Clearing the air for heavy welding
Mining equipment fabricator integrates advanced fume filtration
Joy Global does some seriously heavy fabrication, welding atop mining shovel components several stories tall. Weld fume control was becoming a problem, so the company installed an innovative, nonlocal fume collection system to help clear the air.
Industry advocates tout the new face of manufacturing. It's no longer dark, dank, and dirty, they say. The plants of today are bright and clean. Images of clean rooms and computer chip manufacturing facilities come to mind. But it's probably safe to say these advocates wouldn't identify mining equipment manufacturer Joy Global Surface Mining Inc. as a showpiece of the modern metal fabricator—that is, until recently.
Most welding occurs in two facilities, connected by a breezeway, at the company's 13-building Milwaukee campus. In each building at any given time, between 10 and 50 welders could be striking an arc and laying down some seriously heavy weldments. Certain multipass groove joints are anywhere between 2 and 6 inches thick, and even larger. Every year the company consumes more than 1 million pounds of welding wire (see Figure 1).
"Joy Global's production and sales are at an all-time high," said Ted Leamen, director, global EHS for Joy Global Surface Mining. During his eight-year tenure the company has processed as few as a dozen mining shovels annually. Today it is fabricating at a rate of more than 35 shovels a year. That's a tall order, considering these machines are several stories tall and weigh several million pounds. For instance, the company's 4100 XPC shovel weighs 3.2 million pounds—so big, it's shipped in pieces to customers and assembled on-site.
Such constant welding created that all-too-familiar haze, which hung below the buildings' 55-ft.-high ceilings. Despite the haze, welders actually worked within permissible fume exposure limits, since most of the fume gathered near the ceiling. "Our industrial hygiene testing showed no overexposures at all," Leamen said. "We were below OSHA and the more stringent ACGIH [American Conference of Governmental Industrial Hygienists] specified levels, though we did have some readings that were beginning to increase as our production demand increased."
Until last year the plant used a conventional roof ventilation and exhaust system. Though effective enough to keep workers below permissible exposure limits, the system couldn't clear the air entirely. It certainly didn't help worker satisfaction, either. Workers had complained for years, and for good reason. Although safe, the hazy environment didn't provide a welcoming work atmosphere.
In recent years personnel have executed an operational excellence initiative, and this has included a major lean 6S program (sort, straighten, shine, standardize, sustain, safety). Implementing the program, managers knew that the welding fume wouldn't make the "shining" component of 6S easy. Newly painted walls wouldn't have looked newly painted for long (see Figure 2).
Investment in advanced fume extraction hasn't typically given manufacturers a viable return on investment. That's why forever pragmatic manufacturing managers don't make major investments in large filtration systems unless they need them to keep fume concentration below permissible exposure limits. Fighting fierce global competition, managers keep their eyes on that all-important ROI.
That's the traditional stereotype, anyway. In fact, it's something that Leamen experienced first-hand. Working at other companies years ago, the safety manager led efforts to reduce worker fume exposure limits to permissible levels. Made to abide by safety regulations, the companies considered the purchase of fume-reduction equipment as a cost of doing business. It certainly wasn't seen as an investment.
At Joy Global, the situation changed after several mining executives took a plant tour. The visitors were from one of the largest mining operations in the world. Gazing across the plant, they couldn't see through the haze to the other side—not the best impression for customers who make tens of millions of dollars' worth of purchasing decisions a year. In a matter of minutes, fume reduction transformed from a cost to a vital initiative with a potentially huge return on investment.
Workflow and Fume Collection
Until recently, if a time-lapse camera were placed on the welding floor, the footage would show material moving everywhere, crisscrossing the shop every which way. This certainly wasn't anywhere near an organized part flow. Employees manufacture mining shovels that sell for millions of dollars, so any delay in manufacturing ties up a lot of money.
After some detailed value stream mapping, part of the company's operational excellence initiative, part flow now is much more orderly. Shovel components enter from one side of the building and move their way to the other side, stopping at strategically placed workstations.
Still, workers don't weld the same product time after time. Each massive assembly has weldments in different places, and some welders have to work at high elevations. So no matter how products flow on the floor, the operation really can't use local fume collection for most of its welding.
To develop a nonlocal fume collection system required extensive analysis of airflow, mainly because the company had to take three elevations into account: the workers on the floor, welders 15 to 20 ft. up, and the overhead crane operator at 50 ft., near the ceiling. Until last year fume floated to the ceiling and was exhausted by roof vents, and fresh makeup air from the outside was blown in. Over the years the company installed more roof exhaust fans to try to clear the haze but without much success, though it at least kept fume exposure below permissible levels. Still, all those roof fans running constantly consumed a lot of energy.
One alternative would have been an extensive ducted system, but as sources explained, this wouldn't have provided the flexibility Joy Global needed. Welders had to go where the welds were, and ducts couldn't have been designed to account for all those weld locations. Fume literally could come from anywhere in the plant.
