JPS61286232A - Molding method for optical glass parts - Google Patents

Abstract

PURPOSE:To prepare an optical glass parts having high precision without caus ing shrinking nor fusion-sticking to a mold by press-molding glass while holding a mold temp. within a specified range below the transition point of the glass material, then elevating the mold temp. to near the transition point, finally removing the molded product from the mold. CONSTITUTION:Glass material for an optical glass parts is softened by heating. On one hand, the temp. of the mold for molding the optical glass parts is held at a temp. within a range from the transition point of the glass material to a temp. by 100 deg.C below the transition point. The heat-softened glass material is charged to the mold and press-molded in nonoxidizing atmosphere. The press- molded optical glass is held under pressure and the mold temp. is elevated to near the transition point of the glass material, and then removed from the mold. Thus, an optical glass parts having high precision is molded without causing fusion sticking of the glass to the mold, nor shrink nor fold mark.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for molding optical glass parts such as glass lenses.

[Prior Art] Conventionally, there are a reheat press method and a direct press method as pressure molding methods for optical glass parts such as lenses and prisms.

The former reheat press method involves cutting or roughing a glass plate or block of glass as a material for forming an optical glass component, which has been melted and solidified in advance, and then adjusting it to a predetermined volume or weight through operations such as cutting or rough machining. This is a method of heating and softening the material to a predetermined temperature, placing it in a mold, and pressurizing it to form an optical glass component.

On the other hand, in the latter direct press method, molten glass that has been heated to a high temperature that can be deformed in a glass melting furnace is made to flow down through an orifice connected to the melting furnace, and this flowing glass flow is intermittently cut. This is a method in which the resulting glass gob is placed in a mold and press-molded.

Generally, in these molding methods, the glass material is molded in a mold, and at the time it is taken out from the mold,
Although the surface temperature is cooled to the extent that the shape does not collapse,
The internal temperature is high, resulting in uneven temperature distribution. If the glass is taken out of the mold with a high center temperature, it will be difficult to obtain a constant size when it is cooled, and the pressed shape will not be consistent, causing sink marks. Molding optical glass parts was difficult.

Furthermore, since the viscosity of glass is low (high temperature), the mold surface is easily oxidized and reacts, which causes severe deterioration of the mold and causes fusion, resulting in poor production efficiency. was there.

Therefore, the present invention has been made by focusing on the problems of the prior art as described above, and it is possible to stably mold optical glass parts with high precision without adhesion to the molding die or sinkage of the glass molded product. The purpose is to provide a possible molding method.

[Means for Solving the Problems] The present invention heats and softens the glass material of the optical glass component, and also increases the temperature of the mold for molding the optical glass component from below the transition point of the glass material to 100° C. above the transition point. After maintaining the temperature in a low temperature range, the heated and softened glass material is carried into the mold and press-molded in a non-oxidizing atmosphere. The glass molded product is held under pressure in a mold while raising the mold temperature of the mold to around the transition point of the glass material, and then released from the mold.

[Function] In the method of the present invention, the temperature of the molding die is maintained within the temperature range from below the transition point of the glass material to 100°C lower than the transition point, thereby preventing fusion with the heated and softened glass material. At the same time, the temperature of the optical glass molded product is made uniform while pressurizing and holding the optical glass molded product after press molding in the molding die, and then the mold temperature is again raised to near the transition point of the glass material. By doing so, shape distortions such as sink marks are eliminated, and the shape of the molding die is transferred with high precision during molding.

[Example] Examples of the molding method of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic explanatory diagram of a molding apparatus used to carry out the method of the present invention, FIGS. 2 and 3 are explanatory diagrams showing the glass lens molding process in the molding apparatus shown in FIG. 1, and FIGS. 4 a and b.
, c are diagrams showing reflected wavefronts on the molding surface of the glass material and the molding surface of the press molding die in each molding process.

