US3639799A

US3639799A - Shadow mask with reinforcing ring for colored television picture tube

Info

Publication number: US3639799A
Application number: US822792A
Authority: US
Inventors: Myron C Kirchner
Original assignee: Tubal Ind Inc
Current assignee: Tubal Ind Inc
Priority date: 1969-04-02
Filing date: 1969-04-02
Publication date: 1972-02-01
Anticipated expiration: 1989-02-01
Also published as: GB1230891A; JPS4923619B1; BE748376A; FR2042025A5; DE1947433A1; NL7004423A

Abstract

A shadow mask for color TV picture tubes contains the conventional foraminous or translucent area formed by a multiple of miniature apertures in a curved portion of a thin metal sheet through which the electron beams pass in traveling from the electron guns at the rear of the tube to the viewing face at the front of the tube. Around the translucent area is an imperforate section formed into a wall and a flange and containing strengthening ribs. A reinforcing ring rigidly attached to the flange provides additional stability.

Description

0 United States Patent [151 3,639,799 Kirchner Feb. 1, 1972 [54] SHADOW MASK WITH REINFORCING 3,351,996 11/1967 Fiore ..1....3l3/85 X N F RED TELEVISION 3,376,451 4/1963 Meats... ..3l3/92 3,479,546 11 196 Mears ..3l3/85 PICTURE TUBE 3,349,272 10/1967 Bathelt et a1 ..3l3/85 [72] Inventor: Myron C. Kirchner, Itasca, lll.

Pma Ea --Ro Lake [73] Asslgneez Tubal Industries, Inc., Elk Grove Village, g g figg Attorney-Stryker and Jacobson [22] Filed: Apr. 2, 1969 2 79 [57] ABSTRACT l l. N i 1 App 0 2 A shadow mask for color TV picture tubes contains the con; ventional foraminous or translucent area formed by a multiple [52] U.S.Cl ..3l3/85 of miniature apertures in a curved portion of a thin metal 5| 1 lm. Cl. 41101] 29/46 sheet through which the electron beams P in traveling from 53 Field in Search ..313/85 s, 92, 64 the electron guns at the rear of the tube to e viewing face at the front of the tube". Around the translucent area is an imper- 56] References Cited forate section formed into a wall and a flange and containing strengthening ribs. A reinforcing ring rigidly attached to the UNITED STATES PATENTS flange provides additional stability.

2,897,392 7/1959 Fiore ..313/85 X 10 Claims, 5 Drawing Figures SHADOW MASK WITH REINFORCING RING FOR COLORED TELEVISION PICTURE TUBE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is used in the construction of colored TV picture tubes containing aperture or shadow masks.

2. Description of the Prior Art The conventional shadow mask contains the curved translucent area formed by a, multitude of miniature apertures through a metal sheet surrounded by an imperforate section or portion of the same metal sheet. The practice heretofore has been to attach the mask to amounting ring to form an assembly and then the entire assembly is mounted in some convenient fashion onto the glass bulb. The primary function of the mounting ring is tostabilize the mask. But it and its associated hardware became a substantial portion of the mass of the mask assembly. This technique not only makes the mask assembly costly and quite heavy, but also, because of the mass involved, there is usually produced a fairly large temperature gradient in the assembly before it is able to reach a uniform ambient temperature level. This usually requires a considerable amount of operational time. The temperature gradient results in some warping or twisting of the face of the mask which adversely affects the registration of the mask apertures with respect to the phosphor dots on the face of the picture tube and the electron beams from the guns located at the rear of the tube. Recently, attemptshave been made to eliminate the traditional mounting ring assembly with its inherent disad vantages. An example of this is a type of shadow mask described in US. Pat No. 3,376,451. Although these recent innovations have been somewhat successful, they still have had some diawbacks, primarily in the area of mechanical stability. Therefore, they have not been accepted by the colored TV industry to the extent desired.

