Shadow mask heating apparatus for color CRT of the flat faceplate type

A shadow mask heating apparatus for a color CRT of the flat faceplate type includes upper and lower heated platens, each provided with heating means therein. One of the platens includes a plurality of mask support elements having a predetermined height radially disposed in an equally spaced relation on the top surface. The mask support elements preferably consist of a plurality of long and short, in length, mask support element. A plurality of passages radially formed on the top surface result between the mask support element. A plurality of adjusting pins disposed on the peripheral area of the top surface thereof of the one platen keeps the two platens separated a precise distance. The arrangement of radially disposed mask support elements minimizes shadow mask deformation during manufacture.

FIELD OF THE INVENTION 
The present invention relates to a shadow mask heating apparatus for a 
color cathode ray tube of the flat faceplate type, and, more particularly, 
to an improvement of such a heating apparatus capable of minimizing the 
deformation of a shadow mask due to nonuniform thermal expansion thereof 
and of enhancing the uniform thermal expansion of the shadow mask. 
BACKGROUND OF THE INVENTION 
In general, a color cathode ray tube of the flat faceplate type, as shown 
in FIG. 1, includes a flat type shadow mask S made of an apertured 
metallic foil, which is welded to a support frame T under a predetermined 
tension and located alongside the inner surface of a flat faceplate P 
sealed to a funnel F. Flat faceplate CRT's are manufactured as, for 
example, 9-21 inch CRT screens. The thin foil type shadow mask S cannot 
easily maintain its shape, (i.e., its planarity) because of processing 
difficulties. 
The prior art process for fixing the above-mentioned shadow mask is 
summarized as follows: 
I) Heating the shadow mask for the thermal expansion in a heating 
apparatus. 
II) Clamping the thermally expanded shadow mask to a fixture frame (not 
shown); 
III) Cooling the clamped shadow mask to room temperature, thereby creating 
tension in the mask to be taut and planar; 
IV) Welding the shadow mask to the support structure adjacent to the inner 
surface of the faceplate; and 
V) Removing the fixture frame from the panel after trimming off the 
periphery of the shadow mask. 
In the above-described steps, the shadow mask heating apparatus tends to 
thermally expand by heating the shadow mask. Clamping to the fixture frame 
by clip means provided on the fixture frame prevents the thermally 
expanded shadow mask from shrinking when subsequently cooled. In the taut 
state, the effective area of the shadow mask is welded to the support 
frame and finally trimmed to remove the fixture frame from the shadow 
mask. 
In U.S. Pat. No. 4,772,238, there is disclosed a foil mask stretching 
apparatus 10, which is illustrated in FIGS. 3 and 4 of the present 
invention drawings. The stretching apparatus illustrated in FIG. 3 
comprises upper and lower heated platens 11 and 12, each having a heating 
element 13 located therein and made of heat resistant steel. A shadow mask 
S is located between the platens 11 and 12 to be heated for thermal 
expansion. 
Migrant particles are shed from the clamping machine, the clothing of the 
operator or other nearby pollution sources. These particles may become 
trapped between or on the platens 11 and 12, the shadow mask S. Such 
particles can plug the shadow mask apertures and also dent the mask when 
it is heated. In order to prevent the shadow mask from being damaged by 
migrant particles, recesses 12a are formed on the lower platen 12 so that 
the migrant particles fall in the recesses 12a. 
However, when the shadow mask is heated to be thermally expanded, it can 
sag into the recesses 12a. When the mask sags excessively into recesses 
12a, the mask cannot maintain the required planarity, even after cooling, 
and thus the mask remains in a deformed state. 
Excessive sagging is somewhat prevented by matrix type mask support 
elements 12b provided on the top surface of the lower platens 12 and also 
made of heat resistant steel. Mask support elements 12b define a plurality 
of square type recesses 12a. 
For heating, the shadow mask S is inserted between the platens 11 and 12, 
and then a voltage is applied to the heating elements 13 incorporated in 
the platens 11 and 12. Accordingly, the heat produced from the heating 
elements 13 is transmitted via the platens 11 and 12 to heat the shadow 
mask S. 
This heat is transmitted to the mask S over recesses 12a by indirect 
conduction such as convection and radiation. However, the temperature on 
the portions of the mask located immediately above each recess 12a is 
substantially lower than the portion in direct contact with the mask 
support element 12b. Because of this conduction, enhanced by the flat 
surface of mask support elements 12b, the whole surface of the mask is not 
uniformly heated and undesired distortions and deformations still occur. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the present invention to provide a shadow 
mask heating apparatus for a color cathode ray tube of the flat faceplate 
type through which a shadow mask having a high quality planarity is 
obtained by uniformly heating the shadow mask while minimizing the shadow 
mask deformation caused during a thermal expansion process. 
To achieve the above object, the shadow mask heating apparatus for a color 
cathode ray tube of the flat faceplate type, in accordance with the 
present invention, includes upper and lower heated platens, One of the 
platens is provided with a plurality of heat transferring mask support 
elements having a predetermined height for maintaining more even heat 
distribution to the shadow mask. A plurality of adjusting pins are 
disposed on the peripheral area of the top surface to keep the other 
platen a predetermined distance from the shadow mask. 
