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Mick Andrews, the superintendent of the Murex Welding Process Centre, explains manual metal arc (MMA) welding and the advantages offered by this process.

MMA welding, or ‘stick’ welding as it is sometimes known colloquially, has been used commercially for around 100 years and is based on the concept of an arc being struck between the workpiece and a consumable electrode, with the heat generated by the arc melting the electrode and the surface of the workpiece so that material from the electrode is deposited in the weld pool.

To protect the arc and the weld pool from atmospheric contamination, the electrode is coated with a flux.

After welding, the slag from the flux is chipped off the workpiece.

The process has developed considerably and operators today have a wide choice of equipment and electrodes to suit different applications and workpiece materials.

Both AC and DC power supplies are available and electrodes are offered for general-purpose and specialist applications.

MMA is still one of the most commonly used welding processes for carbon steel, but it is also suitable for welding cast iron, stainless steels and alloy steels.

Thicknesses normally range from around 1.5mm upwards, with power sources typically capable of delivering up to 250A on a 35 per cent duty cycle.

It should be noted that MMA can join dissimilar metals and be used for hard-facing steels.

Compared with metal inert gas (MIG) and tungsten inert gas (TIG) welding, MMA is a low-cost process to get started with, as the power supply is simpler and cheaper, there is no wire feed unit, the electrodes can be purchased in small quantities and there is no need to hire bottles of shielding gases.

The fact that MMA needs no shielding gas is also a benefit for outdoor applications, where shielding gases can be blown away by wind, and in applications for which portability of the equipment is important.

An MMA welding set can be run from a small generator, so this process is particularly useful for site work and field repairs.

Murex, which has been involved in MMA welding since 1910, offers a range of 16 types of electrode.

Six of these are classed as general-purpose (GP) grades for applications such as the fabrication of fencing and gates and agricultural equipment repairs.

A further three types of electrode are low-hydrogen, high-strength grades and there are three stainless-steel types, one iron-powder type and an armoured type.

Recent developments have resulted in significant improvements to stainless-steel electrodes to reduce the amount of spatter created.

Spatter is harder to remove from stainless steel than it is from carbon-steel surfaces and it is important that a good finish can be achieved more easily.

However, skilled welders are readily capable of producing high-quality, high-integrity MMA welds for pressure vessels and other safety-critical fabrications.

As a result of the levels of spatter created by MMA, compared to MIG or TIG welding, it is common practice to use anti-spatter sprays.

Even if such sprays are used, however, the time required to remove the slag and any remaining spatter should not be neglected.

Although MMA is a cheap way to start welding, the issues of post-weld cleaning and the fact that electrodes have to be changed frequently mean that overall productivity is usually lower than with MIG welding.

To achieve good-quality MMA welds, it is important to store the electrodes correctly.

If not, the flux coating can become chipped, which might mean that the arc is hard to strike or that part of the weld will not be adequately protected.

The coating may also absorb moisture from the atmosphere, resulting in porous welds.

Some electrodes are supplied vacuum packed so that they do not need to be stored under special conditions or rebaked prior to use, whereas standard electrodes need to be oven dried then used immediately or stored in a holding oven or heated quiver until they are needed.

When purchasing MMA welding equipment and electrodes, there is a wide variety of manufactures from which to choose.

A cheap welding set is unlikely to be of as high a quality as a slightly more expensive set, with lower performance and dubious reliability.

Additionally, if something should fail outside the warranty period, spares may be difficult to obtain, making it unfeasible to repair the machine if downtime cannot be tolerated.

Buyers should also be careful not to select MMA equipment that is only just adequate for their existing requirements, as purchasing a slightly more powerful welder will mean that welding can occasionally be performed on thicker material without risking poor penetration and weak welds.

The level of technical support also varies considerably from one supplier to another.

Murex, for example, has a Welding Process Centre in Waltham Cross from where advice is available regarding the selection of equipment and consumables and the optimisation of the welding process.

Provided that a sample can be posted or couriered, the Murex welding engineers can undertake trials and recommend a suitable welding process.

If required, onsite trials can also be carried out to ensure that the customer is fully satisfied before committing to a particular welding process, equipment or consumable.

Murex Welding Products

Murex Welding Products is today part of one of the world’s leading manufacturers of welding products, the ESAB Group. The company offers a full range of arc and gas welding and cutting products, welding consumables and personal protective equipment as well as welding accessories. The Murex Saffire brand is renowned for its associations with welding safety whilst the company also offers a comprehensive range of Gas Equipment Inspectors’ Training Courses, also designed to promote safety in the workplace.

At its UK headquarters in Waltham Cross in Hertfordshire, Murex Welding Products has a team of highly experienced and qualified staff who are always available to offer technical help and advice on all aspects of welding and cutting.

Murex Welding Products still remains “At the HEART of every good weld”.

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