SUMMARY The present invention, which is sometimes referred to as a uniframe mask, is somewhat of a variation and modification of the aperture mask described in the aforementioned patent. It contains the conventional curved translucent area surrounded by an imperforate section which bends back to form a rearwardly extending wall and terminating with an inward extending flange from the rear edge of the wall. A circumambient groove around the translucent area provides a first strengthening rib and a continuous groove in the wall section provides additional strengthening. Further strengthening can be provided by cross ribs in the wall section which may be extended onto the flange area. A metal ring or annulus is rigidly attached to the flange area for reinforcement. Not only does this arrangement reduce the mass of the mask quite considerably from that of the former ring-mask assembly so that uniform temperature appears throughout the mask assembly in a very short time after the tube is first energized but the strengthening ring on the flange also prevents the translucent area from warping or twisting to interfere with the passage of the electron beams to the face of the tube during the warrnup period. Even though the mass is reduced the mask assembly is still rigid enough so that during normal handling, such as when the mask is inserted and removed during the process of forming the phosphor dots on the face of the picture tube, there is no substantial shift in location of the tiny apertures so that they return each time to the same location. Furthermore, masks constructed in this manner are much lighter in weight and are less costly than the mask assemblies which have been used for the most part in the past.

BRIEF DESCRIPTION OF THE DRAWING FIG. lis a rear view of the shadow mask for a colored TV picture tube constructed according to the teachings of the invention;

FIG. 2 is a view of the shadow mask from the front;

FIG. 3 is a sectional view taken along viewing line of 3-3 of FIG. I;

FIG. 4 is a side elevational view of an embodiment of the invention; and

FIG. 5 is a sectional view takenalong viewing line 5-5 of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The shadow mask of the present invention'may be of any form suitable for use in picture tube assemblies, the most general forms being rectangular or circular. Since the former is most popular today, the invention will be described as used in producing a rectangular shadow mask.

The mask contains the conventionalforaminous or translucent area 10 formed by a myriad of miniature apertures which are usually chemically milled through a thin sheet of metal, such as stainless steel. In normal use, when incorporated into the final picture tube assembly the shadow mask is located near the front viewing face of the picture tube between it and the electron guns. When the tube is in operation, the electron beams are suitably directed through the translucent area of the mask to impinge upon the colored phosphor dots on the inside of the face of the picture tube. The mask is also used during the process for laying down the color phosphor dots in the conventional triad pattern. Without delving into this process to any great degree, it is merely pointed out that during the dot-forming steps, the mask ordinarily must be removed and repositioned with respect to the face of the picture tube a number of times so it is apparent that stability is critical to make sure that the tiny apertures return to virtually their exact previous location each time the mask is temporarily removed and replaced. It is also apparent that temperature stability is quite critical so that the translucent area does not shift and interfere with the passage of the electron beams as they travel from the guns to impinge upon the respective color phosphor dots.

Conventionally, the translucent area 10 is partially domed or curved, usually aspherically, to conform to the curved inner face of the picture tube. Over the years, methods, procedures and equipment have been developed and are today widely known and used throughout the color TV industry for etching out the translucent area 'and for curving or shaping the mask face to the desired contour. These methods, procedures and equipment are not considered part of the present invention.

Around the translucent area 10 is a marginal imperforate area 11 which is merely a continuation of the same metal sheet but which has not been etched through. In area 11, near the outer edge of the translucent area 10, there is a continuous, inward-projecting, shallow groove 12 which serves as a strengthening rib for the face area of the aperture mask. This rib is formed in a press using standard techniques. Just a little beyond the rib I2, the metal bends backward at about a angle, with respect to a planar projection of the mask face to form a rearward extending wall section 13 which, similar to the marginal section 11, is preferably a further continuation of the same metal sheet. The depth of draw to form wall 13 may vary from mask to mask depending on the size and type of mask being formed. However, it is referred to in the trade as a deep-drawn mask, as differentiated from a shallow-drawn mask which ordinarily has its wall section extending only a short distance rearward. Typically, with no limitation intended, the wall 13 may be in the order of 1% inches deep for an aperture mask used in a 21 or 24 inch picture tube. Wall 13 contains a continuous groove or strengthening rib which strengthens the wall section. Selection of the location and size of rib 14 in wall 13 depends on a number of factors, including the size of the mask, the depth of the wall, the metal thickness, etc. The choice can and must be made by the skilled artisan for each application and no definite formula to cover all applications appears to be reasonably determinable. Investigations have shown that in some instances additional ribs, similar to rib 14, may be formed in the wall 13 to provide some additional strength.

