JPH0455980B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for molding optical glass parts, in which a molding material for optical glass parts is softened by heating and then press-molded using a molding die. BACKGROUND ART Conventionally, many optical glass parts such as lenses, prisms, and filters have been formed by a method that mainly involves polishing a molding material for optical glass parts such as glass. However, this polishing process requires considerable time and skill, and in particular,
To form an aspherical lens through a polishing process,
More advanced polishing techniques were required, and the processing time became longer, making it difficult to manufacture large quantities of optical glass parts in a short period of time. Therefore, a method has been developed and is attracting attention for forming optical glass parts such as lenses by simply inserting and arranging a molding material for an optical glass part into a pair of molding molds and pressurizing the molding material. Pressure molding methods for optical glass parts generally include a reheat press method and a direct press method. In the reheat press method, the required amount of glass material, for example, as a molding material for optical glass parts that has been melted and solidified in advance is measured, heated to a predetermined temperature to soften it, and then put into a mold for molding. This is a method of forming optical glass parts by applying pressure. However, this reheat press method did not clarify the relationship between glass viscosity and mold temperature, which caused various problems such as sticking, sink marks, and folding, making it impossible to form stable high-precision optical glass parts. It was hot. On the other hand, the direct press molding method is conventionally carried out by the method shown in the first figure, and the specific method will be explained below. First, the apparatus for carrying out the method will be described. A rotary table 3 is located below an orifice 1 connected to a glass melting furnace (not shown) and is rotatably driven and stopped via a main shaft 2. is arranged, and on this rotary table 3 there are lower molds 4, 5, 6, for molding molten glass.
Four pieces of 7 are arranged at positions that equally divide the circumference into four. When the rotary table 3 is stopped, that is, before lens molding starts,
The opening 8 of the orifice 1 is configured to face the upper position of the lower mold 4 (the lower mold on the left side in the figure), and the upper position of the lower mold 5 adjacent to this lower mold 4 is A plunger 10 for press-molding the molten glass 9 in the lower mold 5 in cooperation with the mold 5 is disposed so as to be freely slidable in the vertical direction. Also, the opening 8 of the orifice 1 and the lower die 4 located below the opening 8
A cutting peg 11 is disposed between the opening 8 and the cutting peg 11, which can be opened and closed to cut a predetermined amount of the molten glass 9 flowing down from the opening 8. The rotary table 3 is controlled to repeatedly rotate and stop at 45 degree increments, and one stroke ends when the lower mold 4 repeats rotation and stop at 45 degree increments four times and is restored to its original position. is configured to do so. To explain the method of forming a lens using the above-mentioned apparatus, first, the molten glass 9 is made to flow and hang down from the orifice 1 into the lower mold 4, and an appropriate amount of the molten glass 9 is cut through the cutting scissor 11. Next, move the rotary table 3 counterclockwise by 45 degrees in the figure.
After rotating once, it is stopped, and the lower mold 4 filled with molten glass 9 is moved to a position directly below the plunger 10. Then, in that state, plunger 1
0 downward, this plunger 10 and the lower die 4
The molten glass 9 is pressed by the cooperative action of
Press molding of the molten glass 9 is performed. In this case, the heat of the molten glass 9 is removed by the plunger 10. After press molding, the plunger 10 is moved upward, and then the rotary table 3 is rotated 45 degrees counterclockwise in the figure and then stopped. That is, the lower mold 4 stops at the position of the lower mold 6 in the figure. At this stop position, no work is performed; only the shape of the molded glass (molded lens) 9 is maintained. Then, the lower mold 4 is stopped at a position where the rotary table 3 is further rotated by 45 degrees, that is, at the position of the lower mold 7 in the figure, and the molded lens 9 inside the lower mold 4 is pushed up from below to take out the molded lens 9. The lens molding method is completed. The method for molding the lens includes lower molds 4, 5, 6,
7, respectively, whereby lenses are continuously molded. The molded lens 9 taken out from the lower mold 4 is placed in a slow cooling furnace (not shown) and cooled to room temperature while creating a temperature gradient to prevent distortion. However, the direct press molding method has the following problems. First, the molten glass must be allowed to flow and hang down into the lower mold at a high temperature of about ¹⁰³ poise.
