TIN, LEAD AND THEIR ALLOYS

§ I. STRUCTURE AND PROPERTIES OF TIN AND LEAD

Tin and lead, among other technical metals, are distinguished by their relatively low melting point, low hardness and high corrosion resistance.

These properties predetermined the main areas of application of these metals. Lead in its pure form is used in chemical apparatus manufacturing, for cable sheaths, protection against X-rays and γ-rays, and in other areas. Lead and tin are widely used for the production of antifriction (bearing) alloys, low-melting alloys and solders, anti-corrosion coatings, and also as additives for brasses, bronzes and other alloys.

The industry produces tin and lead of various purities (Tables 42 and 43). The physical and chemical properties of these metals are given in Appendix 1.

Tin, depending on temperature, is characterized by two crystal structures (modifications). Directly upon solidification, tin crystals with a tetragonal lattice are formed, with periods a = 5.82 A, c -3.17 A. This modification of tin is called β = Sn. Tin in the form of modification is stable up to a temperature of 18°, and then goes into a new modification ά = Sn with a diamond-type lattice with a period a = 6.46 A.

The transition from one modification to another is accompanied by sharp volumetric changes, which leads to the destruction of tin and its transformation into black powder. It should be noted that at a temperature of 18° and somewhat lower, the rate of this transformation is very insignificant and can be practically ignored. However, at subzero temperatures (especially minus 30-40°), the process of polymorphic transformation proceeds very intensively. Dark growths first appear on the products, and then they are completely destroyed. The described phenomenon is often called the “tin plague” in practice. Tin that has been “sick” with the tin plague can only be restored by melting it down.

Some impurities (lead, antimony, etc.) in small quantities sharply reduce the rate of transformation of tin from one modification to another, and three certain concentrations (0.5% and above) almost completely protect against the “tin plague.”

Common white tin (β = Sn) crystallizes from the melt in the form of large columnar crystals.

Spontaneous annealing of very pure tin already occurs quite completely at room temperature.

When crystallized, very pure lead also produces large grains.

Lead does not harden during cold deformation, since its recrystallization temperature is below room temperature.

Technical tin and lead always contain some impurities. All impurities in tin, except antimony, are practically insoluble at room temperature. The main impurity in tin is lead, which in some grades intended for the manufacture of alloys is allowed in significant quantities (up to 1-2%).

As already noted, pure tin has good chemical resistance. It does not oxidize in humid air and is stable in organic acids and boiling water. This has long allowed the use of tin for tinning dishes, tin and other anti-corrosion coatings. Impurities significantly reduce the corrosion resistance of tin. If lead or arsenic is present in tin, it becomes unsuitable for food utensils and equipment.

Strong acids and alkalis dissolve tin. In this regard, lead is a more resistant material. Lead is especially resistant to sulfuric acid due to the formation of a protective oxide film on its surface. Lead is stable in hot sulfuric acid up to a concentration of 80%, in cold - up to a concentration of 92%. Lead is stable in hydrochloric acid up to a concentration of 10%. Nitric acid has the most powerful effect on lead.

In dry air, lead does not oxidize; in humid air it becomes covered with a dull oxide film, which has good protective properties.”

§ 2. TIN AND LEAD ALLOYS

Five groups of alloys based on tin and lead are widely used in industry:

1) anti-friction alloys;

2) low-melting alloys;

3) solders;

4) printing alloys:

5) alloys for cable sheaths.

The structures, properties and applications of these alloys are discussed below.

1. Anti-friction alloys

Chemical composition industrial antifriction alloys based on tin and lead are indicated in table. 44. The most important physical and mechanical properties of these alloys are presented in table. 45.

Indicated in the table. 44 alloys can be divided into three groups:

1. Tin-based alloys (B93, B90, B83).

2. Lead-based alloys (BS, BK).

3. Tin-lead alloys (B16, BN, BT, B6).

Tin-based alloys

Purchase of tin-lead solders

Solder PIC is a metal alloy used to join metal parts by melting solder.

