JPH0360152B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a tungsten wire for a bulb filament, and more particularly to a tungsten wire with excellent vibration resistance and droop resistance.

[Technical background of the invention and its problems]

Thin tungsten wire is used in the filaments of various light bulbs. Such tungsten wires are often used at temperatures near or higher than the recrystallization temperature, and their crystal structure changes during use. The mode of this change has a major impact on the strength, brittleness, and drooping properties of the filament.
In particular, droop resistance (non-sag) at high temperatures
is an important characteristic.

In order to improve this non-sag property, it is necessary to create a structure in which the recrystallized grains are elongated and in which the recrystallized grains penetrate each other in the axial direction in a wedge shape and overlap each other. That is, when the length of the recrystallized grain is L and the width is W, the important required characteristics are that L/W is large and that the recrystallized grains penetrate each other in a complicated manner.

However, when the wire diameter of the tungsten wire is made thinner, even if the L/W is large, the recrystallized grains do not penetrate into each other in a wedge shape, and in extreme cases, only one recrystallized grain is formed. The recrystallized grains are connected one after another in the wire axis direction to form one wire rod as a whole.

Under such conditions, the L/W is large and the sag-free property is excellent, but on the other hand, when used in applications with strong vibrations such as filaments in automobile light bulbs and filaments in lamps for copying machines, various vibrations may occur. It may be cut from the grain boundaries (simple grain boundaries) of recrystallized grains. That is, there is a problem in vibration resistance.

[Purpose of the invention]

An object of the present invention is to provide a tungsten wire for filament that has not only non-sag properties but also excellent vibration resistance.

[Summary of the invention]

The present inventor has found that even if the L/W of recrystallized grains is large,
We discovered that when we observe the cross-section of a wire, the number of recrystallized grains present in the cross-section (what is observed is its cross-sectional shape) has a large effect on the vibration resistance of the wire, and we have developed the tungsten wire of the present invention. I have come to develop it.

That is, the tungsten wire of the present invention has a length/width ratio (L/W) of recrystallized grains of 7 or more, and the number of recrystallized grains included in a cross section of an arbitrary portion is 4 or more. It is characterized by being a strong organization.

The recrystallized grains according to the present invention have a wire diameter of 0.25 to 0.5
This refers to recrystallized grains that precipitate when a mm tungsten wire is heated with a fusing current of 70 to 90%. In such recrystallized grains, when L/W is smaller than 7, the non-sag property decreases. Usually, L/W is
In the wire diameter of 0.2 to 0.5 mm, about 12 to 25 is preferable.

Furthermore, if the number of recrystallized grains contained in the wire is less than four in its cross section, the recrystallized grains do not penetrate through the grain boundaries of each other, resulting in a decrease in vibration resistance as a whole. Usually, it is preferably about 6 to 10 in the wire diameter of 0.2 to 0.5 mm.

Such a wire can be easily manufactured by appropriately selecting the tungsten powder used as a raw material, its forming conditions, sintering conditions, and processing conditions such as rolling and wire drawing.

The tungsten wire of the present invention is drawn to the wire diameter of the filament to be applied (for example, 0.1 mm, 0.05 mm) and put into practical use.

[Embodiments of the invention]

A tungsten wire with an average L/W of 14.0 and an average number of recrystallized grains in the cross section of 6 and a wire diameter of 0.39 mm (example) and a wire with an average L/W of 18.0 and the average number of recrystallized grains in the cross section of 3 A tungsten wire (comparative example) with a diameter of 0.39 mm was prepared.

After drawing these two wires to 43MG, they were made into coil filaments for incandescent light bulbs.

The non-sag properties and vibration resistance of two types of coil filaments were measured. Non-sag properties were investigated by measuring the droop value when a current was passed through the filament and the temperature was raised to 2500°C for 100 hours.

In addition, the vibration resistance is 70% of the fusing current in the filament.
%, 80%, 90% current for 3 seconds, then
The coil was reheated at 2700°C for 60 seconds, then cooled to room temperature, pulled at 40MG at room temperature, and the elongation of the coil was measured. This elongation value was expressed as a percentage of the original length of the coil. . The larger this value is, the better the vibration resistance is.

There was almost no difference in non-sag properties between the two wires. However, in terms of vibration resistance, as shown in the figure, the wire rod of the present invention exhibited very excellent characteristics.

〔Effect of the invention〕

As is clear from the above description, the tungsten wire of the present invention has excellent non-sag properties and excellent vibration resistance, and is useful as a filament for light bulbs used in locations subject to severe vibration.

[Brief explanation of drawings]

The figure is a diagram showing the vibration resistance of coil filaments manufactured from wire rods of Examples and wire rods of Comparative Examples.

Claims (1)

[Claims] 1. The length-to-width ratio of recrystallized grains is 7 or more, and
A tungsten wire for filament, characterized in that the number of recrystallized grains contained in a cross section of an arbitrary portion is 4 or more. 2. The tungsten wire for filament according to claim 1, wherein the tungsten wire has a diameter of 0.25 to 0.5 mm.