There was a problem in that each member such as 5, 6, 7 and plunger 10 was easily oxidized, and the life of each of these members was shortened. Second, it is difficult to remove heat uniformly from the molten glass 9 during molding, and the surface of the falling glass stream becomes cold when it comes into contact with the outside air, increasing its viscosity. However, there was a problem in that the glass flow formed a sinking flow at the inflow position, and was likely to cause folds, bubbles, etc. Thirdly, since the viscosity of glass is low (high temperature), the mold surface is easily oxidized and reacts.
There are problems in that the mold deteriorates severely, the optical glass parts are difficult to release after molding, and production efficiency is poor. Fourthly, it is difficult to maintain the plunger 10 at a molding temperature (temperature suitable for molding), which requires a device to cool the plunger 10, making the device complicated. Purpose of the Invention The present invention was developed in view of the problems in the conventional molding method, and aims to prolong the life of a mold, improve mold releasability, and keep molding conditions constant. Accordingly, it is an object of the present invention to provide a method for molding optical glass parts that can manufacture optical glass parts with stable optical properties in large quantities at low cost. Summary of the Invention The present invention involves placing a glass molding material having a preformed molding surface on a transfer table with good mold releasability, and passing the glass molding material through a preheating furnace and a main heating furnace. Temperature) ~ (Knikku point temperature -
30℃), and a mold release member is slidably arranged on the outer periphery of each mold material, and the heating softening process is performed between a pair of upper and lower molds heated to a temperature near the transition point of the molding material. A step of transporting the glass molding material, a step of pushing the molding material up from the conveyor table with a lower mold, and press-molding it into an optical glass component with upper and lower molds in a non-oxidizing atmosphere, and a step of pressing the molding material onto the outer periphery of the optical glass component While bringing the lower mold release member into contact with the molding surface of the lower mold, the molding surface of the lower mold is released from the optical glass component, and with the optical glass component attached and held on the upper mold, the lower mold and the lower mold are separated. a step of moving the mold and a lower mold release member downward; a step of arranging a conveying member for conveying the optical glass component into a slow cooling furnace facing the main heating furnace below the upper mold; A step of bringing the upper mold release member into contact with the outer periphery and releasing the optical glass component from the molding surface of the upper mold, and transporting the conveying member with the optical glass component mounted into the slow cooling furnace to allow the gradual distortion temperature region. It is equipped with the step of passing through. Examples The molding method of the present invention will be explained below with reference to the drawings. FIG. 4 shows an outline of an apparatus directly used for carrying out the molding method of the present invention. In the figure, 20 is a glass lens 50 as an optical glass component, which is composed of a pair of molds, an upper mold 21 and a lower mold 22. In this press molding mold, both upper and lower molds 21 and 22 of the mold 20 are as follows:
Both upper and lower molds 2 are provided with mold release members 23 and 24 that are slidable in the vertical direction on their respective outer peripheries.
1 and 22 are slidably vertically supported by guide members 25 and 26, respectively, and are disposed opposite to each other. Further, both the upper and lower dies 21 and 22 are connected to drive parts (not shown) that move in opposite directions. Furthermore, both the upper and lower molds 21 and 22 are made of 13 chromium-based stainless steel material or other ultra-hard material whose surfaces are coated with a film of chromium nitride or titanium nitride, and the mold release members 23 and 24 are
is the contact surface 23 with the outer peripheral edge 51 of the glass lens 50 after press molding with the molding surfaces of both the upper and lower molds 21 and 22.
It is made of a rigid member with low elasticity, with a woven fabric part made of carbon and glass fibers or a woven fabric part made of alumina wool provided on a and 24a. Reference numeral 30 denotes a mounting table that supports a glass gob 52 as a molding material via a gob stand 31 of the glass gob 52, and is mounted on both upper and lower molds 2 of the press molding mold 20.
It is constructed between 1 and 22. Further, the gob stand 31 is provided with a through hole 32 in the center thereof having a diameter larger than the outer diameter of the lower mold 21 of the press molding die 20, and a glass gob 52 consisting of a stepped portion is engaged with the upper opening edge of the through hole 32. A retaining edge is formed to form a receiving portion 33 for the glass gob 52. Furthermore, as will be described later, the gob stand 31 is heated together with the glass gob 52 held by the receiving part 33 in the heating furnace to a temperature near the knick point of the glass gob 52, so that it can withstand this temperature. The receiving portion 33 is made of a heat-resistant material and has a releasability from the glass gob 52 which is softened by heating. That is, the gob stand 31 is made of a material that is difficult to wet with glass, such as BN (boron nitride).
