FIG. 4 ) or by a compression coupling method using pipe enlargement in the same manner as in  FIG. 3 . Each lateral frame  24  may be united to the longitudinal members  4  by welding or by a combination of welding and convexo-concave coupling. Here, the term “convexo-concave coupling” means a coupling method in which depressions  26 , each of which has a shape corresponding to the cross-section of the corresponding longitudinal member  4 , are formed in the lateral frame  24 , and the longitudinal members  4  are fitted into the respective depressions  26 . In the convexo-concave coupled state, the welding operation may be selectively conducted. 
     Furthermore, the installation of the frames  22  and  24  can be conducted by various methods, but this is not the main point of the present invention. 
     Another embodiment of the present invention is shown in  FIG. 5 . In this embodiment, each lateral member  2 ′ is made of a twisted linear member having a circular cross-section. Each longitudinal member  4 ′ has coupling holes  10 , each of which has an area (shown by the dashed line) less than the cross-sectional area of the lateral member  2 ′. Thus, the lateral member  2 ′ is force-fitted into the corresponding coupling holes in the longitudinal members  4 ′, so that the lateral member  2 ′ is compression-coupled to the longitudinal members  4 ′. In the force-fitted state, as shown in the drawing, perimeters  4 ′ a  of the coupling holes  10  of the longitudinal members  4 ′ are bent in the direction in which the lateral member  2 ′ is fitted into the coupling holes  10 . 
     In a modification of this embodiment, the present invention may be constructed such that a screw rod is used as each lateral member  2 ′ and an internal thread is formed in the inner surface of each coupling hole  10  of the longitudinal member  4 ′ by tapping, so that the lateral member  2 ′ is screwed into the longitudinal members  4 ′. 
     Hereinafter, an apparatus for manufacturing a grating according to an embodiment of the present invention will be described with reference to  FIGS. 6 and 7 . 
     The grating manufacturing apparatus  30  is horizontally placed on the ground using a base frame  32  thereof. In this embodiment, the grating manufacturing apparatus  30  is constructed such that three lateral members  2  are coupled to a plurality of (for example, ten to twenty) longitudinal members  4 . 
     The base frame  32  provides a rail  34 . A tensioning device  36  is provided at a predetermined position on the base frame  32 . In the embodiment, a hydraulic cylinder (or a pneumatic cylinder), which generates linear motion, is easily controlled, and is relatively quiet, is used as the tensioning device  36 . A movable block  40 , which is provided so as to be movable along the rail  34 , is coupled to the end of a piston  38  of the tensioning device  36 . The movable block  40  is movable along the rail  34  using wheels  42 . 
     Three holders  44 , which are parallel to each other, are provided in the movable block  40 . A stop plate  48 , through which three through holes  46  are formed at positions spaced apart from each other at regular intervals, is provided on the base frame  32  ahead of the tensioning device  36  in the direction perpendicular to the rail  34 . The stop plate  48  serves to prevent the lateral members  2  from moving in longitudinal directions during the process of coupling the lateral members  2  to the longitudinal members  4 . 
     Furthermore, a support block  50  is fastened to the base frame  32  ahead of the stop plate  48  in the same plane as the rail  34 . A plurality of longitudinal slots  52 , into which the respective longitudinal members  4  are inserted, is formed in the support block  50 . Three lateral slots  54  are formed in the support block  50  in a direction perpendicular to the longitudinal slots  52 . That is, the stop plate  48  and the support block  50  serve as a means for holding the lateral members  2  and the longitudinal members  4 . 
     A coupling means, which passes through the lateral members  2 , is removably coupled at a first end thereof to the tensioning device  36 , in detail, to the holder  44 , and is coupled at a second end thereof to the forming weight  12 . In this embodiment, a tension rod  56 , which is integrally formed with the forming weight  12 , is used as the coupling means. As described above, a wire may be substitute for the tension rod  56 . 
     A holding part  58 , which is held by the holder  44 , is formed in the rear end of each tension rod  56  by cutting part of the tension rod  56 . 
     After the lateral members  2  and the longitudinal members  4  are set in the support block  50 , the tension rods  56 , each of which is provided with the forming weights  12 , are inserted into the lateral members  2 , and the rear ends of the tension rods  56  are held by the holder  44 . Thereafter, when the tensioning device  36  is operated, the forming weights  12  pass through the corresponding coupling holes  10  in the lateral members  2 . In this process, the inner diameters of the coupling holes  10  are increased. Thereby, the lateral members  2  are coupled to the longitudinal members  4 . Preferably, a removal prevention means for preventing the longitudinal members  4  from being removed from the support block  50  upwards during the operation of the tensioning device  36  is provided, although this is not shown in the drawings. 
     INDUSTRIAL APPLICABILITY 
     As described above, in a grating having a structure such that lateral members and longitudinal members are coupled to each other in a lattice shape, the present invention provides a method and an apparatus for manufacturing the grating which can markedly enhance productivity through the elimination of an operation of welding a large number of junctions between the lateral members and the longitudinal members. The method and apparatus of the present invention can solve a problem of separation of the lateral members from the longitudinal members, ensure a superior appearance of the grating, and reduce the cost of manufacturing the grating.