JPH09328324A - Forming of glass tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a glass tube by which the glass tube without sticking a metallic foreign material to the inner surface thereof can be obtained by keeping the inner temperature of a blowing air feeding pipe at a specific temperature or below. SOLUTION: This method for forming a glass tube is to keep the inner surface temperature of a blowing air feeding pipe, arranged in a forming member and made of a heat resisting steel at <=600 deg.C in the method for forming the glass tube comprising continuously taking out a glass while feeding the blowing air from the tip of the forming member thereto and forming the glass into a tubular shape. The forming member is a sleeve, a mandrel, a cone and further a member having the blowing air feeding pipe inserted and arranged in the interior thereof. A cooling means such as the circulation of a liquid coolant such as superheated water or a low-melting metal or attachment of a heat pipe to the outside of the blowing air feeding pipe is preferably installed in order to keep the inner surface temperature of the blowing air feeding pipe. The method for forming the glass tube is useful as the method for forming the glass tube requiring an ultrahigh inner surface temperature such as a neck tube for a cathode-ray tube(CRT).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a glass tube, and more particularly to a method for forming a glass tube such as a CRT neck tube which requires extremely high cleanliness on the inner surface.

The term "molded member" as used in the present invention refers to a sleeve (Dunner method), a mandrel (down-draw method), a cone (up-draw method), and a blow-air supply pipe arranged therein. Is inserted and arranged, for example, a sleeve shaft is included.

[0003]

2. Description of the Related Art As a method for industrially mass-producing glass tubes, methods generally called the Dunner method, the downdraw method, and the updraw method are adopted. Each of these molding methods is a method in which glass is continuously drawn from the tip of the molding member while the blow air is supplied to mold the glass into a tubular shape.

In these molding methods, blow air is supplied to control the outer diameter and wall thickness of the glass tube, dust is removed through a multilayer filter, and the blow air is inserted and arranged in the inner hole of the molding member. It is blown into the glass tube from the blow air supply pipe.

[0005]

However, there is a case in which metallic foreign matters are mixed into the blown air that has been cleaned of dust and is cleaned, and adheres to the inner wall surface of the glass tube at a temperature equal to or higher than the softening point. This is due to the high temperature atmosphere during glass tube molding,
This is because a brittle and thick oxide film is formed on the inner surface of the blow-air supply pipe made of heat-resistant steel, which is a blow-air supply path, and this is peeled off and mixed into the blow-air.

If a glass tube having metal foreign matter adhered to its inner surface is used in an application requiring extremely strict inner surface cleanliness, such as a CRT neck tube, it may cause dielectric breakdown of the neck when a high voltage is applied. There is.

An object of the present invention is to provide a glass tube molding method capable of obtaining a glass tube in which metal foreign matter does not adhere to the inner surface of the blow air because the metal foreign matter is not mixed into the blow air.

[0008]

As a result of repeated experiments, the inventors of the present invention have found that the temperature of the inner surface of the blow air supply pipe is about 700 to 800 ° C. when the glass tube is molded, and the blow air supply amount is When the amount is low or the supply is stopped, the temperature rises to about 800 to 1000 ° C,
It has been found that the above object can be achieved by maintaining the temperature at 0 ° C or lower, preferably 500 ° C or lower, and is proposed as the present invention.

That is, the glass tube molding method of the present invention is arranged in the molding member in the glass tube molding method in which the blown air is supplied from the tip of the molding member and the glass is continuously drawn to form a tube. It is characterized in that the inner surface temperature of the heat-resistant steel blow air supply pipe is maintained at 600 ° C or lower.

[0010]

When the temperature of the blow air supply pipe rises due to the molding of the glass tube, an oxide film is formed on the surface, but if the thickness is 1 μm or less, the adhesion strength with the base material is strong, so a long time has passed. Even if it is peeled off, it does not fall off. However, as the surface temperature of the pipe rises, the thickness of the coating increases, and at a temperature exceeding 600 ° C., the coating becomes a brittle coating having a thickness of more than 1 μm and easily peels off.

In the method of the present invention, the temperature of the inner surface of the blow air supply pipe is 600 ° C. or less, preferably 5
Since the temperature is kept at 00 ° C or lower, even if an oxide film is formed on the inner surface of the pipe, it does not grow into a thick and brittle film. When the temperature of the inner surface of the pipe is lowered, the temperature of the blow air passing through the inside also decreases, but if the temperature of the blow air becomes too low, the dimensional accuracy of the glass tube is adversely affected. For this reason, the temperature of the inner surface of the pipe is preferably set to a temperature at which the temperature of the blow air is not too low and does not hinder the molding of the glass tube, specifically, 100 ° C. or higher.

