1. Occupational safety.

a. Driven.

Basically, welding is almost always associated with strong currents or explosive gases, toxic exhaust gases, dangerous light and heat development as well as sprayers of liquid metals. The hazards depend on which welding process is used. The welding core often contain carcinogenic substances. This is always the case, especially when welding highly alloyed substances. The use of chrome and/or nickel-containing welding materials in the form of chromats, and/or nickel compounds also creates carcinogenic smoke. Acute poisoning by inhaling dusts with a very high manganese content can lead to inflammatory reactions in the lungs. This toxicity manifests itself as bronchitis and can develop into a fibrous lung disease. If the suction is properly used, the limit for manganese and its connections will not be exceeded. Nevertheless, a special health examination of the lungs is required for welding staff (G39).

In Germany, the TRK limit values ​​for heavy metals must be observed. Many other components are also stressful and to be assessed accordingly (TRGS403, MAK values). In the TRGS 528, which has replaced the BGR 220 (welding screw), the requirements for the welding workstation are regulated, among other things.

b. Measures.

It is to be created for welding workplaces a risk assessment. All ingredients of the welding smoke must be taken into account here, including Titandioxide, fluorides, magnesium oxide, calcium oxide, iron oxides and its alloy components such as nickel, cobalt, chrome and manganese. In the case of high -alloy steels, if possible, to avoid electrode welding and to avoid protective gas welding or automated procedures, because the lack of covering the electrode releases less chromate. A correspondingly expert instruction is imperative for all dependent employees according to the Occupational Safety Act (ArbSchG); Furthermore, proof of training (skilled worker letter or course examination of a Chamber of Crafts) is common. A welding supervision is required in many industrial areas, for rail applications.

When welding to autogen, you need protective glasses so that there are no glowing parts or sparks in the eyes. The glasses are colored so that the welding environment can be observed glare -free.

The arc welding arises ultraviolet radiation, which damages the skin, but especially the eyes.

Furthermore, infrared radiation (heat radiation) is created, which not only can generate burns on unprotected body parts, but can also damage the retina.

Therefore, protective glasses must be used that shield these two types of radiation. The protective classes for such glasses are defined in the European standard EN 169. For example, the protective classes 2 to 8 are intended for autogen welding, while classes 9 to 16 are intended for open arc welding. The protective glasses bear a label that characterizes the properties of the glass. The information is as follows: protection class, manufacturer, optical class 98, DIN standard. The modern replacement for protective glasses are automatic welding protection filters.

Since the UV radiation also damages the skin, an umbrella is used that covers the whole face. Before the actual almost black glass, there is usually a normal glass that stops the sparks and can be replaced cheaper. In order to have both hands free, the umbrella can be attached to a protective helmet or a device on the head. In addition, special flammable welding clothes must be worn, which covers all skin surfaces safely. Many welding processes are very loud, so adequate hearing protection is therefore necessary.

When welding, the finest dust particles are also created that have to be sucked off so that they cannot get into the welder's lungs and diffuse from there into the bloodstream. For this purpose, mobile or stationary welding smoke filters are used, which suck and filter this fine dust. The status of today's technology is so-called EPTFE filters (surface filtration). If no effective suction of the welding smoke can be ensured, the welder must be protected by personal protective equipment in the form of a blower filter device (papr). These devices do not protect against lack of oxygen or harmful gases in shafts and containers. If sufficient ventilation is not possible, air -independent respiratory protection devices must be worn. Particular caution is offered when flaming and preheating with gas burners, in insufficiently ventilated, narrow rooms, since the flame consumes part of the breathing oxygen

When welding, the people in the area must also be protected from radiation and noise. There are also welding lamella and welding curtains as well as soundproof partition systems. In the case of arc hand welding, the electrical hazard of the welder must be particularly observed. The arc voltage lies below the - generally - endangering area, but especially when working, with special electrical risk, for example when working in tight electrically conductive rooms (boiler, tubes, etc.), a number of precautionary measures are to be observed, which are under also proposed in the BGI 553 of the metal professional cooperative.

