Despite the fact that in modern construction, during electrical work, aluminum cables are increasingly being replaced by copper cables, aluminum remains an indispensable material in the manufacture of large-section wires and cables.
The reasons for this lie on the surface - the electrical resistivity of aluminum is approximately one and a half times greater than that of copper, and the volumetric weight is three times less.
With a large conductor cross-section, when weight is more important than strength, the choice in favor of aluminum is obvious. The cross-sectional area of an aluminum conductor will be one and a half times greater than that of a copper conductor, and at the same time, aluminum will still be two times lighter than copper. Soldering, among other methods, is used to connect wires.
Soldering methods
The problem with using aluminum conductors is their rapid oxidation.
The oxide film significantly impedes the passage of electric current during connections. To do this, twisted aluminum wires are soldered. You can solder aluminum wires in a junction box using a soldering iron or a gas torch. It is more difficult to use a soldering iron due to the inability to accurately heat to the required temperature. And for aluminum, overheating is just as unacceptable as underheating.
Metal has high thermal conductivity, and the insulation over a large area from the soldering point can simply melt.
It is easier to regulate the heating temperature with a gas burner, but it takes a long time to prepare the surface. However, it is the torch that will need to be used if it is necessary to solder any massive parts to each other. In any case, when soldering aluminum wires, they need to be prepared.
Inverter type devices
Advantages of welding inverters
The advantages of inverter units are well known to specialists. Certain models are equipped with a strap that allows you to carry the inverter on your shoulder. This makes it possible to carry out welding work with twisting in a junction box while standing on a stepladder. The inverter can be connected to household electrical wiring, since the device has low power consumption.
Inverters have a wide range of electric current regulation. Their arc is very stable and ignites perfectly at low welding currents. For this reason, even an untrained electric gas welder can quickly achieve an amazing effect and achieve optimal quality of wire welding.
Household welding devices are marked with the abbreviation MMA. Then numbers are indicated indicating the operating current - 200 or 250 V. The professional device operates in a temperature range of up to 150 degrees. The home device has a spectrum from 0 to +30. Another difference between a home device and a professional and industrial device is the duration of the operating cycle.
Algorithm of operation of the welding inverter
A professional type inverter will operate for 8 hours with short breaks, an industrial type - 24 hours with a break of 30 minutes. The device, intended for household use, operates without interruption for 30 minutes, and then cools down for an hour.
When welding a copper type cable, a special copper-plated carbon electrode is used, which is popularly called a “pencil”. If you don't have a carbon electrode, you can take a standard carbon rod from an unusable battery. Welding current, depending on the cross-section and number of wires, is used at different voltages. A suitable mode is one in which the electrode does not stick to the welding area and the arc is stable.
Preliminary processing
The difficulty with soldering is that aluminum itself is a very low-melting material (660 ℃) and if heated carelessly it can melt.
Another factor that makes soldering aluminum wires difficult is rapid oxidation in air.
The oxide film on the surface of the material reliably protects aluminum from the effects of all kinds of external factors, but it also prevents the adhesion of solder to the material and must be removed.
It is almost impossible to mechanically remove the oxide film under normal conditions. The material is instantly oxidized and covered with a new film. You can mechanically remove the oxide film under the oil layer.
But before this, the oil must be heated to 200 ℃ in order to remove any active oxygen that may be present there. This method is very inconvenient at home and labor-intensive.
Therefore, the ends of aluminum conductors must be tinned before soldering. Using rosin or most other fluxes will not work due to the high chemical resistance of the oxide film. It does not dissolve even with organic acids.
To tin the wires, you must use both a special flux and a mechanical method.
Of course, this must be done before the wires are twisted, otherwise it will not be possible to mechanically clean the entire surface of the wire. Only the tinned ends can be twisted together and soldered.
Welding pencils
We are talking about a welding rod. The product is a rod resembling a pencil with a diameter of 4 to 15 mm, a length of 7 -20 cm. Only instead of a rod there is an exothermic mixture inside. Such products were used by the military when repairing mats. parts in the field.
Principle of operation
The burning mixture releases a large amount of heat sufficient to melt thin sheet metal or copper cable cores. A thin rod can be set on fire with an ordinary match; thicker ones have a special wick that is ignited with a regular lighter. The burning time of such a pencil is from 20 seconds to 5 minutes. Which is quite enough to weld several twists, naturally observing safety precautions when holding the rod and preventive fire-fighting measures, for example, placing a bucket of water next to it so that in case of a fall the burning rod falls into the water, laying a metal sheet, and preparing a fire extinguisher.
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Working with a soldering iron
In order to solder aluminum with a soldering iron, there are several methods, the essence of which is to clean immediately under the flux layer in direct contact with the molten solder.
The first method is that aluminum conductors, before soldering, are cleaned with a hot tinned soldering iron using a mixture of rosin and steel filings.
Sawdust has an abrasive effect, rosin removes all impurities and immediately the cleaned areas are covered with solder, which should be on the soldering iron tip.
The second method involves stripping the aluminum wire on medium-grit sandpaper directly under the influence of a hot soldering iron with solder and flux.
Gas burner
Processing with a gas burner is carried out when the parts are in the position relative to each other in which they will be used. The processing smoothly transitions into the soldering process itself.
