Although various steps of the metalcasting process have grown more and more automated, the process of cleaning castings in most cases remains labor intensive. It is estimated that anywhere from 20-35% of the manufacturing costs associated with an average casting can be attributed to cleaning and/or finishing. Controlling production costs and maintaining profit margins is a constant effort, so many metalcasters are on the lookout for strategies for reducing machining costs.
Addressing the problem up front
The amount of sand adhering to castings, as well as san carryover, may be the most important aspects of cleaning and finishing. Thus, reducing, or even eliminating, the sand going into the casting cleaning department may result in tremendous cost savings. It isn’t just a saving on shot-blasting costs, either. By pre-cleaning castings in the shakeout system, there are cost savings relating to less wear on dust collectors, less waste streams, no airborne silica dust, and less clean up time. Having cleaned gates, runners, and sprue from the shakeout department that go directly to the melt department relieves the cleaning department bottleneck. If the gates, runners, and sprue are too much to shot blast, then the melting department faces excessive slag build up, reduced furnace lining life, and lower melting efficiency. The savings in the melting department alone may justify the need to have clean returns directly from the shakeout department. Cleaner melting, finishing, and shakeout areas all add up to a better and safer workplace.
Saint-Gobain Pipelines’ Sinclair Works in Telford, England, improved its shakeout and finishing operations by installing a Didion Rotary Media Drum to eliminate shot blasting altogether. The Mark 5 Rotary Media Drum processes sand and castings from a DISA vertically parted molding line.
The sand is separated from the castings and is screened twice to -9 mm in the Didion unit. All the metallics are thoroughly cleaned by a recirculating bed of prismatoid media, which also protects and cools the castings. Upon discharge from the drum, the castings are submerged into a water quench for final cooling. The clean and cooked castings are automatically conveyed to the grinding stations in the finishing department. The clean gates, runners, and sprue go directly back to the melting department.
Return on investment
This streamlined approach led to the Saint-Gobain foundry’s decision to add Didion’s latest Mark 5 Series Rotary Media Drum in 2003. The Mark 5 design offers features such as external sand screening, automatic chain tensioner, split pillow block design with quick change bearing inserts, duplex chain, thicker liners with contoured rifling, cast in dam retention rings, and a self relieving tapered media separation chamber for fragile castings.
Other foundries in the U.K. that have benefited from the Mark 5 Series machines include Castings PLC, Vald Birn, William Lee, and Triplex Foundry.
Combining sand-casting separation, dual-sand screening, plus casting cleaning and cooling, has proved so successful that paybacks are calculated in four to five months. The foundry that installs the system will also have less capital equipment to purchase, install, and maintain. Less equipment means less dust collection requirements and less daily energy consumption. (Didion has installed the Mark 5 series rotary media drum in 42 countries.)
The machines are custom designed to handle aluminum, brass, bronze, ductile iron, gray iron, and steel castings. Greensand, shell, lost-foam, and no-bake foundries all have benefited from this unique patented approach.
Benefits at home
United Machine & Foundry in Winona, MN, installed a new Didion Mark 5 Series machine. “With the installation,” reveals director of operations, Steve Renk, “we have improved three facets of the UMF operation — safety, quality, and productivity. Improvements in these areas are critical to our ability to succeed in the ever-competitive foundry industry.
“Prior to installing our new equipment, we operated a vibratory shakeout system,” continues Renk. “Standing over a vibrating shakeout, trying to hook castings and place them in tote boxes is difficult and is compounded by dust, steam, and heat. By installing the Mark 5, we have eliminated a safety hazard.”
Renk says the company has realized quality improvements, too. “The Rotary Media Drum’s ability to blend hot and cool sand also has benefited our sand system. With the vibratory shakeout, the sand-storage system had layers of hot sand on top of layers of cool sand, making the compactability of the sand difficult to control. The new system has helped reduce big swings in sand temperatures, thus allowing our compactability controller to run much more efficiently.
“Productivity gains and reduced costs have proved to be an added bonus for UMF operations. Many of the castings that we produce are no longer shotblast,” says Renk. “UMF has reduced the man-hours in shotblasting, and reduced operating hours on the maintenance-intensive shotblast machines, which has allowed us to use production and maintenance personnel more effectively. We have significant annual savings from reductions in labor, sand disposal costs, shot purchases, accidents, maintenance/repair costs.”
Other metalcasters (including TK-Waupaca Foundries, Wescast, Intermet, Grede, and Victaulic) have modernized shakeout/cleaning operations with Mark 5 drums, too. Ductile iron castings, with gating systems that are difficult for workers to remove manually, can be automatically de-gated in the Didion. Labor savings for this difficult and dangerous job may justify the cost to modernize the shakeout department. How? Approximately 20% of the cost to produce a 10-kg ductile casting comes from shakeout, fettling, and cleaning. By combining shakeout, sand screening, casting cleaning, and casting cooling, ferrous foundries may reduce these costs by 50% and save as much as $80/ton in operating costs.