JPS62207837A - Metal mold for forming optical glass device - Google Patents

Abstract

PURPOSE:To obtain a metal mold for forming capable of forming an optical device which is free from sticking of foreign matters and has optically smooth forming surfaces, by forming at least the forming surface of a Co-base alloy principally composed of prescribed weight ratio of C, Ni, W, and Cr. CONSTITUTION:In the metal mold for forming of this invention, at least the forming surface is formed of the Co-base alloy containing, by weight ratio, <=0.1% C, 5-20% N, 10-15% W, and 18-24% Cr as principal components. Accordingly, in said forming surface, defects of conventional metal mold materials for hot forming are improved, and said surface has a degree of smoothness comparable to that of glass formed by polishing work and, moreover, by use of this metal mold, high-quality optical glass devices with high transparency can be hot-formed industrially and continuously in large quantity with obviating the necessity of grinding and polishing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a mold used for molding an optical glass element such as an optical lens.

[Prior Art] Optical glass elements have conventionally been molded mainly by polishing, but this has resulted in poor molding efficiency and high costs. For this reason, it has been proposed to use hot forming instead of polishing, which makes it possible to form high-quality optical glass elements with shapes and structures that are impossible with conventional polishing methods. It has also become possible to significantly reduce manufacturing costs.

Although it is disclosed in Japanese Patent Publication No. 56-11624 that an optical glass element is formed by hot forming, the S-dense surface shape and surface required for image-forming optical lenses are particularly difficult to solve due to problems such as mold releasability. characteristics have not yet been fully achieved. This is because the mold releasability largely depends on the wettability of the glass resulting from the material of the mold used for hot forming.

Recently, the use of molds made of glassy carbon, tungsten alloys, or quartz glass has been proposed in U.S. Pat.
No. 596 and Dutch Patent No. 80030, and US Pat. No. 316.861 discloses the use of a mold made of 5US400 stainless steel.

However, when molding high-quality optical glass elements using molds made of the various materials mentioned above, the following drawbacks occur, so that they cannot actually be used as molds.

(1) Due to poor oxidation resistance, a non-uniform oxide film is likely to be formed under Km atmospheric conditions. In addition, phenomena such as coarsening of crystal grains and progress of grain boundary reactions occur. Due to these effects, the mold surface loses its smoothness within a short period of time and becomes wavy from a macroscopic perspective, resulting in a rough surface known as yuzu skin.

(2) In the case of a mold surface with low hardness, mirror polishing is difficult and mold flaws are likely to occur during hot processing.

(3) Amorphous materials, especially glassy carbon types, are structurally weak, have low thermal conductivity, and have low fracture impact resistance. On the other hand, quartz glass has wettability to the same glass and has low thermal conductivity. In any event, these materials are undesirable for use in hot forming.

As mentioned above, hot forming using molds made of conventional materials shortens the life of the mold because it tends to get wet with the glass, and the surface of the glass molded product can be damaged by the peeling and mold scratches that occur in a short period of time. Naturally, it cannot be used in a mold that satisfies the surface characteristics required for optical glass elements.

In addition, these molds require repeated mold replacement many times during actual operation, which hinders work efficiency and requires great consideration in mold management.

Therefore, there is currently a strong demand for the development of mold materials that have desired glass molding properties and have improved structural and thermal properties.

[Object of the invention] The present invention improves the various drawbacks of the conventional hot molding mold materials described above, and produces a high-quality optical glass with high transparency and smoothness comparable to glass formed by polishing. It is an object of the present invention to provide a mold material that can industrially hot-form multiple elements continuously without grinding or polishing.

[Structure of the Invention] In order to achieve the above-mentioned object, we focused on a cobalt-based alloy that has excellent physical properties such as oxidation resistance, incompatibility with glass, and maintenance of mirror-like state after long-term heating at high temperatures. As a result of various experiments with different component ratios, the weight ratio was C50.1%, Ni: 5-20%, W: 1G-15.
%, Cr: 18-24% as a basic component, and Ta: 0.1-10%, Nl) as a selective addition component.
: 0.05-5%, V: 0.05-5%, 13e
: 0.01~2%, La: 0.01~4%,
Cobalt group containing at least one selected from the group consisting of 1yln: 0.5-3%, 3i: 0.1-2%, and Fe: 1-4%, with the remainder consisting of Co and inevitable impurities. We have discovered that alloys have a remarkable effect on improving properties as mold materials.

