Carbide for welding: what is it, why is it needed, where to buy, price

Welding silicon-based carbide involves direct contact with water, during which a significant amount of acetylene gas and a lot of heat are released. Due to this operational characteristic, it is not so easy to ensure safe storage of this material. In order to do this, the carbide is placed in completely sealed tanks made of roofing metal. They should fit from 100 to 130 kg.

When welding with carbide, a large amount of acetylene is released, a gas that is highly flammable, so when opening such cans, care should be taken to ensure that there are no sparks or open flames nearby. Welding work using carbide dust with a particle size of 2 mm or less will not be carried out, since such dust dissolves almost instantly in water. If you add too much of this dust to the water, there is a real possibility of an explosion. By the way, a kilogram of carbide can lead to the release of almost a whole cubic meter of pure acetylene.

Carbide is widely used for gas-type welding, as well as for cutting metals. When acetylene begins to burn with oxygen, the flame temperature can reach over 3000 degrees Celsius. This allows this material to be used even when working with refractory materials.

What is needed for acetylene welding?

Gas welding requires two types of gases, the first is oxygen and the second is acetylene. The oxygen compound is necessary to promote the combustion of acetylene during welding and other types of work. Acetylene itself is a flammable substance.

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Calcium carbide in welding

For welding work, carbide is almost an ideal substance, because when it interacts with water, it releases volatile acetylene gas into the surrounding space, which serves as the basis for metallization, soldering, oxygen welding and many other processes related to the processing of metal alloys.

This composition is created at very high temperatures (up to 2400 degrees) by melting quicklime and coke inside an electric arc furnace. Then the hot liquid substance is placed in special molds (molds), where it freezes and hardens. Then the carbide is split into pieces no larger than 8 cm in size. As a result, the resulting substance will consist of approximately 78% calcium carbide, and the remaining 22% is lime oxides, impurities and other substances.

Since carbide releases a large amount of acetylene gas and thermal energy when exposed to water, this makes its storage significantly more difficult. To avoid deterioration of the substance , it is often placed in sealed steel containers. When opening these metal vessels, it is necessary to avoid open flames and sparks, otherwise there may be dire consequences.

Carbide dust (particles up to 2 mm) is unsuitable for use because it dissolves in water almost instantly. In addition, when storing large amounts of dust, the risk increases that the use of the composition will ultimately lead to an explosion of the tank. Experts note that a kilogram of the substance in question can release more than 260 cubic inches of acetylene when interacting with water.

Carbide is often used for gas cutting and welding. When burning, acetylene comes into contact with oxygen and reaches a temperature of 3150, which makes this gas absolutely indispensable when processing refractory metal alloys. For safety reasons, acetylene is made in special generators based on coal, oil, natural gas or calcium carbide.

Chemical properties

Chemical properties are also important. They are also taken into account when using the material. The main characteristics include the following qualities:

Calcium carbide is characterized by its ability to absorb moisture well. It is worth considering that such a procedure is manifested by a vivid chemical reaction associated with the decomposition of the substance.
When working with the material in question, it is worth considering that the resulting dust has an irritating effect on the mucous organs. In addition, a similar reaction can occur when crystals or dust come into contact with the surface of the skin. That is why when working with the compound in question, you should use a respirator and some other protective equipment.
Crystals actively react to the influence of other substances, often only when heated. This may result in the formation of calcium carbonate.
In some cases, a crystalline substance is combined with nitrogen, resulting in calcium cyanamide.
When heated, a reaction can occur with arsenic and chlorine, as well as phosphorus.

Calcium carbonate

The most important chemical quality is considered to be susceptibility to decomposition when exposed to water.

Application area

Calcium carbide (Calcium carbide) is used to produce calcium cyanamide (by reaction with nitrogen), from which cyanide compounds and fertilizers are synthesized, for the production of carbide-urea plant growth regulators and carbide powder reagent.

Autogenous work and lighting, the production of acetylene black and other materials: synthetic rubber, alkonitrile, styrene, vinyl chloride, acetic acid, acetylene chloride derivatives, artificial resins, ethylene, acetone, etc., cannot be done without this substance. It is also used in the gas welding process, production of carbide lamps.

