QUALITY THAT CAN STAND THE HEAT

Welding technology covers a very wide range of procedures. The DIN EN 4063 standard defines well over 100 different welding methods. The range of gases and applications that Messer offers you in this area is correspondingly diverse.

Shielding gases for welding are typically used in oxyfuel processes, which use fuel gas/air mixtures or, preferably, fuel gas/oxygen mixtures. Shielding gases for welding are also indispensable in arc welding, where the necessary thermal energy for the process comes from an arc. The same applies to TIG and MIG welding, where gas mixtures dominate today’s market. These mixtures feature a range of possible components, including argon and CO2 as well as oxygen, helium, hydrogen and nitrogen.

A great variety of these standardised gas mixtures is now available for the aforementioned applications. Messer sells its range of shielding gases for welding in a clearly structured system using standardised group-wide names that are based on the materials being worked:

Ferroline - Shielding gases for plain and low-alloy steels
Inoxline - Shielding gases for high-alloy steels and Ni-based alloys
Aluline - Shielding gases for aluminium and non-ferrous metals

As a manufacturer of industrial gases, we not only deal with those processes that involve the use of industrial gases, but also with processes that are in competition with this. Messer’s advisory service on shielding gases for welding will gladly show you which shielding gas is the right one for your application: in a personal consultation and through on-site demonstrations.

These procedures can be roughly divided into the following manufacturing processes:
Cutting / Joining / Coating

MAG WELDING OF PLAIN STEELS

Messer is pleased to help you choosing your shielding gas for welding.

MAG WELDING OF HIGH-ALLOY STEELS

TIG WELDING OF HIGH-ALLOY STEELS

MIG AND TIG WELDING OF ALUMINIUM

FORMING

PLASMA CUTTING

LASER CUTTING

GASES FOR OXY-FUEL TECHNOLOGY

The different properties of the fuel gases determine the applications that they can be used for.

For all applications, we recommend using oxygen instead of air as the combustion gas.

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.

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.

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
   

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:

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.

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.

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. 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). Plasma welding is mostly used for butt welding of sheet metal and pipes. Its main advantages are controlled penetration and high weld quality.

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.

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.

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.

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.

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.

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.

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.

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.
• Gas dynamic cold spraying of copper, steel, nickel or other metals and alloys with sufficient ductility

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.

CONSULTING, BY PHONE AND ON-SITE

Messer offers a comprehensive program of gases, which is not always a matter of course. But that is far from all.
We can give advice on the choice of process or on questions of automation, we can tell you which type of supply - cylinder, bundle or cryogenic liquid supply - is the right one for you. We would also be glad to talk to you about the cost-saving potentials which may exist for your company in welding, cutting and related processes.
We would be happy to advise you!

ON-SITE TROUBLESHOOTING

If you are experiencing problems in your manufacturing processes, we will carry out analyses of our products free of charge and help you remedy the faults. The main focus is on measuring moisture and oxygen. This makes it possible to eliminate other error sources at the same time.

PROCESS OPTIMISATION

We can help our customers optimise their existing production process. This can be done either on site or at our technical centres in Europe.
Our equipment enables us to flexibly supply and mix individual gas mixtures or various standard gas mixtures on site. All the parameters are determined on the customer’s system, eliminating the need for subsequent correction. A comparison of product quality –before and after – can be seen straight away.
If production cannot be interrupted, we prepare the conversion in one of our technical centres. To do this, we use the same components as used by the customer and determine new production parameters in our welding laboratory.
To ensure cost-effectiveness, we will prepare a costing on request.

In order to be able to ensure the quality of your products, we will arrange the necessary tests on request. These include:

• Macrosections
• Microsections
• Radiographic tests
• Layer thickness measurements
• Measurement of penetration and blending
• Temperature measurement
• Measurement of current and voltage parameters
• X-ray tests

RESEARCH AND DEVELOPMENT

Our activities in research and development also benefit our customers. In the course of our projects we are gaining a detailed insight into the individual welding processes and at the same time developing special gas mixtures.

In arc spraying, the liquid material is atomised conventionally by compressed air.
The deposition process can be controlled through the targeted use of nitrogen, argon, oxygen and other gases. This results in a focussed coating jet with less overspray and reduced oxide formation.

before                         after

When welding aluminium, once the thickness of the material exceeds a certain value, then preheating is necessary. With complex components, this is often impossible due to lack of accessibility. In these cases, the additional energy needs to come from the welding process.

We will be happy to advise you on any questions you may have regarding the selection of a shielding gas for welding. Please do not hesitate to contact us.