Industrial (metallurgical) flux: what it is, its characteristics, how and where it is used

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The metallurgical industry is one of the most significant industries of our time. Why know its basics?

The answer is simple - to be able to make the necessary parts from any metals and endow them with such properties that they can be used in many fields of activity.

In order to obtain a finished part from a certain metal, in addition to technology, metallurgical industrial flux is used.

In this article we will talk about all its characteristics and areas of application, we will analyze in detail where and how it can be used.

General information
Types of industrial flux
General properties and characteristics
Summarize

Metallurgical fluxes

The formation of slags is a process that requires special materials.
They are called fluxes. Popular among them are: bauxite, fireclay, lime, fluorspar, limestone. Each type of flux has unique features. Since they are part of the charge placed in steel melting units, they must have suitable technological characteristics. Bauxite

accelerates the formation of toxins. This creates the required level of viscosity of the raw materials formed in open-hearth furnaces. Al2O3, SiO2, Fe2O2 – components of the material. Silica affects the lining of the unit, reducing its durability. At the same time, the volume of slag increases. The optimal amount of compound in bauxite is 10 – 12%. Alumina has a positive effect on slag. Thanks to it, the desired effect is achieved.

When transporting and storing bauxite, it is important to ensure that the moisture level of the raw material does not exceed twenty percent in order to protect the cargo from unexpected losses. Before use, it must be thoroughly dried. This procedure must be carried out carefully, since excess moisture will reduce the beneficial properties of bauxite. It is then placed in a steelmaking plant to increase the rate of slag formation.

There are various grades of bauxite, differing in their properties. For example, B-6 contains 37% Al2O3. At the same time, the content of sulfur and P2O3 does not exceed 0.2% and 0.6%, respectively. SiO2 and Al2O3 are more than 2.1 percent.

Another type of flux is fireclay

. Electric steelmaking units are its main application. In arc furnaces, fireclay waste affects the level of slag viscosity. This effect is achieved due to the absence of iron oxides and water. However. Due to its quantity, the silica contained in fireclay can increase the amount of slag. In addition, the flux contains from thirty to forty percent Al2O3 and SiO2, less than 1% Fe2BO3.

The next type is limestone

used in large quantities. This is a natural type of calcite. This amount of flux during the production of a product using the scrap ore process reduces the temperature in the converter smelting mode. As the temperature increases, calcite dissociates as follows:

Here we see the chemical reaction that occurs in an open-hearth furnace when pouring smelt. As shown in the picture, limestone absorbs heat. But the best effect is achieved with lime, as the heat balance improves. But lime has special properties that require high costs for its storage and production. Therefore, limestone is used for open-hearth departments operating in scrap-ore mode. It does not require special storage conditions and is available in large quantities. The initial period of smelting is characterized by a high level of heat as the torch heats the bath.

Once the limestone is supplied, the temperature drops, so additional measures must be taken. The contents of the bath are mixed with carbon dioxide. It is released during the dissociation of calcite. This allows for improved heat transfer between the torch and the bath. Almost half of the total oxygen is used to make oxidation happen faster. However, a higher quality lime product that has undergone additional processing will significantly reduce the time spent on the melting process. Therefore, it is used during the finishing process.

The Elenovskoye and Novortoitskoye deposits provide limestone to the south of Ukraine. The flux used at enterprises in this region contains 0.01% phosphorus, 0.04% sulfur, 2 - 4% sulfur and aluminum oxide and up to 54% calcium oxide. Another type of limestone mixed with dolomite contains about 14% magnesium oxide.

The product of heat treatment of limestone is called lime. The firing process takes place in tube, shaft, and fluidized bed furnaces. The fuel content has an impact on the resulting product. For example, when using sulfur coke, up to 0.3% sulfur can be found in lime. Such sulfur copes poorly with the role of a desulfurizer. The optimal fuel for producing lime, with a low sulfur content, is natural gas.

Roasting determines the metallurgical parameters of lime. If the firing was carried out in a “soft way”, in which it is quickly heated to the maximum temperature and quickly lowered the temperature, then it will have more pores and cracks. This flux quickly dissolves in the slag. It is important to prevent the process of recrystallization; it occurs if the lime is exposed to high temperatures for too long. The metallurgical properties of such lime leave much to be desired, since its dissolution rate is low.

Lime is hygroscopic; already in air it absorbs moisture from the atmosphere. As a result of a chemical reaction, Ca(OH)2 is formed. Such lime is not suitable for use in metallurgy. It will take more fuel to dissociate the resulting compound. High quantities of hydrogen and low quantities of calcium hydroxide powder are a typical result of using hydrated sulfur.

To prevent this flux from absorbing moisture, special conditions must be created. A closed bunker is suitable for storing lime. At the same time, lime retains its beneficial properties during the first 24 hours before being fed into the steelmaking unit. To get rid of the consequences of storing lime in the open air, “nedopal” is used in metallurgy. It is a product of partial calcination of limestone. Its chemical composition is 10 - 14% CO2, Ca - up to 85%, and 4% SiO2. This ratio reduces hygroscopicity.

The optimal size of a lime block should not exceed 150 mm in open hearth furnaces. The converter method of steel melting requires pieces ranging in size from 10 to 50 mm. These dimensions allow the flux to completely dissolve in the slag.

Fluorite is a natural form of fluorspar (CaF2). It increases the rate of lime dissolution, forming a mobile, highly basic slag. This result is achieved due to the chemical composition of the flux. Fluorspar contains 90 to 95% CaF2 and less than 5% SiO2.

However, poor distribution and high cost reduce the range of its application. The main area of application of fluorspar is electric arc furnaces for steel smelting. It is used in minimal quantities in steel production. At the same time, it must pass through oxygen converters based on two-slag technology. The flux content should not exceed 2% by weight of the metal.

What types of fluxes are there for soldering?

Most often, soldering material is prepared from 10 grams of ammonium chloride and 30 grams of zinc chloride , dissolving them in 60 milliliters of water.

"Soldering acid" or "soldering fluid" is also used. They can be prepared from preserved hydrochloric acid and zinc metal:

pour the acid into a porcelain or glass container and add zinc in portions;
as a result of dissolving zinc in acid, oxygen should begin to be released and zinc chloride should form;
after the release of oxygen slows down, the container should be placed in warm water;
at the end of the reaction, the liquid is drained and only undissolved zinc remains, to which ammonia must be added (2 grams of ammonium per 3 grams of metallic zinc).

The liquid can not be drained, but evaporated to dryness. Then, immediately before soldering, the resulting mixture is dissolved in water (1:2).