At the rear end of wall 13 the metal sheet is bent inward and forms flange 16 which is approximately at a 90 angle to the wall 13. Flange 16 completely encircles the opening at the rear of the mask. Overlaying flange 16 and rigidly attached thereto, such as by welding, is a metal reinforcing ring 17. Preferably. ring 17 is made out of the same metal as the mask. It may be the same thickness as the metal sheet from which the mask is formed but for the most part, it has been found preferable that the ring metal be somewhat thicker, and a thickness in the order of twice that of the flange has worked very satisfactorily. As a further feature, the inner edge 18 of ring 17 can be flared partially upward for shielding. in addition, as shown in the FIG. 5 embodiment, the ring 17 may extend out beyond wall 13 for further shielding to prevent leakage of light and reflection around the outside of the mask between the glass bulb and the mask assembly. It has been found that ring 17 welded to the flange l6 reinforces the mask to such a degree that the stability and strength is many times that of the mask without the ring.

Directing attention back to the wall 13, as most clearly seen in FIGS. 4 and 5, additional strengthening and supporting measures are obtained by pressure-formed, shallow, grooved ribs 20 in wall 13. In the embodiment illustrated, these ribs 20 are substantially equally spaced along wall 13, are parallel to one another and extend rearward from rib 14 down to the end of the wall section and further extend at least part way down flange 16. Although this arrangement may be preferable, it is contemplated and has been shown that variations thereof may and will produce substantial additional supporting strength and so should be considered to come within the spirit and scope of this invention. For example, the ribs 20 may not be parallel to one another and/or may be at other than a right angle to rib 14. Here again, the number of ribs 20 and the dimensions of the grooves is a matter of design or choice depending upon many factors such as the dimension and shape of the mask. The practicing artisan can make this choice based upon his experience and knowledge. Another factor which must be taken into account when determining the size and location of the supporting cross ribs 20, as well as the continuous rib 14, is that these ribs should not interfere with the mounting pads or springs (not shown) which are normally attached to the wall 14 for the finished mask to the glass bulb.

Tests have shown that masks having reinforcing ring 17 when mounted in picture tubes show little or no evidence of shift brought about by temperature differentials and the masks appear to warm up to uniform temperature in a matter of moments as compared to the 30 to 90 minutes before the former ring-mounted assembly was able to reach a fixed temperature level.

The process steps for fabricating the aperture mask will now be described. Initially, a fiat metal sheet, called a blank, which contains the translucent area formed by chemically milling out the tiny apertures, is annealed to reduce its hardness, to improve its machinability, to facilitate cold working, to produce a desired microstructure and to obtain desired mechanical, physical or other properties. After annealing, the metal blank is subjected to roller-leveling which is a process whereby the blank is sent over and through a series of rollers which break down the molecular structure so that the metal blank can later be drawn down and formed without distorting or otherwise damaging the miniature apertures. The blank is next placed in a press where the face of the mask is drawn down to the desired curvature. All of the steps listed heretofore are commonplace and have been used in the industry for a considerable period of time and so are not considered a novel part of the present invention. Yet they are necessary steps in the fabrication of masks constructed according to the teachings of the present invention.

