JP5581001B2 - Method for forming glass taper tube for area flow meter - Google Patents

Description

The present invention relates to a method for forming a glass taper tube for an area flow meter.

The tube used in the area flow meter is a glass taper tube whose diameter increases in the upward direction in which the fluid flows. In general, in order to obtain a glass taper tube, as disclosed in Patent Document 1, a straight tube glass tube is heated with a gas burner as a heating source, and a soft taper tube is subjected to a predetermined taper using a jig. It is in shape.

  However, in order to soften the glass tube, it is necessary for a specialized technician to blow the flame of the gas burner onto the glass tube. The flame of the burner is as high as about 1500 to 2000 ° C, so it is difficult to apply the flame during molding. There are plenty of optimizations such as flame size, air, mixing ratio of oxygen and combustible gas, and flame angle. Experience is required.

Therefore, the quality depends on the skill of the technician, and it is inevitable that the quality and shape of the molded product vary. Moreover, because of the heating by the flame, there is a large loss in the amount of heat input, and the work environment is high and the work environment is always exposed to high temperatures, and it is difficult to train successors. In particular, it is difficult for a skilled person to manufacture a glass tapered tube.

JP 2005-272250 A JP-A-8-26753

  Patent Document 2 discloses processing a glass tube by an electric furnace without using a burner. Patent Document 2 relates to the production of a glass cell, in which a metal core of a predetermined shape is inserted into a glass tube, the glass tube is softened by heating, and the glass tube is pressed against the metal core from the outside and molded.

  However, heating by an electric furnace using a general nichrome wire heater or halogen heater adopts a heat insulation structure and facilitates temperature control. However, as will be described later, most of the radiant heat generated by the heater passes through the glass. For this reason, the thermal efficiency of the glass tube heating is poor.

  Furthermore, the radiant heat that has passed through the glass tube heats the cored bar more than necessary before the glass tube, so the properties of the glass surface in contact with the high-temperature cored bar may affect the quality, There are also problems such as shortening.

An object of the present invention is to provide a method for forming a glass taper tube for an area flow meter that can eliminate the above-mentioned problems and can suitably form a glass taper tube without extremely heating the first and second cores. It is to provide.

In order to achieve the above object, a method for forming a glass taper tube for an area flow meter according to the present invention comprises a cylindrical first cored bar that approximates the inner diameter of the glass tube at the bottom in a glass tube sealed at the bottom. Is inserted, and then a second metal core having a tapered lower end is inserted on the glass tube, and the glass tube is heated by an electric heater that emits a large amount of radiation energy having a low transmittance in the wavelength transmission characteristics of the glass tube. heating the tube, wherein the first said glass tube and vacuum the glass tube at least the softening temperature of the glass tube, is adhered to the second metal core, the glass around the first metal core after cooling The tube is cut into a ring shape, the first core metal is extracted, the second core metal is extracted from the upper end of the glass tube, and a glass taper tube having cylindrical portions at both ends is formed. .

According to the method for forming a glass taper tube for an area flow meter according to the present invention, a bottomed glass tube enclosing a cylindrical first metal core and a tapered second metal core is formed by radiant heat of an electric heater. heated, so that molded glass tapered tube was raised to the softening temperature, molding is performed reliably, surface finish of the glass tapered tube that Do good.

It is a block diagram of the glass taper tube shaping | molding apparatus of an Example. It is an expansion cross-sectional view of the 2nd metal core . It is a transmission spectrum characteristic figure of borosilicate glass. It is a radiation intensity spectrum characteristic view of a heater. It is a graph figure of temperature progress with respect to time, such as a metal core at the time of shaping, a glass tube. It is a longitudinal cross-sectional view of a state in which the glass tube is in close contact with the cored bar. It is a longitudinal cross-sectional view of the glass taper tube obtained by shaping | molding.

The present invention will be described in detail based on the embodiments shown in the drawings.
FIG. 1 shows a configuration diagram of a molding apparatus for molding a glass tube into a tapered tube, and an opening 1 a is provided in the upper center portion of the heating furnace 1. A carbon heater 2 wound in a coil shape is disposed in the heating furnace 1, and a glass tube as a heated object inserted from the opening 1 a is surrounded by the carbon heater 2. In the carbon heater 2, for example, a stranded wire of carbon fiber is inserted into a quartz tube, and the carbon heater 2 is sealed with an insoluble gas.

The opening 1a of the heating furnace 1 is made large in order to accommodate glass tubes of various diameters, and has an inner diameter of about 25 mm, for example, and the inner diameter of the coiled carbon heater 2 is remotely controlled by radiation energy. Is added to the glass tube 3 to make it larger. A cored bar is inserted into the glass tube 3 to be processed inside the heating furnace 1 from the opening 1a and inserted by hand means (not shown) so that it can be fixed at a predetermined height position.

  The carbon fiber of the carbon heater 2 can be energized from the power source of the temperature control device 5, and using a temperature sensor 6 such as a radiation thermometer or a thermocouple thermometer arranged in the vicinity of the carbon heater 2, The temperature inside the heating furnace 1 can be controlled.

In FIG. 1, the 1st metal core 7 which consists of borosilicate glass and approximates the internal diameter of the glass tube 3 is inserted in the bottom part of the glass tube 3 which sealed the bottom part. Next, a second metal core 4 made of tapered heat-resistant steel or SUS having a small diameter at the lower end is inserted. The first metal core 7 is preferably made of the same material as the second metal core 4.

As shown in FIG. 2 , the second cored bar 4 is formed with a plurality of notches 4a along the inner wall of the glass taper tube to form ribs for stably moving the float up and down. Yes. Incidentally, the ribs from necessarily inscribed circle of the same diameter regardless of the vertical position of the glass tapered pipe, the depth of the notch 4a of the second core bar 4 is thin taper of the second core metal 4 The position is shallower.