However, fluxes prepared in this way are not suitable for all metals. According to the degree of effectiveness, they are divided into three groups:

Due to their weak activity, protective or non-corrosive materials They are mainly used for joining copper, its alloys and cadmium-, tin- or silver-plated steel products. In this case, solders should only be low-melting. Protective fluxes include rosin and its various solutions, petroleum jelly, stearin, wax, and wood resins.
Slightly corrosive substances are more active than non-corrosive substances. Most often these are mineral oils, animal fats, organic acids (oxalic, benzene, stearic, oleic, citric, lactic, etc.) dissolved in alcohol, water or organic acid derivatives. In order to weaken the corrosive effect of such substances, rosin or other substances that do not cause corrosion are added to them. Slightly corrosive substances are used when soldering only with low-melting solders, since they easily decompose, burn and evaporate.
Corrosive soldering fluxes consist of metal fluorides and chlorides and inorganic acids. They are capable of destroying any resistant films of non-ferrous and ferrous metals, therefore they are effective when soldering by any method. Corrosive materials are used in the form of aqueous solutions in paste and solid states.

Fluxes for steelmaking processes

Fluxes are materials that are added to the charge to form slags in steelmaking units that have the necessary set of physical and technological properties. The following are most often used as fluxes in the main steel-making units: limestone, lime, bauxite, fluorspar, etc.

Limestone is supplied in large quantities to the smelting charge during steel production in open-hearth furnaces using the scrap-ore process; it can also be used as a coolant for converter smelting.

Limestone is a natural form of existence of calcite (CaCO3). At high temperatures, calcite undergoes thermal dissociation according to the reaction

Reaction (8.13) occurs with the absorption of a large amount of heat. Therefore, to improve the heat balance of smelting, the use of lime is much more profitable. However, the production of lime in the quantities required for open-hearth shops operating with scrap ore, as well as storing it in dry form, is very difficult. Therefore, when a large consumption of calcium oxide is required for charging open-hearth furnaces, limestone is usually used.

When smelting steel in open-hearth furnaces, limestone is usually used as filler. In the initial period of smelting, the intensity of heat transfer from the torch to the bath is quite high, which makes it possible to compensate for the heat losses associated with the thermal dissociation of limestone within an acceptable time. Stirring the bath with carbon dioxide released during the dissociation of CaCO3 improves heat transfer from the torch to the bath. Oxygen CO2, used at approximately 50%, accelerates the oxidation of bath impurities, which reduces iron ore consumption. But all this does not allow us to fully compensate for the heat costs for the decomposition of limestone, so the use of high-quality lime for filling would provide a significant reduction in the duration of smelting.

What is flux and its key features

So, flux is a metal alloy with a low-melting structure that is used for soldering two different materials. This alloy can be made with your own hands if you know the peculiarities of joining two different materials during heat treatment.

The joining of two materials using flux can only be achieved if a certain temperature is maintained at the seam level. Depending on what material is taken, the temperature varies from 50 to 500 degrees . The melting temperature of the solder must be much higher than the melting temperature of the material you are processing.

Such a thing as soldering flux has several varieties; it must be selected depending on the following factors:

metal;
soldering temperature.
temperature of the flux itself;
work surface parameters;
material strength;
its resistance to corrosion.

There are two groups of fluxes:

solids that have a high temperature threshold;
soft, such flux has a low melting point.

Refractory solder has a melting point of 500 degrees or more ; it creates a fairly strong type of connection. But its disadvantage is that sometimes high temperature can cause a key part of the structure to overheat and fail.

And the melting temperature of low-melting solders ranges from 50 to 400 degrees . This type of flux includes the following components:

lead;
tin;
other impurities.

Such fluxes are mainly used for soldering radio equipment during installation.

There are also ultra-low-melting solders that are used for soldering and connecting transistors. The melting temperature of these fluxes can reach a maximum of 150 degrees .

To solder thin surfaces, soft fluxes should be used, and to solder large-diameter wires, you need to use hard solder, which has a high temperature threshold.

The required flux characteristics are:

ability to conduct heat and current normally;
structural strength;
stretching ability;
corrosion resistance;
differences in temperature indicators when melting solder and base materials.

The following materials are used in the form of solder:

rods;
ribbons;
wire spools;
colophonium tubes;
other flux.

The most common form is a tin rod, the cross-sectional diameter of which is 1-5 meters.

There are also multi-channel types of fluxes that have multiple sources of solder to create stronger connections. They may be sold in skeins or flasks , have a spiral shape and are contained in reels . For one-time use, it is best to take a small piece of wire the size of a match.

To solder electrical circuits, it is necessary to use tube fluxes that contain colophonium. This is a resin that acts as solder. This filler material is excellent at joining types of metals such as:

copper;
silver;
brass.

Key features of the use of industrial flux in metallurgy

The metallurgical industry is one of the most significant industries of our time. Why know its basics?

The answer is simple - to be able to make the necessary parts from any metals and endow them with such properties that they can be used in many fields of activity.

In order to obtain a finished part from a certain metal, in addition to technology, metallurgical industrial flux is used.

In this article we will talk about all its characteristics and areas of application, we will analyze in detail where and how it can be used.

General information
Types of industrial flux
General properties and characteristics
Summarize

General information

Cast iron is an alloy of iron and carbon that is made in blast furnaces. This is the result of melting iron ore in large structures called blast furnaces.

This is one of the main and common methods in ferrous metallurgy.

The auxiliary component used in this process is the charge. A charge is a combination of materials (ore or its concentrate) and fuel (mostly coke) mixed in certain parts.

Also, gas or liquid fuel can be used as fuel. Metal industrial flux in this process performs a protective function. Let's take a closer look.

Types of industrial flux

Depending on the rock that does not contain the required amount of useful substances and will be loaded into the blast furnace, the flux is divided into basic, acidic and aluminous.

Due to the fact that the main metallurgical industrial flux contains calcium oxide, it is the most common. If the waste rock contains silica, it will be most effective to use the main flux.

Also, it allows you to achieve the required proportion of basic and acidic oxides.

Limestone stone is one of the most used in the blast furnace process as a flux. Its locations are distributed throughout the world. This is one of the few minerals that is formed under natural conditions.

In natural conditions, perfect metallurgical industrial flux is not found, so its composition must include, in certain proportions, calcium oxide and silicon.

To produce flux under laboratory conditions requires a lot of labor; it is not entirely effective. That is why limestone is the most suitable product as an industrial flux.

The main criterion for use should be the absence of phosphorus in the composition. Only sulfur content is allowed in limited quantities.

In rare cases, so-called dolomite is used. It also contains magnesium. Magnesium content affects the dolomitization process.

I use it only when, as a result of melting, it is necessary to achieve high physical and chemical properties. In such cases, the percentage of magnesium in the content simply changes.

An increase of about 10% allows, with a change in temperature, not to lose the basic properties.

Types of fluxing

Depending on the technological process, fluxing can be performed in two different ways: dry or wet. It should be noted that the quality of the result does not change depending on the method of processing steel and other metals. In wet fluxing, a fluxing layer is applied to the surface of molten zinc, through which the workpiece subsequently passes until it comes into contact with the zinc. With the dry method, parts that have gone through the etching and washing stage are first sent to a fluxing solution consisting of zinc and ammonium chlorides. Such fluxing leads to the formation of a film on the surface of the product that protects against oxidation and promotes a better reaction of zinc with the metal. The preparation process for galvanizing is completed in a drying oven, where excess moisture is removed and the parts are heated to the required temperature.

If you have any questions regarding steel fluxing or the galvanizing process itself, please contact us at the numbers listed on the “Contacts” page. Our specialists will be happy to provide the necessary additional information and help you place your order.

General properties and characteristics

The limestone mined in the former CIS countries is light in color, mostly white. But there are deposits with different shades of gray or brown. It depends on the percentage of chemical elements it contains.

The strongest and most compact is limestone stone. Before use in a blast furnace, it is grouped. The fine fraction has not been used before, but is now being increasingly used in industry.

Although it does not have high strength indicators. It can only be used as an industrial flux if it enters the furnace together with the agglomerate.

Summarize

In general terms, industrial flux is an additional component. Which is used in welding, as well as in the large metallurgical industry.

As a protective component, it manifests itself when welding is used to connect metal parts. It also affects the evenness of the weld.

In blast furnace production it performs a slightly different function. This includes regulation of the melting temperature, which directly affects the chemical characteristics of the ore and its alloys.

Industrial flux is a kind of stabilizer in the blast furnace process and removes sulfur.

Thus, it became clearer to us what flux is and why it is used in industry. It may seem that understanding this technological process is not so easy.

But, if you know the intricacies of this process, you can easily figure out all the other nuances of creating cast iron.

Fluxing metal during galvanizing process

The fluxing process is a very important stage of surface preparation immediately before dipping the product into the melt. As a result of etching and subsequent washing, the surface of the product becomes clean and ready to accept the coating. But at the same time, this surface is vulnerable to active interaction with oxygen. While the product is covered with a thin layer of liquid film on the surface, surface oxidation reactions proceed very slowly, but a wet product cannot be galvanized, and a dried product is again covered with an oxide film. In addition, no matter how hard we try to remove the oxide layer from the surface of the zinc melt, it immediately forms again, and its presence also creates obstacles to successful galvanizing.

It has been shown that dipping products into a special solution (flux) containing certain salts creates conditions for the destruction of both interfering factors. It was found that if a product with a newly created clean (juvenile) surface is dipped into a flux solution (consisting of a mixture of zinc chloride and ammonium chloride) and then dried, a salt film that is poorly permeable to oxygen is formed on the surface, preventing oxidation of the surface, in addition Ammonium chloride on the surface of the product creates a reducing environment.

Another task of the flux is to destroy the film of zinc oxide, which is always present on the surface of the molten zinc. Flux also copes with this task. At a temperature of about three hundred degrees Celsius, the flux crust located on the surface of the product melts. This melt dissolves zinc oxide well, which is in contact with the flux when the product is immersed.

Finally, the third task of the flux is evaporation after the first two processes have been completed. Having solved the first two problems, the flux evaporates.

This creates ideal conditions for contact of a still clean surface of a steel product with a clean, oxide-free molten zinc.

The latter does not mean that the galvanizing process will proceed smoothly. There are features in the product that may prevent high-quality galvanizing. These features include

defects in the product design;
poorly executed welds;
metal deficiencies caused by the peculiarities of its production technology;
low flux temperature.

You may also be interested in the following articles:

Information technologies in ensuring the quality of metal products
Galvanizing of VGP pipes
Lead and its electrolytes
Fick's Laws | Diffusion Basics
Mechanisms for degreasing the surface of parts

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Flux in metallurgy, what is it?

Fluxes

Fluxes (fluxes) are substances that are included in the charge and form low-melting alloys with waste rock, fuel ash and other contaminants, which are separated from the metal in the form of slag. The importance of fluxes in metallurgy is very great, since the successful progress of smelting and the production of metal of the required qualities depend on their presence. Waste rock of iron ores most often contains an excess of silica (Si02), and in order to form a low-melting slag, limestone CaC03 or dolomite CaC03 • MgC03 is added to the charge as a flux. By liquefying the slag and making it fusible, lime flux promotes slagging of ash and sulfur. The consumption of limestone in the smelting of iron and steel is very high. For 1 ton of cast iron, from 0.40 to 0.80 tons of limestone are consumed; for 1 ton of basic open-hearth steel - about 0.10-0.12 tons of limestone. Limestone is a very common rock. Metallurgical limestone, depending on the grade, contains from 49 to 52% CaO, no more than 1.75-4.0% Si02 and no more than 2.0-3.0% sesquioxides (A1203 4-Fe203). When making steel, fluorspar (CaF2) is also used as a flux, which reduces the viscosity of the slag and partially removes sulfur.

Preparation of raw materials for blast furnaces Preliminary preparation of raw materials for blast furnaces is of great importance for increasing the productivity of blast furnaces and reducing fuel consumption. Modern theory and practice of blast furnace production impose very specific requirements on the quality of ore going into smelting, on the size of its pieces and the uniformity of composition in terms of iron content in it. The largest size of pieces of raw material entering the smelting, depending on its physical and chemical properties, is set: 30-100 mm for ore, 30-80 mm for limestone and 25-80 mm for coke. Based on many years of experience, it is believed that every 10% of fines in the charge (pieces less than 5 mm in size) reduce the furnace productivity by 3% and, in addition, increase coke consumption. Preparation for blast furnace smelting of iron ores with high iron content most often consists of crushing them, sorting by size of pieces, averaging and agglomeration. For coke blast furnaces, ore is crushed in jaw and cone crushers into pieces measuring 30-100 mm. Roll crushers are used for fine crushing of ores. After crushing, the ore is sieved on screens and sorted into classes. To increase the percentage of iron in ore, wet and magnetic enrichment and ore roasting are used. By means of wet enrichment, clay and sandy rocks are washed from ore. Roasting of ore is carried out with the aim of changing the physical state of the ore or its chemical composition (reducing the sulfur content, removing moisture, CO *, etc.). For example, difficult-to-reduce ores crack during roasting and become porous, as a result of which they become easily reducible. Ore averaging is an operation with the goal of equalizing the quality of the raw materials entering the smelting, i.e., bringing the composition of individual portions of materials closer to its average composition. The most common method of averaging is laying raw materials in thin layers in piles, from which the material is removed by an excavator or other machine. Sintering is the process of sintering ore fines and dust into large porous pieces suitable for use in a blast furnace. Using a burner operating on gas or liquid fuel, the top layer of the charge is heated to a temperature of 750-850°. The most productive are conveyor-type sintering machines, in which the processes of loading the charge, ignition, sintering and unloading the finished sinter occur continuously. This machine is an endless conveyor of rectangular cast-iron carts (called pallets), the surface of which consists of grates (Fig. 75). Under the grate of the machine there are chambers located under a vacuum created by a powerful fan - an exhauster. Air is sucked through the mixture layer from top to bottom. Combustion that begins in the upper layer spreads downward. The temperature in the charge layer reaches 1300-1600°. The trolleys fit tightly together with their long sides, forming a continuous sintering belt. The belt speed varies within 0.5-2 m/min. A sintering machine with an area of 50 m2 produces up to 1500 tons of sinter per day. During the agglomeration process, iron oxide is converted into magnetic oxide-oxide: 3Fea03-C0=2Fe304-|-C04 (reduction), 6Fe20;,->4Fe304-t-0a (dissociation). In addition to sintering the ore into separate pieces, agglomeration allows you to remove harmful impurities contained in iron ores, in particular, sulfur may burn out during this process. The use of sinter in blast furnaces increases their productivity and reduces iron ore consumption. The introduction of flux into the charge during sintering makes it possible to obtain a fluxed agglomerate, which simplifies the blast furnace process.

Fluxes

Details Category:

FLUXES

, fluxes, mineral substances added to the charge of metallurgical furnaces to obtain slag of a certain chemical composition and the required physical properties. The purpose of adding fluxes is to both lower and increase the melting point of the slag. Depending on the nature of the slag, fluxes are usually divided into acidic and basic; aluminous fluxes are less commonly used. In exceptional cases (for example, catastrophic failures), it is necessary to resort to strong fluxes, which make it possible to obtain low-melting slags to quickly correct the abnormal operation of furnaces or the abnormal condition of their refractory lining. Similar fluxes are also used systematically to obtain sufficiently liquid-melting (mobile) and, therefore, more active slags. However, in these cases the use of only very small quantities of such highly active fluxes is limited.

Fluxes in ferrous metallurgy

. In metallurgical processes for producing (and heating) ferrous metal (cast iron, iron and steel), the following fluxes are usually used. Acidic fluxes (quartz, quartzite, quartz sand, broken silica brick, siliceous brick, broken red brick) are used relatively rarely and in limited quantities. This is explained mainly by the fact that most iron ores and almost all types of mineral fuels (coke, anthracite) have siliceous or siliceous-alumina waste rock and usually require not an acidic, but a basic flux. Acid flux is introduced into the charge in the form of low-grade ores with siliceous waste rock (ferruginous quartzites) or acidic pig slag (Bessemer slag, slag from welding furnaces, heating wells, and so on). Sometimes low-grade siliceous ores or pigment acid slags are added to the charge simultaneously with the main fluxes in order to increase the total amount of slag. This is done, for example, in blast furnace production when smelting foundry cast iron for more successful recovery of silicon with an increased amount of slag. It is advisable to use the same technique for introducing new slag in open-hearth furnaces. Siliceous fluxes (quartz sand, ground quartzite) often also serve as a fairly cheap and fast-acting means for liquefying thick slags and for corroding (“bleeding off”) the main deposits and solid formations on the bottom of the main open-hearth furnaces or in the forge (in the shaft) of blast furnaces. In these cases, acidic flux should be used with great care (to avoid corroding the walls and hearth of the furnace). Acid flux (quartz sand) is usually used to easily remove scale in the form of liquid slag from heating wells and welding furnaces if working on a “dry hearth” (made of magnesite brick or soapstone) is considered less convenient.

Aluminous fluxes are used even less frequently than acidic fluxes. This happens not only because pure aluminous fluxes, for example, bauxite, are quite rare and quite expensive, but also because in most practical cases the natural content of alumina in slag is quite sufficient from the point of view of their physical qualities. From a chemical point of view, the alumina content in slags is usually not given much importance. In practice, fireclay bricks or clay have to be used as aluminous fluxes. This leads to the fact that a significant amount of silicic acid is introduced along with alumina, i.e., a siliceous-alumina flux is produced. Despite the seeming irrationality of adding such fluxes, their use in some cases is completely justified. Thus, when operating charcoal blast furnaces on ores with highly magnesian waste rock, the addition of clay or shale makes it possible to obtain slag that is quite normal in terms of liquid fusibility (previous operation of blast furnaces on Styrian ore, modern operation of the Trans-Baikal Petrovsky Plant on ores of the Balyaginsky deposit). Aluminous fluxes also have a very beneficial effect on the properties of steelmaking slags. This is sometimes used when working in crucibles, in acidic open-hearth furnaces and in electric furnaces. The addition of aluminous materials simultaneously with the main fluxes should be considered a completely rational measure for the addition of final slags in the main open-hearth and electric furnaces. Such an additive is advisable in all cases where it is necessary to increase the amount of slag in order to reduce the concentration of those components that are too difficult to melt and make the slag too thick. As an example, we can cite the slags of the main open-hearth furnaces, which process large quantities of chromium waste (slag, deposits, furnace scraps, etc.) or process cast iron with a high chromium content (Khalilov cast iron with 2.5-3.0% chromium). The addition of aluminous fluxes (discarded tableware from earthenware factories) is sometimes practiced for welding furnaces (welding small pipes from Bessemer strip billets in American factories).

Basic fluxes play a much more important role in ferrous metallurgy. Among the latter, it should be noted: limestone, lime and dolomite. The consumption of the main flux (limestone and lime) in modern metallurgical plants reaches enormous figures, as can be judged, for example, from the following data: for 1 ton of cast iron smelted in coke blast furnaces, from 0.40 to 0.80 tons of limestone are consumed; For 1 ton of basic open-hearth steel, about 0.10-0.12 tons (i.e., about 10-12%) of limestone are consumed, and for 1 ton of Thomasov steel, about 0.12-0.15 tons (i.e., 12 -15%) burnt lime. Such widespread use of basic flux in ferrous metallurgy is explained not only by the fact that siliceous-alumina gangue ore and coke ash require a significant amount of basic oxides for their fluxing, but also by the fact that most production processes in ferrous metallurgy have as their main task the fight against harmful impurities - sulfur and phosphorus. Successful completion of this task is only possible when working on basic slags, the formation of which requires the addition of significant quantities of basic (lime) flux. Limestone is usually used as the main flux in coke (and sometimes charcoal) blast furnace smelting. He d.b. quite cheap and pure in terms of the content of silicic acid, sulfur, phosphorus, arsenic and other impurities (SiO2 content within 1-3%), free from earth and clay, and quite durable. Limestone is used in crushed form (pieces up to 150 mm in diameter) with mandatory screening of fines and debris. In coke blast furnace smelting, part of the lime flux can be successfully replaced with dolomite, which is used in the same form as limestone. Replacing lime flux with dolomite is allowed by 1/4-1/5 (up to a content of about 10% MgO in blast furnace slag) and improves the physical properties of the slag (increased melting point at the same melting temperature). This greatly facilitates the operation of the blast furnace, especially with fairly viscous aluminous slags. However, the use of dolomite in some areas is hampered by the higher prices (transport) for dolomite compared to limestone. This unfavorable ratio was observed at all our southern factories. Some American plants (Pennsylvania), on the contrary, have the opportunity to obtain dolomite at very low prices (the blast furnaces of some plants are built on dolomite rock) and widely use this opportunity to improve the physical properties of blast furnace slag. From this point of view, it can be considered quite appropriate to use dolomitized limestones, i.e., limestones containing a certain amount of magnesia, in blast furnaces. The use of burnt lime or burnt dolomite as a blast furnace flux is not allowed, since it cannot be used. justified on any grounds. As a surrogate for the main flux in blast furnaces, iron-smelting cupola furnaces and in gas generators operating with the production of liquid slag, basic open-hearth slag containing a fairly high percentage of lime and magnesia (up to 50%) with a fairly significant content of metal oxides (total oxides of iron and manganese 20-25% and higher). This recycled slag is a kind of low-grade iron ore with a core gangue and a high content of manganese and phosphorus. The utilization of recycled open-hearth slag in blast furnace production is increasing every year and provides significant economic benefits. It is relatively rarely possible to use waste ore or fuel ash as the main flux. However, these cases also occur in some metallurgical regions. Thus, thick deposits of oolitic brown ironstones "minette", located in Alsace-Lorraine, Belgium and Luxembourg, contain ore grades with both acidic and basic waste rock. This makes it possible to smelt a mixture of these ores without the addition of fluxes (limestone) or with a small amount of it. Obtaining such a self-melting charge not only eliminates the cost of purchasing limestone, but significantly improves the overall technical and production performance of blast furnaces. Sometimes coke (for example, in Upper Silesia) contains a significant amount of basic oxides (CaO and MgO) in the ash. The ash of this coke can be considered self-melting, which significantly reduces the consumption of the main flux (limestone) compared to working with conventional coke (siliceous-alumina ash).

The consumption of the main flux in blast furnace production depends on the richness of the ore, the composition of its waste rock, the relative consumption of coke, the content of ash in it, the composition of the latter, etc. When smelting brown iron ore in Cleveland (England), the consumption of limestone reaches 0.8-1. 0 per 1 ton of cast iron. The main fluxes used in steelmaking are subject to the same requirements as in blast furnace production, in the sense of a low content of sulfur, phosphorus, arsenic and insoluble sediment (SiO2 + Al2O3). But unlike blast furnace flux, limestone going into open-hearth furnaces should not contain noticeable amounts of magnesia (no more than 2-3% MgO), and dolomite is absolutely not allowed as a flux for the open-hearth process, since the magnesium content in the main open-hearth slag is quite high due to corrosion of the main (magnesite or dolomite) welding of the hearth and slopes of the furnace. Instead of limestone, burnt lime is partially used in the main open-hearth furnace, and always in electric furnaces and the Thomas Converter. The benefit of using lime is motivated by the following considerations. 1) The decomposition of limestone requires a fairly significant amount of heat for the reaction:

CaCO3 = CaO+CO2 -13920 Cal.

It is more profitable to carry out this simple operation in a special lime kiln, and not in such an expensive production unit as an open-hearth furnace. 2) Slagging reactions with limestone at the end of the operation involve greater heat absorption, require more time and make the bath very cold, i.e., ultimately reduce the productivity of the furnace. 3) At high temperatures of the open-hearth process, carbon dioxide released during the decomposition of limestone can oxidize metal impurities, for example, carbon by the reaction:

2C+2CaCO3+(FeO)2·SiO2 = (CaO)2·SiO2+4CO+2FeO -161816 Cal,

whereas when working with lime one would expect the reaction to proceed according to the following equation:

2C+2CaO+(FeO)2·SiO2 = (CaO)2·SiO2+2CO+2Fe -62196 Cal,

i.e., with a significantly lower heat consumption and a higher metal yield due to the fact that the oxidation of carbon occurs due to the oxygen of the ore and is accompanied by the reduction of iron (instead of 12 parts by weight of carbon, 56 parts by weight of iron are reduced). However, working with burnt lime also has its disadvantages: 1) it requires the installation of lime kilns, 2) it necessitates the need to have covered warehouses and a special rolling railway. composition, 3) significantly increases the cost of fluxes, which is not always covered by the advantages of working on burnt lime, 4) complicates storage in warehouses, 5) worsens the sanitary and hygienic conditions of working personnel, 6) reduces the intensity of mixing the bath during decomposition (“boiling”) of limestone . Working in basic open-hearth furnaces using burnt lime is widely practiced in German factories; in US factories, on the contrary, work in such kilns is carried out almost exclusively on raw limestone. Studies conducted by individual American factories even suggest that in American practice, the use of lime in open-hearth furnaces when working with a duplex process does not even increase productivity and seems less profitable compared to working with raw limestone. The issue of using limestone or lime must be resolved for each particular case separately, taking into account all local technical and economic conditions. However, there is no doubt that in the second half of the smelting process only burnt lime should be fed into the kiln. It is possible that such a combined method of working with raw limestone for filling and burnt lime for final finishing of the slag may turn out to be the most rational and cost-effective for most practical cases.

The stated position does not contradict the fact that in American practice, when working in an acidic open-hearth furnace, raw limestone is sometimes added at the end of smelting in order to slow down the silicon reduction process. This additive is produced in very small quantities and aims not only to reduce the concentration of free SiO2 in the slag (which could be done with the help of a CaO additive), but at the same time tends to lower the temperature of the metal bath due to the heat consumption for heating and decomposition of CaCO3 . A slight addition of basic flux quite significantly changes the composition of acidic open-hearth slag and is usually practiced so that the slag contains 5-8% CaO. Burnt lime for Thomasovsky and open-hearth production should contain >2-3% SiO2, >0.2% sulfur, >2-3% MgO, etc. freshly burned, without dust and fines, in pieces measuring 75-150 mm, and underburning is allowed (CO2 content up to 2-4%). For electric kilns, lime should be stored in closed bins and supplied to the kilns with the lowest possible content of moisture absorbed from the air.

The most effective flux of the main open-hearth process is fluorspar, or calcium fluoride (CaF2). The use of CaF2 is based on its ability to greatly increase the melting point of the main open-hearth slag, and, consequently, significantly increase its activity and accelerate the interaction reactions between the slag and the metal, for example, when removing sulfur in the main open-hearth furnace through the reactions:

FeS+CaO = CaS+FeO + 6573 Cal,

MnS+CaO = CaS+MnO -13481 Cal.

The beneficial effect of fluorspar on the removal of sulfur is also reflected in the fact that fluorine is apparently capable of producing volatile compounds with sulfur (presumably SF6), etc. finally remove some of the sulfur from the balance of open-hearth smelting. The consumption of fluorspar, depending on the quality of the resulting steel, usually ranges from 0.1-0.4% of the weight of the metal charge. In especially difficult cases of working with thick slags (high content of chromium oxides, etc.), the CaF2 consumption increases to 2% or more (Khalilov melting). As experiments carried out by German technicians (Schleicher and others) have shown, an increase in the CaF2 content in the slag above 2.5% (of the weight of the slag) does not bring any noticeable benefit, but begins to greatly affect the durability of the silica masonry of the walls and roof of the open-hearth furnace, which can be explained by the formation of the volatile compound SiF4 through the following reactions:

2CaF2+2H2O = 2CaO+4HF,

4HF+SiO2 = 2H2O+SiF4,

2CaF2+SiO2 = 2CaO+SiF4.

Fluorspar is a reagent that is quite easy to store and handle. The only drawback is its comparative high cost (the pre-war price of fluorspar imported from England and Bohemia was in the range of 35-50 kopecks per pood at our factories). Fluorspar d.b. pure with respect to SiO2 and should not contain pyrite inclusions clearly visible to the naked eye. Currently, CaF2 is produced by our factories from Transbaikalia. Calcium chloride (CaCl2) acts similarly to fluorspar (CaF2), the use of which in steelmaking was proposed by the Englishman Saniter. However, due to its natural properties, CaCl2 is a much less convenient reagent at high temperatures. Its use gave more varied, less stable results and was soon completely abandoned. Strong alkaline fluxes also include a number of patented products, known under various industrial names and used for desulfurization of liquid iron cast into a ladle from a blast furnace or cupola iron foundry. The composition of such desulfators usually includes: lime, fluorspar, soda, sometimes calcium chloride or sodium chloride and other compounds that produce a very low-melting slag that mixes well with metal and can easily form fairly strong sulfur compounds with alkalis (CaS, Na2S, etc.). d.). Already a small amount of such an energetic reagent (up to 0.1% of the weight of cast iron) contributes to a significant transfer of sulfur from the metal into slag (up to 35-50% and even higher than all sulfur). Low-melting alkaline fluxes (for example, rock salt NaCl) are sometimes used to quickly correct abnormalities in the operation of blast furnaces when the hearth is cluttered with low-melting deposits. Typically, NaCl was introduced through tuyeres in very small quantities using special apparatus by introducing salt into a stream of air (blast blast). The noticeable content of alkalis in the charge of blast furnaces and coke ovens has a destructive effect on refractory masonry, which is why the use of alkaline fluxes cannot be recommended. (Na2O and K2O). On this basis, it is necessary to recognize the introduction of NaCl in the form of salted coke as irrational (for example, during experimental smelting of Khalilov ores). Oxides of iron and manganese can sometimes be used as fluxes, usually serving as oxidizers for impurities in the metal bath. Manganese ore can be successfully used to obtain significant quantities of replaceable (discharge) manganese slag during the processing of highly sulfur cast iron (Shelgunov’s experiments), as well as for corroding (“etching”) refractory deposits in acid (Bessemer) retorts and in the shafts of blast furnaces. In the latter case, manganese-containing blast furnace slag obtained from the smelting of ferromanganate is often used. They try to obtain highly ferrous slags in all cases where it is impossible or undesirable to raise the process temperature. In particular, by adding small portions of iron ore, just like by adding lime, it is possible to slow down the process of silicon reduction at the end of acid open-hearth smelting. This circumstance is used in the English method of smelting low-carbon steel in acid open-hearth furnaces.

Chemically pure limestone consists of 56% CaO and 44% CO2; The best varieties of lime flux contain about 1% insoluble residue (SiO2 + Al2O3), the average up to 3%, the worst up to 5%. Chemically pure dolomite contains: 30.45% CaO, 21.75% MgO and 47.80% CO2. Typically, dolomites are less pure than limestones, and the content of ∑(SiO2 + Al203) in them reaches 5% or higher. Dolomites with a high (normal) magnesia content (18-20% MgO) are more often used as a refractory material and less often used as magnesium flux, for which dolomitized limestones with a MgO content of up to 12-15% are usually used.

The total consumption of limestone as a flux in ferrous metallurgy reaches 50-60% of the weight of the cast iron being smelted, and about 3/4-4/5 of this amount goes to the flux for blast furnace smelting. A comparative assessment of lime flux should be made depending on the composition of the slag used for fluxing. To simplify control of the chemical composition of the flux in limestone, only the amount of insoluble residue R = ∑(SiO2+Al2O3) is usually determined. The amount of free CaCO3 (and MgCO3 for blast furnace) will be determined depending on the composition of the slag by the formula:

where K is the ratio between ∑(CaO+MgO) and ∑(SiO2+Al2O3) in the slag, R is the amount of insoluble residue in limestone, 100/56 ≈ 1.8 is the approximate ratio between CaCO3 and CaO. For coke smelting blast furnace slag K ≈ 1, and the formula takes the form:

CaCO3 free = 100-2.8 R.

In addition to this formula, there are more complex formulas for the commercial evaluation of flux.

Fluxes in non-ferrous metallurgy

. Almost the same materials are used as flux as in the metallurgy of ferrous metals. The most common fluxes are: limestone, dolomite, iron ores, manganese ores, quartz and aluminosilicates; In addition, fluorspar, sulfides (for example, pyrite), gypsum and barite are used as flux. The influence of silicic acid materials and limestone on the formation of slags, see above. Sulfides are used for the purpose of sulfurization, i.e., to form matte, in order to avoid the transfer of valuable metals into slag in the case of ores containing little sulfur. Lime in the metallurgy of non-ferrous metals can be useful only in special conditions with high freight rates for fluxes. In lead smelting, lime (limestone) is introduced, replacing iron in the slag according to the equation:

4FeO 2SiO2+2PbS+2CaO+2C = 2Рb+2FeS+(2CaO SiO2+2FeO SiO2)+2СО.

In addition, lime, being a strong basic flux, is capable of displacing most other bases from silicates, for example by the reaction:

ZnО·SiО2+Ca0 = CaО·SiO2+ZnO.

Iron ores are used for fluxes in the form of FeO and Fe2O3. Iron oxide (FeO) is a very cheap component of the slag, forming liquid and fusible slag, but it increases the specific gravity of the slag and the transition of Cu2S into it. Ferrous flux is the basis for silicate ore:

FeO·SiO2+FeO = 2FeO·SiO2.

When reduced with carbon or carbon monoxide, iron oxides act as a precipitant in relation to lead according to the reactions:

2PbS+4FeO SiO2+C= 2Pb+2FeS+2FeO SiO2+CO2

4PbS+2Fe2O3+3C = 4Pb+4FeS+3CO2.

The fluxing ability of iron ore is higher, the purer it is. The SiO2 present in the ore not only binds part of the iron oxide, but also consumes a certain amount of CaO to form the corresponding slag. The following iron ores are used as flux: hematite Fe2O3, limonite Fe2O3 nH2O and, less commonly, siderite FeCO3. The expediency of using Fe3O4 (magnetic iron ore) is disputed in a number of cases, since it sometimes complicates the smelting process. Iron oxide (Fe2O3) does not form silicates and slags to form the latter after reduction to FeO. If Fe2O3 goes into the slag without reduction, then the slag becomes thick. With bases, iron oxide forms ferrites that are heavy in specific gravity and very refractory, which affects the properties of the slag. Manganese oxide (MnO) is similar to iron oxide and replaces the latter in slags in equivalent quantities. Slags containing MnO and FeO have greater fluidity than slags containing FeO alone. The most common flux is manganese peroxide (MnO2) - pyrolusite. Manganese oxides oxidize ZnS and reduce the dissolving ability of slag for ZnO, MgO and BaS. Gypsum and barite provide sulfur necessary for the formation of matte, and at the same time - CaO and BaO, which become part of the slag. Fluorspar melts at a temperature of 1378°C; it is very liquid in the molten state and dissolves the refractory constituents of the ore. Currently, fluorspar is almost never used as a flux.

Source: Martens. Technical encyclopedia. Volume 25 - 1934

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All about welding

Metallurgy is one of the most important crafts for modern man. Knowing the basics and features of this area of production, you can obtain the necessary metals or change their properties, weld parts of any size or obtain metal alloys.

To carry out high-quality production of, for example, cast iron, in addition to equipment, we need raw materials and, of course, metallurgical flux. In this article we will tell you everything about industrial flux, talk about the nuances of its use and understand what its role is in a modern metallurgical plant.

general information
Types of fluxes
The role of fluxes
Instead of a conclusion

general information

Blast furnace production is a set of industrial processes that result in the production of cast iron. For these purposes, the method of reduction smelting of iron ore or its concentrates is used. Melting takes place in a large furnace called a blast furnace. This type of production belongs to ferrous metallurgy and is one of the most important industries in modern production.

In addition to iron ore, additional materials called charge are used in production. Often this is manganese ore, pellets, sinter, or special fuel for the furnace. The most common fuel is coal coke. Sometimes the coke is replaced with gas or liquid fuel, which is blown into the top (called the hearth) of the blast furnace. Metallurgical flux is used as protection. We will talk about it in this material.

Types of fluxes

First you need to understand the types of industrial flux. Experienced craftsmen say that metallurgical flux can be basic, acidic or aluminous. The type of flux is selected based on the composition of the waste rock that is introduced into the furnace. In our case, waste rock is, in fact, the same iron ore. In a broad sense, waste rock is the rock that does not introduce significant changes into the production process and is used only as a base.

The most widespread is the basic metallurgical flux. This is due to the fact that gangue in most cases already contains silica, and the ratio of the total content of basic oxides to the total content of acidic oxides should be approximately 0.9-1.4. The main flux has all these properties, since it contains calcium oxide.

In blast furnace production, limestone stone is used as the main flux. Its deposits are found in many countries of the world and the reserves are very large. From a chemical point of view, limestone is a calcite mineral synthesized by nature. Pure laboratory calcite is half calcium oxide and half silica, an ideal metallurgical flux, but it does not occur naturally.

The production of artificial flux is too complex and expensive, so natural calcite (also known as limestone) is used. Unlike pure calcite, limestone contains silica impurities, which is not critical. It is important that the stone does not contain phosphorus. A small sulfur content is allowed within the permissible norm.

In addition to ordinary limestone, you can also use dolomitized limestone or, less commonly, dolomite. Chemically, such a stone is also a mixture of calcite and dolomite, but with magnesium content. The more magnesium, the more dolomitized limestone turns into dolomite. The use of such stones as a flux is justified when it is necessary to obtain cast iron with increased stability of physical and chemical characteristics. To do this, it is necessary to increase the magnesium oxide content in the slag to 5-10% in order to maintain the very stability of properties that we wrote about above when the melting temperature changes.

Most limestone mined in the former USSR is white or light gray in color, but other variations (from beige to dark gray) are found throughout the world. Limestone becomes darker in color if it contains organic substances, or becomes brown if the content of iron oxides is high.

Limestone stone is an extremely durable and dense material. Before loading into the oven, it is sifted, removing small fractions. But now the fine fraction is increasingly used in production, despite its fragility and increased crushing. The fine fraction of limestone is simply put into the furnace along with the sinter and this mixture can already be used as a flux.

Despite this, most industries have strict control over the size of the fractions entering the furnace. The largest permissible size is no more than 130 mm, and the smallest is up to 25 mm. Even if larger particles arrive at the plant, they are crushed. Indeed, in quarry limestone deposits, large stones are simply crushed into fractions of arbitrary size and transported to the workshop.

It is important to consider that limestone comes in different qualities. During melting, part of the free oxides of calcium and magnesium contained in the composition will be spent on slagging of its own waste rock, or, more simply, on the formation of an insoluble residue, which is in no way useful in production. Therefore, in order to determine the quality of limestone, it is enough to find out the amount of basic oxides in the composition of a particular batch of flux. The fewer there are, the better.

Fluxes - definition, purpose

Fluxes are chemical active substances with the help of which soldered surfaces are cleaned of grease and oxide films. Surface tension on parts treated with flux is reduced, resulting in improved solder flow. In addition, this chemical can protect joints from environmental influences.

Without flux treatment, solder may not adhere to the surface of the workpiece. Therefore, the material should be selected carefully, guided by the following requirements:

The flux must have a melting point lower than that of the solder.
It should not react chemically with the solder. That is, when these two materials melt, two immiscible layers should form.
In the gaseous state, the material should allow the solder to flow.
In a liquid state, it should spread well, wetting the products being connected and flowing between them.
The material must destroy and remove non-metallic films formed on them from surfaces.
It must be minimally active or chemically inert with respect to soldered alloys and metals.

The role of fluxes

What is flux in metallurgy and what is its role? Let's turn to the concept of flux in general. So, flux is a special additive used in amateur and professional welding, as well as in large-scale production. When welding, flux performs a protective function. It also helps to form a high-quality, even seam.

As you understand, in blast furnace production there is no welding process, so fluxes play a slightly different role here. With their help, it is possible to reduce the melting temperature of ore and give the molten mass the necessary physical and chemical properties. In addition, during the smelting process, fluxes remove excess sulfur from cast iron and stabilize the operation of the blast furnace.

Features of fluxing processes during soldering

Lecture 7

Soldering methods are classified according to GOST 17349-79 according to the following characteristics: by the method of removing the oxide film, by the mechanism of formation of the solder joint and by the heating method.

The oxide film on the surfaces of the soldered metal and molten solder prevents interaction between them. To remove the oxide film during the soldering process, fluxes, self-fluxing solders, controlled gas environments, vacuum, and physical and mechanical means are used. The oldest of these means of removing oxide film are fluxes.

Flux is a non-metallic substance that is designed to remove adsorbed oxygen or oxide films from the surface of the soldered metal and solder and prevent their formation during soldering in air, to change the surface tension at the interface between the solid and liquid phases.

In general, the flux must meet the following requirements: the melting temperature of the flux can be 50 - 100 O C lower than the melting temperature of the solder; the flux should spread well over the surface of the soldered metal and solder to form a continuous film that protects these surfaces from the harmful influences of the environment; reduce the surface tension of the molten solder, ensuring the most complete wetting of the metal being soldered; the flux should not change its composition when heated in the soldering temperature range; must maintain fluxing properties throughout the entire soldering process; can be easily removed from the surface of the part after soldering; do not cause corrosion.

The fluxing process during soldering generally involves three steps:

wetting the soldered metal and solder with flux; removing oxide films from the surface of the soldered metal and solder; displacing flux from the joint gap with molten solder.

The mechanism of the fluxing action of flux solutions and melts consists, depending on the nature of the fluxing component, of the following processes: 1) chemical interaction between the main components of the flux and the oxide film; the products of the fluxing reaction dissolve in the flux or are released in a gaseous state; 2) from the dispersion of the oxide film as a result of the adsorption decrease in its strength under the influence of the flux melt; 3) from the chemical interaction between the active components of the flux and the metal being soldered, as a result of which the oxide film gradually separates from the surface of the metal and transforms into flux; 4) from dissolving the oxide film in the flux; 5) from the destruction of the oxide film by fluxing products; 6) from the dissolution of the soldered metal and solder in the molten flux.

The variety of physicochemical properties of metals and alloys used in soldered products, and consequently, differences in the composition and properties of the oxide films formed on their surface, necessitated the use of various fluxing substances.

Some of them have a certain degree of versatility, that is, they can be used for a number of metals and alloys, others have a highly specialized purpose.

The most universal fluxes for high-temperature soldering turned out to be those based on sodium tetraborate Na2B4O7 (dehydrated borax) and boric acid H3BO3. For low-temperature soldering, the most universal fluxes are based on zinc chloride (ZnCl2).

Most fluxes consist of many chemicals. For example, flux 34A for soldering aluminum alloys consists of four components and has the composition:

Potassium chloride KCl – 50%

Lithium chloride LiCl – 32%

Floral sodium NaF – 10%

ZMNC chloride ZnCl2 – 8%

When analyzing flux compositions of complex composition, one can see that, on the one hand, they contain components that do not give a noticeable reaction either with the oxide film or with the base metal.

These substances are the basis of the flux, which serves to form a protective film during soldering, as well as to dissolve other components of the flux and fluxing products. In fluxes composed of halide salts, the role of such a base is played by chlorides of alkali and alkaline earth metals, which readily dissolve other components of the flux in their composition, and are also carriers of products formed during the fluxing process.

On the other hand, a flux of complex composition contains active substances. In flux 34A, such substances are sodium fluoride, which energetically dissolves metal oxides, and zinc chloride, which interacts directly with aluminum.

The fluxing process is associated with the interaction of oxide films or metals directly with molten fluxes, among which, according to the fluxing mechanism, two main groups can be distinguished:

Ø oxide fluxes;

Ø halide fluxes.

Oxide fluxes react primarily with the oxide film, while the basis of fluxing with halide fluxes is reactions with the base metal.

Oxide fluxes include fluxes based on sodium tetraborate, boric acid and their alloys, used for high-temperature soldering, as well as glass-type fluxes. When the soldered metal is wetted with oxide flux, interaction reactions occur between the oxides that are part of the oxide film, MeO(op) and the flux oxides - MeO(F) according to the following scheme:

MeO(op) + MeO(F) = MeO(op) * MeO(F)

As a result of these reactions, complex compounds are formed that destroy the oxide film.

When fluorides are introduced into oxide fluxes, simultaneously with the chemical interaction between the oxides, the oxide film dissolves in the fluorides. In some cases, to increase the activity of fluxes, fluoroborates are added to their composition, along with fluorides, for example, potassium fluoroborate KBF4 and sodium fluoroborate NaBF4.

Potassium fluoroborate decomposes when heated according to the reaction:

KBF4 = KF + BF3

The released potassium fluoride dissolves the oxides of the oxide film, and boron trifluoride enters into active chemical interactions with them.

For example, when soldering stainless steels, boron trifluoride reacts with chromium oxide according to the following reaction:

Cr2O3 + 2BF3 = 2 CrF3 + B2O3.

Boric anhydride, released during this reaction, interacts with oxides, forming complex compounds, usually amorphous and easily removed.