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Clearing the Air at Acme Foundry: Integrated Engineering Design of a New Casting Cleaning and Finishing Facility
Acme Foundry, Inc. in Coffeyville, Kansas, produces 19,000 tons/year of gray iron castings, primarily for the hydraulic valve industry. During 1997-1998, the foundry planned and implemented an expansion of its cleaning and finishing area to meet the increasing casting demand. From the inception of this project, Acme Foundry committed itself to creating a processing facility that would be a safe, productive, and desirable workplace. Accordingly, the company used an integrated engineering approach to ensure that appropriate consideration was given to material flow, ergonomics, silica dust exposure, stack emissions, noise, climate control, lighting, and other issues. This integrated engineering program resulted in a production facility that meets company goals, complies with Occupational Safety and Health Administration (OSHA) requirements, and satisfies the needs of customers and the community.
The engineering effort was supervised by Don Pusa, Vice President for Engineering, and was supported by plant engineering and maintenance staff. Outside consultants were employed as needed. This team assured the desired project integration by deliberating all engineering issues face-to-face to achieve consensus on the design before the foundry made any construction commitments.
Cleaning and Finishing Processes
The company decided to expand the cleaning and finishing department before undertaking a planned molding department renovation and expansion. Cleaning and finishing of castings is done after the processes of retrieving castings from molds, removing appendages from the castings, and cleaning the surfaces of the castings using shot blasting. After castings are blasted, they are segregated by size as they are transported into cleaning and finishing. Large castings (50 to 300 pounds) move along roller conveyors to casting grinding booths, where they are hoisted onto ventilated workbenches (Figure 1).
Small castings (2 to 50 pounds) are moved on conveyor belts to an elevated sorting and inspection station (Figure 2). From here, castings slide down chutes, first to snag grinding stations (Figure 3), and from there to ventilated hand finishing benches. A series of workstations within the room are dedicated to detailed inspections of the internal cavities of valve and cylinder castings, using optical magnification devices (Figure 4). Castings arrive in the inspection department in customer containers, which group castings throughout the quality control and shipping steps. Layout of the room was focused on material handling; however, consideration for noise control resulted in isolating the powered cleaning stations from final inspection operations.
Dust Control and Climate Control
All dust-producing cleaning and finishing operations (98 stations) are locally exhausted. The close capture hoods employed were designed based on parameters recommended in the American Conference of Governmental Industrial Hygienists’ Industrial Ventilation Manual. The hoods are manifolded and ducted to a series of air cleaners, most of which are located on an elevated mezzanine in the cleaning and finishing department. The indoor location was selected so that the cleaned exhaust could be recirculated back into the foundry.
Cartridge-type collectors were employed to accommodate the height of the mezzanine. One air cleaner, a non-recirculating baghouse handling snag grinders, was located outdoors. A baghouse was selected for snag grinding to guard against the bridging of cartridge pleats with fibers. Bridging has been known to occur with the use of the high-speed, vitreous bonded wheels used on foundry snag grinders. Precautions against bridging were taken in all cartridge filters by using open pleat designs.
Dust consolidation and disposal was simplified through the use of a pneumatic transport system. It transfers the collected dust from all of the air cleaners on the mezzanine to a single ground-level filtered receiver where the dust is automatically loaded into large sacks.
Recirculation of cleaned exhaust air back into the cleaning and finishing area is very reliable because of the use of a three-stage filter system. Air passing through the primary dust collectors is automatically refiltered by secondary dust collectors, referred to as safety monitoring filters (SMF). If a cartridge in a primary filter unit develops a leak, the SMF will filter out any dust leakage through its automatically recleaned filters and signal that there is a leakage. High efficiency, particulate air (HEPA) filters are employed as a final stage, to backup the recirculation system.
The air mass balance of the new casting cleaning facility is presented in Figure 5. The facility has positive pressure in those foundry areas that are attached to the system. This pressure is created by tempered (i.e., heated or evaporatively cooled) makeup air units, which direct air to individual adjustable air drops at the 98 workstations. Workers prefer these air drops because they are located close above their heads and the amount and direction of the air can be individually adjusted. Their use completely eliminates the need for pedestal fans to cool workers. The roof fans and sidewall supply fans provide summer heat relief only.
The entire ventilation system is continuously monitored by a programmable computer with a touch screen. Airflow parameters are controlled within preset ranges, with alarms to indicate any out-of-range parameter.
Ventilation System Performance
Following completion of construction and the start of process operation, air sampling was conducted to assure that stack emissions complied with the limits set by the foundry’s Environmental Protection Agency permit and that exposure of the workers to respirable silica complied with OSHA’s permissible exposure level (PEL). Worker training is ongoing in the new facility to educate workers how to process a myriad of different size and shape castings in a manner that maximizes the effectiveness of exhaust capture hoods.
Acme Foundry, its employees, customers, and neighbors are reaping the benefits of a well-engineered foundry process addition. The company achieved improved productivity, safety and health, and worker acceptance by integrating these considerations throughout the design and implementation of the project.
Source: Don Pusa, Vice President, Engineering; Mark McCullough, Maintenance Superintendant, Acme Foundry, Inc., Coffeyville, Kansas
The views expressed herein do not necessarily represent the official position or policy of the U.S. Department of Labor (DOL).
As of February 2010.
Figure 1. Large casting grinding is done on ventilated workbenches in semi-enclosed booths (center) and in enclosed booths (right).
Figure 2. An elevated sorting conveyor is equipped with a continuous, overhead "air island."
Figure 3. Snag grinding stations with ventilated hoods and overhead "spot" ventilation drops.
Figure 4. An inspection station equipped with an exhaust hood and air drops.
Figure 5. Air Mass Balance for New Cleaning and Finishing Facility.
TEXT VERSION OF FIGURE 5:
Type: Flow chart and table
Content: Contains two flow charts and two tables illustrating the air mass balance of the new casting cleaning facility.
Page last updated: 03/11/2010