SMAW EQUIPMENT Prayer Heavenly Father and Your Beloved Son Jesus Christ, We thank you for giving us another life, We thank you for another Beautiful Morning. As we go on through our lessons today, May you make us instruments to do good things. Please enlighten our minds, Give us the strength to participate in our subject today. Thank you for this opportunity to learn and serve others, and help me to always remember the Truth of Your Glory! In Jesus’ name. Amen SHILEDED METAL ARC WELDING Shielded metal arc welding (SMAW) is often the first welding process learned by the new welders. SMAW is extremely versatile and it can be used for so many types of applications. Though it requires a electrical power source, the equipment is fairly simple and inexpensive, making it well suited for welding practice, repair welding, and inthe-field welding. SHILEDED METAL ARC WELDING SMAW can weld carbon steel, low and high-alloy steel, stainless steel, cast iron, and ductile iron. While it is less popular than other processes for welding nonferrous materials. It can be used on nickel, copper, and aluminum alloys. ELECTRICAL PRINCIPLE ELECTRICAL PRINCIPLE • When welding using smaw, an electrical circuit is created. An electrical circuit is a path taken by electric current flowing from one terminal of the welding machine, through a conductor, and to the other terminal. Current is the amount of electron flow through an electrical circuit. • A conductor is any material through which electricity flows easily. Conductors can be found in the form of wire, cable, or busbars. • A person can act as an conductor of electricity when not following proper safe practices. WELDING CURRENT Welding Current • The melting rate of an electrode is affected most directly by welding current when current moves through a wire, resistance to the flow of electricity generates heat. The greater the current flow, the greater heat generated. • The generated during the SMAW process comes from an arc that develops when electricity jumps across a gap between the end of an electrode and the base metal. • The gap produces a high resistance to the flow of current. This resistance generates intense heat that can range from 6,000°F to 10,000°F . VOLTAGE VOLTAGE • Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential between two points, which is defined as the work needed per unit of charge to move a test charge between the two points. • Travels in a straight line, and in one direction only. • Commonly produced by sources of stored energy such as batteries. • Sources of dc voltage have positive and negative terminals. Terminals establish polarity in a circuit, and polarity can be used to determine if a circuit is dc or ac. • Commonly used in battery-powered portable equipment (autos, flashlights, cameras). VOLTAGE • Voltage drop is the decrease of electrical potential along the path of a current flowing in an electrical circuit. Voltage drops in the internal resistance of the source, across conductors, across contacts, and across connectors are undesirable because some of the energy supplied is dissipated. • Open circuit voltage (usually between 80v and 100v for industrial power source) is voltage produced when a welding machine is ON but no welding is being done. High open-circuit voltage aids in an arc starting. Arc voltage is the present after an arc is struck (usually between 10v to 35v). WELDING MACHINE OUTPUT WELDING MACHINE OUTPUT Welding machine output can be alternating current o(AC) or direct current (DC) or alternating current / direct current (AC/DC), depending on the welding task. See the figure of the electrode used must match the current produce by the welding machine. Alternating Current • AC current output provides a constantly alternating current that can be used for SMAW welding. AC current allows a welder to easily maintain an arc during welding. Other features of AC current include low operating and maintenance cost. And high overall electrical efficiency. AC welding machine typically operates on single-phase primary power • The electrode and work cables can be connected to either output terminal on AC-only welding machines. Direct Current • DC current output for SMAW may use single-phase or three-phase primary electrical power. The most stable DC welding is provided by welding machines that provides three-phase transformers and full-wave rectifiers. • DC output welding machines have output terminals identified as positive (+) and negative (-). If they have a polarity switch, the output terminals are identified as work and electrode. AC / DC (Alternating Current / Direct Current) • AC/DC current output is available on constant current welding machines that typically operate using a primary power source. The main difference between AC and AC/DC output for SMAW is that AC/DC contains rectifier. Rectified welding power is not as stable as rectified three-phase DC welding power. • AC/DC welding machine are commonly used for SMAW. CONSTANT CURRENT WELDING MACHINE CONSTANT CURRENT WELDING MACHINE • This type of power sources is used with manual processes like Shielded Metal Arc Welding (SMAW) and Gas Tungsten Metal Arc Welding (GTAW), Plasma Arc Welding (PAW), as well as with some Submerged Arc Welding (SAW) applications. Constant current power sources are sometimes called droopers because the volt-ampere curve that demonstrates the relationship between output voltage and output current is steep. See also Welding Power Source and Constant Voltage Power Source. STATIC POWER SOURCES Static Power Sources • Static power source used in a welding machine have no internal moving parts. They convert power from a utility line to the power needed for welding. Utility line power is typically supplied by a local utility company. Common static power sources include transformers, transformer-rectifiers, and inverters. • Based on the welding task, the welding leads are connected to the terminals on the front of the welding machine to supply the desire welding current • Depending on how the leads are connected, current is supplied for electrode positive or electrode negative. TRANSFORMERS • Transformer welding machines are the most economical type of arc welding machine when used with proper electrodes, they can produce quality welds for a large number of welding fabrications and repair applications. A transformer is an electrical device that changes AC voltage from one level to another. In welding machines, a transformer is used to transform a high voltage and low-current input into a safe and useable low voltage and high current output. TRANSFORMER RECTIFIER • Transformer rectifier welding machines are capable of producing constant DC. They contain a transformer, reactor, rectifier and choke or inductor. Singlephase input welding machines commonly produce AC/DC output. Three-phase welding machines are typically DC output. DC produces the highest quality SMAW welds. DC is also required for many electrode including most code-quality arc welding electrode. INVERTERS • An inverter welding machine converts alternate current to a lower usable voltage output. For instance, from 240V AC power supply to 20V DC power output. Inverter-based appliances use a couple of electronic parts to transform power. • An inverter operates by increasing the primary power supply frequency from 50Hz up to 20,000 – 100,000Hz. • This is done using the electronic buttons that switch the power on and off fast (up to one-millionth of a second). By using this way to control the power supply before it gets into the transformer, the size of the transformer can be greatly lessened. Inverter Arc Welding Machine posses the following Advantages Compact and Lightweight Model • Because of its minimal design, you can the inverter welding machine nearly everywhere. As compared to other conventional welding machines, these welders are compact. You can stow them in any compact space, thanks to the device’s space-saving structure. IGBT Techniques • These inverter welding machines can quickly gather power using any gate current appliance. This is possible because of its insulated gate bipolar transistor technology. The inverter welder’s switch also operates fast and uses less energy to do the final operation. Inverter Arc Welding Machine posses the following Advantages Output Voltage and Present Stability Many traditional welding machines use alternating current (AC) and, therefore, these appliances don’t get continuous current and power output. In such a case, these machines’ arcs need several re-ignitions, around 100 to 120 times every second. Contrary to conventional welding machines, the inverter welder doesn’t take long to generate heat. Cooling Facility These brilliantly made inverter welding machines have an inner cooling fan. It lessens operating heat and stops extra heat from being produced. With the help of cooling fans, not only do machines stop overheating, but also lead to an increase in the life expectancy of the devices. Inverter Arc Welding Machine posses the following Advantages Efficiency and Power Saving • Not only are inverter welding machines energy-efficient, but also back stress-free and no-cost connection. These inverter welders are a perfect replacement for conventional welders when it comes to generating heat and consuming energy. Better Efficiency • With the inverter welding machine, you can adjust the weld bead profile as per the thickness you require. Inverter welders improve the appearance of the weld and at the same time maintain the welding quality. ENGINE DRIVEN POWER SOURCE Engine Driven Power Source – Provides welding current and auxiliary power for many welding applications. They play a critical role in producing the highquality welds required in construction sites, bridges, and cross-country pipelines and for fields repairs o heavy agricultural, construction, mining, and military equipment. The Main Advantages of each Type of Engine Include the Following: • Gasoline Air-Cooled – Lightweight, less expensive • Gasoline Water-Cooled – High Current, Long Hours • Propane Air-Cooled – In-plant welding, underground welding • Diesel Air or Water-Cooled – High current, long hours, fuel efficient In addition to the selection of engine type, the type of power generation equipment is taken into construction. WELDING MACHINE RATINGS Welding Machine Ratings • Welding machine ratings – are rated (sized) according to their current at voltage output at 60% duty cycle, such as 150 A, 200 A, 250 A, 300 A, 400 A, 500 A, or 600 A. • The rating is the current output at the working terminal. Thus, a machine rated at i50 A can be adjust to produce a range of power up to 150 A. The welding machine rating required is determined by the type of welding performed. A general guide to welding machine rating (size) and service is as follows: • 150 A – 200 A, Light to medium duty welding. Excellent for all fabrication purposes, and rugged enough for continous operation on light or medium production work. • 200 A – 300 A, an average welding requirement used in plants for production, maintenance, toolroom work, and general shop welding. • 400 A – 600 A, Large capacity heavy duty welding. Used extensively in heavy structural work, fabricating heavy machine parts, heavy pie and tank welding, cutting scrap and cast iron, and for a wide range welding applications. RATED OUPUT CURRENT in AMPERES DUTY CYCLE • Duty cycle is the percentage of time that a machine will safely operate (or weld), within a certain time period, at a given amperage. For example the Weldforce WF205MST multi-function welder has a duty cycle of 200 Amps @ 30%. This means that it will operate at 200A for 3 minutes within a 10 minute time period. For the remaining 7 minutes, the machine will switch to thermal overload to cool down. • All welding machines are (or should be) fitted with thermal overload protection which means the machine will cut out when internal critical components reach a certain temperature, to prevent damage. The machine will then re-start when it returns to a safe temperature. DUTY CYCLE • Duty cycle will change at different amperages. At higher amperage output the machine will heat up more rapidly, and the duty cycle will reduce. At lower amperages, the duty cycle will increase. • For example - if we look at the WF-205MST machine again; • Duty cycle at 200 amps = 30% • Duty cycle at 145 amps = 60% • Duty cycle at 110 amps = 100% Check Point! The National Electrical Manufacturers Association (NEMA) has set a standard for duty cycle based on a 10 minutes period. The duty cycle standard expresses the actual operation time that a welding machine may be used at its rated load without exceeding the temperature limits of the insulation of the component parts. Thank you!
