Note: Descriptions are shown in the official language in which they were submitted.
D Berner-R. Reidinger-R. Vollath 1-1-5
(Revision)
3S~7~
MASK-FRAME ASSEMBLY AND METHOD OF
MANUFACTURING THE SAME
Background of the Invention
Field of the Invention
The present invention relates to a mask-frame
assembly for use in a color-selecting-electrode
system in color-television tubes, and to a method of
manufacturing the same.
Description of the Prior Ar_
In a color-television tube of conventional design,
the three electron beams must strike exactly their
assigned red, green, and blue phosphor areas on
screen. The necessary angle-dependent assignment of
the phosphor areas to the electron beams is achieved
by means of the so-called mask. For every trio of
phosphor areas on the screen, there is one aperture
in the mask, which is just behind the screen and
parallel to it.
The requirements placed on the positional and
dimensional accuracy of such a mask are very stringent,
for the proper mask-screen relationship mus~ be
achieved over the entire area of the mask during pro-
duction and then maintained over the whole life of
the tube. In particular, there must be no change
in position due to the temperature rise when the set is
turned on. The resulting rPquirements can only be
fulfilled by optimizing the design of the product and
the manufacturing technology used, so that compara~
tively high costs are incurred.
D Berner et al 1-1-5
(Revision)
--2--
In conventional methods, the mask and its frame are
assembled after be.ing blackened separately, so that
dimensional changes due to the temperature of about
600 C during blackening can be largely compensated
for during assembly. After being assembled by spot
welding, the mask-frame assembly is stabllized at about
450~ C to reduce internal stresses in the material which
were caused by the welding process. The two thermal
treatments of the mask and the frame in separate opera-
tions and facilities involve high handling costs andre~uire two furnace installations. The separate stack-
ing of masks and frames during the thermal treatments
very easily results in distortion of the masks and
frames under their dead weight, so that the masks and
fra~les cannot be stacked to save factory space and re-
duce the amount of equipment required. When the mask
and the frame are welded together and the mounting
springs are welded on, splashes of welding flux are
unavoidable because the surfaces had become poor con-
ductors during the blackening process. Another dis-
advantage is that t'ne hitherto used maximum temperature
during blackening results in a high subsequent deforma-
tion ("collapsing"~ of the mask.
Summary of the Invention
The aim of the invention is to make such a fabrica-
tion process simpler and, thus, more economical. This
is achieved by an improvement in design which allows
for simplification of the fabrication process. '~he
invention centers on the operations necessary to blacken
the mask and the frame supporting it~ which may also be
called "surface passivation" and serves primarily to
prevent corrosion of the sheet iron used, make the sur-
faces nonreflecting, and ensure good heat-radiating
capacity.
Accordingly, the object of the invention is to
provide a simplified manufacturing method which does
not have the above disadvantages, and a design of the
mask-frame assembly which is suitably improved, particu-
larly with regard to the novel manufacturing method.
The inven-tion provides a mask-.Erame assembly for a
screen of a color television tube, comprising: a mask in the form
of a thin sheet of metal which contains a plurality of apertures;
a bent flange formed about the periphery of -the mask; a frame to
which -the mask flange is welded; connecting merrlbers consisting oi
bimetallic-spring holders and moun-ting springs welded -to said
frarne, wherein said n,etallic-spring holders are welded to said
frame to receive said mounting springs anci wherein the neares-t
metallic-spring holder weld along the long side of the mask with
reference to the cen-ter of the long side of the mask is a-t a
distance A from -the center of the side where A is chosen so that
4D5~ A < 2D4 and on the short side of the mask, the dis-tance B
between a metallic-spring weld and the nearest corner of the mask
is chosen so that 8D4~ B ~ 3Do that the wid-th C of the flange near
an edge where the welds are located,is chosen to be C~ llo6D ~ where
D is the length of the screen diagonal; welds also being disposed
at the corners of the mask to weld said mask to said frame; and
stress-relief means disposed on bo-th sides of -the corner welds for
relief of mechanical stress.
