Soldering is a complex physical and chemical process of obtaining a permanent connection of materials, as a result of the interaction of a solid brazed (part) and liquid filler metal (solder), by melting them when wetting, spreading and filling the gap between them, followed by its crystallization.
The formation of a solder joint is accompanied by a solder joint between the solder and the brazed material. The strength characteristics of a solder joint is determined by the occurrence chemical bonds between the boundary layers of the solder and the soldered metal (adhesion), as well as the adhesion of particles inside the solder or the soldered metal to each other (cohesion). Soldering can connect any metals and their alloys.
Solder - a metal or alloy introduced into the gap between the parts or formed between them during the soldering process and having more low temperature start of melting than brazed materials. Pure metals are used as solder (they melt at a strictly fixed temperature) and their alloys (they melt in a certain temperature range).
For a high-quality connection of metals, the solder must spread and “wet” the base metal. Good wetting occurs only on a completely clean, non-oxidized surface.
Fluxes are used to remove the oxide film (and other contaminants) from the surface of the base metal and solder, as well as to prevent oxidation during soldering.
Advantages of soldering:
Allows you to connect metals in any combination;
connection is possible at any initial temperature of the soldered metal;
it is possible to combine metals with non-metals;
most solder joints can be soldered;
the shape and dimensions of the product are more accurately maintained, since the base metal does not melt;
allows you to get connections without significant internal stresses and without warping;
high strength and high productivity in capillary soldering.
Soldering technology
Getting a solder joint consists of several stages:
preliminary preparation of soldered joints;
removal of contaminants and oxide film from the surfaces of soldered metals using flux;
heating the parts to be joined to a temperature below the melting point of the soldered parts;
introducing a liquid strip of solder into the gap between the soldered parts;
interaction between soldered parts and solder;
crystallization of the liquid form of solder between the parts to be joined.
Copper soldering
Copper is one of the metals that lends itself perfectly to soldering. This is due to the fact that the metal surface can be relatively easily cleaned of contaminants and oxides without the use of particularly aggressive substances (copper is a slightly corrosive metal). There is a large number of low-melting metals and their alloys that have good adhesion to copper. When heated in air during melting, copper does not enter into violent reactions of interaction with surrounding substances and oxygen, which does not require complex or expensive fluxes.
All this makes it easy to carry out any type of soldering with copper with a large selection of solders (giving a wide range of solder joint properties) and fluxes for any environment and working conditions. As a result, over 97% of the world's soldering is made of copper and copper alloys.
In application to copper pipelines, the so-called "capillary" soldering has been developed. This required more stringent requirements for the geometry of the pipes used. But it made it possible to reduce the installation time of the capillary connection to 2-3 minutes (up to 1.5 minutes during the competition). As a result, soldered copper piping in plumbing is a plumbing classic.
Types of soldering
Connection technique copper pipes light and reliable. The most common joining technique is capillary brazing and brazing. Non-capillary soldering is not used when connecting pipes.
capillary effect.
The process of interaction between molecules or atoms of a liquid and solid body at the interface between two media leads to the effect of surface wetting. Wetting is a phenomenon in which the attractive forces between the molten solder molecules and the base metal molecules are greater than the internal attractive forces between the solder molecules (the liquid "sticks" to the surface).
In thin vessels (capillaries) or crevices, the combined action of surface tension forces and the wetting effect is more pronounced and the liquid can rise upwards, overcoming the force of gravity. The thinner the capillary, the more pronounced this effect.
To obtain the effect of capillarity in copper pipelines connected by soldering, "telescopic" connections are used. When inserting a pipe into a fitting, there is a gap not exceeding 0.4 mm between the outer diameter of the pipe and the inner diameter of the fitting. What is enough for the occurrence of capillary effect during soldering.
This effect allows the solder to spread evenly over the entire surface of the mounting gap of the connection, regardless of the position of the pipe (for example, solder can be fed from below). With a gap of no more than 0.4 mm, the capillary effect creates a cut with a width of 50% to 100% of the pipe diameter, which is sufficient to create a heavy-duty connection.
Using the capillary effect makes it possible to fill the mounting gap with solder very quickly (almost instantly). With well-prepared surfaces for soldering, this guarantees a 100% solder joint and does not depend on the responsibility and care of the installer.
Depending on the solder used, the heating temperature will be different. Low-temperature (up to 450°C) solders include relatively low-melting and low-strength metals (tin, lead, and alloys based on them). Therefore, they cannot give a soldered seam of great strength.
But with capillary soldering, the soldering width (from 7mm to 50mm, depending on the pipe diameter) is sufficient to plumbing pipelines provide extra strength. To improve the quality of soldering and increase the adhesion coefficient, special fluxes are used, and the soldering surfaces are pre-cleaned.
All copper pipes with a diameter from 6mm to 108mm can be joined by capillary low temperature soldering. The temperature of the coolant should not exceed 130°C. For soldering, it is very important that the solder has the lowest melting point and meets the requirements that apply to it. This is due to the fact that at high temperatures copper loses its hardness (annealing). It is for this reason that low-temperature soldering is preferred over high-temperature soldering.
High temperature soldering
High-temperature soldering is used for pipes with a diameter of 6mm to 159mm or having a longer length, as well as in cases where the temperature of the coolant is more than 130°C. In water supply, high-temperature soldering is used for pipes with a diameter of more than 28 mm. However, in all cases, excessive heating should be avoided. High-temperature soldering on small diameters requires high skill and experience, as it is very easy to burn or cut the pipe.
Solders based on copper and silver and a number of other metals are used for high-temperature soldering. They give greater strength to the brazed seam and a high allowable temperature for the coolant. When using solder based on copper and phosphorus or copper with phosphorus and silver, flux is not used when soldering copper parts.
