Material Handling: Go With Flow
Every metalcasting facility is unique, but a department-by-department examination may highlight ways to improve operations and reduce costs.
A Modern Casting Staff Report
(Click here to see the story as it appears in the October issue of Modern Casting.)
No matter the size of a metalcasting operation, whether it’s a small, family-run shop or a mega facility with volumes in the millions, the question of modernization is not an “if” but a “when.” Machinery fails. Maintenance gives way to replacement. Upgrades need to be made.
Projects can be as simple as swapping out an old welding machine for a new one. They also can involve many more moving parts, such as a new molding line, which requires engineering and logistical planning far more advanced than simply sticking a plug in the wall. Every improvement project requires planning and engineering to ensure it fits into the broader facility-wide material flow and handling.
Misplaced equipment or poorly designed material flow can increase labor, safety risks and costs—inefficiencies that may be avoided by rethinking the facility’s layout. Making changes in addition to a specific installation will increase the cost of that project, but that one-time cost, ideally, would be recovered by eliminating daily cost increases related to unnecessary material handling procedures. If a metalcaster misses an opportunity to improve the flow of material, the bottleneck in handling and flow will be a drain on profits that continues until the proper action is taken.
Design considerations for metalcasting equipment are different for every plant, but almost every site needs to consider available square footage, building size and configuration, placement of existing equipment and the relationships between departments.
“A lot of existing installations have been put together over years and generations, where one thing is added here and another there,” said Wil Tinker, president, Tinker Omega Mfg. LLC, Springfield, Ohio. “Each project for existing facilities is one that balances primary objectives with what’s possible within a project’s budget.”
Ideally, the layout between melting, molding, coreroom and cleaning-finishing departments should provide a continuous process flow from the material entering the plant, through each department and eventual shipment. This basic methodology keeps product moving through the metalcasting operations, though each department will require specialized configurations based on the building’s overall shape and size.
The melting department should be located on an outside wall due to the high volume of metallic materials required for the melting process. Material handling in the melting department is important because it involves both newly acquired metal and returns from within the facility.
Facilities that pour more than one alloy at the same time have additional considerations because melting operations will run side-by-side. Also, the method and location for metal returns to the melting departments need to be considered. Returns such as risers, sprues and pouring basins may occur at different locations throughout the cleaning process. These pick-up points must be incorporated into the material flow because they require transportation back to the melting department. The location of metal removal operations should be as close to the melting department as possible to reduce the distance returns must travel.
Minimizing the distance metal travels from melting/holding units can reduce the required temperature of the metal tapped from the melting/holding furnace. Long distances increase the metal’s temperature, leading to increased energy consumption and cost.
Automatic pouring units, if possible, should be positioned to retrieve the metal directly from the holding/melting furnace. If not, a heated trough can be used to transfer the metal to the pouring unit. Locations of the melting/holding furnaces and automatic pouring are an important feature in the melting department layout.
When making improvements to or installing new molding equipment, four key features must be considered during initial planning and engineering:
- Selection of a molding machine system.
- Method of handling the molds away from the molding machine.
- Method of core delivery from the core machine to the mold.
- Location for setting cores in the molds.
Different molding systems require different handling methods. Establishing pouring as close as possible to the melting department should be a high priority in material handling, although it requires considerable planning to maximize efficiency.
Matchplate jolt-squeeze machines require either a pallet line or the use of a roller conveyor to move molds from the molding machines. These systems require the melting furnaces to be located at one side of the mold handling line so metal can be delivered and poured on the pallet line. Molding/handling also may be located at the opposite end, away from the molding machines, so metal can be delivered to the molds along each roller conveyor line.
An automatic molding system requires the melting department to be at the side near the molding machine to minimize the distance metal travels. A chemically bonded mold and core system requires the completed molds to be delivered to the melting department. Extra large molds, which are more difficult to transport, require a molding area adjacent to the melting/holding furnaces.