During the step of bowing or curving the face of the mask, the strengthening rib 12 in the face of the mask is formed. Rib 12 may be located immediately adjacent the outer edge of the translucent area 10 or may be located adjacent the corner where wall section 13 meets margin area 11 or anywhere between. This is a choice which may differ with mask shape, size and other factors. After the curvature and rib 12 have been formed on the mask face area. the mask then goes through a second press operation to form wall 13. This merely involves drawing down the metal at the correct angle, about while the face area is held firmly in place. An added feature of rib 12 appears during this process step. Because the face area is clamped in position in the area of rib 12, it prevents the draw-down operation on the wall portion 13 from adversely affecting the curvature or the hole sizes of the translucent area in the face of the mask. It is contemplated that the draw-down of the wall portion may be a single step operation or may be accomplished by a series of press operations. This is a matter of choice and design depending on many factors and is determinable by those skilled in press operations and techniques. There follows another press operation in which rib 14 is formed in sidewall 13 and the rear end wall 13 is tucked inward at about a 90 angle to form flange 16. Finally, ring 17 is placed over flange l6 and welded thereto. Ordinarily, ring 17 is previously cut to size and is located and'held over the flange in a suitable fixture and a number of welding guns are strategically located to weld the ring onto the flange. In some cases ring 17 has been found to provide suitable reinforcement when it is the same thickness as the metal sheet from which the rest of the mask is made. In those cases the ring 17 can be cut from what otherwise would be scrap metal leftover from the unused portion of the metal sheet. But for the most part, even though ring 17 is made from 'the same metal it is necessary to have it a thicker gauge to provide the necessary degree of stability. lt has been found preferable that prior to welding ring 17 to flange 16 the two parts be cleaned and run through a furnace for blackening the metal and relieving any stresses and strains. This is a process step which also has been used in the industry for a number of years and has become quite well known. It is contemplated that the parts can be welded together first and then cleaned and blackened in the special furnace. Here again the sequence is a matter of choice and design depending upon any number of different factors and can be selected by those familiar with such fabrication process steps. Lastly, mounting pads or springs must be attached to the outer wall of the shadow mask for use in mounting the mask to the inside of the 'glass envelope. The design and construction of the mounting springs is not considered a part of the present invention nor is the process by which these mounts are attached. Of course, they are essential to the overall assembly of the picture tube.

lclaim:

1. A reinforced shadow mask for a colored television picture tube, comprising: a thin metal sheet having a front section containing a curved translucent area defined by a myriad of miniature apertures through the metal sheet, an imperforate margin area around the translucent area, a further imperforate section bent back from the margin area at about 90 to form a rearwardly directed wall, said wall containing a continuous strengthening rib, the other end of the wall section being bent to form an inwardly directed flange; and a planar metal reinforcing ring rigidly attached to said flange with the ring in surface to surface contact with the flange.

2. The invention as in claim 1 wherein the strengthening rib is a continuous groove formed in the metal sheet.

3. The invention as set forth in claim 1 further including a plurality of shallow grooves in said wall extending in a direction across said continuous rib, said grooves forming strengthening cross ribs.

4. The invention as set forth in claim 3 wherein said cross ribs extend along said wall rearwardly from the continuous rib in said wall.

5. The invention as set forth in claim 3 wherein said cross ribs are parallel to one another.

6. The invention as in claim 3 wherein said cross ribs extend at least part way onto the flange.

7. The invention as set forth in claim 1 wherein the inner edge of said annulus is flared rearwardly.

8. The invention as set forth in claim 1 wherein said annulus is characterized by being thicker than the metal sheet and forms a thermally stable combination with the metal sheet.

9. The invention as set forth in claim 8 wherein the annulus is in the order of twice the thickness of the metal sheet.

10. The invention as set forth in claim 8 wherein said metal annulus also flares outwardly beyond said wall section.

l 1! t 8 i 5

Claims

1. A reinforced shadow mask for a colored television picture tube, comprising: a thin metal sheet having a front section containing a curved translucent area defined by a myriad of miniature apertures through the metal sheet, an imperforate margin area around the translucent area, a further imperforate section bent back from the margin area at about 90* to form a rearwardly directed wall, said wall containing a continuous strengthening rib, the other end of the wall section being bent to form an inwardly directed flange; and a planar metal reinforcing ring rigidly attached to said flange with the ring in surface to surface contact with the flange.