Want cleaner air? As environmental and health standards increase for the U.S. metalcasting industry, two facilities established methods to improve their in-plant air quality.

Have you ever been on your melt deck and couldn't see 20 ft. in front of you? This most likely is due to the smoke and dust emitted from the furnaces and molten metal. Your casting facility might have some emissions collection systems, but they might be too far away or too weak to work efficiently. This can pose a hazard for breathing conditions and physical safety as your visibility is limited.

To avoid such situations, two metalcasting facilities developed solutions to enhance the air quality in their casting operations. This article details the trials both firms employed in their plants and how the new systems provided a working environment with cleaner air.

Keeping Fumehoods On

Seneca Foundry Inc., Webster City, Iowa, had been improving in-house ventilation at its iron casting plant since the mid-90s after its president, Kirk McCollough, made air quality a priority at the facility. Seneca had installed a baghouse system for its two 2-ton induction melting furnaces and also installed furnace fumehoods. However, the overhead fumehoods were 10 ft. (3.05 m) away from the furnace, which left too much open space for proper ventilation. In addition, the melt operators often would be subjected to immediate furnace emissions.

Improvements were made to reduce the excessive dust on the shop floor, including replacing a wet collector with a new baghouse system and adding high-wall exhaust fans in the core room to remove heat and stray gases. But the melt deck still posed a problem.

Although permissible exposure limits (PELs) were exceeded rarely, smoke from the furnaces and transfer ladles increased air opacity, which resulted in hazy working conditions. Seneca examined the possibilities of installing more efficient fumehoods, but ran into difficulties as the models they looked at were either too expensive, required too much maintenance or would not collect all air from the furnaces. The casting firm spent several years trying to determine what could work best for its operation when personnel developed an idea for its own fumehood. This design called for a "bonnet" and "pickup box" attached to one of its induction furnaces.

The firm proposed a project that would place a fumehood at preheat operations, a close capture hood on each furnace and a hood at the transfer point on the pour deck. The charge bucket would be internally ported for forced airflow when on a furnace. Also, a booster fan and large spark trap box would be added, and the baghouse would be modified for fire protection. Seneca hired a consultant to survey the proposal, and the firm created a prototype air-quality system.

The firm's plant engineer worked closely with the melt deck operators in developing a full-scale cardboard model of the furnace fumehood, which the operators believed would reduce heat and eliminate the need for dust masks. Production personnel sketched the model and fabricated each cardboard part in steel, which then was welded together. The updraft bonnet was mounted to the furnace lid, so when the lid was closed, the bonnet collected all the fumes generated in the furnace.

The pickup box, which was mounted next to the bonnet, routed all the fumes through the attached 12-in. (30.48-cm) steel aspiration pipe to the booster fan, which sent the air to a dropout box and eventually to the baghouse. When the furnace lid was opened for charging operations, the charge bucket was set on top of the furnace, and the pickup box would collect all the fumes from the bucket. The box also served as a swivel joint so that when the furnace was tipped for pouring, the airflow was not disrupted.

The prototype was tested with a temporary fan setup. Airflow and temperature data were taken while observations of the effectiveness of smoke capture were made. A second furnace fumehood of the same design was built on another furnace soon after the first.

Meanwhile, the firm also worked to install a 52-ft. (15.9-m) "fresh air island" at the pour deck. This incorporated a roof-inlet makeup fan, which pulled in ambient air from outside the building and sent it down a vent where it was dispersed through eight diffusers along the pouring monorail at breathing zone height, which was 6-7 ft. (1.8-2.1 m) above the ground. This would give the pouring personnel fresh air to breathe while working with the ladles.

Further, Seneca built a pivoting fumehood with a 16-in. (40.64-cm) pipe to collect smoke and carbon monoxide from its charge preheat station and constructed a fixed fumehood for collecting magnesium treatment smoke at the location where metal is transferred to the pouring ladle.

The casting firm filed a new application to the Iowa Dept. of Natural Resources to modify its existing air permit. This new permit called for a reduction of total baghouse cfm, with air-to-cloth ratio of 3:1 or less, and the department approved the new permit.