When laser welding, the laser beam itself is an additional source of danger. It is usually invisible. While radiation in the nearby infrared (solid body laser, fiber laser, diode laser) penetrates the skin and the eye and also causes retail damage at low intensities (spreading), the radiation of the CO2 laser (medium infrared) on the surface (skin and corneal of the eye is ) absorbs and causes superficial burns. Skin burns caused by lasers in the nearby infrared are u. Also dangerous because the radiation is absorbed under the skin in deep areas, where there are no temperature -sensitive nerves. Laser welding devices are usually safe (locked protective doors, laser protection windows), they then fall under laser class I and can be operated safely without laser protection glasses.

2. Electrode welding and arc welding.

The arc hand welding (e-hand welding EN ISO 4063: Process 111) is one of the oldest electrical welding processes for metallic materials that are still used today. Nikolai Gawrilowitsch Slawjanow replaced the coal electrodes, which had previously been common to the arc welding, with a metal rod, which was also an arc carrier and welding additive. Since the first stable electrodes were not covered, the welding site was not protected from oxidation. Therefore, these electrodes were difficult to weld.

An electrical arc between an electrode melting as an additional material and the workpiece is used as a heat source for welding. Due to the high temperature of the arc is melted at the welding site. Welding transformers (lusty field transformers) serve as sweat flow sources with or without welding rectors, welding converters or welding agers. Depending on the application and electrodent type, you can weld with DC or AC.

Covered stable electrodes, for example for unalloyed steels according to ISO 2560-A, develop gases and sweat slags when melting. The gases from the wrapping stabilize the arc and shield the welding bath before oxidation by the air oxygen. The welding slag has a lower density than the melt, is washed to the weld seam and ensures additional protection of the weld seam from oxidation. Another desired effect of the welding slag is to reduce the welding shrinkage voltages due to the slower cooling, since the component has more time to develop the plastic deformation.

Due to the electron fire, the anode (plus pole) heats up more. In most welding processes, consuming electrodes are operated as anodes, the workpiece as a cathode (minus pole). In the case of enveloped stable electrodes, the polarity depends on the electrode wrapping. If the cover is made of poorly ionizable components, as is the case with basic electrodes, the electrode is welded at the hotter plus pole, otherwise due to the lower current load.

The main area of ​​application of the arc hand welding is the steel and pipeline construction. Due to the significantly lower welding speeds, electrode welding is preferred in the assembly area, since the machine effort is relatively low compared to other procedures. Electrode welding can also be carried out without errors even under unfavorable weather conditions, such as wind and rain, which is particularly important during external work. Another advantage is that, in contrast to other procedures, the welding can often be carried out without defects if the welding joint is not fully metallic.

3. MIG - Mag welding (metal protection gas welding).

The partial mechanical metal protection gas welding (MSG), optionally as a MIG (metal welding with inert gases, EN ISO 4063: process 131) or Mag welding (metal welding with active, i.e. reactionable gases, EN ISO 4063), is a arc welding process, in which The melting welding wire is continuously tracked by a motor at a changeable speed. The used welding wire diameter are between 0.8 and 1.2 mm (less often 1.6 mm). At the same time as the wire feed, the welding site is fed over a nozzle. The protective or mixed gas with approx. 10 l/min (rule of thumb: protective gas volume flow 10 l/min per mm wire diameter). This gas protects the liquid metal under the arc from oxidation, which would weaken the weld seam. In the case of metal -active gas welding (MAG), either with pure CO2 or a mixed gas made of argon and small proportions CO2 and O2 (e.g. "Corgon") is worked. Depending on their composition, the welding process (insertion, drop size, splash loss) can be actively influenced; MIG) is used as a noble gas argon, also the expensive noble gas helium.

