Discover the characteristics of these welding consumable types
Shielded metal arc welding (SMAW) and submerged arc welding (SAW) are two versatile, slag-based welding processes that operate without external shielding gas. However, they cater to vastly different applications and require distinct operator competencies.
SMAW is a manual process, demanding an operator skilled in interpreting the arc and manipulating the electrode, although some electrodes necessitate less expertise and training than others. SAW, on the other hand, is typically a mechanized process, requiring an operator adept at handling the intricate setup details. SMAW allows welding in various positions, while SAW is restricted to flat and horizontal applications. SMAW is often employed for non-uniform or hard-to-access joints, whereas SAW necessitates precise joint preparation but can consistently deliver high-speed welds. SMAW finds extensive use in construction sites, while SAW is generally prevalent in manufacturing facilities. For both SMAW and SAW, selecting the appropriate consumable for the task at hand is paramount. A convenient online resource (lincolnelectric.com/en/Welding-and-Cutting-Resource-Center/Welding-Guides) lists consumables compatible with specific base metals.
Consumable Classification
Welding consumables are frequently manufactured and classified according to AWS A5 filler metal specifications. The electrode classification system simplifies the selection and comparison of electrodes. AWS A5.1, Specification for Carbon Steel Electrodes for Shielded Metal Arc Welding, was the pioneering filler metal specification, introduced over eight decades ago by a joint committee of ASTM International and AWS. The A5 Committee has periodically revised this document, with another revision planned for 2023.
Currently, AWS maintains nine distinct A5 filler metal specifications for SMAW electrodes, each dedicated to a specific alloy (mild steel, stainless steel, etc.), including one for underwater wet welding electrodes. For Excalibur® 7018 MR® to bear the AWS classification of E7018 H4R, it must meet the test criteria and requirements outlined in AWS A5.1. These encompass chemical composition, mechanical properties, diffusible hydrogen level, and moisture pickup. Additionally, there are stipulations regarding usability, sizing, packaging, and labeling.
SMAW Electrodes
When determining the appropriate SMAW electrode for a task, several factors must be considered, including base metal selection, thermal conditions, joint design, machine parameters, and welding code requirements. While many SMAW electrodes share similarities, certain characteristics render specific electrodes more suitable for particular applications. SMAW electrodes for carbon steel can be categorized into four groups based on their usability characteristics.
Rapid Solidification Electrodes
Rapid solidification electrodes (e.g., E6010 and E6011) possess the ability to deposit weld metal that solidifies rapidly, offering advantages when welding joints with poor fit-up or when welding in vertical/overhead positions (Fig. 1). These electrodes typically provide deep joint penetration and maximum admixture while demanding a high degree of operator skill.
Rapid Deposition Electrodes
Rapid deposition electrodes (e.g., E7024-1 and E7028) can deposit metal swiftly in the heat of the arc, enabling the creation of very large welds on flat and horizontal surfaces. They are well-suited for novice welders due to their ease of use. The coverings of rapid deposition electrodes contain approximately 50% iron powder, yielding high deposition rates.
Fill-Freeze Electrodes
Fill-freeze electrode characteristics are intermediate between rapid solidification and rapid deposition electrodes. Fill-freeze electrodes offer medium joint penetration and medium deposition rates. These electrodes are particularly well-suited for welding sheet metal and are typically used in all welding positions. They are the go-to electrodes for home or farm welding applications. Examples include E7014 and E6013.
Low-Hydrogen Electrodes
Low-hydrogen electrodes (Fig. 2) exhibit either rapid deposition or fill-freeze characteristics. They typically produce welds of radiographic quality with excellent notch-toughness properties. These electrodes reduce the risk of underbead cracking and are desirable for higher-carbon and low-alloy steels. Low-hydrogen electrodes may also mitigate the need for steel preheating. Although low-hydrogen electrodes should arrive in hermetically sealed containers, once opened, they become susceptible to moisture pickup.
Proper storage and handling of low-hydrogen electrodes are crucial for preserving their unique properties. Electrodes designated H4—for example, E7018 H4 and E7016-1 H4R—are designed, manufactured, and tested to be resistant to moisture absorption.
SAW Consumables
SAW employs two separate consumables (flux and electrode) to produce a weld deposit. The weld metal is a combination of both, necessitating the classification of the flux/electrode combination.
Techniques for Classifying SAW Consumables
It is essential to recognize that the AWS specifications outline two methods for classifying SAW consumables: a multiple-pass technique and a two-run technique (used exclusively in A5.23). The two-run method involves a single pass made from each side of the plate (Fig. 3). This approach is common in the manufacture of pipe sections, wind towers, and various other industries. Due to the recognition of these two distinct techniques, the same flux/wire combination may be certified to multiple classifications, each with significantly different strength and toughness designators. This discrepancy arises from substantial variations in the degree of base metal dilution, the weld metal geometry, and the extent of microstructural grain refinement between the different welding conditions. For instance, Lincolnweld® 761/L-61 is classified as both F7A2-EM12K and F8TAZG-EM12K. A straightforward way to identify a two-run classification is the presence of a T following the number for the strength designator.
Many real-world SAW applications fall between the two-run and multiple-pass conditions of the AWS consumable classification test. The drive for increased productivity often results in a designed multiple-pass weld consisting of only 3–4 passes (Fig. 3C). In such scenarios, the weld metal toughness will often be closer to the two-run condition. It is advisable to consider both the multiple-pass and two-run classifications reported by the manufacturer to determine if the chosen flux/wire combination is likely to meet the required mechanical properties. An easy way to accomplish this is by utilizing an online certificate site such as lincolnelectric.com/en/Certificate-Center.
Conclusion
Whether SMAW or SAW, achieving quality welds typically begins with using quality consumables. High-quality consumables often bear a classification in accordance with an AWS A5 specification. Knowing the appropriate consumable for the job will facilitate the development of the ideal welding procedure. Optimal input variables (welding consumables) are key to achieving desirable output variables (products).
source: www.aws.org February 2023 “An Introduction to SMAW and SAW Consumables” https://www.aws.org/magazines-and-media/magazine-and-journal/welding-journal/wj-feb-23-feature-2-melfi-lincoln-an-introduction-to-smaw-and-saw-consumables/