Abstract:
There is provided a hook assembly attached to a shadow mask frame including a base and a spring with a hole in one end thereof and the other end attached to said base, wherein a middle portion of said base is arched such that the arched portion takes the shape of a tunnel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hook assembly for use in a shadow mask frame assembly and in particular to a hook assembly that attaches a shadow mask frame to the face panel of a CRT. The present invention also relates to a shadow mask frame assembly with such a hook assembly. 
     2. Description of the Related Art 
     A shadow mask frame assembly for use in flat CRT comprises a pair of support bars  11 , 12 , a pair of tension bars  13  and  14  of which ends are welded to an each end of the support bars  11  and  12 , a shadow mask  20  supported by the support bars  11  and  12  and a plurality of hook assembly  9  attached to the support bars  11  and  12  and/or the tension bars  13  and  14 , as shown in FIG.  1 . Also, as shown in a circle indicated by “A”, there are provided with plurality of slots  22  between strips  21  connected with tie bars  23 . 
     The shadow mask frame assembly is installed in the face panel of the flat CRT by means of the hook assembly  9 . More specifically, it is installed in the face panel by inserting stud (not-shown) formed on the inner surface of the skirt portion of the face panel into the hole  28  of the hook assembly  9 , comprising base  26  and a spring  27 , welded on the support bars  11  and  12  and the tension bars  13  and  14  of a shadow mask frame, as illustrated in FIG.  1 . 
     FIG. 2 is an exploded view of the hook assembly  9  further showing welding points. The hook assembly is firmly attached to the support bars 11  and  12  and/or the tension bars  13  and  14  of a mask frame by spot welding at a couple of points  29 , i.e., on the part of the base  26 . Welding must be very strong because the metallic mask frame is rather heavy. The more so recently since flat panel CRTs use relatively heavier frames. The base  26  of the hook assembly  9  welded on the bars is thick and may suffer heat-induced deformation. For instance, while hook assembly is being welded at one spot it may deform so that the next welding point can be off its spot. The deformed hook assembly results in welding weaker than desired and can cause the mask to shift from intended position. 
     SUMMARY OF THE INVENTION 
     It is an objective of the present invention to provide a hook assembly that is less deformable subjected to heat such that the hook assembly can be attached by welding to the predetermined location of the mask frame without error. 
     The objective is achieved by proving a buffer zone in the middle of a base of the hook assembly in a variety of ways so that possible deformation of the hook assembly at one part during welding can prevented from spreading to the rest of the hook. The buffer zone may be tunnel like arch or indention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objective and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
     FIG. 1 is an exploded view of a shadow mask frame assembly; 
     FIG. 2 shows a conventional hook assembly welded on a mask frame; 
     FIG. 3 shows a hook assembly according to a first embodiment of the present invention; 
     FIG. 4 shows a hook assembly according to a second embodiment of the present invention; 
     FIG. 5 shows a hook assembly according to a third embodiment of the present invention; and 
     FIG. 6 shows a hook assembly according to a fourth embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described in detail. First referring to FIG. 3, the base  31  of a hook assembly to be welded to the support bars and/or tension bars of a mask frame has tunnel-like arch portion  32  in the middle of the base  31  and a flat portion  35  on either side of the base  31 . The spring  33  having a hole  34  in one end is welded at a point  37  in the lower part of one flat portion of the base  31 . 
     Welding points of the base  31  to the support bars and/or the tension bars are indicated by reference numeral  39 . Welding is performed at two points, for an instance, in sequence. With the present invention, while welding is performed at one point, possible heat-induced deformation around the point does not spread to a part of the base  31  where a second welding is to be performed next since the arch portion  32  function as a zone absorbing most of the deformation. 
     The base  31  of a hook assembly according to the present invention shown in FIG. 3 has a length L 2  and widthW 2  and its arch portion  32  has a length L 1  and a width W 1 . The thickness of the base  31  represented by t. These dimensions should be determined in accordance with the size of the welding spots at points  39 . The welding spots are an area of the hook assembly at which spot welding is perform in order to couple the hook assembly to a mask frame assembly. Let the diameter of average welding spots, which substantially round, be D′. Then it is preferred that L 2  is greater than D′ (L 2 &gt;D′), while L 2  is equal to or greater than L 1  (L 2 ≧L 1 ). Further the width W 1  of the arch portion should be greater than the thickness t of the base  31  and yet should be less than a value which is obtained by subtracting the twice the welding spot diameter D′ from the whole base width W 2 . The relation can be represented by an in equation t&lt;W 1  &lt;W 2 − 2 D′. 
     The spring  33  is shown welded to the base  31  at one point  37 . However, it could have more than one welding point and further the part of a spring that contacts the base  31  may be longer than the width of the base  31 . Also, the spring  33  may have an tunnel-like arch portion of its own to closely overlap the arch portion  32  of the base  31 . In other words, the surface of the spring arch would match the outer surface of the base arch. 
     FIG. 4 shows a second embodiment of the present invention. Here the length L 1  of the arch portion  42  is less than the whole length L 2  of the base  41  while the spring  43  formed with a hole  44  is to be attached flat portion  45  of the base  41  under the arch portion  42 . 
     FIG. 5 shows a third embodiment in accordance with the present invention. It is similar to shown in FIG. 4 in that a tunnel-like arch portion  52  is joined by a flat portion  56  but has a hole  55  under the arch portion  52 . The hole  55  is located about in the centre of the hook base  51 . The hole  55  servers a function of distributing stress during the welding of the base  51  at one point, thereby pr deformation of the hook. A spring  53  formed with a hole  54  is welded to the flat portion  56  of the base  51 . 
     FIG. 6 shows a fourth embodiment according to the present invention. 
     An indention  64  is made on the top and bottom sides of the base  61  such that the base  61  would look like the letter H. A spring  62  with a hole  63  in one end is attached to the base  61  across the lower indention  64 . Due to the gap between one welding point  67  and another welding point  67  the stress the base  61  suffers when it is welded to the support bars and/or the tension bars at one welding point can spread to the rest of the hook base, particularly to around the next welding area.