JPS62297229A - Forming of optical glass element - Google Patents

Abstract

PURPOSE:To produce a high-accuracy optical glass element in high productivity, by applying a noble metal layer to a surface of a cemented carbide matrix composed mainly of WC, induction-heating the obtained forming mold and pressing a glass gob with the mold. CONSTITUTION:A forming mold used in the present process is produced by coating a cemented carbide matrix composed mainly of tungsten carbide (WC) with a noble metal layer having chemical stability to glass. The mold is heated by induction heating and a glass gob is pressed with the mold to effect the deformation of the surface layer of the glass gob contacting with the forming mold and to obtain the objective optical glass element. In the above molding process, the shape of the glass gob is selected to match the shape of the forming mold as far as possible. For example, in the case of producing an optical glass element having convex face, the radius of curvature of the glass gob should be larger than that of the forming face of the mold. The glass gob is ground with a grinding sand to attain the rough shape of the object and match the weight to the target weight and then subjected to polishing, etching or heat- treatment to smoothen the surface.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention Industrial Application Field The present invention is a highly accurate optical glass element that does not require a polishing process after press molding in the production of optical glass elements such as lenses and prisms. This relates to a molding method.

2. Description of the Related Art In recent years, there has been a trend toward aspheric optical glass lenses, which can simultaneously simplify the lens structure of optical equipment and reduce the weight of the lens portion. In manufacturing this aspherical lens, direct press molding is considered to be a promising method, since processing and mass production are difficult using the polishing method, which is a conventional method for manufacturing optical lenses.

This direct press-molding method involves press-molding molten optical glass in an aspherical mold that has been finished to the desired surface quality and surface precision in advance, or press-molding the molten optical glass into a shape close to the desired optical glass element. This is a method of manufacturing an optical glass element by heating and press-molding an optical glass material that has been processed up to 100 degrees (for example, Japanese Patent Publication No. 54-38126).

Problems to be Solved by the Invention In the method for manufacturing optical glass elements using the above-mentioned direct press molding method, the series of molding steps in which molten or heated glass is pressure molded and then cooled takes a long time, resulting in low productivity. It has the disadvantage of being low. Therefore, in putting the direct press molding method into practical use, it is necessary to reduce the time required for the series of molding steps described above.

Means for Solving the Problems The present invention solves the above problems by coating a cemented carbide base material mainly composed of tungsten carbide (WC) with a noble metal layer that is chemically stable to glass. The present invention provides a method for molding an optical glass element in which a surface layer of a glass material to be molded that is in contact with the mold is deformed by induction heating using the mold.

Function As mentioned above, optical glass elements have traditionally been formed by pressurizing and deforming a thermally softened glass material to form the desired shape of the optical glass element.
In the present invention, the entire glass material is heated, the entire glass material is heated, pressure molded, and then cooled, which inevitably lengthens the molding cycle.

Instead of cooling, the glass material is processed in advance to a shape close to the desired element shape, and only the surface layer thereof is heated and press-molded, thereby shortening the molding cycle time. Normally, with this method, distortion remains in the optical glass element or sink marks occur, making it difficult to produce a high-precision optical glass element.The present invention heats only the surface layer of the glass material. This is based on the discovery that even when pressurized, a highly precise optical glass element can be obtained by adjusting the heating and cooling conditions.

A highly accurate optical glass element means that the surface accuracy is within 5 Newton rings, within 1 Ayu, and has no birefringence, and these cannot be achieved if there are sink marks or residual distortion.

In order to produce such a highly accurate optical glass element by the method according to the present invention, the shape and surface condition of the glass material to be formed are important. The shape of the glass material to be molded should match the shape of the mold as much as possible. For example, when producing a convex optical glass element, the curved surface of the glass material to be molded should have a radius of curvature larger than the molding surface of the mold. There is a need. After grinding with grinding sand to obtain the general shape of the glass material to be formed and to match the weight, polishing, etching, or heat treatment is performed to smooth the surface.

By using a glass material to be molded whose surface has been smoothed by appropriately performing these surface treatments depending on the type of the glass material to be molded, a highly precise optical glass element with an excellent surface condition can be molded.

EXAMPLE Hereinafter, an example of the method for molding an optical glass element of the present invention will be described with reference to the drawings.

