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 solder joints are due mainly to the possibility of forming a solder seam below the melting point of the materials being joined. This 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 recovered from flux salts (reactive flux soldering), or formed during contact-reactive melting of soldered metals, contacting interlayers or soldered metals with interlayers (contact-reactive soldering). In contrast to autonomous melting (a one-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 occurs in contact equilibrium along the surface of contact with a solid, liquid, gaseous body of different composition. This is a multi-stage process that occurs through different mechanisms; liquid phase during contact melting solid a solidus is formed below its temperature.
Soldering ensures the production of defect-free, durable and operable solder joints under long-term operation conditions, 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 be used to connect all metals, metals with non-metals, and non-metals with each other. It is only necessary to ensure such activation of their surface that it would be possible to establish strong bonds between the atoms of the materials being joined and the solder. chemical bonds.
To form a junction, it is necessary and sufficient to wet the surface of the base metal with the solder melt, which is determined by the possibility of the formation of chemical bonds between them. Wetting is in principle possible in any combination of base metal and 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. If it is physically possible to form a junction (physical solderability), solderability is already to some extent guaranteed from a technological point of view, provided that 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 under 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 wetting of the metal surface with solder, but also an additional important reserve for increasing the properties of solder joints. When assessing solderability, it is necessary to take into account the temperature range of flux activity.
Soldering flux 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 (varnish, paint). The mechanism of fluxing with fluxes, self-fluxing solders, controlled gas environments, in a vacuum, by physical and mechanical means can be expressed:
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, as a result there is a gradual separation of the oxide film from the surface of the metal and its transition to flux;
3. In dissolving the oxide film in the flux;
4. In the destruction of the oxide film by fluxing products;
5. In dissolving the base metal and solder in the molten flux.
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 fluorobrons are introduced, as a result, simultaneously with the chemical interaction between the oxides, the oxide film dissolves in the 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 gas environments, 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 active components of the media or chemical interaction with gaseous fluxes, the products of which are volatile substances or low-melting slags; reducing environments include hydrogen and gaseous mixtures containing hydrogen and carbon monoxide as reducing agents for metal oxides.
Nitrogen, helium and argon are used as neutral gas environments; the role of the gas environment is reduced to protecting metals from oxidation. As a gaseous environment, vacuum protects metals from oxidation and helps remove oxide films from their surface. When soldering in a vacuum, as a result of rarefaction, the partial pressure of oxygen becomes negligible and, therefore, the possibility of metal oxidation decreases. During high-temperature soldering in a vacuum, conditions are created for the dissociation of the oxides of some metals.
According to the conditions for filling the gap, soldering methods are divided into capillary and non-capillary.
Capillary soldering According to the method of formation of a junction, 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 parts being soldered and is held there by capillary forces. Capillary soldering, in which ready-made solder is used and the seam hardens when cooled, is called soldering with ready-made solder. Contact-reactive soldering is capillary soldering, in which solder is formed as a result of contact-reactive melting of the materials being joined, intermediate coatings or gaskets with the formation of a eutectic or solid solution. With contact-reactive soldering there is no need to pre-make solder. The amount of liquid phase can be adjusted by changing the contact time, the thickness of the coating or layer, because The contact melting process stops after one of the contacting materials is consumed.
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 layers of other metals applied by galvanic methods, spraying or laid in the gap between the parts being connected, or as a result of contact solid- gas melting. The purpose of diffusion soldering is to carry out the crystallization process in such a way as to ensure the most balanced structure of the connection and increase the temperature of desoldering of the connections.
For reactive flux soldering Solder is formed as a result of the reduction of metal from flux or the dissociation of one of its components. The composition of fluxes used in reactive flux soldering includes easily restored compounds. The molten metals formed as a result of the reduction reaction serve as solder elements, and the volatile components of the reaction create a protective environment and promote the separation of the oxide film from the metal surface.
