Abstract:
A method of cleaning the neck of a funnel of a CRT during the manufacture thereof. The method comprises: inserting a drain tube within the neck, wherein a gap exists between the drain tube and the neck; directing a fluid through the gap; and draining the fluid that was directed through the gap through the drain tube, whereby the fluid removes material from the neck that was applied during a prior coating process and any dirt. The drain tube is part of a cleaning apparatus that further comprises a housing and a labyrinth flow controller positioned within the housing adjacent to the drain tube forming a laminar flow section whereby fluid is directed through the housing and into the tube.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a divisional of co-pending U. S. patent application Ser. No. 09/997,661, entitled “Neck Cleaning Method For A CRT” filed on Nov. 29, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention generally relates to the manufacture of cathode ray tubes and, in particular, to a method of cleaning the neck of a cathode ray tube.  
         BACKGROUND  
         [0003]    The color cathode ray tube (CRT) typically includes an electron gun, a shadow mask, and a screen. The tube has a funnel shape, i.e., a wide opening that leads to a narrow neck. The electron gun is mounted in the neck of the tube and the screen is mounted proximate to the wide opening of the funnel of the tube. The shadow mask is interposed between the electron gun and the screen. A faceplate is sealed to the wide opening of the funnel. The screen is located on an inner surface of the faceplate of the CRT. The screen has an array of three different color-emitting phosphors (e.g., green, blue and red) formed thereon. The shadow mask functions to direct electron beams generated in the electron gun toward the appropriate color emitting phosphors on the screen of the CRT.  
           [0004]    As part of the manufacturing process for a color CRT, the inside surface of the tube is coated with a conductive coating used to carry high voltage from a location on the side of the tube to the shadow mask. One method of applying the conductive coating is to use a flow coating process. The flow coating process comprises pouring the conductive coating material into the wide opening of the funnel and allowing the material to flow out along the funnel and through the neck of the tube. The material completely coats the funnel and neck. However, to create an operational CRT, the coating cannot extend along the entire neck of the tube. As such, it is necessary to clean the coating from a portion of the neck to a controlled dimension along the neck. The transition from the uncoated to coated portions of the neck must be uniform and the neck should be free of all contaminants.  
           [0005]    Presently, the process for cleaning the neck consists of inserting a multi-blade squeegee into the neck to a predefined distance along the neck. The squeegee is rotated to wipe the coating material from the inner surface of the neck. The problem with this system is that the squeegee wears during use and will ultimately leave streaks of coating material within the neck.  
           [0006]    Therefore, there is a need in the art for a more effective method and apparatus for cleaning the neck of a color CRT.  
         SUMMARY OF THE INVENTION  
         [0007]    A method of cleaning the neck of a funnel of a CRT during the manufacture thereof. The method comprises: inserting a drain tube within the neck, wherein the outer dimensions of the drain tube are less than the corresponding inner dimensions of the neck and a gap exists between the drain tube and the neck; directing a fluid through the gap; and draining the fluid that was directed through the gap, through the drain tube, whereby the fluid removes material and dirt from the neck.  
           [0008]    The method utilized a cleaning apparatus, wherein the apparatus comprises: a cleaning unit having a housing that surrounds the neck; the drain tube that extends through the bottom of the housing into the neck to a predefined position within the neck which is below the top end of the housing; and a labyrinth flow controller positioned within the housing adjacent to the drain tube forming a laminar flow section whereby a flow of fluid is directed through the housing and along the interior of the neck and into the end of the drain tube. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The invention will now be described in greater detail, with relation to the accompanying drawing, in which:  
         [0010]    [0010]FIG. 1 is a schematic view of the apparatus for cleaning the neck of a picture tube in accordance with the present invention;  
         [0011]    [0011]FIG. 2 depicts a cross-sectional view of the cleaning unit of the present invention; and  
         [0012]    [0012]FIG. 3 depicts a top plan view of the labyrinth flow controller of FIG. 2.  
     
    
     DETAILED DESCRIPTION  
       [0013]    [0013]FIG. 1 depicts a schematic view of the apparatus for cleaning the neck of a tube of a CRT in accordance with the present invention. The apparatus  100  comprises a warm air source  102 , a mechanism  128  for supporting the funnel  106 , a cleaning fluid source  104 , and a cleaning unit  112 . Prior to being mounted in support mechanism  128 , the funnel  106  is heated to between 50 and 55° C. before being coated with a layer  108  of graphite, iron oxide or other conductive material, along the entire inner surface of the funnel  106  and the neck  114  of the funnel  106 . The coating process is conventional and well known in the art.  
         [0014]    Once coated, the funnel  106  is mounted in the support mechanism  128  before the coating has time to fully cure. The support mechanism  128  generally supports the funnel  106  above the cleaning unit  112 . Since the layer of coating material is not completely cured, the coating material can be removed using a non-caustic cleaning agent such as de-ionized water. The support mechanism  128  is positioned at location  122  above the cleaning unit  112  by a predefined distance  120 . When mounted, the neck  114  is inserted into the cleaning unit  112 . The distance  120  represents the length of the neck  114  that shall remain coated with the conductive coating material. The reference line  124 , which is a predefined position, approximates the location up to where the coating material will be removed. Once the funnel  106  is mounted, a warm air source  102  blows heated air toward the inner surface of the funnel  106 . A conduit  118  directs the warm air toward the neck  114 . Cleaning fluid source  104  provides cleaning fluid through the conduit  110  to the cleaning unit  112 . The flow of cleaning fluid through the cleaning unit  112  causes any dirt and the conductive coating within the neck to be removed (cleaned) completely from the neck and up to the reference line  124 .  
