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Applications overview

Joining

Cutting

Coating

Gas welding/oxyacetylene welding
The manual oxyacetylene welding process is one of the oldest joining procedures. It involves heating the metal to be joined to melting temperature in the joining area using a fuel gas/oxygen flame. The addition of a filler metal (welding wire) causes the components that are to be joined to melt and a strongly coalesced joint to be formed. Only acetylene is used as fuel gas. This process is still popular today in assembly and maintenance work.

The advantage of oxyacetylene welding is the fact that it has a reducing flame and that this flame can be adjusted to suit the particular welding requirements. Further benefits include good gap bridging, minimal groove preparation and the fact that the process can be used anywhere. This process can be used to weld steel as well as non-ferrous metals.
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Flame brazing
Flame brazing, too, involves the use of a fuel gas/oxygen flame. However, the surfaces of the parts to be joined are not themselves melted but heated to just above the melting temperature of the solder material. The solder, which is usually in the form of a wire, is added while the joint is being continuously heated so that it melts. A small gap must be maintained between the parts to be joined, into which the solder can flow by capillary action. The use of a flux improves the adhesion of the components with the solder. This also results in the formation of a strongly coalesced joint.

Soldering and brazing are among the oldest and, at the same time, most modern joining processes. Technological progress and its demands as well as cost-conscious production planning have led to the use of all common hydrocarbons and hydrogen as fuel gases.

By adding a flux to the fuel gas flow (flux brazing), the process can also be automated in either linear or rotary brazing machines.
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GMA welding
GMA welding is the most popular welding process. Depending on the material to be welded and the shielding gases that are used, the processes are divided into the following categories:

  • Metal Active Gas welding (MAG)
  • Metal Inert Gas welding (MIG)

Both processes are similarly structured. An endless wire electrode is supplied to the arc by a wire transport device and melted away under a shielding gas. The image shows the structure of a GMA welding process.

The shielding gases have different properties depending on their composition and therefore influence the welding result in different ways. The main task is to shield the liquid melt from the atmosphere, which contains nitrogen, oxygen and moisture. Depending on the material to be welded, these can have an adverse effect on the weld or even result in the failure of the welding process.

Shielding gases influence the following aspects:

  • Metal transfer
  • Flow behaviour of the melt
  • Ignition behaviour of the arc
  • Stability of the arc
  • Heat transfer
  • Penetration profile
  • Chemical composition of the weld
  • Spatter frequency and size

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GMA brazing
For the joining of thin galvanised sheet metal (up to approx. 40 µm thickness), gas metal arc brazing, or GMA brazing for short, has important advantages compared with metal active gas (MAG) welding. It has a high level of process reliability, better quality of seams, very good joint strength and very good corrosion resistance. For this reason, GMA brazing has become firmly established in car manufacturing.

Gas metal arc brazing is similar to MAG welding. The only difference is that the filler metal is replaced by a wire consisting of suitable solder. Selecting the right parameters – current, voltage, wire feed – prevents melting of the surfaces of the components to be joined. A joint is formed in the same way as with flame brazing. Frequently used brazing materials include the following:

Name

Melting range

[°C]

Yield point

[N/mm²]

Tensile strength

[N/mm²]

Expansion

[%]

CuSi3

900 - 1025

250>120

340 - 460

40-46

CuAl8

1030 - 1040

180

380 - 450

40

CuAl8Ni2

1030 - 1050

290

530 - 590

>30

CuAl5Mn1Ni1

1043 - 1074

-

430

35

The standard shielding gas used in GMA brazing is argon. But this does not always lead to optimum results. Based on extensive experience, Messer recommends using a shielding gas mixture consisting of argon and small quantities of active gas for GMA brazing. This will result in seams with a smooth surface and good transitions between the seams and the base metal.
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TIG welding
The main difference between TIG welding and GMA welding lies in the addition of the filler material, which is not continuously supplied to the process as an electrode, as it is with GMA welding. With TIG welding, the arc burns between the workpiece and a non-melting tungsten electrode. As with oxyacetylene welding, the filler material is added manually. The role of the shielding gas is to protect the electrode and the molten pool from the negative effects of the atmosphere. Oxygen, in particular, would lead to a deterioration of the electrode.

TIG welding is particularly well suited for welding high-alloy steels, aluminium and other non-ferrous metals. For high-alloy steels and nickel-based materials, a small amount (2% to 7.5%) of hydrogen is added as a reducing component. For light metals and copper, the addition of helium (up to 90%) has proved effective, depending on the thickness of the workpiece. The process can be operated with direct current as well as alternating current. Direct current with a positive electrode is generally used for welding steels, copper, nickel alloys, titanium and zirconium. Alternating current is used for aluminium.
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Plasma welding
Plasma welding is similar to TIG welding. With this type of welding, the arc is covered by a narrow nozzle and constricted by the small aperture and the high outflow velocity of the gases.