Example-1 The glass used was heavy flint optical glass 5F-8, and the gob-shaped glass material was ground and processed into a shape close to the desired optical glass element, and then polished with cerium oxide. A preform 10 as shown in FIG. 1 was produced. The desired optical glass element is a biconvex lens with a diameter of 15 m and a center wall thickness of 8 mm. The radius of curvature of this lens is 200 mm on one side and 100 mm on the other side. As a mold, platinum-iridium-
A material coated with osmium alloy was used. Second
As shown in the figure, the upper mold 12 for molding was fixed to the upper mold block 11. After placing thermocouples 20 and 21 in the upper mold 12 and clay mold 13, the preform 10 is placed in the lower mold 13, and a 10 kHz alternating magnetic field is applied to the heating coil 19. 12 and the lower mold 13 were heated at the same time to bring the mold temperature to 520°C. Mold temperature is 52
When the temperature reached 0° C., the plunger 16 was actuated downward and the preform 10 was press-molded.

The pressing pressure was 50 kg/cd, and the pressing time was 30 seconds. After press molding, the upper mold 12 and the lower mold 13 were cooled. At this time, press pressure is 1 to 5 kg/cal.
While monitoring the center wall thickness of the lens with the positioning sensor 18, the mold was cooled until the mold temperature reached 420°C. When the mold temperature reached 420°C, the pressure of the press was removed, and while the glass was held in the mold, it was further cooled until the mold temperature reached 350°C. The surface accuracy of the lens obtained by the method described above is within 3 double-kneeton rings, within 1/2 inch, and the surface roughness is 0.01 μm, so it can be said that it is a very high-precision lens.

Further, the time required for the above series of molding steps was approximately 2 minutes, and heating and cooling during molding were performed extremely efficiently.

Comparative Example-1 Using heavy flint glass 5F-8, a preform 10 as shown in FIG. 1 was produced in the same manner as in Example-1, and molded under heat and pressure using the molding apparatus shown in FIG. 3. . In FIG. 3, the same molds as in Example-1 were used as the upper mold 32 and the lower mold 33, and the molding conditions were the same as in Example-1. However, the glass material is heated by energizing heaters 39 and 42 embedded inside each of the upper mold block 31 and lower mold block 34, and heating the inside of the upper mold 32 and lower mold 33 for molding. The temperature was detected by thermocouples 40 and 41, and the temperatures of the upper mold 32 and lower mold 33 were controlled. Mold temperature 520℃, press pressure 50k
The glass was molded under the conditions of g/c+J and press time of 30 seconds, and cooled until the mold temperature reached 420°C. At this time, the press pressure was reduced to 1 to 5 kg/aJ. Mold temperature is 4
When the temperature reached 20°C, the press pressure was removed, and while the glass was held in the mold, the mold temperature was further increased to 350°C.
The surface precision of the lens obtained by the method of cooling to 0°C or above achieved the same high precision as in Example-1, but the time required for the above series of molding steps was about 20 minutes. Therefore, a longer molding time was required compared to the molding method of the present invention.

Effects of the Invention As is clear from the above explanation, the method for forming an optical glass element of the present invention is a method of forming an optical glass element by forming a noble metal chemically stable with respect to glass on a cemented carbide base material mainly composed of tungsten carbide (WC). The method is characterized in that the surface layer of the glass material to be molded in contact with the mold is deformed by heating and pressurizing the mold by induction heating using a mold coated with a layer. A method for forming optical glass elements,
Rather than heating and pressing the entire glass material, only the surface layer is heated and pressed, making it possible to significantly shorten the molding cycle time.

Therefore, the method for molding an optical glass element of the present invention makes it possible to manufacture highly accurate optical glass elements with good mass productivity, and has extremely great industrial value.

[Brief explanation of drawings]

FIG. 1 is a side view of a molding die in an example of the present invention, FIG. 2 is a side sectional view of a molding device used in the same example, and FIG. 3 is a side sectional view of a molding device used in the comparative example. It is. 10... Preform, 11... Upper mold block, 12... Upper mold for molding, 13...
... Lower mold for molding, 14 ... Lower mold block, 15
...Glass to be formed, 16...Plunger, 17...Stopper, 18...
Positioning sensor, 19... Heating coil, 20.
21...Thermocouple, 22...Shell, 3
1... Upper mold block, 32... Upper mold for molding, 33... Lower mold for molding, 34...
Lower mold block, 35...Glass to be formed, 36.
... Plunger, 37 ... Stopper, 38 ... Positioning sensor, 39.42 ...
... Heater, 40.41 ... Thermocouple, 43.
...Wow. Name of agent: Patent attorney Toshio Nakao Figure 3

Claims (1)

[Claims] Using a mold in which a cemented carbide base material mainly composed of tungsten carbide (WC) is coated with a noble metal layer that is chemically stable to glass, the mold is heated by induction heating. A method for molding an optical glass element, characterized in that the surface layer of the glass material to be molded that is in contact with the mold is deformed by applying pressure.