SMAW Equipment (Shielded Metal Arc Welding- commonly called “stick welding”, or “arc welding”) How a “Buzz Box” works: Terms and Theory • Typical SMAW machine (arc welder, buzz box) Electrons- what we need for Electricity! Electrons are negative. And remember… opposites attract. Electrons- defined Electron- electrons are negatively charged particles that move through a conductor when current is flowing. Because electrons carry a negative charge, electron theory states that they are attracted by positively charged bodies and therefore move from negative to positive. Circuits- defined Circuit- Any system of conductors that is designed to complete the path of an electric current is called a circuit. Current flows in the conductor when voltage is applied to it. Circuits – power via wall outlet Current Flow- Measured in Amperes (Amps) Current flow is the movement of electrons. The greater the number of electrons, the higher the measure of Amps. Amperage- defined Amperage (heat setting) - the strength of a current of electricity measured in amperes. This is the electrical property that causes the electrode, the parent metal, or both, to be melted. High Amps= quick metal deposit and deep penetration Low Amps = slower deposit rate and less penetration Voltage- defined Voltage- Voltage is the electrical pressure or force that causes current to flow in a conductor, or to cross a gap, as occurs in welding. Voltage is often called EMF, which stands for electromotive force. (Battery example) Voltage in arc welding is responsible for the following: - Starting the arc - Maintaining the arc - Puddle fluidity and puddle flow (the amount of voltage is determined by the type and size of electrode being used) Voltage-Amperage relationship.. Voltage pushes Amperage through resistors (Ohms Law) Arc- In welding, an arc is created when there is enough amperage and voltage available at the electrode tip to overcome the natural resistance to the flow of electricity. This resistance is usually caused by the air gap between the electrode and the work. Resistance- defined Resistance- Resistance is the property of an electrical conductor to oppose the flow of current, causing electrical energy to be turned into heat. Resistance is measured in ohms. The air gap offers resistance to current flow. It is this resistance to the flow of current across the arc that creates the heat needed for welding. Alternating Current- Defined Alternating Current (AC) - Current that flows in one direction during any half cycle, then reverses and flows in the opposite direction during the next half cycle. The rate at which this alternating occurs is measured as cycles per second (60 cycle AC is common). Frequency- Frequency relates to the speed at which alternating current changes its direction of flow. A high frequency current is used in some welding processes to allow for non-touch arc starting or to provide a path for the weld current to follow. Direct Current (DC) Direct Current (DC) - Electric current that flows in one direction only and has either a positive or negative value. There is no change of direction as there is with AC. The electron theory states that current flows from negative to positive since that is the direction that electrons flow in. Polarity Straight Polarity- In a SMAW DC welding circuit, straight polarity occurs when the electrode cable is connected to the negative terminal of the welding machine, thus making the electrode negative, in relation to the work-piece. Reverse Polarity- In a SMAW DC welding circuit, reverse polarity occurs when the electrode cable is connected to the positive terminal of the welding machine, thus making the electrode positive, in relation to the work-piece. SMAW Welding Machine (Buzz Box) Components Primary Coil- The primary coil on a welding transformer takes power directly from the AC input power line. The current flowing into the primary coil causes a magnetic field to form. Secondary Coil- the secondary coil is located on the main transformer core of an AC welding machine. The energy created in the magnetic field by the primary coil is induced into the secondary coil. Inductance- Inductance is the ability of a conductor to transfer current onto a neighboring body without physical contact. For example, in a transformer welder, current is brought to the primary coil where a magnetic field is created due to the iron core. The magnetic field induces current flow into the secondary coil without physical contact. Magnetic Field- A magnetic field is created when current is forced to flow through a coil that is wrapped around an iron core. The strength of the magnetic field determines the power capacity of welding machines. Movable shunt in relation to primary and secondary coils.. Core- The core is the magnetic link between the primary and the secondary coils of a welding transformer. The core can be moved into or out of the coil as a method of current control. This type of current control is called movable shunt. A movable shunt means that the core can be moved into different positions thus influencing the magnetic link between the primary and secondary coils. The shunt is usually moved mechanically by an external hand crank that controls its movement on a slide assembly. This allows for any setting between minimum and maximum of the machine’s output potential. Duty Cycle- All welding machines are rated based on maximum output over a ten-minute time period. This rating is expressed as a percentage of time that the machine can run at maximum rated output current before it must be allowed to cool down. Exceeding duty cycle ratings can damage or ruin a welding power source.