JP2750234B2 - Manufacturing method of silica-based lightweight reflector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a reflector used in astronomical observation, beam focusing, and other space industries, and more particularly, to a light-weight, high-strength, highly operable structure. The present invention relates to a method for manufacturing a lightweight reflector having optical characteristics.

[0002]

2. Description of the Related Art Conventionally, astronomical reflectors and high energy beams have been used.
The reflector used for optical condensing such as a mirror is made of, for example, a metal-deposited film such as aluminum as an optical reflection layer on the mirror surface of a bubble-free reflector plate made of quartz glass or high-purity silicate glass. Is formed, and this is mounted on an operation support base and freely rotated. Such a reflector is
It is required to maintain accuracy that is not affected by the temperature of the reflecting surface or an internal force change.

[0003] Such a reflecting mirror has hitherto had a diameter of 5 to 5.
A small size of about 20 cm was the mainstream, but in recent years, a diameter of 30 cm to 1 m that can obtain a practically desirable high light collection rate,
Or larger ones have been required. However, such large ones are extremely heavy,
As a result, the operability is significantly reduced, and there is a problem that the mirror surface is deformed by its own weight due to a change in the support posture of the reflector during the rotation operation, and the mirror surface undulates, thereby deteriorating the optical performance of the reflector. Was.

[0004] As the size of the reflector increases, the volume change and deformation of the reflector due to the radiation of the condensing beam and the change of the environmental temperature increase, and the mirror surface swells easily. Since the problem of significantly lowering the performance is accompanied, such disadvantageous phenomena, particularly quartz glass and high silicate glass, which have a small change in thermal expansion, have come to be used as materials for reflectors.

[0005] However, large-sized reflectors made of these quartz glasses are very heavy and their operability is significantly reduced. Therefore, it is required to reduce the weight of the reflector as much as possible to improve operability. In line with such practical demands, attention has been paid to the weight reduction of large reflectors, particularly to the weight reduction of the support portion that holds the reflector plate, and there are many techniques for sufficient strength and weight reduction technology as a support member for the reflector plate. A proposal was made.

For example, Japanese Patent Publication No. 63-57761 discloses a light-weight reflector material for a celestial body, which has a support grid made of several rows of tubes between a transparent reflector plate (front plate) and a rear plate. Each tube of the tube row is staggered so as to have a contact line or contact zone with two tubes of an adjacent row, and the thickness of the tube wall in the area of the contact line or the like is such that the remainder of the wall A special tube structure is disclosed in which the tubes are welded together along contact lines and the like.

However, the astronomical reflector material having such a special structure has a complicated structure, is not easily manufactured, and is extremely disadvantageous industrially. Further, such a reflector material has a remarkably weak strength in the surface direction of the reflector, and cannot be said to be a satisfactory supporting member for the curved surface polishing finish of the integrated reflector plate.

Further, in such a reflector material, it is difficult to make the effective height of the tube material, which is a support grid, strictly constant at the time of manufacture, and therefore, the tube material is not uniform on the laminated transparent reflector plate. The unevenness remains as a distortion, which causes a temporal change such as swelling of the mirror surface at a later date, which is a major factor in the performance degradation of the reflector. Also, due to its structure, when the mirror surface is horizontal and vertical with respect to gravity, the rigidity against its own weight changes and the surface accuracy changes slightly depending on the mirror surface, so the posture is movable. However, it is difficult to use for applications that require operability.

Japanese Patent Publication No. 61-26041 discloses, in particular,
A lightweight astronomical mirror having a structure in which a support grating made of quartz glass is fused and integrated between a front plate and a rear plate of quartz glass so as not to move to these plates is described. I have. The support grid is composed of a plate member made of quartz glass and / or a tubular member placed on a support plate, each of which has a shape of 2 mm.
The space remaining between the pieces is filled with the substance to be sintered, consisting of granules, small tube pieces, small particles, small platelets, etc., or a mixture thereof, the arrangement being held together by a graphite ring. These are then heated in a furnace to a sintering temperature in a non-oxidizing atmosphere, and the support grid so formed may be connected to the front and rear plates by heat fusion so as not to move. It has been disclosed.

