Purpose

These instructions apply to soldering HIT electrical circuits using an electric soldering iron.

The instructions should be followed when developing technological processes, soldering, repair, control and acceptance of soldered structures.

Deviations (tightened or reduced requirements) from these instructions can be included in route maps (or other technological documents) in agreement with the chief technologist and the customer’s representative. Auxiliary materials, fixtures, equipment and tools required for low-temperature soldering are given in the Appendix.

Low-temperature soldering using an electric soldering iron must be carried out in compliance with the safety regulations set out in the safety instructions.

Preparing an electric soldering iron and servicing it during operation

Plug in the electric soldering iron and heat it to the melting temperature of rosin (120 °C).

Remove scale from the working part of the soldering iron using a file or brush.

Immerse the working part of the soldering iron in rosin and coat it with an even layer of solder.

Do not allow the soldering iron to cool during operation, because In this case, solder oxidation occurs and soldering conditions deteriorate.

Do not allow the soldering iron to cool down to the melting temperature of the solder, since soldering with such a soldering iron deteriorates the quality of the soldered seam.

It is necessary to work with an electric soldering iron connected to the network through a temperature controller in cases where this requirement is specified in the route map for soldering the product.

Preparing the surface of parts for soldering

Degrease the surface of parts with oil or other contamination by galvanic means.

Clean mechanically until the coating is completely removed (in the soldering zone) from the surface of parts whose soldered seams require tightness.

Do not clean parts with a tinned surface.

Mechanically clean the soldering area of parts (not provided for in the previous paragraph) to a metallic shine:

having paint and varnish coatings;
not having galvanic coatings in the form of tinning, silvering, copper plating, galvanizing;
with a nickel-plated surface, the design of which does not allow the removal of flux residues (after tinning) by washing.

Degrease the surface of all parts using one of the following methods:

galvanic;
immersion in a bath of solvent;
by wiping the soldering area with a calico swab dipped in solvent.

Store parts in a clean and dry place for no more than three days.

Re-clean if the storage time exceeds three days.

Submit parts for continuous quality control inspection according to the requirements of Table 1.

Tinning

Prepare the electric soldering iron for operation in accordance with the requirements set out in the section “Preparation of the electric soldering iron and its maintenance during operation.”

Cover with a brush thin layer flux zone for soldering parts.

Use a 5-7% solution of zinc chloride and ethyl alcohol as a flux when tinning steel and nickel-plated parts, the design of which allows you to remove flux residues by washing. In other cases, use flux LTI-1 or LTI-120.

Using a soldering iron, heat the surface of the part to the melting temperature of the solder.

Immerse the working part of the soldering iron in rosin and collect excess solder on it.

For tinning, use solder of the same brand as when soldering the assembly.

Press the soldering iron onto the part and rub the solder over the surface to be served.

Carry out work with intense heating of the part and with minimal tinning time.

Cover the tinning area with an even and thin layer of solder.

Add additional flux to the tinning area if the solder does not spread over the surface to be treated.

Do not supply excess (more than necessary) solder and flux to the tinning area.

Stop tinning after the workpiece surface is covered with an even and thin layer of solder.

Allow tinning of parts to be carried out by immersion in a bath of molten solder.

Remove flux residues from parts after tinning by washing in a solvent. Allow flux residues to be removed by wiping with a calico swab dipped in alcohol.

Submit parts for continuous quality control inspection in accordance with the requirements of Table 1.

Store parts after tinning in a clean and dry room.

Preparing wires for soldering and tinning

Cut wires and insulating tubes to size according to the drawing.

Remove insulation from the wires to the length indicated in the drawing.

Removal of insulation is permitted by technical means or with a tool that prevents cutting of wire strands (for example, using an electrical device under exhaust ventilation).

Secure the ends of the insulating braiding of the wires using AK-20 nitro glue or using a marking tag on glue or marking tape.

Clean the ends of the non-plated wires with sandpaper.

Tin the ends of the wires (if provided for in the route map) in accordance with the requirements set out in the “Tinning” section.

Soldering

Assemble components and parts for soldering, observing the following requirements:

Maintain a gap between the assembled parts of 0.1-0.15 mm - for untinned surfaces and no more than 0.05 mm - for tinned ones;

Perform the assembly in such a way that the possibility of parts moving relative to each other is completely excluded, both at the time of soldering and during the cooling process of the assembly after soldering.

Install a heat sink device on the soldered assembly, if provided for in the route map.

Degrease the surface of the parts to be soldered with a calico swab dipped in alcohol. Do not degrease only if there are appropriate instructions in the route map.

Using a brush, coat the soldering area of the parts with a thin layer of flux.

Prepare the electric soldering iron for operation in accordance with the requirements set out in the section “Preparation of the electric soldering iron and its maintenance during operation.”

Using a soldering iron, heat the surface of the parts to the melting temperature of the solder, ensuring the greatest thermal contact between the soldering iron and the parts.

