Welding - general information

Weldingis the joining of two or more, similar or dissimilar materials, by melting or pressure, with or without adding additional material in such a way as to obtain a homogeneous welded joint (welded joint without errors with required mechanical and other properties).

The first use of native copper began 10,000 years ago, but the use of the metal was not widely possible until man learned to extract metals from ores by smelting.
Pie 7000 years, about 5000 years before Christ in Persia and Afghanistan, the extraction of copper metal from ore - stone, by melting in fire.
ONko 3800 gp K. bronze was discovered in the Middle East, and later the skill of obtaining it was transferred to China, which helped the flourishing of Chinese civilization, especially for the Chang dynasty around 1500 gpK Bronze is much harder than copper, so it was also more useful for use . The melting point of copper and bronze is significantly lower than the melting point of iron, which makes it easier to obtain them.
Zavadigging developed as an integral part of the skills of blacksmiths, goldsmiths and casters when making work tools, weapons, vessels, jewelry and buildings (fences, doors, bridges, fittings, window bars...).

Ljewelding has developed in parallel with the art of casting. Beautiful thin-walled cast bronze vases also have "welded" parts on them. Various holders, supports and figures were connected to the base body of a vase or other object that had been cast earlier by later casting..

Soldering is joining by melting an alloy with a lower melting point than the material of the objects to be joined. Throughout history, soldering as a joining technique has been applied to jewelry and figurines.

Forge welding.

The best swords made of steel in the Middle Ages were made of low-carbon steel, and blades (strips) of high-carbon steel (1.0-2.1%C) were welded to their edges (by blows of a hammer in a hot state), which, with certain heat treatment, gave hard , solid and sharp edges. Swords, arrowheads and spearheads, daggers and other weapons where blacksmith welding was used were known in Greece, the Frankish state, China, Japan, Indonesia, and in Syria.
The technique is knownika joining strips from different types of iron materials by forging as "damasking" (from Damascus-Syria) 2, with the aim of achieving special good properties for swords and guns. Even for today's stage of technical development, this technology of making parts from composite materials by forge welding is interesting.

YesThe blade was also first used natively. At first it was found on the surface of the earth from a meteorite (a meteorite is a meteor that reaches the earth), so the Sumerians called it "heavenly metal".
The first traces of extracting iron from ores date back to around 2500 gpK, and its wider application came later. The Iron Age, i.e. iron objects, begin to be found around 1500 BC, and the first records (Herodotus) about blacksmiths welding iron in ancient Greece say that it was weldedit was used in the 6th century BC, for the manufacture of vessel bases. Getting steel starts around 1000 gpK in India.

The development of today's welding procedures

  • 1802. Petrov researches the electric arc for general purposes; not yet for welding.
  • In 1856, Joule was the first to apply electro-resistance welding of wires.
  • 1882 NN Bernardos (Russia) is the first to use an electric arc between a carbon electrode and metal as a source of energy for welding by adding wire to the metal bath. He used a battery of galvanic cells (accumulators) as a source of direct current. Until then, an electric arc between two carbon electrodes was used for lighting.
  • In 1888, NS Slavjanov (Russia) proposed the procedure of electric arc welding with a metal electrode. An electric arc is established between the metal electrode and the metal objects, which are connected.
  • 1894 Sottrand welds for the first time with an O2+H2 gas flame. Later, he developed gas welding with an oxygen-acetylene (O2+C2H2) flame, which has been successfully and widely used in industry since 1916.
  • 1895. Aluminothermic welding begins to be used for welding rails and for repairing castings.
  • In 1907, Oscar Kjelberg (Sweden) was the first to patent and apply a coated electrode. The coated electrode was produced by immersing the bare wire in a mineral solution, and since 1936 the coating has been applied by extrusion. Basic electrodes began to be produced in 1940. Mr.
  • 1925. Discovery of the welding procedure in a protective atmosphereri of hydrogen "arcatom".
  • In 1930, the application of automatic welding under powder - EP in US shipbuilding began.
  • In 1936, the application of welding in a protective atmosphere, the He-TIG procedure, began.

Before, and especially after the Second World War, the development and application of welding in shielding gases TIG (arc-atom with hydrogen, and argon-arc with argon or helium as a shielding gas) began. MIG welding began to be used in 1948 as the Sigma process (Shielded Intert Gas Metal Arc), and in 1953, the MAG process with CO2 shielding active gas was used for the first time in the former USSR. Cold welding under pressure has been used since 1948.

