Arc Welding
Arc Welding
Basic Technique of Arc Welding
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The technique of electric arc welding consists in the fusion of a metal at high temperature by using a differential of potential and value of determined electric current intensity. By means of this potential difference the air is ionized and the electrons are transported through the electrodes and the part to be welded. The heat generated (4000 C) melts both the base material and the filler material which is deposited and creates the so-called weld seam. The electrodes are also known as “input” material are coated with a non-metallic substance whose chemical composition is very varied (Cellulose, Titanium Oxide, Calcium Carbonate and Calcium Fluoride). Other types of electric arc welding are:
Arc Welding Process
Both the electrodes and the surfaces to be welded must be free of all types of contamination, as well as grease, dust, humidity and surface defects.
Knowing the relation intensity/voltage we can choose the characteristics of the arc. Generally, a voltage between 40 and 110 V is required; this voltage drops to maintenance values between 15 and 35 V.
Materials and Equipment
Welding machine (Power Supply), most of the workshops use welding machines with 220 V or 380 V sockets with ground line. The change of polarity is made only if the machine is turned off.
Materials and Equipment
When the electrode holder is not in use, it should never be left on the table or in contact with any other object that has a direct line to the surface where it is welded. The danger in this case is that the electrode holder, in contact with the ground circuit, causes a short circuit in the transformer of the equipment. Welding is not a risky operation if the appropriate preventive measures are respected. This requires a knowledge of the possibilities of damage that can occur in welding operations and a usual safety precaution by the operator.
Arc Welding Procedure
While holding the electrode over the joint, an electric spark occurs as the base and electrode melt, forming the weld bead. The appearance of a bright spot indicates that the metal has reached its melting point when this state is maintained.
Principle of arc welding
The principle of arc welding is based on the principle of raising the temperature to the melting point by using an electric arc.
It is the heating created by the resistivity of the metals through which electricity travels that raises the temperature at the welding point to the temperature required for melting the metal.
The welding station delivers an electric current (alternating or direct current):
– The part to be welded is connected to one pole and on the second pole it is an electrode that carries the electric current.
– The operator operates the electrode holder to bring the electrode to the surface of the part to be welded.
– The electric arc that is created causes the metal of the part to be welded to heat up and possibly melt the electrode.
Of course, if the electrode were to come into contact with the part to be welded, the device would be short-circuited, hence the characteristics and internal protections of the welding station.
Arc welding equipment
The arc welding equipment consists of an arc welding station which is an electrical generator connected by a cable to the part to be welded and by another to the electrode holder.
The welding electrode can be either a continuous wire: the welding wire, or a welding electrode of different metals and sizes depending on the metal to be welded and the type of electrode fusible (melting during welding) or non-fusible (without loss of electrode material during welding) in this case, a filler metal is required by the use of welding rods.
As the electric arc emits heat, but also a dazzling light arc, the welding mask is the basis of the protective equipment.
The variations of arc welding
Each metal having its properties in terms of melting point and oxidation rate; and each part having its thickness and malleability characteristics, arc welding is defined as:
– spot welding,
– welding to the coated electrode,
– semi-automatic welding,
– MIG-MAG welding,
– TIG welding,
– plasma welding.
The electrode holder
The electrode holder of the arc welder machine is a thermally and electrically insulated handle.
In this handle you attach a coated electrode (welding electrode) which will serve to create the electric arc at the desired location.
The welding electrode will melt as the electric arc raises its temperature; by melting, it deposits on the melting zone, its metal which becomes the filler metal of the weld and its coating which forms the slag.
Manual arc welding
Manual arc welding is a relatively unproductive and slow process. But it is very simple and flexible. In addition, the acquisition costs for the required equipment are low, so that it is mainly used in workshops and on construction sites. In terms of productivity, it only surpasses gas fusion welding. But it is very flexible and suitable for many applications. Although it is dependent on electrical energy, it can also be generated on construction sites with generators and does not have to be drawn from the grid.[7] It is suitable for all welding positions (overhead, falling, etc.) and many materials.Â
Metallurgical Composition
The metallurgical composition of the weld seam can be specifically influenced by selecting the appropriate cladding and core wire. With basic coated electrodes, weld seam qualities (especially strengths) can be achieved that exceed those of other processes. Poorly accessible joints are also relatively easy to reach with electro manual welding. The influence of wind on the protective effect of the shielding gases and slag is relatively low, so that it can be used well on construction sites.[8] It can even be used under water,[9] which is used, for example, for repairs to ships or drilling rigs.
Safety: the precautions to take
Arc welding therefore uses electrical current and generates a melting temperature of up to 4000 C.Â
For your safety, it is imperative to respect these instructions:Â
– Always wear appropriate protective equipment: goggles, gloves, a welding mask essential to protect you from the intensity of the light caused by welding.Â
– Wear appropriate clothing (cotton) to protect you from sparks, as well as a welder’s apron.Â
– Always work in a secure, clean and dry area. Beware of water: you use electricity. Keep away from any flammable product or material: think of sparks that can cause fire.
welding machine and the electrodes
The arc welding machine is actually an electric generator (just plug it into a 230V power supply). It is connected by two cables to the elements to be welded and to the electrode:
• Cable connected to the electrode: phase cable (often red), with an electrode holder.
• Cable connected to the elements to be welded: cable of mass (often black), with a clamp to fix on the elements to be welded.
The electrode is a rod coated with metal also called filler metal. Depending on the diameter of this rod (to be chosen according to the thickness of the elements to be welded), the welding machine must be set to deliver a DC or AC current of variable intensity.
Prepare the elements to be welded
• Clean the elements to be welded and brush them with the metallic boss.
• If necessary, at the level of the weld to be made, deburr the elements with a metal file, cutting their edges at an angle (so that they form a V when assembled), in order to increase the resistance of the weld.
• Install the parts to be welded on a clean and dry worktop, not electrically conductive.
• Secure them with clamps. Â
Set and prepare the welding machine
• Always read carefully the instructions for your welding machine, to adjust it to the required intensity depending on the electrode rod used.
• Attach the ground clamp to the workpieces.
• Attach the coated electrode to the electrode holder: read the instructions on the packaging of your electrodes as all the electrodes do not connect in the same way.
Prime the electrode arc
• Equip gloves, welder’s apron, and mask.
• Turn on the welding machine.
• Prime the solder arc by rubbing the tip of the electrode on the workpiece to produce sparks.
• Move the electrode a half centimeter to create the electric arc.
• Once the arc has been established, move the electrode 2 to 3 mm closer to the area to be welded and begin welding.
Perform the arc welding
• When welding, always keep a few millimeters of space between the workpiece and the electrode: the length of the electric arc (in between) must be equal to the diameter of the electrode.
• Keep the electrode inclined at 60 � C to the workpiece.
• Always follow the same direction of movement to avoid weakening the weld: work from top to bottom and lower your hand as the electrode wears out.
• You must make a regular weld bead, with identical and curved waves, with a width equal to 2 times the diameter of the electrode.
Finishes
• Allow the welded parts to cool well: the slag formed by melting and the oxidation of the electrode will solidify.
• Remove the slag using the prick hammer.
• Brush the welded parts with the wire brush to remove the excess.
• You can tidy up with the file or the grinder, to obtain a smooth surface.
General recommendations for arc welding
Before starting any arc welding operation, a complete inspection of the welder and the area where it will be used should be done. All objects susceptible to burning must be removed from the work area, and there must be an appropriate extinguisher of Dry Chemical or CO2 powder at hand, but not before remembering that sometimes you can have mechanical foam hose.
The switches of the machines necessary for welding must be able to be disconnected quickly and easily. The power supply will be disconnected as long as it is not welding, and it will have a ground connection. It must have a differential circuit breaker that covers the electrical installation that feeds the welding equipment.
The electrode holders should not be used if the cables are loose and the clamps or insulators are damaged. There should be no points of false contact (or poor contact), to avoid heating zones or arc breaks.
The welding operation must be carried out in a well ventilated place. The roof of the place where it is welded will have to be high or have an adequate ventilation system.
Personal protection equipment
The radiation of an electric arc is enormously damaging to the retina and can cause cataracts , partial loss of vision, or even blindness. The eyes and face of the welder must be protected with an approved welding helmet equipped with an appropriate grade filtering visor. Welding mask filters must comply with UNE EN 175 “Individual Eye Protection Facial and Eye Protectors for Welding and Related Techniques”.
The appropriate clothing to work with arc welding should be loose and comfortable, resistant to temperature and fire. It must be in good condition, without holes or patches and clean of fats and oils. Shirts must have long sleeves, and pants must be long, accompanied by insulating shoes or boots that cover. It is recommended leather clothes type discarded and gloves of long sleeves to avoid burns by drops of molten metal.
Above all, electric shocks, which can be fatal, should be avoided. To do this, the equipment must be properly insulated (cables, tongs, electrode holders must be insulated), as well as dry and free of grease and oil. The welding cables must be kept away from the electrical cables, and the soldering iron separated from the ground; either by a rubber mat, dry wood or by any other electrical insulator. Electrodes should never be changed with bare or wet hands or with wet gloves.
