Today, people are actively using glass for a variety of purposes. The glass melting process itself is the smelting of raw materials or of a charge. Glass melting furnaces are used to melt the material. They come in many forms and are classified according to several criteria.
What is a charge?
It is important to note here that the glass melting process is already one of the last stages of production. The mixture supplied as a material for manufacture is already enriched raw material. Of the main elements, this includes quartz sand, soda, limestone. As additional impurities, dyes, illuminants or darkers are used. In addition, the mixture, which enters the furnace, has the desired percentage of moisture, the required consistency and uniformity of mass.
Features and arrangement of the furnace. Pool
A glass melting furnace is a special device designed to melt a charge. Gas can be used as fuel, solid fuel can be burned, and there are also electric stoves. It is worth noting that despite the variety of species, all furnaces have approximately the same device. The main elements of a glass melting furnace are a pool, a vault and a fiery space.
The pool consists of a bottom and sides. It carries out the cooking of the mixture, the process of clarification of the material, cooling, and the direct production of glass. If we talk about the classification of glass melting furnaces by the device of the pool, then there are systems with a common pool. They lack division into several zones. There are also completely opposite to them the arrangement of the pool with clearly delimited areas. Such baths have a zone where cooking and lighting work takes place, and it is called heated. A zone with cooling and working out is called a development zone.
In the heated part of the bath of the glass melting furnace there is a fiery space located between the walls and the arch. It is characterized by the presence of openings for the supply of fuel and air, as well as for the removal of hot gases that occur during the combustion of fuel.
Masonry bath and precautions
During the construction of glass melting furnaces, particular attention should be paid to the vault of the bathtub. It must be laid out of a special refractory brick called dinas.
A suitable brick can only be considered one that at least 93% will consist of a material such as silica. The thickness of the walls of the bath should be 500-600 mm, and the thickness of the arch 300-450 mm.
Due to the fact that the process of cooking the mixture in glass melting furnaces takes place under the influence of very high temperatures, during this process various chemical reactions will occur, accompanied by the release of harmful steam. This led to the fact that one of the main precautions was the complete sealing of the interior of the furnace. In addition, in the workshops where glassmaking equipment is located, a special ventilation system should be equipped that removes all harmful impurities and other fuel combustion products from the air.
Speaking about ventilation systems, it should be noted that a similar design of smoke removal should be installed in the furnace itself. The difference between conventional ventilation and modular will only be that the modular is designed to maintain the necessary composition of air inside the equipment.
General description of the types of oven
Here it is worth starting with the fact that there are 2 classifications of furnaces.
The first of them divides all cameras into two categories, depending on the device of the working camera. It can be pot glass melting furnaces or bathtubs.
As for the second classification method, here the main criterion was the method of heating the glass melt. In this case, there are three main types - flame, electric and gas-electric methods.
Pot and bathroom equipment
Pot equipment is currently considered unprofitable. This is due to the fact that this type of furnace belongs to batch devices. Because of this, a large amount of heat, and hence fuel, goes first to the kindling of the furnace itself, and only then to the melting of the charge.
Glass melting bathtubs, unlike pot furnaces, are continuous devices. Naturally, the continuous process completely solves the problem of wasting resources on periodic heating of the furnace, spending fuel only on melting raw materials.
The oven by itself is a huge tank filled with molten tin. Due to the fact that the density of the glass melt will be significantly lower than the density of this metal, they will not mix with each other, being in the same container. Tin itself is used in furnaces for the gradual cooling of glass melt from a temperature of 1600 degrees Celsius to 600. This method and material were chosen due to the fact that during cooling by this method no internal stresses are created in the mass. Their occurrence will adversely affect the quality of the finished product, and therefore they should be avoided. It is also worth noting here that the glass mass is distributed evenly, allowing you to get a perfectly flat sheet.
Another advantage of using tin is the thermal polishing process during cooling. Through this process, strength and transparency are improved.
Flame melting furnaces
This type of furnace is considered the first and in it melting of glass is carried out by burning solid fuel. It should be noted here that the generated heat will be spent not only on heating the charge, but also on boilers for cooking, the efficiency will be low. In flame furnaces, the efficiency is 25-30%.
Electrical units
If we talk about efficiency, then today the first line will be occupied precisely by electric furnaces. Their efficiency reaches 60%, which is considered the highest rate to date. This is achieved due to the fact that electricity will be transmitted directly to the glass mass itself, heating it. Thus, it was possible to avoid unnecessary waste of energy on heating boilers and other things.
The principle of operation of this device is based on the fact that at high temperatures glass is able to conduct electric current. In this regard, depending on the method of heat transfer to the mass, three types of electric furnaces are distinguished: induction, arc, direct and indirect resistance.
However, this type of equipment also has a drawback consisting in the need for a reliable and constant source of cheap electric energy.
To transfer electric energy to the pool, where the charge for melting is located, electrodes are used. It is precisely because of the difference in resistance that heating occurs, and later melting of the glass melt. As for the electrodes themselves, they are usually made of graphite. This material is less susceptible to deformation under the influence of high temperatures.
Gas-electric furnaces
This type of device combines the principle of the two previous ones. Gas is used for heating the chamber and primary melting of the charge; liquid fuel is used much less frequently. For heating and melting the glass melt itself, the principle of electrical resistance will be applied. Most often, such furnaces are used if there is a need to increase the efficiency of a conventional flame furnace, but there is no source of cheap and constant electric energy.
At the end of the classification, it is worth adding that there are horseshoe-shaped glass melting furnaces. The direction of movement of the flame in such equipment may differ, and by this sign there are three small categories of devices, which include horseshoe-shaped ones. Their feature is that they are used, if necessary, to produce mineral and glass wool.
Repair of equipment
In the manufacture of glass, furnaces undergo quite severe wear, and therefore the issue of their maintenance is quite relevant. Repair of a glass melting furnace can be of three types: current, hot and capital.
As for the current repair, it is quite simple and consists in the replacement of some nodes and some elements of the vault of the bath.
A hot type of repair is carried out without stopping the production process. Before proceeding with the work itself, the flame supply to the heated chamber should be stopped. After this, it becomes possible to replace many elements on which the first signs of damage appear. This allows you to significantly increase the term of use.
Cold, it is also a major overhaul, carried out within the time limits provided for in the production plan. It got its name due to the fact that it is carried out only after a complete stop of the equipment, cessation of heat supply and removal of all glass from the bath.
Overhaul
First you need to stop the flow of the charge. Stop feeding raw materials to the glass melting pool should be 8-10 hours before it stops. After that, glass mass is introduced, heated to 1500 degrees Celsius (this increases its fluidity), and removed through special channels. This glass melt goes through a granulation process and can be used in the future as a recyclable material. Extreme caution should be taken to turn off the burners. The temperature should change gradually, since its sharp drop can cause the destruction of the arch. Repair work is commenced only after all these actions and only after the oven cools down to 100-150 degrees Celsius.
Usually, during overhaul, all damaged areas of masonry are removed, and refractory boards and bricks are replaced as necessary. During the overhaul, the arch of the furnace regenerator is also being repaired.
Level control
For bath furnaces, it is very important to maintain a constant level of glass melt, as they belong to continuous devices. Fluctuations in the level will adversely affect the quality of the finished product, as well as cause some other detrimental effects. For this reason, it is necessary to install equipment that controls this indicator. As measuring instruments, it is possible to install float, pneumatic, and optical level gauges for monitoring and regulating the level of glass melt in a glass melting furnace. Electrical installation of devices should be carried out only by highly qualified specialists.