However, according to this method, a large number of plate-like members and tubular members having an appropriate shape are prepared in advance, and a predetermined space arranged in parallel is filled with a sintering substance, or a reinforcing tubular member filled with a sintering substance is filled. Since it requires troublesome operation, labor, and time for appropriately arranging the front plate and the rear plate and fusing the front plate and the rear plate, it is difficult to industrially adopt the method. In addition, the method using this tubular member is insufficient in weight reduction, and the flat plate is difficult to polish because the portion of the front plate for the reflector to which the tubular support member is fused is distorted, and optical precision is impaired. Problem.

A silica glass reflecting mirror surface and a bottom surface are fused and integrated on the upper and lower surfaces of a foam formed into a predetermined shape, and the peripheral side surfaces of the peripheral side portion are sequentially heated and fused with a strip-shaped silica glass plate by a combustion flame or the like. However, the larger the size of the reflector, the more difficult it is to process, and the side surface of the foamed porous material softens and melts, causing the bubbles to collapse or the closed cells to burst, changing the surface shape. Is not preferred.

[0012]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a practically desirable lightweight reflector base having excellent operability and having a strength such that the reflection mirror surface does not generate distortion due to a temperature change or the like. Is to provide. Yet another object is to provide an effective method by which such a lightweight reflector can be manufactured industrially advantageously.

[0013]

SUMMARY OF THE INVENTION The gist of the present invention is a method for manufacturing a silica-based light-weight reflecting mirror comprising the constituent elements described in the claims.

In the method of the present invention having the above constitutional requirements, in particular, a porous silica glass body placed in a vessel made of silica glass as a reflecting mirror is heated and the foam body is pressed by an upper silica glass plate. Plastic deformation so as to spread it into the container, and integrate the inner porous body with the container and the silica glass plate, and weld the opening edge of the container and the peripheral edge of the silica glass plate to form a porous body. It is characteristic to have a structure that completely surrounds the body. According to such a method, there is an advantage that the foam does not need to be preformed into a desired shape because the foam is freely filled in the reflector surrounding shell.

The plate surrounding the outside of the reflecting mirror used in the method of the present invention is formed of silica glass. Particularly, the plate for forming the reflecting mirror surface is preferably formed of silica glass having as high a purity as possible. A transparent plate without bubbles is used. Also,
The plate for forming the bottom surface and the plate for forming the side surfaces do not necessarily need to be high-purity silica glass, and may not be highly transparent or may contain some air bubbles. These plates vary depending on the size of the reflector, but their thickness is usually about 2 to 5 mm.

In the method of the present invention, for example, a cylindrical plate forming a peripheral side wall and a disk-shaped plate for forming a front plate or a back plate made of silica glass into which a porous silica glass material is inserted are previously formed. It is formed into a cylindrical container with a bottom and an opening that is integrated by fusion. On its inner surface, a columnar foam corresponding to the contents of the container is placed, and a silica glass plate or a bottomed cylindrical container as described above having a cylindrical plate portion forming a part of the peripheral side wall from above. The silica glass plate is applied and pressed in a predetermined high-temperature heating atmosphere to fill the foam into the container and, at the same time, the surrounding shell is fused and integrated at the joint to form the porous body. Is formed inside.

At the operating temperature at which the porous body is plastically deformed, it is difficult to expect fusion of the surrounding shell formed of the plate to obtain a completely sealed state. Varnish or silicone whose main bone is
The mirror can be sealed with rubber or the like to form a completely sealed reflector.

Further, the porous silica glass material filled in the inside thereof can be produced by a generally known method for producing foam glass,
For example, a method in which a substance which reacts at a high temperature, such as carbon powder, is mixed with silica powder to cause heat fusion and foaming.The glass is heated and reacted with ammonia in an ammonia atmosphere, and this is heated to a higher temperature. It is manufactured by a method of foaming using the desorbed gas or a method of mixing and sintering boron-based glass that easily elutes in acid, and treating this with acid to make it porous.

In order to reduce the weight of the reflector and secure the strength as a support for the reflector, the silica glass porous material preferably has an apparent density of, for example, about 0.1 to 1 g / cm ^3. The porous body is subjected to a press-filling operation under a condition of being thermally deformed at a temperature of, for example, 1400 to 1700 ° C. In this filling, silica powder can be interposed between the inner surface of each plate and the porous foam, and particularly, the gap is filled to promote fusion and integration, which is effective in increasing the strength. Yes,
desirable. The filling pressure is usually 1 to 50 g /
It is carried out at a pressure of cm ² , preferably operating under reduced pressure.

