Shielded Metal Arc Welding Equipment & Setup

Shielded Metal Arc Welding Equipment & Setup

Shielded Metal Arc Welding Equipment & Setup Level 1 chap 7 Objectives When we have completed this chapter, you should be able to do the following: Identify and explain SMAW safety Understand welding current Understand welding machines Set up arc welding equipment for SMAW

Identify tools for weld cleaning 1.0.0 Introduction Shielding metal arc welding (SMAW) is often referred to as stick welding.

The welding process can use either alternating current (ac) or direct current (dc). The electrodes, also called rods, use a claylike coating called flux to provide a gas shield and a coating to protect the weld puddle from the atmosphere. The coating cools and hardens over the weld bead and is called slag. The slag is removed from the weld by chipping or brushing. 2.0.0 SMAW Safety

Welding is a dangerous profession, not because of the welding itself, but because of the environments in which the work is often performed. Primary safety concerns involve the following: Moving welding equipment Electrical hazards Lifting hazards Working at heights Welding hazards 2.1.0 Moving Welding Equipment

Engine driven machines may be mounted on the back of a truck, on a skid, or on a trailer and can easily be moved by a truck or forklift. Use caution when moving trailer mounted machine because they are top heavy and may tip over. There will be times when the welding machine

must lifted by a crane. Many welding machines have lifting eyes for this purpose. When lifting a welding machine, always use a shackle. 2.2.0 Electrical Hazards

Welding machines use electrical power. Most operate on 110v, 120v, 240v, or 480v. Electrical shock or possible death can result if you encounter the electrical power supplied to a welding machine. Make sure that all welding cables are in good condition and that your workpiece clamp is properly installed. 2.3.0 Lifting Hazards

Remember the basics of lifting whenever you must transport a welding machine. Get help if you must lift a heavy object by hand. Always remember to use tag lines when hoisting heavy objects that tend to spin or swing. 2.4.0 Working at Heights

Remember to always wear approved fall protection devices when working at heights of 6 or higher. Make sure to inspect your fall protection equipment each time you use it and be certain that it is current and up-to-date. 3.0.0 Welding Current

The arc that is produced during SMAW is current that jumps across the gap from the tip of the electrode to the surface of the workpiece. If the electrode tip is touched and held against the workpiece instead of allowing for a gap between the two, the electrode will pass the electricity directly to the workpiece without creating an arc. 3.1.0 Types of Welding current

SMAW welding machines are designed to produce an output of constant current (cc). The current may be AC or DC. The type of current used depends on the type of welding being done and/or the equipment being used. 3.1.1 AC Welding Current

Alternating current (AC) in welding machines is derived from either a transformer-type machine or an alternatortype machine. The transformer changes high-voltage, low current AC power to low voltage, highcurrent power for welding. The alternator uses an electric or fuel driven motor to turn a rotor inside a number of electromagnets to produce the welding current. 3.1.1 AC Welding Current

AC current alternates between positive and negative values only because the voltage changes from positive and negative values. In one complete cycle, the wave crosses the axis or zero point twice. The number of cycles completed in one second is called the frequency. The standard frequency in the U.S. is set

at 60 cycles per second. 3.1.2 DC Welding Current Direct welding current (DC) has no frequency. Direct current in welding is derived either from a transformer-rectifier type system or from a generator. In a transformer-rectifier type system, AC

voltage first is reduced (transformed) to lower voltage level through the application of a transformer and then converted (rectified) into DC voltage Most engine driven SMAW welding machines produce DC current through a generator. 3.2.0 Polarity

Polarity only applies to DC current. Polarity in welding is determined by the way the welding leads are connected to the welding machine. The universally accepted theory is that DC current always travels from the negative to the positive pole. The plus marked terminal on the welding machine is the positive terminal. The minus marked terminal on the welding machine is the negative terminal 3.2.0 Polarity

When the electrode holder lead is connected to the plus or positive terminal on the welding machine and the lead with the ground clamp is connected to the minus or negative terminal this is direct current electrode positive (DCEP or DC+) If the leads are switched this is direct current electrode negative (DCEN or DC-) 3.2.0 Polarity

DCEN generates more heat in the work piece than at the electrode and is used for GTAW DCEP puts more heat at the electrode than at the work piece. 3.3.0 Characteristics of Welding Current

The voltage in a welding machine, whether the machine is connected to commercial power or driven by an engine, is reduced or stepped down by a transformer called a step-down transformer. The step-down transformer reduces the voltage level and raises the current level. 3.3.1 Voltage

Voltage is the measure of the electromotive force or pressure that causes current to flow in a circuit. Two types of voltage are associated with welding current: Open-circuit voltage Operating voltage Open-circuit voltage is the voltage present when the welding machine is on but no arc is present.

3.3.1 Voltage Operating voltage, or arc voltage, is the voltage measured after the arc is struck. The higher open-circuit voltage is required to establish the arc because the air gap between the electrode and the work has higher resistance to current flow. Once the arc is established, less voltage

is needed. 3.3.2 Amperage Amperage is a measurement of the electric current flowing in a circuit. The unit of measurement for current is the ampere (amp or A).

The number of amps produced by the welding machine determines the amount of heat available to melt the electrode. The current is increased or decreased according to the size of the electrode being used and the position in which the welding is being performed. 4.1.0 SMAW Machine Classifications SMAW machines are classified by the type of welding current they produce:

AC, DC, or AC/DC Welding machines that produce only DC welding voltage and current can be further classified by the characteristics of the welding current they produce. 4.1.0 SMAW Machine Classifications If the welding current varies between the higher open-circuit voltage and the lower operating voltage, it is classified as a variable-voltage constant-current machine. This type machine is used for SMAW and tig welding (GTAW). If open-circuit and operating voltage are

nearly the same, the machine is classified as a constant-voltage DC welding machine. This machine type is used for GMAW and FCAW. 4.2.0 SMAW Machine Types Several different type of basic SMAW welding machines are available. They include: Transformers

Transformer-rectifiers Inverter Engine driven generators Transformer, transformer-rectifiers, and electric motor generators all require electrical power from commercial power lines to operate called the primary current. The primary power required for this type machine is 240-volt single-phase or 480-volt

4.2.1 Transformer Welding Machines Transformer welding machines without rectifiers produce AC welding current. They use a voltage step-down transformer, which converts highvoltage, low-amperage current from commercial power lines to lowvoltage, high-amperage welding current. 4.2.1 Transformer Welding Machines

Special light-duty transformer welding machine s used for sheet metal work are designed to be plugged into 120-volt outlet. However, most light-duty transformer welding machines operate more efficiently on 240V primary power. A transformer welder called a buzz box has an ON/OFF switch, an amperage control and weld lead terminals.

6.1.0 Transformer Welding Machines 4.2.2 Transformer-Rectifier Welding machine A rectifier is a device that converts AC current to DC current. Depending on their size, transformerrectifier machines require 240-volt three-phase or 480-volt three-phase.

Multiple transformer rectifiers are available grouped into a single cabinet called a pack. 6.2.0 Transformer-Rectifier Welding machine 4.2.2 Transformer-Rectifier Welding machine Break Time 15 minute break

4.2.3 Inverter Power Source Inverter power sources increase the frequency of the incoming primary power. This provides a smaller, lighter power source. An inverter supports both GTAW and SMAW processes

4.2.4 Engine Driven Generator and Alternator Machines Welding machines can also be powered by gasoline or diesel engines. The engine can be connected to a generator. Engine-driven generators produce DC

welding current. 4.2.4 Engine Driven Generator and Alternator Machines Engines that power generators have governors to control engine speed. Most governors have a welding speed switch The governor will automatically

increase the speed of the engine for welding when the electrode is touched to the base metal and slow the engine when no welding has been done for 15 seconds. 4.2.4 Engine Driven Generator and Alternator Machines Engine-driven generators often have an auxiliary power unit to produce 120-volt current for power tools and

lighting. When 120-volt current is required the engine must run at welding speed. 4.2.4 Engine Driven Generator and Alternator Machines Engine-driven weld machines have engine control and welding current controls. Some of the basic controls are: Starter Voltage gauge

Temperature gauge Fuel gauge Hour meter Many engine-driven machines are mounted on trailers, which makes them portable so they can be used in the field. 6.3.0 Engine Driven Generator and Alternator Machines 4.3.0 SMAW Machine Ratings

The size of a welding machine is determined by the amperage output of the machine at a given duty cycle. The duty cycle of a welding machine is based on a ten-minute period. It is the percentage of ten minutes that the machine can continuously produce its rated amperage without overheating.

4.3.0 SMAW Machine Ratings For example: A machine with a rated output of 300A at 60% duty cycle can deliver 300A of welding current for six minutes out of ten without overheating. The duty cycle of a welding machine

will be 10%, 20%, 30%, 40%, 60%, or 100%. If the amperage is set below the rated amperage, the duty cycle will increase. 4.4.0 Welding Cable

The conductors inside the cable are made of fine strands of copper wire. The copper strands are covered with layers of rubber reinforced with nylon or dacron cord. The size of a welding cable is based on the number of copper strands it contains. Typically the smallest cable size is #8 and the largest is 4/0 (4 aught). The larger cable has more copper so it can carry more current. 4.4.0 Welding Cable

4.4.0 Welding Cable The longer the distance the current has to travel, the larger the cable must be to reduce voltage drop and heating caused by electrical resistance. When selecting welding cable, consider the rated capacity of the welding machine and the distance to the workpiece.

4.5.0 SMAW Cable Connections End connections used on welding cables include: Lugs Quick disconnects Ground clamps Electrode holders 4.5.1 Lugs and Quick Disconnect

Lugs are used at the end of the welding cable to connect the cable to the welding machine. Lugs come in various sizes to match the welding cable size and are mechanically crimped onto the welding cable. These lugs are normally ringed to prevent the welding lead from pulling loose from the stud connector on the machine. 4.5.1 Lugs and Quick Disconnect

4.5.2 Workpiece Clamps 4.5.3 Electrode Holders Workpiece ground clamps establish the connection between the workpiece and the welding lead. The size of the ground clamp is the rated amperage that it can carry without

overheating. Electrode holders grasp the electrode and provide the electrical contact between the electrode and the welding cable. The physical size of the holder is proportional to is its amperage capacity. 4.5.2 Workpiece Clamps 4.5.3 Electrode Holders 5.1.0 Selecting the proper SMAW Equipment To select the proper SMAW machine,

the following factors must be considered: The welding process SMAW requires a constant current (cc) power source The type of welding current AC or DC The maximum amperage required consider the composition of the material, and its thickness The primary power requirements is there power available and what type 5.2.0 Welding Location Machine

The welding machine should be located near the work to be performed but out of the way of workers. The area should be free from explosive or corrosive fumes and be free as possible from dirt and dust. If an engine-driven machine is used it should be located so it can be easily refueled and serviced.

5.4.0 Stringing Welding Cable Before stringing welding lead check it for cuts or breaks in the insulation Welding cable must be strung to prevent tripping hazards or damage from traffic. If welding cables must cross a

walkway, string them overhead When stringing cables overhead, use rope to tie off the cables 5.5.0 Locating the Workpiece Clamp The workpiece clamp must be properly located to prevent damage to equipment If the welding current travels through

any type of bearing, seal, or valve it could cause severe damage from arcing, which would require the part to be replaced. Welding current passing through electrical or electronic equipment will 5.5.0 Locating the Workpiece Clamp

If welding near a battery, remove the battery. Batteries produce hydrogen gas, which is extremely explosive. A welding spark could cause the battery to explode Ground clamps must never be connected to pipes carrying flammable or corrosive materials 6.1.0 Energizing Electrical Welding Machine

Electrical requirements for electrical welding machines will be on the equipment tag on the machines Most machines will require singlephase 240-volt current or three phase 480-volt current 240-volt power requires a 3 prong plug 480-volt power requires a 4 prong plug

6.1.0 Energizing Electrical Welding Machine 6.2.1 Starting Engine Driven Welding Machines Many facilities will have prestart up check list that must be completed be operating a engine driven equipment

Check the oil, coolant and fuel be starting a engine Engine-driven welders should be allowed to warm up 5 10 minutes before they are needed for welding 6.2.3 Stopping the Engine 6.2.4 Preventive Maintenance 6.2.3 - If no welding is required for 30 or

more minutes, stop the engine by turning off the ignition switch. 6.2.4 Engine-driven welding machines require regular preventive maintenance to keep the equipment operating properly. Most sites will have a preventive maintenance schedule based on hours the engine operates. 7.1.0 Tools for Cleaning Welds

It is extremely important that the base metals are thoroughly cleaned and prepared before welding. Many mechanical methods have been developed to clean metal However, many welders prefer simple manual procedures using tools such as files, wire brushes, and chipping hammers. 10.0.0 Tools for Cleaning Welds 7.2.0 Pneumatic Cleaning and Slag Removal Tools

Weld slag chippers and needle scalers are pneumatically powered. Weld slag chippers and needle scalers are also excellent for removing paint or hardened dirt but are not very effective for removing surface corrosion.

Weld slag chippers have a single chisel Needle scalers have about 18 to 20 10.2.0 Pneumatic Cleaning and Slag Removal Tools Summary Shielded metal arc welding is often referred to as stick welding and remains one of the most widely used

forms of welding in the industry because of its simplicity and low cost. Proper selection and set up of equipment is necessary in order to achieve a reliable weld while maintaining a safe work environment. The End Review questions 1 15 Trade Terms Quiz on pg 7.22

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