AU480077B2 - Fabrication of "focus grill" type cathode ray tubes - Google Patents

Description

48.922/72

This invention relates to a method of fabricating

a cathode ray tube including a cup-shaped panel having a

pattern of phosphor material on the inner bottom surface of the panel and a wire grill spaced from the bottom panel

surface. Color television picture tubes of the "focus

grill" type use this kind of structure.

One type of "focus grill" color picture tube

comprises a glass envelope including a cup-shaped panel

having a phosphor screen on the inside surface thereof, and

a funnel-shaped envelope member with the large end thereof

sealed to the open end of the panel in co-axial relation

therewith. For the purpose of properly focusing or

directing an electron beam or beams onto desired portions

of.the screen, a "grill" comprising one or more sets of parallel fine wires is disposed within the.tube closely

adjacent to the panel screen. In the fabrication of such tubes, according to

one prior art techinque, a plurality of grooves are provided

in the end surface of the side wall of the cup-shaped panel,

and the phosphor screen is printed on the inside of the

panel in preselected relation with the grooves. Fine

wires are disposed within the grooves under tension and

extending across the.panel opening. The funnel member

is frit-sealed to the end surface of the panel side

wall, the frit joint closing the grooves and anchoring the

wires therein.

One problem with this prior art fabrication

techinque is that the panel grooves are preferably shallow,

to provide a reliable, hermetic seal with the funnel, and

during movement of the tube assembly prior to and during 480.077

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the sealing operation, the fine grill wires are subject

to being displaced from the grooves. This adversely affects the alignment of the grill wires with the phosphor pattern

on the screen and results in defective picture tubes. -In accordance with an embodiment of the invention,

a helix of wire is wound around the outside of and along the

panel; the turns of said helix extending across the open

end of the panel in a preselected relationship with respect

to the pattern of phosphor material on the bottom of said

panel. Portions of the helix turns are sealed to the side wall of said panel, and then the portions of the helix

extending around the outside of the panel are removed. In accordance with another embodiment of the

invention, the winding of the helix of wire includes disposing

a member having a thermal expansion greater than that of the

wire between the helix and the panel, for maintaining the

turns of the helix under tension during the sealing operation. In the drawing: Figure 1 is a side view, partlybroken away, of a cathode ray tube of a type in which the instant invention has utility. Figure 2 is a cross-sectional view, partly broken away, taken along line 2-2 of Figure 1. Figure 3 is a plan view of a panel member of a type used in the practice of the method of this invention. Figure 4 is a side view, partly broken away, and partly schematic, showing apparatus for winding a wire around and along the panel member shown in Figure 3; and Figure 5 is a plan view of the apparatus shown in Figure 4. Focus grill cathode ray tubes, with which the invention has particular utility, are known, see, for example, United States Patents 3,030,536, issued April 17, 1962 and 2,842,696, issued July 8, 1958. In general, as shown in Figure 1, herein, such 3 490077

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tubes comprise a glass envelope 10 including a cup-shaped panel

member 12, a frusto-conical shaped funnel member 14, and a

cylindrical neck tubulation member 16. The panel and funnel

members are frit-sealed together in co-axial relation, e.g.,

the contacting edges of the separate members are coated

with a glass frit, the contacting edges are abutted against

one another and heated to liquify the glass frit, and the

liquid glass, upon further heating, solidifies to bond the

edges together. The funnel 14 and the neck 16 are sealed

by softening and fusing the abutting glass edges thereof.

The inside surface 18 of the bottom wall or

faceplate 20 of the panel 12 is provided with a plurality of

parallel adjacent strips 22 of phosphor arranged in sets

of three adjacent strips 22, the strips of each set being of

different phosphors to provide different colors when the

strips are excited by an electron beam. The phosphor

coated panel surface 18 is the "screen" of the tube. The

screen 18 has a generally rectangular shape, having a major

axis 24 (FIGURE 2) and a minor axis 26.

Disposed within the tube in spaced, close relation

with the screen 18 is a grill 30 comprising a plurality of

fine wires 32 which extend parallel to the phosphor strips 22.

The funnel member 14 may include various focusing

and accelerating electrodes, and the neck member 16 may

include one or more electron guns. Details of these latter

members are known and form no part of the instant invention.

Also, the operation of tubes of this type is generally known.