Tin-lead solders- the most common group of solders. In labeling tin-lead solders The letters indicate the composition of the solders; the numbers indicate the percentage of tin.

Main components tin-lead solders are tin and lead.

Tin-lead solders can be very effective if you know the basic principles of operation and the scope of their application.

Solder seams are divided into several groups:

1. dense and durable seams - withstand the pressure of gases and liquids;
2. strong seams - able to withstand mechanical loads;
3. tight seams - do not allow gases and liquids under low pressure to pass through.

The quality of soldering depends on the diffusion rate. Clean soldering surfaces increase diffusion. But if the metal surface oxidizes, diffusion sharply decreases or stops altogether.

Tin-lead solders must have both maximum viscosity and high resistance; the soldering method directly depends on the melting temperature of the solder.

Tin-lead solder POS60 widely used for soldering electrical equipment and radio components, printed circuits. The tin content of 60% ensures a low melting point, which averages 183-188 degrees Celsius.

Solder POS61 used when soldering thin parts, when overheating the parts is contraindicated.

Solder POS62 has the lowest melting point and contains 62% tin. So leaden tin solder used for connecting thin wires.

Solder POS40 avoids overheating when soldering. The cross-section of tin-lead solder is thin, 1 or 2 mm in diameter. Due to the small diameter of the wire, the exposure time of high temperature to lead-tin solder POS40 is minimal. Solder POS40 similar to POSS4-6 solder in terms of strength. Tin solder is used for soldering copper, lead, iron, and tinplate.

Tin-lead solder POS30 used for soldering copper, brass, iron, galvanized, galvanized sheets, radio equipment, flexible hoses.

Solder POS18 When butt soldering it has high adhesive strength. Tin solder is used in cases where the melting temperature is not critical.

Solder POS90 Widely used for soldering internal seams of food items.

Popular soft solders for soldering radio components - low-temperature alloys:

• Tin-lead solders with antimony;
• Tin-lead solders POSC with cadmium;
• Tin-lead solders POS30 for tinning and soldering zinc sheets, radiators;
• Tin-lead solders POS40 for tinning and soldering of galvanized iron parts, radiators;
• Tin-lead solders POS60 for soldering radio components;
• Tin-lead solders POS61 for soldering radio components;
• Tin-lead solders POS63 for soldering radio components;
• Tin-lead solders POS90.

By using tin-lead solders soldering work is carried out, two main operations are performed:

• tinning and
• soldering.

Tinning - coating metal surfaces with pure tin or an alloy of tin and lead with a small percentage of impurities - provides a strong connection and is a preparatory process for soldering parts.

Soldering is the connection of wires and radio components using solders in a molten state. After the tin-lead solder hardens, a strong connection is formed.

The more tin in the solder, the softer the solder. Solders containing pure tin are used for soldering internal seams of cookware for food products.

Purchase of tin-lead solders:

At TINKOM LLC you can buy tin-lead solders:

Antimony-free solders

Low antimony solders

Antimony solders

Price for tin-lead solders

Prices for tin-lead solders different markings depend on the size of the ordered batch.

Wholesale purchases of tin-lead solders They are much cheaper than retail.

There is always a certain quantity in the warehouse of TINKOM LLC tin-lead solders which you can buy in our minimum lines at the best price.

Do purchase of tin-lead solders you can by calling work time by contact numbers or by placing an order on the website.

Today we can buy tin-lead solders in the form of pigs, rods, wires.

At wholesale purchases of tin-lead solders preferential discounts are provided.

The alloy of tin and lead has special parameters that allow it to be used in various industries industrial production. Specifications And physical properties Each metal is determined by their use for long-term storage of products, soldering and surface treatment of parts in order to increase service life.

An alloy of tin and lead is used to give strength to manufactured parts.

Physical properties of lead

Lead, a waste product from silver processing, turned out to be a very useful metal in production.

