How To Reduce Dross and Slag During Plasma Cutting
Plasma cutting produces clean and accurate cuts when set correctly. But certain maladjustments and errors can cause excessive dross and slag to form on the cut edge, which impairs your productivity. Nobody wants to clean the dross, especially not from a large batch of cut pieces.
Whether you rent plasma cutters or buy them, you can’t experience all benefits of plasma cutting unless you minimize or eliminate dross. So, let’s discuss some effective ways to prevent and remove dross on your plasma cuts.
Understanding Dross And Slag in Plasma Cutting
Dross, sometimes called slag, forms underneath or on top of the cut edge when plasma cutting. While eliminating simple and common errors leading to dross formation usually provides a clean cut, it’s not uncommon that even experienced plasma cutter operators get dross buildup.
What is Dross/Slag?
Dross is a molten metal that solidifies at the edge because the air/gas pressure didn’t blow it away. As you plasma cut, the compressed air/gas blows away the molten metal from the cut line, but there are many reasons why a part of the blown metal can adhere to the cut edge.
Sometimes you’ll see people refer to dross as slag. But, “dross” is the most accurate term since slag is usually associated with the protective residue when performing MMA or FCAW welding processes. Still, dross can resemble slag appearance, so these terms can be used interchangeably to define the re-solidified metal at the plasma cut line.
Why Are They a Problem in Plasma Cutting?
If you run a fabrication shop, you know how bad any bottlenecks in production can get. No one wants to miss deadlines or hold back on taking more jobs. But, plasma cutting a large batch, like 500 machinery parts, will take significantly longer if every part needs dross removal on some or all edges.
To make things worse, removing certain kinds of hardened dross requires using an angle grinder, which can leave a relatively large visually-altered area due to the abrasiveness of the grinding stone. In addition, stainless steel or other sensitive metals may experience discoloration, warping, and loss of mechanical properties during post-cutting dross removal.
Some metalworking shops may not have enough workforce to manually remove the dross from a large batch of cut parts. A small shop could take on a big job and struggle to manually clean the edges if there is a significant amount of hardened dross.
Preventing Dross and Slag Formation
The best cure for dross is prevention. If you set up your plasma cutting parameters correctly, you can save significant labor hours on dross removal and achieve clean cuts.
Choosing the Right Plasma Cutting Parameters
“It’s vital to synchronize your plasma cutting speed with the amperage output for the cut material type and thickness.”
It’s vital to synchronize your plasma cutting speed with the amperage output for the cut material type and thickness. Every cutting system has detailed settings in the manual. You can rent plasma cutters from Red-D-Arc, and they all come with instructions for setting up the cutting parameters. Even portable plasma cutters, like the Hypertherm Viper 45, include details on how to set them up for the cut thickness and material.
But, even if you do set the plasma cutting system correctly, you can sometimes get some dross on the cut edges. Slight differences in material thickness and alloy can cause this, and the simple solution is to fine-tune the settings to find the sweet spot.
Generally, using too high of a cutting speed or low amperage causes dross to accumulate on the bottom edge as hard globs of metal, due to the arc lagging behind the torch. These metal globes are challenging to remove and require extensive grinding or machining to get a clean edge. Sometimes excessive travel speed can also cause dross to form on the top edge of the piece depending on the torch standoff distance, material type, and cut thickness.
On the other hand, too low of a cutting speed or too high amperage output produces very thick dross at the bottom of the cut. That’s because a slow-moving arc focuses more energy than necessary per inch of cut metal. So, the arc stays for too long in the area that’s already been pierced. As a result, the arc widens and starts “eating” the walls of the cut because it is looking for more electrically conductive metal; if it can’t find it in front, since it’s moving slowly, it will find it left and right. But, eventually, the kerf widens so much that the air/gas pressure can’t physically force the molten metal to fly off from the cut, resulting in thick dross formation.
Maintaining Proper Torch Height and Standoff Distance
If the torch distance from the cut piece is too low, you’ll get a similar dross formation effect as cutting with low speed. Reducing the standoff distance causes too much energy buildup.
Cutting with too high a standoff distance, or torch height, can cause the opposite effect. Too high a torch distance reduces your arc power, causing a similar effect as when cutting too quickly ‒ hard dross accumulation.
Using High-Quality Consumables
Using high-quality consumables, like the SYNC consumables available with SYNC Hypertherm plasma cutters, will help you make clean cuts. But, regardless of the used plasma cutting consumables, they need to be in good condition to make clean edges without dross.
Nozzles showing signs of wear, like orifice turning elliptical, should be replaced. The poor consumable condition can contribute to dross accumulation.
Effective Techniques and Solutions for Dross and Slag Removal
You can employ several methods to remove the dross. But, choosing the dross removal technique depends on the dross hardness, material type, and time/labor constraints.
Mechanical Methods
Mechanical slag/dross grinders can remove the dross from the cut parts by rotating tiny pins opposite to the metal being fed into the machine. As a result, pins hit and break off any dross accumulated on the metal’s surface.
Using Chipping Hammers or Scrapers
Chipping hammers, scrapers, and chisels work well for the dross that hasn’t hardened and when working with low-volume part batches. Even if the slag breaks off just by scraping it off with a putty knife, it can be time-consuming to clean many parts.
Grinding and Sanding Techniques
One of the most effective ways to remove medium-thickness slag is the angle grinder with a flap disc. It’s fast, effective, and won’t gouge out much of the parent material. But, if the slag is thick and hard, the angle grinder with a grinding disc will get the job done. However, grinding with a disc can damage the face of the cut part.
If you are dealing with light dross, you can use an angle grinder with a wire brush wheel to remove it. While it’s significantly faster than using a chipping hammer for large batches, grinding is a safety hazard. Wearing eye and body protection is non-negotiable when using an angle grinder.
You can also use a sanding belt to grind off dross of any size and strength. But, they are also better suited for dross removal on non-ferrous materials like aluminum. You can’t use regular grinding discs for aluminum because it’s too soft for them. Grinding discs can load on aluminum, posing a safety hazard and significantly reducing efficiency. But, sanding belts expand the sandpaper’s narrow grooves, making them less likely to clog up on aluminum.
Chemical Agents
You can use anti-spatter sprays to prevent dross from adhering to the cut edge to an extent. The degree of success will depend on the chemical composition and the brand’s quality.
Best Practices for Dross and Slag Management
Now that we’ve covered how to prevent dross from forming and how to remove it if it does develop, let’s discuss some practices for dross and slag management in your shop.
Regular Cleaning and Maintenance of Plasma Cutting Equipment
“Letting the metal dust pile inside the power source may impede the cut quality.”
To reduce the dross accumulation, your plasma cutting equipment needs to be in tip-top shape. If the consumables are regularly replaced, your cuts are less likely to have dross. In addition, a clean and dust-free plasma cutting power source will deliver accurate and consistent amperage output. So, it’s important to conduct regular maintenance of your equipment. Letting the metal dust pile inside the power source may impede the cut quality. The same goes for the CNC table and other equipment you rely on to behave according to the set cut speed, amperage, torch distance, and cut path.
Proper Disposal of Dross and Slag
Regardless of how small pieces of metal are produced when chipping away the dross, they still pose a safety hazard. Workers can experience cuts and eye injury from dross removal and subsequent handling.
Workers must wear full personal protective equipment (PPE), like work gloves, pants, jackets, and eye protection that meets ANSI Z87.1 standards.
Collected dross should be sent to recycling, along with other scrap metal from a fabrication shop. While fabrication shops today produce far less scrap than in the past, some metal parts, like the dross, are pure waste that can’t be used again without recycling.
Conclusion
Using the correct settings for amperage output and travel speed with high-quality consumables, will significantly reduce the amount of produced dross. If you still get some dross on the cut line, change the cut parameters incrementally. Sometimes the gas choice, material type, thickness, and other variables require slightly different parameters than described in the user manual.
