EP0063322B1 - Mask-frame assembly and its manufacturing process - Google Patents

Description

The invention relates to a mask-frame combination, as used as a selection electrode in color television tubes, and a method for its production.

In a conventional color television tube, the three electron beams must hit the red, green and blue phosphor areas of the screen assigned to them exactly. The necessary angle-dependent assignment of the color areas to the electron beams is achieved with the so-called mask. In front of each group of three dye areas of the screen there is an opening in this mask, which is located at a short distance behind the fluorescent screen.

The requirements for the accuracy of the position and the dimensions of such a mask are very high, since the assignment of the mask and screen structure must be achieved in the production in the entire area of the mask area and must be maintained during the operation of the tube over its entire service life. In particular, the heating may not cause any disruptive changes in position during commissioning. The resulting conditions for the design and manufacture can only be met by optimal design of the product and the manufacturing technology used, so that a comparatively high effort must first be borne.

The aim of the invention is to enable the economy of such manufacture by further simplifying the manufacturing process. This is achieved through an improvement in the design form that is tailored to this process simplification. The focus is on the so-called blackening of the mask and its support frame, which can also be called surface passivation and mainly serves to prevent corrosion of the iron sheets used and to make the surfaces reflection-free and good heat radiation. So far, the mask has been assembled with its frame after it has been blackened separately, in order to be able to largely compensate for dimensional changes due to the temperature effect of approximately 600 ° C. during blackening. After assembly by spot welding, the mask-frame combination was stabilized at approx. 450 ° C, thus reducing internal stresses in the material that were caused by the welding.

The two-time heat treatment of the mask and frame in separate operations and devices has caused a great deal of handling and the need to provide two furnace systems, which made it particularly difficult that the separate stacking of both masks and frames during the heat treatments very easily Warping under their own weight leads to the fact that the stacking cannot be used to save manufacturing capacity, i.e. manufacturing space and device effort. When welding the mask and frame together and when welding the fastening springs, it was not possible to avoid welding spatter due to the surfaces that had become poorly conductive during blackening. Another disadvantage was that at the previous maximum temperature during blackening, a high post-deformation (ce collapse ») of the mask occurred.

The object of the invention is therefore to provide a simplified manufacturing process which does not have the disadvantages mentioned and to describe an improved form of construction of the mask-frame combination which is particularly suitable with regard to the new manufacturing process.

The problem is solved with the measures shown in method claim 4 and in claim 1, for which purpose the sub-claims contain advantageous further developments.

• Die Lage der Schweißpunkte wird, wie im Anspruch 1 angegeben, so gewählt, daß die bei der Temperaturbehandlung auftretenden bzw. verbleibenden inneren Spannungen im Material von der Konstruktionsform durch funktionsmäßig noch zulässige Verformungen aufgenommen werden, die innerhalb des elastischen Bereiches bleiben. Kerbunden, Aussparungen und Einsickungen erfolgen zur Entkopplung gemäß dem Wortlaut von Anspruch 1. Der Maske wird damit die Möglichkeit gegeben, die infolge von Erwärmung auftretenden Dehnungen ohne zu große Wölbung optimal nach allen Seiten auszugleichen, so daß die maximale Lageänderung klein genug bleibt, wenn die gemeinsame Wärmebehandlung der Masken-Rahmen-Kombination nach dem Wortlaut des Anspruchs 4 durchgeführt wird.

It has been found that the requirements for the design of the manufacturing process which mainly determine the previous manufacturing process are no longer mandatory if the following technical instructions are followed in accordance with the invention:

• The location of the welding points is chosen, as indicated in claim 1, so that the internal stresses occurring or remaining during the heat treatment in the material are absorbed by the structural shape by functionally permissible deformations which remain within the elastic range. Notches, recesses and sumps are made for decoupling according to the wording of claim 1. The mask is thus given the opportunity to optimally compensate for the expansion occurring due to heating without excessive curvature on all sides, so that the maximum change in position remains small enough when the joint heat treatment of the mask-frame combination is carried out according to the wording of claim 4.

• Figur 1 zeigt schematisch die Funktion einer Schattenmaske 1 mit Öffnungen 2, durch welche Elektronenstrahlen 3 auf Leuchtstoffbereiche 4 eines Bildschirms 5 treffen.
• In Figur 2 ist die gesamte Schattenmaske 1 mit einem Rahmen 6 auf dem sie durch Punktschweißung entlang ihres Randes festgeschweißt ist, dargestellt. Verbindungsglieder 7 dienen zur Befestigung (« Einknöpfen ») der Masken-Rahmen-Kombination in die Schirmwanne 8 einer Fernsehröhre.
• Figur 3 gibt die Verteilung von Schweißstellen 9 entlang des Randes der Schattenmaske.
• Figur 4 zeigt, wie die Schweißstellen 9 durch Einschnitte 10 oder Ausschnitte 11 entkoppelt werden. Eine Sicke 12 dient dem Dehnungsausgleich.
• Figur 5 gibt einen Querschnitt und zeigt die Sicke 12, wie sie in der Fig. 4 zu sehen ist, und die Lage der Schweißstellen 9 außen am Rand der Maske 1 auf dem Rahmen 6.
• Figur 6 stellt einen Ablaufplan der erfindungsgemäßen Masken-Rahmen-Fertigung dar. Die einzelnen Verfahrensschritte in Fig. 6 sind durch Kästchen dargestellt.

The invention will now be described with reference to the figures.

