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FOREWORD
This Submerged Arc Welding Handbook has been prepared by the ESAB Welding & Cutting Products for shop foremen, welding engineers and other supervisory personnel.
It does not give specific apparatus operating instructions nor more than an elementary explanation of basic theory. Its function is to present procedures, tables, and other operating data helpful in the planning and execution of basic submerged are welding or surfacing applications. For information on multiple electrode welding, high speed welding, special hard-facing compositions, welding materials to meet government and industry specifications, welding power supplies, or any other aspect of submerged arc welding not covered herein, consult your ESAB representative or the nearest ESAB sales office. Operating instruction booklets for ESAB equipment are available on request to any sales office. Each contains precautionary information which should be read and observed by all machine operators.
Copyright 1999, ESAB Welding & Cutting Products, Florence, SC 29501.
Introduction General Description of Submerged Arc Welding Definition Submerged are welding is a method in which the heat required to fuse the metal is generated by an arc formed by an electric current passing between the welding wire and the workpiece. The tip of the welding wire, the arc, and the workpiece are covered by a layer of granulated mineral material known as submerged arc welding flux. There is no visible arc and no sparks, spatter or smoke. General Scope Welding Current - Currents up to 2,000 amperes, a.c. or d.c., on a single welding wire electrode have been used. Thicknesses - One-pass welding up to 1-1/2-in. thick and multipass welding to any thickness can be done. Practical minimum thickness is 18-gage. Welding Speed - Up to 150 inches per minute with a single welding wire. Higher speeds may be attained with multiple electrodes in the same welding zone. Position - High welding current with resulting high rate of heat input creates a large pool of liquid metal. Under such conditions, welds must be kept horizontal to prevent spilling. Welds in which the pool is small may be inclined as much as 15 degrees from the horizontal without causing difficulties. If the size of the individual passes is limited, horizontal welds can be made on vertical surfaces if a suitable support is provided for the welding flux.
Elements of Submerged Arc Welding Four elements are present in the making of a submerged arc weld:
1. Heat generated by the passage of an electric current through an arc.
2. Welding wire of consumable bare metal.
3. The pieces which are to be welded.
4. Submerged Arc Flux - a granulated mineral welding composition.
5. A fifth element, present in making all except mold and plug welds, is relative motion between the welding head and the work.
General Sequence of Operations Reducing submerged arc welding to its simplest terms, with one frequently used equipment assembly, the general sequence of operations in making a submerged arc weld is as follows:
1. Setting Up the Welding Equipment (Simple Portable Installation).
a) The Submerged Arc Welding Head is assembled in accordance with the instructions supplied.
b) The head, control, and wire reel are mounted on the self- propelled carriage.
c) The travel path is made ready.
d) The welding power supply is connected to the power line. Welding cable connections are made from the power supply to the welding head, and to the work. e) Electrical connections (described in the instruction book) are made to the control unit, welding head, or self-propelled carriage, and the work.
2. Preparing the Workpieces
a) The most suitable type of joint design for the particular welding is determined. The metal edges are prepared, shaped, and cleaned.
b) Weld backing (if the joint is not structure-backed) is placed under the seam. c) The pieces to be welded are placed in position for welding. Usually they are tacked welded, clamped together or held in jigs to maintain the desired position.
3. Preparation for Welding
a) Each element of submerged arc welding has an effect upon the finished weld. The values for welding voltage and current, the composition and diameter of welding wire for the type of joint selected and the material to be welded, are determined from applicable tables. It is the responsibility of the operator to set and check the proper welding conditions, and to adjust the equipment to fit these conditions. It is the function of the equipment to maintain these preset conditions and produce the finished weld.
b) The coil of welding wire is installed on the wire reel. The end of the coil is inserted to the feed rollers of the wire feed mechanism and fed down until it reaches the workpieces. The welding head is then positioned so that the wire is ready to begin the weld.
c) Submerged arc welding flux of the required grade and particle size is placed in the hopper of the welding head. A quantity of the flux is deposited to cover the welding zone at the starting point of the weld.
d) The controls are set to establish the proper welding conditions: welding current, welding voltage and carriage speed.
4. The Welding Operation When the apparatus is set into operation, several things occur in quick sequence:
a) An electric arc is established as the current flows between the electrode and the work.
b) The wire feed mechanism begins to feed the welding wire into the weld at a controlled rate.
c) The carriage is started (manually or automatically) to travel along the seam. d) The submerged arc welding flux feeds through the hopper tube and continuously distributes itself over the seam a short distance ahead of the welding zone.
6 FIG. 1 - Cutaway View of Welding Zone
The tremendous heat evolved by the passage of the electric current through the welding zone melts the end of the wire and the adjacent edges of the workpieces, creating a puddle of molten metal. This puddle is in a highly liquid state, and is turbulent. For these reasons, any slag or gas bubbles are quickly swept to the surface. The submerged are welding flux completely shields the welding zone from contact with the atmosphere. A small amount of the flux fuses. This fused portion serves several functions: it completely blankets the top surface of the weld, preventing atmospheric gases from contaminating the metal, it dissolves and thus eliminates impurities that separate themselves from the molten steel and float to its surface, and it also can be the vehicle for adding certain alloying elements. The combination of all these factors results in a sound, clean, homogeneous weld. As the welding zone moves further down the seam, the fused submerged arc welding flux cools and hardens into a brittle, glass-like material which protects the weld until cool, then usually detaches itself completely from the weld. Since properly made submerged arc welds are made without arc flash sparks, protective equipment against harmful radiations is not needed. There is no spatter to be removed. Basic Principles -Theory of Welding Wire Feed Control The high welding speeds and high deposition rate which are characteristic of submerged arc welding require automatic control of the motor that feeds the welding wire into the weld. No hand welder could smoothly deposit welding wire at speeds comparable to those of a submerged arc welding machine. Nor could he maintain the same precise control of welding conditions. The automatic control and power supply system used in submerged arc welding operates to maintain a constant voltage and current.
1. Relationship of Welding Voltage to Distance between Welding Wire and Workpiece The welding voltage is proportional to the length of the current path between the welding wire and workpiece:
a) If the distance between wire and workpiece increases, the welding voltage will increase.
b) If the distance between the wire and workpiece decreases, the welding voltage will decrease.
c) If the distance between wire and workpiece remains constant, the welding voltage will remain constant.
2. Rate of Wire Melt-Off vs. Rate of Wire Feed
a) Constant Current Power If, for any short period of time, the current flowing through the welding zone melts off the wire at a faster rate than it is being fed, the distance between wire and work will increase, and welding voltage will increase. Conversely, if for any short period of time, wire is fed faster than it melts off, the distance between wire and work will decrease, and welding voltage will decrease. A constant welding voltage can be maintained if a control unit is used which will automatically vary the rate of wire feed with change in welding voltage.
b) Constant Potential Power With a constant potential power system the arc voltage is maintained by the power supply. Arc current is controlled by the wire feed speed with increased wire feed producing increased current. Therefore, the wire feed system is simplified to a constant speed device and arc control is performed by the power source.
Precautions and Safe Practices
WARNING: These Safety Precautions are for your protection. They summarize precautionary information from the references listed in Additional Safety Information section. Before performing any installation or operating procedures, be sure to read and follow the safety precautions listed below as well as all other manuals, material safety data sheets, labels, etc. Failure to observe Safety Precautions can result in injury or death. PROTECT YOURSELF AND OTHERS -- Some welding, cutting, and gouging processes are noisy and require ear protection. The arc, like the sun, emits ultraviolet (UV) and other radiation and can injure skin and eyes. Hot metal can cause burns. Training in the proper use of the processes and equipment is essential to prevent accidents.
Therefore:
1. Always wear safety glasses with side shields in any work area, even if welding helmets, face shields, and goggles are also required.
2. Use a face shield fitted with the correct filter and cover plates to protect your eyes, face, neck, and ears from sparks and rays of the arc when operating or observing operations. Warn bystanders not to watch the arc and not to expose themselves to the rays of the electric-arc or hot metal.
3. Wear flameproof gauntlet type gloves, heavy long-sleeve shirt, cuffless trousers, high-topped shoes, and a welding helmet or cap for hair protection, to protect against arc rays and hot sparks or hot metal. A flameproof apron may also be desirable as protection against radiated heat and sparks.
4. Hot sparks or metal can lodge in rolled up sleeves, trouser cuffs, or pockets. Sleeves and collars should be kept buttoned, and open pockets eliminated from the front of clothing
5. Protect other personnel from arc rays and hot sparks with a suitable non-flammable partition or curtains.
6. Use goggles over safety glasses when chipping slag or grinding. Chipped slag may be hot and can fly far. Bystanders should also wear goggles over safety glasses.
FIRES AND EXPLOSIONS -- Heat from flames and arcs can start fires. Hot slag or sparks can also cause fires and explosions.
Therefore:
1. Remove all combustible materials well away from the work area or cover the materials with a protective non-flammable covering. Combustible materials include wood, cloth, sawdust, liquid and gas fuels, solvents, paints and coatings, paper, etc.
2. Hot sparks or hot metal can fall through cracks or crevices in floors or wall openings and cause a hidden smoldering fire or fires on the floor below. Make certain that such openings are protected from hot sparks and metal.“
3. Do not weld, cut or perform other hot work until the workpiece has been completely cleaned so that there are no substances on the workpiece which might produce flammable or toxic vapors. Do not do hot work on closed containers. They may explode.
4. Have fire extinguishing equipment handy for instant use, such as a garden hose, water pail, sand bucket, or portable fire extinguisher. Be sure you are trained in its use.
5. Do not use equipment beyond its ratings. For example, overloaded welding cable can overheat and create a fire hazard.
6. After completing operations, inspect the work area to make certain there are no hot sparks or hot metal which could cause a later fire. Use fire watchers when necessary.
7. For additional information, refer to NFPA Standard 51B, "Fire Prevention in Use of Cutting and Welding Processes", available from the National Fire Protection Association, Batterymarch Park, Quincy, MA 02269.
ELECTRICAL SHOCK -- Contact with live electrical parts and ground can cause severe injury or death. DO NOT use AC welding current in damp areas, if movement is confined, or if there is danger of falling.
1. Be sure the power source frame (chassis) is connected to the ground system of the input power.
2. Connect the workpiece to a good electrical ground.
3. Connect the work cable to the workpiece. A poor or missing connection can expose you or others to a fatal shock.
4. Use well-maintained equipment. Replace worn or damaged cables.
5. Keep everything dry, including clothing, work area, cables, torch/electrode holder, and power source.
6. Make sure that all parts of your body are insulated from work and from ground. 7. Do not stand directly on metal or the earth while working in tight quarters or a damp area; stand on dry boards or an insulating platform and wear rubber-soled shoes. 8. Put on dry, hole-free gloves before turning on the power.
9. Turn off the power before removing your gloves.
10.Refer to ANSI/ASC Standard Z49.1 (listed on next page) for specific grounding recommendations. Do not mistake the work lead for a ground cable.
ELECTRIC AND MAGNETIC FIELDS — May be dangerous. Electric current flowing through any conductor causes localized Electric and Magnetic Fields (EMF). Welding and cutting current creates EMF around welding cables and welding machines.
Therefore:
1. Welders having pacemakers should consult their physician before welding. EMF may interfere with some pacemakers.
2. Exposure to EMF may have other health effects which are unknown.
3. Welders should use the following procedures to minimize exposure to EMF: a. Route the electrode and work cables together. Secure them with tape when possible. b. Never coil the torch or work cable around your body.
c. Do not place your body between the torch and work cables. Route cables on the same side of your body.
d. Connect the work cable to the workpiece as close as possible to the area being welded.
e. Keep welding power source and cables as far away from your body as possible.
FUMES AND GASES -- Fumes and gases, can cause discomfort or harm, particularly in confined spaces. Do not breathe fumes and gases. Shielding gases can cause asphyxiation.
Therefore:
1. Always provide adequate ventilation in the work area by natural or mechanical means. Do not weld, cut, or gouge on materials such as galvanized steel, stainless steel, copper, zinc, lead, beryllium, or cadmium unless positive mechanical ventilation is provided. Do not breathe fumes from these materials.
2. Do not operate near degreasing and spraying operations. The heat or arc rays can react with chlorinated hydrocarbon vapors to form phosgene, a highly toxic gas, and other irritant gases.
3. If you develop momentary eye, nose, or throat irritation while operating, this is an indication that ventilation is not adequate. Stop work and take necessary steps to improve ventilation in the work area. Do not continue to operate if physical discomfort persists.
4. Refer to ANSI/ASC Standard Z49.1 (see listing below) for specific ventilation recommendations.
5. WARNING: This product, when used for welding or cutting, produces fumes or gases which contain chemicals known to the State of California to cause birth defects and, in some cases, cancer. (California Health & Safety Code §25249.5 et seq.)
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