Heat more intensively parts with greater mass or parts made of material with lower thermal conductivity.

Immerse the working part of the soldering iron in rosin, and then apply excess solder to it. The brand of solder is indicated in the drawing.

Press the soldering iron onto the parts to be soldered and rub the solder over the surfaces to be joined.

Cover the soldering area with an even and thin layer of solder.

Add additional flux to the soldering area if the solder does not spread over the surface to be treated.

Allow direct supply of solder to the soldering zone if the soldered seam is long and the heat contact area between the soldering iron and the parts is small.

Do not supply excess solder to the soldering area (exceeding what is necessary to ensure the drawing dimensions).

Allow soldering of IKZ unit insulators and other small parts to be carried out under the casing of an electric stove connected to the network through a temperature regulator, with mandatory temperature control in the soldering zone using a thermocouple. Count operating temperature one that would exceed the melting point of solder by 50-70 °C.

Perform work under intense heat and minimal soldering time.

Monitor soldering time only if the route map contains appropriate instructions.

Stop soldering once the solder fills the gaps between the parts being soldered and the soldering area is covered with a thin layer of molten solder.

Remove flux residues from the parts with a calico swab (or brush) soaked in alcohol. If the route map contains instructions about the inadmissibility of using alcohol, then remove the flux by mechanical stripping.

Submit parts and assemblies after soldering for continuous quality control inspection in accordance with the requirements of Table 2.

Soldered seam defects must be corrected taking into account the following requirements:

It is allowed to solder the same soldered seam defect no more than twice.

Unsolder the assembly using a soldering iron and clean the surface of the parts from flux and solder residues.

Prepare parts for re-soldering taking into account the requirements of the previous sections.

Resolder the unit taking into account the requirements of this section.

Submit parts and assemblies for repeated continuous quality control inspection after re-soldering or soldering.

Carry out control taking into account the requirements of Table 2.

Cover the soldered seam with electrical insulating varnish type NTs-62 or UR-231, lightly tinted with rhodamine, if there is a corresponding instruction in the route map.

Send for assembly or other methods of control, in accordance with the technical requirements of the drawing, parts and assemblies that have passed quality control in accordance with Table 2.

Table 1 - Sorting of parts arriving for tinning and after tinning

Name of defect	Result of sorting	Correction Methods
Traces of corrosion, rust, oxide strip, paint, oil and other contaminants	Not allowed
Burrs on the edges of soldered parts	Not allowed	Eliminate by mechanical cleaning
Galvanic coatings (except tinning) in the soldering zone on parts whose soldered seams are subject to tightness requirements	Not allowed
Nickel coating on parts, the design of which does not allow the removal of flux residues by washing	Not allowed	Eliminated by mechanical cleaning
A cut of conductors during mechanical stripping of the ends of wires or when removing insulation from them	Marriage
Roughness of tinning surface	Not allowed	Eliminate by re-tinning
Foreign inclusions in the solder	Not allowed	Eliminate by re-tinning
Do not solder (presence of a partially untinned surface)	Not allowed	Eliminate by re-tinning
Presence of flux residues on the tinned surface or part	Not allowed	Eliminate by re-washing

Table 2 - Sorting of parts after soldering

Name of defect	Result of sorting	Correction Methods
Don't get lost	Not allowed	Eliminate by soldering
Don't sleep	Not allowed	Eliminate by soldering
Shrinkage porosity in a soldered seam	Not allowed	Eliminate by soldering
Cracks in the solder seam	Not allowed	Eliminate by resoldering
Undersizing the solder seam	Not allowed	Eliminate by soldering
Oversizing the soldered seam: not interfering with elements of further assembly in which further assembly is impossible	Allowed Not allowed	Eliminate by resoldering
Presence of flux residues on the soldered seam of the material being soldered	Not allowed	Eliminate by re-cleaning
Flux flow through down conductors when soldering them with borns: not reaching the insulating sleeves reaching the insulating sleeves	Allowed Not allowed	Eliminate by re-cleaning

Materials

Tin-lead solders (wire with a diameter of 2-4 mm) GOST 21931-80.
Silver solders (wire with a diameter of 2-4 mm) GOST 19738-74.
Tin (wire with a diameter of 2-4 mm) GOST 860-75.
Flux LTI-1, prepared according to technical specifications.
Pine rosin, grade 1, GOST 19113-84.
Technical zinc chloride, grade 1, GOST 7345-78.
Technical ethyl alcohol GOST 17299-78.
Varnish NTs-62 TU 6-21-090502-2-90.
Solvent grade 646 GOST 18188-72.
Rhodamine “S” or “6ZH” TU6-09-2463-82.
Varnish UR-231, prepared according to TI.
Gasoline "galoshes" TU 38-401-67-108-92.
Cotton calico fabric of the GOST 29298-92 group.
Knitted gloves GOST 5007-87.
Waterproof sanding paper GOST 10054-82.
Artistic brush KZHKh No. 2,2a TU 17-15-07-89.
Flux LTI-120 STU 30-2473-64.