Non-capillary soldering divided into soldering-welding and welding-brazing. Solder welding refers to the processes of correcting defects in cast iron, aluminum and other parts, leveling the surface, eliminating dents, i.e. pouring molten solder using technical capabilities low and high temperature soldering. Typically used for cast iron products and performed using brass solders with the addition of silicon, manganese, and ammonium. Welding and soldering is used to join dissimilar metals by melting a lower-melting metal and wetting the surface of a more refractory metal with it. The required heating temperature of the surface of the refractory metal is achieved by regulating the amount of displacement of the electrode from the axis of the weld to the more refractory metal. When preparing products for soldering, if necessary, apply metal coatings. Technological coatings (copper, nickel, silver) are applied to the surface of difficult-to-solder metals, or metals whose surface intensively dissolves in solder during soldering, which causes deterioration in wetting and capillary flow of solder in the gap, brittleness in joints, erosion and undercuts appear at the place where 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.
For capillary soldering, lap, butt, ridge, T-joint, corner, and 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 brazed joints have some advantages over lap welded joints, in which the transmission 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 contours the concentration reaches significant values. Comparison 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. Soldered joints usually cause less permanent deformation;
4. Brazed structures in most cases have a lower stress concentration compared to welded ones.
The strength of solder joints is also determined by the influence of defects that can form if optimal conditions and soldering mode. Typical defects that reduce the strength of soldered joints are pores, cavities, cracks, flux and slag inclusions, and solder failures.
All continuity defects in solder joints are divided into defects associated with filling capillary gaps with liquid solder, and defects arising during cooling and solidification of solder joints. The occurrence of the first group of defects is determined by the peculiarities 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 soldered seams can occur under the influence of stress and deformation of the metal of the product or the seam during the cooling process. Cold cracks occur in the weld zone when layers of brittle intermetallic compounds form. Hot cracks are formed during the crystallization process; If during the crystallization process the cooling rate is high and the resulting stresses are high, and the deformation capacity of the weld metal is small, then crystallization cracks occur. Polygonization cracks in the weld metal occur already at temperatures below the solidus temperature after solidification of the alloy along the so-called polygonization boundaries, which are formed when dislocations line up in the metal in rows and the formation of a dislocation network under the influence of internal stresses. Non-metallic inclusions such as flux or slag can arise as a result of insufficiently thorough preparation of the surface of the product for soldering or when the soldering regime is violated. When soldering is heated for too long, the flux reacts with the base metal to form solid residues that are difficult to remove from the gap by the solder.
Soldering is a complex physical and chemical process of obtaining a permanent connection of materials as a result of the interaction of solid solderable (part) and liquid filler metal (solder), through their melting during wetting, spreading and filling the gap between them, followed by its crystallization.
The formation of a solder joint is accompanied by a seal between the solder and the soldered material. The strength characteristics of a soldered joint are determined by the occurrence of chemical bonds between the boundary layers of solder and the soldered metal (adhesion), as well as the adhesion of particles inside the solder or soldered metal to each other (cohesion). Soldering can be used to join any metals and their alloys.
Solder is a metal or alloy introduced into the gap between parts or formed between them during the soldering process and having more low temperature the beginning of melting than the materials being soldered. Used as solder pure metals(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 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 desoldered;
the shape and dimensions of the product are more accurately maintained, since the base metal does not melt;
allows you to obtain connections without significant internal stresses and without warping;
greater strength and high productivity in capillary soldering.
Soldering technology
Obtaining a solder joint consists of several stages:
preliminary preparation soldered connections;
removal of contaminants and oxide film from the surfaces of soldered metals using flux;
heating the parts being connected to a temperature below the melting point of the parts being soldered;
introducing a liquid strip of solder into the gap between the parts being soldered;
interaction between soldered parts and solder;
crystallization of the liquid form of solder located between the parts being connected.
Soldering copper
Copper is a metal that can be easily soldered. This is due to the fact that the metal surface can be relatively easily cleaned of impurities and oxides without the use of particularly aggressive substances (copper is a slightly corrosive metal). There is a large range of low-melting metals and their alloys that have good adhesion with copper. When heated in air during melting, copper does not enter into violent reactions with surrounding substances and oxygen, which does not require complex or expensive fluxes.
