DE1596429C - Process for the production of optical elements by hot pressing - Google Patents

Description

The invention relates to a method for the simultaneous production of several transparent polycrystalline optical elements made from uncompacted crystalline powders of inorganic compounds.

It is known individual ones that are transparent to infrared rays optical elements made from uncompacted crystalline powders of inorganic compounds by hot pressing Manufacture by placing the powder at a high temperature below the melting point and subject to high mechanical pressure while they are enclosed in a die. It has has shown that under certain conditions of temperature and pressure it is possible to use "i inorganic powders

ίο to a greater_ density 'than 99% "of the theoretical Density of a "single crystal of the same material to condense, so that the resulting polycrystalline Element for infrared rays and usually also for visible light is permeable

So far, individual elements of such a thickness have always been produced by hot pressing, the larger ones than the thickness of the optical elements desired as final products is the obtained thick, hot-pressed one The blank was then sawn into several thinner elements, which then became the desired elements Size have been processed. A hot-pressed blank with a diameter of 15.24 cm and a thickness of 1.27 cm can be used, for example, to produce individual pieces 0.254 cm thick.

_2J - saws, grinds and polishes. This technique has been used to create both flat disk elements and elements that are in the form of hollow domes or caps. Although this method works satisfactorily in itself, it has certain disadvantages, such as high costs, long production times and the great effort that it requires in order to subdivide the thick starting blanks into thin elements for the subsequent optical finishing. In addition, there is a not insignificant amount of valuable crystalline. Material lost in the sawing process.

The object of the invention is therefore to create a method according to which it is possible simultaneously produce several transparent optical elements in a reasonable time and without major losses to separate from each other in crystalline material.

The invention relates to a method for the simultaneous production of several transparent polycrystalline optical elements made of uncompacted, critical

4j stalline powders of inorganic compounds, so that

"" is characterized by the fact that the powders are made into a stack of several loosely on top of each other.

- Between the blanks having a density of less than 99% of the theoretical density for every two adjacent blanks a layer of separating material that cannot be mixed with the blanks inserts that the stack is hot-pressed under such temperature and pressure conditions that the The density of the blanks after hot pressing is above 99% of the theoretical density and that the obtained elements separates from each other.

The stacks are hot-pressed in a hollow mold using a mechanical or manually operated ram or plunger.

The invention achieves that at the same time several individual elements that approximate the correct one Thickness for the element desired as the end product, can be produced in a reasonable time can without the need to saw the elements as in the previous methods consists

To carry out the method of the invention

all inorganic compounds that have already been successfully hot-pressed before are suitable. Called be for example:

Magnesium fluoride

Zinc sulfide

Calcium fluoride

Zinc selenide

Magnesia

Cadmium telluride

Lanthanum fluoride

Cadmium sulfide

Zinc oxide

Strontium fluoride

Titanium dioxide

Canadian Patent 646,436 U.S. Patent 3,131,025 Canadian Patent 701,845 Canadian Patent 688,568 U.S. Patent 3,236,595 Canadian patent 731,706 French patent 1,476,277

U.S. Patent 3,206,279 Canadian Patent 723,556 Canadian Patent 706,800 Canadian Patent 727,530 U.S. Patent 3,459,503.

10

15th

The optimal temperature, pressure and time conditions are listed in the references listed above for each particular compound. In general, temperatures above 500 ° C. and pressures above 665 kg / cm ² are expediently used

The drawing serves to explain the invention in more detail.

Fig. 1 is a schematic partial vertical view Level, partly in elevation, through a device for cold pressing powders into blanks less than 99% of theoretical density, which are then stacked and hot-pressed;

F i g. 2 is a schematic partial view in a vertical plane through a device for hot pressing a stack of flat blanks and

Fig. 3 is a schematic partial vertical view Plane through part of a device for hot pressing a stack of arched Blanks.

According to FIG. 1, a mass 11 consists of an uncompacted Powder of an inorganic compound introduced into the cavity of a die 13, whereupon by means of a ram 15 pressure is exerted, which the powder to a flat disc 17 of substantially, lower density than the original powder. The temperature can Be room temperature. However, the mold can also be heated, although this is of no particular advantage located. Instead of a single blank, it is also possible to use several at once in one die with multiple cavities and cooperating plungers. The expression "Cold pressing," as it is used here, means that the temperature used in the pressing process is much lower than the temperature used later during hot pressing, so that the resulting Blanks are not transparent, but opaque and a. Have density well below 99% of the theoretical density

The cold pressing can be done quickly and the individual blanks can, as well as them are removed and then stacked in axial alignment for hot pressing. Around To avoid the blanks from melting together, a layer of one is made with the material of the Blanks immiscible separating material 19 introduced between adjacent blanks (Fig. 2). In Advantageously, the separating material is also attached under jund_ over the blanks in order to achieve a to ensure easy separation of the stacks from the hot-pressing device. The stack can then be transferred to the Cavity of a mold 21 are inserted within a furnace 23, during the pressing process is electrically heated. . .