The invention also provides a method of manufac-turing a
mask and a frame assembly, -the parts of which are welded together~
surface-blackened, and thermally stabilized, comprising the steps
of: spo-t welding the mask and the frame; a-ttaching to -the frame
bimetalli.c-spring holders and moun-ting springs by welding; and
surface-treating and simultaneously thermally stabilizing as a unit
-the mask, frame, bimetallic-spring holders, and mounting springs,
the thermal treatment being carried out until the mask and the
frame have reached a common final temperature TE, and the hea-ting-
-2a-
7~
up process being timed so that the maximum temperature difference
between the frame and the mask is less than abou-t 1/3 of the
common final temperature TE of 500 -to 600 C and that -the mask-
frame assembly is blackened by the use of generator gas as the
furnace atmosphere in the surface treatment effected simultaneously
with the -thermal stabilization.
-2b-
~53~
--3--
It was found that the main requirements determin-
ing the sequence of operations in the conventional
fabrication process are no longer imperative if,
according to the invention, the following technical
instructions are followed.
The positions of the welds must be chosen so that
the internal stresses in the material cause~ during or
remaining a~ter the thermal treatment are taken up by
permissible deformations which remain within the
elastic range. Notches, recesses, and creases must
be formed to provide stress relief. If these require-
ments are followed, the mask is allowed to optimally
compensate for thermal expansion toward all sides without
being curved too much, so that the maximum change in
position remains sufficiently small when a joint thermal
treatment of the mask-frame assembly is carried out.
Brief Description of the Drawings
Fig. l shows schematically the operation of a
shadow mask.
Fig. 2 shows the assembly of the shadow mask, frame and
television tube faceplate.
Fig. 3 shows the distribution of the welds along
the flange of the shadow mask.
Figs. 4a and 4b show how the welds are stress-
relieved by indentations or cutouts.
Fig. 5 is a cross-sectional view of the mask and
frame.
Fig. 6 shows a flowchart of the mask-frame manu-
facture according to the invention. The individual
process steps are shown by rectangles.
Description of the Invention
Referring to Figure 1, there is show~ schema~ically
the operation of a shadow mask 1 having apertures 2
through which electron beams 3 strike selected phosphor
areas 4 formed on an inner surface 5 of a faceplate 8,
Figure 2 shows the shadow mask 1 having a flange 13
mounted to a frame 6. Frame 6 is provided with connect-
ing members 7 consisting of bimetallic spring holders 7a
and mounting springs 7b. The connecting members 7 function
` :
D. Berner e~ al 1-1-5
~ ~7 ~ (Revision)
to moun~ the shadow mask frame assembly within the
faceplate 8 of a televisi.on tube.
Referring to Figures 4a, 4b and 5, the shadow mask l
is sho~l to have indentations 10 as shown particularly in
Figure 4a or cutou~s 11 as shown particularly in 4b
formed in the flange 13 for the purpose of stress rellef.
In addition, a crease 12 is formed about the periphery
of the shad~w mask for the purpose of compensatin~ for
thermal expansion. The location of welds 9 along the
flange 13 of mask 1 for attaching the mask to the frame 6
are shown in Figure 3.
Re~erring specifically to Figure 3, the distance A
between the center of the long side of the mask and the
nearest weld 9 is chosen so that 4D5 is less than or
equal to A, which is less than or equal to 2.4 where D
is the diagonal dimenslon across the shadow mask. ~n
the short side of the mask, the distanee B between the
weld 9 and the nearest corner of the mask is chosen so
~ that ~ is equal to or less than B, which is equal to or
less than 3Ø The width C of the flange 13 near ~he
edge 14 on which the welds are located is chosen so
that C is equal to or greater than ~
The welds 9 at the corners of the mask are relieved
of mechanical stress by the stress release means 10 or
ll formed on each side of said weld as shown in
Figures 4a and 4b.
Turning now to the unique method of asse~bly of the
mask frame and faceplate, Figure ~ shows that in Step 15,
the frame is washed and degreased. According to the
invention, blackening, Step 16, is performed together
with the stabilizing of the welded parts 1, 6, and 7 in
Step 23. In Step 17, three connecting members 7 are
welded onto the frame. The mask 1 is first processed
in the conventional manner by heating as shown in Step 18,
rolling as shown in Step 19 and drawing as shown ln
Step 20. After the mask is washed as shown in Step 21,
the mask 1 is secured by spot welding in Step 22.