Archaeological artifacts indicate that this chemical element was known to man more than 6000 years ago. Its discovery is associated with the presence of metal in ores containing silver. When they were smelted, the material was thrown into waste, but over time they began to make various products from it: figurines, water pipes. Currently, lead is used:

• for the production of batteries;
• in the cable industry - to create a protective seamless sheath;
• for the manufacture of paints and solders;
• during the construction of protective structures - for sources of radiation pollution (sarcophagi);
• for the production of alloys based on it (babbitt);
• for the production of printing compositions;
• in medicine.

The main consumer of lead is the automotive industry, where babbits are widely used. The production of lead-acid starter batteries is constantly growing, and improvements are being made to developments.

IN chemical industry the material is used to coat steel products: apparatus, tanks, pipelines. Since iron and lead do not combine with each other, a thin layer of molten tin is first applied to the products. This processing process is called tinning.

In production, not only pure lead is used, but also its compounds. For example, lead oxide is used in glass making. A slight addition of the compound to the material when melting glass makes it possible to give crystal products the transparency of a natural mineral - rock crystal.

Technical Parameters of Tin

Tin - from spoon to radiator

This chemical element has been known for more than 3,500 years and was originally intended for the manufacture of tableware. Modern consumption of tin is associated with the canning industry.

Patent for a method of storing food in tin cans belongs to a chef from France. Since 1810, humanity has been able to store food for a long time.

Tin is the main component of solders used for soldering and tinning of heat exchangers, radiators of automobile engines, and tinning of medical and food equipment.

The material is used for the production of tin bronze, which has excellent mechanical, casting, and anti-corrosion properties. Such alloys are used in parts intended for use in special conditions and and under special load.

An alloy with a low coefficient of friction is babbitt. It contains 83% tin, antimony and copper. It is used in the production of bearings. Thanks to the stable compound of antimony and copper, the alloy has high hardness.

The bearing operating mechanism and composition components eliminate the occurrence of mechanical damage on the surface of the part.

Tin has specific physical properties:

1. Its deformation is accompanied by a sound generated as a result of shear under the influence of force.
2. At temperatures of -39 °C and + 161 °C, tin turns into powder.

History knows cases of such transformations. Buttons made from pure material lost their shape in the cold, and the “tin plague” destroyed metal ingots.

The main differences between metals and their alloys

Even in ancient times, these materials were distinguished only by color and were called white and black tin. There are differences between them that can be easily established without additional analysis.

The mass of lead is 1.5 times higher than that of tin. But tin has a higher hardness and cracks when deformed. Lead easily oxidizes to form a gray film.

It is more difficult to determine what components the tin-lead alloy contains. An approximate indicator can be obtained by recording the temperature and melting pattern of the compound.

Bearing materials containing tin and lead, an alloy of metals with nickel, tellurium, and calcium, are highly resistant to wear.

Tin and lead complement each other perfectly, which makes their alloy indispensable in production

Solders based on these metals differ in melting temperature. Soft, with a melting point up to +300 °C, contain bismuth and cadmium. Hard (refractory) solders, which turn into a liquid state at +500 °C, contain silver, zinc, and copper.

For soldering alloys with a high tin content, which do not contain lead, it is recommended to use dilute nitric acid reagents. When the composition is etched, the base turns black, and areas with a low metal content remain light, which makes it possible to improve the quality of soldering of parts.

Molten pure lead does not slide over the surface without wetting it, but an alloy with tin allows you to obtain a high-quality coating. The operating temperature of the baths is set depending on the fractional content of the alloying metal.

If it is necessary to reduce the oil clearance of bearings and improve the operating conditions of parts, surface coating with tin or lead alloys is used.

To cover a carbon-free surface, an alloy containing 90% lead, 5% tin and 5% antimony is used as a semi-solid. The composition of the alloy affects the fluidity of the material, which varies depending on the ratio of the components.

Tin and lead are ductile, low-melting metals with increased resistance to corrosion in atmospheric and some acidic conditions.

Lead is a metal with a face-centered cubic lattice and does not undergo allotropic transformations in the solid state. The melting point of lead is 327 ºС.