A ram or plunger 25 is applied to the top of the stack desired pressure is brought about by downward movement of the plunger or plunger. Preferably an inert atmosphere is maintained within the furnace 23, which is achieved by applying a vacuum through line 27 or by introducing an inert gas such as argon through the same line can be done.

If necessary, the stack can also be placed inside the compression mold by alternately introducing separating materials and blanks can be built.

The in F i g. 3 is operated in the same way. A pile of cold-pressed, 'Trough-like curved blanks 31, interspersed with spacers 32 within a The mold 33 is pressed with an upwardly directed concave bottom 34. The pressure piston 35 has in this Case a convex end which is adapted to the mold.

■ The spacers 19 and 32 can be made of any suitable material that the separation of the blanks and allows them to stick together at the high temperatures and pressures of the Prevents hot pressing. Suitable materials consist, for example, of metal, paper and graphite. Suitable metals are copper, molybdenum, titanium and stainless steel. Also can be a decomposable material such as paper, as the residue obtained by charring also causes separation. Ceramic materials such as sintered aluminum oxide can also be used, and with or without mold release agents, such as a colloidal carbon suspension.

Instead of using special spacers, the cold-pressed blanks can also be used individually a surface coating of a release agent, e.g. a colloidal carbon suspension which can be applied by spraying, brushing or plating. This can in particular be advantageous when processing complex structures, z. B. in the case of hollow structures, e.g. B. hollow domes, where the total volume of the uncompacted charge compared to the compacted charge. Dispatch differs in an unsymmetrical manner by a factor of four or five. Since formed Spacers made of metal or the like. For complex structures are quite expensive, surface coatings are used preferred in these cases

Instead of a special compression of the powder by cold pressing, compression can be preferred in the same mold 13 or 33 in which the hot pressing is carried out. If ν If flat disks are made, the correct amount of powder for a blank is poured into the mold 13 introduced and then compressed by the introduction of a pressure piston which is put into action by hand can be. Then a spacer 19 is placed on the surface and another batch of the Powder introduced onto the surface of the spacer and compacted. These measures are

alternately repeated until the desired size of the stack has been obtained. Then the hot pressing, carried out as described above.

In a further preferred embodiment, the powder fillings are in the hot press mold 13 or 33 by mechanical actuation of the ram or the plunger 15 instead of the above Compression described by hand. This is particularly advantageous in the manufacture of Elements in the form of hollow domes, which are advantageously secured by a mold release agent, e.g. one colloidal carbon suspension that is brushed or sprayed onto each blank, from each other be separated. ~

Without the initial formation of loosely packed blanks, it is almost impossible to obtain Finally, hot-pressed elements of the required exact shapes and sizes to ensure. Without this important step, the special spacers in the die become angular and the end product is thicker on one side than the other.

In addition, if the spacers are angular, the various elements can fit into one another Come in contact and melt together. In addition, when a surfactant is used, a solid surface for the formation of a continuous Coating, in order to maintain the separability of the elements, essential.

Expediently, all the inner surfaces of the molds and the The end of the plunger is coated with a mold release agent, e.g. a colloidal carbon suspension.

The following examples are intended to explain the process of the invention in more detail.

example 1

80 g of magnesium fluoride powder with a particle size of less than 0.10 mm are introduced into a cylindrical mold 13 with a diameter of 9.14 cm and ^{cold-pressed at room temperature at a pressure of 352 kg / cm 2} to give a body with a thickness of 0.762 cm Nine of these cold-pressed blanks are then stacked with stainless steel cutting disks 0.254 mm thick placed between the individual blanks. Other disks of the same material are placed on the bottom of the mold 21 and on top of the stack.

The furnace 23 is heated to 704 ° C. Then the pressure piston 25 is pressed onto the stack of blanks ^{at a pressure of 2110 kg / cm 2.} A vacuum is applied through line 27 and the hot press conditions are maintained for 30 minutes after which time argon is introduced through line 27 and the furnace is allowed to cool to room temperature. '

The stack of blanks is then removed from the Taken from the shape. The individual blanks are separated from each other and from the spacers 19, whereupon they can be processed further.

of the cold pressing of 200 g batches in the mold 33. The surfaces of the blanks were each after withdrawing the plunger 25 and ■ before introducing the next batch with a suspension coated with colloidal carbon.

. After the surface of the last blank was painted, the plunger became again

■ introduced and the oven and its contents were heated to 704 ° C. At the same time, a mechanical pressure of 2110 kg / cm ^{2 was} applied for 30 minutes while a vacuum was created in the oven. The furnace was then allowed to cool, whereupon the vacuum was released by introducing argon and the stack was removed from the. Shape by removing the cylindrical part of the

υ shape was taken. The individual domed parts were then separated from one another.

Example 3

Using the ■ in Fig. 2 shown advantages device 2 zinc sulfide discs with a diameter of 16.51 cm by successive. the cold pressing of 500 g batches of zinc sulphide powder with a particle size of less than 0.075 mm at 2110 kg / cm ² , the surface of the first blank being coated with a suspension of colloidal carbon after the plunger was withdrawn and before the second batch was introduced .