After 1950, many new procedures were developed such as: welding under slag (1951), friction (1956), electron beam (1957), ultrasound (1960), laser (1960), plasma in the USA (1961) .) and others.
The first welding and thermal cutting in space was performed on October 16, 1969 in the Soviet spaceship "Soyuz 6". Welding is also performed under water (different techniques are used).

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Development of welding in Croatia

A more significant development of welding in Croatia was achieved on the eve of World War II. World War II, when several larger buildings were built in welded construction. Among them is a large welded road bridge over the Sava river, in the extension of the Sava road in Zagreb. It is one of the first major usof pedestrian welded bridges in the world. It was made and installed by the company
e "Ðuro Đaković", Slavonski Brod. (then "The First Yugoslav Bridge and Carriage Machinery Factory"). On that bridge, sheets up to 95 mm thick, with a strength of 440 MPa, were welded, with preheating and control by industrial radiography (Röntgen).

In the period 1950 - 1960, riveted constructions were quickly abandoned, and in addition to the REL process, other welding processes were gradually introduced that are still used today (semi-automatic and automatic processes).

Complexity of work in the field of welding and further development

Welding is an interdisciplinary technology. To understand and use this technology, knowledge in the fields of:

  • Materials science and metallurgy (welding metallurgy),
  • thermodynamics (temperature fields during welding),
  • electrical engineering (current sources, electric arc, connection of different sensors – U, I, sound, light,...),
  • chemistry (metallurgical and other processes that take place during welding),
  • informatics (expert systems, various calculations, databases, ...) and others.

The scope of welding on only one object can be large. On the example of an 82,000 t tanker ship built in our shipyard, 261.6 km of corner joints and 11.6 km of butt joints are welded. There are 10,000 to 100,000 welded connections of pipes under pressure at large thermal power plants or at nuclear power plants and oil refineries.It is enough for just one weld to fail (fracture, crack, porosity, leakage...) to lead to costly downtime or, in a less favorable case, to catastrophic damage with serious consequences for people, property and the biological environment.
Pran accident is a fracture of the primary pipeline of the nuclear power plant at the point of the welded joint. Since the welded joint can be the weakest point in the structure, it is the most important to investigate. "A chain is only as strong as its weakest link".

Some of the subjects of study:

• welding procedures
• temperature fields
• power sources for welding
• welding metallurgy
• weldability of the material
• weldability tests
• shaping of welded joints and welded structures (technology)
• designing welding technologies (pwps, pqr, wps, ...)
• quality classes, reliability, attenuation
• possible failures of welded joints and welded structures
• case studies of termination "case studies"
•control (kbr and ksr) and quality assurance

Representation of modern welding procedures in the world

It can be qualitatively assessed taking into account different criteria. One approach is to take into consideration the representation of welding procedures for some group of welded products or semi-products (profiles, pipes, cars, bridges, pressure vessels, ...).
Approaches are also possible with regard to the type and thickness of the material (unalloyed, loweged, high-alloy steels of different thicknesses), welding position (horizontal, vertical, wall, overhead), amount of molten material, etc.
Considering the global application of welding procedures in practice, the qualitative assessment of the application of welding procedures is:

  • electric arc processes by melting,
  • electrical pressure resistant,
  • high frequency pressure currents,
  • other procedures.

Today, the emphasis in the world is on the quality, that is, the reliability and safety of welded products. This implies:
• application of modern welding equipment (inverters, pulsed welding currents, devices, mechanization, automation and robotization of welding, ...)
• high reproducibility of welding,
• modern methods and equipment for control with and without destructive methods (KBR and KSR),
• application of modern materials for the construction of lighter, more durable, more economical and more reliable ZK.

Weldability is the ability to join materials by welding. It can be qualitative (descriptive, comparison) and quantitative (numerical, e.g. Equivalent).

Welding related techniques

  • Soldering (hard and soft)
  • Spraying of material
  • Thermal cutting of materials (gas flame, plasma, laser, electron jet) and thermal grooving (electric arc, plasma, carbon electrode)

There are two basic groups of welding procedures:

  • welding talby
  • pressure welding

An electric arc is a permanent and strong discharge in ionizing gas in the space between the tip of the electrode and the workpiece in the current circuit during electric arc welding.

Elements of a welded joint using the fusion welding process are:

  • melting zone (weld metal) i
  • heat affected zone

Each of the mentioned zones consists of a number of areas. It is enough for a weakening to occur in any area of one of the zones of the welded joint and for the possibility of failure of the welded joint and the welded product to occur (the chain is only as strong as the weakest link in the chain!). In most materials, structural transformations occur in the welded joint during fusion welding, while some do not (e.g. aluminum, ferritic steels, ...).

Principle of REL welding:

An electric arc is established by a short circuit - cutting between the electrode and the workpiece, i.e. connections to the poles of the electric current (Direct Current or Alternating Current). This is followed by the uniform addition of the electrode to the electric arc by the welder, and the melting of the electrode and the formation of the welded joint.

REL pconcession has wide possibilities of application: in production welding, surfacing and repair welding of most metal materials. However, due to its economy (small kg/deposit per hour), it is used to perform shorter welds, usually with a thickness of no more than 15 mm (20 mm in the case of butt welds).ich joints, running angle joints with a smaller weld thickness (where increased penetration in the root of the weld is usually not required).

The main parameters of REL welding are:

  • welding voltage (U), which ranges from 18 to 26 V during welding;/li>
  • the strength of the welding current (I), which during welding varies depending on the diameter of the electrode (orientation values of 40 ⋅φ electrode, A)
  • welding speed (v), which varies depending on the applied welding technique (pulling or swinging of the electrode), the diameter of the electrode and the orientational welding parameters from 1.5 to 2.5 mm/s. The no-load voltage is usually 60 V. The degree of utilization of energy for melting is 0.75 - 0.85.

Advantages

  • developed a wide range of additional welding materials,
  • lower price of welding equipment (welding device) compared to MAG and EP welding process,
  • suitable for minor production and repair welding,
  • possibility of welding in all welding positions,
  • suitable for working in the field, especially where there is no electricity (units),
  • very easy handling of the equipment,
  • good mechanical properties of the weld,

Disadvantages

  • low welding speed and low productivity compared to MAG and EP,
  • the quality of the weld depends significantly on the skill of the welder - man,
  • the time to train a good welder is long,
  • there is inevitable electrode waste - "chip" (8-10%), and loss of mat. due to splashing into the environment,
  • more difficult slag cleaning after welding and loss of time due to slag cleaning,
  • there is a strong flash during welding, harmful gases develop (good ventilation of the room is necessary),
  • long-term work can have harmful effects on the welder's health (rheumatism, damage to the respiratory system...)
Types and application of additional welding materials

The role of protecting the electric arc and molten material during welding

  • Physical
  • Electric
  • Metallurgical

Physical function:

a) Creation of a protective atmosphere, whose presence prevents the unfavorable influence of O, N and H on the molten metal.
b) The presence of a layer of molten viscous slag around the droplet and on the surface of the bath protects the molten metal. By its presence, the slag presses the metal and the solidified metal gets a smooth surface under the slag

Electrical function

Kjelberg already discovered in 1908 that the coating of the electrode gives an electrically more stable arc. The electric arc is easier to light and easier to maintain. It is necessary to add arc stabilizers to the electrode coating: Cs, K, Ca or other elements that have a low ionization energy.

Metallurgical function

  • Refining of molten metal by removing S and P, forming sulfides and phosphides, which float to the surface of the metal pileke and are removed with the slag.
  • Hydrogen bonding e.g. in HF, which comes out of the molten metal, thus reducing the risk of cold cracks.
  • Doping of elements that burn in an electric arc (Cr, Ni, Mn, Si). Ferro-chromium, ferro-nickel, ferro-manganese and ferro-silicon are usually added to the coating.
  • Addition of elements to create a fine grain: Ti, Al, because these elements form a lot of crystallization seeds in the solidification phase.
  • Addition of elements for deoxidation of molten metal: Al, Si, Mn.
  • Addition of Fe powder to increase productivity (randman) - the amount of molten deposit.


Types of electrode coating according to the composition of the coating

  • A (Acide) ........................acid coating,
  • B (Basic) ........................basic coating with high hydrogen content
  • C (Cellulosic) .................cellulosic
  • R (Rutile) ......................rutile (rutile = TiO2)
  • O (Oxide) ...................FeO, SiO2

It is not recommended to use acid electrodes for welding steels with a higher sulfur content due to the risk of hot cracks. These electrodes can be used in all welding positions with the use of direct current or alternating current sources for welding. These electrodes do not need to be dried under normal welding conditions (without ambient humidity, with good storage and handling of the electrodes).

BAzic electrodes provide a welded joint with good mechanical properties (espelongation and toughness), and due to the lower presence of harmful gases and non-metallic inclusions (the composition of the slag binds O2, H2, S and P), there is less tendency to cracks and porosity. The disadvantages of using these electrodes are: more difficult cleaning of slag, porosity in the root of the weld if the electric arc is longer (welding at 90!), somewhat rougher appearance of the weld surface, weaker stability of the electric arc during welding (due to the high content of CaF2), great dependence of the properties of the weld about the welder. These electrodes are used when welding demanding welded constructions.

