What is an alloy of lead and tin used for? Types of tin-lead solders. Group of special alloys

Tin is a soft and ductile shiny metal of a silvery-white color. Characterized by good corrosion resistance in atmospheric conditions, soluble in dilute strong acids and concentrated alkalis. Tin is used for coating (tinning), obtaining alloys and solders for soldering, and also as alloying additives.

Tin alloys are tin-antimony-copper and tin-antimony-lead systems, which contain from 3 to 90% tin. They are used as antifriction alloys - babbits for pouring bearings and as solders. The use of lead reduces the cost of solder, and the introduction of antimony increases the strength of the weld.

Lead

Lead is a soft malleable ductile metal of light gray color with a bluish tinge. Much softer than tin, cut with a knife and scratched with a fingernail, easily rolled into thin sheets. Lead is resistant to corrosion and a number of chemicals, especially sulfuric acid. Lead smelting was one of the first metallurgical processes. It is widely used in the chemical industry to protect equipment from corrosion. Sheaths are made from lead to protect electrical cables, shot, paint and lead batteries.

lead alloys

Lead alloys have high density and low mechanical strength. They are fusible and resistant to corrosion. Lead-dominated alloys are much cheaper than those based on tin. They are used as anti-friction alloys - babbits, as printing alloys and solders. Lead with additions of tin and antimony becomes much harder.

It is unlikely that anyone will name the exact date of the appearance of tin-lead solder. However, the compound designated "POS" has been known since the Middle Ages. It has optimal qualities for joining many metals.

It is easy to melt, and the lead and tin included in the composition were mined several thousand years ago. Currently, POS solder is the most common type consumable used in daily practice.

Popularity and lead due to several factors.

The main feature of the alloys is the ability to form a composition with eutectic properties at a certain ratio of components. This is an intermetallic system whose melting point is lower than expected values.

One can imagine the joy of the discoverers who discovered that a tin-lead alloy could be heated to a lower temperature to become liquid.

Interestingly, the eutectic mixture can serve as a solvent in which a certain additional amount of any metal is distributed upon addition.

Thus, various grades of POS solders were developed. In their technical specifications proportions, values ​​of physical constants are indicated.

It is visually noticeable that with the predominance of tin in the tin-lead alloy, the solder has a pronounced metallic luster. If there is more lead in the alloy, the surface has a grayish color with a blue tint.

Characteristics of individual brands

Manufacturers supply solder products:

• in cast ingots;
• in the form of wire products;
• ribbon-like foil;
• tubular products with fluxes inside;
• powders or pastes.

In general, there is an unambiguous pattern. The less mass fraction tin in tin-lead solder, the higher its melting point and the lower strength characteristics.

More than half of the tin

In an alloy containing 90% tin, the rest of the mass is lead. POS-90 solder has a melting point of 220℃.

It is used for soldering products that will subsequently be galvanized with gold or silver.

Tin-lead solder with 61% tin has a more accessible melting point of 191 °C. POS-61 is used for the manufacture of thin contacts of parts from copper and steel alloys in various measuring instruments. Places of application of the alloy should not be exposed to strong heat.

Solder can be used for soldering wires with a thickness of up to 0.08 mm in the winding. It may be exposed to high frequency currents.

Solder is used in all situations that require great strength and reliability of the connection of radioelements, microcircuit components. They can solder wires protected by a PVC sheath.

Tin-lead solder containing equal parts of two metals is designated as POS-50. It melts at 222℃. Let's apply in all situations where POS-61 can be used.

The difference is that this solder has a higher melting point. If the contact can heat up this quality will be useful.

Less than half tin

Seams, for which there is a high probability of heating to even higher temperatures, should be soldered using POS-40 solder. The melting point of a tin-lead alloy containing from 39% to 41% tin is 238 °C.

Please note that the figures presented are typical for the final melting of the alloy. The process starts at slightly lower temperatures.

The alloy is designed to work with wires, parts made of different metals. The resulting seam has a lower margin of safety than the joints obtained by alloys with a higher mass fraction of tin. Solder is used to obtain joints that are not subjected to high mechanical stress.

The POS-30 alloy has an even higher final melting temperature. It is equal to 256℃.

This tin-lead solder is used for non-stress soldering of copper and steel materials.

Solder POS-18 finally melts at 277℃. The resulting seam has little mechanical stability.

The presented tin-lead alloy can be used for tinning, soldering unloaded copper parts, galvanized iron products.