In the fabrication of a tube of the type shown in

FIGURE 1, in accordance with this invention, a panel 12 is

first provided as a separate member including, as shown in 480,077

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FIGURE 3, a pattern of contiguous phosphor strips 22 on the

faceplate 18 thereof, and a plurality of grooves 42 in the

end surface 44 of the side wall 46 of the panel. The

grooves 42 are disposed in two arrays 50 and 52 of grooves

on oppositely disposed portions of the side wall 46, each

groove 42 in one array 50 having a corresponding oppositely

disposed groove 42 in the other array 52.

The phosphor strips 22 can be provided on the

screen by known printing methods using a photosensitive

binder, and the arrays 50 and 52 of grooves can be provided

by known means such as etching.

Of importance, is-that the arrays 50 and 52 of

grooves are located in accurate relation with respect to

the strips 22. Such accurate location can be provided, for

example, by the use of indicia means on the panel 12 to which

both the grooves 42 and the strips 22 can be referenced. For

example, the panel 12, in this embodiment, is provided with

three positioning lugs 54 which are integral therewith.

After the panel is formed, as by molding, according to known

processes, the lugs 54 are accurately machined, as by

grinding, to provide indicia means which are the same from

panel to panel. A further function of the lugs 54 is

described hereinafter.

Having provided the panel 12, the grill 30 therefor

is next provided by winding a helix-of a fine wire 32 around

and along the panel. To this end, a winding cradle

(FIGURES 4 and 5) comprising a cup-shaped member is provided

for receipt of the panel 12 therein with the side wall 46

of the panel extending at least slightly beyond the side wall

62 of the cradle, as shown. The cradle 60 is provided with

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and 65 which extend three positioning screws 63, 64, and two leaf springs 66 through the cradle side wall 62, the side wall 62. When a and 67 mounted on the inside of cradle 60, the screw 63, panel 12 is disposed within the 66, is used to position the in combination with the spring 68 of the cradle, and the panel 12 along the major axis with the spring 67, are screws 64 and 65, in combination in the direction perpendicular used to position the panel 12 as to angularly orient the to the cradle axis 68 as well The purpose of angularly panel 12 within the cradle 60. to the cradle 60 is orienting the panel 12 relative combination described below. The screws 63, 64, and 65, in to lock the panel 12 with the springs 66 and 67, serve clamps 71 can be within the cradle 60. Additionally, panel 12 in place. provided to further lock the with two co-axial The cradle 60 is also provided means of which the cradle pointed cylindrical pins 69 by axis 68 of the cradle. can be rotated about the major panel 12, the cradle To wind a wire helix about the is mounted between with the panel 12 located therein, winding apparatus (not centers of a conventional lathe-like its axis 68, and a shown), the cradle 60 is rotated about 4) is attached to the cradle wire 32 from a spool 70 (FIGURE thus drawn onto and around by a suitable clamp 74 and is provided the panel and cradle. Known means, not shown, are

a direction parallel to the for advancing the spool 70 in

axis of rotation of the cradle. 68 of rotation As shown in FIGURE 5, the axis off-set from the major axis 24 of the cradle 60 is slightly of the off-set is to off-set of the panel 12. The purpose 48 0.07 7

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the grooves 42 of each groove array 50 and 52 from each

other an amount equal to the amount of advance of Lhe spool

during the cradle rotation in order that each turn of

the helix wound about the cradle-panel assembly is disposed

within a pair of corresponding grooves 42 of each groove

assembly. Selection of the off-set of the cradle axis 68

relative to the panel major axis 24, the rate of rotation of

the cradle 60, and the rate of advance of the spool 70 in

order to properly lay the wire 32 in successive pairs of

corresponding grooves 42 of the groove arrays 50 and 52 is

well within the skill of persons familiar with the helix

winding art. Aside from providing the off-set of the panel

and cradle axis, as described, the positioning screws 63,

64, and 65 allow adjustment of the position of the panel 12

relative to the winding apparatus.

As shown in FIGURES 4 and 5, as a result of the

winding operation, a helix of wire 32 is wound about the

cradle-panel assembly. The end turn of the helix is also

secured to the cradle by a suitable clamp, not shown. A

reason for winding the wire 32 around the cradle 60, as well

as around the panel 12, is described hereinafter.

The wire 32 is preferably wound at a relatively

high tension for maintaining the wire turns firmly in place

around the cradle 60 and within the grooves 42 of the panel

12. Thus, during subsequent processing of the cradle-panel

assembly, the sealing of the funnel 14 to the panel 12,

little danger exists that the wire 32 will be displaced from

the grooves 42.

