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Laser Technology

Smoke gets in your eyes

By Russ Olexa

January 2009 - When you walk into a factory and see blue haze around the lights, you know there’s a problem with air pollution--one that could cause the owner a great deal of trouble with the Occupational Safety and Health Administration and possibly worker-related health concerns.

It’s Pat Gilmour’s job to solve these air pollution problems. He’s an account manager for Plaser, a division of Great Lakes Air Technologies Inc., Clawson, Mich. He’s found that welding processes and laser and plasma cutting are three of the largest sources of air pollution for sheet metal processing companies. "You can fill a plant in 20 minutes with welding fumes or in two minutes with a plasma system, depending on the plant’s size," he says. "Lasers take longer because of their fine-cutting kerf, but they’re still polluters."

Cleaning the air
"OSHA always plays a part in any air-quality issues," says Gilmour. "They establish the permissible exposure limits that are federal law, and a facility can’t exceed those over a given time period, usually an eight-hour shift. However, customers don’t want to violate the law and put employees at risk. But oftentimes employers will be pre-emptive in eliminating air pollution for several reasons. One is the overall hygiene of the plant, and another is that if they have a dirty plant, it can affect equipment and employees."

Smoke makes up most of the air pollution that must be eliminated. It’s composed of micron-sized particulates, such as a fine mist of oil and steel from welding or particles of aluminum from a laser cut. All of it has to be extracted from the air. The easiest way could be opening a shop’s doors and letting the wind blow out the smoke or strategically placing large fans throughout the building. But often those aren’t the best way, especially for a facility that’s heated or cooled and must meet OSHA requirements for a certain process, such as cutting stainless steel that releases hexavalent chromium into the air.

A collectible is a particle that’s seen as smoke. It can be made up of microscopic steel particles produced during welding or it can be made up of the oil on the surface of steel that's been converted by the heat introduced during a cutting process. With welding, collectibles relate to the electrode, which is usually carbon steel wire. This electrode will convert to 1 percent to 2 percent of a collectible material within a fume system. For instance, for every robot that does welding and has a 1,000-lb. welding pack of wire, a company is looking at 10 lbs. to 20 lbs. of material that will be collected in the filtration system.

Of all the fumes generated in welding, 85 percent comes from the electrode. The other 15 percent comes from burn-off from whatever is on the welded metal’s surface, such as oil or galvanizing material.

"For welding aluminum, 6 to 7 percent of the welding wire converts to a collectible material, but it’s a different particle," says Gilmour. "It’s dry, somewhat like a flour consistency. Steel particulate tends to be oilier. This has to do primarily with the oils that are placed on it from an upstream process such as stamping."

He mentions that for plasma cutting, an especially dirty operation because of the amount of particulates sent into the air, collectible material is composed of the cut width, multiplied by the thickness of the metal, and then multiplied by the length of the cut. What lies in the bottom of the table or on the ground after cutting is a small percentage from the cut.

With plasma, 100 percent of the fumes become collectible material. The metal that made up the kerf becomes particles in aerosol form, which will go everywhere in a facility.

"Welding fumes are released as a wafting gas that expands, whereas plasma cutting is gas assisted with compressed air," says Gilmour. "You have a driving force that’s blowing the metal out of the cut area, but it’s being released with 60, 80 or 100 psi of back pressure. So it distributes over an area and expands. Keeping this under control can often be a challenge. Even if it’s being blown down into a cutting table, you have to keep the gas below the metal plate, or it’ll release into the plant."

With a laser, the assist gas can also be high, but because it’s focused to a narrower cut width, fume generation is lower. Gilmour notes that most laser manufacturers offer their systems with fume extractors or will package their systems with a product like the Plaser air filtration system, which will be optimally sized for the specific application. These systems usually have a down-draft table beneath the cutting surface that pulls air from the cutting area down into the air filtration system, which will clean it and then release it back into the shop.

"It’s in the laser manufacturers’ best interests to have fume extraction because otherwise a dirty environment can easily cause problems with the laser," Gilmour says.

He also says clean air is important for overall machine and shop maintenance.

"In the metalworking industry, any time you release a particle through welding, plasma, laser cutting or even grinding, it comes off with a negative or positive polarity," Gilmour says. "Whatever its polarity, it’s a free-roaming, very fine, submicronic particle in your facility looking for something to attach to that has the opposite polarity. Often, power supplies have a fan running across circuitry that’s blowing cool air across it to keep the temperature down, and here you have this free-roaming particle that gets sucked into the fan and blown across circuitry. It finds its opposite polarity, and they attach themselves. This tends to blow out power supply boards for welders and other equipment.

"It’s brutal on an employee to work in a contaminated environment," he says. "They’ll just keep looking to find a better one. If a company has spent a lot of money training their employees, they should realize that a clean environment is important to keeping them. No one wants to work in a dingy, polluted facility. Also, how does the facility appear to a customer? If it’s dark and filled with fumes, they’ll have second thoughts about working with you."

A company should look at the ability to recirculate clean air through a system rather than blowing it outside. This will save both heating and air conditioning costs, which can be dramatic in certain areas of the United States.

Spark generation
Another important aspect of air filtration is how a system addresses sparks that welders, lasers and plasma systems produce, which can easily lead to fires.

"In the metal cutting industry, the No. 1 byproduct of cutting is spark generation," Gilmour says. "These systems all create a plume of sparks. [For] any ventilation system that’s installed in any of these industries, if the sparks aren’t addressed and a live or active spark is sucked into the system and hits a paper-based filter that has particulate matter built up on it, a fire can be a direct result of this collision.

"Our Plaser system has a spark arrestor built into every unit," he says. "Plus, we have a fire-suppression shutdown system. If a spark should bypass our spark arrestors, the unit will shut itself down and trip an alarm and strobe light to notify personnel if a fire occurs."

Automated cleaning
Some air filtration systems don’t have a cleaning function other than replacing the filter media as needed. But some offer a way to back-pressure the filters using high-pressure shop air. The air pulses the filters, allowing anything stuck to them to be blown off. These particulates then fall to the bottom of the filter system, where they can easily be disposed of. This adds to longer filter medium life, less overall maintenance and lower system costs.

"However, some filtration systems, such as ones for welding, might deal with such a high oil concentration in the air that once the oil impregnates the filter, it can’t be cleaned by pulsing--it has to be replaced," says Gilmour. "Sometimes you can increase the upfront pre-filtration, trying to drive the oil out, but you’ll get the bigger particles, [and] then the smaller particles will pass downstream to the filter paper. So you’ll have to be careful in choosing what technology you use for an application and how it works."

Reducing insurance costs
Gilmour says that with the right filtration system, even insurance costs can be reduced to help pay for a system.

"One of our customers was originally using fans to get rid of particulate matter, but he still had a huge cloud in the plant," he says. "The customer made a big investment to clean up the air. He brought in OSHA to do testing. He wanted to know what the degree of cleanliness was from a before and after standpoint to have analytical data for this. Then he compared the air once the filtration systems were being used. Once he had this information, he tested the outside air. He found that the air in his plant was cleaner than the air outside. At this point, the insurance company was asked why the company was a high-risk manufacturer. They said [it] was a manufacturing facility that had hot sparks flying around that could cause fires. The owner said that he still might have hot sparks, but now he had all the air filtration systems in place to reduce any risks. He wanted a payback on the systems because of his reduced environmental exposure. And sure enough, when he negotiated his contract with the insurance company, he’d received a significant reduction in his premium."

Participating systems
Before purchasing an air filtration system, it’s best to call the manufacturer of the machinery. Some models may not be adaptable to certain systems.

"All Mazak lasers come with the capability to add a fume extraction system," says Mark Mercurio, application manager at Mazak Optonics Corp., Schaumburg, Ill. "We set up the equipment with an outlet and ducting internal to the machine, so they can be hooked up to an external dust collector."

He also says Mazak’s new Chicago-area sales and service building will be able to demonstrate 17 laser systems. Mazak has been working with Great Lakes Air Technologies to develop a fume collection system for these lasers.

For fume extraction on a large scale, it’ll use a system that has attachments to each laser but has one central filtration system to handle all the fumes generated.

"Today, good dust collection saves maintenance costs and helps the laser process," Mercurio says. "Without the smoke that gets under the table, the laser can cut parts faster."

He also notes that on some laser systems, the fumes can dirty a lens, which will shorten its life and increase maintenance. However, fumes don’t affect Mazak’s laser systems’ optics because of their design.

When a company orders a laser with an air filtration system, it’ll be properly sized to handle fumes for any type of cutting, whether it’s 1-in.-thick steel plate or 1/2 -in.-thick aluminum plate. But with an older laser or other process that generates fumes and no filtration, it’s best to work with an air filtration specialist to get the correct system for the application. FFJ

 

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Sources

  • Mazak Optonics Corp.
    Schaumburg, Ill.
    phone: 847/252-4500
    fax: 847/252-4599
    www.mazaklaser.com

  • Plaser (Great Lakes Air
    Technologies Inc.)

    Clawson, Mich.
    phone: 248/655-1800
    fax: 248/655-1801
    www.plaservent.com
    e-mail: info@plaservent.com

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