Why Does Welding Turn Black
Welding turns black due to the presence of excess soot after the welding process.
Several factors can contribute to the formation of excess soot, including too long of an arc length, not enough weld energy, incorrect direction of travel, incorrect gun angle, travel speed that is too fast, and insufficient gas flow coverage.
To prevent black spots on weld areas of zinc-plated gears made of En24 and En8 steel, solutions such as stripping and running the parts again, raising the concentration of hydrochloric acid dip, determining a pre-treatment cycle to remove flux left on the part, and using a hot water dip after plating can be employed.
Dipping welded parts in hot water, de-hydrogen embrittlement cleaning with nitric acid and hot water, and using a centrifugal hot dryer for better drying of plated parts are also recommended.
Brown marks near some welds can be caused by heat scale, torch angle, insufficient shielding gas, and spatter spray.
It is important to clean off the brown color, but it is necessary to ensure that the plating is still intact.
Seeking ways to fix parts and avoid the problem in the future is recommended.
Did You Know?
1. When welding turns black, it is due to the formation of a coating known as black slag. This slag is the result of impurities in the metal being burned during the welding process.
2. Welding can turn black due to a phenomenon called “carbon migration.” This occurs when carbon atoms from the electrode or the base metal combine with oxygen to form carbon dioxide, leaving behind a black residue.
3. Interestingly, the composition of the metal being welded can also affect the color outcome. For instance, stainless steel tends to turn black when welded due to its high chromium content, which reacts with the heat and creates a blackened surface.
4. The skill level of the welder can also play a role in why welding turns black. Inexperienced welders might inadvertently apply excess heat or use improper welding techniques, resulting in more oxidation and blackening of the welded joint.
5. It is worth noting that the black color in welding is not always a negative outcome. In some cases, intentional blackening is done for aesthetic purposes, such as creating an attractive blackened finish on certain metal artworks. This technique is called “patina” and is achieved through controlled oxidation.
Factors Causing Excess Soot In Welding
When welding, a common issue that may arise is the blackened appearance on the welded surface, primarily caused by excess soot. To minimize this problem, it is important to consider the following factors during the welding process:
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Too Long of an Arc Length: Maintaining an appropriate arc length is crucial for producing clean welds. If the arc length is too long, it can result in a higher amount of soot production. To avoid excessive soot formation, make sure to keep the arc length within the recommended range.
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Not Enough Weld Energy: Insufficient weld energy can lead to incomplete fusion and poor weld quality, which may result in the formation of excess soot. Providing adequate weld energy is essential for creating a strong and clean weld.
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Incorrect Direction of Travel: The improper direction of travel during welding can contribute to excessive soot formation. Welding in the wrong direction or changing directions too frequently can disturb the shielding gas flow, leading to the accumulation of soot on the weld.
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Incorrect Gun Angle: The angle at which the welding gun is held significantly impacts achieving a clean weld. If the gun angle is incorrect, the shielding gas may not adequately protect the molten weld pool, resulting in soot formation.
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Travel Speed Too Fast: Excessive travel speed can affect the weld’s quality and contribute to the production of soot. Welding too quickly can hinder the effectiveness of the shielding gas in reaching the weld pool, leading to the formation of soot.
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Insufficient Gas Flow Coverage: Ensuring sufficient gas flow coverage is crucial in preventing soot accumulation during the welding process. Insufficient gas flow can lead to inadequate shielding, allowing contaminants to interact with the molten metal and cause soot formation.
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Factors contributing to excess soot during welding:
- Too long of an arc length
- Not enough weld energy
- Incorrect direction of travel
- Incorrect gun angle
- Travel speed too fast
- Insufficient gas flow coverage
Checking Gas And Flow Rate For Proper Shielding
To mitigate the issue of excess soot in welding, it is crucial to take the following steps:
2.1 Checking the Gas Being Used
Verify the type of gas being used for welding. Different welding processes require specific shielding gases to prevent oxidization and soot formation. Use the appropriate gas for the specific welding application.
2.2 Verifying the Flow Rate
Check the flow rate of the gas. Insufficient gas flow can result in inadequate shielding, leading to soot formation. Ensure proper flow rate for effective coverage and protection of the weld.
2.3 Pushing to Shield Ahead of the MIG Weld
In MIG welding, push the shielding gas ahead of the weld to create a clean and protected environment for the molten metal. This technique minimizes the possibility of soot formation.
2.4 Pre-Flow to Ensure the Starts Are Shielded
Use a pre-flow of shielding gas before initiating the welding process to ensure the initial part of the weld is fully shielded. This procedure helps prevent the formation of soot during the critical starting phase.
2.5 Checking for Leaks in the Gas Delivery System
Periodically inspect the gas delivery system to identify any leaks or problems that may compromise the shielding gas delivery. Even small leaks can disrupt the shielding gas flow, leading to soot formation. Promptly address any detected leaks.
- Verify the type of gas being used for welding.
- Check the flow rate of the gas.
- Push the shielding gas ahead of the MIG weld.
- Use a pre-flow of shielding gas to ensure the starts are shielded.
- Periodically inspect the gas delivery system for leaks.
Solutions For Black Spots On Zinc-Plated Gears
In certain applications like zinc-plated gears made of En24 and En8 steel, black spots may appear on the weld areas.
To address this issue, several solutions can be implemented:
3.1 Strip and Run the Parts Again
If black spots occur after the welding process, stripping the parts and running them through the welding process again can help remove the black spots. This method allows for a fresh start, ensuring the quality of the welds and preventing black spot formation.
3.2 Raise the Concentration of Hydrochloric Acid Dip to Improve Cleaning
Increasing the concentration of the hydrochloric acid dip during the cleaning step can enhance the removal of black spots on zinc-plated gears. This solution improves the cleaning process and helps eliminate any contaminants that may contribute to the black spot formation.
3.3 Determining a Pre-Treatment Cycle to Remove Flux Left on the Part
A pre-treatment cycle can be implemented to remove any remaining flux from the part before further processing. Flux left on the part may cause black spots during subsequent plating, so a specific pre-treatment process can ensure the complete removal of flux.
3.4 Using a Hot Water Dip After Plating
To remove chloride-laden chemicals after plating, a hot water dip can be employed. This step helps wash out any remaining chemicals that may contribute to black spot formation. Proper rinsing and drying afterward ensure a clean surface without residual contaminants.
3.5 Further Research and Development to Find a Solution
In some cases, finding a comprehensive solution requires further research and development. It may be necessary to explore alternative methods or consult with experts in the field to identify innovative techniques or materials that can prevent black spots on zinc-plated gears.
Combating Black Spots From Silica And Base Metal Waste
4.1 Cleaning Process with Alkali Cleaner and Hydrochloric Acid Not Effective on Silica
Traditional cleaning processes, such as using an alkali cleaner and hydrochloric acid, may not be effective in removing silica from the welded parts. Silica is a challenging substance to remove, and alternative methods must be considered to ensure its elimination.
4.2 Sandblasting as a Method to Remove Black Spots
Sandblasting can be an effective method for removing black spots caused by silica and base metal waste. By subjecting the welded parts to controlled abrasive blasting, the silica and waste material can be properly removed, providing a clean surface for further processing.
4.3 Hiring a Certified Welder Trainer to Improve the Weld Process
To improve the weld process and minimize the occurrence of black spots, organizations may consider hiring a certified welder trainer. These experts can provide guidance, training, and supervision to ensure proper welding techniques are followed, reducing the probability of black spot formation.
Quality Issues And Rework Procedures In Welding And Plating
The combination of welding and subsequent plating can present several quality issues, including black marks and brown marks near the welds. To address these concerns, the following steps can be taken:
- 5.1 Black Marks Noticed in Welded Areas After Trivalent Plating
Black marks observed in welded areas after trivalent plating can be attributed to flux slag from the welding process. To prevent these black marks, it is essential to implement proper cleaning and blasting processes before initiating the plating step.
- 5.2 Rework Procedure: Use of Aluminum Paint
If black marks occur after trivalent plating, a rework procedure can be employed using aluminum paint. This step involves applying a coat of aluminum paint over the black marks to cover any imperfections and enhance the aesthetic appearance of the finished product.
- 5.3 Rust and Short Salt Spray Life Mentioned as Quality Issues
Apart from black marks, rust formation and short salt spray life are additional quality issues that can arise in welding and plating. To combat these issues, it is crucial to prioritize proper cleaning, ensure thorough rinsing, and employ appropriate corrosion-resistant coatings to enhance the durability of the plated parts.
- 5.4 Consulting a Plating Consultant for Assistance
In instances where quality issues persist or become increasingly challenging to resolve, consulting a plating consultant can provide valuable expertise and guidance. These professionals can help identify underlying problems, suggest improvements to the process, and ensure optimal quality outcomes.
In conclusion, the occurrence of blackening in welding can be attributed to various factors such as arc length, weld energy, direction of travel, gun angle, travel speed, and gas flow coverage. To combat this issue, it is crucial to check the gas being used, verify the flow rate, and implement appropriate techniques such as pre-flow and pushing to shield ahead of the weld. Additionally, specific solutions should be implemented for black spots on zinc-plated gears and black spots resulting from silica and base metal waste. Quality issues related to welding and plating can be addressed through rework procedures, proper cleaning, and consultation with plating experts. By understanding the causes and implementing effective solutions, it is possible to minimize the occurrence of blackening in welding, ensuring high-quality and visually appealing welds.
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Frequently Asked Questions
Why is my Aluminium weld black?
When aluminum is welded, the intense heat causes oxidation, resulting in the formation of aluminum oxide and magnesium oxide particles. These particles blend together to create a black appearance on the welded surface. This phenomenon is common when using a 5XXX filler such as 5356 due to the specific composition and characteristics of the alloy. It is important to remember that this black discoloration does not indicate a flaw or defect in the weld, but rather a natural chemical reaction caused by the welding process.
Why is my stainless welds black?
When stainless welds turn black, it is an indication of excessive heat during the welding process. The high temperature causes the stainless steel to oxidize, resulting in a dull grey or black color. This oxidation occurs not only on the surface but throughout the weld, compromising the corrosion resistance of the stainless steel. It is essential to ensure proper heat control while welding to maintain the integrity of the stainless steel and preserve its stainless properties.
What is the black stuff on a weld?
The black substance found on a weld is the result of a combination of silica from the tig rod and waste materials leftover from the base metal. These black spots are consistently found at the termination points of the weld. As the tig rod is used during the welding process, the silica can mix with the base metal waste, resulting in the formation of these distinctive black marks. While they may appear concerning, these spots are generally harmless and do not affect the integrity or quality of the weld.
What is the black spot after welding?
The black spot that appears after welding is an indication of a low current arc. This black dot is formed due to the insufficient heat generated during the welding process. When the current is not high enough, the weld does not penetrate the materials properly, resulting in a weaker bond and the formation of this distinctive black spot. By recognizing this visual cue, it becomes clear whether a Tip Arc Relay should be added to achieve the desired welding quality.