When soldering together elements from different copper alloys: copper with bronze or copper with brass or bronze with brass, the use of flux is always necessary. It is also mandatory to use a flux when using solder with large quantity silver (more than 5%). High temperature soldering with a torch must be performed by a qualified and experienced technician.
This method of connecting copper pipes gives the strongest seam in terms of mechanical and temperature parameters. Allows you to make withdrawals to already installed system without dismantling it. The main connection method in solar systems and gas distribution pipelines.
When connecting pipes with high-temperature soldering, the entire system can be monolithic using methods acceptable in copper plumbing. The peculiarity of this connection is that during high-temperature soldering, the metal softens. In order for the loss of strength properties to be minimal, the cooling of the joint during soldering should be natural - air.
As the metal ages, as practitioners say, copper becomes more solid and the strength of the annealed metal increases. When the joint is cooled with water during high-temperature soldering, an intensive annealing of the metal occurs and its transition to soft state. Therefore, this cooling method is not used for high-temperature soldering.
Flux
Fluxes are active chemicals used to improve the spreading of liquid solder over the soldered surface, to clean the surface of the base metal from oxides and other contaminants (hydrochloric acid, zinc chloride, boric acid, borax) and to form protective coating and preventing oxidation during soldering (rosin, wax, resin). Naturally, the types of metals and solders to be joined are taken into account.
For a high-quality connection of metals during soldering, the solder must spread under the action of capillary forces and “wet” the base metal. A strong seam is obtained by protecting the soldering from air oxygen. Good wetting occurs only on a completely clean, non-oxidized surface. Therefore, to obtain high-quality soldering, multicomponent fluxes with multilateral action are usually chosen.
Depending on the temperature range of activity, low-temperature (up to 450°C) fluxes (solutions of rosin in alcohol or solvents, hydrazine, wood resins, petroleum jelly, etc.) and high-temperature (more than 450°C) fluxes (borax and its mixture with boric acid, mixtures of chloride and fluoride salts of sodium, potassium, lithium).
When soldering, taking into account preliminary mechanical cleaning, you can use the minimum amount of flux that actively interacts with the metal. After soldering, carefully clean off its remnants. After installation of the pipeline, technological flushing is carried out for the final removal of residues. If flux residues are not removed after soldering, this can cause corrosion in the joint over time.
Solders.
The quality and strength of soldering, the physical parameters of the connection depend to a large extent on the type of solder. Low-temperature (up to 450°C) solders, although they do not provide increased strength of the seam, but allow soldering at a temperature that has little effect on the strength of the base metal and does not change its main characteristics High-temperature (over 450°C) solders give greater strength to the seam high temperature for the coolant, but require high qualifications, since the metal is annealed
According to the melting temperature, solders are divided into low-temperature - up to 450°C and high-temperature - over 450°C. By chemical composition solders are divided into tin-silver, tin-copper and tin-copper-silver (low-temperature), copper-phosphorus, copper-silver-zinc, as well as silver (high-temperature) and a number of others.
Lead, lead-tin and any other lead-containing solders are prohibited in drinking water pipes due to the toxicity of lead.
In practice, in most cases, the soldering of joints is carried out using several basic brands of solders. For soft soldering, solders of the S-Sn97Cu3 (L-SnCu3) or S-Sn97Ag5 (L-SnAg5) type are usually used, which have high technological properties and provide high strength and corrosion resistance of the joint.
Silver solders with copper and zinc L-Ag44 (composition: Ag44% Cu30% Zn26%) are used for high-temperature soldering of copper and its alloys. They have increased thermal and electrical conductivity and high ductility, strength and corrosion resistance. Be sure to use flux in this case.
Copper-phosphorus solders CP 203 (L-CuP6) with the composition: Cu 94% P 6% or copper-phosphorus with silver CP 105 (L-Ag2P) with the composition: Cu 92% Ag2% P 6% are used as substitutes for silver solders in hard soldering. They have high fluidity and self-fluxing properties. In this case, you can not apply the flux. The seams are strong, but not elastic in low temperatures.
Heat
Soft soldering (low temperature) takes place at a temperature of 220°C-250°C, depending on the solder used. To heat the connection, gas-flame heating is used with mixtures: propane-air, propane-butane-air. The use of acetylene-air is acceptable.
In the case when it is unacceptable to use an open flame for small diameters, apply electric heaters electrical induction type. Recently, electrocontact has become widespread. Outwardly, they resemble large tongs with interchangeable graphite heads for covering pipes. different diameters. The heating rate with such devices may not differ from the heating rate with a burner.
Hard (high-temperature) soldering takes place at temperatures of 670°C-750°C. For soldering, only the gas-flame heating method is used. Mixtures are used: propane-oxygen, acetylene-air. Acceptable acetylene-oxygen.
For soldering-welding and welding, high-temperature heating is used at the melting point of copper. Gas welding takes place at temperatures of 1070°C-1080°C. Flame heating with acetylene-oxygen is used. Electric welding takes place at a temperature of 1020°C-1050°C. Electrical equipment is used for arc welding.
soldering process
soldering rules.
When preparing the pipe for connection, burrs are removed.
A capillary gap of the connection is formed or a ready-made fitting is used.
Metal surfaces are cleaned.
Check the relative position of parts and clearances.
Apply a minimal amount of flux to the outside of the pipe.
Collect the connection.
A slightly decreasing flame is applied, which creates maximum heat, and cleans the joint.
When soldering copper to copper using copper-phosphorus solders, flux is not required.
For soldering, heat the joint evenly to the required temperature.
Solder is applied to the mounting gap of the joint.
For uniform distribution of solder in the joint at large diameters, it is possible to introduce additional solder from the opposite side.