All this makes it easy to carry out any types of soldering with copper at large selection solders (giving a wide range of properties of a soldered seam) and fluxes for any environment and operating conditions. As a result, more than 97% of the world's soldering is made of copper and copper alloys.
In application to copper pipelines, the so-called “capillary” soldering was developed. This required tightening the 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 (during the competition to 1.5 minutes). As a result, copper piping in plumbing using low-temperature soldering is a classic of plumbing.
Types of soldering
The technique for connecting copper pipes is easy and reliable. The most common joining technique is capillary low-temperature and high-temperature soldering. Non-capillary soldering is not used when connecting pipes.
Capillary effect.
The process of interaction of molecules or atoms of a liquid and a solid 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 upward, overcoming gravity. The thinner the capillary, the more pronounced this effect.
To obtain the capillarity effect in copper pipelines connected by soldering, “telescopic” connections are used. When inserting a pipe into a fitting, there remains a gap not exceeding 0.4 mm between the outer diameter of the pipe and the inner diameter of the fitting. Which is enough to cause a 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 (you can, for example, feed solder from below). With a gap of no more than 0.4 mm, the capillary effect creates a gap with a width of 50% to 100% of the pipe diameter, which is enough to create a super-strong connection.
Using the capillary effect makes it possible to very quickly (virtually instantly) fill the mounting gap with solder. If the surfaces are well prepared for soldering, this guarantees 100% solder joints and does not depend on the responsibility and care of the installer.
Low temperature soldering
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 provide a soldered seam with great strength.
But with capillary soldering, the soldering width (from 7mm to 50mm, depending on the pipe diameter) is sufficient to plumbing pipelines provide excess strength. To improve the quality of soldering and increase the adhesion coefficient, special fluxes are used, and the surfaces for soldering are pre-cleaned.
All copper pipes with a diameter from 6mm to 108mm can be connected by capillary low-temperature soldering. The coolant temperature should not be higher than 130°C. For soldering, it is very important that the solder has the lowest melting point and meets the requirements that are placed on it. This is due to the fact that at high temperatures copper loses its hardness (annealing). It is for this reason that preference is given to low-temperature rather than high-temperature soldering.
High temperature soldering
High-temperature soldering is used for pipes with a diameter from 6mm to 159mm or longer, as well as in cases where the coolant temperature is more than 130°C. In water supply, high-temperature soldering is used for pipes with a diameter greater than 28 mm. However, in all cases, excessive heat should be avoided. High-temperature soldering on small diameters requires high qualifications and experience, since it is very easy to burn or cut the pipe.
For high-temperature soldering, solders based on copper and silver and a number of other metals are used. They give greater strength to the soldered seam and high permissible temperature for coolant. When using solder based on copper and phosphorus or copper with phosphorus and silver, no flux is 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 necessary to use flux when using solder with a large amount of silver (more than 5%). High temperature soldering using a torch must be performed by a qualified and experienced technician.
This method of connecting copper pipes gives the most durable seam in terms of mechanical and temperature parameters. Allows you to make bends to already installed system, without dismantling it. The main connection method in solar systems and gas distribution pipelines.
When connecting pipes using 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 must be natural - air.
As the metal ages, according to practitioners, copper passes into a harder state and the strength of the annealed metal increases. When the joint is cooled with water during high-temperature soldering, intense annealing of the metal occurs and it transitions to soft condition. Therefore, this cooling method is not used for high-temperature soldering.
Flux
Fluxes are active chemical substances 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 being connected 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, there are low-temperature (up to 450°C) fluxes (solutions of rosin in alcohol or solvents, hydrazine, tree resins, petroleum jelly, etc.) and high-temperature (over 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 a minimal amount of flux, which actively interacts with the metal. After soldering, carefully clean off its remains. After installation of the pipeline, technological flushing is carried out to completely remove 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 seam strength, do allow soldering at a temperature that has little effect on the strength of the base metal and does not change its basic characteristics. High-temperature (over 450°C) solders provide greater seam strength and high temperature for the coolant, but require high qualifications, since this involves annealing the metal
Based on 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 supplies due to the toxicity of lead.
