by Emily Newton
Welding slag is a by-product of some fabrication methods. It forms when molten metal impurities combine with flux or other materials. It creates a hardened layer on the weld that requires removal using mechanical processes, such as chipping the extra material away.
Despite its unsightly appearance, slag protects newly welded areas from oxidation and atmospheric contaminants. It also maintains the weld pool positioning in the joint during cooling, which is especially valuable for out-of-position welding. Many producers seek to prevent slag buildup to optimize quality. What steps can they take to do this?
Recognize the Signs and Outcomes of Slag Inclusions
Slag comprises the nonmetallic by-products of chemical reactions due to base metal impurities. Slag’s low density makes it rise to the top of the welding pool, solidifying as it reaches the surface. That solid layer prevents reactions between the air and molten metal. However, problems arise when slag gets trapped underneath the weldment, causing an issue called slag inclusion.
This phenomenon interferes with the uniform composition of high-quality weld joints and usually causes visible surface characteristics. They are typically thin lines or pinholes and have a transparent, glassy appearance. People identify those deeper in the weldment with nondestructive testing methods, such as ultrasounds and X-ray scans.
Slag inclusion can also contribute to numerous problems that could reduce weld performance later. Gaps filled with this by-product concentrate stress and cause localized strain, potentially compromising the weld strength.
Other complications can occur depending on the application of the welded material. Gas or liquid can seep through inclusions, compromising the usability of industrial vessels. These imperfections may also introduce corrosion, with rust quickly forming and worsening if not promptly addressed.
Novice welders or those learning a new method should receive slag incursion detection content in their training. People who know how to spot this defect can catch it early and ask their supervisors if they must rework.
Choose a Different Welding Type
Welders can prevent slag buildup by knowing more about what causes it.
- Shielded metal arc welding: Also known as stick welding, this technique relies on a flux-coated, consumable electrode. Slag builds up as the arc reacts with impurities caused by the melting electrode.
- Flux-cored arc welding: This option — often used for construction welding and working with heavier fabrication materials — features a flux-filled wire, with the flux creating slag as the wire melts. The slag that forms protects the weld from oxidation.
- Gas-shielded flux-cored arc welding: This type also relies on a flux-filled wire but uses shielding gas. Because flux forms to create clean welds, workers must use slag removal tools later.
- Submerged arc welding: This popular option for applications such as shipbuilding and pipelines requires using flux to cover the welded area, protecting it from contamination. Fabricators work with a continuous wire electrode in this method.
Methods such as tungsten inert gas welding and metal inert gas welding use gas as a shield rather than flux. People who want to prevent slag buildup should consider using methods that do not create it. Some of those solutions are also excellent automation candidates. Automated systems minimize many quality issues, making them wise investments.
Understand How to Prevent Slag Buildup
Welding shop managers who notice ongoing issues with slag incursions in new welds should examine internal processes to determine the root causes. Parameters such as low amperage, low electrode travel speeds and oversized electrodes can increase slag incursion rates.
Poor welding technique also contributes to the problem, especially if fabricators have irregular arc gaps and electrode angles. Because of the time required to break bad habits and strengthen existing skills, managers may have fabricators make repairs to ensure products pass quality control checks and meet clients’ expectations.
Plasma gouging is a solution for all conductive metals, making it extremely versatile. This method uses an ionized gas arc to melt metal before a high-velocity gas stream blows it away. People use this option for surface preparation, weld removal and repairs.
Managers may examine fabricators’ process stages to find room for improvement. Preprocessing steps support flaw-free products by removing dirt, oil and dust from the material. People should also check for surface irregularities because slag can get trapped between gaps or inside craters.
As welders seek ways to tweak their technique, they can optimize outcomes by maintaining angles that harness gravity, using that force to make slag smoothly enter the weld pool instead of causing incursions.
If supervisors identify ongoing mistakes to target, innovative training solutions such as virtual reality offer engaging ways to enhance performance. For example, welding students in Mississippi can take advantage of a recently opened VR training facility to improve their skills as future shipbuilders. That center gives them a safe and realistic place to learn while supporting workforce development.
Select the Best Slag Removal Tools
People must remove slag from weld joints to inspect them. Numerous mechanical methods get the desired results. Because slag usually only adheres loosely to surfaces, workers can tackle it with chipping hammers, chisels or wire brushes. Some fabrication shops also have abrasive belts or wheels to address slag buildup. Abrasive blasting equipment and media may offer the best removal solutions when the issue occurs over a large surface area.
Companies also sell chemical slag-removal products, which use acids to neutralize the alkaline buildup, typically after remaining on the surface for one to two minutes. Specialized slag removal tools can also increase productivity if the buildup occurs in particular places and takes a long time to address.
One business offers a dedicated machine to clean slag buildup off plasma cutting tables’ support slats. The design features front and rear rollers and four rotating cutters that simultaneously target both sides of each slat. Operators stand on the floor or machine bed when working with it.
Decision-makers should evaluate the extent of slag accumulation issues in the workplace before determining which products can address them. Asking for worker feedback may also uncover practical process changes.
Treat Slag Buildup Removal as Integral to Weld Quality
Though slag naturally occurs during numerous welding types, its accumulation interferes with thorough inspections, and slag incursions can cause performance issues later. Creating and maintaining a process to manage slag buildup and pursue continuous improvement helps welding shop managers impress current clients and attract new ones.