Tin can be found in two crystalline modifications: a-Sn (gray tin) with a diamond lattice - below +13 ºС and b-Sn (white tin) with a body-centered tetragonal lattice. In the cold, plastic b-tin crumbles into gray a-Sn powder. This phenomenon is called tin plague . The melting point of tin is 232 ºС.

Calculation of the temperature threshold for recrystallization in accordance with the rule of A.A. Bochvara (T p = 0.4 T pl) gives figures of –123 and –147 ºС, i.e. the temperature threshold for recrystallization lies significantly below 0 ºС. Thus, plastic deformation of lead and tin at room temperature is hot deformation. Hardening during such deformation is not observed in these metals.

The main area of ​​application of pure tin is tinning of tin. Pure lead is used for lining sulfuric acid production apparatus and containers for hydrochloric acid. Lead is also used for cable sheaths to protect them from soil corrosion.

An important area of ​​application for lead and tin is solders, as well as alloys for typographic fonts, anatomical casts, and fuses. These alloys contain, in addition to lead and tin, bismuth and cadmium. In pairs, all these elements form among themselves systems with low-melting eutectics without intermediate phases and chemical compounds, i.e. form simple eutectic systems (Figure 8.8). In ternary systems, ternary eutectics are formed between these elements, which are even more fusible than double eutectics. The melting point of these eutectics is 90-100 ºС. In the quaternary system of these components, a quaternary eutectic is formed with a melting point of 70 ºС. The practically used Wood's alloy is close in composition to eutectic (50% Bi, 25% Pb, 12.5% ​​Sn and 12.5% ​​Cd).

To obtain even more low-melting alloys, mercury is introduced into them, for example an alloy containing Bi-36%; Pb-28%; Cd-6% and Hg - 30% have a melting point of 48 ºС.

Both pure tin and lead-tin alloys containing tin from 3 to 90% and a small amount of antimony (up to 2% Sb) are used as solders for soldering copper, steel and many other products.

The melting point of solders depends on the tin content and can be approximately determined from the Pb-Sn double diagram. The most fusible solder is an alloy with 61% Sn, marked POS 61. There are alloys POS 18, POS-40, POS-61, POS 90, etc. Alloys of lead with antimony and arsenic (10-16% Sb and 1-4% As) are used for printing fonts.

Tin-lead solders in products, GOST 21931-76

Solders- filler metals (alloys), capable of filling the gap between the products being soldered in the molten state and, as a result of solidification, forming a permanent, strong connection.

Available in round wire, strip, triangular, round rods, flux-filled round tubes and powder

Some types of solders:

• POS - 90 - for tinning and soldering internal seams of food utensils and medical equipment;

• POSSU 4-4 - for tinning and soldering in the automotive industry.

Tin-lead solders in ingots, GOST 21930-79

This standard applies to tin-lead solders (PLS) in ingots and in products used mainly for tinning and soldering parts. The indicators of this standard correspond to the highest quality category.

Low antimony

Antimony

One of the main elements of electrical installation and radio installation work is soldering. The quality of installation is largely determined by the correct choice of the necessary solders and fluxes used when soldering wires, resistances, capacitors, etc.

To facilitate this choice, below is brief information about hard and light solders and fluxes, their use and their manufacture.

Soldering is the joining of hard metals using molten solder, which has a melting point lower than the melting point of the base metal.

The solder should dissolve the base metal well, spread easily over its surface, and well wet the entire soldering surface, which is ensured only if the wetted surface of the base metal is completely clean.

To remove oxides and contaminants from the surface of the metal being soldered, to protect it from oxidation and to provide better wetting with solder, chemicals called fluxes are used.

The melting point of fluxes is lower than the melting point of solder. There are two groups of fluxes: 1) chemically active, dissolving oxide films, and often the metal itself (hydrochloric acid, borax, ammonium chloride, zinc chloride) and 2) chemically passive, protecting only the surfaces to be soldered from oxidation (rosin, wax, stearin and etc.). .