Although there are still some obstacles to surpass, Seneca has found success in the implementation of the prototype clean-air system into its daily operations. The fumehoods allow the melt deck operators to work in cooler temperatures and cleaner air. The silica and dust levels on the deck are well below the PEL, and plant opacity has improved significantly. Even though the preheat fumehood needs some redesign to be more efficient and the melt operators now have the additional task of removing the furnace fumehoods every week, the personnel acknowledge that the improvement in air quality is worth the extra work.

Pushing and Pulling

Like Seneca, Rochester Metal Products Corp., Rochester, Ind., found the need to reconfigure its emissions-capturing capabilities. This was to achieve a state-qualified air permit.

In 2003, the Indiana Dept. of Environmental Management (IDEM) conducted a stack test for Rochester's air-capture system, which was found to be insufficient as it did not meet the mandatory 100% capture efficiency. The plant possessed two pulse-jet dust collectors (one at 30,000 cfm, the other at 50,000 cfm) and a side-draft canopy emission-capture system.

But this posed a problem for Rochester as its narrow melt deck with monorails and conveyors did not seem to be the most conducive for effective air-capture. For example, near the furnace tapping area, the ladle monorail divides the side-draft canopy from the dust collector intakes, and for charging, the side-draft canopy intakes catch little emissions from the facility's open-top charge bucket.

The Rochester staff therefore sought to improve its emissions-capture operation with several trial-and-error techniques. It needed to determine a means to clean the air around its five 35-ton induction furnaces, two preheaters and two 10-ton charging cranes.

One method was to use 30-36-in. (76.2-91.44-cm) floor fans to push the melt emissions into the side-draft canopy hood, as the canopy previously was taking in only 30,000 cfm compared to the required 200,000 cfm. But the fans caused workers to be hit with foreign objects, and there was still no control of emissions during charging.

Another means to improve the air quality was to reduce the negative air pressure. To do this Rochester turned off its six 20,000 cfm roof fans to lower this air pressure. Unfortunately, this caused excessive heat conditions for the pouring deck operators.

The firm also looked into close capture hoods for the furnaces and charge buckets, but this idea would not account for tap emissions and the charge buckets would need to be altered.

Then Rochester came across the theory of push-pull ventilation. The push-pull method calls for a volume of air to be pushed from the sides of a furnace toward the furnace center. The air then is pulled by the side-draft canopy into the dust collector intakes. This is done via two 12-in. (30.48 cm) diameter push headers that each have 25 nozzles ranging in size from 0.75-1 in. (1.9-2.54 cm) in diameter. The push headers each are supplied by a 2,000-cfm blower and are located 7 ft. (2.1 m) above the furnace deck. During the charge sequence, a suspended 1,200-cfm blower located on the overhead crane trolley provides an additional push toward the side-draft canopy. This blower incorporates 18 1.5-in. (3.81-cm) nozzles in order to direct the knifelike air stream toward the canopy. By doing this, Rochester gained a melt deck with cleaner air and better visibility.

The main advantages of the push-pull system are that it covered all emissions from charging to melting to tapping, and it did not cause any changes to the charge system. Unfortunately, 25,000 cfm per furnace is needed to operate the system to meet the standards, and it's still susceptible to cross-air drafts at the deck level.

Currently, Rochester is developing a design for a covered charge bucket and coordinating an emission-capture project with a possible melt capacity upgrade. Although the push-pull method has improved the clean air capacity at the plant, Rochester is examining options for a total close capture system that could save in operations costs while maintaining good air quality.

This article was adapted from presentations at the AFS Environmental, Health & Safety conference held Aug. 21-24, 2005 in Dearborn, Mich.

About the Authors

Phil Strohbehn is the Plant Engineer at Seneca Foundry Inc., Webster City, Iowa.

Andrew Murdock is the Environmental and Project Engineer at Rochester Metal Products Corp., Rochester, Ind.

For More Information

"History Holds Keys for Future Environmental, Health & Safety Issues," K. Bauer, MODERN CASTING, Oct. 2004, p. 35-38.