This happens as follows:
- the burner heats the surfaces of aluminum parts;
- upon reaching the temperature at which the metal is reduced from the oxide, the film is mechanically peeled off;
- under the influence of a flame, the parts are coated with flux, and solder is introduced into the soldering area.
If the parts are thick, then their edges must be cut at an angle of 45°. Typically, heating occurs to the melting point of tin, when the solder spreads and fills the twist groove.
Features and Requirements
When purchasing any equipment for inverter welding, it is easy to notice that the standard supply set is extremely meager. The standard welding cable included in the kit does not always satisfy users even for standard mass work. The main task of such wires is to supply electric current. One line is connected to the device itself, and the other is intended for the workpiece (or, as they say, for the mass). The connection allows you to form and close an electrical circuit, without which the welding process is unthinkable.
However, any engineer, electrical engineer, and especially welder will immediately pay attention to important specifics. To obtain a welding cable, a more powerful and reliable wire is used than usual
Such products must work stably in both hot and cold weather.
The quality of insulation plays an important role. In all decent models it consists of two layers. A large margin of safety must be provided. It is needed to ensure reliable operation even in particularly extreme situations. Products are always selected for specific temperature and humidity conditions; The optimal cable length is also taken into account.
Differences in technology when using flux
Thanks to the achievements of modern science and technology, flux compositions for aluminum have been obtained that actively dissolve the oxide film and protect the material from further oxidation.
Examples of such drugs are formulations labeled F-59A and F-61A. The letter A means that these compounds are intended for soldering aluminum.
When using these fluxes, soldering aluminum wires is greatly facilitated. It is enough to simply treat the finished twist with flux, without even heating it, and then, after heating it with a soldering iron or torch, apply solder.
It will spread over the entire surface of the wires and adhere well, providing a strong and electrically conductive solder joint.
DIY pulse welding
Pulse welding - what is it? In essence, this is ordinary electric arc welding, during which additional short-term pulses are applied. Please do not confuse this type of welding with spot welding. Pulsed spot welding and pulsed arc welding are two radically different methods of joining metals.
But what if you want to try this method of joining metals in your practice, but do not want to spend a lot of money on buying a high-quality welding machine? There is a solution! You can make homemade pulse welding. Pulse welding can be assembled on your own in one and a half to two hours, and all components are inexpensive. In this article we will tell you in detail how to make pulse welding with your own hands and what is our experience in using a homemade welding machine.
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CONVERTER
Let's start by assembling the converter. Which is also called the power part of the welding machine. Below you can see a detailed assembly diagram.
Can it be connected to copper?
Situations often arise when it is necessary to connect an aluminum wire to a copper wire. This is perhaps the only case where soldering cannot be used.
It's all about the aluminum itself. It cannot be soldered to other metals at all due to its physical and chemical properties. When connecting directly to copper, galvanic corrosion will occur between the two active metals and will quickly destroy the connection.
And if they are soldered using solder that is neutral to both materials, then the different coefficients of thermal expansion of the metals will quickly destroy the soldered contact. After all, when current passes through a conductor, it will certainly heat up, and after switching off, it will cool down.
What novice welders need to know
If you have virtually no experience in welding, but the work needs to be done, then you need to remember the following nuances.
- The seam will be of high quality, well-welded, and no burns will appear on the metal if you constantly monitor it. Therefore, it is recommended to arrange the parts to be welded in advance so that it is convenient to observe the welding progress.
- The simplest option is welding in the lower position. Beginner welders should start with this one. Then you can move on to the circular joints, and after them to the vertical ones. The latter are the most difficult to perform.
- For convenience, it is better to make overlapping joints. If you weld joint to joint, you can accidentally weld to the table on which the elements lie.
- If defects appear during work, they must be removed. To do this, the problem area is additionally boiled or first selected using a grinder, and then fused again.
- If you have to weld thick parts, then for complete penetration it is necessary to chamfer the edges. The gap between the edges depends on the thickness of the elements, but should not be less than 0.5 mm.
Safety precautions
Safety precautions when soldering aluminum wires boil down to observing general precautions when working with electric heating devices, open flames and aggressive liquids, such as fluxes.
It is unacceptable to use faulty soldering irons with damaged insulation and with more power than necessary.
Do not use burners near flammable objects. When working indoors, forced ventilation must be properly organized.
Difficulties in soldering aluminum wires
The main difficulty when soldering aluminum wires, as indicated above, is the presence of an oxide film on the surface of the metal. Fighting it greatly slows down the soldering process.
And if you consider that aluminum wires are now used mainly for laying external power wiring, it becomes obvious that a regular soldering iron and sandpaper will not be enough in this case. Welding is increasingly being used to connect such wires.
Spring terminals
Spring clamps are the simplest, most effective and fastest connection. According to user reviews, the most reliable terminals are from the German company Wago. The principle of operation and the design of the terminals can be seen in the picture.
The advantages of this connection:
- Can be used without any special knowledge;
- There is no need for additional core insulation;
- Quick connection, some connections are made by pressing a button or lever on the clamp body.
Flaws:
- Spring terminals can be used for cables with a diameter of no more than 4 mm 2.;
- A 15% safety margin must be taken into account. For example, if the network is designed for 16A, then the terminal block must be at least 20A;
- Also, the disadvantages include their high cost; one Wago terminal can cost about 12 rubles.