Depending on the chemical composition and melting temperature of the solders, soldering is distinguished between hard and soft solders. Hard solders include solders with a melting point above 400°C, and light solders include solders with a melting point up to 400°C.

Basic materials used for soldering.

Tin- a soft, malleable metal of silvery-white color. Specific gravity at a temperature of 20°C - 7.31. Melting point 231.9°C. It dissolves well in concentrated hydrochloric or sulfuric acid. Hydrogen sulfide has almost no effect on it. A valuable property of tin is its stability in many organic acids. At room temperature it is difficult to oxidize, but when exposed to temperatures below 18°C ​​it can transform into a gray modification (“tin plague”). In places where gray tin particles appear, the metal is destroyed. The transition of white tin to gray accelerates sharply when the temperature drops to -50°C. For soldering it can be used both in pure form and in the form of alloys with other metals.

Lead- bluish-gray metal, soft, easy to process, cut with a knife. Specific gravity at a temperature of 20°C is 11.34. Melting point 327qC. In air it oxidizes only from the surface. It dissolves easily in alkalis, as well as in nitric and organic acids. Resistant to the effects of sulfuric acid and sulfuric acid compounds. Used for the manufacture of solders.

Cadmium- silver-white metal, soft, ductile, mechanically fragile. Specific gravity 8.6. Melting point 321°C. It is used both for anti-corrosion coatings and in alloys with lead, tin, bismuth for low-melting solders.

Antimony- brittle silvery-white metal. Specific gravity 6.68. Melting point 630.5°C. Does not oxidize in air. It is used in alloys with lead, tin, bismuth, cadmium for low-melting solders.

Bismuth- brittle silver-gray metal. Specific gravity 9.82. Melting point 271°C. Dissolves in nitric and hot sulfuric acids. It is used in alloys with tin, lead, and cadmium to produce low-melting solders.

Zinc- bluish-gray metal. When cold it is fragile. Specific gravity 7.1. Melting point 419°C. In dry air it oxidizes, in humid air it becomes covered with a film of oxide, which protects it from destruction. When combined with copper, it produces a number of durable alloys. Easily dissolves in weak acids. Used for making hard solders and acid fluxes.

Copper- reddish metal, viscous and soft. Specific gravity 8.6 - 8.9. Melting point 1083 C. Dissolves in sulfuric and nitric acids and ammonia. In dry air it is almost impossible to oxidize; in damp air it becomes covered with green oxide. Used for the manufacture of refractory solders and alloys.

Rosin-a product of processing the resin of coniferous trees. Lighter varieties of rosin (more thoroughly purified) are considered the best. The softening temperature of rosin is from 55 to 83°C. Used as a flux for soft soldering.

Tin-lead solder in products and ingots GOST 21930-76, this standard applies to tin-lead solders used for tinning and soldering parts. Depending on the chemical composition, tin-lead solders are manufactured in the following grades:

Antimony-free- POS-90, POS-63, POS-61, POS-50, POS-40, POS-30, POS-10;

Low antimony- POSSU 61-05, POSSU 50-05, POSSU 40-05, POSSU 35-05, POSSU 30-05, POSSU 25-05, POSSU 18-05;

Antimony- POSSU 40-2, POSSU 30-2, POSSU 25-2, POSSU 18-2.

Tin-lead solders are manufactured in accordance with the requirements of this standard according to the technological instructions approved in in the prescribed manner. The chemical composition of solders must comply with the requirements of Table 1, the mass fraction of impurities is indicated in Table 2.

Chemical composition of tin-lead solders GOST 21931-76

Table 1

Impurity composition of tin-lead solders GOST 21931-76

table 2

Soft solders.

Soldering with soft solders has become widespread, especially during installation work. The most commonly used soft solders contain significant amounts of tin. In table Table 1 shows the compositions of some lead-tin solders.

Table 1

When choosing the type of solder, it is necessary to take into account its characteristics and use it depending on the purpose of the parts being soldered. When soldering parts that do not allow overheating, solders with a low melting point are used.

