A color cathode-ray tube (CRT) includes an electron gun for generating and directing three electron beams to a screen of the tube. The screen is located on the inner surface of a cylindrical faceplate of the tube and is made up of an array of elements of three different color emitting phosphors. A color selection electrode is interposed between the gun and the screen to permit each electron beam to strike only the phosphor elements associated with that beam. The color selection electrode may be a tension mask or a tension focus mask. The tension mask comprises a thin sheet of metal, such as steel, that is contoured to somewhat parallel the inner surface of the cylindrical faceplate of the tube. The tension mask generally comprises parallel strands of wire attached to a relatively massive support frame which maintains tension on the strands. The tension focus mask comprises dual sets of conductive strands that are perpendicular to each other and usually separated by an insulative layer. The first set of strands is identical to those described with respect to the focus mask. The second set comprises cross strands electrically insulated from the strands of the first set.
In either type of color selection electrode, it is necessary that the strands of the tension mask are attached to the support frame, and that the tension be maintained during operation of the tube. A drawback of prior support frames is that during the thermal processing cycle, in which the faceplate panel is sealed to the funnel of the tube, the sealing temperature, which is in the range of about 440-460.degree. C., causes a permanent elongation, or "creep" of the mask strands which lowers the tension in the strands during normal tube operation. High strand tension during operation is desirable for good microphonic performance and to absorb the thermal expansion of the strands due to heating by the electron beam during normal operation. The heating during normal operation generally raises the temperature of the tension mask to less than about 65.degree. C.
U.S. Pat. No. 5,111,107, issued to Kume et al. on May 5, 1992, describes a stainless steel structural element that is attached to the underside of the portion of each of the resilient members of the support frame. The stainless steel structural element has a larger thermal coefficient of expansion than the resilient frame member to which it is attached. During thermal processing of the mask and tube, the stainless steel element expands causing the frame to bow in a manner that reduces the tension in the mask and prevents creep of the mask strands. A drawback of the stainless steel structural element is that it does not precisely control the tension in the tension mask strands during thermal processing and the structural element adds additional cost and weight to the tube. Additionally, the attachment of the stainless structural element, by welding, increases the probability of a tube reject due to weld splash particles within the tube. Finally, the structural element may be subjected to localized heating, during tube operation, thereby inadvertently decreasing the tension in the tension mask strands and adversely affecting the microphonic performance of the tube. Accordingly, a more reliable, lower cost way of reducing tension in the mask strands, during processing, is desirable.