Shielded Metal Arc Welding Teknologi Las Kapal Shielded Metal Arc Welding

Arc Welding PPE Teknologi dan Rekayasa

Hand shield so person may hold shield in front of face Hand and Head Shields Brilliant light caused by electric arc contains two kinds of invisible rays which injure eyes and skin Ultraviolet Infrared Rays affect eyes within 50 feet; and skin any distance within 20 feet Fibre-Metal Products Co. Hand shield so person may hold shield in front of face Teknologi dan Rekayasa

Hand and Head Shields Attached to adjustable headband Also called hood or helmet Attached to adjustable headband Allows it to be moved up or down as wearer desires Dependable protection Both hands free to grasp electrode holder Partial protection Must also wear leather or nonflammable cap for adequate protection Fibre-Metal Products Co. Teknologi dan Rekayasa

Heat The arc welder must produce sufficient heat (electric arc) to melt the electrode and the base metal to the desired depth. The amount of heat produced is determined by the amperage. Amperage is limited by the diameter of the electrode and the capacity of the welder. Teknologi dan Rekayasa

Heat The amount of heat needed to complete the weld is determined by several factors: Thickness of the metal Type of joint, Electrode type Electrode diameter Weld position Excessive heat. Electrode easier to start Excessive penetration (burn through) Excessive bead width Excessive splatter Electrode overheating Insufficient heat. Hard to start Reduced penetration Narrow bead Coarse ripples Teknologi dan Rekayasa

Electrode Electrode must be compatible with base metal. Carbon steels The SMAW process uses a consumable electrode. Electrode must be compatible with base metal. Electrodes are available for different metals. Carbon steels Low alloy steels Corrosion resisting steels Cast irons Aluminum and alloys Copper and alloys Nickel and alloys Teknologi dan Rekayasa

Electrode The AWS system distinguishes the tensile strength, weld position and, coating and current. Manufactures may and do use there own numbering system and produce electrodes that do not fit in the AWS system. Teknologi dan Rekayasa

Welding Currents Alternating Current (AC) Not all electrodes are designed to work with all currents. Common SMAW currents. Alternating Current (AC) Direct Current straight polarity (DCSP) or (DCEN) Direct Current Reverse polarity (DCRP) or (DCEP) Teknologi dan Rekayasa

Electrode Grouping Electrodes are also grouped according to there performance characteristics. Fast-freeze Mild steel Quick solidification of weld pool Deep penetrating Recommended for out of position welds Deep penetrating arc Fast-fill Highest deposition rate Stable arc Thick flux Flat position and horizontal laps only Teknologi dan Rekayasa

Electrode Grouping Fill-freeze General purpose electrodes Characteristics of fast-freeze and fast-fill Low hydrogen Welding characteristics of fill-freeze Designed for medium carbon and alloy steels Teknologi dan Rekayasa

Electrode Storage Electrodes are damaged by rough treatment, temperature extremes and moisture. The should be kept in their original container until used. They should be stored in a heated cabinet that maintains them at a constant temperature. The storage of low hydrogen electrodes is very critical. Designed to reduce underbead cracking in alloy and medium carbon steels by reducing the the amount of hydrogen in the weld pool. The flux is hydroscopic--attracts moisture (H2O). Moisture in the flux also causes excessive gasses to develop in the weld pool and causes a defect in the weld caused worm holes. Teknologi dan Rekayasa

Selecting Electrode Size The optimum electrode diameter is determined by the thickness of the base metal, the welding position and the capacity of the welding power supply. A smaller diameter is usually recommended for out of position welding. When completing root passes in V-joints, a smaller diameter maybe used and then a larger diameter is used for the filler passes. A diameter of 3/32 or 1/8 inch can be used on metals up to 1/4 inches thick without joint preparation. ROT: the diameter of the electrode should not exceed the thickness of the metal. Teknologi dan Rekayasa

SMAW Welding Process Electrode Flux Gas Electrode shield metal Slag Penetration Molten puddle Bead Base metal Teknologi dan Rekayasa