The molten solder flows towards the hotter joint.
When the solder crystallizes, the joint must be motionless.
Flux residues are carefully removed after soldering.
The heating cycle should be short and overheating should be avoided.
After the assembly of the pipeline, technological flushing is mandatory for the final removal of flux residues and contaminants.
Adequate ventilation must be provided when soldering, as harmful fumes (cadmium fumes from solder and fluorine compounds from flux) can be generated.
Connection preparation
To obtain a capillary effect when soldering, the mounting gap should be 0.02mm-0.3mm. Therefore, when preparing the joint, the pipe cut must be kept to a minimum. And the ends of the connected pipes are strictly cylindrical. This is especially important for the fitting-free connection method.
Since when working with a hacksaw it is possible to obtain a non-perpendicular cut, this can lead to a decrease in the soldering belt and a decrease in the reliability of the connection. And cutting off the soft pipe with a pipe cutter can cause the pipe to jam. In this case, an uncontrolled increase in the mounting gap and the receipt of non-soldering is possible. In addition, the narrowing of the flow area of the pipe increases the flow rate and the possibility of erosion.
Using a manual calibrator for the internal and external diameter of the pipe, you can obtain the ideal mounting gap for capillary soldering.
At the same time, there is another mandatory installation operation - deburring. Otherwise, flow turbulence and, as a result, erosion (including cavitation) may occur. In practice, such cases can lead over time to a rupture of the pipe.
Surface cleaning
The strength of solder adhesion (adhesion) depends on the quality of the stripping of the surfaces to be soldered. This means that any impurities and impurities on the metal prevent the surfaces of the parts to be joined from being completely wetted and reduce the fluidity of the solder so that it cannot be completely distributed over the surface. In many cases, this is the reason why a satisfactory soldering state cannot be achieved.
Two complementary methods are used to clean the metal surface: mechanical and chemical. To clean the outer surface of the pipe and the inner surface of the fitting from the oxide film (and at the same time from fats and other contaminants), use a metal wire brush, steel grinding wool or fine sandpaper. When stripping, they remove contaminants and oxides, which contributes to the free distribution of solder over the surface. Preliminary mechanical cleaning allows you to reduce the amount of flux used, which is an active chemical.
The most convenient are special nylon-based wipes, because after them, unlike sandpaper and a steel sponge, it is not necessary to remove stripping products that may contain abrasive residues or steel particles. During mechanical cleaning metal surface microscopic grooves are formed, which increase the surface of the soldering, and therefore, contribute to a significant increase in the adhesion force of the solder and metal.
Chemical method involves etching with an acid that reacts with oxides and removes them from the metal surface. Or the use of a multicomponent flux, which, among other things, has the ability to clean metal.
Flux application and connection assembly
Flux should be applied immediately to the cleaned surface of the pipe (to avoid oxidation). The flux is applied without excess only to the collar of the pipe that will be connected to the fitting or socket, and not to the inside of the fitting or socket. It is strictly forbidden to apply flux inside the connection. Flux absorbs a certain amount of oxides. The viscosity of the flux increases when it is saturated with oxides.
After applying the flux, it is recommended to immediately connect the parts to prevent foreign particles from entering the wet surface. If, for some reason, soldering itself will take place a little later, then it is better for the parts to wait for this moment already in assembled. It is recommended to rotate the pipe in the fitting or socket, or vice versa, the fitting around the axis of the pipe, in order to make sure that the flux is evenly distributed in the mounting gap and to feel that the pipe has reached the stop. Then it is necessary to remove visible flux residues with a rag, after which the connection is ready for heating.
For conventional "soft" soldering, fluxes based on zinc or aluminum chlorides are used. Fluxes are aggressive substances. Therefore, an excessive amount of flux is undesirable. If flux residue is not removed after soldering, flux will enter the joint and, over time, may cause corrosion and leakage. After soldering, all visible flux residues are also removed from the pipe surface (because during heating, as a result of thermal expansion and solder displacement, a certain amount of flux from the mounting gap will again appear on the pipe surface).
When hard (high-temperature) soldering with silver solders or soldering with bronze solder, borax is used as a flux. It is mixed with water until a viscous slurry is obtained. Or use ready-made fluxes for high-temperature soldering. When using copper-phosphorus solder for soldering copper parts, flux is not required, mechanical cleaning is sufficient.
The most acceptable is the use of matched solder and flux for a particular type of soldering from one manufacturer. In this case, the quality of the soldered seam and, accordingly, the entire joint is guaranteed.
Solders.
The quality and strength of the soldering, the withstand temperature of the joint depends on the solder used. In most cases, soldering joints is carried out using several brands of solders.
For soft soldering, tin-based alloys are mainly used, with the addition of silver or copper. Lead solders are not used in drinking water supply. They are usually produced in the form of a wire with D = 2mm-3mm, which is convenient when working with capillary connections.
For hard soldering, mainly two groups of solders are used: copper-phosphorus, copper-phosphorus with silver and multi-component based on silver (silver not less than 30%). Copper-Phosphorus and Copper-Phosphorus with Silver - hard solders are specially designed for soldering copper and its alloys, while they are self-fluxing.
Unlike copper-phosphorus alloys, silver hard solders do not contain phosphorus. These solders have high ductility, strength and corrosion resistance. Compared to copper-phosphorus, they are more expensive. They are produced in the form of solid bars with D = 2mm-3mm. Soldering requires flux.
Careful precautions must be taken when using low temperature copper solder containing cadmium due to the poisonous effects of cadmium vapor.
Joint heating during soft soldering
As a rule, heating for soft soldering is carried out with propane (propane-air or propane-butane-air) torches. The contact spot between the flame and the surface of the joint is constantly moved to achieve uniform heating of the entire joint, and at the same time, from time to time, the solder rod is touched to the capillary gap (usually, with practice, the sufficiency of heating is determined by the color of the surface and the appearance of flux smoke). Electrical connection heating fundamental differences does not have a solder.
If the solder does not melt during the control touch with the bar, heating is continued. Do not heat the solder rod. At the same time, in no case should one forget about the need to move the flame so as not to overheat any separate plot connections. As soon as the solder begins to melt, the flame is turned aside and the solder is allowed to fill the mounting (capillary) gap.
Due to the capillary effect, the installation gap is filled automatically and completely. It is not necessary to put in excess amounts of solder as this is not only wasteful but can also lead to excess solder flowing into the joint.
When using standard solder rods with D=2.5mm-3mm, the amount of solder is approximately equal to the diameter of the pipe. In practice, the section of solder required along the length is bent in the form of the letter “G”. In this case, solder is not consumed excessively, and the moment “soldered - not soldered” is clearly controlled, which is important when large volume work.
Joint heating during hard soldering
For hard soldering, heating is carried out only by a gas-flame method (propane-oxygen or acetylene-air, acetylene-oxygen is acceptable) at an ambient temperature of -10 ° C to +40 ° C. When using copper-phosphorus solder, soldering is possible without flux. Since the solder seam is much stronger, some reduction in the width of the soldering is allowed compared to soft soldering. Hard soldering requires high qualification and experience, otherwise it is very easy to overheat the metal and breaks are possible.
The burner flame must be "normal" (neutral). A balanced gas mixture contains equal amounts of oxygen and gaseous fuel, causing the flame to heat the metal without any other effect. Torch of the burner flame with a balanced gas mixture (bright blue and small).
A decreasing burner flame indicates an excess amount of gaseous fuel in the gas mixture that exceeds the oxygen content. The slightly reduced flame heats and cleans the metal surface for the soldering operation faster and better.
A supersaturated oxygen mixture is a gas mixture containing an excess amount of oxygen, resulting in a flame that oxidizes the surface of the metal. A sign of this phenomenon is a black oxide coating on the metal. Oxygenated burner flame (pale blue and small)
The pipes to be connected are heated evenly over the entire circumference and length of the connection. Both elements of the connection are heated by a burner flame at the junction to a dark cherry color (750°C-900°C), evenly distributing heat. It is allowed to perform soldering in any spatial position of the parts to be joined.
The connection must not be heated to the melting temperature of the metal from which the pipes are made. Use an appropriately sized burner with a somewhat reduced flame. Overheating the joint enhances the interaction of the base metal with the solder (i.e., enhances the formation of chemical compounds). As a result, such interaction negatively affects the service life of the connection.
If the inner tube is heated to soldering temperature, and outer pipe has a lower temperature, then the molten solder does not flow into the gap between the connected pipes and moves towards the heat source
If the entire surface of the ends of the pipes to be soldered is evenly heated, then the solder supplied to the edge of the socket melts under the influence of their heat and evenly enters the joint gap. The brazing tubes are warm enough if the brazing rod melts on contact with them. To improve soldering, the solder bar is preheated a little with a burner flame.
Manufacturers produce small-sized gas burners with disposable cartridges that allow heating for hard and soft soldering, but with hard soldering, the diameter of the joints is two times smaller than with soft soldering.
Peculiarities
Butt soldering of copper pipes and fittings is not allowed. When using welding for diameters over 108 mm (wall thickness over 1.5 mm), butt joint is allowed.
Soldering more than two elements should be done at the same time. In this case, the sequence of filling mounting gaps with solder (for example, in a tee) is observed - from the bottom to the top. In this case, the rising heat does not interfere with the cooling and crystallization of the solder.
Alternate connection of elements is permissible when using two types of soldering: first high-temperature, and then low-temperature. It is not allowed to use high-temperature soldering on a joint with low-temperature soldering.
Forbidden
Soldering of fittingless joints obtained without extending the end of the pipe with an expander, for example, bell joints - obtained by flaring or rolling the end of the pipe. Adapter sleeves should be used.
Soldering bends made without special tools or in the bend (elbow) of the pipeline. Standard tees or an elbow formed with a special tool should be used.
Soldering any non-standard connections obtained without expanding the pipe with an expander or a special tool for extracting a branch.
Overheat
When doing soldering work, it is very important to avoid "overheating", as this can lead to the destruction of the flux, which loses the ability to dissolve and remove oxides. In many cases, this is the cause of unsatisfactory soldering quality. To avoid overheating, it is recommended to ensure that the temperature has reached the melting point of the solder. To do this, it is necessary to periodically touch the heated joint with solder.
Or use a flux with solder powder for this purpose: as soon as drops of melted powder solder shone in the flux, the joint is heated. Some fluxes, when heated enough for soldering, emit signal smoke or change color.
During high-temperature soldering, metal is annealed, and when overheated, copper loses its strength properties, becomes loose and very soft. This can lead to pipe ruptures. The control method is the same as for soft soldering - periodically touch the joint with solder. With sufficient experience, the sufficiency of heating will be determined by the colors of the tint. It is important not to use a heat source that is too powerful, such as an oxy-acetylene torch to weld a size 12 fitting.
Final procedures
After filling the mounting (capillary) gap with solder, it must be allowed to harden, which means an absolute requirement to exclude the mutual movement of the articulated parts. After the solder has solidified, it is necessary to remove all visible flux residues with a damp cloth, and if necessary, use an additional amount warm water.
When soldering and welding, metal burrs (burrs) may form, which, if necessary, must be removed. In any type of soldering and welding, metal flows (burs) inside the joint that interfere with the fluid flow are not allowed. They must be removed.