From a special fraction of calcium carbide (processed using waste and substandard raw materials) by reaction with water, acetylene gas and a by-product - slaked lime - are obtained. This procedure is accompanied by the release of a significant amount of heat. The volume of gas produced depends on the purity of calcium carbide (the purer the material, the more acetylene will be released) and varies between 235-285 liters from 1 kg of carbide.

Theoretically, 0.56 liters of water are required to decompose 1 kg of calcium carbide, but in practice, 5 to 26 liters of liquid are used to better cool the acetylene and ensure the safety of the process. The rate of decomposition will depend on the granulation and purity of the starting material, as well as on the temperature and purity of the water (the purer and smaller the size, the higher the temperature, the faster the reaction rate).

Physical properties

Colorless tetragonal crystals.
Density: 228 (+20 °C, g/cm3).
Specific heat capacity at constant pressure (in J/g·K): 0.92 (+20–325 °C).
Standard enthalpy of formation ΔfH (298 K, kJ/mol): −62.8 (t).
Standard Gibbs energy of formation ΔfG (298 K, kJ/mol): −67.8 (t).
Standard entropy of formation S (298 K, J/mol·K): 70.3 (t).
Standard molar heat capacity Cp (298 K, J/mol·K): 62.34 (t).
Melting enthalpy ΔHmelt (kJ/mol): 32.2.
Calcium carbide has a strong garlicky odor.

What is carbide?

Homemade bombs. This is what comes to mind first when we hear the word carbide . And no, the production of these dangerous toys was not carried out by defense industry enterprises, but, as a rule, by boys, about ten years old.

Twenty years ago it was a favorite pastime among teenagers. Now everyone sits at their tablets, but back then the world was ruled by the inquisitive mind of a child who strove to try everything in practice.

In order to feel like Rimbaud, you needed to get one miracle stone. Children most often found them at construction sites. And then everything was simple: a plastic vessel, a stone, water, a tightly screwed cap. All this was zealously shaken, and at best, thrown away. And in the worst case, the “shell” exploded right in the hands, then injuries could not be avoided.

Calcium carbide

There were also safer ways to use the find, for example, simply throwing it into a puddle, then you could observe something similar to the effect of modern bath bombs. So what kind of popular “toy” is this? Most of us believed that nature produced carbide as we know it. But actually it is not. And today you will see this.

So, this substance is always very hard, plus, in order to melt it, you need to make a remarkable effort. They look like dark, light, greenish stones, or powder, it all depends on the composition. Its shelf life is short, usually six months. It will not be possible to place containers in a general warehouse; such potentially dangerous substances must have their own compartment.

As you already know, carbide constantly strives to explode. Moreover, some connections do not even need special conditions. It is enough just to pour the powder from container to container, and it can suddenly explode.

Content:

Welding carbide or full name calcium carbide is the main substance for producing acetylene gas.
In fact, it is an active chemical compound of calcium and carbon and, when finished, is a solid composition with a dark gray or brown tint. The smell of carbide resembles the pungent smell of garlic and reacts with water to release heat. Calcium carbide is an ideal substance for welding, since upon contact with water it releases acetylene, a volatile gas that is the basis for oxygen welding, soldering, metallization and other processes associated with metal processing. Calcium carbide is created at temperatures up to 2300 degrees Celsius by fusing coke and quicklime in an electric arc furnace (Figure 1). After this, the molten substance is poured onto molds, and in them it cools and takes on a solid state. After this, the carbide for welding is crushed into pieces, the size of which does not exceed 8 cm. As a result, the substance will consist of 75 percent calcium carbide, and the rest - impurities, lime oxide, etc.

Features of application

This substance is used everywhere in welding. This is done according to the following scheme:

The carbide pieces are placed in a basket. The optimal size of the elements is 8 cm. Such “pebbles” can ensure optimal production of acetylene gas. Experts do not recommend pouring carbide dust into the generator. Particles less than 2 mm in diameter release acetylene almost instantly, which can lead to equipment explosion.
The basket is placed in a special tank with water. Its neck must be closed with a tight lid with a screw fastening.
By rotating the screw flywheel, the basket with pieces of the substance is immersed in water, and the generation of acetylene gas begins. By decreasing/increasing the immersion depth of the basket, you can regulate the intensity of acetylene production, maintaining optimal intensity in the welding device’s burner.

During welding operations, carbide acts as a fuel that saturates the gas generator. And without its use it will be difficult to use an acetylene torch. After all, a gas cylinder is very difficult to move. And the carbide pieces just need to be placed in a sealed container and transported to absolutely any distance, preventing the appearance of moisture.