Optionally, filling wires can also be used in metal protection gas welding, also called tube masters (with active gas welding EN ISO 4063: Process 136, with Inertgas EN ISO 4063: Process 137). Inside, these can be provided with a slag picture and, if necessary, alloying additives. They serve the same purpose as the envelopes of the stable electrode. On the one hand, the ingredients contribute to the welding volume, on the other hand they form a slag on the welding caterpillar and protect the seam from oxidation. The latter is particularly important when welding gemstelles, since the oxidation, the "starting" of the seam must also be prevented even after continuing the burner and thus continuing the protective gas bell.

History of MIG-MAG procedure
The MSG welding was first used in the USA in the USA in 1948 in the inert gas or noble gas variant, at that time it was also referred to as Sigma welding.

In the Soviet Union, an active gas was used for welding instead of the expensive noble gases such as Argon or Helium, namely carbon dioxide (CO2). This was only possible because wire electrodes have now also been developed, which compensate for the higher burning elements that compensate for the higher burn -out.

In Austria, the CMT (Cold Metal Transfer) was developed in Austria until 2005, in which the welding current is pulsed and additional wire is moved back and forth with high frequency in order to achieve targeted drops of drops with low heat input.

4. Plasma cutter.

The plasma cutter consists of a power source, handpiece, mass cable, power supply and compressed air supply line. A plasma is an electrically conductive gas with a temperature of around 30,000 ° C. The arc is usually ignited with high frequency ignition and constricted at the exit by an isolated, usually water -cooled copper nozzle. Some systems also use the lift arc ignition, which is also used for WIG welding devices. With these devices, the burner is placed on the workpiece at the interface, and there is a low stream that is not sufficient to damage the burner. The gas flow presses the burner from the workpiece surface, the arc ignites and the electronics of the welding current source increase the current to the thickness required for the cut. The metal melts through the high energy density of the arc and is blown away by a gas beam, which creates the cutting joint. Compressed air is often used as a gas for blowing out. For a better cutting joint, protective gas mixtures are also used, which prevent or weaken oxidation. Characteristic of plasma cutting joints is to round off the edge at the entry point.

The procedure is characterized by a number of advantages over other melting welding processes. In conjunction with the WIG pulse welding and WIG-ACCUSTROM welding, every melting-safe material can be added. There are practically no welding splashes in WIG welding; The health burden of welding racks is relatively low. A special advantage of the WIG welding is that it is not worked with a melted electrode. The addition of the welding additive and the current are therefore decoupled. The welders can optimally match his welding current to the welding task and only has to add as much welding additive as is currently required. This makes the procedure particularly suitable for welding root layers and welding in forced situations. Due to the relatively low and small -scale heat input, the default of welding of the workpieces is lower than in other procedures. Because of the high weld seams, the WIG process is preferred where the welding speeds resign towards the quality requirements. These are, for example, applications in pipeline and apparatus construction in power plant construction or the chemical industry.
The WIG welding system consists of a power source that can be switched on the same or alternating current welding in most cases, and a welding torch that is connected to the power source by a hose package. In the hose package there are the welding current line, the protective gas supply, the control line and for larger burners the feed and return of the cooling water.

5. Plasmashweißen.

When plasma whites (plasma metal inert gas welding, EN ISO 4063: Process 151), a plasma beam serves as a heat source. Plasma is an electrically conductive gas due to an arc. In the plasma grenner, the flowing plasmagas (Argon) is ionized and an helping light sheet (pilot light arch) is ignited by high frequency pulse. This burns between the negatively polished tungsten electrode and the anode trained as a nozzle and ionizes the gas column between the nozzle and plus -poled workpiece. This makes it possible to ignite contactless ignition of the arc. Gas mixtures made of argon and hydrogen or argon and helium are used as plasmagas that protect the melt from oxidation and stabilize the arc. The slight additions of helium or hydrogen increase the incorporation and thereby increase the speed of welding. The narrowing of the plasma by the water-cooled copper nozzle into an almost cylindrical gas column results in a higher energy concentration than with WIG welding, which enables higher welding speeds. The delay and tensions are therefore less than with WIG welding. Due to the plasmal light arch, which is still stable at the lowest current thickness (less than 1 a) and the insensitivity at a distance of the nozzle to the workpiece, the process is also used in the micro -white technology. With the microplas machine (welding current area 0.5-15 a), sheets can still be welded with 0.1 mm. The plasma stinghole or keyhole welding is used from a sheet metal thickness of 3 mm and, depending on the material to be welded, can be used to a thickness of 10 mm for the single-layer welding without seam preparation. The main areas of application are the container and apparatus construction, the pipeline construction and space travel.