Plasma welding differs from TIG welding by virtue of the arc that is constricted by a water-cooled nozzle. This arc exits the nozzle as a plasma jet with a high temperature and power density. An additional shielding gas layer surrounds the plasma jet and protects the melt from the surrounding air. Plasma welding is mostly used for butt welding of sheet metal and pipes. Its main advantages are controlled penetration and high weld quality. In most cases, the gas surrounding the electrode is argon. In addition to this plasma gas, you also need a shielding gas to prevent oxidation of the weld pool (usually argon with 5% of hydrogen).
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Forming
When welding high-alloy steels, the root must also be protected against contact with atmospheric oxygen. Root protection is often used in MAG welding too. Generally, a residual oxygen content of less than 20 ppm is required at the root. The amount discoloration to be permitted depends on the intended use of the component in question. In the case of small pipes, the weld root is protected by passing shielding gas through them. The important thing here is the adjusted outlet opening. In the case of larger pipes, the backing gas is targeted at the weld with special equipment. The gas flow has to be applied for a sufficiently long period before welding is started.

Generally, so-called forming gases – nitrogen/hydrogen mixtures – are used. The hydrogen component provides greater security against residues of atmospheric oxygen. For this reason hydrogen content is always higher in building site applications than in workshops. Previous tests have shown that the presence of hydrogen in the backing gas has no negative effects, even on duplex steels.

Precise measurements can be carried out to check that conditions are oxygen-free. It is important to follow the correct procedure here.

Forming can also be used for welding plain steels or aluminium, where it produces an even, oxide-free root. The forming gas used here is welding argon.
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Cutting

Flame cutting
With flame cutting, the component to be cut is heated to ignition temperature at the surface by the heating flame. Once the material has reached ignition temperature, it is burned with an oxygen jet. Hence the name “flame cutting”. As this continuous process is exothermic, no additional energy is required to heat up the entire thickness of the sheet. The heating flame supplies all the heat for heating up the surface. The heating flame is arranged in the form of a ring around the cutting channel in order to allow the cutting direction to be changed without turning the cutting nozzle. Flame cutting requires the ignition temperature of the material to be lower than its melting temperature. This is not the case with higher-alloy steels or non-ferrous metals, hence these are cut with the plasma or laser process.
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Plasma cutting
Plasma cutting is particularly suitable for high-alloy steels and non-ferrous metals with greater thicknesses. The arc is bundled by the high pressure of the cutting gas. The extremely high temperature of the arc causes the material to be melted or heated to ignition temperature. The material can now be burned or pushed out of the groove by the cutting gas. With smaller thicknesses, plasma cutting is inferior to laser cutting in terms of cutting quality, but it is more economical when cutting thicker sheet metal. Particularly high cutting quality is achieved with fine-beam plasma cutting.
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Laser cutting
With laser cutting, the laser beam is the heat source. Here, too, the material is burned or blown out of the groove by the cutting gas jet when it has reached ignition temperature or been melted.
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Flame gouging
Flame gouging follows the principle of flame cutting. In contrast to that process, a curved flame cutting nozzle is used. The burnt material (slag) is removed from the groove by the oxygen jet and the waste gases from the heating flame. This process is particularly suited to removing defective welds.
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Flame cleaning
Flame cleaning is used for surface cleaning and the pre-treatment of concrete and steel. A block burner consists of closely spaced nozzles, producing a row of small heating flames. This burner is now passed directly over the surface to be cleaned. When cleaning concrete (DVS Guideline 0302), momentary heating of the surface results in a thin layer flaking off. Any paint, moss or other impurities that may be present are also removed in the process. The result is a clean surface that is suitable for the application of paint, plaster or other coatings.

When cleaning steel, both ferrous and non-ferrous components on the surface are burned, reduced or detached and removed mechanically by the pressure of the flame. The application is widely used, for example, in shipbuilding and bridge construction. However, this kind of work should only be carried out by suitably qualified / trained staff.
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Flame-jet drilling
Flame-jet drilling involves the use of an oxygen lance. This consists of a tube that is filled with steel wires. One end of this lance is heated to ignition temperature while the other end is purged with oxygen. As a result, the lance starts to burn by itself. This tool can now be used to drill in concrete or steel. This process is also recommended for starting the cut when flame cutting thicker sheet metal.
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Coating

Thermal spraying
Thermal spraying has developed into one of the most important coating processes. The main variants of the process are as follows:

  • Flame spraying with powder or wire
  • Atmospheric plasma spraying, plasma spraying in a vacuum or a controlled atmosphere
  • High velocity flame spraying with powder or wire.

The range of gases required is as diverse as the surface coatings offered by these thermal spraying processes.

While flame spraying allows acetylene and pressures up to 2.5 bars to be used, much higher pressures between 5 and 8 bars are preferred for high velocity flame spraying. However, the trend is continuing towards higher pressures, up to 10 bars and more. High velocity flame spraying is used to produce high quality coatings with a high density as well as good adhesion and wear resistance. In order to guarantee these properties, it is necessary to work with high pressures.
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YOUR CONTACT
hildebrandt

Dr. Bernd Hildebrandt
Application Technology
Manager TM Welding & Cutting
Phone: +49 (0) 2151 7811-236
Fax: +49 (0) 2151 7811-503
[E-Mail]