The acquired experience in work allows using the optimal amount of solder when soldering, which does not lead to the formation of burrs in the joint.
After the installation of the system is completed, it is necessary to carry out a technological flushing of the system as soon as possible to remove flux residues from the internal surfaces, since the flux that has got into the joint during soldering and being an aggressive substance can lead to unwanted metal corrosion.
Soldering quality control
Quality control is the most important operation. In order to unify soldered assembly units, establishing norms and requirements for soldered products, the standard GOST 19249-73 “Brazed joints. Basic types and parameters". The standard defines the design parameters of a solder joint, its symbols, contains a classification of the main types of joints.
Solder joint defects
The quality of brazed products is determined by their strength, degree of performance, reliability, corrosion resistance, ability to perform special functions (tightness, thermal conductivity, resistance to temperature changes, etc.). The most typical defects in soldered joints include pores, shells, slag and flux inclusions, non-solders, and cracks.
The reason for the formation of non-solders may be blocking of gas with liquid solder in the presence of uneven heating or uneven gap, local lack of wetting of the surface of the soldered metal with liquid solder. Cracks in soldered joints can occur under the action of stresses and deformations of the metal of the product during cooling.
Non-metallic inclusions such as flux or slag occur when the surface of the product is not thoroughly prepared for soldering or when its regime is violated. If heated for soldering for too long, the flux reacts with the soldered metal to form solid residues that are poorly displaced from the gap by the solder. Slag inclusions can also form due to the interaction of solders and fluxes with atmospheric oxygen or a burner flame.
Proper design of a solder joint (no closed cavities, gap uniformity), assembly accuracy for soldering, metered amount of solder and fluxing media, heating uniformity are the conditions for a defect-free solder joint.
Methods for quality control of soldered products
To assess the quality of soldered products, control is used without destruction and with destruction. Technical inspection products with the naked eye or with the use of a magnifying glass, in combination with measurements, it is possible to check the quality of the surface, the filling of gaps with solder, the completeness of the fillets, the presence of cracks and other external defects.
In accordance with the requirements of the technical specifications, soldered products are subjected to other methods of non-destructive testing. If necessary, use the desoldering of the connection, which gives a complete picture of the quality of the connection. Used as a sampling control.
Safety
Compliance with safety rules is important When performing soldering work, safety rules must be observed, as fluxes and alloys can contain harmful substances. Fluxes applied during cold or hot soldering break down and release fumes that can contain toxic substances and be harmful to health.
Careful precautions must be taken when using low temperature copper solder containing cadmium due to the poisonous effects of cadmium vapor. Adequate ventilation must be provided when soldering, as harmful fluoride fumes can be produced from fluxes that use fluorine.
To avoid harm, it is recommended to carry out all work in a well-ventilated area, make sure that this product is manufactured in accordance with current regulations established for toxic substances, carefully study the description of their properties, which is available on the label.
In high-temperature soldering, acid and alkali solutions can be used to pickle connecting parts. It is necessary to work with them in rubber gloves and acid-resistant clothing. Face and eyes must be protected from splashes goggles. Wash hands thoroughly after finishing work and before eating.
When soldering with a gas burner, before starting work, it is necessary to check the tightness of hoses and equipment. Gas cylinders must be stored upright. Containers with solutions after work are handed over to the warehouse, it is not allowed to drain solutions and alkalis into the sewer.
When performing work on the installation of copper internal plumbing systems, it is necessary to comply with safety requirements in accordance with SNiP 12-04.
In some countries, the use of fluxes when brazing copper pipes intended for water supply and gas pipelines requires, according to local regulations, to obtain permission from the authorities.
Regulatory documentation for soldering and welding: GOST 1922249-73 and GOST 16038-80. European standard TN 1044. The use of gases for flame brazing and welding is regulated by GOST 5542-87, and GOST 20448-90.
According to the classification given in the state standard, solders are divided into groups according to several criteria, one of which is the melting point. In the process of soldering at a temperature exceeding 450℃, only high-temperature solders can be used.
Other compositions of such a thermal load will not withstand. High-temperature soldering is carried out in different modes. When carrying out the process up to 1100 ℃, compositions with medium fusibility are suitable for use.
In the range from 1100℃ to 1850℃, high-melting mixtures should be used. At higher temperatures, only refractory compositions are suitable.
It is surprising that, despite the classification of GOST, even in textbooks there is a different presentation of materials.
Exists a large number of finished compositions recommended for use at elevated temperatures. Often the composition of high-temperature solders includes:
- copper;
- silver;
- zinc;
- phosphorus.
Silicon, germanium and some other elements are added to high-temperature alloys to change their properties. Low-temperature solders are considered:
- lead based;
- tin;
- with the addition of antimony.
The choice of specific solders is determined by the type of alloy from which the parts are made and the soldering conditions.
Zinc is sometimes added to low-temperature solders to increase the corrosion resistance of the weld, and special low-temperature alloys are developed for specific conditions of use. In everyday life, low-temperature soldering is carried out using a soldering iron, and high-temperature soldering is carried out with a gas burner.
For high temperature alloys
High-temperature solders are used for stainless and heat-resistant steel alloys. Soldering of such alloys is carried out using solders based on copper, copper with zinc, silver.
The process is carried out in furnaces surrounded by hydrogen or ammonia solution vapors. When soldering with copper, copper-zinc compositions, borax is used as a flux additive.
Silver high temperature solders can only be used in combination with active fluxes. The seams obtained by this method can withstand heating up to 600 ℃. Compounds obtained with copper-containing compounds tolerate high temperatures worse.
Nickel-chromium solders with platinum or palladium are sometimes used as an alternative. Such high-temperature materials are more expensive. Seams have high thermal and corrosion resistance.