In order to maintain the temperature of the inner surface of the blow air supply pipe at 500 ° C. or lower, a cooling liquid such as superheated water or a low melting point metal is circulated outside the blow air supply pipe, or a heat pipe is attached. A cooling means for preventing the temperature rise of the air supply pipe may be provided.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

FIG. 1 is a schematic view of a Danner type glass tube forming apparatus 10 suitable for carrying out the method of the present invention, and FIG. 2 is an explanatory view showing the structure of a sleeve 11 used in the glass tube forming apparatus 10. .

The refractory sleeve 11 is a metal nose 1
2, a fixture 13, a spring 14, and a nut 15 are fixed to a sleeve shaft 16 made of heat-resistant steel, and a motor 17 supports the muffle furnace 18 in a slanting downward direction and provides rotation.

The sleeve shaft 16 is a cooling liquid circulation unit 1.
6a and the heat dissipation part 16b. The cooling liquid circulation unit 16a is
A cooling pipe 162 filled with the cooling liquid is welded to the outside of the blow air supply pipe 161, and circulation pipes 163 for circulating the cooling liquid are welded to both ends of the cooling pipe 162. The circulation pipe 163 is spirally wound around the cooling pipe 162, and when the sleeve shaft 16 rotates, the cooling liquid moves upward in the circulation pipe 163, and the cooling pipe 162 and the circulation pipe 163 are hermetically sealed. The blow air supply pipe 161 is circulated in the created space to cool the blow air supply pipe 161. Heat sink 1
6b is connected to the rear of the cooling liquid circulation unit 16a,
Fresh water is always supplied from an unillustrated cooling water inlet to the inner hole portion 165 of the shaft 164 and is discharged to the outside after heat exchange with the cooling liquid. Further, the opening of the blow air supply pipe 161 on the side of the heat radiating portion 16b is connected to a blow air supply device (not shown) via the blow pipe 19 and a multilayer filter (not shown).
Here, blow air supply pipe 161, cooling cylinder 162,
The circulation pipe 163 and the shaft 164 are made of Fe-Cr-.
It is made of heat-resistant steel such as Al-based alloy and Ni-Cr-Fe-based alloy. Further, as the cooling liquid filled and sealed in the cooling cylinder, for example, superheated water or low melting point metal such as solder can be used.

When a glass tube is formed by using such an apparatus, the molten glass G is guided onto the refractory sleeve 11, homogenized while being rotated in the muffle furnace 18, and flows down to the tip of the sleeve 11. Then, the glass is continuously drawn into a tubular shape while blowing the blow air supplied from the blow air supply device. The blow air supplied from the blow air supply device is dedusted by a multilayer filter, then passes through the blow pipe 19 and the blow air supply pipe 161, and is drawn out of the glass tube g.
Although blown into the interior, the blow air supply pipe 161 is constantly cooled by the cooling liquid and the inner surface is kept at a temperature of 600 ° C. or less, so that metallic foreign matter caused by peeling off of the oxide film is mixed into the blow air. do not do. Therefore, the obtained glass tube has no foreign metal attached to its inner surface.

In this embodiment, the Dunner method is used for explanation, but the downdraw method and the updraw method can also be applied. Further, the example in which the blow air supply pipe is cooled by circulating the cooling liquid has been shown, but another cooling method, for example, a heat pipe may be used.

[0019]

According to the method of the present invention, it is possible to obtain a glass tube in which metal foreign matter does not adhere to the inner surface because the foreign matter is not mixed into the blow air. It is suitable as a method for molding a glass tube whose temperature is strictly controlled.

[Brief description of drawings]

FIG. 1 is a schematic view of a glass tube forming apparatus used in the method of the present invention.

FIG. 2 is an explanatory view showing the structure of a sleeve used in a glass tube molding device.

[Explanation of symbols]

 11 Sleeve 16 Sleeve Shaft 16a Coolant Circulation Unit 16b Radiating Unit 161 Blow Air Supply Pipe 162 Cooling Tube 163 Circulation Pipe

Claims (1)

[Claims] 1. A glass tube molding method for continuously drawing glass to form a tube while supplying blow air from the tip of a molded member, wherein a heat-resistant steel blow air supply pipe disposed inside the molded member. A glass tube molding method, characterized in that the surface temperature is maintained at 600 ° C. or lower.