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Additive helps foundry improve green sand properties.

Donsco, Inc., Wrightsville, Penn., is a company that has always been interested in innovation and adopting new technologies designed to provide its customers a competitive advantage. This open-minded approach to business provided the framework and setting for reviewing the objectives, targets and implementation of Hydrobond, an engineered and patented sodium western bentonite developed by Bentonite Performance Minerals (BPM), Brookfield, Wis.

The additive was designed to yield performance values not attainable through mixtures of southern (calcium) and western (sodium) bentonites. The additive also provides several advantages over the sodium bentonites now available.

The main objectives at Donsco during the initial stages of implementing the Hydrobond technology were to develop higher green strength and lower dry strength. Chris Buck, Donsco's Technical Director, said two things were evident immediately when Hydrobond was introduced into the foundry's sand system--scrap rates and amount of bond used was reduced, resulting in cost savings. According to Buck, the material costs more, but a total net savings occurred.

The additive combines optimized performance and more complete utilization of the bentonite clay in sand. Teaming with BPM, Donsco executed a sequential evaluation of its entire green sand system to address the primary variables: materials, sand mulling, sand flow, sand temperature, equipment performance and resultant green sand properties. This joint research effort also included an evaluation of the return sand equipment.

This effort was conducted to quantify the loss of usable green sand at each stage of the process. For example, on the shakeout conveyor, castings with shallow to deep pockets were filled with sand, which resulted in increased sand to the landfill and longer shot blast times. The addition of Hydrobond eliminated this problem and reduced the shot blast cleaning cycle by 30%.

The additive reduced the amount of non-productive dead clay in the system by 14% and the average moisture sponge percentage dropped from 3.2% to 1.0%. New sand additions were significantly reduced because the sand system stayed cleaner with less dead clay and ash material. Loss of ignition levels were lowered by 25% and volatile levels went down 55%. The preservation of useful clay is attributed to the high thermal durability of the additive. As a result, baghouse fines could be re-introduced into the prepared green sand, reducing both waste removal costs and raw material costs.

The additive also improved the cumulative mulling effect of the return sand by increasing the water bonding capabilities. With the additive, sand is less sensitive to water evaporation between the muller and the molding machines. The compactability at the muller is maintained 2% higher than the molding machine target, a reduction from 8%. The overall moisture level in the sand system was reduced 0.3%, which led to a decrease in moisture-related defects in the castings.

Through the testing, Hydrobond was shown to improve mulling times and efficiencies, resulting in higher green strength, lower moisture contents, higher green tensile strength, lower sand friability and lower dry strength. The pounds of clay per ton of iron poured were lowered 31%. This not only resulted in raw material cost savings but also savings in the disposal of less waste sand and dust.

Donsco's new green sand property targets were determined through an extensive design of experiment at BPM's laboratory using materials processed from Donsco's operation. The major sand variables were tested to see how they were affected by other process changes. This allowed the green sand team to effectively monitor and control the range of the green sand system properties.

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Title Annotation:Case History
Publication:Modern Casting
Date:Jan 1, 2004
Previous Article:Counter-pressure casting system eases aluminum pouring for high integrity components.
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