Functionality of the MMA welding method

Synonymous terms for the MMA method (Manual Metal Arc Welding) it: 

• submerged arc welding; 
• SMAV welding; 
• 111 welding. 

How should arc welding be carried out? 

SMAV manual arc welding is a process in which a permanent connection is achieved by melting the weld material with an arc of a fusible covered electrode, with the help of heat. The mechanism of welding with a covered electrode begins when the act of so-called contact, i.e. contact between the weld material and the end of the electrode, occurs. The electrode then begins to melt, while the droplets of molten metal fuse together to form a weld pool, which turns into a weld when it cools down. A very important aspect in the correct progression of this process is to precisely maintain an unchanged arc length, while moving the end of the electrode along the welding axis. The cladding will produce a gas that prophylactically protects the molten metal from external influences, which will form a slag cluster on the metal surface. The resulting slag should be tapped with a hammer at the end of the work to remove it from the metal surface. The end of welding is marked by the removal of the covered electrode from the work piece, as the electric arc is then interrupted. 

Basic functions of the lagging: 

• the formation of a slag film over the solidifying weld metal and the liquid pool; 
• prophylactic shielding of the arch against the weather; 
• adjustment of the chemical composition of the weld; 
• the introduction of nitrogen-fixing, deoxidising and liquid metal refining elements into the resulting weld. 

The above functions essentially serve to ensure the performance properties and the required quality of the welded joint. 

Equipment required for MMA arc welding: 

• welding transformers; 
• welding generators; 
• rectifier welding power supplies; 
• welding inverters. 

Types of arc electrodes 

We can divide arc electrodes into four basic types, distinguished by the lagging used in them: 

• (A) - Acid electrodeselectrodes in which the coating consists of iron oxides and deoxidisers. These electrodes are only dried if there are problems with welding or efflorescence. They are ideal if you want to achieve a smooth and flat weld. 
   
• (B) - basic electrodesThe lagging consists of magnesium and calcium carbonates and fluorites. The butt weld produced with these electrodes is distinguished by its high resistance to potential cracking. It should be noted, however, that a disadvantage of these electrodes is that they must be dried for about two hours at 300-350°C before welding. 
   
• (C) - cellulose electrodeselectrodes in which the coating is made of cellulose and deoxidisers. The advantage of these electrodes is that they contain very little water, so they do not dry out before use and are therefore perfectly suited to demanding field work (e.g. welding of pipelines). 
   
• (R) - rutile electrodesThey are the most versatile of the electrodes available on the market, easy to use, have a smooth weld deposit and usually do not require drying. These are the most versatile electrodes on the market; they are easy to use, slag comes off easily, they have a smooth weld and usually do not require drying. The negative side of their construction, however, is their relatively brittle surface. 

• (RA) - rutile-acid electrodeswhich combine the basic features of rutile and acid electrodes. 
   
• (RB) - rutile-base electrodeswhich combine the basic features of rutile and basic electrodes. 
   
• (RC) - rutile-cellulose electrodeswhich combine the basic features of rutile and cellulose electrodes. 
   
• (RR) - rutile-thick electrodeswhich have the basic features of rutile electrodes, but are characterised by a greater lagging thickness. 

Preventive storage of arc electrodes 

A characteristic feature of the electrodes is their hygroscopicity, due to which they should be stored in a dry room, preferably at room temperature. The alkaline electrode type (B) absorbs water the fastest, even from the air, so it is advisable to additionally place it in a special thermos at the temperature recommended by the manufacturer. Electrodes should not be removed from the original packaging in which they are received, nor should they be stored in stacks. 

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