In one embodiment of the invention, the wire 32

comprises 2 mil diameter stainless steel, and the wire is

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of 6 ounces. wound at 40 turns to the inch under a tension and have a The grooves 42 have a circular cross-section,

width of 3 mils and a depth of 2 mils. cathode The wound panel 12 is now assembled into a

ray tube using known techniques. Thus, for example, a

end surface 44 of layer of glass frit is disposed along the edge of the the panel side wall 46 and along the mating 12 are pressed into funnel member 14, the funnel 14 and panel abutting edges an abutting, co-axial relationship, and the frit to of the members are heated to soften the glass In the sealing provide a frit seal of the contacting edges. carrier process, the funnel 14 can be disposed on a suitable of the funnel of a conveyor system, with the large open side is disposed facing upwardly, the cradle-panel sub-assembly 12 facing within the carrier with the open end of the panel end of the downwardly and disposed in contact with the open an funnel 14, and the loaded carrier is conveyed through

oven to perform the sealing process. The use of such

tube arts. conveyors and oven is known in the cathode ray

During the funnel-to-panel sealing process, the the glass frit flows into the grooves 42 thereby sealing

grooves and sealing the wires 32 therein. Preferably, in

the panel, a order that the wires 32 are firmly anchored to The use of wire 32 is used which is wet by the glass frit. of cathode glass frit for sealing together envblope portions to metal ray tubes and for making adherent, hermetic seals

members is generally known.

Then, the portions of the wires 32 disposed on the

outside of the tube envelope are removed, as by cutting with

a razor edge, to complete the inventive process. The tube

480,07 7'

48.92 2/f2

can then be separated from the cradle. If desired, electrical

contact to the various wires 32, for the purpose of applying

an electric potential thereto, can be made by disposing a

conductive paint on the tube envelope 10 around the joint

between the panel 12 and the funnel 14. Since the wires 32

extend at least a small distance outwardly of the envelope

after the cutting operation, the wires are contacted by the

conductive paint.

During the heating step to seal the panel 12 to

the funnel 14, the wire 32 of the helix around the panel

and cradle is unavoidably heated. This causes thermal

expansion of the wire, and, if nothing were done to avoid

it, a lessening of the tension of the helix turns. However,

by using a cradle made of.a material, such as aluminum, having

a thermal expansion greater than that of the wire 32, the

cradle expands more than the wire turns, thus maintaining

the tension of the helix turns and minimizing the danger of

the turns becoming displaced from the panel grooves during

the panel-to-funnel sealing operation.

While the use of a cradle 60 of the type shown

provides a simple means for both mounting the panel 12 for

rotation and maintaining the helix turns under tension during

heating thereof, the use of the particular cradle 60 described

herein is not essential. For example, other fixture means

employing suitable jaws or the like-can be used for mounting

the panel 12 for rotation. Also, other expansion means can

be used to maintain the helix turns under tension during the

envelope sealing process. For example, a separate plate of

aluminum or the like can be disposed along the outside of the

bottom wall 20 of the panel between the helix turns and the 480.07 7

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panel. Or, in place of a thermal expansion member, such

as the aluminum plate, a compressive expansion member, such

as a hollow cylinder, can be used; the member being compressed

as the helix is wound thereover, and expanding to increase

the helix turns length upon heating of the helix. The

increase of turns length at least partly compensates for the

loss of tension caused by heating of the helix.

Claims (3)

1. 48.922/72 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

   A method of fabricating a cathode ray tube 1.

   including a funnel-shaped member and a cup-shaped panel

   having a pattern of phosphor material on its

   inner bottom surface and a wire grill spaced from said

   bottom surface, said method comprising the steps of

   winding a wire helix around said panel and an expansion

   member disposed therebetween such that each turn of the

   helix extends across the open end of said panel in a

   predetermined relationship with respect to said

   pattern of phosphor material, said expansion member having

   a thermal expansion coefficient greater than that

   of said wire for maintaining the turns of said helix

   under tension during sealing; sealing portions of said

   turns to the side wall of said panel by frit-sealing the

   open end of said funnel-shaped member to

   said open end of said panel; and removing the portions

   of said helix extending around the outside of said

   panel.
2. 2. A method substantially as hereinbefore

   described with reference to the accompanying drawings.
3. 3. A cathode ray tube fabricated by the method

   of any one of the preceding claims.

   DATED THIS llth DAY OF JANUARY. 1977.

   RCA CORPORATION. By Its Patent Attorneys,

   CLEMENT HACK CO.. Fellows Institute of Patent Attorneys of Australia.

   S11 480,071