The most commonly used solder is POS-40 grade solder. It is used for soldering connecting wires, resistances, and capacitors. POS-30 solder is used for soldering shielding coatings, brass plates and other parts. Along with the use of standard grades, POS-60 solder (60% tin and 40% lead) is also used.

Soft solders are manufactured in the form of rods, ingots, wire (up to 3 mm in diameter) and tubes filled with flux. The technology of these solders without special impurities is simple and quite feasible in a workshop: lead is melted in a graphite or metal crucible and tin is added in small parts, the content of which is determined depending on the brand of solder. The liquid alloy is mixed, carbon deposits are removed from the surface and the molten solder is poured into wooden or steel molds. The addition of bismuth, cadmium and other additives is not necessary.

For soldering various parts that do not allow significant overheating, especially low-melting solders are used, which are obtained by adding bismuth and cadmium or one of these metals to lead-tin solders. In table Table 2 shows the compositions of some low-melting solders.

table 2

When using bismuth and cadmium solders, it should be taken into account that they are very brittle and create a less strong junction than lead-tin solders.

Hard solders.

Hard solders create high weld strength. In electrical and radio installation work they are used much less frequently than soft solders. In table Table 3 shows the compositions of some copper-zinc solders.

Table 3

The color of the solder changes depending on the zinc content. These solders are used for soldering bronze, brass, steel and other metals with a high melting point. PMC-42 solder is used when soldering brass containing 60-68% copper. PMC-52 solder is used for soldering copper and bronze. Copper-zinc solders are made by alloying copper and zinc in electric furnaces in a graphite crucible. As the copper melts, zinc is added to the crucible; after the zinc has melted, about 0.05% phosphorus copper is added. Molten solder is poured into molds. The melting temperature of the solder must be less than the melting temperature of the metal being soldered. In addition to the above-mentioned copper-zinc solders, silver solders are also used. The compositions of the latter are given in table. 4.

Table 4

Silver solders have great strength; the seams soldered by them bend well and are easy to process. PSR-10 and PSR-12 solders are used for soldering brass containing at least 58% copper, PSR-25 and PSR-45 solders are used for soldering copper, bronze and brass, PSR-70 solder with the highest silver content is for soldering waveguides , volumetric contours, etc.

In addition to standard silver solders, others are used, the compositions of which are given in table. 5.

Table 5

The first of them is used for soldering copper, steel, nickel, the second, which has high conductivity, is used for soldering wires; the third can be used for soldering copper, but is not suitable for ferrous metals; The fourth solder has a special fusibility and is universal for soldering copper, its alloys, nickel, and steel.

In some cases, commercially pure copper with a melting point of 1083°C is used as solder.

Solders for soldering aluminum.

Soldering aluminum is very difficult due to its ability to easily oxidize in air. IN Lately finds application in aluminum soldering using ultrasonic soldering irons. In table Table 6 shows the compositions of some solders for soldering aluminum.

Table 6

When soldering aluminum, organic substances are used as fluxes: rosin, stearin, etc.

The last solder (hard) is used with a complex flux, which includes: lithium chloride (25-30%), potassium fluoride (8-12%), zinc chloride (8-15%), potassium chloride (59-43%) . The melting point of the flux is about 450°C.

Fluxes.

Good wetting of solder joints and the formation of strong seams largely depends on the quality of the flux. At the soldering temperature, the flux should melt and spread in an even layer, and at the moment of soldering it should float to the outer surface of the solder. The melting point of the flux should be slightly lower than the melting temperature of the solder used.

Chemically active fluxes(acid) are fluxes that in most cases contain free hydrochloric acid. A significant disadvantage of acid fluxes is the intense formation of corrosion of solder seams.

Chemically active fluxes primarily include hydrochloric acid, which is used for soldering steel parts with soft solders. The acid remaining on the surface of the metal after soldering dissolves it and causes corrosion. After soldering, the products must be rinsed with hot running water. The use of hydrochloric acid when soldering radio equipment is prohibited, since during operation a violation may occur. electrical contacts in soldering areas. Please note that hydrochloric acid causes burns if it comes into contact with the body.

