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SMA-welding-tipsHow to do What and Why.SOLUTIONS with Effective, Powerful AdviceSMA-welding-tips are useful reminders of basic information items that every good welder has embedded into his/her own skill whenever brandishing the torch. Nevertheless by reviewing this page anybody might find hints on long forgotten practical SMA-welding-tips useful in specific situations. Shielded Metal Arc Welding (SMAW) is one of the oldest practical processes that uses electrical energy as the power source, and it is still one of the most widely applied. It evolved in time, with the progress in understanding the functions of the ingredients in the shielding cover, to the point where it stands now as the baseline process to which all other processes are compared. Among SMA-welding-tips one should remember that this is the process that uses an electric arc between a covered electrode (stick) and the work, melting base and filler metal to produce the weld. The electrode cover, heated by the arc, decomposes and evolves shielding gases that protect the weld pool and the hot metal and leaves a solid slag cover that prevents the weld from being oxidized and contaminated by contact with the surrounding air.
The process is versatile, useful for an extensive range of applications, materials, shapes and dimensions. It produces welds of suitable mechanical properties even in hard to reach spots.
SMA-welding-tips on Advantages
An Article on Gravity Welding was published in the July 2006 Issue of Practical Welding Letter No. 36. To read the article click on PWL#036. An Article on Backing Bars was published in the January 2007 Issue of Practical Welding Letter No. 41. To read the article click on PWL#041. A special issue of Practical Welding Letter, Mid Month Bulletin for May 2008, is full of Online Resources on SMAW. Click on PWL#057B to see it.
SMA-welding-tips on Limitations
SMA-welding-tips on Power sources SMA-welding-tips: from the available types, whether transformer, rectifier, generator or inverter, the selection is based mostly on personal experience and work requirements as listed hereafter. We think that, before purchasing, welders should look for leasing for a short time the equipment they need in order to test it and find out if it meets their expectations. SMA-welding-tips: on inverters, that owe their popularity to their light weight, a big advantage for portability, when needed, an article was written in Issue 5 of Practical Welding Letter for January 2004. To see the article click on PWL#005. SMA-welding-tips on Selection
Depending on welder's skill, useful SMA-welding-tips suggest suitable electrode types that can be selected for specific applications. Electrode type may prescribe the preferred current. SMA-welding-tips on AC: it is generally preferred:
Note that cables carrying ac should not be coiled because of inductive losses. SMA-welding-tips on DC: it is preferred:
SMA-welding-tips on Polarity It is known that heat generated by an electric arc is not equally divided between its two ends. One can distinguish the electrode end from the work side. When the electrode is connected to the negative terminal, the major part of the heating is concentrated on the work side. When the electrode is connected to the positive terminal, the major part of the heating is concentrated on the electrode end. Therefore by changing polarity one changes quite substantially the heat balance between electrode and work. Some confusion on the interpretation of the results may follow because the electrode size and current are rarely maintained when changing polarity and it is therefore difficult to compare results. It is generally agreed that with straight polarity (electrode negative) melting and deposition rate is higher than with opposite polarity. SMA-welding-tips on Penetration Some argue that with electrode negative penetration is shallow, making it suitable to weld thin sheet metal. Other authors write that electrode negative produces deep, narrow weld beads. We think that the difference of opinions stems form the different conditions used in the tests. If the electrode size is kept constant, the current should be reduced when connecting it to the positive terminal, otherwise the same current as before (when the electrode was connected to the negative terminal) might overheat the electrode. If the electrode size is changed, to compare penetration at the same current level, then the current density in the electrode changes, which again changes conditions so that the results are not comparable. Our practical SMA-welding-tip or suggestion, if penetration and weld shape is important, is to conduct two independent sets of tests to decide which polarity to select. Provided that the electrode cover supports both polarities, the electrode size and the current level should be selected for each polarity to produce an acceptable weld. Then shape and penetration should be examined in macro sections, see Weld Macro, to determine which of them is more suitable to the intended application. SMA-welding-tips on Electrode Classification
We report hereafter a few SMA-welding-tips on characteristics of covered electrodes of specific types: E6010: suitable for direct current electrode positive (DCEP). Recommended for all welding positions with substantial penetration. The slag is thin, easily removable. E6011: designed for use with alternating current (AC), to reproduce the characteristics and mechanical properties obtained with E6010. E6012: may be used with direct current electrode negative (DCEN), suitable for vertical welding with low penetration and dense slag. May produce higher yield strength and lower ductility than the first two above. E6013: can work with AC at low amperages and low open circuit voltage. Suitable for light sheet metal welding with low penetration. Easy slag removal. Otherwise similar to E6012. E6019: electrodes of this type provide deep arc penetration with good ductility. Meet requirements for radiographic standards and specific impact properties at low temperature. Suitable for use with all currents (AC, DCEP or DCEN). E6020: suitable only for flat or horizontal fillet position welding on thick material because of low viscosity slag. Medium to deep penetration depending on current level. With iron oxide in the covering. E6022: suitable for flat and horizontal single pass welding at high speed with high current. E6027: suitable for thick base metal in flat and horizontal position with all types of current with medium penetration. Thick cover containing iron. Easily removable slag. E7014: similar to above E6012 and E6013 but usable at higher amperage. With iron powder in the covering to increase deposition efficiency. Suitable for all positions and wide root gap due to poor fit. Easily removable slag. E7024: With iron powder in the covering, suitable for all types of current, low arc penetration. High travel speed possible. E7024-1: Similar to the above (without suffix) but for greater ductility and lower Ductile to Brittle Transition Temperature. E7027: Similar to E6027 but with higher mechanical properties. Must meet specified requirements on chemical composition. SMA-welding-tips on Low Moisture Electrodes (Low Hydrogen). The following electrodes, designated with the suffixes -15, -16, -18, -28 and -48 are needed for welding steels whenever the conditions require that no or minimum Hydrogen be introduced in the weld for preventing Hydrogen cracking. Ingredients in the covering reduce oxide inclusions and promote higher impact properties. Hardenable carbon steels and thick materials should be welded with this class of electrodes because they are prone to Hydrogen Induced Cracking. SMA-welding-tips require that all these electrodes be stored in dry conditions and, if exposed to dampness must be dried in an oven for sufficient time before use. Arc length should always be kept short to reduce the risk of porosity. E7015: like all the -15 electrodes, are used with DCEP for welding thick materials, also for high sulfur and enameling steels, in all welding positions (excluding the larger sizes). The heavy slag is easy to remove. E7016: (and other -16 electrodes) have a potassium rich covering to stabilize the arc in AC. Otherwise the characteristics are similar to the above. E7016-1: have higher manganese content, intended to develop lower transition temperature. E6018: electrodes similar to E7018 (hereafter) but at lower strength level. Suitable as buffer layers in cladding applications. E7018: similar to E7015 but with iron powder in the thicker cover. For AC and DCEP in all welding positions. Useful also for high strength high carbon and low alloy steels. E7018-1: higher manganese content than the above, for lower transition temperature. E7018M: intended for optimum mechanical properties, but sometimes classified as E7018 E7028: similar to E7018 but limited to flat or horizontal position. With iron content in the cover to produce higher deposition rate. E7048: again similar to E7018, optimized for vertical down+ applications, but difficult to achieve consistently good X-Ray quality results in multiple pass applications. All electrodes have optimum current ranges for each size, as specified by manufacturers and usually published on the cardboard box. We report hereafter, as practical SMA-welding-tips, a few AWS Specifications for Covered Electrodes. ANSI/AWS A5.1/A5.1M:2004 ANSI/AWS A5.5-96 ANSI/AWS A5.4/A5.4M:2006 ANSI/AWS A5.15-90R ANSI/AWS A5.3/A5.3M:1999 ANSI/AWS A5.6-84 ANSI/AWS A5.11/A5.11M:2005 ANSI/AWS A5.13:2000 ANSI/AWS A5.21-2001
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