In practice, in most cases, soldering joints is carried out using several main brands of solders. For soft soldering, solders of the type S-Sn97Cu3 (L-SnCu3) or S-Sn97Ag5 (L-SnAg5) 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. In this case, you should definitely use flux.
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 do not need to use 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 cases where the use of an open flame is unacceptable for small diameters, electric induction type heaters are used. IN Lately Electric contacts have become widespread. Outwardly, they resemble large pliers with replaceable graphite heads for gripping pipes different diameters. The heating speed with such devices may not differ from the heating speed 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 used: propane-oxygen, acetylene-air. Acetylene-oxygen is acceptable.
For soldering-welding and welding, high-temperature heating is used at the melting temperature of copper. Gas welding takes place at temperatures of 1070°C-1080°C. Gas-flame heating with acetylene-oxygen is used. Electric welding takes place at a temperature of 1020°C-1050°C. Electric welding equipment is used for arc welding.
Soldering process
Soldering rules.
When preparing the pipe for connection, burrs are removed.
Form a capillary gap of the connection or use a ready-made fitting.
Metal surfaces are cleaned.
Check the relative position of parts and gaps.
Apply a minimal amount of flux to the outside of the pipe.
Assemble the connection.
A slightly decreasing flame is used which creates maximum heat and cleans the joint.
When soldering copper to copper using copper-phosphorus solders, no flux is required.
For soldering, the joint is heated evenly to the required temperature.
Solder is applied to the mounting gap of the connection.
For uniform distribution of solder in the joint on 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 connection must be motionless.
Flux residues are carefully removed after soldering.
The heating cycle should be short and overheating should be avoided.
After assembling the pipeline, technological flushing is required to completely remove flux residues and contaminants.
When soldering, it is necessary to ensure adequate ventilation, as smoke may be harmful to health (cadmium vapor from solder and fluoride compounds from flux)
Preparing the connection
To obtain a capillary effect when soldering, the installation gap should be 0.02mm-0.3mm. Therefore, when preparing a connection, the bevel of the pipe cut should be minimal. And the ends of the connected pipes are strictly cylindrical. This is especially important with the fittingless connection method.
Since when working with a hacksaw it is possible to obtain a non-perpendicular cut, this can lead to a reduction in the soldering belt and a decrease in the reliability of the connection. And cutting a soft pipe with a pipe cutter can cause the pipe to become jammed. In this case, an uncontrolled increase in the installation gap is possible and a solder gap may result. In addition, narrowing the pipe bore increases the flow rate and the possibility of erosion.
Using a hand calibrator for the internal and external diameter of the pipe, you can obtain the ideal mounting gap for capillary soldering.
In this case, there is one more mandatory installation operation - deburring. Otherwise, flow turbulence and, as a result, erosion (including cavitation) may occur. In practice, such cases can lead to pipe rupture over time.
Surface cleaning
The strength of solder adhesion (adhesion) depends on the quality of cleaning of the surfaces being soldered. This means that any impurities and contaminants on the metal prevent the surfaces of the parts being 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 condition cannot be achieved.
To clean the metal surface, two complementary methods are used: 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 wool or fine sandpaper. When stripping, they remove contaminants and oxides, which promotes free distribution of solder over the surface. Preliminary mechanical cleaning allows you to reduce the amount of flux used, which is active chemical.
The most convenient are special nylon-based wipes, since after them, unlike sandpaper and steel sponge, there is no need to remove stripping products that may contain abrasive residues or steel particles. During mechanical cleaning, microscopic grooves are formed on the metal surface, which increase the soldering surface, and therefore contribute to a significant increase in the adhesion force of the solder and the metal.
Chemical method involves etching with an acid, which reacts with oxides and removes them from the metal surface. Or use a multicomponent flux, which also has the property of cleaning metal.
