Presentation on theme: "Unit Objective: SWBAT Identify and explain SMAW equipment."— Presentation transcript:
Unit Objective: SWBAT Identify and explain SMAW equipment.
Shielded metal arc welding (SMAW) is often referred to as stick welding. This welding process can use either alternating current (AC) or direct current (DC). The electrodes (rods) that are used have a coating called flux. During the welding process the flux forms a gas shield that protects the weld puddle from atmospheric contamination. SMAW is currently used in a wide variety of industry applications.
What does SMAW stand for? A.) Shielded Metal Arc Welding B.) Strong Metal Attaching Weld C.) Shielded Material Air Welding D.) Safe Metal Arc Welding
Welding can be a dangerous profession, not so much because of the welding itself, but because of the work environment where the work is often performed. SMAW has its own safety precautions that need to be taken when it is used. UV Radiation Hot metal and slag Flying sparks Smoke and fumes Electrical hazards PPE for SMAW includes but is not limited to: Safety glasses Welding helmets shade Gloves Welding Jacket
ARC Welding machines use electrical power. Most machines operate on 110V, 120V, 240V, or 480V power levels. Regardless of the voltage level, it is important to be aware of the electrical power source used by your machine. Another concern wile using electricity is moisture, especially water. Electricity, water, and the human body are a dangerous mix. Make sure that your welding cables are in good condition and that your work piece clamp is properly installed.
Welding machines operate on which voltages? A.) 110V B.) 240V C.) 480V D.) All of the above
When the term current is used as a noun, in means a flow or a stream. In electrical terms current is the flow of electricity from one point to another. One point being a ground and the other being a source of electricity. In welding there must be current flow between the work piece and the welding machine. The arc that is produced during SMAW is an electrical current that jumps the gap from the tip of the electrode to the surface of the work, as long as the work piece lead from the machine is attached to the work. If the electrode is held against the work piece instead of allowing for a gap the electricity will pass directly from the electrode to the work without creating an arc. No welding can take place with out an arc across the gap to create the heat necessary to melt the electrode and the work piece.
There are two types of welding current used. Alternating Current (AC) Direct Current (DC)
The most commonly used form for SMAW is Direct Current (DC). In which the current always flows in one direction, from negative to positive. With DC we have polarity. Polarity is determined by the way the welding leads are connected to the machine and work. By swapping the electrode and work leads we can change the polarity. SMAW is most often done with Direct Current Electrode Negative (DCEN), but can also be used with Direct Current Electrode Positive (DCEP).
The other and more seldom used is Alternating Current (AC). In AC the current still flows from negative to positive, but the positive and negative poles alternate back and forth. A cycle is when the pole switches from positive to negative and back to positive. The number of cycles per second is called the frequency and is measured in Hertz. The frequency of AC is determined by the generator producing the current. In the United States the standard frequency of AC is 60 Hertz.
What are the two types of welding current? A.) Amperage and Voltage B.) Negative and Positive C.) Direct and Alternating D.) Polarity and Frequency
If the tip of the electrode is held directly against the work piece, A.) Welding will take place. B.) No welding will take place. C.) The arc will be twice as hot. D.) The electrode will not get hot.
When the SMAW machine is set to DCEN, the current flows A.) From the work to the electrode. B.) From the electrode to the work. C.) Both to and from the electrode. D.) Depends on the electrode used.
SMAW machines can come in many different shapes and sizes. The size of a welding machine is determined by its duty cycle. The duty cycle of a welding machine is based on its ability to produce its rated amperage over a 10 minute period without over heating. Example, a 200amp machine that has a 60% duty cycle can produce 200amps for 6 minutes out of 10 without over heating. Running a machine above its rated amperage will reduce its duty cycle.
Work piece clamps often called ground clamps establish the connection between the work and the work piece lead that runs to the machine. Work piece clamps are selected based on the amount of current it can carry without overheating. Electrode holders grasp the electrode and provide electrical contact between the electrode and the welding cable. Electrode holders are also rated and selected based on the amount of current it can carry without overheating.
What does “Duty Cycle” refer to? A.) The % of time in a 24 hr period that a machine can run at rated output. B.) The % of time in a 10 min period a machine can run at rated output. C.) Length of time a machine can work doing the work it was designed for. D.) Life cycle of the machine before it needs to be serviced.
SMAW cannot take place without electrodes, often called sticks. SMAW electrodes have a metal wire core coated with a flux. The wire core conducts the welding current from the electrode holder to the work. The arc at the end of the electrode melts the wire core, the flux coating, and the base metal at temperatures exceeding 6,000 o F.
The flux coating on the electrodes creates a slag coating that must be cleaned from the weld. Chipping hammers, hand files, and wire brushes are a few of the hand tools that can be used for post weld cleaning.
SMAW is often referred to as stick welding. SMAW remains one of the most widely used forms of welding in the industry because of its simplicity and a relatively low cost. SMAW is the basis on which all other welding processes have been developed. Understanding the SMAW process and its techniques is crucial for achieving success with other welding processes.