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New Rotary Media Drums Clean Up Foundry, Improve Profit Margins

Jan. 22, 2010
For cleaner castings and better profit margins, focus improvement efforts on ways to reduce airborne silica dust.

The Didion Mark 5 Series rotary media drum combines sand/casting separation, sand conditioning, double sand screening, casting cleaning, and casting cooling so the foundry stays cleaner and makes more money.

If you need a cleaner casting operation and a better profit margin, focus on areas that generate the most airborne silica dust. When a green sand mold is dumped onto a conventional vibrating shakeout, a huge amount of fine silica dust is released into the foundry. Since it is very difficult to capture all the steam laden with silica dust, due to the amount of open area, the foundry becomes dirty.

The amount of effluent is directly related to the sand temperature at shakeout. When the average sand temperature exceeds 100°C, convection currents carry silica dust into the atmosphere. The higher the sand temperature at shakeout, the greater will be the convection current velocity and amount of steam and dust to be captured.

With a sand-to-metal ratio lower than 6.9:1, the average sand temperature will exceed 100°C. The convection current velocity increases significantly from 100° to 200°C . As the sand temperature rises, so does the convection current velocity that affects the amount of effluent released into the foundry atmosphere.

The heat-affected zone of the mold is the area where the molten metal comes into direct contact with the sand grains (mold face.) As the sand expands in this zone, internal stresses cause weak grains to fracture. Since sand quality varies around the world, the source of supply will have a direct impact upon fines generated from both mechanical and thermal aspects.

Another important calculation tells us that for every kilo of metal poured into the mold, 15% by weight of new sand should be added to replenish the losses and keep the sand system in balance. Since the amount of cores can vary with each job, using core sand as new sand additions is a hit-or-miss method unless it is separated from the green sand and then metered back in at a given rate.

The second source of airborne silica dust is from the sand still attached to the castings after shakeout (in pockets, cavities, and corners.) As the heat from the metal drives out the moisture, the loose sand falls off and contaminates downstream operations. Workers in the cleaning, finishing, and melting departments are exposed to silica dust from sandy metallics.

The next source of dust comes from shot-blasting sandy castings. The sand that enters the shot-blast system not only accelerates equipment wear, but it is degraded and added to the waste stream. This increases sand-disposal costs. The sandy returns that go back to remelt without being shot-blasted lower the melting efficiency and increase slag, slag-handling, and slag-disposal costs.

Responding to the demand to clean up these areas in the foundry, and to lower operating and labor costs, made Didion International Inc. the world leader in rotary foundry equipment. Innovations in sand casting separation and cleaning have saved foundries hundreds of thousands of dollars annually.

Didion’s latest invention is the new Mark 5 Series rotary media drum which performs shakeout, sand conditioning, double sand screening, casting cleaning, and casting cooling in one efficient step, so the foundry stays much cleaner with less airborne silica dust. By combining these processes the foundry can save $40.00-80.00 per ton. The patented design has the lowest operating cost per ton in the industry, worldwide.

Foundries benefit in a number ways, including less capital equipment to purchase, less floor space occupied, much lower energy costs, less maintenance time and costs, lower shot consumption, less replacement parts, cleaner working conditions, and cleaner returns back to remelt reduces slag build-up. The new Mark 5 Series streamlines production with cool and clean castings going directly to the finishing department. The return sand is blended and conditioned to be consistent in temperature and moisture content, providing better control at a mixer. The sand stays in the system where it belongs so environmentally the foundry stays cleaner. Dust collection is extremely efficient due to the small open area of the drum. The Didion requires 75% less dust collection than a vibrating shakeout rated at the same capacity. Counterflow air eliminates fugitive dust from escaping, protecting workers from airborne silica dust.

Many foundries shot-blast their castings twice: first to preclean the castings and returns; then, after casting to blend in the grinding marks. Since the Didion also cleans the castings, the first shot-blast step can be eliminated. The gates, runners, and sprue are often removed in the Didion, eliminating hard manual labor and sending clean returns directly to remelt.

Didion offers the first and only shakeout system that separates core sand from green sand and discharges each one separately — a popular feature for high-production automotive foundries with heavy cored work that need to meter only 15% core sand back into the green sand system.

These variable-speed machines let the operators control the action. The media bed protects nonferrous and fragile castings during cleaning and cooling: Custom lining configurations are available for aluminum, brass, malleable grey, ductile, and steel castings. Installations include green sand, shell, no-bake, and lost foam systems.

Recent improvements to the Mark 5 Series include new interlock liners that are thicker and wider for longer life, with 50% fewer seams and contoured rifling for delicate castings, self-relieving tapered separation chambers, split pillow block endtrucks with quick change bearing inserts, and automatic chain tensioning.

System improvements include water quenching directly following the machine to eliminate long cooling conveyors, further saving equipment costs, energy, time, and space. For foundries using casting baskets and stage cooling, water quenching following the rotary media drum can streamline production flow and eliminate the bottleneck in the cleaning room.