If there are large gaps on steel products made of stainless and heat-resistant alloys, a good connection is provided by solder powders containing components identical to the chemical elements of the alloys.
The resulting seams can withstand heating up to 1000 ℃. The process is carried out in a vacuum environment filled with argon and gaseous flux.
For aluminum and its alloys
Aluminum and its alloys are materials that are difficult to work with. The low-temperature process is complicated by the presence of a refractory surface layer of oxides.
Active fluxes could help, but their use is fraught with increased formation of corrosion products at the weld site. Special technological methods for soldering on pre-applied coatings have been developed.
In addition, low-temperature compositions with the addition of expensive gallium are used for aluminum.
High-temperature soldering is carried out by using high-temperature solders based on aluminum with the addition of copper, zinc, silicon.
Most often, 34A compositions, as well as silumin, are used for soldering aluminum parts. Each of these solders has a corresponding flux. 34A solder promotes the formation of a seam that is stable at 525 ℃.
High temperature solder compound made of aluminum and silicon makes it possible to obtain a joint that can withstand 577 ℃. During the work, fluxes made from alkali metal chlorides are used. The strength of the formed seams does not always meet the requirements of production.
If it is necessary to obtain compounds of high thermal and corrosion resistance, soldering is carried out in a high vacuum surrounded by magnesium vapor.
The process is carried out without fluxes using complex technology. Silumin is used as solder. The seam obtained by this method can withstand significant loads.
Working with copper
In water supply systems, heating systems and some production schemes, copper pipes are installed that are not intended for increased thermal load. In such situations, the use of low-temperature solder is acceptable for soldering.
Large diameter pipelines made of copper alloys are sometimes subjected to high heat. In such cases, copper and copper-based alloys require special refractory composites.
Typically, high-temperature solders are used on a copper, silver base, containing other metals, as well as silicon or phosphorus.
Compositions of copper and zinc are denoted by a combination of letters PMC and numbers indicating the percentage of copper. Such high-temperature solders have a multifunctional effect and are suitable for working with other alloys.
The resulting seams have a moderate resistance to mechanical stress. To improve the strength properties of the joints, soldering agents are alloyed with various additives.
Based on copper and phosphorus
High-temperature compositions based on copper and phosphorus are indicated by the letter combination PMF and numbers indicating the concentration of phosphorus in the total mass.
The agent becomes liquid at a temperature of 850 ℃, which makes it possible to obtain seams of good corrosion resistance. Solder is applicable not only for copper, but also jewelry made of precious metals.
Only steel cannot be soldered in this way. As a result, phosphites are formed on the steel seams, which reduce mechanical strength seam, lead to the formation of a brittle joint. The advantage of copper-containing solders with phosphorus lies in the possibility of soldering without fluxes.
For work with copper, some steel, cast iron parts, high-temperature solders based on brass are also recommended. It can be a pure brass alloy or a tin-silicon composite. Means possess the fluidity sufficient for formation of a strong, resistant seam.
Silver based
High-temperature soldering agents based on silver have very good properties. They fit almost everyone metal products. The only drawback is that the price of the noble metal limits the possibility of frequent use.
There are alloys (PSr-15) with a low concentration of silver. They cost less than concentrated formulations and can be used more frequently.
Compositions (PSr-45) with a content of silver - 45%, copper - 30%, zinc - 25% have very good properties: viscosity, fluidity, malleability, resistance to oxidation and mechanical stress. These alloys are used as needed, if financially possible.
By varying the ratio of these components, you can change the maximum temperature values that the future seam can withstand. The high-temperature composition with a silver content of 65% demonstrates even better qualities, but it is very expensive.
Working with titanium
For soldering refractory metals and alloys, the capabilities of most of the described solders are not enough. You need completely different high-temperature components. Such a chemical element is titanium, which has a melting point of about 1700 °C.
It forms strong seams even on products with oxide residues. The process must be carried out in an atmosphere of pure argon or helium with a significant decrease in pressure in the working area.
High-temperature compositions of titanium and copper, nickel, cobalt, and other metals exhibit the properties of eutectic systems. By themselves, they are fragile, used in the form of powders, pastes.
Wire, tapes, strips of these alloys cannot be made. It is impossible to work with a soldering iron with refractory composites.
In some cases, contact melting technology is implemented in practice. A foil made of titanium or its alloys is placed in the gap of the product to be soldered.
When the temperature reaches 960 ℃, the formation of a eutectic alloy, which plays the role of solder, begins, and when the readings reach 1100 ℃, it ends.
Products to be used at very high temperatures are subject to soldering using alloys with silicon and iron additives. To implement such technological processes, powerful sources of energy are needed.
The required temperature is reached in vacuum furnaces, plasma torches. For this purpose, the electrocontact method or exposure to an electron beam can be used.
High-temperature soldering of parts is a labor-intensive process that requires special knowledge and skills. Having good auxiliary means, the equipment can cope with a production task of any degree of complexity.
Soldering joints with a soldering iron is still the most common method of soldering when making field joints, however, the productivity of this method is not high. More efficient is low-temperature soldering by immersion in molten solder(Fig. 5.6).
Brazing
Soldering soldering with immersion in molten solder is carried out on special installations, on which baths with flux and molten low-temperature (soft) solder are mounted. The workpieces are pre-cleaned and degreased, then immersed first in a bath with flux, and then with molten solder, after which they are removed and cooled in air to room temperature. The specified temperature of the solder is controlled and maintained using a special device with a thermocouple placed in the bath.