6. Wolfram - Inert gas welding (WIG).

The Wolfram-Inert gas welding (WIG welding process, English tig, EN ISO 4063: Process 141) dates from the USA and became known there in 1936 under the name Argonarc welding. It was not until the beginning of the 1950s that it began to assert itself in Europe. In English -speaking countries, the procedure is called TIG or GTAW. The tig stands for the tungsten inert-gaswelding and GTAW for gas tungsten Arc Welding. In both abbreviations, the word "tungsten" is found, this is the English term for Wolfram.

There are two types of igniting the arc, contact and high-frequency ignition:
In the historical contact inflammation (string or arrival ignition), similar to the electrode welding, diewolfram electrode is briefly painted on the workpiece - like a match - on the workpiece and thus a short circuit is generated. After lifting the electrode from the workpiece, the arc burns between tungsten electrode and workpiece. A major disadvantage of this procedure is that there is some material from the tungsten electrode with every ignition, which lies behind as a foreign body in the melting bath due to the higher melting temperatures of the tungsten. Therefore, a separate copper plate, lying on the workpiece, was often used for ignition.
The high -frequency ignition has practically completely replaced the stroking ignition. In the case of high -frequency ignition, the gas between the electrode and the workpiece is ionized with the help of a high -voltage impulse generator, which gives a high voltage on the tungsten electrode, which lit the arc. The high -voltage impulse generator has a harmless power.
A variant of contact inflammation is the lift arc ignition. The electrode is placed directly at the welding site on the workpiece. There is a low current that is not sufficient to damage the electrode. When lifting the burner, the plaslichicht arch ignites and the electronics of the welding machine lights the electricity to welding current thickness. The advantage of this method is to avoid electromagnetic disorders that can occur in high -frequency ignition.

Most of the time, the noble gas argon, rare helium or a mixture of both gases is used. The relatively expensive helium is used due to its better thermal conductivity to increase heat insulation. In the case of austenitic non -rust steels, small amounts of hydrogen can reduce the viscosity of the melt in protective gas and increase the speed of sweat (it is no longer an inert, but reducing gas, see planned change in EN ISO 4063.

The protective gas is directed to the welding site by the gas nozzle. The rule of thumb is: gas nozzle diameter = 1.5 × melting bath width. The amount of protective gas depends, among other things, on the seam shape, material, welding position, protective gas and nozzle diameter; Information on this can be found in the manufacturers' data sheets.

WIG welding can be worked with both with and without an additional material. As with gas melting welding, manual welding are usually used for stabbing -shaped additives. However, confusion with the gas welding rods must be avoided because the chemical compositions differ from each other.

In the WIG welding, a distinction is made between equal and alternating stream welding. DC welding with negative polished electrode is used to weld all kinds of steels, N-metals and their alloys. In contrast, alternating current welding is mainly used to weld the light metals aluminum and magnesium. In special cases, light metals are also welded with direct current and with a positive electrode. Special welding burners with a very thick tungsten electrode and helium are used as protective gas. The plus polarity of the tungsten electrode for light metals is necessary, since this usually forms a hard oxide layer with a very high melting point (as with aluminum oxide, magnesium oxide) on its surface. This oxide layer is broken up for a minus polarity of the workpiece, since the workpiece now acts as the electrons of emitting poles and negative oxygen ions.

The BGI 746 (handling of thorough oxide-containing tungsten electrodes in the tungsten gas welding (WIG)) contains information on the safe handling of thorium oxide-containing tungsten electrodes for tungsten-inert gas welding and describes the necessary protective measures that must be taken to exclude possible threats by handling these electrodes or to minimize to a reasonable level. This is necessary due to the low radioactivity of the thorium and the dust of the heavy metal. Due to the availability of tungsten electrodes alloyed with Lanthan or rare earths, tungsten electrodes can be used today.