Equipment, devices, tools

Electric soldering iron GOST 7219-83.
Devices for stripping wires from insulation PR 3081.
Device for cutting wires FK 5113P.
Electric stove GOST 14919-83.
Small-sized soldering station type SMTU NCT 60A.
Assembly devices (indicated in route maps).
Work table with exhaust ventilation.
Line GOST 427-75.
Side cutters GOST 28037-89.
Tweezers GOST 21214-89.

For aluminum and aluminum alloys use various ways rations. Soldering happens:

high temperature soldering - and

In English:

brazing and
soldering, respectively.
Hard solders include those with a high melting point ( liquidus above 450 °C).
Soft solders melt below 450 °C.

Figure - Repairing an aluminum pipe by soldering with soft solder

Soft solders for aluminum

Since soft soldering is carried out at temperatures below 450 °C, then, naturally, in this case, hard solders - aluminum-based solders - are not used. Previously, most aluminum soft solders contained zinc, tin, cadmium and lead. Currently, cadmium and lead are recognized as harmful to humans and environment. Therefore, modern soft solders for soldering aluminum are alloys based on tin and zinc.

Tin-zinc alloys

Tin-zinc alloys are specially developed for soldering aluminum to aluminum and aluminum to copper:

91% tin / 9% zinc - eutectic alloy with a melting point of 199 ° C
85% Sn / 15% Zn - melting range from 199 to 260 °C
80% Sn / 20% Zn - melting range from 199 to 288 °C
70% Sn / 30% Zn - melting range from 199 to 316 °C
60% Sn / 40% Zn - melting range from 199 to 343 °C

Eutectic and non-eutectic solders

Eutectic solders are widely used for furnace soldering and other automatic systems aluminum soldering. This minimizes applied heat for thin-walled products by rapidly melting and solidifying at 199°C.

The solidification interval of the solder, when it is in a semi-liquid-semi-solid state, allows you to perform additional operations until the solder has completely hardened.

An increased zinc content promotes better wetting of the solder, but with an increase in zinc content, the temperature of complete solidification of the solder (liquidus) increases significantly.

Features of soft soldering

Soft soldering of aluminum differs from similar soldering of other metals. The oxide film on aluminum - dense and fire-resistant - requires active fluxes that are developed specifically for aluminum. Soldering temperature must also be more tightly controlled.

For aluminum, corrosion resistance is much more dependent on the composition of the solder than for copper, brass and iron alloys. All soft-soldered seams have lower corrosion resistance than hard-soldered or .

The high thermal conductivity of aluminum requires rapid heating to ensure the desired temperature in the weld.

Soldering of wrought aluminum alloys

Almost all aluminum alloys can be soft soldered in one way or another. However, their chemical composition greatly influences the ease of soldering, the type of solder, the soldering method used, and the ability of the soldered product to withstand various loads in service.

The relative ability for low-temperature soldering - soft soldering - of the main wrought aluminum alloys is as follows:

excellent soldering: 1100 (AD), 1200 (AD), 1235 (≈AD1), 1350 (AD0E), 3003 (AMts):
soldered well: 3004 (D12), 5357, 6061 (AD33), 6101, 7072, 8112;
medium soldered: 2011, 2014, 2017 (D1), 2117 (D18), 2018, 2024 (D16), 5050, 7005 (1915);
poorly soldered: 5052 (AMg2.5), 5056 (≈AMg5), 5083 (AMg4.5), 5086 (AMg4), 5154 (≈AMg3), 7075 (≈B95).

Alloys that contain more than 1% magnesium cannot be soldered satisfactorily with organic flux, and alloys with more than 2.5% magnesium cannot be soldered with active fluxes. Alloys that contain more than 5% magnesium cannot be soldered with any flux.

When soldering aluminum alloys containing more than 0.5% magnesium, molten tin solder penetrates between the grains of the metal. Zinc is also capable of penetrating along the grain boundaries between the grains of aluminum-magnesium alloys, but with a magnesium content of more than 0.7%. This intergranular penetration is aggravated by the presence of stresses, external or internal.

Aluminum alloys alloyed with magnesium and silicon are less susceptible to intergranular penetration than binary aluminum-magnesium alloys.

Aluminum alloys containing copper or zinc as the main alloying elements usually also contain sufficient amounts of other elements. Most of these alloys are susceptible to intergranular solder penetration and are not typically soldered.

Heat-strengthened alloys typically have a thicker oxide film than what occurs naturally. This film makes soft soldering difficult. For such alloys, chemical surface preparation is usually used before soldering.