         [0015]    [0015]FIG. 2 depicts a cross-sectional view of the cleaning unit  112  while FIG. 3 depicts a top plan view of the cleaning unit  112 . To best understand the invention, the reader should simultaneously refer to both FIGS. 2 and 3 while reading the following disclosure.  
         [0016]    The cleaning unit  112  comprises a housing  200 , a drain tube  230  and a labyrinth flow controller  201 . The housing  200  comprises a sidewall  203  and a bottom  205  that together define a volume in which the labyrinth flow controller  201  is positioned. The sidewall  203  is substantially cylindrical in the depicted embodiment. However, other embodiments may have non-cylindrical surfaces such as hexagonal or octagonal. The drain tube  230  extends through a bore  210  in the bottom  205  of the housing  200 . The drain tube  230  extends a distance into the volume that is defined by the housing  200 . The end  202  of the drain tube  230  is positioned a distance from the top of the housing  200  such that, as cleaning fluid is added to the volume, fluid will flow into the drain tube  230  before overflowing the top edge  240  of the housing  200 . The end  212  of the drain tube  230  has an inner surface  214  that is contoured to facilitate laminar flow of cleaning fluid over the end  212  into the inner portion  226  of the drain tube  230 .  
         [0017]    The labyrinth flow controller  201  comprises a first baffle  204  and a second baffle  206 . The first baffle  204  is mounted within the housing  200  on standoffs  300  to cause the first baffle  204  to be spaced apart from the second baffle  206  of the housing  200  as shown in FIG. 3. The first baffle  204  extends near the top edge  240  of the housing  200  and stops a distance from the bottom  205  of the housing  200 . The second baffle  206  extends from the bottom  205  of the housing  200  and stops near the end  212  of the drain tube  230 . As such, the baffles  204  and  206  define a first, second and third channels  218 ,  220  and  222 , respectively. The channels cause fluid that enters from the conduit  110  to flow downward through the first channel  218 , then up through the second channel  220 , and then through the third channel  222 . When the neck  114  of the tube  106  is inserted into the cleaning unit  112  over the drain tube  230 , a fourth channel  224  is produced that extends from the flare  126  of the neck  114  along the inside of the tube neck  114  to the input end  212  of the drain tube  230 . To enhance the laminar flow of fluid through the labyrinth flow controller  201 , the bottom  205  of the housing  200  is contoured to be sloped, or rounded at location  216  and the fourth channel  224  is caused to be shaped to match the flare  126  of the neck  114  at a second location  208 . Location standoff tabs (not shown in FIG. 2) on the outside surface of the drain tube  230  aids to position the drain tube  230  within the neck to create a desired uniform forth channel  224  between the outside surface of the drain tube  230  and the inside surface of the neck. The position of the drain tube  230  within the neck  114  establishes a distance along the neck  114  where the conductive material is removed. By fixing the distance between the yoke reference line  122  and the input end  212  of the drain tube  230 , the distance  120  along the neck  114  is established.  
         [0018]    Heated dry air is provided through conduit  118  into the neck volume  228 . The heated air dries or cures the conductive coating layer  108  in the neck  114  that is not removed while the uncured conductive coating is removed by the cleaning fluid. (Essentially, a siphon effect is created by the fluid as it drains through the drain tube  230 , thereby helping to draw the heated air downward toward the neck  114  and conductive coating layer  108 .) Typically, deionized water suffices to remove dirt and uncured conductive coatings.  
         [0019]    To insure that the transition from no conductive coating to conductive coating is uniform, the fluid flow through the cleaning unit  112  must have very little turbulence and the flow along the inner surface of the neck  114  of the funnel  106  should substantially be laminar. To facilitate such laminar flow, the forth channel  224  through which the fluid flows along the inside surface of the neck  114  is approximately 0.14 cm. Furthermore, within the forth channel  224  to clean the neck  114 , each sequential channel  218 ,  220 ,  222 ,  224  is provided to create a smooth, uniform, nonturbulent laminar flow.  
         [0020]    The housing  200  and the baffles  204 ,  206  of the labyrinth flow controller  201  may be fabricated of plastic, stainless steel, or some other material that is compatible with both the cleaning solution and the conductive material removed from the tube&#39;s neck  114 . If the cleaning unit  112  is fabricated of plastic, then the various components of the unit are epoxied to one another to form the depicted cleaning unit  112 . For stainless steel components, the components are welded in a conventional manner to form the cleaning unit  112 . In one embodiment of the invention, the cleaning unit has a diameter of the housing  200  of between 15-20 cm and the unit holds a volume of cleaning fluid of approximately 3 liters.  
         [0021]    In this illustrative unit, the first channel  218  is approximately 3.8 cm wide, the second channel  220  is approximately 1 cm wide, the third channel  222  is approximately 0.45 cm wide, the fourth channel  224  is approximately 0.14 cm and the drain tube  230  has an inner diameter of 1.3 cm.  
         [0022]    While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope of thereof, and the scope thereof is determined by the claims that follow. One skilled in the art can appreciate other embodiments wherein the dimensions of the channels and number of channels could be varied to accommodate differing fluid solutions and differing neck dimensions.