First, the molding apparatus will be explained with reference to FIGS. 1 to 3. In the figures, l is an upper mold 2. A mold for press molding a glass lens 30 as an optical glass component consisting of a pair of molds of a lower mold 3. Both upper and lower molds 2 and 3 of this mold 1 are slidable in the vertical direction on their respective outer peripheries. A mold release member 4.5 is provided, and both the upper and lower molds 2, 3 themselves are disposed facing each other while being supported by guide members 6, 7, respectively, so as to be slidable in the vertical direction. Further, both the upper and lower dies 2 and 3 are connected to a drive section (not shown) that moves in opposite directions.

Furthermore, the molding surfaces of both the upper and lower molds 2.3 are made of 13 chromium-based stainless steel material coated with a film of chromium nitride or titanium nitride, or other ultra-hard materials, and the mold release members 4, 5 are The contact surfaces 4a and 5a of the molding surfaces of both the upper and lower molds 2 and 3 with the outer peripheral edge 31 of the glass lens 30 after press molding are provided with a woven fabric part made of carbon and glass fiber or a woven fabric part made of alumina wool. It is made of a rigid member with low elasticity. Reference numeral 10 indicates a glass gob 32 as a molding material, and a gob stand 11 of the glass gob 32.
This is a mounting table that is supported through the press molding die 1 and is installed between the upper and lower molds 2 and 3 of the press molding die 1.

At the same time, a locking edge of the glass gob 32 consisting of a stepped portion is formed at the upper opening edge of the through hole 12, and the receiving portion 1 of the glass gob 32 is
3 is formed. Furthermore, since the gob stand 11 is heated together with the glass gob 32 held in the receiving part 13 of the gob stand 11 to a temperature near the softening point of the glass gob 32 in the heating furnace, it has sufficient heat resistance. The receiving part 13 is made of a material having a mold releasability from the glass gob 32 which is softened by heating.

That is, the gob stand 11 is made of a material that does not easily wet with glass, such as BN (boron nitride) or a composite material that is a combination of a portion of carbon and a polymer.

14.15 shows the glass lens 30 after being press-molded between the heating furnace of the glass gob 32 and the upper and lower molds 2 and 3 of the press-molding mold 1, which are arranged opposite to each other on the left and right sides of the storage stand 10 for the glass gob 32. This is a slow cooling furnace. Further, the heating furnace 14 is equipped with a preliminary heating furnace 17 and a main heating furnace 16, and the heating furnace 14 and the slow cooling furnace 15 are equipped with a glass gob 32 in the receiving part 1.
The gob stand 11 engaged with the
A pair of conveying members 18 and 19, which are conveyed while being clamped by the conveyor belt, are each movable in the front and rear directions.

When molding the glass lens 30 with the molding apparatus having the above configuration, the glass gob 32 is placed on the receiving part 13 of the gob stand 11 while being locked, and is held between the holding parts 18a of the pair of conveying members 18 and 19. , 19a, are carried into the heating furnace 14 while being sandwiched between them, and are passed through the preheating furnace 17 and main heating furnace 16 of the heating furnace 14 to the glass gob 32.
After heating and softening the gob stand 1 as shown in the first figure.
1 is placed on the upper side of the mounting table 10, and the glass gob 32 of the gob table 11 is carried between the upper and lower molds 2 and 3 of the press molding mold 1.

In connection with the conveyance of the glass gob 32, the driving parts of both the upper and lower molds 2 and 3 of the press molding die 1 start operating, and first, the lower mold 3 is connected to the upper mold 2 before the upper mold 2. The clamping portions 18a of the pair of conveying members 18, 19 move upward along the guide member 7 in opposite directions.

The glass gob 32 held by the gob holder 19a and held by the receiving part 13 of the gob holder IT is pushed up from the gob holder 11 while being held by the molding surface 3a of the lower mold 3.

The glass is fixed on the molding surface 3a of this lower mold 3.