Soldering of cast aluminum alloys

Most cast aluminum alloys have a high content of alloying elements, which increases the likelihood that these elements will dissolve in the solder and the solder will penetrate the grain boundaries. Therefore, cast aluminum alloys are poorly soldered with soft solders.

In addition, the inherent surface roughness, tiny cavities or porosity of cast alloys promote flux retention and make flux removal after soldering very difficult.

Three foundries aluminum alloy 443.0, 443.2 and 356 are relatively good and easy to solder with soft solders. Alloys 213.0, 710.0 and 711.0 are somewhat worse, but still acceptable.

Sources:

Aluminum and Aluminum Alloys, ASM International, 1996
EEA Aluminum Automotive manual - Joining - Brazing, EEA, 2015

Soldering - difficult physical-chemical process 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 solder joint are determined by the occurrence 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 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 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 solder seam properties) 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 between molecules or atoms of a liquid and 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 forces surface tension 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, use “telescopic” connections. When inserting a pipe into a fitting, between the outer diameter of the pipe and internal diameter the fitting leaves a gap not exceeding 0.4 mm. 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 diameter of the pipe) is sufficient to provide excess strength for plumbing pipelines. 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 having longer length, 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 becomes 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 a 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 a protective coating and prevent 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, can be used minimum quantity flux that actively interacts with 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 solders containing lead 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, use electric heaters electroinduction type. Recently, electric contact devices have become widespread. Outwardly, they resemble large pliers with replaceable graphite heads for gripping pipes of 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 relative position 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 manual 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 an active chemical substance.

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 metal surface Microscopic grooves are formed, which increase the soldering surface, and therefore contribute to a significant increase in the adhesion force of the solder and metal.

Chemical method involves etching with an acid, which reacts with oxides and removes them from the metal surface. Or the use of 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 soldering itself will take place a little later, then it is better for the parts to wait for this moment already in assembled form. 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 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 in drinking water supply do not apply. 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 connection 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 of a connection has no fundamental differences 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 any particular section of the connection. 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, solder is not wasted unnecessarily, and the moment “soldered - not soldered” is clearly controlled, which is important for a large volume of 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. Hard soldering requires high qualifications and experience, otherwise it is very easy to overheat the metal and cause 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 blue 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 pipes being connected 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 the inner pipe is 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. The use of high-temperature soldering on a low-temperature soldering joint is not permitted.

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). Standard tees or a formed bend should be used 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 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 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 work experience allows you to use optimal quantity solder during 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 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 GOST 19249-73 standard “Soldered connections” was developed. Basic types and parameters". The standard defines design parameters solder connection, it 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 metal being soldered 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 of the product with the naked eye or using a magnifying glass in combination with measurements allows you to check the quality of the surface, 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 methods non-destructive testing. 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 value 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.

For high temperature soldering for etching connecting parts solutions of acids and alkalis can be used. 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 gas burner Before starting work, it is necessary to check the tightness of 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.

Regulatory documentation 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.

As a way permanent connection Soldering of metals has been known for a long time. Soldered metal products used in Babylon, Ancient Egypt, Rome and Greece. Surprisingly, in the millennia that have passed since then, soldering technology has not changed as much as might be expected.

Soldering is the process of joining metals by introducing a molten binding material - solder - between them. The latter fills the gap between the parts to be connected and, when solidified, is firmly connected to them, forming an inseparable connection.

When soldering, the solder is heated to a temperature exceeding its melting point, but not reaching the melting point of the metal of the parts being connected. Becoming liquid, the solder wets the surfaces and fills all gaps due to the action of capillary forces. The base material dissolves in the solder and their mutual diffusion occurs. As the solder hardens, it firmly adheres to the parts being soldered.

When soldering, the following temperature conditions must be met: T 1<Т 2 <Т 3 <Т 4 , где:

T 1 - temperature at which the soldered joint operates;
T 2 - solder melting temperature;
T 3 - heating temperature during soldering;
T 4 - melting temperature of the parts being connected.

Differences between soldering and welding

A soldered joint resembles a welded joint in appearance, but in its essence, metal soldering is radically different from welding. The main difference is that the base metal is not melted, as in welding, but is only heated to a certain temperature, the value of which never reaches its melting point. From this basic difference all the others follow.

The absence of melting of the base metal makes it possible to connect parts of the smallest sizes by soldering, as well as repeated separation and connection of soldered parts without compromising their integrity.

Due to the fact that the base metal does not melt, its structure and mechanical properties remain unchanged, there is no deformation of the soldered parts, and the shapes and dimensions of the resulting product are maintained.

Soldering allows you to join metals (and even non-metals) in any combination with each other.

With all its advantages, soldering is still inferior to welding in terms of strength and reliability of the connection. Due to the low mechanical strength of soft solder, low-temperature butt soldering is fragile, so parts must be connected to the floor to achieve the required strength.