Tin-lead alloy, containing only 10% tin, has the maximum melting point in this series, equal to 299 ℃, and the minimum strength.

POS-10 can be used for soldering, tinning contacts on the surface of relay devices. GOST allows you to use the composition for processing control points in the furnaces of steam locomotives. At present, steam locomotives have remained only in museums, sometimes they have to be repaired and restored.

Solders marked POS are antimony-free consumables.

Group of special alloys

When antimony is added to the metal compositions in small amounts, the strength of suture joints increases significantly.

The material is marked "POSsu", has melting points from 189 ℃ (for composition with a trace content of antimony) to 270 ℃ (for solder with an antimony content reaching 4%, in some even 6%).

Materials of the first subgroup with an additive concentration measured in hundredths of a percent are low antimony grades.

Such solders are used in the aircraft and automotive industries, in the production of refrigeration equipment, food utensils, subject to subsequent tinning.

Table 1. Low antimony solders:

				Application area
POSSu 61-0.5			Rest	Soldering parts sensitive to overheating
POSSu 50-0.5			Rest	Aviation radiators
POSSu 40-0.5			Rest	Galvanized parts of refrigerators, radiator tubes, windings of electrical machines
POSSu 35-0.5			Rest	Cable sheaths for electrical products, thin-sheet packaging
POSSu 30-0.5			Rest	Radiators
POSSu 25-0.5			Rest	Radiators
POSSu 18-0.5			Rest	Heat exchanger tubes, electric lamps

Metal tin-lead compositions with an antimony concentration of 1.5% to 6% are called antimony. They are recommended for use in electric lamps, tubular radiators, tinplate.

The addition of antimony reduces the cost of tin-lead material, but soldering is more difficult. A slight change in the tin-lead composite significantly reduces the wetting ability of the melt. Only professionals can work with this consumable.

Table 2. Antimony solders

				Application area
	Rest			Pipelines operating at elevated temperatures, electrical products
			Rest	Refrigeration devices, thin sheet packaging
			Rest	Refrigerators, electric lamp production, abrasive packaging
			Rest	Automotive products
			Rest
			Rest
			Rest
			Rest	Electric lamp production
			Rest	Tubular radiators, parts operating at elevated temperatures
			Rest	Car body putty, tinplate soldering
			Rest	Automotive products

Low temperature group

Significantly reduces the addition of cadmium. For example, the POSK-50-18 alloy, containing from 49% to 51% tin, from 17% to 19% cadmium, has a melting point of 145 ℃.

This is an easy-to-use quality, doubly pleasant in that the resulting seams have high mechanical strength. Tin-lead solders with cadmium are used when working with metallized and ceramic products.

The question of the use of consumables is decided taking into account the specific production situation.

Nominal alloys

Tin-lead compositions can conditionally include alloys bearing the names of scientists-developers. Rose eutectic alloy has a low melting point, only 94 ℃.

It contains 50% bismuth. The rest of the mass is occupied by tin and lead in approximately equal proportions. The material is used to work with copper, the manufacture of automation elements with a fixed operating temperature.

Wood's tin-lead solder has an even lower melting point. It is equal to 68.5℃. The material contains 50% bismuth, 25% lead, and the rest of the mass is equally composed of tin and cadmium. They are used in the manufacture of fire alarm sensors, precision equipment.

Alloy D, Arce contains about 10% tin, the remaining 90% are bismuth and lead in equal proportions. The material has a melting point of 79℃. It is used for soldering low-melting metals.

The invention relates to non-ferrous metallurgy and can be used in the refining of lead-tin alloys. Lead-tin alloys are treated with zinc. After the introduction of zinc, the alloys are treated with elemental sulfur in an amount of 1–5% by weight of the alloy, which ensures the formation of sulfide zinc-silver removal. The method makes it possible to ensure the extraction of silver from lead-tin alloys up to 99% and to organize the production of silver solders without involving an additional amount of precious metals. 3 tab.

The invention relates to non-ferrous metallurgy, in particular to the production technology of lead-tin solders, and can be used in the refining of lead-tin alloys. Known methods of extracting silver from black lead by extraction at temperatures of 330-350 o C metallic zinc. The use of these methods for the extraction of silver from lead-tin alloys does not positive results , because in the presence of tin, the lead-tin-zinc system has no areas of delamination. With regard to tin-containing alloys based on lead, methods have been proposed that involve treatment at temperatures of 750-950 o C with melts of chlorides and sulfates of alkali, alkaline earth metals. The disadvantages of these methods are the low extraction of silver (30-40%), the impossibility of carrying out the process in known refining apparatuses and the need to organize hydrochemical processing of silver-containing slags. As a prototype, a method for processing zinc alloys, known as the Parkess process, was adopted. Zinc metal or lead-zinc ligature is mixed into the lead-containing melt at a temperature of 330-350 o C. In this case, zinc-silver intermetallic compounds are formed, which, due to delamination of the lead-zinc-silver system, pass into the surface layer of lead in the form of the so-called silvery foam. The foam is removed from the surface and sent for recycling. However, the prototype method does not provide the extraction of significant amounts of silver from lead-tin alloys. This is due to the fact that in the presence of 5% or more tin in lead, the lead-tin-zinc-silver system does not delaminate. The problem is aggravated by the fact that in real lead-tin alloys (solders) produced, for example, at the Ryaztsvetmet plant, the silver content does not exceed 400 g/t, i.e. an order of magnitude less than in black lead. Thus, the prototype method cannot be used to extract silver from lead-tin alloys (solders). The objective of the present invention is to convert silver into refining stocks during the treatment of lead-tin alloys with zinc. This task is achieved by the fact that in the known method of extracting silver from lead-tin alloys, including their treatment with zinc, according to the invention, after the introduction of zinc, the alloys are treated with elemental sulfur in an amount of 1-5% by weight of the alloy. The method is carried out as follows. In the lead-tin alloy, which is at a temperature of 330-600 o C in the refining boiler, interfere with metallic zinc or lead-zinc ligature. The amount of zinc introduced is 1-5% by weight of the alloy. During this operation, the melt acquires microheterogeneity caused by the formation of zinc-silver microgroups. However, the presence of tin in the alloy does not allow the silver-containing zinc phase to separate as an independent product. After the dissolution of zinc, the alloy is treated with elemental sulfur in an amount of 1-5%, i.e. sufficient to bind zinc to zinc sulfide. At this stage, not only the sulfiding of the zinc introduced into the lead-tin alloy and the silver associated with it occurs, but also the separation into an independent phase immiscible with the alloy - crystalline sulfide zinc-silver removal. Silver removal is removed from the surface of the lead-tin alloy mechanically or by centrifugation. In the latter case, after the introduction of sulfur, the alloy is passed through a centrifuge, in which the crystalline material is separated from the liquid lead-tin alloy. A certain amount of lead and tin passes into sulfide zinc-silver removal. The content of silver in zinc-silver removal is 20-30 times higher than in the original alloy. Silver from scraps can be extracted by one of the known methods, for example, redox melting on silver solder. In the process of redox smelting, sulfur is removed in the form of sulfur dioxide, zinc, and partially lead and tin. Due to this, the solder formed during melting is enriched with silver. New in the proposed technical solution is the subsequent treatment of the alloy with elemental sulfur after the introduction of zinc, which ensures the formation of sulfide zinc-silver removal. A distinctive feature of the proposed solution is the sequential treatment of the lead-tin alloy with zinc and elemental sulfur and the separation of silver-containing zinc-sulfide removal. Techniques for the sequential treatment of alloys with zinc and sulfur and the removal of zinc-sulfide removals were not found by us in the patent and scientific and technical literature. The proposed method has been tested and verified in laboratory conditions. Example 1. In 500 g of a draft lead-tin alloy containing 25.0% tin, 0.5% copper, 3% antimony, 0.1% nickel, 0.6% iron, 320 g / t silver, the rest is lead , by stirring and at a temperature of 350-400 o C introduced from 5 to 20 g (ie from 1 to 4 wt.%) metallic zinc. The duration of zinc dissolution is 35-65 minutes. After the dissolution of zinc, there was no delamination and the formation of silver-containing removal - silvery foam. Then, at the same temperature, the formed zinc-containing alloy was treated with 15-25 g (3-5% of the weight of the alloy) of elemental sulfur, which was mixed into the melt for 20-40 minutes. After treatment of the alloy with sulfur, a dry zinc-silver sulfide removal was formed on the surface of the alloy. The output of the removal was from 2 to 6% by weight of the original crude lead-tin alloy. The silver content in the removals is 0.32-0.60%. The recovery of silver for removal depended on the consumption of zinc and sulfur (Table 1) and at the indicated costs amounted to 53-70%. Example 2. In a lead-tin alloy (500 g) (20-25% tin, 310-340 g / t silver), previously refined from copper, iron and other impurities, 1-4% by weight of the zinc alloy is introduced in the form of lead- zinc alloy. The introduction is carried out at a temperature of 500 o C and continuous stirring of the melt for 24-40 minutes. As in example 1, the introduction of zinc did not provide the formation of silver-containing removal. After the introduction of the lead-zinc ligature, the temperature of the melt was lowered to 350 o C and treated with elemental sulfur by mixing it into a silver-containing lead-tin melt for 45-60 minutes. The consumption of elemental sulfur for processing the alloy is 3-5% by weight of the original alloy. As a result of this treatment, dry removal was formed on the surface of the melt, which contained from 0.38 to 0.7% of silver. The yield of removals was 2.6-5.0% by weight of the original alloy. The extraction of silver depended on the amount of zinc introduced and sulfur supplied for processing, and when indicated in table. 2 expenses amounted to 57-63%. The removals obtained in experiments 1-12 (table. 2) were subjected to oxidative firing at a temperature of 750-950 o C in air. The resulting calcine was mixed with silica (20%), calcium oxide (10%), iron oxide (7%), coke (5% by weight of the removals) and melted at a temperature of 1250 o C for 30 minutes. As a result of this treatment, a lead-tin alloy was obtained, which contained 1.25% silver, 35% tin, and the rest lead. According to the content of silver and other metals, the alloy met GOST 19738-74 for silver solder grade PSR-1.0. Example 3. A lead-tin alloy refined from impurities containing 315 g/t of silver is alloyed with metallic zinc, the consumption of which is 1-4% by weight of the alloy. Fusion temperature 600 o C. Then the melt was treated with 3-5 wt.% elemental sulfur. The treatment was carried out by bubbling with a mixture of powdered sulfur and argon. Sulfur consumption was 1-5% of the weight of the removals. As a result of such operations, we obtained (Table 3) silver-containing removal, in which the silver concentration was from 0.4 to 0.8%. Extraction of silver in eat - 53-62%. The removals were directly redox melted onto silver solder. To do this, the removals (100 g) were mixed with sodium sulfate (15%), pyrolusite (10%), quartz (15% by weight of the removals) and heated to a temperature of 1150 o C. The resulting melt was loaded with a reducing agent - coke in the amount of 10% by weight of the removals, and melting was continued for 60 minutes. As a result of melting, solder grade PSR-1.5 and slag were obtained, in which the silver content was less than 5 g/t. Thus, the recovery from silver removals into PSR-1.5 solder was at least 99%. The results given in examples 1-3 testify to the high efficiency of the extraction of silver from lead-tin alloys and the possibility of implementing the method on well-known and mastered in the industry equipment. The implementation of the proposed method will ensure the extraction of silver from lead-tin alloys and will allow, without involving an additional amount of precious metals, to organize, for example, at the Ryaztsvetmet plant, the production of silver solders of grades PSR-1.0-1.5. Sources of information 1. Loskutov F.M. Metallurgy of lead. - M.: Metallurgy, 1965. 2. Copyright certificate 431249. "Method of lead refining, authors A.M.Ustimov and N.N. Kubyshev, BI N 21 dated 05.06.74. 3. Abdeev M.A. , Geukin L.S. and others. Modern ways processing of lead-zinc ores and concentrates. - M.: Metallurgy, 1964, p. 218-220.