The upper mold 2 moves downward along the guide member 6 in response to the upward movement of the lower mold 3 that pushes up the gob 32 from above the gob stand 11, and the molding surfaces 2a of both the upper and lower molds 2, 3 are formed.

A glass gob 32 is press-molded between 3a, and a glass lens 30 is formed as shown in FIG.

After the press molding of both the upper and lower molds 2 and 3, as shown in FIG. Contact surfaces 4a, 5a
contacts the outer peripheral edge 31 of the glass lens 30, and the molded glass lens 30 is released from the molding surfaces 2a, 3a of the upper and lower molds 2.3 by the molds held between mold release members 4, 5.

Immediately after this mold release operation, the upper and lower molds 2 and 3 return to the state shown in the first figure, but at the same time, the glass lens 30 is also placed on the contact surface 5a of the mold release member 5 in conjunction with the movement of the lower mold 3. In this state, the receiver is fixed on the upper surface of the gob stand 11 by moving it downward (see FIG. 3).

Therefore, the glass lens 30 placed on the gob stand 11 is further carried into the lehr 15 by the conveying members 18 and 19 and gradually cooled, and then the glass lens is carried out to a predetermined position by a carrying member (not shown). 30 can be completed, and subsequent molding of successive glass lenses 30 can be accomplished in the same manner.

Generally, in press molding, the surface layer of a glass lens is rapidly cooled and solidified during pressing, but the internal temperature is high and the temperature area becomes uneven, and the temperature of the solidified layer is on the surface and inside. There will be a difference and the surface will be under tension. Therefore, if the mold temperature is too low, the temperature of the contact surface between the glass lens and the mold is low, and the above tension exceeds the strength of the glass, the glass will break.Normally, this will cause the glass to break. , called Kang. Conversely, if the mold temperature is too high, the glass and mold may fuse or
Deformation tends to occur after pressing.

Therefore, in the method of molding the glass lens 30 using the molding apparatus, the present inventor conducted various experiments in view of these points and determined the temperature of the mold 1 as a material to be molded. The temperature is kept constant in the range from below the transition point of the glass material to 100 degrees Celsius below the transition point, and press molding is performed at this mold temperature, and the temperature of the molded glass lens is kept uniform with the mold temperature. After holding until
They discovered that by raising the mold temperature to a temperature close to the glass transition point, it was possible to obtain a glass lens with extremely high dimensional accuracy.

That is, experiments have shown that by maintaining the mold temperature within a temperature range from below the transition point of the glass material to 100 degrees Celsius below the transition point, it is possible to prevent the glass material and the mold from fusion.
Furthermore, by continuing to pressurize and hold the temperature inside the glass lens in the mold at the moment of pressing, the temperature inside the glass lens is made uniform, and after making it the same as the mold temperature, it is kept in the mold. By raising the mold temperature to near the transition point, the shape of the mold can be transferred to the glass lens with high precision.

In the following, specific examples of molding conditions in the molding method using the above-mentioned molding apparatus will be given as Example 1.2.

Example 1 In the method of molding a glass lens 30 in the molding apparatus, SF8 is added to the glass gob 32 as the glass material.
(transition point: 443°C), and heated this glass gob 32 at 483°C for 5 minutes in the preheating furnace 17, and softened it by heating at 640°C for 5 minutes in the heating furnace 16.
It was carried between the upper and lower molds 2 and 3, which were maintained at a mold temperature of 400°C, and press-molded for 1 minute at a press pressure of 110 kgw/cm2, then the press pressure was reduced to 40 kgw/cm2, and the mold temperature was reduced to 6°C/sin. Raise the temperature to 460℃ at a rate of
20℃/sin 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.
The glass lens 30 was molded by lowering the temperature to room temperature. FIG. 4a shows the reflected wavefront of the glass lens 30 immediately after press molding at the mold temperature of 400° C. for 1 minute, and FIG. 4C shows the reflected wavefront of the molding surface of the mold 1. FIG.