That is, at least the molding surface of the mold for molding an optical glass element according to the present invention is formed of a cobalt-based alloy having the composition range described above.

Next, the reason for limiting the range of each component of the cobalt-based alloy used in the present invention will be described.

C≦0.1% When C exceeds the above range, oxidation resistance deteriorates.

Ni: 5-20% Ni provides non-compatibility with glass in the molding material,
Outside the above range, the mold releasability is reduced.

W: 10-15% W is effective in maintaining heat resistance and high-temperature hardness, and is effective at 10%, but when it exceeds 15%, cold and hot workability is significantly inhibited.

Cr: 18 to 24% Cr is effective in refining crystallinity and improving oxidation resistance.
%, the effect appears, and when it exceeds 24%, the oxidation resistance deteriorates.

Selective addition components (Ta, Nb, V, Be, La
.

Mn, Si, Fe, Mo) Mn improves the hot workability of the alloy and acts as a deoxidizer at 1%
Add the following.

Ta is effective in improving Ts temperature hardness and age hardenability, and even when heated at high temperature for a long time, the structure change of the material has an outstanding effect on improving heat resistance.

Nb is also similar to the above Ta.

(2) is effective in refining crystal grains, and the uniform and fine structure is useful for mirror polishing glass molds.

MO is also effective in improving the incompatibility with glass, and 0.1%
The effect is demonstrated above.

[Example] The invention will now be explained with reference to the drawings.

FIG. 1 shows an example of a molding die of the present invention, which comprises an upper mold 1 and a lower mold 2, which are entirely made of a cobalt-based alloy. When the entire body is made of a cobalt-based alloy as in the illustrated example, each molding surface 1a.

2a may be processed by grinding, polishing, etc. to obtain a desired curved surface and smooth it. In the figure, 3 is glass softened by heating.

FIG. 2 shows another example of the molding die of the present invention. In this example, after the upper mold 4 and lower mold 5 of the mold are formed of a cobalt-based alloy material with an appropriate composition, a nitride is coated by a chemical vapor deposition method or a physical vapor deposition method, and the H of the nitride is Membrane layer 6
, 7. The molding surface made of this nitride 1111118.7 reflects the surface condition of the base and can of course be used as a mold surface as is, but if necessary, it can be processed by grinding, polishing, etc. The quality may be further improved. Furthermore, after forming the upper mold 4 and the lower mold 5 from a ceramic material, a cobalt-based alloy is applied to the mold by ESR.
(Electroslag) The molding surface may be formed by a melting method.

Fig. 3 shows a simple schematic diagram in which the wetting of flint-based glass to the mold was examined to determine the releasability from the mold, which is one of the important features of the mold according to the present invention. .

In this case, the wetting angles between the cobalt-based alloy forming surface 8 and the heat-softened glass 9 are θ1(a) and θ2(b), and θ1
〉90°, if θ2<9(1''), it is considered to be a failure.

Next, in order to compare the wetting of the molding surface of the present invention and the conventional mold, nitrogen or a mixed gas of nitrogen and hydrogen (6:1) was introduced at a rate of 71/min and maintained in a non-oxidizing atmosphere. When the heating furnace was heated at a temperature increase rate of 2° C. per minute, the contact angle due to wetting of the flint glass against the molding surface made of various materials of the mold placed in the heating furnace was measured. The measurement results are shown as a graph in Figure 4. ``As is clear from Figure 4, the mold with the molding surface made of the cobalt-based alloy according to the present invention has a wider temperature range than those of stainless steel and quartz glass. It was found that the wetting angle θ was large over the range, and it was difficult to get wet. It has also been found that when a mixed gas of nitrogen and hydrogen is used as the atmosphere, the wetting angle θ is less dependent on temperature and it is easier to release from the mold.

Next, in the hot forming process of glass, oxidation resistance is a particularly important factor because it directly affects the surface quality of the glass. Therefore, in order to confirm this property, we conducted an oxidation resistance test in high-temperature air using a known heat-resistant steel (StJ
H309) and stainless steel (SUS 304).