Rutilee electrodes are widely used due to the good mechanical properties of the weld, the stability of the electric arc, the possibility of using DC and AC welding current, the beautiful appearance of the weld, and the easy cleaning of slag. The lack of application of these electrodes is evident in welding no
elika withhigher sulfur content, possibility of hot cracks, weaker melting zone toughness compared to basic electrodes.

Cellulose electrodesare used for welding in all positions with DC and AC current. Their melting speed is high, and the resulting slag is easily separated. Due to the large penetration, they are used for welding the roots in the pipe.

In MAG weldingthe electric arc is established by a short circuit - cutting between the welding wire and the workpiece, i.e. the connections to the poles of the electric current (direct current - Direct Current) in an atmosphere of active gas. This is followed by an even addition of welding wireit into an electric arc, and the melting of the wire and the formation of a welded joint.

Application
The MAG procedure has wide application possibilities: in production welding, surfacing and repair welding of most metal materials. It has an advantage over REL welding from the point of view of economy (more kg/deposit per hour, greater intermittency of the drive - no downtime for changing electrodes as with the REL process, less weld cleaning). It is used for welding sheets and pipes with a thickness of 1 mm, usually up to a thickness of 20 mm (in some cases, far beyond these thicknesses, when the application of the MAG procedure is economically and technologically justified.
For bigger onesthickness of the base material and longer lengths of welded joints, it is more economical to use the EP process (independently or in combination with the MAG or REL process, e.g. for root drilling). The MAG process is originally a semi-automatic process, but is very often used as an automatic and robotic welding process. The share of robots for MAG welding in the automotive industry is significant.

Parameters
• welding voltage (U), which ranges from 16 to 26 V during welding;
• the strength of the welding current (I), which during welding varies depending on the diameter of the welding wire (guide values 80 to 180, A)
• welding speed (v), which varies depending on the applied welding technique (pulling or oscillating), the diameter of the welding wire and the orientation welding parameterstion from 2 to 4 mm/s. The no-load voltage is usually 60 V. The degree of utilization of energy for melting is 0.75 - 0.85.

Advantages
• developed a sufficiently wide range of additional welding materials,
• lower price of welding equipment (welding device) compared to EP welding procedure (but still slightly higher compared to REL),
• suitable for individual and mass production and repair welding,
• possibility of welding in all welding positions,
• less time lost by the welder (no electrode replacement as with REL welding, less weld cleaning),
• suitable for automation and robotization,
•quality weld and good mechanical properties of the weld.

Disadvantages
• the quality of the weld still depends on the skill of the welder - a human in the case of semi-automatic welding
•welding (but still not as much as with REL welding),
• the time for training a good welder is shorter than for REL welding (although it is a practice for MAG welders to first learn the REL welding procedure),
• strong flashing occurs during welding, gases are released during welding (good ventilation of the room is necessary),
• dlong-term work can have harmful effects on the welder's health (rheumatism, damage to the respiratory system...).

Sources of current for welding are electrical devices that provide electrical current at the welding site with characteristics suitable for welding.

Power sources for weldinggrowing:
• Transformers
• Rectifiers
• Rotary converters
• Aggregates
• Inverters

Welding transformers are the most widespread, most widely used welding power sources that transform alternating current into alternating current with characteristics suitable for welding.

Rectifiers are sources of welding current that provide direct current for welding with characteristics suitable for welding. They are usually powered by three-phase alternating current. After transforming the current using a welding transformer, the current is rectified (semiconductor diodes, thyristors, transistors, ...)

Depending on the purpose (which welding procedure), the static characteristic of the current source can be steep or flat. For example For semi-automatic MAG welding – laid, for EP (up to 3 mm welding wire diameter) – laid, for EP (over 3 mm wire diameter) – steep ...

Version of welding rectifier: Transformer + rectifier part

The advantage of rectifiers over transformers:
• provide a more stable electric arc (there are no changes in the movement of the electric arc 50 times per second)

Disadvantages in relation to transformers:
• they are more expensive than an ordinary transformer,
• are sensitive to voltage drop,
• have a lower degree of utilization,

The welding units are independent of the electrical network, i.e. they are suitable for assembly. They are driven from the sidee diesel or gasoline engine, and it drives a generator that provides current with characteristics suitable for welding. Their price is significantly higher compared to transformers and rectifiers.

Marking of welding procedures according to ISO EN
• 111 ... REL welding
• 12 ... EP welding
• 121 ... EP welding with additional wire
• 21 ... Electro-resistant spot welding
• 22 ... Electro-resistant seam welding