From the figures in FIGS. 4A to 4C, changes in the transfer condition during the molding process of the glass lens 30 can be seen, and it can be seen that the molding surface of the mold 2 is transferred with high precision.

When molding the glass lens 30 using the molding apparatus, press molding is performed in a non-oxidizing atmosphere. Molding is performed in a non-oxidizing atmosphere by introducing nitrogen or a hydrogen-nitrogen mixed gas.

Example 2 SF11 (transition point: 485° C.) was used as a glass material using the above-mentioned molding device. The molding conditions at this time were to be heated at 525°C for 90 seconds in the preheating furnace 17, then heated at 525°C for 90 seconds.
Glass gob 3 heated at 680°C for 90 seconds in the main heating furnace 16
2 is carried between the upper and lower molds 2 and 3 kept at a mold temperature of 430℃,
After press molding for 30 seconds at a press pressure of 110 kgw/cm2, the press pressure was reduced to 55 kgw/cm2, and the mold temperature was raised to 490°C at a rate of 6°C/min.

When the mold temperature reaches 490'O, release member 4 is removed from the mold.
．． 5 and passed through the strain relief temperature range in the slow cooling furnace 15 for 15 minutes at 20°C/min.
The temperature was lowered to room temperature. The glass lens 30 thus molded was an optical glass member on which the molding surface of the mold was transferred with high precision, similar to the first embodiment.

[Effects of the Invention] According to the method for molding optical glass parts of the present invention, the melting of the glass to the mold, which was a problem with the prior art, can be solved by changing the mold temperature from below the transition point to 100°C above the transition point. This problem can be solved by maintaining the temperature in a low temperature range.Furthermore, the shrinkage problem can be solved by using a molding process in which the pressed glass lens is heated to a temperature close to the transition point after being made uniform with the mold temperature. It is possible to mold high-precision optical glass parts without folds or folds.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram of a molding apparatus used to carry out the method of the present invention, Figs. 2 and 3 are explanatory diagrams showing the glass lens molding process in the molding apparatus shown in the if diagram, and i4 Figures a and b.
, c are diagrams showing reflected wavefronts at the molding surface of the glass material and the molding surface of the press molding die in each molding process. 1...Mold for press molding 2.3...Upper and lower molds 4.5...Mold release member 14...Heating furnace 15...Learning furnace 30...Glass lens 32...Glass gob

Claims (5)

[Claims] (1) After heating and softening the glass material of the optical glass component and maintaining the temperature of the mold for molding the optical glass component within a temperature range from below the transition point of the glass material to 100 degrees Celsius lower than the transition point, The glass material after being heated and softened is carried into the molding die and press-molded in a non-oxidizing atmosphere, and the optical glass molded product after being press-molded in the molding die is placed into the molding die. A method for molding an optical glass component, characterized in that molding is carried out by raising the mold temperature of a molding die to around the transition point of the glass material while maintaining pressure, and then releasing the mold. (2) The optical glass component according to claim 1, wherein the glass material is made of SF8 and the mold temperature of the press molding mold is maintained at 400°C during press molding. molding method. (3) The optical glass component according to claim 1, characterized in that the glass material is SF11 and the mold temperature of the press molding mold is maintained at 430°C during press molding. molding method. (4) To raise the temperature after the press molding, when the glass material is SF8, after press molding for 1 minute at a press pressure of 110 kg/cm^2, the press pressure is reduced to 40 kg/cm^2, and the mold temperature is increased. 6℃/min
A method for molding an optical glass component according to claim 1, characterized in that the molding is carried out by raising the temperature to 460° C. at a rate of . (5) The temperature increase after the press molding is such that the glass material is heated to SF11.
In this case, after press molding at a press pressure of 110 kg/cm^2 for 30 seconds, reduce the press pressure to 55 kg/cm^2 and raise the mold temperature to 490 °C at a rate of 6 °C/min. 2. A method for molding an optical glass component according to claim 1, wherein the molding is performed by: