Auto repair shop workers, installers and other welding professionals are now actively turning to semi-automatic soldering. This method is the future, the technology is in many ways comparable to MIG / MAG welding. And it differs mainly in the solid filler wire used, and also in the fact that during MIG soldering, the base material does not melt. We suggest you learn more about the positive aspects of the method, its nuances and areas of its application from our article.

What is semi-automatic soldering

Inert gas MIG soldering, or MIG shielded gas soldering, as it is sometimes called according to existing international standards, is a process of hard soldering in the form of copper wire. An electric arc is established between a constantly melting wire solder and the metal to be welded. The supplied gas protects the arc and molten solder from the effects of ambient air, namely oxygen, which is present in the air and which rapidly oxidizes the molten metal and significantly reduces the quality of welding.

Features of semi-automatic soldering

Semi-automatic soldering is a high-tech process that has its own characteristics.

• When soldering using the MIG / MAG method, a special bronze welding wire, including aluminum or silicon, must be used as an electrode. For example, CuSi3, or a better analogue, 19.30, 19.40. Wire based on bronze or copper is quite expensive, and the difference in price between European production or, for example, Chinese will not be significant. If MAG welding (in an active gas atmosphere) is characterized by an abundance of spatter, the presence of porosity, an unstable arc and strong vaporization, then during MIG soldering, on the contrary, the base metal does not melt, so zinc evaporates to a much lesser extent. This is due to the fact that the melting point of bronze wire is much lower than that of steel, and therefore the welded parts do not melt. Due to the low heat input, the risk of deformation is reduced, even on very thin sheets from 0.3 millimeters thick. That is, the process, being actually soldering, ensures the speed of work and the strength of the joints as in welding.
• Due to the fact that when soldering with a semi-automatic device, thin metal is not melted, it is possible to solder coated steel sheets (phosphated, galvanized, aluminized) and uncoated, sheets of two-layer steel and stainless steel.
• The resulting seam is strong. Such a brazed joint has a higher mechanical strength when compared with the seam formed in the MAG welding process. The degree of thermal deformation of parts during the soldering process is significantly lower than during welding, therefore, on finished product less noticeable distortion. The seam is practically not subject to corrosion, since the zinc layer is intact even in place weld. Another advantage of this technology is good ability to cover the gap.
• Soldering is recommended in the “spot”, pulse mode or the “angle back” method, in which the welder leads the electrode from left to right. In both cases, a "short" arc must be observed.

What is the principle of the semi-automatic soldering method and the difference from MIG welding?

The basic principle of MIG-MAG soldering is that during the process, a metal wire is fed through a welding torch and melted under the influence of an electric arc. If we talk about the difference between welding and soldering technologies, then in the first case, the destroyed zinc coating forms slag with molten weld metal, as well as various shells and pores. This indicates a reduced quality of the seam and the absence of a zinc coating at the welding site. We have to send the parts for galvanic operation again in order to restore the anti-corrosion coating. The discovery of the MIG soldering method avoided such problems.

The MIG soldering method differs from the semi-automatic gas shielded welding method also in the type of wire used. For MIG-braizing, CuSi3 copper wire is used. Due to the low melting point, as mentioned above, the base metal does not melt. The zinc coating eventually forms a chemical compound on its surface that protects the weld from corrosive processes.

Getting ready for work

Before starting work, it is important to correctly set up the semi-automatic welding machine:

1. Determine the strength of the welding current depending on the thickness of the metal being welded. The instructions for the unit provide a table of correspondence of these values. In case of a lack of welding current, the semiautomatic device does not weld well enough.
2. According to the available instructions, determine the required wire feed speed. This indicator can be adjusted using interchangeable gears in the unit. It will directly affect the speed of applying the welded seam. Today, models equipped with special gearboxes are on sale.
3. Set the current source to the parameters you need (voltage and current). We recommend checking your settings on some example. The reason for the error-free operation, stable welding arc, normal bead formation. In this case, you can already act on the main material.
4. Setting up the wire will not cause difficulties. Its flow through a special hose into the mouthpiece or in the opposite direction is determined by the position of the lever, which you will see on the device.
5. An important point is the regulation of the flow of protective gas. To do this, slowly open the valve, and unscrew it until it stops. This is necessary to prevent leakage from the valve. Then you need to press the key located on the handle of the welding torch. The wire should remain "standing" and the gas valve should open. A slight hiss of gas will be heard, which comes out of the nozzle of the gas burner. At this time, the gas flow rate (its value can be seen on the pressure gauge on the flow scale) should be 8-10 liters per minute. This is the optimal indicator when soldering metal with a thickness of 0.8 mm. Therefore, you need to adjust the gas flow rate based on your task.

Where is MIG soldering most commonly used?

This technology has a wide range of applications in various fields.

Auto service and automotive industry. MIG soldering is also used in car body repair, as the zinc coating of the steel sheets is not damaged. In large-scale production of automobiles, this method is used both in manual installations and in fully automated systems.

In addition, small and medium-sized enterprises resort to soldering with a semi-automatic welding machine for various purposes. industrial enterprises by doing:

• installation of air conditioning, ventilation and cooling systems,
• production of light metal structures, elements of facades and roofs, pipes, cases of electrical units, chimneys.

Suitable for soldering are all gas-shielded welding positions and all types of welding seams. Seams in vertical and overhead positions are equally flawless with proper handling of the welding torch. Due to the low heat input, the method is effective both when joining non-alloy steel sheets and galvanized sheets, as well as chromium-nickel sheets.

What equipment and materials are suitable for semi-automatic soldering

Materials for soldering semiautomatically:

• wire - copper with additives,
• gas - argon.

There is no need to use any of the standard fluxes used in standard welding technologies that can cause serious problems. The arc independently activates the surface.

1. With this method, the wire is both a conductive electrode and a filler material.

• When making MIG soldering of galvanized parts, SG-CuSi3 wire is most often used. Its advantage lies in the low hardness of the brazed seam, which makes it easy to machine. Due to the presence of 3% silicon in the composition of the wire, the fluidity of the deposited material is significantly increased.
• Copper wire of composition SG-CuSi2Mn is also used for soldering galvanized parts, but the deposited material is quite hard, so subsequent machining becomes more complicated.
• Welding wires SG-CuAL18Ni2 and SG-CuAL18 are used when it is necessary to solder steel with aluminized coating.

MIG welding wires are softer than steel wires, so the wire feeder should be a 4-roller wire feeder with smooth semi-circular grooves. For low friction in the torch hose mechanism, a Teflon guide channel and massive current collectors must be used.

1. As a rule, in the process of soldering, argon is used as a protective gas with small additions of oxygen and carbon dioxide. The shielding gas supplied to the welding zone protects the arc and the weld pool with molten metal.

Our online store offers a wide range of welding equipment used for MIG soldering.

• Models with the already incorporated function of semi-automatic soldering. Most often, such inverter devices are distinguished by a simplified setting method, which is suitable for inexperienced welders and an in-depth one for real professionals.
• Models that can be soldered, although there are no special programs for it, the process of setting up the device becomes more complicated.

Kazakhstan Respublikasynyn Ministry

Bilim zhane gylym of education and science

Minister of Leagues of the Republic of Kazakhstan

D. Serikbaev atyndagy EKSTU

SHKMTU them. D. Serikbaeva

APPROVE

Dean of the Faculty of MiT

_______________2014

Pіsiru men danekerleu аdіsterі

Zerthanalyk zhұmystar boyinsha adіstemelik

nuskaular

Special Welding and Soldering Methods

Guidelines for laboratory

(practical) work

Specialty: 5В071200, "Engineering"

Specialization: "Technology and equipment of welding production"

Ust-Kamenogorsk

Methodological instructions were developed at the Department of Mechanical Engineering and Technology of Structural Materials on the basis of the State Educational Standard of the Republic of Kazakhstan 3.08.338 - 2011 for students of the specialty 5B071200 "Mechanical Engineering".

Discussed at the meeting of the department "M and TCM"

Head department

Minutes No. 2014

Approved by the Methodological Council of the Faculty of Mechanical Engineering and Transport

Chairman

Minutes No. ____ dated _______________ 2014

Developed

Position Professor

Comptroller

The guidelines provide full descriptions of laboratory and practical work.

Each work consists of a title, goals and objectives, a theoretical part of the issue under study and recommendations for practical implementation, indicating the final table or graph form. In addition, the requirements for the report on the work are indicated and a list of the main questions for self-examination is given.

1 TECHNOLOGY AND EQUIPMENT FOR GAS WELDING

1.1 Purpose of work

aim laboratory work is the study:

welding process;

welding techniques;

Welding station devices;

Purpose of welding devices and fixtures.

1.2 Equipment, fixtures, tools

filler wire;

gas generator;

Gas-burner;

Gas cutter;

Overalls.

In gas welding, to melt the edges of the parts to be joined and the filler material introduced, the heat generated during the combustion of combustible gases (acetylene, propane, butane, kerosene vapor, hydrogen, etc.) in technically pure oxygen is used. In this case, the maximum flame temperatures are 3100, 2750, 2500, 2400, 21000C, respectively. Oxy-acetylene welding is the most widespread due to its economy and efficiency with the maximum quality of the joints.

1.3.1 Oxygen

For welding, gaseous oxygen is used, which is obtained from the air by deep cooling (liquefaction). Oxygen is delivered to the place of consumption in steel cylinders of blue color under pressure of 15 MPa or in liquid form - in special vessels with good thermal insulation. To convert liquid oxygen into gas, gasifiers or pumps with liquid oxygen evaporators are used.

Oxygen has a high chemical activity, forming compounds with all chemical elements except for inert gases. Reactions of the compound with oxygen proceed with the release a large number heat.

When pure gaseous oxygen comes into contact with organic substances, oils, fats, they can spontaneously ignite. Therefore, all oxygen equipment must be thoroughly degreased. Oxygen is capable of forming explosive mixtures with combustible gases over a wide range.

1.3.2 Acetylene (С2Н2)

Acetylene is the main combustible gas for gas welding and cutting of metals, the temperature of its flame when burned in a mixture with commercially pure oxygen reaches 31500C (with an excess of oxygen 34500C).

Technical acetylene at normal pressure and temperature is a colorless gas with a sharp specific odor.

When using acetylene, its explosive properties must be taken into account. The self-ignition temperature of acetylene ranges from 240-6300C and depends on the pressure and the presence of various substances in it.

Increasing the pressure significantly lowers the auto-ignition temperature of acetylene.

Acetylene with air forms explosive mixtures ranging from 2.2 to 81% acetylene by volume at normal atmospheric pressure, and with commercially pure oxygen - in the range from 2.3 to 3% acetylene. The most explosive mixtures containing 7 - 13% acetylene.

The presence of copper oxide reduces the ignition temperature of acetylene to 2400C. Therefore, in the manufacture of acetylene equipment, the use of alloys containing more than 70% copper is strictly prohibited.

The explosiveness of acetylene decreases when it is dissolved in liquids. It is especially soluble in acetone. In one volume of technical acetone at 200C and normal atmospheric pressure, up to 20 volumes of acetylene can be dissolved. The solubility of acetylene in acetone increases with increasing pressure and decreasing temperature.

Acetylene is obtained by decomposition of calcium carbide (CaC2) with water according to the reaction

Directly at the workplace of the gas welder, austylene is either in white cylinders or obtained from calcium carbide in a gas generator.

1.3.3 Oxy-acetylene flame

The structure of an austylene-oxygen flame is shown in Figure 1. It is also characteristic of most gas-oxygen mixtures.

1 - core; 2 - recovery zone; 3 - flame torch

Figure 1 - Scheme of the structure of a gas-oxygen flame.

The core 1 of the flame consists of a mixture of cold gases with clearly defined boundaries. In zone 2, acetylene burns in pure oxygen at a ratio of 1:1 according to the reaction

This zone is characterized by a reducing atmosphere due to the presence of CO and H2 and a maximum temperature of 31500C. When melting and welding with this zone, the process proceeds efficiently and with minimal oxidation of the weld metal.

In the outer zone, the products of incomplete combustion are afterburned due to the oxygen of the ambient air according to the reaction

In this case, a torch of flame 3 is formed, which is used for additional heating of the welded edges and seam.

Depending on the ratio of gases in the mixture, the flame can be normal (Figure 1), carburizing (acetylene) and oxidizing (Figure 2).

a) is normal; b - carburizing; c - oxidative

Figure 2 - Types of acetylene-oxygen flame.

With an excess of acetylene (Figure 2.b), the core increases, acquires a blurry outline and begins to smoke. Such a flame is used when welding high-carbon steels and cast irons. With an excess of oxygen, the core of the flame is shortened and sharpened. Such a flame, despite the higher temperature of 34500C, causes oxidation of the alloy components and should not be used for welding.

1.3.4 Welding methods

Depending on the direction of movement of the torch and filler rod along the seam, left and right welding methods are distinguished. With the left method (Figure 3.a), the filler rod moves ahead, followed by the burner. The left method is simpler and is used for welding small thicknesses up to 3 mm.

a - left; b - right; 1 - filler rod; 2 - gas burner

Picture 3 - Gas welding methods

With the right method, the burner moves ahead, followed by the filler rod (Figure 3.b). The right method is more complicated, but more productive and allows you to effectively influence the liquid metal bath (mix, maintain, move).

Vertical seams are made in the left way, and horizontal and ceiling seams are made in the right way. For better mixing of the metal, it is necessary to immerse the end of the filler rod in the molten bath and make oscillatory movements with it. The diameter of the filler rod is chosen approximately equal to the welded thickness, but not more than 4-5 mm. The filler rod is taken of the same composition as the base metal. The power of the burner is chosen at the rate of 120-150 l/h per 1 mm of the thickness of the welded metal. When welding sheets of different thicknesses, the burner power is selected according to the greater thickness.

Alloy steels and non-ferrous metals are welded using fluxes of appropriate compositions.

1.3.5 Equipment of the welding station

The device of the welding post may differ only in the method of supplying acetylene:

Supply of acetylene in a cylinder;

Production of acetylene at the welding site in the gas generator.

Figure 17 shows the first version of the scheme of the welding post.

In today's unstable world and aggressive external environment a person especially carefully tries to preserve the space around him, to make his "small" world more reliable. The car has long become a necessary element of everyday life, but when we go out on the road, we find ourselves in a zone of increased danger. When purchasing a car, the buyer pays great attention to safety issues. Any participant in the movement wants not only to avoid possible accidents on the roads, but also to stay alive if an accident does occur.

Since 1997, the EuroNCAP European Committee has been conducting independent crash tests of car safety, checking cars in various non-standard emergency situations, assessing its safety for drivers and passengers, and compiling a Safety Assist car safety rating.

All these car crashing efforts are aimed at testing the effectiveness of passive car protection systems. And not in vain, because in the event of an accident, the reliable operation of these systems can save the life of the driver and passengers.

Car manufacturers pay due attention to the safety of passengers. For example, the Ford Fusion body has a specially designed power frame to absorb impact energy in the event of a collision, and the doors are reinforced with steel bars. The body of the Audi A3 has increased rigidity and energy-absorbing skin for the passenger's footwell, which will provide the driver and passengers with reliable protection in the event of an impact.

New requirements - new steels

To increase competitiveness, manufacturers are trying to create economical and safe cars. The new requirements for a modern car body are dictated by the desire to get a more economical, and therefore lighter body; at the same time, passive safety requirements must be at the highest level. All this makes automakers move forward.

New body designs, innovative technologies

New concepts for building a car body are directly related to innovative technologies. As a rule, this is a lightweight structure using ultra-high strength steel, light metals - aluminum and magnesium alloys, the use of fiber reinforced plastics, or various combinations of all these materials in one body structure. All this is dictated by economic tasks solved in mass production, and the desire of consumers to get an economical and safe car.

Today, there are two ways that manufacturers go: hybrid joint technology, light alloys, using glue, which allows you to distribute the load in the joints over the entire contact surface, and mechanical-thermal methods of connection. The goal is to find processes that are easy to implement in production and reproducible later when restoring a body after an accident. Now it is impossible to say which of the methods will become more widespread, since the suppliers of rolled metal, in collaboration with car manufacturers, are constantly developing new alloys and metal processing methods in order to obtain the required characteristics. Often new alloys and new metal processing methods open up new application possibilities.

Types of steels and alloys used in car body construction

Steel

Mild steel up to 200 N/mm2

High strength steel HSS 210-450 N/mm2

Heavy duty steel EHS 400–800 N/mm2

Aluminum alloys

Aluminum magnesium AlMg approx. 300 N/mm2

Aluminum silicon AlSi approx. 200 N/mm2

New steels - new repair technologies

MIG soldering (MIG brazing) - new technology jointing, also called brazing, is used to join high-strength steels of automotive body panels. High strength steels such as Boron have received their high performance stiffness due to heat treatment. But during conventional semi-automatic welding, the temperature of the weld pool is 1500–1600 ° C, which leads to changes in the characteristics of the metals being joined and, as a result, to changes in the entire body structure. As a result, we get a "disabled body" that carries a hidden threat.

The MIG soldering process is a soldering process hard solder. The welding process MIG-soldering (Metal-Inert-Gas), as the name implies, takes place in an environment of inert argon gas. The gas protects the arc, molten solder and workpiece edges from the effects of ambient air. The process itself is simple, like MIG / MAG welding, and is applicable in body restoration conditions. Due to the lower melting temperature of the solder - approximately 1000°C - no diffusion of metals occurs, and due to the relatively low temperature of the bath, the inherent properties of the steels to be joined are preserved. This method virtually eliminates the deformation of the joined sheets.

I would especially like to note that due to the lower melting temperature of the solder, there is minimal burnout of zinc during soldering (zinc melts at 419°C, evaporates at 906°C). The resulting seam has a high resistance to corrosion. Soldering wires are made of copper-based alloy with additives of silicon (CuSi3) or aluminum (CuAl8). The solder combines with the zinc, resulting in a weld with high anti-corrosion properties.

The brazing process takes place at lower current settings, much lower than conventional mild steel welding, which is necessary to obtain a low bath temperature. In this case, the pushing method is used: the torch is driven at an obtuse angle in the direction of the weld. The burner must be tilted no more than 15° from the vertical so that the gas is not blown out of the bath area and protects it. The gas flow must be within 20–25 l/min, for this it is necessary to use a reducer with a flow meter.

When butt-welding two sheets, it is necessary to create a gap between them, approximately equal to the thickness of the sheet being welded (about 1–1.2 mm), and leave room for filling with solder. The wire feed speed is higher than normally used in welding.

You can check how strong the soldering seam is; we got about 30 cycles of bending the seam. The result can be seen in the photographs: the seam remained intact, the connection turned out to be stronger than the main steel plate. The test was carried out with simple steel plates, the first test with high-strength steel did not break; apparently, this requires a special device, and not just a vise.

New repair technologies - new repair equipment

The quality of emergency body repair requires not only uncompromising precision in the restoration of the body structure in accordance with the manufacturer's data, but also the use of methods that will not violate the strength characteristics of the structure. If you are going to carry out repairs in accordance with the requirements of the car manufacturer, you must apply modern methods repairs that are solved using OEM (Original Equipment Manufacturer) equipment.

Now semi-automatic MIG / MAG with the ability to produce welding and soldering have become available for body shops. French manufacturer GYS offers two models with this feature: TRIMIG 205-4S and DUOGYS AUTO. Both devices are designed specifically for body repair. The DUOGYS AUTO model is of the greatest interest, and we will consider it in more detail.

The DUOGYS AUTO professional semi-automatic welding machine is ideal for body repairs at service stations working with modern bodies. It is designed to work with steel, aluminum and braze welding of high-strength steels using CuSi3 or CuAl8 wire.

■ CuSi3 wire is used according to technological requirement Opel and Mercedes.

■ CuAl8 wire is used according to the technological requirements of Peugeot, Citroen, Renault.

■ AlSi12 aluminum wire is used for welding automotive sheets with a thickness of 0.6-1.5mm.

■ AlSi12 aluminum wire is used for welding automotive sheets with a thickness of more than 1.5mm.

This machine is equipped with two four-roller mechanisms with the ability to connect a torch with an integrated Spool Gun feeder. It comes with two three-meter 150 A torches: one for working with steel, and the other for welding and soldering, and a Spool Gun with a four-meter sleeve. Thanks to the synergic mode, the device is easily reconfigured for different operating modes.

DUOGYS AUTO has two setting modes: automatic and manual. In automatic mode, it is necessary to select the type and diameter of the welding wire, set the desired current level on the seven-position switch, and the wire feed speed will automatically adjust according to the specified conditions. In this case, it is possible to fine-tune the speed. If necessary, you can always switch to manual mode and work as with a conventional semi-automatic.

The device has two useful modes. The SPOT mode is convenient for tacking operation. The DELAY delay mode is useful for welding thin sheets of steel and aluminum, while limiting the risk of burn-through or deformation of the sheets being welded.

For body stations with low traffic, we can recommend a professional TRIMIG 205-4S semi-automatic welding machine. It has exactly the same current generator as its older brother DUOGYS AUTO, but only one built-in two-roller drive mechanism and will require additional time to reset the wire spools.

Otherwise, it is the same machine, it can be used to weld steels, braze welding, and by connecting a torch with a built-in Spool Gun wire feeder, and aluminum welding.

Soldering is one of the most well-known methods for joining metals. However, the soldering methods used until recently were used relatively rarely due to low productivity, insufficient connection reliability, the complexity of the technological process and other shortcomings.

Recently, new soldering methods have emerged that use different kinds electric heating: t.v. hours, electron beam, heating in thermal furnaces, ultrasonic soldering, etc. These heating methods, in combination with protective media such as vacuum, inert and reducing gases (hydrogen, CO, etc.), special solders that do not require fluxes, allowed to significantly improve the quality of brazed products and increase the productivity of the soldering process.

New soldering methods make it possible to use the part in products without subsequent machining.

Using new soldering methods, it is possible to join refractory metals and metals with special properties.

Thin-walled structures exposed to high temperatures can be fabricated from such metals under vacuum conditions. soldering in state of the art meets all the requirements of production in terms of economics, since the use of solder joints helps to reduce labor intensity and reduce the cost of the product.

Soldering has become one of the most important technological processes metal compounds in many branches of the metalworking industry. Soldered joints work reliably in critical products in aviation, radio engineering, automotive, instrumentation and other industries.

Soldering is the process of obtaining a permanent connection of materials with heating below the temperature of their autonomous melting by wetting, spreading and filling the gap between them with molten solder and their adhesion during the crystallization of the seam.

Soldering of metals should be carried out at a certain temperature and in environments that ensure good wetting of the metal with solder and mutual diffusion of the liquid solder and the metal of the product to be joined. In this case, conditions must be created for the occurrence of capillary phenomena. The latter ensure the penetration of liquid solder into the gaps between the connected products. The solder penetrates into the gaps between the parts to be joined, crystallizes upon cooling and forms a strong bond. You can heat the product and melt the solder with an arc, the heat released in electrical contact, in resistance furnaces, by induction, by electron beam, by gas flame, by immersion in salt baths or liquid solder, etc.

Soldering has several advantages over welding.. In many cases, soldering uses less heat. Soldering does not cause significant changes chemical composition and mechanical properties of the base metal. As a rule, residual deformations in brazed joints are much less than in welded ones. Therefore, it is possible to maintain the exact dimensions of brazed structures without additional processing. Soldering connects carbon and alloy steels, cast iron, non-ferrous metals and alloys, noble metals, etc., as well as dissimilar materials. The soldering process is easily mechanized and automated.

Most soldering methods are carried out using various solders, and only in cases where fusible eutectics can form between metals during soldering, soldering is possible without special solder.

Solders have a number of requirements general. The solder should spread well over the surface of the base metal, wet and dissolve it, easily fill the gaps between parts, provide the necessary joint strength, etc.

Solders are used in the form of tapes, pastes, rods. Solders are especially common in the form of wire loops and foil spacers, stamped in accordance with the surface of the parts to be joined.

Widely used as solders are high-temperature solders - alloys based on silver, aluminum, copper, etc., which, as a rule, have a melting point above 450-500 ° C (723-773 K). Copper-zinc solders PMC 36, PMC 48, PMC 54 have a tensile strength σ in = 21 35 kgf / mm 2 (206.0 - 343.2 MN / m 2), elongation up to 26%, recommended for soldering copper products , tombac, brass, bronze. Silver solders have a melting point of 740-830° C (413-1103 K). According to GOST 8190-56, solder grades are divided depending on the content of silver in alloys, which varies from 10 (PSr 10) to 72% (PSr 72). They also contain zinc, copper and a small amount of lead. These solders are used for soldering thin parts, connecting copper wires, and in cases where the solder point should not drastically reduce the electrical conductivity of butt joints.

Low-temperature solders have a melting point below 450-400°C (723-673 K). They have little strength. They are used for soldering almost all metals and alloys in their various combinations. In most cases low temperature solders contain a significant percentage of tin.

Low-temperature tin-lead solders (GOST 1499-70) have an upper critical melting point of 209-327 ° C (482-600 K). Tin has a melting point of 232°C (505 K). Its tensile strength is 1.9 kgf / mm 2 (18.6 MN / m 2), relative elongation is 49%, HB is 6.2 kgf / mm 2 (60.8 MN / m 2). Tin-lead solders POS-90, POS-61, POS-40, etc. are used for soldering copper devices, aircraft radiators, brass and iron products, copper wires, etc.

The formation of a high-quality brazed joint largely depends on the possibility of the most complete removal of oxide, adsorbed gas and liquid films from the metal surface. In the practice of soldering, various kinds of fluxes, a reducing atmosphere or vacuum are used to remove surface films. Recently, mechanical destruction of films using ultrasonic elastic vibrations has been successfully used for this purpose.

Soldering fluxes have several purposes. They protect the base metal and solder from oxidation, dissolve or reduce the formed oxides, improve surface wetting, and promote solder spreading. Fluxes can be used in solid, liquid and gaseous form (in the form of powders, pastes, gas solutions). The role of the flux is performed by some special gas atmospheres and vacuum, which can also contribute to the reduction of oxides and improve wetting conditions. In some cases, the fluxing effect is exerted by the individual components that make up the solders. For example, phosphorous solders do not require fluxes when soldering copper alloys.

Soldering can be carried out with general or local heating of the structure. With general heating, the product is placed in an oven or immersed in a salt or metal bath. Under these conditions, the product warms up evenly. This process is suitable for soldering products of relatively small dimensions. With local heating, only a part of the structure in the weld zone is heated.

Soldering with a soldering iron. The most well-known and widely used low-temperature soldering method is soldering with soldering irons. In improved designs of soldering irons, a mechanized supply of solder and its dosage are provided.

Soldering with a gas flame. Gas flames are soldered manually and mechanized. The source of heating is the flame of conventional burners using a relatively low-calorie gas, such as propane, as a fuel. The gas flame only partially protects the junction from oxidation, so the use of fluxes and pastes is recommended.

In some cases, fluxes are fed in the gaseous state directly into the flame. When gas soldering, it is possible to use high-temperature and low-melting solders.

For large parts, a soldering process called "bronze welding" is sometimes used. In this case, brass rods serve as solder, the product is heated with an oxygen-acetylene torch. First, the edges are heated with it, flux is poured, they are tinned with a thin layer of solder, and then the entire volume of cutting is filled with solder. Bronze welding is used in the repair of cast iron and steel parts.

The technological process of soldering includes a set of operations performed, the main of which are the following.

Surface preparation for soldering. The quality of surface preparation for soldering largely determines the level and stability of the solder joint properties. There are the following main methods of surface cleaning: 1) thermal (burners, annealing in a reducing atmosphere, in vacuum); 2) mechanical (processing with a cutting tool or abrasive, hydro-sand-blasting or shot-blasting); 3) chemical (degreasing, chemical etching, electrochemical etching, etching with ultrasonic treatment, combined with degreasing and etching).

Preparation of the part for soldering also includes the application of special technological coatings by galvanic or chemical methods, hot tinning (immersion in molten solder), using ultrasound, cladding, thermal vacuum spraying. Often the assembly includes the application of solder, laying it in the form of metered blanks of wire or foil. When placing solder, it is necessary to take into account the soldering conditions: the location of the product in an oven or other heating device, heating and cooling modes.

Flux application. Sometimes when assembling parts for soldering, it is necessary to apply a flux. Powdered flux is diluted with distilled water to a thin paste and applied with a spatula or glass rod, after which the parts are dried in a thermostat at 70–80°C for 30–60 minutes. During flame soldering, the flux is fed on a bar of heated solder, when soldering with a soldering iron - the working part of the soldering iron or together with solder, in the case of using tin-lead solder - in the form of tubes filled with rosin.

Soldering(heating of the joint or general heating of assembled parts) is carried out at a temperature higher than the melting point of the solder, as a rule, by 50–100 ° C. Depending on the melting temperature of the solders used, soldering is divided into high-temperature and low-temperature soldering.

Surfaces that are not subject to soldering are protected from contact with solder by a special graphite coating with the addition of a small amount of lime. Soldering by dipping into molten solder is used for steel, copper, aluminum and hard alloys, parts of complex geometric shapes. This process consumes a large amount of solder. A variation of soldering by immersion is soldering by a traveling wave of solder, when the molten solder is pumped and forms a wave above the level of the melt. The part to be soldered moves in the horizontal direction. At the moment of touching the bath, soldering takes place. A traveling wave is soldered in the radio-electronic industry in the production of printed radio editing.

3. Soldering methods

Soldering methods are classified depending on the heat sources used. The most common soldering in the industry is radiation heating, exoflux, soldering irons, flame, immersion, electric arc, induction, electrical resistance, soldering in furnaces.

Soldering by radiation heating. Soldering is performed by radiation from quartz lamps, a defocused electron beam or a powerful light flux from a quantum generator (laser). The structure to be soldered is placed in a special container in which a vacuum is created. After evacuation, the container is filled with argon and placed in a fixture, on both sides of which quartz lamps are installed for heating. After the heating is completed, the quartz lamps are removed, and the fixture, together with the parts, is cooled. When applying laser heating, concentrated in a narrow beam thermal energy provides evaporation and spraying of the oxide film from the surface of the base metal and solder, which makes it possible to obtain junctions in an air atmosphere without the use of artificial gaseous media. With the radiation method of soldering, radiant energy is converted into thermal energy directly in the material of the solder and the soldered parts. This method of soldering is short.

Exoflux soldering. Basically, corrosion-resistant steels are soldered in this way. A thin powdery layer of flux is applied to the cleaned joint. The surfaces to be joined are aligned, and an exothermic mixture is placed on opposite sides of the workpieces. The mixture consists of different components, which are laid in the form of a paste or briquettes several millimeters thick. The assembled structure is installed in a fixture and placed in a special furnace in which the exothermic mixture is ignited at 500°C. As a result of the exothermic reactions of the mixture, the temperature on the metal surface rises and the solder melts. This method is used to solder overlap joints and ready-made blocks of small structures.

Soldering with soldering irons. The base metal is heated and the solder is melted due to the heat accumulated in the metal mass of the soldering iron, which is heated before soldering or during the process. For low-temperature soldering, soldering irons with periodic heating, continuous heating, ultrasonic and abrasive soldering irons are used. The working part of the soldering iron is made of red copper. A soldering iron with periodic heating during operation is sometimes heated from an external source of heat. Soldering irons with constant heating are made electric. The heating element consists of a nichrome wire wound on a layer of asbestos, mica or on a ceramic bushing mounted on a copper rod of a soldering iron. Soldering irons with periodic and continuous heating are more often used for flux soldering of ferrous and non-ferrous metals with soft solders with a melting point below 300–350°C. Ultrasonic soldering irons are used for flux-free low-temperature soldering in air and for soldering aluminum with fusible solders. Oxide films are destroyed by ultrasonic frequency oscillations. Abrasive soldering irons can solder aluminum alloys without flux. The oxide film is removed as a result of the friction of the soldering iron on the metal.

Solder assembly is essential. The assembly must ensure fixation of the relative position of the parts with the required gap and the flow of solder into the gap. In those cases where the solder is pre-laid into the joint in the form of a foil and then the assembly is heated (for example, in a vacuum furnace), it is necessary to ensure that the parts are compressed at the soldering temperature with a certain force. If this force is insufficient, then a too thick seam with unsatisfactory strength will be obtained. Excessive compression can damage the solder assembly.

Special devices are used to compress parts during soldering. The necessary compression force is provided by mechanical clamps or the difference between the thermal expansion of the material of the product and the material of the fixture. The latter method is often the only one when oven soldering is carried out at high temperatures.

Gas soldering. When soldering, heating is carried out by a gas burner flame. As a combustible gas, mixtures of various gaseous or liquid hydrocarbons (acetylene, methane, kerosene vapor, etc.) and hydrogen are used, which, when burned in a mixture with oxygen, give a high-temperature flame. When soldering large parts, combustible gases and liquids are used in a mixture with oxygen, when soldering small parts - in a mixture with air. Soldering can be done both with special type burners, giving a wide flame, and with normal, welding blowtorches.

Soldering by immersion in molten solder. The molten solder in the bath is covered with a layer of flux. The part prepared for soldering is immersed in molten solder (metal bath), which is also a heat source. For metal baths, copper-zinc and silver solders are usually used.

Soldering by immersion in molten salt. The composition of the bath is selected depending on the soldering temperature, which should correspond to the recommended bath temperature of 700–800°C when working with a mixture of a certain composition. The bath consists of chlorides of sodium, potassium, barium, etc. This method does not require the use of fluxes and a protective atmosphere, since the composition of the bath is selected in such a way that it fully ensures the dissolution of oxides, cleans the soldered surfaces and protects them from oxidation when heated, i.e. . is a flux.

Parts are prepared for soldering, solder is placed on the seam in the right places, after which it is lowered into a bath with molten layers, which are a flux and a heat source, where the solder melts and fills the seam.

Electric arc soldering. During arc soldering, heating is carried out by an arc direct action, burning between the parts and the electrode, or an indirect arc burning between two carbon electrodes. When using a direct arc, a carbon electrode (carbon arc) is usually used, less often a metal electrode (metal arc), which is the solder rod itself. The carbon arc is directed to the end of the solder rod touching the base metal so as not to melt the edges of the part. A metal arc is used at currents sufficient to melt the solder and very slightly melt the edges of the base metal. Zinc-free high-temperature solders are suitable for direct arc soldering. Using an indirect carbon arc, it is possible to carry out the process of soldering with high-temperature solders of all types. For heating in this way, a special coal burner is used. The current to the electrodes is supplied from the arc welding machine.

Induction soldering (high frequency soldering). During induction brazing, parts are heated by eddy currents induced in them. Inductors are made of copper tubes, mostly rectangular or square, depending on the configuration of the parts to be soldered.

In induction brazing, the part is quickly heated to the soldering temperature using high concentration energy. Water cooling is used to protect the inductor from overheating and melting.

Electrical resistance soldering. With this method of soldering, a low-voltage electric current (4–12 V), but a relatively large force (2000–3000 A), is passed through the electrodes and heated to a high temperature in a short time; parts are heated both due to thermal conductivity from heated electrodes, and due to the heat generated by the current when it passes through the parts themselves.

When an electric current is passed, the solder joint is heated to the melting point of the solder, and the molten solder fills the seam. Contact soldering is carried out either on special installations that provide power with high current and low voltage, or on conventional resistance welding machines.

Soldering in ovens. For soldering, electric furnaces and less often flame furnaces are used. Heating of parts for soldering is carried out in ordinary, reducing or protective environments. Soldering with high-temperature solders is carried out using fluxes. When brazing in controlled environment furnaces, the cast iron, copper or copper alloy parts to be soldered are assembled into assemblies.

Soldering compounds of metals with non-metallic materials. By soldering, metal compounds can be obtained with glass, quartz, porcelain, ceramics, graphite, semiconductors and other non-metallic materials.

Processing after soldering includes the removal of flux residues. Fluxes, partially remaining after soldering on the product, spoil it appearance, change the electrical conductivity, and some cause corrosion. Therefore, their residues after soldering must be carefully removed. The remains of rosin and alcohol-rosin fluxes usually do not cause corrosion, but if, according to the operating conditions of the products, they are required to be removed, then the product is washed with alcohol, an alcohol-gasoline mixture, and acetone. Aggressive acid fluxes containing hydrochloric acid or its salts are thoroughly washed successively with hot and cold water using hair brushes.

Typical solder joints are shown in fig. 2.1. Soldered seams differ from welded seams in their structural form and method of formation.

The type of solder joint is selected taking into account the operational requirements for the node, and the manufacturability of the node in relation to soldering. The most common type of connection is lap soldering.

Rice. 2.1. Typical solder joints

In units operating under significant loads, where, in addition to the strength of the seam, tightness is necessary, the parts should only be joined with an overlap. Lap seams provide a strong connection, are easy to perform and do not require fitting operations, as is the case with butt or mustache soldering.

Butt joints are usually used for parts that are irrational to manufacture from a single piece of metal, as well as in cases where it is undesirable to double the thickness of the metal. They can be used for lightly loaded units where tightness is not required. The mechanical strength of solder (especially low-temperature solder) is usually lower than the strength of the metal being joined; in order to ensure the equal strength of the soldered product, they resort to increasing the area of ​​​​the junction by means of an oblique cut (in a mustache) or a stepped seam; Often, a combination of a butt joint with an overlap is used for this purpose.

Soldering can be used to produce complex configuration units and entire structures consisting of several parts in one production cycle (heating), which allows us to consider soldering (as opposed to welding) as a group method of joining materials and turns it into a high-performance technological process that can be easily mechanized and automation.

When soldering, the following defects are possible: displacement of soldered elements; shells in the seams; porosity in solder seam; flux and slag inclusions; cracks; don't drink; local and general deformities.