The substrate for a light-weight reflector containing a porous body manufactured in this manner can be provided as it is to a mirror polishing finish of the reflector or processing such as metal deposition. This is practically very advantageous because it can be omitted without requiring a final sealing operation.

In addition, the reflecting mirror thus formed and hermetically sealed can completely prevent the inconvenience of fine abrasive or water from entering the inside of the reflecting mirror. Polishing method enables highly precise polishing to a flat surface or a predetermined curved surface, and further, without any trouble, a metal film for a reflecting mirror such as aluminum or silver is excellently formed by vapor deposition or other known means. A reflective mirror layer is formed.

Next, the method of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is an example of a schematic cross-sectional view in an electric furnace for explaining an embodiment of the method of the present invention. FIG. 1A shows a state before heating, and FIG. It is the same figure in the state where the container etc. and the porous body were integrated. FIG. 2 is a perspective view of an example of a large reflecting mirror manufactured by the method of the present invention, FIG. 3 is a sectional view thereof, and FIG. 4 is a perspective view of another lightweight reflecting mirror according to the method of the present invention. is there.

In FIG. 1, a container 1 made of a silica glass and having a container-like silica glass container 1 having a peripheral side plate integrally formed at the peripheral edge thereof and having an open top is formed by a carbon disk 2 and a tubular carbon ring 3. In a carbon mold, a fused silica glass powder 5 is spread on the inner bottom surface of the silica glass container 1, and a porous silica glass body 4 having a height protruding from the upper surface of the opening of the container 1 is placed thereon. Then, the silica glass powder 5 is filled in the peripheral gap between the porous body and the silica glass container 1. A silica glass disk 6 having the same diameter as the silica glass container 1 is applied to the upper side of the porous body 4, and a heat-resistant carbon plate 7 for pressing and a carbon weight 8 are placed thereon. Is heated in an electric furnace 10 equipped with a heater 9.

When the temperature in the carbon mold rises, the porous body 4 starts plastically deforming, and is mainly pressed downward by the weight 8 to be spread out in the container 1, and the silica glass powder 5 is fused by melting. Together with this, the porous body 4 is integrated with the silica glass container 1 and the silica glass plate 6. In this case, at the same time, the silica glass container 1 and the silica glass plate 6 are fused and integrated at the contact portion to form a surrounding shell.

When a gap is formed between the container 1 made of silica glass and the disk 6 of silica glass, the gap is preferably sealed with silicone rubber 11 (FIGS. 2 and 3). Further, in the case where it is integrated with the container-shaped silica glass disk 6 having a rising tube portion on the periphery similarly to the container-shaped silica glass container 1, the gap at the center of the peripheral side plate is formed all around. (Fig. 4).

[0026]

According to the method of the present invention, it is possible to effectively provide a lightweight substrate on which a flat or curved mirror having a stable and excellent optical surface accuracy is formed on a reflecting mirror surface, and a large-sized substrate obtained by the method of the present invention. The reflecting mirror has excellent structural strength despite its light weight, and its high-precision mirror surface is stably maintained over a long period of time, so that excellent reflecting mirror accuracy and high operability are guaranteed.

[0027]

Now, the present invention will be described in further detail with reference to specific examples. Example 1 A silica soot body obtained by a CVD method (thermochemical vapor deposition) of hydrolyzing silicon tetrachloride in an oxyhydrogen flame to obtain a quartz glass soot body was subjected to an ammonia gas atmosphere at a temperature of 800 ° C. Then, the mixture was heated in an atmosphere to cause an ammonia reaction, and then heated at a temperature of 1650 ° C. for 3 hours in a reduced pressure atmosphere (0.1 torr) to produce a porous foam. This was cut into a disk having a diameter of 495 mm and a thickness of 55 mm to obtain a porous silica glass body.

On the other hand, a natural synthetic silica glass for forming a peripheral side plate portion having a diameter of 502 mm, a height (rising width) of 48 mm and a thickness of 3 mm is provided on an outer peripheral edge of a transparent synthetic quartz glass disk for forming a reflecting surface having a diameter of 496 mm and a thickness of 3 mm. The lower peripheral edge of the tubular ring is welded with a silica glass rod with a diameter of 4 mm to form an integral part, and the outer diameter is 502 mm.
A bottomed cylindrical container having a height of 51 mm and a thickness of 3 mm with one opening opened was prepared.