In addition to the soldering method described, to improve the quality of soldered joints, soldering in an inert gas environment(Fig. 5.7), in a vacuum(Fig. 5.8) and in active gaseous medium(Fig. 5.9). The principle of operation of the installations is clear from the figures and does not require additional explanations. The main feature of these soldering methods is that they are performed without the use of fluxes, since the environment surrounding the workpieces during the soldering process prevents the formation of oxide films.
Soldering- this is the process of obtaining a permanent connection of materials in the solid state when heated below their melting point by wetting, spreading and filling the gap between them with molten solder, followed by crystallization of the liquid phase and the formation of a junction.
Advantages of soldering technological process and the advantages of brazed joints are mainly due to the possibility of forming a brazed seam below the melting temperature of the materials to be joined. Such formation of a seam occurs as a result of contact melting of the soldered metal in liquid solder introduced from the outside (soldering with ready-made solder), or restored from flux salts (reactive flux soldering), or formed during contact-reactive melting of the soldered metals, contacting interlayers or soldered metals with interlayers (contact-reactive soldering). Unlike autonomous melting (a single-stage process occurring in a volume at a temperature equal to or higher than the solidus temperature of the materials being joined), contact melting of the same material proceeds at contact equilibrium along the contact surface with a solid, liquid, gaseous body, different in composition. This is a multi-stage process proceeding through different mechanisms; the liquid phase during contact melting of a solid is formed below its solidus temperature.
Soldering ensures the production of defect-free, durable and operable under conditions of long-term operation, soldered joints, if physico-chemical, design, technological and operational factors are taken into account.
The possibility of forming a junction between the soldered metal and the solder is characterized by solderability, i.e. the ability of the soldered metal to enter into physical and chemical interaction with molten solder and form a solder joint. In practice, soldering can connect all metals, metals with non-metals and non-metals to each other. It is only necessary to ensure such an activation of their surface, in which it would be possible to establish strong chemical bonds between the atoms of the materials being joined and the solder.
For the formation of a solder, it is necessary and sufficient to wet the surface of the base metal with solder melt, which is determined by the possibility of forming chemical bonds between them. Wetting is fundamentally possible in any combination of the base metal - solder, provided that appropriate temperatures, high surface cleanliness or sufficient thermal or other type of activation are provided. Wetting characterizes the fundamental possibility of soldering a specific base metal with a specific solder. With the physical possibility of forming a junction (physical solderability), solderability is already to some extent guaranteed from a technological point of view, provided that the appropriate conditions for the soldering process are provided.
The solderability of a material cannot be considered as its ability to be soldered with various solders. You can only consider a specific pair, and in specific soldering conditions. An important point in assessing solderability, both physical and technical, is right choice soldering temperature, which is often a decisive factor not only for ensuring the wetting of the metal surface with solder, but also an additional important reserve for improving the properties of solder joints. When evaluating solderability, it is necessary to take into account the temperature range of flux activity.
soldering flux- this is an active chemical substance designed to clean and protect the surface of the soldered metal and solder, primarily from oxide films. However, fluxes do not remove foreign substances of organic and inorganic origin (lacquer, paint). The mechanism of fluxing with fluxes, self-fluxing solders, controlled gas media, in vacuum, by physical and mechanical means can be expressed as:
1. In the chemical interaction between the main components of the flux and the oxide film, the resulting compounds dissolve in the flux, or are released in a gaseous state;
2. In the chemical interaction between active ingredients flux and the base metal, resulting in a gradual detachment of the oxide film from the metal surface and its transition to the flux;
3. In the dissolution of the oxide film in the flux;
4. In the destruction of the oxide film by fluxing products;
5. In the dissolution of the base metal and solder in the flux melt.
Oxide fluxes interact predominantly with the oxide film. The basis of fluxing with halide fluxes is the reaction with the base metal. To increase the activity of oxide fluxes, fluorides and fluoroborons are introduced, as a result, simultaneously with the chemical interaction between oxides, the oxide film is dissolved in fluorides.
Active gaseous media include gaseous fluxes that work independently or as an additive to neutral or reducing gaseous media to increase their activity. When soldering metals in active gaseous media, the removal of the oxide film from the surface of the base metal and solder occurs as a result of the reduction of oxides by the active components of the media or chemical interaction with gaseous fluxes, the products of which are volatile substances or low-melting slags, reducing media include hydrogen and gaseous mixtures containing hydrogen and carbon monoxide as reducing agents for metal oxides.
Nitrogen, helium and argon are used as neutral gaseous media, the role of the gaseous medium is to protect metals from oxidation. As a gas medium, vacuum protects metals from oxidation and promotes the removal of an oxide film from their surface. When soldering in a vacuum, as a result of rarefaction, the partial pressure of oxygen becomes negligible and, consequently, the possibility of metal oxidation decreases. During high-temperature soldering in vacuum, conditions are created for the dissociation of oxides of certain metals.
According to the gap filling conditions, soldering methods are divided into capillary and non-capillary.
Capillary soldering according to the method of solder formation, it is divided into soldering with ready-made solder, contact-reactive, diffusion and reactive-flux. In capillary soldering, molten solder fills the gap between the soldered parts and is held in it by capillary forces. Capillary soldering, in which pre-solder is used and the seam solidifies when cooled, is called pre-solder soldering. Reactive soldering is called capillary soldering, in which solder is formed as a result of contact-reactive melting of the materials to be joined, intermediate coatings or gaskets with the formation of a eutectic or solid solution. With contact-reactive soldering, there is no need for pre-solder preparation. The amount of the liquid phase can be controlled by changing the contact time, the thickness of the coating or interlayer, because the process of contact melting stops after the consumption of one of the contacting materials.