In this way, the bottomed glass tube 3 in which the first and second core bars 7 and 4 are set is inserted into the heating furnace 1 by hand means, and the bottom of the glass tube 3 is placed in the heating furnace 1. The carbon heater 2 is positioned by placing it on a fixed part and the like, and the temperature of the carbon heater 2 is increased by energizing the carbon heater 2.

FIG. 3 is a transmission spectrum characteristic diagram with respect to the wavelength of borosilicate glass (trade name: Pyrex (registered trademark)) which is a material of the glass tube 3 to be processed . At a wavelength of 3 μm or more, radiation energy is almost equal to that of borosilicate glass. It is absorbed without passing through and contributes to the heating of the glass.

The solid line in FIG. 4 is an intensity spectrum characteristic diagram of the radiant energy of the heat rays emitted from the carbon heater 2. Since the carbon heater 2 has a peak value at a wavelength of about 5 μm, most of it is absorbed by the glass tube 3.

Further, since the halogen heater emits radiant energy having a wavelength of 5 μm or less, most of the halogen heater passes through the glass tube 3 and heats the inner metal bars 7 and 4 without heating the glass tube 3. Furthermore, although the nichrome wire heater is not as large as the halogen heater, there is a large wavelength band that passes through the borosilicate glass. In this case, more than 50% of the input energy is used for heating the core bars 7 and 4.

As described above, when the carbon heater 2 having a main absorption wavelength band of borosilicate glass of 3 μm or more and a radiant intensity peak of about 5 μm is used, 70% or more of the input energy by the radiant heat from the carbon heater 2 is a glass tube. Since the core metal 7, 4 is also heated by the wavelength band that has passed, the glass tube 3 is more efficiently heated in a short time.

FIG. 5 is a graph showing temperature passage with respect to time (seconds) of the core bars 7 and 4 and the glass tube 3 at the time of molding. The glass tube 3 rises at about the same level as the core bars 7 and 4, and the glass tube 3 reaches the softening point when the temperature reaches about 850 ° C. This graph is an experimental example. Actually, the carbon heater 2 does not need to be raised from room temperature for each glass tube 3, but when the glass tube 3 is rapidly heated from room temperature, the glass tube 3 is cracked. It is easy to generate . Therefore, it is preferable to preheat the glass tube 3 or to gradually heat the glass tube 3 while keeping the heating furnace 1 at about several hundred degrees Celsius.

In the heating furnace 1, when it is confirmed by temperature measurement or visual observation that the glass tube 3 has reached the softening point, evacuation of the inside of the glass tube 3 is started by a pipe (not shown) connected to the upper part of the glass tube 3. As a result of the evacuation, the air in the glass tube 3 is removed, and the softened glass tube 3 shrinks in the circular direction as shown in FIG. 6 and is in close contact with the first and second core bars 7 and 4. The glass tube 3 is formed into a predetermined taper shape according to the shape of the core bars 7 and 4.

Upon heating of the glass tube 3, the core metal 7, 4 also be heated to a certain degree of temperature, without the glass tube 3 is deprived of large heat to the core metal 7, 4, also the core metal 7, 4 From the viewpoint of molding the glass tube 3, it is preferable that no great heat is applied. Further, the deformation due to the thermal expansion of the core bars 7 and 4 also falls within a predetermined range, enabling accurate molding, and extending the life of the core bars 7 and 4.

After forming into a tapered tube, the glass tube 3 and the core bars 7 and 4 are taken out from the heating furnace 1 by hand means, and after the natural cooling or forced cooling by gas blowing, the periphery of the first core bar 7 below the glass tube 3 Is cut into a ring shape as shown by the dotted line in FIG.

Thereby, when the bottom part of the glass tube 3 is removed and the metal cores 7 and 4 are pulled out from the upper and lower ends of the glass tube 3, a glass taper tube 8 as shown in FIG. 7 is obtained. The glass taper tube 8 is incorporated into an area flow meter using the upper and lower cylindrical portions 8a and 8b.

In addition, a plurality of ribs are formed in the glass taper tube 8 in the vertical direction so that the float for measuring the flow smoothly moves up and down along the central axis in the formed taper tube. The float can smoothly move up and down while the diameter is in contact with the rib or the rib is engaged with a notch provided in the float.

In the embodiment, the glass tube 3 is moved up and down with respect to the heating furnace 1 by hand means, but the heating furnace 1 moves up and down with respect to the fixed glass tube 3 and the core bars 7 and 4. You may do it.

DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Carbon heater 3 Glass tube 4 2nd metal core 5 Temperature control device 6 Temperature sensor 7 1st metal core 8 Glass taper tube

Claims (3)

A cylindrical first metal core that approximates the inner diameter of the glass tube is inserted into the glass tube with the bottom sealed, and then a tapered second metal core having a small lower end is formed thereon. insert, the glass tube was heated by a number emits electric heater radiant energy of a low transmittance wavelength in the wavelength transmission characteristic of the glass tube, the glass tube and vacuum the glass tube at least the softening temperature of the glass tube In close contact with the first and second metal cores, and after cooling, the glass tube around the first metal core is cut into a ring shape to extract the first metal core, and from the upper end of the glass tube A method for forming a glass taper tube for an area flow meter, wherein the second metal core is extracted and a glass taper tube having a cylindrical part at both ends is formed . A plurality of notches are formed around the second core bar, and a plurality of ribs having inscribed circles having the same diameter regardless of the vertical position are formed on the molded glass taper tube. A method for forming a glass taper tube for an area flow meter according to claim 1. The glass tube is made of borosilicate glass, the heater is forming method area flowmeter glass tapered tube according to claim 1 or 2, characterized in that a carbon heater.

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