The inner bottom of the bottomed container has a particle size of 100
Silica glass powder prepared to be less than μm is spread to a thickness of about 0.5 mm, and the disc-shaped porous silica glass body is placed thereon, and placed on a carbon disc having a diameter of 600 mm and a thickness of 30 mm. Then, the bottom plate side of the container was placed on the lower side, and a carbon ring having a diameter of 550 mm, a height of 51 mm, and a thickness of 10 mm was concentrically installed outside the porous member and the container.

Next, a silica glass powder having a particle size of not more than 100 μm was filled between the porous body and the inner peripheral surface of the container, and a 502 mm diameter, A 3mm thick silica glass disk and 550m diameter on it
m, carbon disc with thickness of 30mm and diameter of 300mm, thickness of 200mm
Were placed concentrically in this order.

The device thus constructed is placed in an electric furnace,
As a result of heating at 1400 ° C. for 1 hour under a reduced pressure atmosphere of 0.1 torr, the porous body is pushed out by a weight, the silica glass powder is melted, and the silica glass container and the porous body are integrated,
The rising upper edge of the container and the peripheral edge of the disk-shaped silica glass were welded to obtain a sealed reflector base. From the volume and weight of the obtained reflector base, the density of the porous foam part excluding the silica glass plate of the outer shell and the filled silica powder is:
It was about 0.2 g / cm ³ .

The outer periphery of the obtained reflector base was ground to a diameter of 500 mm, the plate for the reflecting surface and the plate for the bottom surface were further roughed with a diamond wheel, and the plate for the reflecting surface was further mirror-polished with cerium oxide. It was processed into a lightweight reflector base having a diameter of 500 mm, a thickness of 50 mm, a silica glass reflector plate having a thickness of 2 mm on the outer surface and an outer shell. An aluminum film was formed on the reflection surface of the lightweight reflector base by the CVD method, thereby producing a large-sized reflector. The resulting reflector weighs about 4 kg, and is 81% lighter than a conventional reflector of the same size.

Example 2 A soot body was prepared by hydrolyzing silicon tetrachloride in an oxyhydrogen flame in the same manner as in Example 1 and heated in an ammonia gas atmosphere at a temperature of 800 ° C. to carry out an ammonification reaction. Thereafter, this was heated at a temperature of 1650 ° C. for 3 hours in a reduced pressure atmosphere of 0.1 torr to obtain a porous foam. Then, this is 495m in diameter
m, and cut into a disk having a thickness of 55 mm to obtain a porous silica glass body.

On the other hand, on the outer peripheral edge of a transparent synthetic quartz glass disk for forming a reflecting surface having a diameter of 496 mm and a thickness of 3 mm, a natural silica glass tubular ring for forming a peripheral side plate having a diameter of 502 mm, a height of 21 mm and a thickness of 3 mm is provided. The lower peripheral edge is welded together with a 4 mm diameter silica glass rod to form a united container with a 50 mm outer diameter, 24 mm height, and 3 mm thick bottomed bottomed reflector-like container with one open end. Obtained.

Similarly, an outer peripheral edge of a natural silica glass disk for forming a bottom surface having a diameter of 496 mm and a thickness of 3 mm and a natural silica glass tubular ring for forming a peripheral side plate portion having a diameter of 502 mm, a height of 21 mm and a thickness of 3 mm. The lower periphery is welded together with a 4 mm diameter silica glass rod to form an integral part, with an outer diameter of 502 mm and a height of 2 mm.
A bottomed container for bottom plate having a thickness of 4 mm and a thickness of 3 mm and having an opening on one side was prepared.

Next, silica glass powder having a particle size of not more than 100 μm is laid on the inner bottom surface of the container for bottom plate to a thickness of about 1 mm, and the disk-shaped porous silica glass material is placed thereon. And place it on a carbon disk with a diameter of 600 mm and a thickness of 30 mm.
A tubular carbon ring body of 550 mm, height 51 mm and wall thickness 10 mm was installed concentrically.

