JPS60251137A - Method for forming glass pipe - Google Patents

Abstract

PURPOSE:To form easily a glass pipe having a noncircular cross-section by putting inner dies in a glass pipe having a circular cross-section, placing a lower die provided with a softening deformation sensor under the glass pipe, heating the whole pipe, and deforming it while monitoring the softening state. CONSTITUTION:A glass pipe 1 is placed in an electric furnace so that it is suspended by an inner die 2. When the inside of the furnace is heated to 635- 685 deg.C which is above the softening point of the pipe 1 by 20-50 deg.C, the pipe 1 begins t soften. As softening proceeds, the lower end of the pipe 1 approaches a small hole 4 in the die 3,and a sensor acts to reduce the internal temp. of the furnace to 435-450 deg.C close to the slow cooling point of the pipe 1. The pipe 1 is then cooled slowly to the strain point (395-420 deg.C) or below, and it is allowed to cool to manufacture a glass pipe 1' having an elliptical cross-section. A low voltage discharge lamp having an elliptical or sectorial cross-section which is desirable in respect of pipe efficiency (the quantity of light emitted per unit input) can be easily manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for forming glass tubes used in low-pressure discharge lamps and the like.

[Background technology]

In general, most low-pressure discharge lamps are made with a circular cross-section. The reason for this is that the glass tube used as the material is easiest to make into a cylindrical shape, and a circular cross-sectional shape is the strongest mechanically when maintaining the inside of the lamp near a vacuum.

On the other hand, from the point of view of tube efficiency (amount of light emitted per unit input; in the case of a fluorescent lamp, the amount of mainly 254 nm ultraviolet light that should excite the phosphor), the shape is not necessarily circular in cross section, but rather elliptical or A fan-shaped cross section is often preferable,
- This is because the amount of charge recombination on the tube wall or the diffusion length, which is an important factor in determining tube efficiency, is larger in an ellipse or sector shape than in a circular tube when the cross-sectional area is the same.

However, despite the above-mentioned theoretical background being established, at present, it is difficult to manufacture glass tubes with elliptical or fan-shaped cross-sections, so non-circular cross-section lamps have not been put into practical use. There are very few examples.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object thereof is to provide a method for forming a non-circular cross-section tube that is easy to manufacture.

[Disclosure of the invention]

Hereinafter, the invention will be explained based on examples.

FIGS. 1(a) to 1(d) are process diagrams according to an embodiment of the present invention. In the figure, 1 is a glass tube that is a raw material, and in this embodiment, the outer diameter is 26 fl and the wall thickness is 1.2 H. lead glass was used. 2. 2/ is the inner mold, 3 is the lower mold, and the material is preferably a metal or non-metal that is heat resistant and does not mix with glass.
In this example, carbon material was cut and used. Numeral 4 is a pore for a sensor (not shown) that detects the softening state of the glass tube, and a plurality of sensors are provided in the axial direction of the lower mold 3. This is a type of pressure sensor that detects changes in air pressure and controls the external circuit in an analog manner.

Now, the above members are placed in an electric furnace (not shown) as shown in Figure 1 (
As shown in a), the glass tube 1 is arranged so as to be suspended in the inner mold 2. Next, the temperature in the electric furnace is set to 20 to 50'C higher than the softening point of the raw glass tube (635 to 685 degrees Celsius).
Increase the temperature to. Then, the glass tube 1 begins to soften as shown in FIG. 1(b). As the softening progresses and the lower end of the glass tube 1 approaches the pore 4, as shown in FIG.
35-450°C). Thereafter, slow cooling is performed to below the strain point (395 to 420°C) of the raw glass tube 1,
After that, it is left to cool to obtain an elliptical cross-section tube 11 as shown in FIG. 3(d).

Although the material of the raw glass tube 1 is arbitrary, it can be said that soft glass is preferable to hard glass in that the working temperature can be kept low.

FIG. 2 shows an example of a fluorescent lamp using the elliptical section tube 1'. In FIG. 2, 5 is a fluorescent body, 6 is an electrode, and 7 is a cap.

Next, FIGS. 3(a) to 3(c) are process diagrams according to different embodiments of the present invention, in which the shape of the inner mold 2 is approximately triangular, and pores 4 for sensors are provided at two locations. This embodiment is basically the same as the previous embodiment except that the glass tube 1 is not suspended in the air.

When a large number of fluorescent lamps 8 manufactured using this sector-shaped cross-section tube 1 are turned on, a substantially flat illumination effect can be obtained, for example, as shown in FIG. 4.

〔Effect of the invention〕

As described above, the present invention includes inserting and holding at least one mold into a glass tube having a circular cross section, and disposing a lower die equipped with a means for detecting softening deformation of the glass tube below the glass tube. The method is characterized in that the entire member is heated and molded while monitoring the softening state of the glass tube.
It has the following effects.

■ Non-circular cross-section tubes, which were traditionally difficult to manufacture, can be easily obtained using a very simple board.

■ Molding is performed while the softening state is detected by a sensor, so it is less susceptible to molding variations due to changes in the wall thickness of the raw glass tube.

In addition, since the glass tube formed according to the present invention has a relatively large roundness at a portion of the corner, stress concentration is small, and therefore, there is an additional effect that a large mechanical strength can be obtained.

[Brief explanation of the drawing]

1 (8L) to (d) are process diagrams according to one embodiment of the present invention, FIG. 2 is a perspective view showing an example of a fluorescent lamp using a glass tube formed according to the above embodiment, and FIG. Figure [stock]) ~
(c) is a process diagram according to a different embodiment of the present invention, and FIG. 4 is a simplified sectional view showing an example of a fluorescent lamp using a glass tube formed according to the above embodiment. 1...Glass tube %2...Inner mold, 3...Lower mold. Patent applicant: Matsushita Electric Works Co., Ltd. Representative patent attorney: Toshimaru Takemoto (and two others)

Claims (1)

[Claims] (1) At least one inner mold is inserted and held in a glass tube with a circular cross section, and a lower mold equipped with a means for detecting softening deformation of the glass tube is placed below the glass tube, and the entire member is A method for forming a glass tube characterized by heating the gas tube and forming the tube while monitoring the softening state of the tube.