Equipment Power Supply Polarity Switch Power Cord Electrode Holder Power Switch Electrode Amperage Adjustment Amperage Scale Base Metal (work Piece) Ground Clamp Ground Cable Electrode Cable Teknologi dan Rekayasa

Direct Current straight polarity (DCSP) or (DCEN) A rectifier allows current to flow in one direction only. The direction of the current flow determines the DC polarity. DC- or direct current electrode negative is the arrangement of direct current arc welding cables/leads in which the electrode is the negative pole and the workpiece is the positive pole of the welding arc. When using DC- polarity, the majority of the heat is directed at the electrode. The electrodes designed for DC- polarity produce weld deposits with shallow penetration. Primary applications are fast travel speeds on sheet metal. Teknologi dan Rekayasa

Direct Current straight polarity (DCSP) or (DCEN) Teknologi dan Rekayasa

Direct Current Reverse polarity (DCRP) or (DCEP) DC+ or direct current electrode positive is the opposite of DC- or direct current electrode negative. In this case, the electrode is the positive pole and the workpiece is the negative pole. When using DC+ polarity, the majority of the heat is directed at the work piece. The electrodes designed for DC+ polarity produce weld deposits with deep penetration. Primary applications are for pipe welding, general purpose and maintenance welding, deep penetration applications, and on base material with surface contaminants. Teknologi dan Rekayasa

Direct Current Reverse polarity (DCRP) or (DCEP) Teknologi dan Rekayasa

Comparison of Penetration Contours Teknologi dan Rekayasa

STARTING THE ARC Before you start to weld, ensure that you have all the required equipment and accessories. Listed below are some additional welding rules that should be followed. Clear the welding area of all debris and clutter. Do not use gloves or clothing that contains oil or grease. Check that all wiring and cables are installed properly. Ensure that the machine is grounded and dry. Follow all manufacturer’s directions on operating the welding machine. Have on hand a protective screen to protect others in the welding area from FLASH bums. Always keep fire-fighting equipment on hand. Clean rust, scale, paint, or dirt from the joints that are to be welded. Teknologi dan Rekayasa

STARTING THE ARC When starting the arc, strike the electrode like a match on the work surface by gently and quickly moving it along the weld metal. Next, withdraw the electrode to form an arc length from the work piece of approximately 1/8”. Reduce the arc length to the approximate length required to produce the desired weld. Teknologi dan Rekayasa

Striking The Arc Select the best electrode Set the welder (Fig 26-8) Turn on welder Warn bystanders Lower helmet Start arc (two methods) Brushing Tapping Teknologi dan Rekayasa

Brushing Method Hold end of electrode about 1/4 - 1/2 inch above the surface. Lower helmet Gently brush surface of the metal with the end of the electrode. When arc starts, lift electrode 1/8 inch. If electrode sticks, twist it back and forth. If it does not break loose, release electrode from electrode holder. Do not shut off the welder with the electrode stuck to the metal. Teknologi dan Rekayasa

Tapping Method Set up welder Hold the electrode at the travel angle and 1/4 - 1/2 inch above the metal. Quickly lower the electrode until it touches the metal and then lift it 1/8 inch. Teknologi dan Rekayasa

Electrode Angle The electrode angle influences the placement of the heat. Two angles are important: Travel Work The travel angle is the angle of the electrode parallel to the joint. The correct travel angle must be used for each joint. Beads = 15o from vertical or 75o from the work. Butt joint = 15o from vertical or 75o from the work. Lap joint = 45o. T joint = 45o. Corner = 15o from vertical or 75o from the work. Teknologi dan Rekayasa

Electrode Angle-cont. The work angle is the angle of the electrode perpendicular to the joint. Teknologi dan Rekayasa

Electrode Angle-cont. Teknologi dan Rekayasa

Electrode Angle-cont. The appropriate angle must be used for each joint. Beads = 90o Butt joint = 90o Lap joint = 45o T joint = 45o Corner = 90o The work angle may need to be modified for some situations. For example, a butt joint with two different thickness of metal. Teknologi dan Rekayasa

Arc Length When an arc is too long, the metal melts off the electrode in large globules and the arc may break frequently. This produces a wide, spattered, and irregular deposit with insufficient fusion between the base metal and the weld. When an arc is too short, it fails to generate enough heat to melt the base metal properly, causes the electrode to stick frequently to the base metal, and produces uneven deposits with irregular ripples. The recommended length of the arc is equal to the diameter of the bare end of the electrode Teknologi dan Rekayasa

Arc Length The arc length is the distance from the metal part of the electrode to the weld puddle. The best arc length is not a fixed distance, but should be approximately equal to the diameter of the electrode. Arc length can be adjusted slightly to change the welding process. Excessive length Excessive spatter Reduced penetration Poor quality weld Insufficient length Electrode sticks Narrow weld Teknologi dan Rekayasa

Speed of Travel The speed of travel (inches per minute) is an important factor when arc welding. The best speed of travel (welding speed) is determined by several factors: The size of the joint, The type of electrode The size of the electrode The amperage setting on the machine Deposition rate of the electrode (cubic inches per minute) The deposition rate of an electrode will change with the welding amperage. Teknologi dan Rekayasa

Speed-cont. The ideal speed can be calculated using the volume of the joint and the deposition rate of the electrode. Step one: determine the area of the weld. (Assuming 1/16 inch penetration.) Step Two: knowing the deposition rate of the electrode, determine the welding speed. (Deposition rate = 2.5 in3/min.) Teknologi dan Rekayasa

Speed-cont. The correct welding speed is indicated by the shape of the ripples. Too slow = excessive width, excessive penetration Too fast = narrower width, elongated ripple pattern, shallow penetration. Recommended = width 2-3 times diameter of electrode, uniform ripple pattern, full penetration. Teknologi dan Rekayasa

Current and Speed Teknologi dan Rekayasa

Examples of SMAW Welds Teknologi dan Rekayasa

Square Groove A butt joint can be completed with a groove welded on metal up to 1/8 inch thick with a single pass on one side, with no root opening. Electrode manipulation should only be used to prevent burning through. Teknologi dan Rekayasa

Square Groove Thicker Metal A groove weld on metal up to 1/4 inch thick can be welded with a single pass on one side but, if possible, it should be completed with a single pass on both sides. Metal this thick requires a root opening to achieve adequate penetration. Electrode manipulation will reduce penetration. Teknologi dan Rekayasa

Single V Groove Weld Butt joints on metal greater than 1/4 inch thick require joint preparation. Note that the groove does not extend all the way. A short distance, called the root face, is left undisturbed. The amount of joint preparation is dependent on the diameter of the electrode and the amperage capacity of the power supply. Several different combinations of passes can be used to complete this joint. Teknologi dan Rekayasa

T-Joints In a T-joint the two welding surfaces are at an angle close to 90 degrees from each other. The welding side and number of passes uses depends on the thickness of the metal, the welding access and capacity of the power supply. Common joints include. Plane T T with joint gap Single preparation Double preparation Teknologi dan Rekayasa

Plane T-Joint The plane T joint is very useful for thin metal. Can be completed at angles other than 90 degrees. Can be completed with metal of different thickness. The work angle must be changed to direct more heat to the thicker piece. Teknologi dan Rekayasa

T-joint--Thicker Metal When the metal thickness exceeds 1/8 inch the recommendation is to gap the joint. Improves penetration May not be necessary if larger diameter electrode is used and sufficient amperage is available. The need for a joint gap varies with the type of electrode, but should not exceed 1/8 inch. Teknologi dan Rekayasa

T-joint Single Single Bevel As with other joints, thicker metal must have joint preparation to achieve full penetration with smaller diameter electrodes. Several different preparations can be used. A popular one is the bevel. A bevel can be completed by grinding or cutting. The bevel joint can be completed with electrode manipulation or no electrode manipulation. When when electrode manipulation is used to fill the joint, the first pass should be a straight bead with no manipulation. Teknologi dan Rekayasa

T-joint Double Bevel The double bevel T-joint is recommended for metal 1/2 inch thick and thicker. The root passes should be with not manipulation, but the filler passes can be completed with either straight beads or patterns beads. Alternating sides reduces distortion. Teknologi dan Rekayasa

Flat Position – Butt Joints Earlier reexplained that welding can be done in any position, but it is much simpler when done in the flat position. In this position, the work is less tiring, welding speed is faster, the molten puddle is not as likely to run, and better penetration can be achieved. Whenever possible, try to position the work so you can weld in the flat position. In the flat position, the face of the weld is approximately horizontal. Teknologi dan Rekayasa

Flat Position – Butt Joints Teknologi dan Rekayasa

Flat Position – Butt Joints Teknologi dan Rekayasa

Flat Position – Butt Joints Multipass Teknologi dan Rekayasa

Weaving Motions You may use one of the weaving motions shown, depending upon the type of joint and size of electrode. Teknologi dan Rekayasa

Horizontal Position You will discover that it is impossible to weld all pieces in the flat position. Often the work must be done in the horizontal position. The horizontal position has two basic forms, depending upon whether it is used with a groove weld or a fillet weld. In a groove weld, the axis of the weld lies in a relative horizontal plane and the face of the weld is in a vertical plane. In a fillet weld, the welding is performed on the upper side of a relatively horizontal surface and against an approximately vertical plane Teknologi dan Rekayasa

Horizontal Position – Butt Joints Teknologi dan Rekayasa

Horizontal Position – Lap Joints Teknologi dan Rekayasa

Horizontal Position – Fillet Teknologi dan Rekayasa

Weaving Motions - Fillet Teknologi dan Rekayasa

Vertical Position A “vertical weld” is defined as a weld that is applied to a vertical surface or one that is inclined 45 degrees or less. Erecting structures, such as buildings, pontoons, tanks, and pipelines, require welding in this position. Welding on a vertical surface is much more difficult than welding in the flat or horizontal position due to the force of gravity. Gravity pulls the molten metal down. To counteract this force, you should use fast-freeze or fill-freeze electrodes. Vertical welding is done in either an upward or downward position. The terms used for the direction of welding are vertical up or vertical down. Vertical down welding is suited for welding light gauge metal because the penetration is shallow and diminishes the possibility of burning through the metal. Furthermore, vertical down welding is faster which is very important in production work. Teknologi dan Rekayasa

Vertical Position Teknologi dan Rekayasa

Vertical Position Teknologi dan Rekayasa

Vertical Position – Butt Joints Teknologi dan Rekayasa

Vertical Position - Fillet Teknologi dan Rekayasa

Vertical Position - Fillet Teknologi dan Rekayasa

Vertical Position - Fillet Teknologi dan Rekayasa

Overhead Position Current Settings and Electrode Movement Overhead welding is the most difficult position in welding. Not only do you have to contend with the force of gravity but the majority of the time you also have to assume an awkward stance. Nevertheless, with practice it is possible to make welds equal to those made in the other positions. Current Settings and Electrode Movement To retain complete control of the molten puddle, use a very short arc and reduce the amperage as recommended. As in the vertical position of welding, gravity causes the molten metal to drop or sag from the plate. When too long an arc is held, the transfer of metal from the electrode to the base metal becomes increasingly difficult, and the chances of large globules of molten metal dropping from the electrode increase. When you routinely shorten and lengthen the arc, the dropping of molten metal can be prevented; however, you will defeat your purpose should you carry too large a pool of molten metal in the weld. Teknologi dan Rekayasa

Overhead Position Teknologi dan Rekayasa

Overhead Position – Butt Joint Teknologi dan Rekayasa

Overhead Position – Butt Joint Teknologi dan Rekayasa

Overhead Position - Fillet Teknologi dan Rekayasa

Overhead Position - Fillet Teknologi dan Rekayasa

Overhead Position - Fillet Teknologi dan Rekayasa

Vidio SMAW Over head Teknologi dan Rekayasa

Knowledge is the key to success Teknologi dan Rekayasa