Claim

A method for extracting silver from lead-tin alloys, including treating them with zinc, characterized in that after the introduction of zinc, lead-tin alloys are treated with elemental sulfur in an amount of 1-5% by weight of the alloy.

Tin-lead solders in products, GOST 21931-76

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

Available as round wire, tape, triangular, round bar, flux-filled round tube 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 (POS) in ingots and in products used mainly for tinning and soldering parts. The indicators of this standard correspond to the highest category quality.

Low antimony

				Application area
POSSu 61-0.5			Rest	Soldering parts sensitive to overheating
POSSu 50-0.5			Rest	Aviation radiators
POSSu 40-0.5			Rest	Galvanized parts of refrigerators, radiator tubes, windings of electrical machines
POSSu 35-0.5			Rest	Cable sheaths for electrical products, thin-sheet packaging
POSSu 30-0.5			Rest	Radiators
POSSu 25-0.5			Rest	Radiators
POSSu 18-0.5			Rest	Heat exchanger tubes, electric lamps

Antimony

				Application area
	Rest			Pipelines operating at elevated temperatures, electrical products
			Rest	Refrigeration devices, thin sheet packaging
			Rest	Refrigerators, electric lamp production, abrasive packaging
			Rest	Automotive products
			Rest
			Rest
			Rest
			Rest	Electric lamp production
			Rest	Tubular radiators, parts operating at elevated temperatures
			Rest	Car body putty, tinplate soldering
			Rest	Automotive products

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

To facilitate this choice, the following are brief information about hard and light solders and fluxes, their use and their manufacture.

Soldering is the joining of hard metals with the help of molten solder having a melting point lower than that of the base metal.

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

To remove oxides and contaminants from the surface of the soldered metal, protect it from oxidation and better wetting with solder chemical substances called fluxes.

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 point of solders, soldering with hard and soft solders is distinguished. Hard solders include solders with a melting point above 400°C, light solders include solders with a melting point up to 400°C.

The main materials used for soldering.

Tin- soft, malleable metal of silver-white color. Specific gravity at 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 little susceptible to oxidation, but when exposed to temperatures below 18 ° C, it can turn into a gray modification ("tin plague"). In places where gray tin particles appear, the metal is destroyed. The transition of white tin to gray sharply accelerates when the temperature drops to -50°C. Can be used for soldering 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 20°C 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 compounds. Used for making 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. It 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. It dissolves in nitric and hot sulfuric acids. It is used in alloys with tin, lead, cadmium to obtain low-melting solders.

Zinc- bluish-gray metal. Brittle when cold. Specific gravity 7.1. Melting point 419°C. In dry air it oxidizes, in moist air it is covered with an oxide film, which protects it from destruction. In combination with copper, it gives a number of strong alloys. Easily soluble in weak acids. It is used for the manufacture of hard solders and acid fluxes.

Copper- reddish metal, malleable and soft. Specific gravity 8.6 - 8.9. Melting point 1083 C. It dissolves in sulfuric and nitric acids and in ammonia. In dry air, it almost does not give in to oxidation, in damp air it is covered with green oxide. It is used for the manufacture of refractory solders and alloys.

Rosin- a product of processing the resin of coniferous trees Lighter grades of rosin (more thoroughly cleaned) are considered the best. The softening point 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 produced 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- POSS 40-2, POSS 30-2, POSS 25-2, POSS 18-2.

Tin-lead solders are manufactured in accordance with the requirements of this standard according to the technological instructions approved 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

chemical composition, %						application area
solder grade	main components
antimony-free
					rest	food utensils, medical equipment
					rest	electronic equipment, printed plates, precision instruments
					rest
					rest
					rest	electrical equipment, parts made of galvanized iron
					rest	engineering products
					rest	contact surfaces of electrical devices, devices, relays
low antimony
POSSu 61-05					rest	soldering parts sensitive to overheating
POSSu 50-05					rest	aviation radiators
POSSu 40-05					rest	galvanized parts of refrigerators, radiator tubes, windings of electrical machines
POSSu 35-05					rest	cable sheaths of electrical products, thin-sheet packaging
POSSu 30-05					rest	radiators
POSSu 25-05					rest
POSSu 18-05					rest	tubes of heat exchangers, electric lamps
antimony
					rest	refrigeration devices, thin sheet packaging
					rest	refrigerators, electric lamp production, abrasive packaging
					rest	automotive products
					rest

Impurity composition of tin-lead solders GOST 21931-76

table 2

mass fraction, %
solder grade	impurities, no more
									aluminum
antimony-free
										rest
										rest
										rest
										rest
										rest
										rest
low antimony
POSSu 61-05										rest
POSSu 50-05										rest
POSSu 40-05										rest
POSSu 35-05										rest
POSSu 30-05										rest
POSSu 25-05										rest
POSSu 18-05										rest
antimony
										rest
										rest
										rest
										rest

Soft solders.

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

Table 1

	Chemical composition in %						Temperature
				impurities no more

When choosing the type of solder, it is necessary to take into account its features and apply it depending on the purpose of the soldered parts. When soldering parts that do not allow overheating, solders are used that have low temperature melting.

Solder brand POS-40 finds the greatest application. It is used for soldering connecting wires, resistances, capacitors. Solder POS-30 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 made 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 to it, 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 optional.

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. 2 shows the compositions of some low-melting solders.

table 2

Chemical composition in %				Melting point in °C

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

Hard solders.

Hard solders create high seam strength. In electrical and radio installation work, they are used much less frequently than soft solders. In 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. Solder PMTs-42 is used when soldering brass with a content of 60-68% copper. Solder PMTs-52 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 melts, about 0.05% of phosphoric copper is added. Molten solder is poured into molds. The melting temperature of the solder must be less than the melting temperature of the soldered metal. In addition to the indicated copper-zinc solders, silver solders are also used. The compositions of the latter are given in table. four.

Table 4

	Chemical composition in %					Melting point in o C
				impurities no more
			Rest

Silver solders have great strength, the seams soldered by them are well bent and easily processed. Solders PSR-10 and PSR-12 are used for soldering brass containing at least 58% copper, solders PSR-25 and PSR-45 - for soldering copper, bronze and brass, solder PSR-70 with the highest silver content - for soldering waveguides , volume contours, etc.

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

Table 5

Chemical composition in %					Temperature melting in

The first of them is used for soldering copper, steel, nickel, the second, which has a high conductivity, 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, is universal for soldering copper, its alloys, nickel, steel.

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

Solders for aluminum soldering.

Soldering aluminum causes great difficulty due to its ability to easily oxidize in air. Recently, aluminum soldering with the help of ultrasonic soldering irons has been used. In table. 6 shows the compositions of some solders for soldering aluminum.

Table 6

Chemical composition in %						Note
			aluminum
						Soft solders
						Hard solders with a melting point of 525 ° C

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

The last solder (solid) 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.

The good wetting of solder joints and the formation of strong seams largely depend on the quality of the flux. At the soldering temperature, the flux should melt and spread in a uniform layer; at the moment of soldering, it should float to the outer surface of the solder. The melting point of the flux should be somewhat lower than the melting point of the solder being used.

Reactive fluxes(acid) - these are fluxes that in most cases have free hydrochloric acid in their composition. A significant disadvantage of acid fluxes is the intense formation of corrosion of solder joints.

The 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 product must be washed with hot running water. The use of hydrochloric acid when soldering radio equipment is prohibited, since during operation it is possible to break electrical contacts at the soldering points. It should be borne in mind that hydrochloric acid causes burns when it enters the body.

zinc chloride(etched 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 weight part of zinc in five weight parts of 50% hydrochloric acid in lead or glassware. 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 points, therefore, after soldering, the soldering point must be thoroughly washed in running hot water. Soldering with zinc chloride in the room where the radio equipment is located is not allowed. It is also impossible to use zinc chloride for soldering electrical and radio equipment. Store zinc chloride in a glass container with a tightly closed glass stopper.

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

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

Chemically passive fluxes (acid-free).

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

Stearin does not cause corrosion. It is used for soldering lead sheaths of cables, couplings, etc. with extra soft solders. Melting temperature is about 50°С.

Recently wide application received flux group LTI 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 could not be soldered before, for example, parts with galvanized 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 points only from oils, rust and other contaminants. When soldering galvanized parts, zinc should not be removed from the place of soldering. Before soldering parts with scale, the latter must be removed by etching in acids. Pre-etching of brass is not required. The flux is applied to the junction with a brush, which can be done in advance. Flux should be stored in glass or ceramic dishes. When soldering parts with a complex profile, 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 LTI-1 and LTI-115 fluxes have one big drawback: dark spots remain after soldering, and intensive ventilation is also necessary when working with them. Flux LTI-120 does not leave dark spots after soldering and does not require intensive ventilation, so its application is much wider. Usually, flux residues after soldering can not be removed. But if the product will be operated in severe corrosive conditions, then after soldering, the flux residues are removed using ends moistened with alcohol or acetone. The manufacture of flux is technologically simple: into a clean wooden or glassware alcohol is poured, crushed rosin is poured until a homogeneous solution is obtained, then triethanolamine is introduced, and then active additives. After loading all the components, the mixture is stirred for 20-25 minutes. The flux produced must be checked for a neutral reaction with litmus or methyl orange. The shelf life of the flux is not more than 6 months.

PHYSICAL AND MECHANICAL PROPERTIES OF SOLDERS

Solder grade	Melting point, o C		Density, g / cm 3	Electrical resistivity Ohm * mm 2 /m	Thermal conductivity, kcal/cm * s * deg	Temporary resistance	Relative extension,	viscosity,	Hardness according to Brinell
POSSu 61-0.5
POSSu 50-0.5
POSSu 40-0.5
POSSu 35-0.5
POSSu 30-0.5
POSSu 25-0.5
POSSu 18-0.5