The MMA (Manual Metal Arc welding process was first developed in Russia in and comprised a bare metal welding rod. In the early &#;s the coated electrode was introduced when the Kjellberg process was invented in Sweden. In the UK the Quasi arc method was introduced. The use of the coated electrode was slow due to the high production costs but the demand for higher integrity welds led to the process becoming increasingly used.

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The material is joined when an arc is created between the electrode and work piece melting the work piece and the electrode to form a weld pool. At the same time the electrode has an outer coating sometimes called electrode flux which also melts and creates a shield over the weld pool to prevent contamination of the molten pool and assist in establishing the arc.

This cools and forms a hard slag over the weld which then needs to be chipped away from the weld bead upon completion or before another weld bead is added. The process allows only short lengths of weld to be produced due to the electrode length before a new electrode needs to be inserted
in the holder. The quality of the weld deposit is highly dependent on the skill of the welder.
The power source provides a constant current (CC) output and can be either AC (alternating current) or DC (direct current).

The design of the MMA welding inverter is such that the operator extending arc length will reduce the welding current and shortening the arc length (reducing the arc voltage) will do the opposite i.e. increase the current. As a guide the voltage controls the height and width of the weld bead whilst the current controls penetration, therefore the welder manipulates the electrode to achieve a satisfactory weld.

The power used in the welding circuit is determined by the arc voltage and current.
The voltage (V) is determined by the electrode diameter and the distance between the electrode and work piece. The current within the circuit is dependent on the electrode diameter, the thickness of the materials to be welded and the position of the weld. Most electrode information will show details of current types to be used and optimum current range.

MMA welding power sources which can TIG weld are often referred to as drooper&#;s or drooping characteristic power sources. They are typically basic selector type, magnetic amplifier control or engine driven units with a robust design as they are often required to work in extreme conditions.
The characteristic of the output shape gave rise to the term &#;drooper&#;.

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Modern welding inverter power supplies however can overcome these problems and provide excellent characteristic and performance as the curve can be controlled electronically for each process.

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The small relatively cheap AC sets are generally used in the DIY or small maintenance functions and some larger AC sets often oil cooled may be used in heavier industry but the DC output set are now the most common in use.

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Electrode manufacture means that not all DC electrodes can operate on AC power sources but AC electrodes can operate on both AC and DC. Direct current (DC) is the most commonly used mode. Control of AC units tends to be moving iron core or switched transformers.

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DC output power sources can be used on many material types and can be obtained in wide current ranges. Controls of these units vary from moving iron core control to the latest inverter designs. Inverter design has brought many advantages as they are:

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&#; Very lightweight and portable compared to their predecessors
&#; Very energy efficient power supply and offer energy cost savings

&#; Able to provide higher outputs for lower inputs
&#; High levels of control and performance

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In general it is preferable to weld in the flat or horizontal position. When welding in position is required such as vertical or overhead it is useful to reduce the welding current compared to the horizontal position. For best results in all positions maintaining a short arc, uniform movement and travel speed in addition to consistent feeding of the electrode are required.

What makes up the MMA (Stick) System?

The Welding Inverter Power Source

The welding inverter power source selected should have sufficient power to melt the electrode and weld material with enough capacity to maintain the arc voltage. 

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The MMA (Stick) welding process typically requires high current (50-350 Amps) at relatively low voltage (10-50 Volts). The MMA welding electrodes are designed to operate on different types of output power and voltage and you should always read the manufacturers data.

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All welding electrodes can be used on direct current (DC) but not all on alternating current (AC). Some AC electrodes also have certain voltage requirements. When used in the DC mode the electrode lead should be connected to the polarity recommended by the electrode manufacturer, in most cases this will be electrode positive polarity but there are electrodes that use electrode negative polarity. The power source operates with a &#;no load&#; or &#;open circuit voltage&#; present when no welding arc is struck. This no load voltage rating is defined in the standard EN - (EN ) in accordance with the welding environment or risk of electrical shock.The power source may have a voltage reduction device (VRD) fitted either internally or externally.

The Electrode Holder and Welding Cables

The Electrode Holder and Welding Cables

&#;The electrode holder clamps the end of the electrode with conductive clamps built into its head. These clamps operate either by a twist action or spring-loaded clamp action (crocodile type).