It is partly made of a composite material made of carbon and polymer. Reference numerals 34 and 35 denote a heating furnace for the glass gob 52 and both upper and lower molds 21 of the press mold 20, which are disposed opposite to each other on both left and right sides of the mounting table 30 for the glass gob 52.
Glass lens 50 after being press-molded for 22 hours
This is a slow cooling furnace. Further, the heating furnace 34 is equipped with a preliminary heating furnace 36 and a main heating furnace 37, and the heating furnace 34 and the slow cooling furnace 35 are equipped with a gob stand 31 in which a glass gob 52 is engaged with a receiving part 33, and a gob stand 31 is attached to the holding parts 38a and 39a at the tip. A pair of conveying members 38 and 39 that are conveyed while being clamped are housed inside so as to be movable in the front and rear directions, and the lehr 35 has both upper and lower molds 21 and 2 of the press molding die 20.
A conveying member 40 for conveying the glass lens 50 which has been press-molded and released from the mold in step 2 into the lehr 35 is installed inside the lens 40 so as to be movable in the front and rear directions. Further, a fifth
As shown in the figure, it has a pedestal 41 for receiving the glass lens 50 to be released from the mold, and a woven fabric portion of carbon and glass fiber is provided in the pedestal 41 in consideration of mold releasability with the glass lens 50 after the mold release. It is provided. When molding the glass lens 50 using the molding apparatus having the above configuration while applying the molding method of the present invention, the glass gob 52 is placed while being locked on the receiving part 33 of the gob stand 31, and the glass gob 52 is placed in a pair. Clamping parts 38a, 39a of conveying members 38, 39
It is carried into the heating furnace 34 while being held in between, and the preliminary heating furnace 36 and the main heating furnace 37 of the heating furnace 34 are
After heating and softening the glass gob 52, the gob stand 31 is placed on the mounting stand 30 as shown in the fourth figure.
The glass gob 52 of the gob stand 31 is carried in between the upper and lower molds 21 and 22 of the press-molding mold 20. In connection with the conveyance of the glass gob 52, the driving parts of both the upper and lower molds 21, 22 of the press molding die 20 start operating, and first, the lower mold 22 is moved in advance of the upper mold 21.
moves upward along the guide member 26 in the direction opposite to the upper mold 21, and is held by the holding portions 38a, 39a of the pair of conveying members 38, 39, and is retained by the receiving portion 33 of the gob stand 31. The gob stand 31 receives the glass gob 52 on the molding surface 22a of the lower mold 22.
Push up more. In response to the upward movement of the lower mold 22, which pushes up the glass gob 52 from above the gob stand 31 while being received by the molding surface 22a of the lower mold 22, the upper mold 21 moves downward along the guide member 25, and both the upper and lower molds 21, 22
A glass gob 52 is press-molded between the molding surfaces 21a and 22a, and a glass lens 50 is molded as shown in FIG. 5a. After the press molding of both the upper and lower molds 21 and 22, as shown in FIG. The surface 24a contacts the outer peripheral edge 51 of the glass lens 50, and the molded glass lens 50 is released from the molding surface 22a of the lower mold 22. However, at this time, the glass lens 50 after molding is attached and held on the molding surface 21a side of the upper mold 21. Therefore, in connection with the press molding operation of the glass gob 52 by the cooperation of the upper and lower molds 21 and 22, the pair of conveying members 38 and 39 retreat into the heating furnace 34 and the slow cooling furnace 35, and the lower mold 22 As the glass lens 50 is released from the mold by the mold release member 24, the lower mold 22 moves downward again in advance of the upper mold 21, and as shown in FIG. The state will be restored. Further, after waiting for the lower die 22 to move downward from the inside of the through hole 32 of the gob stand 31, the conveying member 40 moves forward from inside the lehr 35, and its tip 40
The pedestal 41 provided for the upper mold 21 is set under the upper mold 21, and at the same time the mold release member 23 of the upper mold 21 is placed under the upper mold 21.