Applying flux and assembling the joint
Flux should be immediately applied to the cleaned surface of the pipe (to avoid oxidation). Flux is applied without excess only to the pipe collar that will be connected to the fitting or socket, and not inside the fitting or socket. Applying flux inside the joint is strictly prohibited. Flux absorbs a certain amount of oxides. The viscosity of the flux increases when it is saturated with oxides.
After applying flux, it is recommended to immediately connect the parts to prevent foreign particles from entering the wet surface. If for some reason the actual soldering will take place a little later, then it is better for the parts to wait for this moment already assembled. It is recommended to rotate the pipe in the fitting or socket, or, conversely, the fitting around the axis of the pipe, in order to make sure that the flux is evenly distributed in the installation gap and to feel that the pipe has reached the stop. Then you need 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 an aggressive substance. Therefore, an excessive amount of flux is undesirable. If leftover flux is not removed after soldering, it will end up in the joint and can cause corrosion and leakage over time. After soldering, all visible flux residues are also removed from the surface of the pipe (since when heated, as a result of thermal expansion and displacement by solder, a certain amount of flux from the installation gap will again appear on the surface of the pipe).
When hard (high temperature) soldering with silver solders or welding-soldering with bronze solders, 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 to solder copper parts, flux is not required; mechanical cleaning is sufficient.
The most acceptable is to use matched solder and flux for a specific type of soldering from the same manufacturer. In this case, the quality of the soldered seam and, accordingly, the entire connection is guaranteed.
Solders.
The quality and strength of soldering, the withstandable temperature of the connection depends on the solder used. In most cases, soldering of connections is carried out using several brands of solder.
For soft soldering, tin-based alloys with additions of silver or copper are mainly used. Lead solders are not used in drinking water supplies. They are usually produced in the form of 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 multicomponent silver-based (silver at least 30%). Copper-phosphorus and copper-phosphorus with silver - hard solders are specially designed for soldering copper and its alloys, and 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 rods with D = 2mm-3mm. When soldering, flux is required.
Careful precautions must be taken when using low temperature copper solder containing cadmium due to the toxic effects of cadmium fumes.
Heating of the joint 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 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). Electric heating connection fundamental differences does not come in soldering.
If the solder does not melt upon a test touch with the rod, heating is continued. The supplied solder bar should not be heated. At the same time, in no case should we forget about the need to move the flame so as not to overheat some separate plot connections. As soon as the solder begins to melt, the flame is pulled 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. There is no need to inject excessive amounts of solder as this is not only wasteful, but can also cause excess solder to flow 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 required length of solder is bent in the shape of the letter “G”. In this case, unnecessary solder is not consumed, and the moment “soldered - not soldered” is clearly controlled, which is important when large volume work.
Heating of the connection during hard soldering
For hard soldering, heating is carried out only using 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, a slight reduction in the soldering width is allowed compared to soft soldering. To perform hard soldering, high qualifications and experience are required, otherwise it is very easy to overheat the metal and possible ruptures.
The burner flame should be “normal” (neutral). A balanced gas mixture contains equal amounts of oxygen and gaseous fuel, causing the flame to heat the metal without causing any other effect. Burner flame torch with a balanced gas mixture (bright of blue color and small size).
A decreasing burner flame indicates an excess amount of gaseous fuel in the gas mixture, which exceeds the oxygen content. The slightly reduced flame heats and cleans the metal surface for a faster and better soldering operation.
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 connected pipes are heated evenly along the entire circumference and length of the connection. Both elements of the connection are heated with a burner flame at the junction until dark cherry color (750°C-900°C), evenly distributing the heat. It is allowed to perform soldering in any spatial position of the parts being connected.
The connection should not be heated to the melting temperature of the metal from which the pipes are made. Use a burner of the appropriate size with a slightly decreasing flame. Overheating the connection increases the interaction of the base metal with the solder (that is, it increases the formation of chemical compounds). As a result, such interaction negatively affects the service life of the connection.