Next, a container for forming a reflecting mirror surface is placed on the disc-shaped porous body with its opening side facing down, and a silica glass disk having a diameter of 502 mm and a thickness of 3 mm is placed thereon. A carbon disk having a diameter of 550 mm and a thickness of 30 mm and a disk-shaped carbon weight having a diameter of 300 mm and a thickness of 200 mm were further concentrically placed thereon.

The device thus constructed is placed in an electric furnace,
Heated to a temperature of 1400 ° C. for 1 hour under reduced pressure of 0.1 torr. As a result, the porous body was spread and filled with the weight into the two container-like containers, and the two containers and the porous body were fused and integrated.
A 2 mm gap was formed over the entire peripheral edge of the rising peripheral wall between the two containers. The density of the porous foam portion formed by pressing deformation was calculated to be about 0.2 g / cm ³ from the volume and weight of the reflector base.

A 2 mm gap formed over the entire peripheral surface of the thus formed lightweight reflector base is filled with a one-component silicone rubber that is de-acetone-desorbed.
It was left to cure for a period of days to obtain a completely sealed reflector base.

The outer peripheral diameter of the obtained reflector base body was ground to 500 mm, the plates for the reflecting surface and the bottom surface were further roughly cut with a diamond wheel, and the reflecting surface plate side was further mirror-polished with cerium oxide. After processing into a lightweight reflector base having a diameter of 500 mm, a thickness of 50 mm, and a 2 mm thick silica glass reflector surface and outer shell on the outer surface, an aluminum film is deposited on the reflective surface of the lightweight reflector substrate by CVD. Thus, a large reflecting mirror was manufactured.

The manufactured reflector had a weight of about 4 kg.
In addition to achieving 80% lighter weight than the conventional reflector of the same size, there is no penetration of coolant or abrasive grains into the outer shell of the reflector during the grinding and polishing process, and the reflection film During evaporation, a good reflection surface was formed because there was no film abnormality due to the generation of dust or mistakes from the inside of the outer shell.

[0042]

As is apparent from the above embodiments, according to the method of the present invention, a large reflector base having a plate-like silica glass shell can be manufactured more easily and at lower cost than conventional reflectors. Is industrially remarkably advantageous. In addition, the lightweight reflecting mirror manufactured by the method of the present invention can not only polish the reflecting surface with high precision, but also does not have any inconvenience in forming the metal deposition film, and furthermore, the high-precision reflecting surface is safely held. It has excellent strength, and has a very desirable practical value that high operability can be obtained by reducing the weight of even a large one.

[Brief description of the drawings]

FIG. 1 is an example of a schematic cross-sectional view for explaining an embodiment of the method of the present invention, in which (a) shows a state before heating, and (b) shows a porous body and a plate by heating. It is a figure which shows the state integrated with the silica glass surrounding body.

FIG. 2 is a perspective view of an example of a large reflecting mirror manufactured by the method of the present invention.

FIG. 3 is a sectional view of the large reflecting mirror of FIG. 2;

FIG. 4 is a perspective view of another lightweight reflector according to the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Container-shaped silica glass container 2 Carbon disk 3 Tubular carbon ring 4 Silica glass porous material 5 Silica glass powder 6 Silica glass disk 7 Heat-resistant carbon plate 8 Body weight 9 Carbon 10 Electric furnace 11 Silicon rubber

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 5/08 C03C 11/00

Claims (3)

(57) [Claims] 1. A method of manufacturing a silica-based lightweight reflector, comprising:
A vessel-shaped silica glass container in which a peripheral side plate rising at the periphery is integrally formed and opened upward is placed in a heat-resistant mold for heating, and a height projecting from the upper surface of the opening of the container into the silica glass container is set. Insert a silica glass porous body having
A silica glass plate is placed on the upper side, and a heat-resistant plate-like body for pressing is applied from above, and heated and pressed to spread the porous silica glass body into the above-described container, thereby forming a silica glass container and silica glass. A method for producing a silica-based lightweight reflecting mirror, which is integrated with a plate. 2. The method according to claim 1, wherein a gap between the silica glass container and the inserted porous body is filled with silica glass powder, and the mixture is heated and pressed to integrate. 3. The manufacturing method according to claim 1, wherein the silica glass plate to be placed is provided with a peripheral side plate which is opposed to a rising peripheral side plate of a vessel-shaped silica glass container integrally at a peripheral edge.