The experimental conditions were 800'Cx 1GG11? flfl Ren M
heating? The average oxidation increase of five each was measured. The sample dimensions and shape are 2011X 10IIX 211m (horizontal
The entire surface was finished with 1000# paper (length x height). The composition of the experimental samples and test results are shown in Table 1 below.

Note: Cobalt-based alloy (A) is C: 0.1%, Ni: 2G
%, W: 14.5%, Cr: 24%, La: 1%, and the balance is Co, and the cobalt-based alloy (B) is C:
0.1%, Ni: 2G%, W: 14.5%, Cr: 24
% and the balance is Co.

From Table 1, it can be seen that the cobalt-based alloy according to the present invention has the least oxidation weight gain and excellent oxidation resistance. Furthermore, it has become clear that the oxidation resistance is more than 220 times better than other materials. In any case, it can be seen how excellent the oxidation resistance of the cobalt-based alloy according to the present invention is, even when compared with the oxidation weight gain of Material 5US309 and Material 5US304, which were tested as references. Furthermore, the cobalt-based alloy according to the present invention containing La had slightly better oxidation resistance.

As a result, the cobalt base metal used in the present invention has excellent oxidation resistance, does not oxidize when used at temperatures up to 800°C, and has good roughening resistance.

From the above results, the cobalt-based alloy according to the present invention has excellent mold releasability, mirror workability, and roughening resistance, and these physical properties are more preferable as a mold material than conventional metal molds.

Next, nitrogen gas is introduced into the heating furnace at a rate of 3/min to maintain the inside of the furnace in a non-oxidizing atmosphere, and the temperature of this heating furnace is increased to 40°C.
A mold with a molding surface made of a cobalt-based alloy is placed in this heating furnace while being maintained at 0°C, and a flint-based glass lump that has been brought to a temperature suitable for molding in a separate furnace is transferred to the mold.
Optical glass parts were molded.

No foreign matter was observed on the surface of the optical glass component thus obtained, it had a fire-polished appearance and an extremely good surface area.

On the other hand, the surfaces of optical glass parts obtained by molding with conventional molds have foreign matter attached to them and many irregularities, making them unusable as is and requiring finishing work. Ta.

Further, after using the mold having a molding surface made of the cobalt-based alloy according to the present invention several thousand times, the condition of the molding surface was examined, and no change was observed in the surface.

[Effects of the Invention] According to the present invention, a mold in which at least the molding surface is formed of a cobalt-based alloy having excellent properties for molding optical glass parts is used as a mold for molding an optical glass element. Therefore, it is possible to mold an optical glass element having an optically smooth molding surface to which foreign matter does not adhere. Therefore, it is possible to omit post-processing of pressure molding of an optical glass element, which was conventionally required, thereby simplifying the process and having an effect that can greatly contribute to cost reduction. Furthermore, when an optical glass element is hot-formed using the mold according to the present invention, the surface quality of the molded product is significantly improved, and furthermore, this quality can be stably imparted even when continuously molded in large quantities. can.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing an example of a mold for molding an optical glass element of the present invention, the entire mold of which is made of a cobalt-based alloy, and Fig. 2 is a mold for molding an optical glass element of the present invention whose molding surface is made of a cobalt-based alloy. Cross-sectional view showing another example of the mold, Figures 3a and b
FIG. 4 is a schematic diagram showing the wetting of the flint-based glass to the molding surface, and FIG. 4 is a graph showing the temperature dependence of the wetting angle of the flint-based glass with respect to cobalt-based alloys, quartz glass, and stainless steel. 1.4... Upper mold 2.5... Lower mold 1a, 2a...
・Molding surface 3: Glass softened by heating

Claims (2)

[Claims] (1) In terms of weight ratio, C≦0.1%, Ni: 5-20%,
A metal for molding an optical glass element, characterized in that at least a molding surface is formed of a cobalt-based alloy containing W: 10 to 15%, Cr: 18 to 24% as basic components, and the remainder consisting of Co and inevitable impurities. Type. (2) The molding surface of the molding die is formed by coating a thin film layer of nitride on the surface of a mold body made of an appropriate cobalt-based alloy depending on the glass material. A mold for molding optical glass elements.