After the second batch was cold pressed, the oven and its contents were heated to 899 ° C and allowed to glow through for one hour. A pressure of 2110 kg / cm ^{2 was then} applied and maintained for one hour while maintaining vacuum. The furnace was then cooled, argon introduced, and the hot-pressed disks removed and separated

Example 4

Using the apparatus of FIG. 2, three calcium fluoride disks with a 17.78 cm in diameter by sequentially compacting 500 g batches of a particulate. size of less than 0.25 mm with a manually operated plunger. Separating disks were used 0.635 cm thick of solid graphite on the surface of the first and second blanks applied after their manufacture.

Then the plunger 25 was inserted into the mold. The furnace and its contents were heated to 871 ° C. A pressure of 2100 kg / cm ² was immediately applied and maintained for 1 hour. The furnace was then cooled and the vacuum was released by introducing argon. The stack of elements was then removed by first removing the cylindrical portion of the mold. The individual elements could easily be separated from each other and from the graphite disks ..

Example2

4 caps made of magnesium fluoride with a diameter of 7.62 cm were successively

Example 5

There were two discs made of zinc selenide -with made with a diameter of '17.78 cm',

7 '8

placing a 0.635 cm thick graphite disc on the 0.635 cm thick at the bottom of the mold (under

Brought the bottom of the mold 21, a 1000 g batch of the first blank) and placed on the upper blank

Zinc selenide powder with a particle size below

0.075 mm in the mold on the disk, the oven and contents were then heated to 871 "C

Powder by actuating a plunger of J and allowed to glow through for 5 minutes, followed by a

Compressed by hand, a second graphite disc was applied to the pressure of 1410 kg / cm ² for 1 hour

Surface of the first batch and this one was. "_. _

Process with a second 1000 g batch, addition The following steps correspond to those in

a third graphite disc, and introduction of the above examples.
Pressure piston 25 in the form and on the upper graph
phit disc was repeated.

The oven and its contents were then based on Example 7
1204 ⁰ C heated, whereupon glow through for 1 hour

was left. Then a mechanical pressure was applied successively two batches of 150 g

of 1760 kg / cm ² applied and for 30 minutes 15 cadmium telluride powder with a particle size of

maintain. below 0.075 mm at a pressure of 352 kg / cm ² in

Then, as in the above two, a mold 21 with a diameter of 10.16 cm

play described, procedure. cold-pressed, one on both sides with one

colloidal carbon suspension coated mo-

20 lybdenum discs with a diameter of 10.16 cm

Example 6 and a thickness of 0.051 cm on the surface

of the first blank was applied before the

In succession, four 100 g batches were introduced from the second batch.

Formed magnesium oxide of a particle size ten of the blanks were made by heating

of less than 0.075 mm and a content of 1% lithium furnace and contents to 788 ° C anneal select-

umfluorid at a pressure of 211 kg / cm ² in about 15 minutes and then applying a

Form 21 with a diameter of 7.62 cm cold pressure of 1760 kg / cm ² hot for 30 minutes

pressed, one pressed onto the surface of the blanks.

The following steps correspond to those in the

was chen. In addition, graphite disks of one of the above examples were described.

1 sheet of drawings

209527/346

Claims (10)

Patent claims: 1. A method for the simultaneous manufacture of a plurality of transparent polycrystalline optical elements made of uncompacted, crystalline powders of inorganic compounds, characterized in that that from the powders a stack of several loosely stacked one on top of the other, one Density. Of less than 99% of the theoretical density having blanks forms, between each two adjacent blanks a layer of separating material that cannot be mixed with the blanks inserts that the stack is hot-pressed under such temperature and pressure conditions that the density of the blanks after hot pressing is above 99% of the theoretical density and that the elements obtained are separated from one another. 2. The method according to claim .1, characterized in that the organic compound magnesium fluoride, Zinc sulfide, calcium fluoride, zinc selenide, magnesium oxide, cadmium telluride, lanthanum fluoride, Cadmium sulfide, zinc oxide, strontium fluoride, titanium dioxide or cadmium selenide are used. 3. The method according to claim 1 or 2, characterized in that there is a separating material Sheet or foil used. 4. Process according to claims 1 to 3, characterized in that the separating material is in Liquid form applied to the surface of the blanks. 5. The method according to claims 1 to 4, characterized in that the blanks in a Introduces hollow shape and pressed therein by means of a ram. 6. The method according to claim 5, characterized in that layers of the release material arranged between the ram and the stack and between the surface of the hollow mold and the stack. 7. Process according to claims 1 to 6, characterized in that the hot pressing is carried out at a temperature above 500 ° C and at a pressure above 665 kg / cm ² . 8. The method according to claims 1 to 7, characterized in that one for hot pressing The blanks used are produced by cold pressing of crystalline powders. 9. The method according to claims 1 to 8, characterized in that the individual blanks by successively introducing individual batches of powder to be compressed into a hot press mold, successive cold pressing of the individual batches and introduction of layers of release material after cold pressing a batch and before the introduction of the next batch forms. 10. The method according to claims 1 to 9, characterized in that blanks are used, which have the shape of discs or hollow domes.