1 and its contact surface 23
a comes into contact with the outer peripheral edge 51 of the glass lens 50 and is released from the molding surface 22a of the glass lens 50. Therefore, the released glass lens 50 is received in the cradle 41 of the conveying member 40 set on the lower side, and carried into the lehr 35 by the backward movement of the conveying member 40, where it is annealed. Thereafter, molding of the glass lens 50 can be completed by carrying it out to a predetermined position using a carrying member (not shown), and subsequent molding of glass lenses 50 can be continued in the same manner. Incidentally, the glass lens 50 is slowly cooled in the slow cooling furnace 35 by passing through a slow strain temperature region (a region set to a slow strain point temperature lower than the transition temperature) for 15 minutes, whereby the temperature is lowered to room temperature at a rate of 20° C./mm. Ta. In addition, when molding the glass lens 50 using the molding apparatus, in particular, according to the experimental results described below, the press molding is performed in a non-oxidizing atmosphere, for example, the molding part of the press mold 20 is Molding is performed by creating a non-oxidizing atmosphere by introducing helium, argon, xenon, nitrogen, or hydrogen-nitrogen mixed gas while degassing (however,
In the above example, nitrogen (N ₂ ) was introduced at 5/mm) and a glass gob 52
uses a glass gob 52 having a cut surface cut by lateral pressure or a molded surface preformed by a processing method such as direct pressing, heated and softened to a temperature near the knick point of the viscosity-temperature curve determined by the penetration method, Furthermore, it has been found that the press molding mold 20 is required to be heated to a temperature near the glass transition temperature as a molding condition. In other words, for each glass material, in order to determine the molding temperature of the glass material in the reheat press method,
Among the viscosity-temperature curves obtained by the intrusion method, the characteristics of heavy flint glass (SFSO1) and barium lanthanum glass (BaLF3) are shown in Figure 2a.
It is b. In the case of the penetration method, the penetration pin and holder were made of nickel metal. As is clear from Figure 2 a and b, the heavy flint glass (SFSO1) with the highest amount of PbO is 10 ^5.3
The Kunik point is shown near Boaz, and the viscosity of barium lanthanum glass (BaLF3) at the Kunik point is
10 It was around ^7.5 poise. In addition, the viscosity at the Kunik point differs depending on each glass material, but the viscosity range at the Kunik point is approximately 105.3 to ^107.5.
It was hot inside Poise. Furthermore, the relationship between the temperature of each glass material and the temperature of the molding die is shown in the table below.

【table】

[Table] Furthermore, Figure 3 shows the wetting characteristics of heavy flint glass (SFSO1) for various materials.In particular, the wetting angle at 490℃, which is the forming temperature of SFSO1, near the Kunik point, is This indicates that the material is difficult to wet at temperatures above 135°C. In other words, it has been found that, due to the relationship with the molding material of the press molding die 20, if the molding is performed at a viscosity near the sticking point, it will not stick to the press molding die 20 and will be easily released from the mold. In addition, if the molding temperature is raised to a temperature higher than the knick point of the viscosity-temperature curve shown in Figure 2 a and b, it becomes easy to wet, adheres to each material, and becomes difficult to release from the mold. This results in deterioration of surface quality. In addition, Galaman spectroscopic analysis confirmed that at temperatures above the Kunich point of the viscosity-temperature curve, the oxygen anion state in the glass structure changes, and the reproducibility of glass forming is better in the condensed Newtonian region than in the non-Newtonian region. It turned out to be better than molding. While applying such molding conditions, each glass material, SFSO1 (Fig. 6a), BaLF3 (Fig. 6b), SF8 (Fig. 6c), BK7, is formed by the molding apparatus.
The interference images of the glass lens molded using the Fizeau interferometer (FIG. 6 d) are shown by the interference patterns shown in FIGS. 6 a to 6 d. As is clear from such an interference pattern, it is clear that the glass lens molded under the above molding conditions has a surface shape that is equal to or larger than the molding surface of the press molding die, and that it has the same refractive index. As a result of immersion in liquid and examining it under a polarizing microscope, no distortion was observed. Furthermore, when SFSO1 is applied as a molding material and molded by heating and softening it at a temperature above the nail point, 520℃, as shown in the interference pattern in Figure 7a, as shown in the interference pattern in Figure 7a, as well as asperities are observed. When the temperature was higher than this, 540°C, adhesion of the glass lens to the mold after molding was observed. In addition, if the temperature of the press molding die 20 is lowered by 30 degrees Celsius, the center of the mold will be lowered.