Nowadays, among the various methods of creating one-piece parts, soldering takes second place after welding, and in some areas its position is dominant. It is difficult to imagine the modern IT industry without this compact, clean and durable way of connecting electronic circuit elements.

The applications of soldering are wide and varied. It is used to connect copper pipes in heat exchangers, refrigeration units and all kinds of systems transporting liquid and gaseous media. Soldering is the main method of attaching carbide inserts to metal-cutting tools. During body work, it is used to attach thin-walled parts to a thin sheet. In the form of tinning, it is used to protect some structures from corrosion.

Soldering is also widely used at home. It can be used to connect parts made of different metals, seal threaded connections, eliminate porosity of surfaces, and ensure a tight fit of the bushing of a loose bearing. Wherever the use of welding, bolts, rivets or ordinary glue is for some reason impossible, difficult or impractical, soldering, even done with your own hands, turns out to be a life-saving way out of the situation.

Types of soldering

The classification of soldering is quite complex due to the large number of classified parameters. According to the technological classification according to GOST 17349-79, metal soldering is divided: according to the method of obtaining solder, according to the nature of filling the gap with solder, according to the type of crystallization of the seam, according to the method of removing the oxide film, according to the heating source, according to the presence or absence of pressure in the joint, according to the simultaneous execution of connections .

One of the main ones is the classification of soldering according to the melting temperature of the solder used. Depending on this parameter, soldering is divided into low-temperature (solders with a melting point of up to 450°C are used) and high-temperature (solders with a melting point above 450°C).

Low temperature soldering more economical and easier to implement than high-temperature. Its advantage is that it can be used on miniature parts and thin films. The good thermal and electrical conductivity of solders, the ease of performing the soldering process, and the ability to connect dissimilar materials provide low-temperature soldering with a leading role in the creation of products in electronics and microelectronics.

To the benefits high temperature soldering This includes the possibility of producing connections that can withstand heavy loads, including shock, as well as obtaining vacuum-tight and hermetic connections operating under high pressure conditions. The main heating methods for high-temperature soldering, in single and small-scale production, are heating with gas burners, medium and high frequency induction currents.

Composite soldering used when soldering products with non-capillary or uneven gaps. It is carried out using composite solders consisting of a filler and a low-melting component. The filler has a melting point higher than the soldering temperature, so it does not melt, but only fills the gaps between the soldered products, serving as a medium for the distribution of the low-melting component.

Based on the nature of solder production, the following types of soldering are distinguished.

Soldering with ready-made solder- the most common type of soldering. The finished solder is melted by heat, fills the gap between the parts being connected and is held in it by capillary forces. The latter play a very important role in soldering technology. They force the molten solder to penetrate into the narrowest crevices of the joint, ensuring its strength.

Reaction-flux soldering, characterized by a displacement reaction between the base metal and the flux, resulting in the formation of solder. The most well-known reaction in reaction-flux soldering is: 3ZnCl 2 (flux) + 2Al (metal to be joined) = 2AlCl 3 + Zn (solder).

To solder metal, in addition to properly prepared soldered products, you must have a heat source, solder and flux.

Heat sources

There are many ways to heat soldered parts. The most common and most suitable for soldering at home include heating with a soldering iron, a torch with an open flame and a hair dryer.

Heating with a soldering iron is carried out during low-temperature soldering. The soldering iron heats the metal and solder due to the thermal energy accumulated in the mass of its metal tip. The tip of the soldering iron is pressed against the metal, causing the latter to heat up and melt the solder. The soldering iron can be not only electric, but also gas.

Gas burners are the most versatile type of heating equipment. This category also includes blowtorches fueled with gasoline or kerosene (depending on the type of blowtorch). Acetylene, propane-butane mixture, methane, gasoline, kerosene, etc. can be used as flammable gases and liquids in burners. Gas soldering can be either low-temperature (when soldering massive parts) or high-temperature.

There are other heating methods for soldering:

Soldering with induction heaters, which is actively used for soldering carbide cutters of cutting tools. During induction soldering, the soldered parts or parts thereof are heated in an inductor coil through which a current is passed. The advantage of induction soldering is the ability to quickly heat up thick-walled parts.

Soldering in various furnaces.
Electrical resistance soldering, in which parts are heated by heat generated due to the passage of electric current through the soldered products that are part of the electrical circuit.
Dip soldering, performed in molten solders and salts.
Other types of soldering: arc, beam, electrolytic, exothermic, stamps and heating mats.

Solders

Both pure metals and their alloys are used as solders. In order for solder to fulfill its purpose well, it must have a number of qualities.

Wettability. First of all, the solder must have good wettability in relation to the parts being joined. Without this, there will simply be no contact between it and the soldered parts.

In a physical sense, wetting implies a phenomenon in which the strength of the bond between the particles of a solid substance and the liquid wetting it is higher than between the particles of the liquid itself. In the presence of wetting, the liquid spreads over the surface of the solid and penetrates into all its irregularities.