In one preferred embodiment, long mask support elements are radially 
disposed in an equally spaced relation on the top surface of the lower 
platen from the central portion toward marginal portion thereof. Short 
mask support elements are then disposed between the long mask support 
elements on the peripheral area of the lower platen. 
Furthermore, the mask support elements are preferably triangularly shaped 
in cross-sectional dimension, with a edge being rounded. The adjusting 
pins are substantially higher than the mask support elements. Moreover, 
the upper and lower platens are preferably shaped to an elliptical 
configuration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 5 and 6 illustrate a shadow mask heating apparatus 20 for a color 
cathode ray tube of the flat faceplate type, which comprises upper and 
lower heated platens 22 and 23, each having a heating means 21 disposed 
therein and made of heat resistant steel. The platens 22 and 23 are 
preferably shaped to an elliptical configuration. 
The lower heated platen 23 is formed with a plurality of heat transferring 
mask support elements 24 and 24' preferably made of heat resistant steel 
and having a predetermined height on the top surface 23a which is 
preferably 0.5-1 mm in height above the top surface 23a. Long and short 
(in length) mask support elements 24 and 24' are radially disposed on the 
top surface 23a of the lower platen 23 in such a manner that the long mask 
support elements 24 are radically disposed from the central portion of the 
lower platen 23 toward the marginal portion thereof in an equally spaced 
relation, while short mask support elements 24' are interposed between two 
long mask support elements 24 in the peripheral area of the lower platen 
23. 
Passages 26 are thus provided in a radical relation between the mask 
support elements 24 or the mask support elements 24 and 24'. 
Preferably, the cross-section of the mask support elements 24 and 24' is 
similar to a triangle, as illustrated in FIG. 7. An edge portion 24a along 
the top portion of the fins 24 and 24', and the edge portion 24a is 
chamfered to form a rounded shape. 
In addition, a plurality of equally spaced adjusting pins 25 are disposed 
peripherally on the top surface 23a of the lower platen 23 such that the 
height of the adjusting pins 25 are constructed to be substantially higher 
than that of the mask support elements 24 and 24', preferably 1.0-2.0 mm 
above the sop surface 23a so that the upper and lower platens 22 and 23 
are both equally spaced from the shadow mask S. 
In operation, the upper and lower heated platens 22 and 23 are separately 
mounted into a hydraulic press or the like, and the shadow mask is 
inserted between the platens 22 and 23. A gap, typically about 1-2 mm 
between the upper and lower platens 22 and 23 is maintained by means of 
the adjusting pins 25 after the platens are brought to a closed state. 
A voltage is then applied to the heating elements 13 incorporated in the 
upper and lower platens 22 and 23, to heat the shadow mask to about a 
temperature between 210-250 degrees Celsius and provide for thermal 
expansion. The shadow mask is in line contact with the edge portion 24a of 
the heating transferring mask support elements 24 and 24' radially disposed 
on the lower platen 23. This arrangement of mask support elements 24 and 
24' prevents the shadow mask from sagging excessively. 
In addition, since the long mask support elements 24 are radially disposed 
from the central portion while the short mask support elements 24' are 
disposed in the peripheral area of the lower platen 23 between the long 
fins 24, the distribution of the mask support elements 24 and 24' becomes 
uniform between the central and peripheral area of the lower platen 23. 
Moreover, the passages 26 formed between the mask support elements 24 and 
24', transfer heat to the shadow mask by convection and radiation from the 
lower platen 23. The heat freely moves through the passages 26 because the 
radical arrangement and heat distribution becomes uniform. Thus, the 
shadow mask S is uniformly heated and deformation substantially prevented. 
It should also be noted that because mask supports 24 are arranged 
radially, the heat conduction, which is the primary heat transfer, occurs 
perpendicular to the radius of the platen 23, which results in the radial 
thermal expansion of the shadow mask without deformation or distortion, as 
illustrated in FIG. 8. 
Migrant particles shed from the machine, the clothing of the operator, or 
the like, trapped between or on the upper and lower platens 22 and 23 and 
the shadow mask S fall in the passages 26. Thus, the shadow mask is not 
damaged from them. 
As has been described in the foregoing, according to the present invention, 
the shadow mask is uniformly heated from the central portion to the 
peripheral portion. Thus, thermal deformation is prevented. Consequently, 
the shadow mask has uniform tension after subsequent cooling. When the 
shadow mask manufactured using a heating apparatus according to the 
present invention is mounted in the flat faceplate type color cathode ray 
tube, the performance of the color cathode ray tube is significantly 
enhanced. 
Other changes and modifications may be made in the above-described 
apparatus without departing from the true spirit and scope of the 
invention and it is intended that above depiction shall be interpreted as 
illustrative and not in a limiting sense. The true spirit and scope of the 
present invention should be considered with reference to the accompanying 
claims.