The clamping mechanism allows for the quick release of the remaining unused electrode end (stub end).

To ensure the maximum welding efficiency the electrode has to be firmly clamped into the holder, otherwise poor electrical contact may cause arc instability through voltage fluctuations and overheating of the holder.

The welding cable is connected to the holder either mechanically, crimped or soldered.

Electrode holders should conform to IEC -11.

Welding Cable

Welding cable diameter is generally selected on the basis of welding current level. The higher the current and duty cycle,
the larger the diameter of the cable to ensure that it does not overheat (see relevant standard). If welding is carried out some distance from the power source, it may be necessary to increase cable diameter to reduce voltage drop.

The Welding Electrode

The welding electrode consists of a core material of the material type i.e. steel or stainless steel etc. which provides the weld filler metal. This is covered by an outer coating called a flux which helps in creating the arc and shields the arc from contamination with what is called slag.

Types of Flux/Electrodes

The stability of the arc, depth of penetration, metal deposition rate and positional features are significantly influenced by the chemical composition of the flux coating on the electrode. Electrodes can be divided into three main types:

&#; Basic
&#; Cellulosic

&#; Rutile

Basic Welding Electrodes

Basic welding electrodes contain a high proportion of calcium carbonate (limestone) and calcium fluoride (fluorspar) in the coating. This makes their slag coating more fluid than rutile coatings - this is also fast-freezing which assists welding in the vertical and overhead position. These electrodes are used for welding medium and heavy section fabrications where higher weld quality, good mechanical properties and resistance to cracking (due to high restraint) are required.

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Features:

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• Low hydrogen weld metal

• Requires high welding currents/speeds

• Poor bead profile (convex and coarse surface profile)

• Slag removal difficult

   

When these electrodes are exposed to air moisture pick-up is rapid. Because of the need for hydrogen control these electrodes should be thoroughly dried in a controlled temperature drying oven.
Typical drying time is one hour at a temperature of approximately 150oC to 300oC but you should always consult the manufacturer data before use.

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After controlled drying, basic and basic/rutile electrodes must be held at a temperature between 100oC and 150oC to help protect them from re-absorbing moisture into the coating. These conditions can be obtained by transferring the electrodes from the main drying oven to a holding oven or a heated quiver at the workplace.

Metal Powder Electrodes

Metal powder electrodes contain an addition of metal powder to the flux coating to increase the maximum permissible welding current level. Thus, for a given electrode size, the metal deposition rate and efficiency (percentage of the metal deposited) are increased compared with an electrode containing no iron powder in the coating.

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The slag is normally easily removed. Iron powder electrodes are mainly used in the flat and H/V positions to take advantage of the higher deposition rates. Efficiencies as high as 130-140% can be achieved for rutile and basic electrodes without marked deterioration of the arcing characteristics but the arc tends to be less forceful which reduces bead penetration.

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NOTE: The quality of weld relies upon consistent performance of the electrode. The flux coating should not be chipped, cracked or more importantly, allowed to become damp. Electrodes are made with different types of coating and require different handling.

Cellulosic Welding Electrodes

Cellulosic welding electrodes contain a high proportion of cellulose in the coating and are characterised by a deeply penetrating arc and a rapid burn-off rate giving high welding speeds. Weld deposit can be coarse and with fluid slag, de slagging can be difficult. These electrodes are easy to use in any position and are noted for their use in the &#;stovepipe&#; welding technique.

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Features:

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&#; Deep penetration in all positions
&#; Suitability for vertical down welding
&#; Reasonably good mechanical properties
&#; High level of hydrogen generated - risk of cracking in the heat affected zone (HAZ)

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These electrode coatings are designed to operate with a definite amount of moisture in the coating. The coating is less sensitive to moisture pick-up and does not generally require a drying operation. However, drying may be necessary in cases where ambient relative humidity in which the electrodes have been stored in, has been very high.

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Rutile Welding Electrodes

Rutile welding electrodes contain a high proportion of titanium oxide (rutile) in the coating. Titanium oxide promotes easy arc ignition, smooth arc operation and low spatter. These electrodes are general purpose electrodes with good welding properties. They can be used with AC and DC power sources and in all positions. The electrodes are especially suitable for welding fillet joints in the horizontal/vertical (H/V) position.