An interference image was obtained. This is shown in the interference pattern of FIG. 7b. Effects of the Invention According to the method for molding optical glass parts of the present invention,
The molding viscosity varies depending on the type of glass material, but it is higher than ^105.3 poise, which is higher than the molten glass of the conventional technology, and the temperature is below the Kunich point of the viscosity-temperature curve, so oxygen anions in the glass structure are There is no activation, so there is less attack on the mold by oxygen anions, and as a result, the mold surface is not strongly oxidized, extending the life of the mold and improving mold releasability. Furthermore, since the molding is performed at a temperature under a similar Newtonian fluid, an optical glass component with stable optical properties can be obtained if the molding conditions are kept constant. Furthermore, by setting the mold temperature near the glass transition temperature and the heating temperature of the glass to the viscosity-temperature characteristic point, there is no sudden structural change in the glass as a molding material, and the mold temperature can be kept constant. Since the temperature is set at such a temperature that it is easy to remove distortion, it is possible to easily obtain optical glass parts with less distortion than in the prior art. To put the above point in another way, first, since it is molded using a Newtonian fluid, it is possible to prevent the occurrence of sink marks, folds, bubbles, etc. compared to the prior art. Unlike the second prior art, there is no need for slow cooling for a long time, and there is no need for much adjustment of the refractive index, making it possible to mold in a short time. Thirdly, according to this molding method, unlike the prior art, there is no need to heat the mold to the extent that it melts, and therefore the life of the upper and lower molds and their peripheral equipment members can be extended without rapidly oxidizing them. Fourth, as a comprehensive result, it is possible to manufacture optical glass parts that can be formed in a short time, does not require post-processes such as re-polishing, and has a significantly lower manufacturing cost and stable quality. can.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a molding device showing a conventional glass lens molding method, Figures 2a and b are SFSO1,
Figure 3 is a diagram showing the temperature dependence of viscosity by the penetration method of BaLF3, Figure 3 is a diagram showing the wetting characteristics of SFSO1 for each material, Figure 4 is a schematic diagram of the molding equipment used in the molding method of the present invention, Figure 5 Figures a and b are explanatory diagrams showing the state of press molding by the press mold and the release state of the glass lens after press molding;
c, d were obtained by the molding method of the present invention
Interference patterns showing interference images of surface shapes of glass lenses molded with SFSO1, BaLF3, SF8, and BK7 molding materials, Figures 7a and b
is an interference pattern showing an interference image of the surface shape of a glass lens molded using SFSO1 as a molding material under molding conditions that deviate from those of the molding method of the present invention. 20...Mold for press molding, 21...Upper mold, 22
... Lower mold, 23, 24 ... Mold release member, 25, 26
... Guide member, 30 ... Mounting table, 31 ... Gob stand, 32 ... Through hole, 33 ... Receiving part, 34 ... Heating furnace, 35 ... Slow cooling furnace, 36 ... Preheating furnace, 37
... main heating furnace, 38, 39, 40 ... conveyance member,
41... cradle, 50... glass lens, 51...
...Outer rim, 52...Glass gob.

Claims (1)

[Scope of Claims] 1. A glass molding material having a preformed molding surface is placed on a transfer table with good mold releasability, and the glass molding material is passed through a preheating furnace and a main heating furnace (at the Kunikku point). Temperature) ~ (Knick point temperature -30℃)
A step of heating and softening the glass molding material within a range of a step of pushing the molding material up from a conveyor table using a lower mold and press-molding it into an optical glass component using upper and lower molds in a non-oxidizing atmosphere; The molding surface of the lower mold is brought into contact with the mold release member, and the molding surface of the lower mold is released from the optical glass component, and with the optical glass component attached and held on the upper mold, the lower mold and the lower mold release member are brought into contact with each other. a step of arranging a conveyance member below the upper mold for conveying the optical glass component into a slow cooling furnace facing the main heating furnace; and a step of disposing an upper mold release member on the outer periphery of the optical glass component. a step of bringing the optical glass components into contact with each other and releasing the optical glass components from the molding surface of the upper mold; and a step of transporting the conveying member on which the optical glass components are placed into a slow cooling furnace and passing through a gradual strain temperature region. A method for forming optical glass parts characterized by: