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As soon as mankind unveiled the room for usage of iron, gold, copper in its labour activities, it required methods for junction of small pieces into larger ones that could find a use in the human’s daily grind. Since then we mastered hammering, melting, molding and treatment of metals. It has been found that metal heating up during hammering brings amazing results.
As foundry practices advanced, after we learned how to smelt metals and obtain parts and elements, the craftsmen began to weld them to one another. Parts were molded and the joint was filled with molten metal. Afterwards the special low-melting alloys were created. Thus, flow welding found its logical consequence in soldering.
This is evidenced by gold adornments with tin soldering discovered in the Pyramids, as well as lead waterpipes with soldered cross joint found during excavations in Pompeii of the Ancient Rome. In earlier days the hammer welding has wide usage as well; it included metal heating up to plastic state and its pressing at the junctions.
Hammer welding and soldering were the key processes of metals junction technique through to late 19th century. Electric arc discovery opened the door for arc welding which is still up to date. Yet road to this invention has taken as much as eight decades.
In 1802, Vasily Petrov, professor of Physics at Saint-Petersburg Medical and Surgical Academy, brought into view that during the passage of current through two rods made of carbon and metal a dazzlingly glowing arc (electric discharge) of very high temperature emerged between their ends. He studied and described this phenomenon in his treatise “News of Galvanic-Voltaic Experiments” and highlighted the possibility of electric arc energy usage for melting of metals, thus laying the basis for arc welding and electrofounding.
Hammer welding and soldering were the key processes of metals junction technique through to late 19th century
Only in 1882, Russian inventor Nikolay Benardos tested the method for junction of metals using battery powered electric arc between carbon electrode and metal part. Three years later he patented the technique of junction and disjunction of metals by direct action of current. In 1888, Russian metallurgic engineer Nikolay Slavyanov for the first time ever performed arc welding by metal electrode under layer of flux – prior to this only carbon electrodes were used, although Benardos pointed out that carbon was not the only conducting material to this end.
At the World Expo 1900 in Paris Nikolay Benardos demonstrated his patent device for automatic adjustment of arc length using solenoid (single-layer cylindrical coil with tight winding, which length is significantly greater than width – Editor’s note). Also, he proposed options for welding using angle metal electrodes – devices where electrode delivery to the arc zone was performed by spring pressure, as well as different automatic devices for welding that became prototypes of modern automatic and semi-automatic welding machines.
Using arc welding workers rectified spoiled casting, repair parts of steam engines and different large equipment
As to Nikolay Slavyanov, he not only invented and described arc welding in his articles, books and patents, but also widely put this technique into practice manu propria. He specifically trained workers to rectify spoiled casting, repair parts of steam engines and different large equipment using arc welding. Also, he created the first welding generator and automatic arc-length control device, as well as fluxes for improvement of bead quality during welding.
Implementation of welding into production operations was very intense. From 1890 to 1892 over 1.5 thousand of parts were repaired, primarily cast iron and bronze, for a total weight of over 17 thousand poods (approx. 280 thousand kg). The very project was designed for repair of Russian foundry monument – the famous Tsar Bell, but necessary permission for this work never been obtained. Welding methods laid down by Benardos and Slavyanov became the basis for techniques of arc welding widely used in 20th century. In the 1920s, arc welding started to be used in repair of boilers and locomobiles – mobile steam engines; technology finds its use in railway shops. Today this type of welding is designated by ММА abbreviation.
Not only in the air, but under water too
In 1903, French scientists Edmond Fouche and Charles Picard designed the welding torch fueled by oxyacetylene mixture that allowed to reach the gas flame temperature of 3150°С. Proposed design has not been markedly changed until now. In 1906, the first reliable acetylene generators emerged resulting in industrial usage of this welding technique in assembling of gas pipelines and other equipment.
In 1912, the heavy electrode coating was created that represented a wrap made of blue asbestos. Electrodes with heavy coating imbued with liquid glass found their use in armaments industry and ship-building. Heavy flux coating not only provided protection against contamination, but also stabilised the arcing due to ionizable components. This allowed to create flawless welded joints, and for the first time the weld consistency graded up to density of the metal itself.
In the late 1920s, the reputed bridgebuilder and academy fellow Evgeny Paton having evaluated the prospects of electric welding in bridge building and other industries devoted his scientific activity to this endeavor. In 1929, he founded in Kiev the world’s first Institute of Electric Welding. Also he developed quite a number of new and efficient electric welding procedures. During first five-years plans in the USSR the implementation of welding equipment and techniques being state-of-the-art back then contributed to successful creation of Dnieper Hydroelectric Station, Magnitogorsk iron & steel works, Uralmash and other national projects of great importance.
The first feasible method of underwater welding was developed in Moscow Electromechanical Institute of Railway Engineering in 1932 under the leadership of K.K. Khrenov. Arcing in water is stable, the liquid cooling effect is offset by slight increase in arc voltage, melting of metal under water is as effective as in the air. Welding is performed using manual consumable steel electrode with heavy (up to 30% of electrode thickness) waterproof coating. However, underwater welding quality is slightly below to that in the air, and joint metal lacks plasticity.
In 1940 occurs the first usage of tungsten electrode with arc maintained in the helium. Inert gas provided the best arc stabilization and protection against contamination. Today this type of welding is known as TIG.
Welding advancing has allowed to establish production of airplane, tanks and other armaments at plants of Ural and Siberia during The Great Patriotic War. Considerable contribution was made by Evgeny Paton; under his leadership the automatic workbenches were created for welding of tank turrets and hulls, self-propelled guns, aerial bomb cases.
Since 1946, welding of reactive metals and aluminum structures uses argon that proved to be the most pure, safe and relatively low-cost gas, chemically inert to the melts of said materials. Now this welding method is called MIG/MAG by professionals.
In 1960, new multiple electrode welding technology was developed. Its essence is as follows: two or more welding wires under flux are delivered into welding pool and can be used as additive or under voltage. This welding procedure allows to significantly increase the metal melting rate and to improve its functional flexibility.
1960s saw the most of developments in the field of welding. It was then that the metals welding using powder electrode in inert gas and without it, electro-gas welding and other methods were invented.
In the late 1970s, the Institute of Electric Welding n.a. E. Paton performed underwater welding by semi-automatic machine using fluxcored wire (thin steel pipe packed with mixture of powders) continuously delivered into the arc. In this case the powder acts as flux. Underwater welding is performed at a depth of up to 100 m. It has been widely used since in ship-repairing and emergency-rescue operations.
Today there is over 150 types of welding. New welding methods are widely used including powder welding, plasma welding, direct-energy and electric slag welding, welding under water and in-space and other varieties.
Cold pressure welding is highly effective: it provides welded junction, strength of which sometimes exceeds that of the parent material. In addition, most of the times such welding do not cause significant changes in metal chemistry for it does not actually get hot. Due to this feature such welding is irreplaceable in certain industries (e.g., space industry, electrotechnics and electronics industry).
Welding using pressure is performed without heating only by pressure that creates heavy irreversible deformation (up to the yield state) that must be not below defined level representative for specific metal. Before welding the surfaces to be joined are thoroughly treated and cleaned (mechanically in most cases, e.g. using rotating wire brushes). This welding method is suitable for junction of many metallic items (cables, rods, bars, thin wall pipes and envelopes) and non-metallic materials having sufficient plasticity (resins, plastics, glass, etc.).
Cold pressure welding is highly effective for junction of many metallic items and non-metallic materials having sufficient plasticity
Explosion bonding shows non-inferior efficiency. This welding method is also cold, in so much as no significant heating of material is observable after explosion. Bonding takes place due to cleaning of surfaces by jet stream and their compaction by the explosion pressure. Such method suits well for bonding of dissimilar metals. It is irreplaceable for cold plating – coating of bulky item with the thin layer of other material.
Also welding can be performed using mechanical frictional energy. Items are fixed and drawn together until their ends come into contact. Then the electric motor rotates special rod acting as drill that intrudes into the gap between surfaces to be welded and moves along the joint. Friction causes heating and melting of superficial layers of the ends, rotation stops and items are upset. Sheets in the butting position become malleable, metal is intermixed and bonded in the joint. Highly productive and cost-effective friction welding with intermixing is used in aircraft and aerospace industry.
Highly productive and cost-effective friction welding with intermixing is used in aircraft and aerospace industry
Nowadays this particular technology is used by United Wagon Company in the construction of railway tank car model 15-6901 designed for concentrated nitric acid transportation. Considering extreme aggressiveness of this freight its transportation requires a dedicated rolling stock equipped with the aluminum tank shell (aluminum content – 99.5%). Welding of such shell is performed using friction with intermixing. This technique proves to be much more effective as compared to fuse welding. It shows low defect rate and does not affect environment. In order to confirm this welding method suitability for transport machine building and to verify the mechanical parameters of weld samples the mechanical testing was performed by VNIIZhT (The Scientific Institute of Railway Transport). As a result, the weld samples showed the increase of breaking strength by 10% in comparison with the baseline value for the material.
Domestically-produced railcar fleet is renewed today. Outweared rolling stock from the past century is being gradually replaced by new railcars with improved performances that are manufactured using the state-of-the-art technologies. It means the newest welding methods will be consistently in demand with Russian wagon builders.