Example of non-wetting (left) and wetting (right) liquids

If the solder does not wet the base metal, soldering is not possible. An example of this is pure lead, which does not wet copper well and therefore cannot serve as solder for it.

Melting point. The solder must have a melting point below the melting point of the parts being joined, but above that at which the connection will work. The melting temperature is characterized by two points - the solidus temperature (the temperature at which the most fusible component melts) and the liquidus temperature (the lowest value at which the solder becomes completely liquid).

The difference between the liquidus and solidus temperatures is called the crystallization interval. When the joint temperature is in the crystallization range, even minor mechanical impacts lead to disruptions in the crystalline structure of the solder, which can result in its fragility and increased electrical resistance. Therefore, it is necessary to follow a very important soldering rule - do not subject the connection to any load until the solder has completely crystallized.

In addition to good wettability and the required melting temperature, the solder must have a number of other properties:

The content of toxic metals (lead, cadmium) should not exceed the established values for certain products.
There must be no incompatibility between the solder and the metals being joined, which could lead to the formation of brittle intermetallic compounds.
Solder must have thermal stability (maintaining the strength of the solder joint when temperature changes), electrical stability (consistency of electrical characteristics under current, thermal and mechanical loads), and corrosion resistance.
The coefficient of thermal expansion (CTE) should not differ greatly from the CTE of the metals being joined.
The thermal conductivity coefficient must correspond to the nature of operation of the soldered product.

Depending on the melting point, solders are divided into low-melting (soft) with a melting point of up to 450°C and refractory (hard) with a melting point above 450°C.

Low melting point solders. The most common low-melting solders are tin-lead solders, consisting of tin and lead in various ratios. To impart certain properties, other elements can be introduced into them, for example, bismuth and cadmium to lower the melting point, antimony to increase the strength of the weld, etc.

Tin-lead solders have a low melting point and relatively low strength. They should not be used to connect parts that experience significant loads or operate at temperatures above 100°C. If you still have to use soft soldering for connections operating under load, you need to increase the contact area of the parts.

The most widely used are tin-lead solders POS-18, POS-30, POS-40, POS-61, POS-90, which have a melting point of approximately 190-280 ° C (of which the most refractory is POS-18, the most fusible - POS-61). The numbers indicate the percentage of tin. In addition to the base metals (Sn and Pb), POS solders also contain a small amount of impurities. In instrument making, they solder electrical circuits and connect wires. At home, they are used to connect a variety of parts.

Solder	Purpose
POS-90	Soldering of parts and assemblies subjected to further galvanic processing (silvering, gilding)
POS-61	Tinning and soldering of thin spiral springs in measuring instruments and other critical parts made of steel, copper, brass, bronze, when high heating in the soldering zone is not acceptable or undesirable. Soldering of thin (0.05 - 0.08 mm in diameter) winding wires, including high-frequency wires, winding leads, motor rotor leads with collector lamellas, radio elements and microcircuits, installation wires in PVC insulation, as well as soldering in cases where increased mechanical strength and electrical conductivity are required.
POS-40	Tinning and soldering of conductive parts for non-essential purposes, tips, connecting wires with petals, when higher heating is allowed than in cases of using POS-61.
POS-30	Tinning and soldering of non-critical mechanical parts made of copper and its alloys, steel and iron.
POS-18	Tinning and soldering with reduced requirements for seam strength, non-critical parts made of copper and its alloys, soldering of galvanized sheet.

Refractory solders. Of the refractory solders, two groups are most often used - solders based on copper and silver. The first include copper-zinc solders, which are used to connect parts that carry only a static load. Due to a certain fragility, it is undesirable to use them in parts operating under conditions of shock and vibration.

Copper-zinc solders include, in particular, alloys PMC-36 (approximately 36% Cu, 64% Zn), with a crystallization range of 800-825 ° C, and PMC-54 (approximately 54% Cu, 46% Zn), with crystallization interval 876-880°C. Using the first solder, brass and other copper alloys with a copper content of up to 68% are soldered, and thin soldering is carried out on bronze. PMC-54 is used for soldering copper, tombac, bronze, and steel.

To connect steel parts, pure copper and brass L62, L63, L68 are used as solder. Connections soldered with brass have higher strength and ductility compared to connections soldered with copper; they can withstand significant deformations.

Silver solders are of the highest quality. PSR grade alloys contain copper and zinc in addition to silver. Solder PSR-70 (approximately 70% Ag, 25% Cu, 4% Zn), with a melting point of 715-770°C, solders copper, brass, and silver. It is used in cases where the junction site should not sharply reduce the electrical conductivity of the product. PSR-65 is used for soldering and tinning of jewelry, fittings made of copper and copper alloys intended for connecting copper pipes used in hot and cold drinking water supply systems; it is used for soldering steel band saws. PSR-45 solder is used for soldering steel, copper, and brass. It can be used in cases where connections operate under conditions of vibration and shock, unlike, for example, PSR-25, which does not withstand shock well.

