In almost every industry, machine uptime is critical. Downtime from unscheduled maintenance interrupts production at the machine and also affects the downstream processes that rely on those parts to complete a job order.
In plasma and laser cutting processes, an often-overlooked cause of downtime is slag buildup on the slats in the cutting tables. The costs and delays caused by slag buildup result in wasted time, removal costs and unsatisfied workers. While preventing slag is ideal, even when following best practices, slag is still going to occur.
Understandably, the condition of the slats impacts the plasma cutting process. When slag sticks to the top and sides of the slats instead of falling through the gaps, the buildup may create uneven surfaces. If the cutting table is no longer flat, it can result in uneven cuts and decreased quality. If slag continues to build, it can even create a “bridge” between the slats, preventing air from circulating and removing fumes.
“The buildup of slag on the slats is a huge concern because it causes issues with the machine,” says Philip Laforest, R&D product manager, Walter Surface Technologies Inc. “Slag can stick to the parts being cut, which means the parts then have to have that slag ground off, which adds a lot of time. It’s all about having the cleanest parts possible.”
Therefore, it’s critical to consistently clean or replace the slats. However, a typical plasma cutting table has 60 to 100 slats or a slat every 2 in. to 3 in. Cleaning or replacing the slats is labor-intensive, physically demanding and an overall unpleasant job.
“Dealing with slag on slats is a nightmare,” Laforest says. “People try to bang on it or grind it off. Some use a pneumatic hammer-type of tool. There is also a machine that goes on the slats that heats up the slag to make it easier to remove. But all of these processes take a lot of time. To be viable, plasma machines have to run a lot of hours. You can’t lose a machine for a whole day of cleaning.”
Replacing slats typically takes even longer than cleaning them, causing machine downtime lasting a day or two. It requires removing the slats and chipping off any slag on the frame; removing the slag, and any parts that fell through, from the bottom of the machine; and then installing new slats.
Using a wet plasma cutting table helps prevent slag buildup on the slat itself (because the water lowers the heat of the slat and the slag), but it causes other issues when it is time to clean or replace the slats. And while other benefits of a wet table include noise and smoke reduction, it requires more maintenance because there is another fluid involved. Not to mention the rust issues involved with the parts, which requires an anti-rust product be used.
“Slag buildup is such a big issue that some customers prefer to not even clean their slats and just dispose of them and put in new ones,” Laforest says. “But that can be very costly, especially when steel prices are up. It can be up to $20,000 to replace slats on a machine right now, plus labor costs. Changing out slats can be as low as $5,000 if they are made from just bare steel or other cheaper materials, but even that is pricy when a shop has multiple machines.”
A typical plasma cutting table requires slats to be replaced every three to four months. Annually, that could total up to $15,000, and that would be on the low end.
“If the machine is constantly running,” Laforest notes, “I would say you have to replace the slats every three to four months, depending on the usage and the material being cut, but definitely at least three times a year.”
Slats typically require cleaning every month or two, again based on usage and material.
“Aluminum, for example, creates a lot of slag so the slats might have to be cleaned every month,” Laforest says. “Aluminum slag is difficult to remove because the slag is gummier and more ‘melty.’ Because it is so soft, it clogs up the abrasives when you grind it off.”
Whether cleaning or replacing slats, perhaps the biggest challenge today is finding workers to actually perform the tasks. Shops just don’t have the resources to devote people to performing slat maintenance.
One solution to the slag buildup problem on plasma cutting tables is a ceramic-based heat shield coating. Ceramic is known for withstanding high temperatures and Walter Surface Technologies’ E-Weld Plasma is a ceramic solution that is applied to the slats to reduce the buildup of slag over time. The coating is resistant to extreme heat and wear and is cost-effective for a large surface area like a cutting table.
“This is a permanent coating,” Laforest says. “Ours is a ceramic-based coating that offers unique protection to prevent the slag from sticking to the slats. Even if the slag sticks, you can just take a little hammer and tap the slats, and the slag will easily fall off.”
A thin layer of coating is sprayed on the slats, and after a four-hour drying period, a second coating is applied, which needs to dry for about 12 hours or overnight. The best application is on brand-new slats. By using the ergonomic, arm-mounted sprayer, the worker can quickly coat large surface areas. Each 10-kg container provides enough solution to cover 500 sq. ft.
After a certain period of time, the coating is no longer viable and the slats are disposed of as usual. The product adheres the same no matter from what material the slats are made. It can be used on wet and dry tables.
The E-Weld Plasma solution significantly decreases the amount of time and effort needed to clean slag off of slats, which saves a great deal of associated costs. The slats can be used longer before needing to be replaced.
“It typically extends the life of the slats about 50 percent, depending on the application,” Laforest says. “So, if you’re paying $20,000 every three months to replace slats, you will now pay $20,000 every six months. Some customers may only need to spend $20,000 just once a year.
“Nobody else is offering this type of product right now,” he continues. “There are products out there that follow a similar idea, but they aren’t permanent. They have to be applied every day or even several times a day.”
As noted, shops just don’t have the labor supply for these kinds of tasks. They have to rely on a worker to reapply these types of coatings and most workers care more about having the machine running than stopping to apply a coating. And with multiple shifts, it can be even more of a problem if no one knows who is doing the coating.
In addition to reducing the undesirable job of cleaning the slats on a plasma cutting table, the E-Weld Plasma solution improves worker safety. The coating can eliminate the health and safety hazards associated with current cleaning processes, such as grinding. Slats with little or no slag buildup also allowing air to circulate for better ventilation. The coating does not contain harmful chemicals or corrosive substances.
As mentioned, E-Weld Plasma also works for laser cutting, as the cutting tables are similar.
“The only issue with using the coating on a laser cutting table is the power can’t be more than 10 kW because it will burn the coating surface,” Laforest says. “The beam is so powerful it will burn the surface.”
In addition to protecting cutting tables, some customers are applying the coating to nearby areas to prevent slag from sticking to exposed equipment, such as work tables. Also, ceramic heat shield solutions are available for welding torch nozzles and contact tips.
So, while cleaning the slag off of any surface, especially cutting table slats, isn’t a fun task by any means, E-Weld Plasma provides great surface protection that increases the life of the equipment and makes cleaning operations faster and safer.