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Plasma Technology

Clean plasma cutting

By Lynn Stanley

Shipbuilder finds a clean-air solution for plasma cutting with a modular dust collector

May 2011- Jeffboat, Jeffersonville, Ind., uses dual torch plasma cutting systems to cut painted mild steel plate 3/8 in. to 2 in. thick and 10 ft. by 40 ft. long. The cut plate is used to make bulkheads and runners for barges. Challenged with keeping its work environment clear of dust and smoke generated by its plasma cutting operation, Jeffboat found a clean-air solution and an unexpected return on investment with a Gold Series modular dust collector from Camfil Farr Air Pollution Control, Jonesboro, Ark.

The manufacturing arm of American Commercial Lines Inc., Jeffersonville, Ind., Jeffboat is the largest inland shipbuilder and repair facility in the United States. The company occupies 68 acres, including 5,600 ft. of frontage on the Ohio River. Jeffboat designs and builds custom inland and ocean service barges ranging from towboats and hopper barges to tank barges with up to 30,000-barrel capacity for inland waterways or limited load line and oceangoing tank barges with 30,000 to 50,000-barrel capacity.

"Jeffboat tried several downdraft systems with disappointing results," says Jonathan White, a mechanical engineer for PlasmaCraft Inc., Muscle Shoals, Ala. PlasmaCraft specializes in CNC plasma and oxy-fuel cutting equipment. The company is a longtime supplier for Jeffboat’s equipment, retrofit and service needs. "Jeffboat installed a water table, a more costly option when compared to downdraft systems, but it wasn’t very effective at collecting the plasma cutting operation’s residue," says White.

With a water table, the metal plate typically is positioned on a bed of slats. Air is forced into or exhausted out of a chamber concealed below the slats, causing the water level in the table to rise or fall accordingly. Cutting plate about 3 in. below the water is best for reducing noise, glare and smoke, but most shops cut plate slightly above or just below the water level.

"Jeffboat is very safety-oriented," White says. "They didn’t want any smoke being released into the air. A water table can remove smoke, but they found the system didn’t capture dust very efficiently and, once used, the water must be treated as waste water. The process for removal is quite costly, requiring the water to be sealed in barrels and picked up by an Environmental Protection Agency representative for proper disposal. The water table system also has a tendency to rust, creating the potential to leak waste water."

Designing a system
When White saw the Gold Series modular dust collectors perform in other facilities, he knew it was the right solution for Jeffboat. "In addition to seeing the Gold Series systems operate, I also knew Farr’s distributor, Scott Reimer, Universal Torch & Equipment, Cattaraugus, N.Y. The company’s knowledge and service sets it apart." Universal Torch and Equipment represents a variety of cutting equipment, replacement parts and consumables.

Jeffboat agreed to test the Gold Series dust collector. The company’s purchasing, engineering and maintenance departments worked with Reimer and Farr engineers to evaluate the shipbuilder’s needs. "Most companies don’t understand the relationship between the table design, the length and design of the duct work, and the cubic feet per minute of air draw and static pressure of the collector," says Reimer. "You also have to ensure you will achieve free air flow. Something as simple as a blunt corner can cause loss of velocity in air draw. These are all critical elements in designing the right system for the customer’s needs. Farr is able to combine knowledge and field experience with technology to offer innovative equipment with the capability to perform in difficult work environments."

Following evaluation of Jeffboat’s needs, the company selected Farr’s Gold Series modular dust collector system with 48 HemiPleat Gold Cone filter elements. Related components included a sprinkler system, spark trap inlet and silencer to reduce noise levels. By eliminating the need to incur costs for disposal of waste water produced by the water table, the team also determined the savings would pay for the new downdraft system in just 18 months.

Jeffboat runs one to three work shifts processing, cutting and fabricating 1 million to 3 million tons of mild steel annually. "With Universal Torch, we had a single source for both the new dust collector and the downdraft table," says White. "It was the largest table they had ever designed and built."

The table was built using design variables that included table volume, steel thickness, the number and size of the plasma cutting systems, volume of smoke and dust generated and the duct work design for the collector. "Each system Farr builds is tailored to the special requirements of the customer," says Reimer. "Once the table is designed, the Farr dust collector is matched to the specifications of the table."

Jeffboat’s downdraft table is 25 ft. wide and totals 110 ft. long. "Jeffboat wanted a mechanical table for longevity," says White. "They also needed some on-site modifications made to the dust collector system."

Eight cranes run the length of Jeffboat’s manufacturing facility loading and unloading the tables with steel plate. "We modified the assembly system to lower the height of the unit so it would clear the cranes and built special hoppers and shorter retrieval points to accommodate Jeffboat’s retrieval bins for reclamation of steel dust," Reimer says.

The downdraft table and dust collection system were installed in 2009. With the dust collector fitted inside the manufacturing facility, a double set of duct work totaling 40 ft. with a tube diameter of 20 in. was used to attach the system to the downdraft table and achieve a good seal.

When the system was turned on, the results were immediate, says White. "With the new system, the workers could see each other across the table. The smoke was virtually eliminated. Without the system, the whole facility would have been filled with smoke in just minutes."

The OSHA personal exposure limit is 5 milligrams/m³ for hexavalent chromium generated from cutting metal. "The Gold Cone filter cartridge provides an efficiency rating of 99.999 percent removal for 0.5 microns or larger, making it especially effective on the microscopic particles that make up plasma cutting smoke," says Reimer.

The dust collection system requires minimal maintenance. Built with heavy-duty carbon steel construction, the carbon steel components are 5-stage acid washed prior to powder coating for maximum paint adhesion and corrosion resistance.

A return on investment
Vertical design of the Farr filter cartridges provides efficient pulsing of dust, eliminating uneven dust loading associated with horizontally mounted cartridges. The system’s online filter-cleaning process allows the unit to run continuously. Channel baffles installed in the inlet protect the filters from incoming dust and separate the larger particles directly into the hopper, reducing the load on the filters. "After three years of operation, the filters have yet to be changed," says White.

The Farr system also allows Jeffboat to reclaim iron dust and recycle it as steel. The slag goes into a separate bin and is recycled. Once the dust is collected into the system’s chambers, the chambers are emptied into the scrap bins. The steel dust and slag then go to the recycling facility. "The ability to recycle allows Jeffboat to recoup costs and enjoy additional savings, so it’s a win-win situation all around," says White.

Because the dust collector can meet airflow requirements with 25 percent smaller housing, the system takes up less factory floor space. "In addition to meeting Jeffboat’s safety requirements to maintain clean air in the work environment, the marriage of the downdraft table with the Farr dust collector has proved a perfect match for the company’s needs." FFJ

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