Considerations for a casting facility’s sand system include available floor space, core and metal removal, shakeout, sand mulling and sand delivery. New sand storage hoppers should be located along an outside wall with the return hopper located as close to the sand muller as possible, usually inside the building. The sand cooler is located after shakeout, with the metal and core removal system prior to the sand cooler. After mulling, the sand is then transferred back to the molding machines.
Green sand shakeout systems require separation of sand and cores from the castings and the elimination of core sand from the return sand. Chemically bonded molding systems may not require core sand separation, but metal must still be removed from the sand prior to reclamation, which will improve the quality of the sand returning to the muller.
“Recent price increases for silica sand have made reclamation systems (both mechanical and thermal) financially viable for many medium and smaller sized casting operations,” Tinker said. “You want to close the loop as much as possible.”
Many reclamation installations are added to existing sand lines, which will lead to specific engineering considerations. Collaboration between engineers from the equipment manufacture and the metalcaster can help improve the material flow and handling of such add-on projects.
Core production should be located near the molding area. Because core production rates rarely mirror mold production rates, storage space between the coremaking and molding departments must be allotted. While often unavoidable, the storage of cores can lead to a few problems:
- Core scrap may increase due to the extra handling to and from storage.
- Cores in storage may collect moisture that could produce scrap castings.
- Storing cores ahead of molding operations can increase the difficulty of tracking casting scrap.
Production of cores at the same rate as molds is the ideal solution because it eliminates handling, reduces core and casting scrap, eliminates the need for storage and improves troubleshooting between coremaking and molding departments.
Solidified castings must be cooled before they enter the cleaning process. The cycle time of the cooling process provides an opportunity to transport the casting a distance away from the mold shakeout area while it moves to post processing. This allows flexibility in the location of casting cleaning procedures, and may allow cleaning and finishing operations to be designed in a straight line for continuous casting flow.
The continuous flow of castings into the cleaning area also provides the opportunity for a continuous casting cooling process. Continuous operations require the use of a vibrating pan conveyor or an overhead chain conveyor to deliver the castings to the first cleaning station.
Because the location for starting the cooling cycle for castings is flexible, the design can be based on a number of factors:
- The removal of metal from the casting creates a considerable amount of material to return to the melting area, so placing the cooling system near the melting department will reduce material handling and distance.
- Automatic return systems can reduce material handling considerations and minimizes contamination and mixing of metals being charged.
- The pick-up points and delivery to a designated bin in the metal storage area can be cost effective and improve the plant environment.
At the completion of the cooling cycle, the casting’s metal determines the first operation in the cleaning process, whether that is shakeout, cut-off or knockout operations.
The next operation is shotblasting, with the exception of aluminum castings, which are normally shotblasted at the end of the cleaning process. Continuous shot-blasting reduces manpower necessary for loading and unloading, while batch shotblasting may increase handling due to the ebb and flow of prepared castings.
Grinding may be done with a variety of tools, including stand grinders, belt sanders and chipping tools. From this point, many castings will require heat treatment, reblasting and inspection before being ready for shipping.
The metalcasting facility with ideal material flow and handling may not exist, but company executives are becoming more receptive to improved efficiency in an effort to reduce costs and improve performance.
“We’ve seen a definite shift toward efficiencies, both in production and operational equipment,” Tinker said. “We’ve seen [metalcasters] analyzing utility consumption, to where it’s a crucial part of their economic decision-making.”
Early planning provides the time to design an efficient flow program that reduces handling inefficiencies. The results of an effective continuous material flow include:
- Reduced material and casting
- Reduced manufacturing time.
- Reduced inventories.
- Reduced delivery times.
- Improved customer relations and satisfaction.
- Reduced scrap.
- Improved casting quality.
- Cleaner work environments.
- Improved employee relations and satisfaction.
If a metalcasting facility can successfully implement equipment improvements and installations, the metalcaster can expect real, tangible benefits.