Hobart Institute - Shielded Metal Arc Welding: (EW-472)

EW-472 TECHNICAL GUIDE Shielded Metal Arc WeldingHOBART INSTITUTE OF WELDING TECHNOLOGYHOBART INSTITUTE OF WELDING TECHNOLOGY , 400 TRADE SQUARE EAST, TROY400 TRADE SQUARE EAST, OHIO 45373 U.S.A., TROYTable of ContentsChapterPage 1. Introduction to the Process......................... 2. Principles of Operation........................... 3. 4. 4.

Covered Electrodes............................ 5. Welding Applications........................... 6. Cost of Shielded Metal Arc Welding................... 7.

Welding Metallurgy............................ 8. Weld and Joint Design.......................... 9. Welding Procedure Variables....................... 10.

Welding Procedure Schedules...................... 11. Preweld Preparations........................... 12. Welding Discontinuities and Defects................... 13.

Postweld Procedure........................... 14.WelderTrainingandQualification.................... 15. Welding Safety.............................. Index ................................... 2012 Hobart Institute of Welding Technology ISBN 978-1-936058-16-7 CHAPTER 1INTRODUCTION TO THE PROCESS Shielded Metal Arc Welding (SMAW) is an electric arc METHODS OF APPLICATION welding process where the heat for welding is generated by an electric arc between a covered metal electrode and The shielded metal arc welding process is basically a the work.

The filler metal is deposited from the electrode manually operated process. The electrode is clamped in and the electrode covering provides the shielding. Some an electrode holder and the welder manipulates the tip slang names for this process are stick welding or stick of the electrode in relation to the metal being welded. electrode welding: A diagram of this process is shown in The arc is struck, maintained, and stopped manually by Illustration 1-1. the welder. There are several variations of this process which are done automatically.

These are grav ity welding, fire cracker welding, and massive Shielding Gas electrode welding. These methods comprise Molten Weld Metal Electrode Wire only a very small percentage of welding done Slag Electrode Coating by the shielded metal arc welding process. Arc They will be explained in Chapter 5. Solidified Weld Metal Droplets Metal ADVANTAGES AND LIMlTATl0NS Base Shielded metal arc welding is widely used Metal because of its versatility, portability, and com paratively simple and inexpensive equipment, Illustration 1-1 Shielded Metal Arc Welding And it does not require auxiliary gas shielding or granular flux. The shielded metal arc welding process is one of the most simple and versatile arc welding processes. This The shielded metal arc welding process can be used for process can be used to weld both ferrous and nonferrous making welds in any position that can be reached with an metals and it can weld thicknesses above approximately electrode.

Electrodes can be bent so they can be used 18 gauge in all positions. The arc is under the control of to weld blind areas. Long leads can be used to weld in the welder and is visible. The welding process leaves a many locations at great distances from the power source. slag on the surface of the weld bead which must be re Shielded metal arc welding can be used in the field be moved. cause the equipment is relatively light and portable.

This process is also less sensitive to wind and draft than gas The most popular use for this process is for the welding shielded arc welding processes. of mild and low alloy steels. The equipment is extremely rugged and simple, and the process is flexible in that the Shielded metal arc welding can be used to weld a wide welder only needs to take the electrode holder and work variety of metal thicknesses. This process is more useful lead to the point of welding. than other welding processes for welding complex struc tural assemblies because it is easier to use in difficult Most sources give credit for the invention of the electric locations and for multi-position welding. Shielded metal arc to Sir Humphrey Davy of England, in 1801.

For the arc welding is a popular process for pipe welding. Weld most part, the electric arc remained a scientific novelty joints with high quality and strength can be obtained with until 1881, when the carbon arc street lamp was invented shielded metal arc welding. and the first attempts to weld using the carbon arc pro cess were made. The metal arc welding process came The shielded metal arc welding process has several limi-into being when the carbon electrodes were replaced tations. Operator duty cycle and overall deposition rates by metal rods in 1889. Coverings for the bare wire elec-for covered electrodes are usually less than provided trodes were first developed in the early 1900s.

The first with a continuous electrode process. This is because major use occurred during World War I, especially in the electrodes have a fixed length and welding must be shipbuilding industry. After the war, there was a period of stopped after each electrode has been consumed. The slow growth until the early 1930s when shielded metal portion of the electrode that is clamped into the holder arc welding became a major manufacturing method and must be discarded. Another limitation is that the slag a dominant welding process. Today, the shielded metal must be removed from the weld after every pass.

Finally, arc welding process is a widely used welding process, the shielded metal arc welding process cannot be used even though its relative importance had been declining to weld some of the nonferrous metals. slowly in recent years. CHAPTER 2PRINCIPLES OF OPERATION The shielded metal arc welding process uses the heat of sirable when the welder wants to achieve maximum weld the electric arc to melt the consumable electrode and the ing speed on some welding jobs. The steeper slope gives work being welded. The welding circuit includes a power less current variation with changing arc length and it gives source, welding cables, an electrode holder, a work clamp a softer arc. The types of machines that have this kind of and a welding electrode.

One of the welding cables con curve are especially useful on sheet metal. Machines with nects the power source to the electrode holder and the this characteristic are typically used with large diameter other cable connects to the workpiece. electrodes and high amperages. On some applications, a less steep volt-ampere characteristic is more desirable, The welding begins when the arc is initiated by momen such as welding over rust, or all position pipe welding tarily touching the electrode to the base metal which where better arc control with high penetration capability is completes the electrical circuit. The welder guides the desired. Machines with the less steep volt-ampere curve electrode manually, controlling both the travel speed and are also easier to use for depositing the root passes on the direction of travel.

The welder maintains the arc by joints that have varying fitup. This type of power source controlling the distance between the work material and characteristic allows the welder to control the welding the tip of the electrode (length of the arc). Some types current in a specific range, by changing the arc length and of electrodes can be dragged along the surface of the producing a more driving arc. The variations in the power work so that the coating thickness controls the arc length, sources are caused by the differences in the basic power which controls the voltage. source designs. Illustration 2-1 shows volt-ampere curves for different performance characteristics.