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Hi all, so this is my first post, and I thought it would be fitting to post my questions here rather on the introduction section. To explain my situation, I am a mechanical engineer student and we got this mechanical shop class where I recently did a report about arc welding. We haven't done any form of welding yet in class so I had to rely on the internet for information. After my report, the professor gave me some questions that he wants answered by next meeting. The problem is, I can't seem to answer two of his questions. Here they are:
1.Is the tensile strength value written on the welding electrode refer to the welding electrode before welding or after welding (the welding bead)?
2.Why does the metal (I think he was referring to the electrode core wire?) melts first during welding and the coating remains to cover the core wire?
Well, for the first question, I think it refers to after welding because I think that would make much more sense. While for the second one, I think the metal melts first because the heat is concentrated there and not on the coating. However, I am still not sure about these answers and haven't welded firsthand yet and would like to ask the help of some experienced welders out there. I also tried looking up the internet but haven't found any luck and I do not know any welders near my home. Many thanks for reading it up to here.
Stick welding is a skill that takes much practice to master, and selecting the correct electrode for the job can be equally challenging. Stick electrodes are available in a wide range of types, each of which provides different mechanical properties and operates with a specific type of welding power source. Factors you should consider when selecting a stick electrode include base metal type, joint fit-up and welding positions. Before you power up your machine and pick up your electrode holder, consider these basic guidelines.
Assess Your Base Metal
The first step in choosing an electrode is to determine your base metal composition. Your goal is to match (or closely match) the electrode composition to the base metal type, which will help ensure a strong weld. If you&#;re in doubt about the composition of your base metal, ask yourself these questions:
1. What does the metal look like? If you&#;re working with a broken part or component, check for a coarse and grainy internal surface, which usually means the base material is a cast metal.
2. Is the metal magnetic? If the base metal is magnetic, chances are good that the base metal is carbon steel or alloy steel. If the base metal is not magnetic, the material could be manganese steel, 300 series austenitic stainless steel or a non-ferrous alloy such as aluminum, brass, copper or titanium.
3. What kind of sparks does the metal give off when touched by a grinder?As a rule of thumb, more flare in the sparks indicates a higher carbon content such as in A-36 grade steel (see Photo 1).
4. Does a chisel &#;bite&#; into the base metal or bounce off?A chisel will bite into a softer metal, such as mild steel or aluminum, and bounce off of harder metals, such as high carbon steel, chrome-moly or cast iron.
To prevent cracking or other weld discontinuities, match the minimum tensile strength of the electrode to the tensile strength of the base metal. You can identify a stick electrode&#;s tensile strength by referring to the first two digits of the AWS classification printed on the side of the electrode. For example, the number &#;60&#; on an E electrode indicates that the filler metal produces a weld bead with a minimum tensile strength of 60,000 psi and, as a result, would work well with a steel of similar tensile strength.
Some electrodes can be used with only AC or DC power sources while other electrodes are compatible with both. To determine the correct current type for a particular electrode, refer to the fourth digit of the AWS classification, which represents the type of coating and type of compatible welding current (see Figure 1).
The type of current you use also influences the penetration profile of the resulting weld. For example, a DCEP compatible electrode, such as an E delivers deep penetration and produces an extremely tight arc. It also has the ability to &#;dig&#; through rust, oil, paint and dirt. A DCEN compatible electrode, such as an E, provides mild penetration and works well when bridging two joints or welding high speed, high current fillet welds in the horizontal position.
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An AC compatible electrode, such as an E, produces a soft arc with medium penetration and should be used to weld clean, new sheet metal.
Base Metal Thickness, Shape and Joint Fit-Up
Thick materials require an electrode with maximum ductility and low hydrogen to prevent weld cracking. Electrodes with AWS classification numbers ending in 15, 16 or 18 provide excellent low&#;hydrogen properties and good toughness (high impact values) to accommodate for residual stress.
For thin materials, you will need an electrode that produces soft arcs, such as a , Also, smaller diameter electrodes will provide shallow penetration to help prevent burn-through on thinner materials.
You&#;ll also want to assess the joint design and fit-up. If you&#;re working on a joint with a tight fit-up or one that is not beveled, use an electrode that provides a digging arc to ensure sufficient penetration, such as an E or E. For materials with wide root openings, select an electrode, such as an E, that creates a concave weld face suitable for bridging gaps and making groove welds.
To determine what position(s) a particular electrode is qualified for, refer to the third digit in AWS classification. Here&#;s how you decipher the qualified electrode position:
1 = flat, horizontal, vertical and overhead
2= flat and horizontal only
For example, a electrode can be used in the flat, horizontal, vertical and overhead positions.
Next, make sure to assess the conditions that the welded part will encounter throughout its service. If it will be used in high heat or low temperature environments, subjected to repetitive shock loading, a low hydrogen electrode with higher ductility will reduce the chance of weld cracking. Also, be certain to check for welding specifications if you&#;re working on critical applications such as pressure vessel or boiler fabrication. In most cases, these welding specifications will require you to use specific types of electrodes.
To achieve the best results, you should always remove excessive mill scale, rust, moisture, paint and grease. Clean base metals help prevent porosity and increase travel speeds. If cleaning your base metal is not possible, E or E electrodes deliver a deep penetrating arc that has the ability to cut through contaminants.
Final Thoughts Consideration of the above factors will help you overcome the challenges of selecting the correct stick electrode for your particular application. However, given the wide range of available electrodes, several solutions may exist for one application. If you need additional assistance with electrode selection, your local welding supply distributor or a company representative of a reputable filler metal manufacturer can serve as an excellent resource.
Contact us to discuss your requirements of Rods Gouging Torch Exporters. Our experienced sales team can help you identify the options that best suit your needs.