Zinc chloride(etching acid), depending on the soldering conditions, is used in the form of a powder or solution. Used for soldering brass, copper and steel. To prepare the flux, it is necessary to dissolve one part by weight of zinc in five parts by weight of 50% hydrochloric acid in a lead or glass container. A sign of the formation of zinc chloride is the cessation of the release of hydrogen bubbles. Due to the fact that there is always a small amount of free acid in the solution, corrosion occurs at the soldering joints, so after soldering the joint must be thoroughly washed in running hot water. Soldering with zinc chloride should not be carried out in the room where the radio equipment is located. It is also prohibited to use zinc chloride for soldering electrical and radio equipment. Zinc chloride should be stored in a glass container with a tightly closed glass stopper.

Borax(aqueous sodium salt of pyroboric acid) is used as a flux when soldering with brass and silver solders. Easily dissolves in water. When heated, it turns into a glassy mass. Melting point 741°C. Salts formed during brown soldering must be removed by mechanical cleaning. Borax powder should be stored in hermetically sealed glass jars.

Ammonia(ammonium chloride) is used in powder form to clean the working surface of a soldering iron before tinning.

Chemically passive fluxes (acid-free).

Acid-free fluxes include various organic substances: rosin, fats, oils and glycerin. Rosin (in dry form or a solution in alcohol) is most widely used in electrical and radio installation work. The most valuable property of rosin as a flux is that its residues after soldering do not cause corrosion of metals. Rosin has neither reducing nor dissolving properties. It serves solely to protect the soldering area from oxidation. To prepare alcohol-rosin flux, take one part by weight of crushed rosin, which is dissolved in six parts by weight of alcohol. After the rosin has completely dissolved, the flux is considered ready. When using rosin, soldering areas must be thoroughly cleaned of oxides. Often, for soldering with rosin, parts must be pre-tinned.

Stearin does not cause corrosion. Used for soldering lead sheaths of cables, couplings, etc. with especially soft solders. Melting point is about 50°C.

Recently, it has been widely used LTI flux group, used for soldering metals with soft solders. In terms of their anti-corrosion properties, LTI fluxes are not inferior to acid-free ones, but at the same time, they can be used to solder metals that previously could not be soldered, for example, parts with galvanic coatings. LTI fluxes can also be used for soldering iron and its alloys (including stainless steel), copper and its alloys and metals with high resistivity (see Table 7).

Table 7

When soldering with LTI flux, it is enough to clean the soldering areas only from oils, rust and other contaminants. When soldering galvanized parts, you should not remove zinc from the soldering area. Before soldering parts with scale, the latter must be removed by etching in acids. Pre-etching of brass is not required. Flux is applied to the joint using a brush, which can be done in advance. Flux should be stored in glass or ceramic dishes. When soldering parts with complex profiles, you can use solder paste with the addition of LTI-120 flux. It consists of 70-80 g of petroleum jelly, 20-25 g of rosin and 50-70 ml of LTI-120 flux.

But fluxes LTI-1 and LTI-115 have one big drawback: after soldering, dark spots remain, and intensive ventilation is required when working with them. Flux LTI-120 does not leave dark spots after soldering and does not require intensive ventilation, so its use is much wider. Usually, flux residues after soldering do not need to be removed. But if the product will be used in severe corrosive conditions, then after soldering, flux residues are removed using ends moistened with alcohol or acetone. The production of flux is technologically simple: alcohol is poured into a clean wooden or glass container, crushed rosin is poured until a homogeneous solution is obtained, then triethanolamine is added, and then active additives. After loading all the components, the mixture is stirred for 20-25 minutes. The prepared flux must be checked for a neutral reaction with litmus or methyl orange. The shelf life of the flux is no more than 6 months.

PHYSICAL AND MECHANICAL PROPERTIES OF SOLDER