• FIG. 1 schematically shows the function of a shadow mask 1 with openings 2, through which electron beams 3 strike phosphor areas 4 of a screen 5.
• In Figure 2, the entire shadow mask 1 is shown with a frame 6 on which it is welded by spot welding along its edge. Connecting links 7 are used for fastening ("buttoning") the mask-frame combination into the screen pan 8 of a television tube.
• Figure 3 gives the distribution of sweat make 9 along the edge of the shadow mask.
• Figure 4 shows how the welds 9 are decoupled by incisions 10 or cutouts 11. A bead 12 is used to compensate for the expansion.
• FIG. 5 shows a cross section and shows the bead 12, as can be seen in FIG. 4, and the position of the welding points 9 on the outside at the edge of the mask 1 on the frame 6.
• FIG. 6 shows a flow chart of the mask frame production according to the invention. The individual method steps in FIG. 6 are represented by boxes.

In 15 the frame is washed and degreased. The blackening carried out in FIG. 16 is now carried out according to the invention together with the stabilization of the parts 1, 6 and 7 already welded to one another in FIG. 23. In method step 17, three connecting links 7 are welded to the frame, on which the mask 1 is also fastened by spot welding in FIG. 22. Then the joint heat treatment for blackening and simultaneous stabilization takes place in step 23. Step 24 denotes the insertion into the glass pan 8 and the attachment of the fourth connecting member. The manufacturing process is then continued with shielding 25.

The connecting links 7 consist of bimetallic spring holder 7a and fastening spring 7b. With the fourth fastening spring, the welding only takes place after simultaneous blackening and stabilization. All other welds can be carried out as spot welds before blackening the parts to be connected. This results in firmer welds and has the great advantage that hardly any spatter is created which could get stuck in the openings of the mask.

A previously necessary production step of relieving the mask and frame and the associated effort of a continuous furnace can be omitted because, according to the invention, the temperature profile during the blackening of the previously welded mask-frame combination is limited to a maximum temperature of 580 ° C., and the effect of this temperature the mask only lasts until the frame is at the same temperature. By narrowing the process parameters, the deformation of the mask ("collapse") and the warping of the frame are so small that they can be changed within a maximum of 0.3 mm due to the inventive design of the mask-frame combination in the range of elastic expansion within the permissible range Limits can be included. To compensate for the small amount of “incidence” that still occurs, in order to guarantee the target mask contour on the production product, this remaining change in size is compensated for by dimensional provision on the mask embossing mold. The relaxation that occurs during the blackening of the previously welded mask-frame combination results in sufficient aging of the metal parts. The classification according to the invention of the production step “blackening stabilization into the process during the manufacture of the mask-frame combination is shown in FIG. 6. The dashed line also indicates where blackening has previously taken place and the arrows indicate where it used to be Mask and frame separately performed work step has been integrated together.

The simplification and improvement of the method is thus possible through the constructive design shown in FIGS. 1 to 5, in particular the mask, and the suitable choice of its dimensions and the position of the welding points. The slightly curved mask 1 is intended to absorb the expansions which occur during production and operation with minimal changes in shape and position in the elastic range. This is achieved through the selection of A, B and C (see also FIGS. 3 and 4) and with decoupling. The incisions 10, cutouts 11, the circumferential bead 12 and edges 13 (“aprons •) are used here as decouplings. It is not always convenient to carry out all welds. In particular, those that are close to the corners are not always useful and may also be left out.

If dimensions A, B and C are adhered to and the fastening points are not too tight and not too close to corners and edges, sufficient care is taken to ensure that sufficient rebound is possible between them. Thus, the choice of the position of the connection and decoupling points keeps the change in position of the mask during manufacture and also during operation so small that the improved and simplified process for producing the mask and support frame can be realized.

Claims (6)

1. Mask-frame assembly comprising a mask (1) in the form of a thin sheet of metal which contains the apertures (2), has a bent flange (13), and is supported by a frame (6) provided with connecting members (7) consisting of bimetallic-spring holders (7a) and mounting springs (7b), for use as a colour-selecting-electrode system in colour television tubes, the mask, frame and connecting parts (1, 6 and 7) being welded together, surfaceblackened and thermally stabilized, characterized in that along the longer side of the mask the distance A between the centre of this side and the nearest weld (9) is chosen so that D/4.5 < A < D/2.4, that on the shorter side of the mask the distance B between the weld and the nearest corner of the mask is chosen so that D/8.4< B < D/3.0, and that the width C of the flange (13), near the edge (14) of which the welds are located, is chosen so that C≥(1.6·D)/100, where D is the length of the screen diagonal, and that the welds at the corners of the mask are relieved of mechanical stress by stress-relief means (10, 11) on both sides thereof.

2. A mask-frame assembly as claimed in Claim 1, characterized in that the stress-relief means are indentations (10).

3. A mask-frame assembly as claimed in Claim 1, characterized in that the stress-relief means are cutouts (11).

4. Method of manufacturing a mask-frame assembly as claimed in any one of Claims 1 to 3, the parts of which (1, 6, and 7) are welded together, surfaceblackened, and thermally stabilized, characterized in that, after being joined together by spot welding, the mask (1) and the frame (6) are provided with bimetallic-spring holders (7a) and mounting springs (7b) and then surface- treated and simultaneously thermally stabilized as a unit consisting of 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 heating-up process being timed so that the maximum temperature difference between the frame and the mask is < about 1/3 of the common final temperature T_E of 500 to 600 °C, preferably 570 to 580 °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.

5. A method as claimed in Claim 4, characterized in that the mask-frame assembly is additionally passivated in the presence of 2 to 3 % oxygen.

6. A method as claimed in Claim 4, characterized in that after the stabilization and the surface treatment, the cooling of the mask-frame assembly is so accelerated by suitable reduction of the heating power in the furnace and suitable choice of the time of removal from the furnace that the temperature of the frame falls below T_E/2 within about 4 minutes, so that the thermo-bimetal of the mounting springs does not excessively change its properties.

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