WIG - impulse welding

A further development of the WIG welding is welding with pulsating electricity. In the WIG pulse welding, the welding current pulsates between a basic and impulse current with variable frequencies, basic and pulse current heights and widths. The pulse frequency, the pulse width and the pulse height can be adjusted separately. The WIG pulses with a variable current course can only be carried out with a special welding system (welding). The finely meterable heat insulation in the WIG pulse welding enables good cleft bridging, good root welding and a good welding in compulsory situations. Welding seam errors at the beginning of seam and seam ends, as with pipe welding, are avoided

All descriptions are manual or partially mechanized WIG welding with supplementary material mainly Ø 1.6 mm. When pulse welding of light metals (namely: AA6061), melting on the surface can be achieved and thus prevents <1.0 mm through meltdowns in thin sheets. Especially with throat seams, the corner is captured rather than with standard welding with constant electricity. Sheets with a thickness of 0.6 mm were also flawlessly welded, since the stability of the arc and the concentrated heat insulation allow a small defined melting bath. Issue is the main problem when a gap is present and so oxygen has access side. The influence of tungsten electrical alloy and the composition of the protective gas is important; These parameters significantly influence the process.

7. Purpose of welding.

In the event of the definition, a distinction is made between the connection and welding welding according to the purpose of welding. Connection welding is the merging (DIN 8580) of workpieces, for example with a pipe longitudinal seam. Welding welding is coating (DIN 8580) of a workpiece by welding. If the basic and the contract material is different, a distinction is made between contract welding from tanks, plates and layers of buffers.

Melting welding is welding with local melting flow, without the use of strength with or without the same welding additive (ISO 857-1). In contrast to soldering, the liquid temperature of the base materials is exceeded. In principle, all materials that can be transferred to the melting -fluid phase can be connected by welding. The most common application is used for the fabric connection of metals, thermoplastics or in the glass, both for utility products and for connecting fiber fibers in news technology. Depending on the welding process, the connection is made with a welding seam or a welding point, and also flat when welding on friction. The energy necessary for welding is supplied from the outside. The term railway welding is used for automated welding when using robots.

a. Influence of welding on the base material.

The base material can have a disadvantageous properties due to the heat of welding and the subsequent relatively fast cooling. Depending on the material and the cooling processes, hardening or brassening can be caused, for example. In addition, high self -voltages in the transition of the weld seam to the base material can arise. This can be countered by a variety of countermeasures in the production. These include welding measures, such as the selection of suitable welding processes, welding supplementary materials and welding seam process procedures, preheating of the workpiece as well as constructive and manufacturing measures, for example the correct welding and thus assembly, selection of suitable suture forms and, if possible, the selection, the selection of the right base material.

b. Lifespan extension through post -treatment methods.

The operating strength and lifespan dynamically stressed, welded steel structures are determined in many cases by the weld seams, in particular the welding seam transitions. Through targeted aftercare of the transitions by grinding, raying, ball rays, high -frequency hammering, etc., the lifespan can be increased significantly with simple means in many constructions.

c. Welding suitability of the steel.

Steels with a carbon content of more than 0.22 % are only considered to be limited, additional measures such as preheating are required. However, the carbon content of the steel alone makes no statement about the weldability, since this is also influenced by many other alloy elements. The carbon equivalent (CEV) is therefore taken into account for assessment. In many components, depending on the construction and material, additional measures are required, preheating or slow cooling, tension -arm glow or buffer welding. In general, highly or fermented steels are more difficult to sweat and require special knowledge and controls of the finishing company. In addition to the mandatory tested welders, all companies are also appointed a responsible welding supervision. Without an order, the company owner is automatically liable for welding supervision. From class B, specially trained welding specialists, such as welding engineer/technician/man, must be used to ensure the necessary technical support for welding work.