Designing the System
Today a welder at Joy Global Surface Mining can stand on a scissor lift and rise 20 ft. to lay down bead (see Figure 1). He might need to work near one of the new fume filtration wall units, which blows clean, filtered air—occasionally onto a workpiece. This is an extreme rarity, but it can happen, and when it does the welder notifies a group leader to either redirect the airflow or turn off the nearby wall unit temporarily, so that return airflow doesn't disturb his weld pool during operation. The other fume collection units can handle the extra load temporarily. No one on the floor notices anything, and the air remains clear.
That's because the plant now has 39 fume collection units on the walls and 23 ceiling units mounted in the rafters. Integrated by Hastings Air Energy Control Inc. of New Berlin, Wis., the system is designed so that all units work in concert to create multiple air patterns that capture the welding fume.
These units perform a juggling act of sorts, pushing the air in certain directions and then catching that air to extract it. A juggler monitors all the balls in the air, ensures they're spaced properly, and moves his hands at just the right time to maintain ball spacing and speed. Joy Global's fume collection system effectively does the same thing, only with atmospheric pressure, air speed, and air volume, measured in cubic feet per minute (CFM).
Because of the three worker elevations it covers, the fume filtration system must do some fancy juggling. The 62 units, all of which have four-way directional louvers, work in concert to create two airflows. Fume generated at higher elevations catches an upward airflow toward the ceiling units, far away from the crane operator, and then is pushed toward the side wall units. For floor welding, fume rises and, before it reaches people working at higher elevations, catches an airflow that pushes it diagonally upward.
"When you're in the plant, it looks like you're looking at a Photoshopped image," explained Kevin Rohde, general manager at Hastings Air. The fume rises for about 10 ft. and then disappears into that air pattern as it catches the air stream on its way to the filter units.
What about the overhead crane operator, sitting 50 ft. in the air? "Once it gets to that level, the fume is either diluted to the point where it's safe for him to breathe, or the fume has already been collected," Rohde said.
The facility's existing makeup air system was retrofitted and enhanced so that it delivers air where needed to create the desired airflow. Ducting also was modified to work in conjunction with the new system, with Hastings adding a few vents, modifying some, and completely closing off others. Installers also closed off unneeded roof exhaust units, which previously were the company's only means of evacuating the fume. All this was done to maintain an even air pattern for the fresh makeup air coming into the plant.
Collected particulate is sent to one collection point outside the plant, through a secondary dust collector, and ultimately into two 55-gallon drums (see Figure 3), which together hold about 600 pounds of compacted particulate. The air then is circulated through another filtration system and clean air is sent back into the plant. Once a week workers empty the drums of packed welding fume. All told, the system extracts about 30,000 lbs. of particulate a year.
Less Energy, More Grants
The retrofit made the entire airflow system more efficient, which meant it took less energy to blow and distribute heated air throughout the facility. It also helped stabilize the temperature. The plant is heated in the winter but has no air conditioning for the summer. "Previously the building was too cold in the winter and too hot in the summer," Leamen said. "We've now changed our building temperature by about 7 degrees. It became 7 degrees warmer in the winter, and 7 degrees cooler in the summer."
Everything is connected to a central control, which ensures all units load at even levels to avoid overloading the filter media. This requires real-time sensing, because the amount of welding (and, hence, weld fume) can vary greatly. Sensors monitor air pressure, and once a filter unit reaches a preset pressure differential, these sensors trigger the filter to go into a cleaning queue, essentially "getting in line" to perform a pulse-cleaning cycle. This involves pulses of high-pressure air that force particulate off the filter media. The system ensures only one unit can shut down and pulse-clean at a time. An excessive number of units shutting down at once would lead to some obvious problems.
According to Rohde, the filtration saves energy and extends filter life by running as much as it needs to, but no more. Because sensors take real-time air pressure readings, they can tell the fan motors how fast to run. So if less welding occurs during a specific shift, or if a certain filter was just cleaned, the fan speeds may be slowed. With variable-frequency drives, every fan essentially has a dimmer switch. They can slide all the way on to full speed, stop entirely, or run at various RPMs in between.
Leamen said that because of the new ventilation system, the company qualified for $500,000 in grants offered by Wisconsin's Focus on Energy program. (He added that other states offer similar programs.)
Joy Global Surface Mining Engineer Brett Ansley recalled the day his team turned on the new filtration system in July 2011. It had come after a few hectic months.
The side units could be installed during the workday, but not the overhead units, which required a lockout/tagout of the crane—an obvious essential for heavy equipment manufacturing. Because business was so brisk, the welding plant was operational 13 days out of every two weeks. So every other Sunday over several months, a team worked to install the ceiling filtration units above the rafters.
After periodic testing and tweaking, the go-live date finally arrived. The units started, and the air finally cleared. "Today, if you were to turn the whole system off, let the building fill with fume, then turn it back on, within about 10 minutes the air would look clear," Ansley said.
Thanks to optimized part flow and 6S, the welding shop is churning out more than 35 incredibly massive mining machines each year. And they're doing it in a clean environment, sans haze.
Images provided by Hastings Air Energy Control Inc., 5555 S. Westridge Drive, New Berlin, WI 53151, 262-364-0500, www.hastings air.com.
Joy Global Surface Mining Inc., 4400 W. National Ave., Milwaukee, WI 53214, 414-671-4400, www.joy global.com
The FABRICATOR is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971.