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Features:

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&#; Moderate weld metal mechanical properties
&#; Good bead profile produced through the viscous slag
&#; Positional welding possible with a fluid slag (containing fluoride)

&#; Easily removable slag

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The rutile coatings can tolerate a limited amount of moisture and coatings may deteriorate if they are over dried. Always consult the manufacturer data before use.

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Hard Wear/Facing Welding Electrodes

&#;Hard facing or wear electrodes are used primarily to put a hard surface over a softer base material. There is an extensive range of these types of products and a common use area is the repair of wearing surfaces such as teeth on earth moving and mining equipment.

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DC Copper Coated Welding Electrodes

&#;This is the most common type because of its comparatively long electrode life. These electrodes are constructed by mixing and baking carbon, graphite and a binding agent and coating them with copper. They provide stable arc characteristics and uniform grooves.

DC Plain Electrodes

These are constructed in the same way as the DC copper coated electrode but without the copper coating. They are more rapidly consumed compared to copper coated in use

AC Coated Electrodes

These electrodes are constructed by mixing and baking carbon, graphite and a special binding agent with added rare earth materials to help with arc stabilization.
They are copper coated.
The process uses compressed air at between 80-100 psi at the electrode holder.

Increasing air pressure will not remove metal more efficiently.

Welding Electrode Storage

Electrodes should always be kept in a dry and well-ventilated store. It is good practice to stack packets of electrodes on wooden pallets or racks well clear of the floor. Also, all unused electrodes which are to be returned should be stored so they are not exposed to damp conditions to regain moisture.

Good storage conditions are 10°C above external air temperature. As the storage conditions are to prevent moisture from condensing on the electrodes, the electrode stores should be dry.

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Under these conditions and in original packaging, electrode storage time is practically unlimited. Modern electrodes are now available in hermetically sealed packs which remove the need for drying. However, if necessary, any unused electrodes must be redried according to manufacturer&#;s instructions

Drying of Electrodes

&#;Drying is usually carried out in accordance with the manufacturer&#;s recommendations and requirements will be determined by the type of electrode.
Many electrodes are now available in hermetically sealed containers. These vacuum packs obviate the need for drying the electrodes immediately prior to use. If however the container has been opened or damaged, it is essential that the electrodes are re dried according to the manufacturer&#;s instructions.

Electrode Selection

The electrode diameter selection is based on the work piece thickness, welding position, joint form, welding layer etc.

Welding current level is determined by the size of electrode - the normal operating range and current are recommended by manufacturers. Typical operating ranges for a selection of welding electrode sizes are illustrated in the table.

• Electrodes should be dry and used according to the instructions.
  This will reduce the hydrogen in the molten pool and welding seam, avoiding the blowholes and cold cracking.

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• In the welding process, the arc must not be too long; otherwise, it will cause unstable arc burning, large amounts of spatter, light penetration, undercut, blowholes etc. If the arc is too short, it will cause electrode sticking to the work piece.

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• In MMA welding the arc length is usually equal to 0.5~1.0 times the diameter of the electrode. The basic electrode&#;s arc length is not more than the electrode diameter and short arc welding is preferred. When using acid electrodes the arc length is equal to the electrode diameter.

Inverter Controls Used in MMA (Stick) Welding

Welding Current Control (A)

The current control regulates the amount of current output from the welding inverter and hence the deposition rate dependent on the electrode diameter.

Often current can be controlled via remote controls on more modern electronic welding inverters.

Hot Start

&#;At the start of welding the hot start provides an increased amount of current to enable the electrode to strike the arc without sticking to the work piece. Some machines have an automatic hot start current with a set time and level others have variable hot start control for an operator to select.

Arc Force

During welding the arc voltage is normally in the region of 20V. Often the situation may demand a shorter arc which results in a lower voltage and the electrode is prone to &#;sticking to the work piece&#; as the arc has actually extinguished. The arc force control will overcome this problem by increasing the current when the arc voltage falls to ensure the metal transfer of the electrode and prevent the electrode sticking. Some machines have an automatic arc force current others have variable arc force control for an operator to select the required level.

MMA (Stick) Welding Problems

What Does MMA Mean in Welding?

