The technology of soldering has been known since ancient times, it is enough to recall the famous filigree or samovars, in the manufacture of which it was used everywhere. Now the scope of its application is much wider: it is necessary to connect not only metal, but also plastic products, such as polypropylene pipes. However, to have an idea of how this happens is one thing, but to know what is needed to solder metals, what solders, fluxes and tools are required is quite another.
General information about soldering
It means the connection of two metals (non-metals) using additional material with a melting point lower than that of the main ones. It is carried out to assemble individual elements into a single whole or to obtain a new product. The parts themselves do not melt, and the overall structure is formed due to the diffusion of the solder into the metal structure.
This is possible if the thermal effect on the solder is 50-100 ° C higher than its melting point. For heating, special furnaces, gas burners, electric soldering irons and other similar equipment are used. But just raising the temperature to the required value is not enough. Under the influence of atmospheric oxygen, an oxide layer forms on the surface of metals, which prevents the formation of a high-quality compound.
To remove the oxide film and protect the place of the future seam from the effects of oxygen, special fluxes are used. The essence of the soldering process is as follows:
- the oxide film is removed at the point of contact of the parts (using a flux);
- The solder deposited on the surface melts and spreads over it, filling the pores and capillaries, then forming a strong connection during solidification.
The most common and easily soldered metals include:
- steel and iron;
- brass;
- copper;
- bronze;
- gold;
- silver.
Aluminum can also be soldered, but requires the use of special fluxes. The same is true for stainless steel.
Thus, to make such a connection, at a minimum, you need:
- a soldering iron or special equipment for a similar purpose;
- solder;
- flux;
- auxiliary tools and devices.
Soldering iron
As technology evolved, both the technology itself and the equipment used changed. The first were heat soldering irons, i.e. heated on an external fire, examples of which are shown in the photo below. Most often, they were used to perform a variety of tinning work.
Electric soldering irons, which differ in size and power, are now the most common.
Although gas burners are widely used in the same capacity.
And for manual soldering of miniature radioelements and microcircuits, special stations are best suited.
Moreover, this does not exhaust the list of possible equipment for combining metals. Such a variety of soldering irons is caused by the different working conditions. The main parameter when choosing a product suitable for specific purposes will be its power, it is it that determines the amount of heat that comes from the equipment. For soldering conventional radio elements, a 40 W device is sufficient, but to connect tubes with walls up to a millimeter thick, high power is required - about 100 W. The same happens as the size of the parts increases, the more massive ones require more heat for soldering.
An additional factor influencing the choice of the tool is the thermal conductivity of the material to be joined: the higher it is, the more heating must be provided by the soldering iron. The supplied heat will be removed from the place of heating, which will lead to a significant deterioration in the quality of the connection.
Solder
It combines several elements into a single whole and, accordingly, must have:
- high mechanical strength;
- good electrical and thermal conductivity;
- Sufficient fluidity at the soldering temperature to ensure that the solder hits the right place;
- high wettability and adhesion to the brazed metal;
- corrosion resistance.
Different types of solders are used to perform soldering. They are made on the basis of various metals and, depending on their composition, are divided into soft and hard. In addition, the melting point of the solder has an influence on this classification.
Soft solders
Their distinguishing feature is melting at temperatures below 400 ° C. The strength of the soldered connection with their use is up to 10 kg / sq. mm. By their composition and characteristics, soft solders are:
- POS (tin-lead solders) of various types. They are made on the basis of a combination of tin and lead in different percentages, melt at 183-265 °.
- Low-tin, lead-tin (melting point 327 °) and lead-silver (304 °).
- Low-melting, with a melting point of 60-145 ° on the basis of alloys of lead, bismuth and cadmium. Their main purpose is to solder parts that are critical to overheating. The mechanical strength of such a connection is negligible.
- Special. They are used in cases where it is impossible to achieve a high-quality connection with conventional solders, most often when soldering aluminum. They are based on tin.
Similar solders are made in the form of rods, tapes, tubes filled with rosin flux. Their main area of application is electrical work.
Brazing alloys
Their melting temperature exceeds 400 °, the strength of the brazed joint is up to 50 kg / sq. mm. There are:
- copper (1083 °);
- copper-zinc (845-900 °);
- copper-phosphorous (700-830 °);
- silver (635-870 °).
Usually, such solders have a fairly narrow range of applications, and in some cases their use requires special equipment.
Flux
It is generally accepted that it is the flux that determines the quality of the soldering. If it is selected correctly and the desired temperature regime is selected, then the result will always be positive. A wide variety of fluxes are available to provide the solderability of various metals. Nevertheless, all their types must meet the following requirements:
- melt at lower temperatures than solder;
- have good melting fluidity;
- dissolve the oxides of the metal being joined;
- Do not react with solder and brazed metals;
- Cover the soldered area to prevent oxidation;
- can be easily removed when rinsing after soldering.
The most widely used fluxes are:
- Acidic. Usually it is a solution of zinc chloride in water or a flux-paste based on it with appropriate fillers. Such fluxes cannot be used for soldering electrical radio products. After completion of work, they must be washed off, since they cause corrosion of metals.
- Anti-corrosion. They are based on phosphoric acid with various organic solvents.
- VTS is a mixture of petroleum jelly with salicylic acid and ethyl alcohol.
- Acid-free. Most in demand among radio amateurs. They are based on rosin. It is a mixture of resin acids and, when molten, is capable of dissolving oxides. Rosin is chemically inactive, and it can be used only if the parts have been properly prepared before brazing - protected and tinned. Natural rosin and its solution in alcohol are most often used as a flux.
- Activated. In their manufacture, rosin is used with the addition of special substances - activators. One of the best in this group is aniline flux.
This is not a complete list of components used for soldering. Most of them are used in production conditions, including with hard solders. In domestic conditions, in amateur radio practice, alcohol-rosin fluxes and POS-type solders are used. For soldering some types of metals, aluminum, stainless steel, special fluxes are used.
However, the above is not limited to the list of tools required for soldering metals. There is a whole class of items that greatly simplify the execution of work.
Accessories
Among them it is worth noting a stand for a soldering iron, for example, the one shown in the photo.
Of course, they can be anything, but it is much more convenient to work if there is a napkin on which you can wipe the tip of the soldering iron. Many more things may be required for comfortable work.
But in order to connect several parts or solder a broken wire, from the given set, tweezers and a knife will be enough.
Preparing for work
Before work, it will be necessary to tin the soldering iron without fail, especially if it is new and will be used for soldering for the first time. The tip must be pre-processed with a file, then the soldering iron is heated, dipped into rosin and then into the solder.
To ensure its normal adhesion, a sting should be carried out several times over the wooden plank from side to side. The operation (except for file processing) must be repeated several times. How a tinned soldering iron tip looks like is shown in the photo.
Now we can assume that everything needed for soldering has been done.
Soldering refers to one of the oldest and widespread methods of joining metal and other parts. It is widely used in instrumentation, electrical industry and other fields. The existing variety of soldering irons and torches, solders and fluxes allows you to solve a variety of tasks in any field of activity.
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