This is followed by the joint heat treatment for blacken-
ing and simultaneous stabilization, Step 23.
, D. Berner et al 1-1-5
7~ (Revision~
--5--
The assembled mask 1, frame 6, bimetalllc spring
holders 7a and mounting springs 7b are in Step 23
simultaneously surface-treated and thermally stabilized,
with the treatment being carried out until the mask and
the frarne have reached a common final temperature T~,
and the heating up process being timed so that the
maximum temperature difference between the frame and
the mask is less than about 1/3 of the final temperature
TE, which temperature is within the range of 5~0 to
600 C and preferably 570 to 580 C. The mask frame
assembly is blackened by the use of a generator gas in
the furnace atmosphere so that surface treatment is
accomplished simultaneously with the thermal stabiliza-
tion. The passivation step may also include passiva-
tion in the presence of 2 to 3 percent oxygen. It is
preferable that after the stabilization and surface
treatment is accomplished, the cooling of the mask
frame assembly be accelerated so that the temperature
of the frame falls below TE within approximately four
minutes so that the bimetal does not excessively change
its properties. Step 24 designates the insertion into
the glass faceplate 8 and the attachment of the fourth
connecting member. The fabrication process then con-
tinues with the coating of the screen, Step 25.
Each of the connecting members 7 consists of a
bimetallic~spring holder 7a and a mounting spring 7b.
The fourth mounting spring is not welded on until after
the simultaneous blackening and stabili~ing process.
All other welds can be made by spot welding prior to
the blackening of the parts to be joined. This gi~es
stronger welds and has the big advantage that there
are hardly any splashes of welding flux which could
settle in the apertures of the mask.
The process step hitherto required to stress-
relieve the mask and the frame as well as the contirluous
furnace necessary thereor can be dispensed with
because, in accordance with the invention, the maxi~.um
temperature during the black~ning of the welded mask-
frame assembly is limited preferably to 5~0~ C, and
:!
D Berner et al l-1-5
~ ~3~ 3~ ~ (Revision)
because this temperature acts on the mask only until
the frame is at t~e same temperature. By narrowing
down the process parameters, the deformations of the
mask ("collapsing") and the frame distortion are kept
so small (maximum dimensional variations: 0.3 mm) that
they can be received by the mask-frame assembly in the
elastic range within permissible limits. To compensate
for the small amount of deformati.on referred to as
"collapsing", i.e., to ensure the desired mask contour
of the finished product, this remaining dimensional
variation is allowed for in the design of the mask-
stamping die. The stress relief caused during the
blackening of the welded mask-frame assembly results in
sufficient aging of the metal parts. Fig. 6 shows how
the "blackening-stabilizing" step is integrated in the
sequences of operations for manufacturing the mask-
frame assembly. The rectangles 16 indicate where the
blackening takes place in conventional fabrication
- processes, and the arrows indicate where this process
step, hitherto performed separately for the mas~ and
the frame, is now carried out as a single operation.
The simplification of and improvement on the
prior art method is thus made possible by the design
shown in Figs. 1 to 5, particularly the design of the
mask and the suitable choice of its dimensions and
of the positions of the welds. The slightly curved
mask 1 is designed to take strains in the elastic
range which are caused during manufacture and opera-
tion, while deformations and changes of position are
kept to a minimum. This is achieved by suitable
choice of ~, B, and C (see Figs. 3 and 4) and by pro-
viding stress-relieving means in the form o~ indenta-
tions 10, cutouts 11, the circumferential groove 12,
and the flange 13 ("skirt"), which serve to take strains.
It is not always advantageous to make all welded joints;
particularly those near ~he edges may be omitted
under certain circu~stances.
If the distances A, B, and C are chosen as
claimed, and the-joints are not too close together
~ 3~ ~ D. Berner et al 1-1-5
and too close to corners and edges, sufficient
elasticity is ensured. Thus, by suitable choice of
the positions of joints and stress-relief points, the
displacement of the mask during manufacture and opera-
tion is kept so small that an improved and simplifiedsequence of operations is possible during the manufac-
ture of the mask and the support frame.
PCV:jn
March 9, 1982
