How telescope glass is made. Optical glass factory report

In the 17th century, Galileo was the first to direct a telescope into the sky and turn it into a telescope. We are now receiving signals from distant galaxies, discovering new stars and studying dark matter. "Cherdak" visited the Lytkarinsky optical glass plant of the "Shvabe" holding and found out how to create optical glass for telescopes and not only. The plant produces glass for laser systems, aerospace monitoring, medical technology and scientific instruments. What is the difference between optical glass and ordinary glass, what it consists of, how it is cast and what happens at the next stage of processing, see the report.

Mikhail Gulyugin, head of the optical glass melting bureau:

- Optical glass occupies a certain niche in the production of all glasses in general, and it is very important, because practically no production can do without the production of optical glass, without the products in which it is used. In particular, all television equipment, photographic equipment, computer equipment - elements with the use of optical glass are used everywhere.

Unlike ordinary glass, which is widely used in our construction, in everyday life, optical glass has a number of specific requirements for its properties. It has high transmittance, high requirements for the quality of glass, that is, the absence of any foreign inclusions that can affect the images we receive from optical glass products. The very process of production of all glasses in general (and optical glass as well) begins not in this workshop, but far from here. It begins at the deposits, where the raw materials are mined, from which we then get glass. In the production of optical glass, the purest component is used, a mineral that contains silicon oxide. It is veined quartz. In the future, it is processed, and we get either quartz grit or quartz flour. We can get ready-made such material (in the form of quartz grains or quartz flour). In addition to quartz-containing raw materials, other materials are used. For example, it can be soda (sodium carbonate). It can be carbonate salts such as calcium carbonate, chalk. There may be magnesium carbonate and other components. Also materials containing aluminum oxide (Al2O3), alumina and so on. But in the production of optical glass, as a rule, extremely pure materials are used - of high purity. The initial mixture of these raw materials is called "charge". From this mixture, we subsequently receive glass.

Cooking takes place in batch-type pot-type gas ovens. The name itself ("pot" and "gas") already says a lot. "Pot" means that cooking takes place in a pot. Well, the pot is actually quite large, with a volume of 500 or 700 liters, made from a special refractory material - chamotte. It is placed in a natural gas fired glass furnace. The temperature in the oven reaches 1550 degrees. In addition to the raw materials, which I spoke about, when melting optical glasses, the so-called battle is added in a fairly large amount. This is a good homogeneous glass left over from the processing of previously obtained glasses. These battles are necessary in order to reduce consumption, say, to switch to waste-free production. Initially, fights are poured in order to coat the pot, protecting it from the action of the mixture, which later melts in this pot. Then the charge is poured. As a rule, the mixture is poured to a certain level in the pot, then battles are added on top. This mixture should melt. It melts, takes up part of the pot, and after it has melted, the mixture and fights are again added to the pot. This process continues until the pot is completely filled with silicate or glassy melt. It's not glass yet. It's just melt.

Next comes the process of clarification and homogenization. It takes place at a higher temperature. After we have passed all the processes (i.e. clarified and homogenized the glass), we take a sample and see the quality of the glass. What exactly are we watching? Clarification, the presence of bubbles, what optical constants are present - in particular, the refractive indices. Does it match or not? If this glass meets all the requirements, the so-called "closing of the brew" takes place, and our pot in the oven, together with the molten glass, slowly cools down in a certain mode to a temperature when it can be removed from the oven and cast into a mold. If the temperature is higher, the glass will be liquid. When we pour it out, it will pour out like water, and as a result we will get the so-called "marriage" in the form of a string, which should not be allowed. If it is thick, then we cannot just pour it out. Technologically, these are all temperatures, all the time determined - both theoretically and experimentally. These modes are individual for each brand of glass. And, as I have already told you, we have about two hundred marks. Do you see how complex all these processes are?

Further, when the glass is ready for us, in order to remove it from the oven, we raise the stirrer device. The stirrer is removed from the pot. A cartoon crane is suitable. After we raise the damper, a cartoon crane comes in and grabs a pot of glass with pliers - and leaves the oven. Remove the screed. The screed is the top layer of glass, which will be cold when it cools. Like everything that cools down and has a large capacity, there are cold layers on the outside, and hot on the inside. To ensure that the layers are uniform in temperature, remove this upper cold screed. Plus, there may be some inclusions in this layer. Maybe a tiny bubble floats on the surface; as if they clean the glass melt. And then it goes to low tide.

It is made into shape. There are different shapes: it can be square, rectangular. The height of the mold is also different, depending on the customer. For example, usually it is 140-150 mm (up to 200 mm). For windows of radiation-biological protection, a greater thickness is required. That is, the shape is smaller, but thicker.

So, a faucet with a pot fits into the mold, is set at a certain level, turns over - and the glass is poured into the mold. The form is preheated. After that, the pot is put back in the oven. And this process of cooking and pouring in a pot - depending again on the composition, on the aggressiveness of the glass that we are brewing - can reach 12 times. Maybe less.

Mikhail Gulyugin, head of the optical glass melting bureau:

- After we have molded the glass into a mold, it cools down with us. But if we leave this glass to simply cool in air to ambient temperature, then, unfortunately, we will not get a finished product. During the cooling process, stresses will arise in the glass layers, which will lead to its spontaneous destruction. The glass can simply crack, break into small pieces, with which we can no longer get anything. This effect is not unique to optical glass. The appearance of internal stresses during cooling is typical for all glasses.

To ensure that our glass does not break down, we carry out a special heat treatment. This is, say, cooling according to a certain mode. It allows us to remove the voltage that can arise in the glass and, as a result, get a block at the output from which we can make something, then send it for processing and receive the product. This is a special directional cooling process called "annealing" and can take two to three weeks for blocks.

There is also a process called fine annealing. The fact is that each of those glasses that we cook must have certain optical characteristics. As I already mentioned, these indices include refraction, dispersion, and others. We also need to obtain such a result (to anneal the glass, to cool it this way) so that these constants remain constant over time. The structure must reach an equilibrium state - the most compact in order to obtain the most stable values of optical constants. Thus, we have preliminary annealing and optical annealing. As I already mentioned, preliminary annealing can take two or three weeks. Optical annealing can take a month or longer.

After we have annealed, cooled our block to ambient temperature, the furnace in which this block was located rises. We extract the block. Then this block is accepted by the Quality Control Department (technical control department), samples are taken, all the necessary indicators are checked. And after it turns out that our workpiece meets the requirements, we send it further to other workshops, to other areas for cutting and preparation for processing in order to get a finished product out of it. It can be cutting, grinding, polishing, and so on. This is done in other workshops.

See, the corner of this block has been broken off? At first glance, you might think that this is a marriage. In fact, this is an operation that is standardized and necessary in order to determine the properties of a given block. We can look at it, visually evaluate it. This assessment is mandatory. The presence of any inclusions is checked - gas, crystalline, and so on. But in addition, we need to evaluate such optical characteristics as refractive index, dispersion, transmission, radiation resistance, and others. We must somehow characterize this block.

How can I do that? Of course, you can take it, cut it all up and saw it. What if it doesn't suit us? We will carry out some additional operations that will go to us at a loss. All glasses that we produce comply with GOST. There is a GOST for optical glass. There is an OST for optical glass. All brands of glass are produced in accordance with these regulations. Our enterprise is the only one in the Russian Federation that produces optical glass, and is part of the innovation holding "Shvabe".

Source: https://tass.ru/