If inner tube heated to soldering temperature, and outer pipe has a lower temperature, the molten solder does not flow into the gap between the connected pipes and moves towards the heat source
If you uniformly heat the entire surface of the ends of the pipes being soldered, then the solder supplied to the edge of the socket melts under the influence of their heat and uniformly enters the joint gap. The pipes to be soldered are sufficiently hot if the brazing rod melts on contact with them. To improve soldering, preheat the solder bar slightly with a torch flame.
Manufacturers produce small-sized gas torches with disposable cartridges, which allow heating for hard and soft soldering, but with hard soldering, the diameter of the joints is half that of soft soldering.
Peculiarities
Butt soldering of copper pipes and fittings is not permitted. When using welding for diameters over 108 mm (wall thickness over 1.5 mm), butt joints are allowed.
Soldering connections of more than two elements should be carried out simultaneously. In this case, the order of filling the mounting gaps with solder (for example, in a tee) is observed - from bottom to 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. High-temperature soldering is not permitted on a low-temperature soldering connection.
Prohibited
Soldering of fittingless joints obtained without expanding the end of the pipe with an expander, for example, bell joints - obtained by flaring or rolling the end of the pipe. Transition couplings should be used.
Soldering of bends made without special tools or in a pipe bend (elbow). You should use standard tees or a bend formed with a special tool.
Soldering of any non-standard connections obtained without distributing the pipe using an expander or a special tool for drawing out the outlet.
Overheat
When carrying out soldering work, it is very important to avoid “overheating”, as this can lead to the destruction of the flux, which loses its 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 reaches the melting point of the solder. To do this, it is necessary to periodically touch the heated connection with solder.
Or use flux with powdered solder for this purpose: as soon as drops of melted powdered solder sparkle in the flux, the connection is heated. Some fluxes, when heated enough for soldering, emit smoke or change color.
During high-temperature soldering, the 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, as with soft soldering, is to periodically touch the joint with solder. With sufficient experience, the adequacy of heating will be determined by the colors of the tarnish. It is important not to use too much heat, such as an oxyacetylene 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 prevent mutual movement of the articulated parts. After the solder has hardened, it is necessary to remove all visible flux residues with a damp cloth, and if necessary, use additional amount warm water.
When soldering and welding, metal deposits (burst) may form, which must be removed if necessary. For any type of soldering and welding, metal deposits (burst) inside the joint that interfere with the flow of liquid are not allowed. They must be removed.
The acquired experience in work allows you to use the optimal amount of solder when soldering, which does not lead to the formation of burrs in the connection.
After completing the installation of the system, it is necessary to carry out technological flushing of the system as soon as possible to remove flux residues from the internal surfaces, since flux that gets inside the joint during soldering and, being an aggressive substance, can lead to unwanted corrosion of the metal.
Soldering quality control
Quality control is a critical operation. In order to unify soldered assembly units, establishing standards and requirements for soldered products, the standard GOST 19249-73 “Soldered connections” was developed. Basic types and parameters". The standard defines the design parameters of a solder joint, its symbols, contains a classification of the main types of connections.
Solder joint defects
The quality of soldered products is determined by their strength, degree of operability, reliability, corrosion resistance, ability to perform special functions (tightness, thermal conductivity, resistance to temperature changes, etc.). The most typical defects in solder joints include pores, cavities, slag and flux inclusions, missing solders, and cracks.
The reason for the formation of unsoldered joints may be the blocking of gas by liquid solder in the presence of uneven heating or an uneven gap, or a local lack of wetting of the surface of the soldered metal with liquid solder. Cracks in soldered seams can occur under the influence of stresses and deformations of the metal of the product during the cooling process.
Non-metallic inclusions such as flux or slag appear when the surface of the product is not thoroughly prepared for soldering or when its conditions are violated. When soldering is heated for too long, the flux reacts with the metal being soldered to form solid residues that are difficult to remove 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.
Correct design of the solder joint (absence of closed cavities, uniformity of the gap), accuracy of assembly for soldering, dosed amount of solder and fluxing media, uniformity of heating - the conditions for a defect-free solder joint.