MMA stands for manual metal arc, a style of welding in which an electric arc burns between the electrode flux coated metal rod and the workpiece, which both melt to create the weld. It&#;s one of the most popular and commonly utilised arc welding techniques around. It may also be referred to as shielded metal arc welding (abbreviated to SMAW), flux shielded arc welding and stick welding. Amongst other things, it is commonly used to weld steel and iron. Today, we&#;re going to take a closer look at MMA welding, how it works, and what it&#;s used for.

What is MMA Welding?

In MMA welding, an electric current flows through a metal electrode, or &#;stick&#;, forming an arc between the end of the flux coated electrode and the workpiece. The arc melts both the metal on the workpieces that are to be joined (the base metal) and the metal in the rod (the filler metal). As the melted filler metal is ejected from the rod, it coalesces with the melted base metal to form the weld. Since the electrode is constantly melting and becoming a part of the welded structure, MMA welding is a consumable electrode process.

As the electrode is heated, the flux coating releases protective gases that help to shield the weld and stabilise the arc. The remaining coating melts and covers the weld with a protective layer of slag that aids in shaping &#; but it must be removed once the weld has solidified. Since the gases produced by the flux coating completely protect the weld, there&#;s no need for other shielding equipment like regulators or hoses. This means that, in comparison to other welding processes, MMA welding equipment is often simplistic, and the quality of the weld will be determined by operator skill. 

MMA Welding Power Sources

As mentioned earlier, MMA welding equipment is often very straightforward, sometimes as simple as only having two controls on the machine &#; one for current and one for polarity. Two insulated wires and connected to the welding machine. One lead ends in a clamp that is attached to the workpiece &#; this is called the work lead. The other wire leads to an electrode holder, which grips the end of the electrode that isn&#;t coated in flux.

Polarity

The polarity of the MMA welding setup determines how the electricity flows to the workpiece and back to the machine. The current will either be in AC or DC. In AC, the directional flow of electricity constantly changes between the leads, but in DC, one lead is always positive and the other negative. MMA welding regularly uses DC, but it is best to check your welding machine manufacturers guidelines to ensure you&#;re operating with the correct polarity.

Electrodes in MMA Welding

MMA welding electrodes can be made from various metal alloys and flux compositions. When choosing an electrode for stick welding, you&#;ll need to consider the following:

• Is it going to be strong enough?
• Is it compatible with the base metal it will be fusing with?
• Is it compatible with the position of the joint you want to weld?

To make choosing the correct electrode for your application easier, each stick will have a classification code printed onto the flux. This code will denote tensile strength, the flux coating type and the correct welding position.

The chemical composition of the flux material can significantly influence the weld. There are three main groups of electrodes used in MMA welding:

Cellulosic Electrodes

These contain a high level of cellulose in their flux coating, allowing for deep penetration in all positions and a rapid burn off for high welding speeds &#; but as a result, de-slagging can be difficult.

Rutile Electrodes

These electrodes contain a high proportion of titanium oxide, promoting efficient arc ignition and low spatter. In addition, they offer moderate tensile strength, a good bead and easily removable slag.

Basic Electrodes

Basic electrodes contain high levels of calcium carbonate &#; limestone &#; and calcium fluoride. These electrodes are suitable for medium and heavy fabrications where a high-quality weld with good resistance to cracking is required.

Gas in MMA Welding

With MMA welding, you do not need a separate gas, as the electrode flux forms a gas shield as it melts, protecting the molten weld pool and the base metal. This can be convenient, particularly for amateur welders, as you will require less equipment to get started &#; however, there are downsides to this method.

Deposition rates in MMA welding are low. This rate refers to the amount of useable weld metal that can be deposited onto the base metal continuously without breaks for electrode changing or de-slagging. As a result, MMA has largely been replaced with MIG/MAG welding. You will require gas for MIG welding, but the deposition rates are better, and you&#;ll get good penetration, strong fusion and a nice weld appearance with minor spatter. In comparison, MMA welds are often less visually attractive. If you&#;re interested in learning more about MIG welding, take a look at our top tips for MIG welding beginners.

Here at Bottle Gases, we stock a range of welding consumables suitable for various welding styles. We&#;re also reputable bottled gas suppliers and can supply both hobbyist and professional welders with the gas they need for whichever type of welding you&#;re working with. Contact us today for more information about 3.9kg propane, 4.5kg butane and more.

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