Welding

Thermite welding. The connection of metals is carried out by heating the edges with thermite. This is a special powder consisting of a fine fraction of aluminum and iron scale. Instead of aluminum, magnesium can be used.

The essence of thermite welding is to bring together the two sides of the product, between which a gap is provided. The ends are placed in a refractory mold that insulates the metal from the environment and sets the width and height of the weld. A bunker (crucible) with thermite powder is brought to the mold.

The sides of the product are preheated. Usually a propane-oxygen or kerosene-oxygen flame is used. After that, thermite is set on fire in the bunker with a flame or fuse and covered with a lid. At the same time, the feed is opened from the bottom of the bunker to the docking area.

Liquid metal fills the mold and finally melts the edges. The sides are welded. Then wait until the product has cooled down and remove the form. On the surface, bumps, sagging are possible, so machining may be required.

Arc welding. Electric arc welding is one of the most common because it is suitable for joining most types of metals and is easy to implement. All subspecies of electric arc welding have a common principle - a current with low voltage (for the safety of the welder) and increased power (for melting the metal) is used.

Between the positive and negative ends connected to a current source, when touched, an electric arc is excited. If you keep the gap between the poles at 3-5 mm, the arc burns stably and releases temperatures up to 5000º C. This is enough to melt the edges of the base metal. The method of protecting the weld pool and filling the joint are carried out in different ways, from which electric arc resistance welding is divided into several varieties.

Argon welding. In the international system, TIG is prescribed - Tungsten Inert Gas. In argon arc welding, an electric arc burns between the end of the tungsten electrode and the workpiece. The welder manipulates the torch. The tungsten electrode does not melt, so the gap is easier to maintain. Protection of the weld pool is carried out by supplying argon from the cylinder through the reducer to the burner. The gas starts half a second before the start of welding and continues to blow for a couple of seconds after. This reliably isolates the molten metal from external influences.

Filler wire or filler rods are used to fill gaps and increase the height of the weld. They must be of the same alloy as the base metal. On tightly flattened sides of sheet steels of 1.0-1.5 mm, welding without an additive is possible if high mechanical loads are not applied to the product.

Due to the sharply sharpened tungsten needle, the welding seams are narrow and neat, therefore, after application, they often do not need to be processed. The thickness of the penetration depends on the strength of the current. The most powerful devices for argon welding give out 400 A, which is enough to weld parts with a thickness of 30 mm. In this case, water-cooled burners are used. When welding thin steels up to 5 mm, air-cooled machines are suitable.

Semiautomatic welding. Semi-automatic welding has two designations in the international system. MIG means protection of the weld pool with inert gas (Manual Inert Gas), and MAG - protection with active gas (Manual Active Gas). The inert gases include argon and helium, and the active gases are carbon dioxide. Welding with a mixture of argon 80% and carbon dioxide 20% is possible.

The wire simultaneously acts as a filler material. Since it is fed automatically, the welder only has to control the burner, setting the width and height of the seam. On the device there is an adjustment of the current strength and wire feed speed. Welding is carried out with direct current, but there are AC / DC models.

Submerged arc welding. The arc in submerged arc welding burns between the end of the wire and the workpiece. The wire serves as an electrode and filler material, fed automatically from the drum. A hopper moves ahead of the welding head, from which the flux is fed.

Flux is a granular substance used to protect the weld pool. It melts and releases a gas that repels air. The arc burns in a layer of powder, so sparks practically do not break out to the surface, and minimal spatter of the metal is ensured. There are models that have a suction nozzle after the welding head. It removes the flux from an already applied seam, which saves consumables and cleans the surface. Fluxes vary in composition (high-silicon, low-silicon, non-silicon), which determines their suitability for welding specific metals.

Submerged arc welding can be automatic and semi-automatic. The welding actuator (carriage) moves over the product with the help of rollers, a chain. The current source is located nearby in a stationary place and is connected to the carriage by cables. The technology is used to connect pipes of large diameter, laying highways.

Flame welding. Passed with a flame from the burner. To create a flame, acetylene or propane (as a combustible gas) and oxygen (to increase the power of the flame). The temperature of the torch reaches 2800-3100º C, which allows melting the metal edges. To fill the welding bath, an additive wire is used, a welder's free hand.

Gas welding most often combine ferrous metals, pipes, latch containers. Non-volatility allows you to apply welding in the field, on the roofs, in tunnels, basements. Connection to cylinders is performed through gearboxes with pressure gauges. At the oxygen gearbox manometers two - high and low pressure. Additional components will be required (hoses, mouthpieces, nipples) to connect to one system.

Electroslak welding. The essence of electroslag welding is to combine the two sides of the metal due to heat released by the slag bath. To do this, the zone of docking is filled with conductive flux. The welding electrode (wire) is supplied to it, which warms the flux, forming a liquid slag. The electrode continues to carry out the current, being immersed in the welding slag bath. The method of illuminated. The temperature rises and the metal edges are melted with each other.

The range of thickness of the welded metals with this method is 20-3000 mm.

Plasma welding. Plasma is used for melting edges and additive metal. The equipment consists of a source of direct current, gas argon cylinder, plasma torch. To remove the extra heat from the plasmatone nozzle (burner), water cooling is often envisaged.

Gas is supplied to the plasma torch and heats up the electric arc. Due to this, it increases in volume up to 100 times. Due to the thermal expansion, it begins to expire from the nozzle at high speed. This is plasma. Its temperature is 30 000º C, which exceeds the characteristics of other welding methods.