Methods for quality control of soldered products
To assess the quality of soldered products, non-destructive and destructive testing is used. Technical inspection products with the naked eye or using a magnifying glass in combination with measurements allows you to check the surface quality, filling of gaps with solder, completeness of fillets, the presence of cracks and other external defects.
According to requirements technical specifications soldered products are subjected to other non-destructive testing methods. If necessary, a connection strip is used, which gives a complete picture of the quality of the connection. Used as a random control.
Safety
Compliance with safety rules is great importance When carrying out soldering work, it is necessary to follow safety rules, since fluxes and alloys may contain harmful substances. Fluxes applied during cold or hot soldering will split and release fumes that may contain toxic substances and cause harm to health.
Careful precautions must be taken when using low temperature copper solder containing cadmium due to the toxic effects of cadmium fumes. When soldering, it is necessary to ensure adequate ventilation, as harmful smoke of fluoride compounds may appear from the flux that uses 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 standards established for toxic substances, and carefully study the description of their properties, which is on the label.
During high-temperature soldering, solutions of acids and alkalis can be used to etch connecting parts. It is necessary to work with them wearing rubber gloves and acid-resistant clothing. The face and eyes must be protected from splashes with safety glasses. After finishing work and before eating, you must wash your hands thoroughly.
When soldering with a gas torch, before starting work, you must check the tightness of the hoses and equipment. Gas cylinders must be stored in an upright position. Containers with solutions after work are handed over to a warehouse; draining solutions and alkalis into the sewer is not allowed.
When carrying out 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 in soldering copper pipes for water supply and gas pipelines requires approval from local authorities, according to local regulations.
Normative documents for soldering and welding: GOST 1922249-73 and GOST 16038-80. European standard TN 1044. The use of gases for flame soldering and welding is regulated by GOST 5542-87 and GOST 20448-90.
Home craftsmen try to carry out construction and renovation work independently, which allows you not only to save family budget, but also to be absolutely confident in the quality result. Therefore, they have to master new techniques and technologies, 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 the instruments will be required by the performer. Skills that are useful even in everyday life will make it possible to independently assemble pipelines with excellent performance characteristics.
Copper pipelines are 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 heat resistance, flexibility and durability. after assembly, it can be poured into concrete, hidden in walls, etc. Nothing will happen to them during operation.
Copper pipelines are considered the best, since 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 material for heating or plumbing. In terms of long-term operation, the higher costs are well worth it. In addition to excellent performance characteristics, which copper has, it is quite easy to install. “Scary tales” about difficulties in soldering are most often exaggerated.
Copper is quite easy to solder. Its surface does not require the use of aggressive cleaning agents. Many low-melting metals have high adhesion to it, which simplifies the choice of solder.
Expensive copper fluxes are not needed, since violent reactions with oxygen do not occur when the metal is melted. During the soldering process, the pipe does not deform; its shape and dimensions remain unchanged. The resulting seam can be unsoldered if necessary.
Methods for soldering copper parts
Soldering is considered the best method for joining copper parts. During operation, molten solder fills the small gap between the elements, forming a reliable connection.
There are two most common methods for obtaining such compounds. This is high-temperature and low-temperature capillary soldering. Let's figure out how they differ from each other.
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The reliability and durability of copper pipes is not in doubt. However, soldering copper pipes with your own hands will require more skill than, for example, plastic ones. The choice of technology for connecting products depends on the purpose of the pipeline. Two technologies are most often used. High temperature welding is most often used when the loads on the system are expected to be high. Low-temperature soldering is excellent for arranging household pipelines.
Before you start self-execution works, you should carefully study the technologies, because they require a responsible and attentive approach.
Connecting copper pipes using high-temperature soldering is carried out at temperatures above 450 degrees. The need to use such high temperatures is due to the use of metals with higher high temperature melting than tin. The basis of the mixture for high-temperature solder is copper, silver and some other metals. Solder made using refractory materials produces a so-called drunken seam, which has a number of advantages in terms of technical parameters. Such a seam is indispensable in cases where it is necessary to connect large diameter pipes.