How is carbide obtained?

First about calcium carbide. Its production is in demand. And although such factories require large expenses, especially when it comes to electricity, enterprises do not abandon the usual manufacturing method. Because the demand for such products is in no hurry to fall. After all, it is hardly possible to imagine at least a single construction site without acetylene. To save on electricity, such enterprises are opened in countries with a large number of hydroelectric power stations, in Canada, for example.

Why not switch to working with methane, since such a volatile gas can also be obtained from it? Yes, because calcium carbide produces an almost pure product, it is not difficult to bring it to 98 percent gas. And it is much easier to transport than the one obtained with the participation of methane.

The main object in such industries are electric furnaces. They are loaded with hard coal, which is also called coke, and calcium oxide (lime, any kind of lime will not work, it needs to be purified and homogeneous). All this heats up to 2 thousand degrees. And voila, the reaction started.

The result is a liquid substance, which will then become a familiar compound to us. But first it needs to cool in the molds. After the degree is reduced, these layers are crushed into pieces that are more convenient to use.

Now about the silicon version. We got it absolutely by accident, as usually happens. An American scientist tried to create an artificial diamond. As a result of the experiments, carbides were obtained (by the way, they are in second place in hardness after uncut diamonds).

He patented it and opened the first plant for the production of the material. It’s impossible to say that technology has changed a lot since then. Unless sand and salt were excluded from it, what remained was carbon and silica, which are still heated to maximum temperatures in furnaces.

Appearance and characteristics of technical calcium carbide

The composition in question was first obtained in 1862. The procedure involved the separation of calcium from lime, resulting in a pale gray composition without the characteristics characteristic of metals. As a result of the experiment, carbide was obtained, which subsequently began to be actively used in the production of various products.

At the beginning of the 20th century, calcium carbide began to be used to produce acetylene in large volumes. That is why active research began to be conducted to identify more productive technology.

The technical characteristics of the material determine its wide distribution. The appearance of the substance is characterized by a light gray color; carbides are produced in the form of stone or powder.

Safety precautions

Carbide for welding belongs to the class of explosive substances. Safe use of carbide is ensured by taking into account a number of conditions:

Acetylene is a flammable gas, and dry carbide itself is also explosive, so there should be no open flames near the work site, even small ones such as lighters and lit cigarettes.
It is prohibited to use carbide in granules up to 2 mm or carbide dust, as it dissolves very quickly, which leads to the release of large amounts of gas. Because of this, ultra-high pressure forms in the generator and an explosion may occur.
It is prohibited to work with an angle grinder or an electric welding machine near gas welding operations and places where carbide drums are installed.
The substance must be stored in a dry and sealed place, in which there are no water pipes, sewer pipes and, especially, gas equipment.
Carbide dust upon contact causes irritation to the skin, eyes, and mucous membranes. Work with this substance must be carried out using personal protective equipment - goggles, gloves and a respirator.
If carbide gets on your skin or eyes, rinse it with plenty of warm water and then carefully remove any remaining carbide with tweezers or a damp swab.
When working with carbide in a workshop, all welding equipment must be placed in separate parts of the room, the ventilation system of the room must ensure the removal of flammable gases, and the room must be cleared of flammable materials.

Acetylene generators are prohibited from being installed in basements and residential buildings.
Before starting, the generator should be inspected for visible cracks or dents in the housing.
During work, the generator must remain in a vertical position, the pressure gauge must be in working order and clearly visible to the welder or his assistant.
At the end of the work, the carbide solution remaining in the generator must be completely exhausted, and the resulting lime must be disposed of.
Reuse of wet carbide pieces is not permitted;
Do not open the generator under pressure (during an ongoing reaction).
Acetylene cylinders are stored and transported with special safety caps on the valves.

Compliance with these simple rules will ensure your own safety and the safety of people near the work site.

Carbide should be purchased from reputable welding equipment stores, since purchasing low-quality carbide can complicate welding work.
You can also order it in online stores. The price of carbide varies from 75 to 190 rubles per kilogram, depending on the manufacturer. If there is a need to regularly use equipment for gas welding and cutting, it is better to buy professional equipment manufactured at an industrial enterprise. The use of homemade generators can result in serious injuries and a threat to life.