Diffusion called capillary soldering, in which the solidification of the seam occurs above the solidus temperature of the solder without cooling from the liquid state. The solder used in diffusion soldering can be completely or partially molten, can be formed during contact-reactive melting of the metals being joined with one or more interlayers of other metals deposited by galvanic methods, sprayed or placed in the gap between the parts to be joined, or as a result of contact hard- gas melting. The purpose of diffusion soldering is to carry out the crystallization process in such a way as to provide the most balanced structure of the joint, to increase the temperature of the joint desoldering.
For reactive flux soldering solder is formed as a result of the reduction of metal from the flux or the dissociation of one of its components. The composition of fluxes for reactive flux soldering includes easily recoverable compounds. The metals formed as a result of the reduction reaction in the molten state serve as solder elements, and the volatile components of the reaction create a protective environment and contribute to the separation of the oxide film from the metal surface.
Non-capillary soldering divided into soldering-welding and welding-soldering. Solder welding refers to the processes of correcting defects in cast iron, aluminum and other parts, leveling the surface, removing dents, i.e. pouring with molten solder using technical capabilities low and high temperature soldering. It is usually used for cast iron products and is performed with brass alloys with the addition of silicon, manganese, ammonium. Soldering is used when joining dissimilar metals by melting a more fusible metal and wetting the surface of a more refractory metal with it. The required heating temperature of the refractory metal surface is achieved by adjusting the electrode displacement from the weld axis to the more refractory metal. When preparing products for soldering, if necessary, the soldered surface is applied metal coatings. Technological coatings (copper, nickel, silver) are applied to the surface of metals that are difficult to solder, or metals whose surface is intensively dissolved in the solder during soldering, which causes deterioration of wetting and capillary flow of the solder in the gap, brittleness in the joints, erosion and undercuts appear at the place where the solder is applied. base metal. The purpose of the coating is to prevent unwanted dissolution of the base metal in the solder and improve wetting; during the soldering process, the coating must completely dissolve in the molten solder.
When capillary soldering, lap, butt, cross-butt, tee, corner, contact joints are used. Lap joints are the most common, because. by changing the length of the overlap, you can change the strength characteristics of the product. Lap soldered joints have some advantages over lap welded joints, in which the transfer of forces occurs along the perimeter of the element. In welded structures, any seams are a source of stress concentration in the transition zone from the base metal to the seam, and with unfavorable seam outlines, the concentration reaches significant values. Mapping mechanical properties soldered and welded joints allows us to draw the following conclusions:
1. The use of soldering is most effective in thin-walled structures, no more than 10 mm thick;
2. The productivity of the soldering process is often higher;
3. Solder joints tend to cause less permanent deformation;
4. Brazed structures in most cases have a lower stress concentration compared to welded ones.
The strength of soldered joints is also determined by the influence of defects that can form if the optimal conditions and soldering mode. Typical defects that reduce the strength of brazed joints are pores, cavities, cracks, flux and slag inclusions, non-solders.
All continuity defects in solder joints are divided into defects associated with the filling of capillary gaps with liquid solder, and defects that occur during cooling and solidification of solder joints. The occurrence of the first group of defects is determined by the features of the movement of solder melts in the capillary gap (pores, non-solders). Another group of defects appears due to a decrease in the solubility of gases in the metal during the transition from a liquid to a solid state (gas-shrinkage porosity). This group also includes porosity of crystallization and diffusion origin.
Cracks in brazed seams can occur under the action of stresses and deformations of the metal of products or the seam during cooling. Cold cracks appear in the zone of junctions during the formation of interlayers of brittle intermetallic compounds. Hot cracks are formed during the crystallization process; if during the crystallization the cooling rate is high and the resulting stresses are high, and the deformability of the weld metal is low, crystallization cracks occur. Polygonization cracks in the weld metal already occur at temperatures below the solidus temperature after the solidification of the alloy along the so-called polygonization boundaries, which are formed when dislocations line up in the metal in rows and form a dislocation network under the action of internal stresses. Non-metallic inclusions such as flux or slag may occur as a result of insufficiently thorough preparation of the surface of the product for soldering or in violation of the soldering mode. When heated for soldering for too long, the flux reacts with the base metal to form solid residues that are poorly displaced from the gap by the solder.
Home craftsmen try to carry out construction and repair work independently, which allows not only to save the family budget, but also to be absolutely confident in the quality result. Therefore, they have to master new methods and technologies for themselves - such as soldering copper pipes.
We will tell you how to assemble and connect communications from copper pipes. Here you will find out what consumables and tools the contractor will need. Skills that are useful even in everyday life will make it possible to independently assemble pipelines with excellent performance characteristics.
copper piping rarely used in practice. The reason for this is the rather high cost of materials. However, copper pipelines are rightfully considered the best.
This metal surpasses all other materials in terms of heat resistance, flexibility and durability. after assembly, it can be poured into concrete, hidden in walls, etc. During operation, nothing will happen to them.
Copper pipelines are considered the best, as their service life is comparable to the service life of the building in which they are installed.
This should be taken into account when choosing a material for arranging heating or plumbing. In terms of long-term operation, higher costs are fully compensated. In addition to the excellent performance characteristics that copper has, it is quite easy to install. The "dread tales" about soldering difficulties are most often exaggerated.
Copper is easy enough to solder. Its surface does not require the use of aggressive cleaning agents. Many fusible metals have high adhesion with it, which simplifies the choice of solder.
Expensive copper fluxes are not needed, since during the melting of the metal there are no violent reactions with oxygen. During the soldering process, the pipe is not deformed, its shape and dimensions remain unchanged. The resulting seam can be soldered if necessary.
Methods for soldering copper parts
Soldering is considered the best method for joining copper parts. During operation, molten solder fills a small gap between the elements, thus forming a reliable connection.
There are two most common ways to obtain such compounds. This is a high-temperature and low-temperature capillary soldering. Let's see how they differ from each other.
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