Other types of solder. There are many other solders designed for soldering products consisting of rare materials or operating under special conditions.

Nickel solders are intended for soldering structures operating at high temperatures. Having a melting point of 1000°C to 1450°C, they can be used for soldering products made of heat-resistant and stainless alloys.

Gold solders, consisting of alloys of gold with copper or nickel, are used for soldering gold products and for soldering vacuum electronic tubes, in which the presence of volatile elements is unacceptable.

For soldering magnesium and its alloys, magnesium solders are used, containing, in addition to the base metal, also aluminum, zinc and cadmium.

Materials for soldering metals can come in various forms - in the form of wire, thin foil, tablets, powder, granules, solder pastes. The method of their introduction into the joint zone depends on the release form. Solder in the form of foil or solder paste is placed between the parts to be joined, and the wire is fed into the joint area as its end melts.

The strength of a solder joint depends on the interaction of the base metal with the molten solder, which in turn depends on the presence of physical contact between them. The oxide film present on the surface of the soldered metal prevents contact, mutual solubility and diffusion of particles of the base metal and solder. Therefore it must be removed. For this purpose, fluxes are used, the task of which is not only to remove the old oxide film, but also to prevent the formation of a new one, as well as to reduce the surface tension of the liquid solder in order to improve its wettability.

When soldering metals, fluxes of different composition and properties are used. Soldering fluxes have differences:

by aggressiveness (neutral and active);
according to the soldering temperature range;
according to the state of aggregation - solid, liquid, gel and paste;
by type of solvent - aqueous and non-aqueous.

Acidic (active) fluxes, such as "Soldering Acid" based on zinc chloride, cannot be used when soldering electronic components, as they conduct electricity well and cause corrosion, however, due to their aggressiveness, they prepare the surface very well and are therefore irreplaceable when soldering metal structures. And the more chemically resistant the metal, the more active the flux should be. Residues of active fluxes must be carefully removed after soldering is completed.

Widely used fluxes are boric acid (H 3 BO 3), borax (Na 2 B 4 O 7), potassium fluoride (KF), zinc chloride (ZnCl 2), rosin-alcohol fluxes, orthophosphoric acid. The flux must match the soldering temperature, the material of the parts being soldered and the solder. For example, borax is used for high-temperature soldering of carbon steels, cast iron, copper, hard alloys with copper and silver solders. For soldering aluminum and its alloys, a preparation consisting of potassium chloride, lithium chloride, sodium fluoride and zinc chloride (flux 34A) is used. For low-temperature soldering of copper and its alloys, galvanized iron, for example, a composition of rosin, ethyl alcohol, zinc chloride and ammonium chloride (LK-2 flux) is used.

Flux can be used not only as a separate component, but also as an integral element in solder pastes and tableted types of so-called fluxing solders.

Solder pastes. Solder paste is a pasty substance consisting of particles of solder, flux and various additives. Solder paste is usually used for surface mounting SMD components, but is also convenient for soldering in hard-to-reach places. Soldering of radio components with such paste is carried out using a hot-air or infrared station. The result is a beautiful and high-quality soldering. However, due to the fact that most solder pastes do not contain active fluxes that allow soldering, such as steel, most of them are only suitable for soldering electronics.

Soldering steel

Soldering steel with your own hands is not particularly difficult. Steel products can be successfully soldered even with low-melting solders, for example, POS-40, POS-61 or pure tin. And, for example, low-melting zinc-based solders are unsuitable for soldering carbon and low-alloy steels due to poor wetting, flow into the gap and low strength of soldered joints as a result of the formation of an intermetallic brittle layer along the boundary of the weld and steel.

In general, steel soldering is carried out in the following sequence.

The soldered parts are cleaned from contamination.
The oxide film is removed from the surfaces being joined by mechanical cleaning (with a wire brush, sandpaper or wheel, shot blasting) and degreasing. Degreasing can be carried out with caustic soda (5-10 g/l), sodium carbonate (15-30 g/l), acetone or other solvent.
The parts at the junction are coated with flux.

The product is assembled with the parts fixed in the desired position.

The product is heating up. The flame should be normal or reducing - without excess oxygen. In a balanced gas mixture, the flame only heats the metal and has no other effect. In the case of a balanced gas mixture, the burner flame is bright blue and small in size. A flame supersaturated with oxygen oxidizes the metal surface. The torch of the burner flame, saturated with oxygen, is pale blue and small. You need to warm up the entire connection, moving the flame in different directions, while occasionally touching the solder to the connection. The desired temperature is reached when the solder begins to melt when touching the parts. There is no need to create excess heat. Usually, with practice, the sufficiency of heating is determined by the color of the metal surface and the appearance of flux smoke.

Flux is applied to the joints to be joined.