For the construction of water pipelines, the high-temperature method is used when the temperature of the coolant is above 130 degrees and the diameter of the product is more than 28 mm. Due to the high reliability and strength of the seam resulting from the high-temperature connection, this method has become widespread in the gas industry.
Hard soldering is very often used in devices heating systems. In production plumbing work Using this method allows you to arrange a tap from an already assembled heating system.
The main feature of high-temperature soldering is the annealing of the metal, after which it softens.
To avoid copper losing its strength, it should be allowed to cool. naturally, and excessive heating should be avoided.
Low temperature soldering technology
In domestic heating, water supply, as well as other industries in which the temperature is relatively not high, the method is most often used low temperature soldering. This method is used in systems using temperatures below 450 degrees and for small-diameter products.
This soldering technology avoids annealing the metal, which in turn has contributed to the widespread use of this method in plumbing work. This method is the safest when doing the work yourself.
Main stages of soldering
All soldering work can be divided into the following technological steps:
- Product cutting.
- Cleaning the outer and inner surfaces of the pipe and socket.
- Checking the parts being connected and the gap.
- Applying flux to the surface of the product.
- Assembly.
- Heat.
- Filling the mounting gap with solder.
- Soldering cooling.
- Removing flux residues and cleaning the connection.
Before you start soldering copper pipes, you need to properly prepare the sections - clean them, create technical gaps, and then fill them with a solder mixture. To weld pipes, a special substance called flux is used. Flux allows you to evenly distribute the solder throughout the entire gap and make the seam more reliable. The basic rule when using this substance is to avoid getting moisture on the prepared surface. After following all the rules, you can get to work.
Heating of products during low-temperature soldering
To perform this type of work, you will need low-temperature flux, gas-burner on propane and gas mixture: propane-butane-air. Sometimes an air-propane mixture is used.
For low-temperature soldering, an electric soldering iron can be used, which is also suitable for heating connection elements. If a gas burner is used for heating, then you need to keep in mind that the contact patch must constantly move, which will allow for uniform heating.
If the solder does not melt at the first touch, you need to continue the process. But as soon as the solder has softened, you need to remove the flame and allow the solder to distribute over the technical gap.
Heating of products during high-temperature soldering
High temperature soldering technology is also known as “hard soldering” due to its reliability and strength. For welding using this technology, acetylene-air or propane-oxygen gas mixtures are used. To comply with all technology requirements, the flame must be hot, as evidenced by its bright blue color.
The burner flame should be moved along the entire length of the seam and the circumference of the product, this will ensure uniform heating. The connection parts should be heated to 750 degrees. The desired temperature can be easily determined by the dark cherry color of the heated products.
Video
We present to your attention a video demonstrating the process of soldering copper pipes.
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Heating at high temperature connection
For “hard” soldering, only gas with a mixture of acetylene-air or propane-oxygen is used; gas with an acetylene-oxygen mixture is allowed.
If possible, the heating cycle should be short, with the burner flame constantly moving along the entire length and circumference of the joint. To heat up quickly, the burning gas must have a small, bright blue flame. The connecting parts must be heated with a burner flame until the products have a dark cherry color (750°C), and the heat must be distributed evenly.
When the parts are sufficiently heated, the solder, which is supplied to the edge of the socket, begins to melt and flow into the joint gap. To improve the soldering of the joint, the solder needs to be slightly heated with a torch flame. The solder should melt from the temperature of the heated connection, and in no case from the burner flame.
The art of high-temperature soldering lies in the need to perform such a minimum heating of the joint that one touch of the solder rod will lead to complete filling of the capillary gap with the formation of a fillet.
After the solder has hardened, it is necessary to remove the flux (all visible residues) with a damp cloth. In plumbing, after the installation of the pipeline is completed, a technological flushing of the system is carried out to remove all flux residues that remain on the internal surfaces of the pipes. Flux is an aggressive substance and has a negative effect on the human body.
Now you know how to solder copper pipes. Observing simple rules installation, which consists in conscientiously cleaning the surface, heating the joints to the required temperature, holding the joint immovable while the solder cools, you can be guaranteed to obtain connections with high strength.
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