JPH057812B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an indirectly heated cathode heater which is difficult to break during installation and welding and which does not cause deformation or other inconveniences during use.

[Background of the invention]

As cathode ray tubes, especially television picture tubes, have become lower in power consumption and faster in operation, thin wire double coil heaters have come to be used more and more as indirectly heated cathodes. An example of this type of heater is shown in Figure 1a. In the figure, 1 is a tungsten primary coil (just a tungsten wire wound into a coil), 2 is an alumina coating, and 3 is a secondary coil (a primary coil further wound into a coil).

However, the general drawbacks of this type of heater are that disconnections are likely to occur when welding it to the support, and that the primary coil part near the support that is not coated with alumina is temporarily overheated and deformed during the initial energization period during use. This part also had problems such as being vulnerable to sparks.

Generally, heaters are made by winding a primary coil of tungsten or tungsten alloy wire around a molybdenum mandrel wire, further winding the coil to form a secondary coil, and then dissolving only the mandrel wire in acid. As shown by 4 in Figure b, if only the mandrel wire at the end of the heater foot is left (remaining molybdenum mandrel 4 at the end of the foot) and alumina coating 2 is applied to a part of this part,
The various drawbacks mentioned above can be almost eliminated.

In order to realize such countermeasures, Japanese Patent Application Laid-open No. 1983-
No. 133725 and Japanese Unexamined Patent Publication No. 133726/1986 propose that after coating with alumina and sintering, the mandrel wire is immersed in acid except for the end of the heater leg to melt the mandrel wire. However, this method not only takes a long time to melt through the alumina layer, but also leaves the end of the mandrel wire 5 left at the end of the foot in an irregular shape as shown in Figure 2a. However, it has a fatal drawback that the resistance of the heater is not constant. This occurs because the unimmersed portions are dissolved due to capillary action, and the same phenomenon occurs even when the alumina coating is not applied.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an indirectly heated cathode heater in which the secondary coil side end of the mandrel wire left at the end of the heater leg always has a constant shape and a cut surface close to a plane.

[Summary of the invention]

In order to achieve the above object, in the present invention,
In an electrolytic solution, only the mandrel wire (molybdenum wire) is selectively dissolved when an electrolytic electric field is applied, and neither the heating coil wire (tungsten wire or its alloy wire) nor the mandrel wire is dissolved when no electrolytic field is applied. Therefore, we decided to leave the mandrel wires at the heater foot ends by electrolyzing them without applying an electric field to the heater foot ends.

[Embodiments of the invention]

Fig. 3 shows a thin wire coarsely wound heater according to the present invention, in which 2 is alumina coating, 3 is a secondary coil part, and 4 is a thin wire coarsely wound heater.
is the remaining molybdenum mandrel, 7 is the coarsely wound part,
8 is the electrolyte level, and 9 is the mixed acid level.

3MG tungsten rhenium alloy wire diameter
A 0.125mm molybdenum wire is used as a mandrel for winding in a combination of coarse and fine lines. The dense area is 190 turns/cm, and the coarse area is 3 turns/cm. This is formed into a double helically wound heater as shown in FIG.
Next, after performing treatments such as shaping annealing and alumina coating sintering on the secondary coil portion 3, clip an appropriate number of molybdenum wires to the water level at the position where the molybdenum wires shown at 8 in Figure 3 should be melted. It is immersed in an electrolytic solution to selectively electrolyze only molybdenum. What is required in this case is that the liquid does not dissolve tungsten and molybdenum when no electric field is applied, but selectively dissolves only molybdenum when an electric field is applied. This electrolysis (electrolytic processing) utilizes the fact that when a pair of electrodes is inserted into an electrolytic solution and a current is passed between the electrodes, metal melts at the interface between the electrodes and the electrolyte. By performing electrolysis using a molybdenum wire as one electrode, the molybdenum wire is melted to the interface where the molybdenum wire and the electrolyte come into contact, and the end surface of the molybdenum wire becomes the second electrode.
As shown in Figure b, the surface is nearly flat. 85% concentrated sulfuric acid or sulfamic acid 15g/+chromic acid 30g
The purpose can be achieved by using an aqueous solution of g/g as the electrolyte. As a result of this electrolysis, the melted end of the mandrel wire left at the end of the foot has a good shape as shown in Figure 2b and can achieve the desired purpose, but the immersed coil part (particularly the alumina-coated and sintered end to maintain the shape) It is normal for insoluble molybdenum to remain in the secondary coil part (which has been subjected to quenching treatment).
In order to remove this, it is subsequently immersed in a nitric-sulfuric acid mixed acid solution a little shallowly, that is, to the water level 9 in FIG. 3. At this time, as described above, the alumina coating is still applied only to the secondary coil portion, and since the end of the alumina coating is in the mixed acid solution, the dissolution of molybdenum proceeds rapidly. After the above treatment, alumina is applied and sintered until a portion of the molybdenum remaining at the end of the foot is covered, as shown in FIG. When the heater manufactured as described above was actually used, it was confirmed that the intended improvement objective was achieved.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to stably and easily manufacture a low-power, quick-starting indirectly heated cathode heater that overcomes the drawbacks of conventional indirectly heated cathode heaters that use thin wires. .

[Brief explanation of the drawing]

Figure 1a is a general example of an indirectly heated cathode heater, b is a cross-sectional view of the case where the mandrel is left at the foot end of the heater, and figure 2a is a diagram of the case where the mandrel is left behind using only the conventional mixed acid dissolution method. Fig. 3 is an enlarged sectional view of the foot end portion, b is an enlarged sectional view of the same portion of an embodiment of the present invention, and Fig. 3 is a partial sectional view of an embodiment of the present invention. 1...Tungsten primary coil, 2...Alumina coating, 3...Secondary coil section, 4...Remaining molybdenum mandrel at the foot end, 5...Mandrel wire,
6... Coil, 7... Roughly wound portion, 8... Water level of electrolyte solution, 9... Water level of mixed acid.

Claims (1)

[Claims] 1. Using a molybdenum wire as a mandrel, a tungsten-rhenium alloy wire is wound in a combination of coarse and dense windings, and this is double-helically wound to form a heater having a secondary coil portion, and then shaped, annealed, The secondary coil is coated with alumina and sintered, and the water level at which the molybdenum wire should be dissolved is 85% concentrated sulfuric acid or sulfamic acid 15g/1 + chromic acid 30g.
The molybdenum wire is selectively electrolyzed by immersing it in an electrolytic solution consisting of either g/1 to form a residual molybdenum mandrel at the end of the heater foot.Subsequently, a secondary coil part coated with alumina is placed in a nitric acid mixed acid solution. An indirectly heated cathode heater characterized in that the molybdenum wire remaining in the secondary coil is immersed in the secondary coil to melt the molybdenum wire remaining in the secondary coil, and alumina is coated and sintered from the secondary coil to a part of the remaining molybdenum mandrel at the end of the heater foot. Production method.