Metal soldering: applying flux. The photo shows solder coated with flux.

Solder is supplied to the joint area (in the form of a wire, or a piece laid in the joint) and the part and the solder are heated until the latter melts and flows into the joint. Under the influence of capillary forces, the solder itself is drawn into the gap between the parts.

The solder should melt not from the flame of the burner, but from the heat of the heated connection.

After soldering is completed, the product is cleaned of flux residues and excess solder.

If possible, you can first tin the parts to be connected with solder at the point of contact. Then connect the parts and heat them to the melting temperature of the solder. In this case, a stronger connection may be obtained.

Soldering temperature is determined by the brand of solder.

Reasons for failure. If the solder is not distributed over the surface of the parts, this may be due to the following reasons:

Insufficient heating of parts. The duration of heating should correspond to the massiveness of the parts.
Poor preliminary cleaning of the surface from contamination.
Using the wrong flux. For example, stainless steel or aluminum require very reactive fluxes. Or the flux may not match the soldering temperature.
Using the wrong solder. For example, pure lead wets metals so poorly that they cannot be used for soldering.

Soldering other metals

Features of soldering cast iron. Gray and malleable cast iron are soldered; white cast iron cannot be soldered due to poor workability and brittleness. When soldering cast iron, two problems arise that interfere with obtaining a high-quality joint: the occurrence of volumetric and structural changes under conditions of local gas-flame heating, and poor wettability of cast iron due to the presence of free graphite inclusions in it.

The first problem can be solved by soldering at temperatures no higher than 750°C.

To solve the second problem, instructions for soldering cast iron require the removal of loose graphite from the soldered surfaces. This can be done in several ways: thorough mechanical cleaning, oxidation of graphite into volatile carbon oxide, treating the joint to be joined with boric acid or potassium chlorate, burning off the carbon with a burner flame, followed by cleaning with a wire brush. There are also highly active fluxes for cast iron that remove graphite inclusions well.

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§ 10. Soldering of metals. High-temperature and low-temperature soldering. . Fluxes for soldering with copper, copper-zinc and copper-nickel solders.

Soldering is the process of obtaining a permanent connection of metals and their alloys without melting them by filling the gap between them with solder - an intermediate metal or alloy in a liquid state.

There are two main types of soldering: high temperature And low temperature(GOST 17349-71). The melting point of solders for low-temperature soldering is below 550° C, and for high-temperature soldering - above 550° C. With low-temperature soldering, the tensile strength of the connection is 5-7 kgf/mm 2, and with high-temperature soldering - up to 50 kgf/cm 2.

Low temperature soldering Usually carried out with electric soldering irons, and high-temperature - with torches operating on acetylene or gases that are substitutes for acetylene.

Low melting point solders (soft solders) are based on lead, tin, antimony, and high melting point solders (hard solders) are based on copper, zinc, cadmium and silver.

Types of solder seams are shown in Fig. 95.

Rice. 95. Types of soldered joints (seams):

a - butt, b - overlapping, c - with flanging, d - sleeve, d - special (for patches on aluminum parts)

For high-temperature soldering, copper-zinc solders PMC-36, PMC-48, PMC-54, etc. are used.

Soldering is carried out using fluxes - active chemical substances designed to clean and maintain clean the surfaces of the metal being soldered in order to reduce surface tension and improve the spreading of liquid solder. The compositions of some fluxes for soldering are given in table. 48.

48. Fluxes for soldering with copper, copper-zinc and copper-nickel solders

Components	Compound, %	Scope of application
Boric acid Borax Calcium fluoride	70 21 9	Soldering of structural stainless and heat-resistant steels with brass and heat-resistant solders
Borax	100	Soldering of carbon steels, cast iron, copper, hard alloys with copper-zinc solders
Borax Boric acid	80 20	Brazing of low-carbon steels and copper alloys
Borax Boric acid	50 50	Soldering of stainless steels, hard and heat-resistant alloys with copper-zinc and copper-nickel solders. Flux is diluted with a solution of zinc chloride
Boric acid Borax Calcium fluoride	78 12 10	Soldering of carbon, stainless and heat-resistant steels, hard and copper alloys with copper solders
Borax Boric acid Calcium fluoride	50 10 40	Soldering of hard alloys with copper, copper-zinc and copper-nickel solders
Borax Potassium permanganate	95 5	Soldering cast iron with copper and copper-zinc solders. Flux is diluted with a concentrated solution of zinc chloride
Borax Calcium fluoride Sodium fluoride	75 10 15	Soldering with copper-based solders
Boric acid Borax Calcium fluoride Ligature (4% Mg, 48% Cu, 48% Al)	80 14 5,5 0,5	Soldering of stainless steels and heat-resistant alloys with brass and other solders with a melting point of 850-1100 ° C
Borax Boric acid Calcium chloride	58 40 2	Soldering brass and copper