Vacuum mixing guarantees constant cooling to 40C with optimum preparation of the bentonite-bonded molding material--even under varying initial and environmental conditions. In the past, the technology was only available for an output in the range of 60 m3/h and above, but now it is offered starting at an output of 7.5 m³/h. 

ZMM Stomana, formerly one of the largest machine tool manufacturers in Bulgaria, specializes in the manufacture of woodworking machines. The company also has a foundry. The production facilities are undergoing thorough modernization. In a first step, ZMM Stomana invested in a Laempe LL30 automatic core shooter and a HWS HSP-1 molding machine. The next logical step is modernizing the preparation system for molding material. The contract was awarded to Maschinenfabrik Gustav EIRICH GmbH & Co KG, who was able to offer an innovative and at the same time economical solution.

Up to now, the molding material has been prepared in a muller mixer and supplied to eight vibro-press molding machines. The recirculated used sand is intermediately stored in bins without cooling and moistening. This results in major quality problems, especially over the summer months. The fluctuation in molding material quality causes higher reject rates. The modernization of the molding material preparation system is intended to ensure the eight vibro-press molding machines and the new HWS molding line will be reliably supplied with molding material of reproducible quality, tailored to the specific requirements. ZMM Stomana wanted a preparation system for molding material that would use state-of-the-art technology to achieve the highest level of cost effectiveness and meet the following requirements:

• Integration into the existing equipment.
• Re-use of system units already existing. 
• Cooling of the sand to 40C.
• Availability of the system above 98 percent.
• Reproducible molding material qualities.
• Lower emissions, higher environmental compatibility.
• Autonomous, fully automated manufacture, including quality monitoring/control.

In order to fully meet these requirements, EIRICH developed a new concept.

The desired integration of the new preparation system for molding material onsite was a challenge. Installing a cooler with a downstream mixer was not feasible as the space available was limited. EIRICH decided to adopt a new approach. This decision was largely influenced by the need to cool the sand to 40C. In the development and project phase, a new system concept was therefore developed together with ZMM Stomana:

• The existing return sand line, including magnetic separation, screening and storage as well as additive storage and feeding equipment, was reused or adapted by the customer.
• A solids scale was integrated into one of the module frames. Return sand, new sand, bentonite, carbon dust, and filter dust are fed to the solids scale via screw feeders.
• The vacuum peripherals of the EVACTHERM mixer, necessary for cooling the sand, are positioned on the same module frame.

On account of the modular design and the relatively small amount of molding material required, EIRICH developed a new vacuum periphery. The main components were combined in just two units, the condenser and the pump module. The advantages are obvious: The costs for the vacuum peripherals are substantially lower. 

The heart of the system, the EIRICH EVACTHERM RV11VAC Mixer with a desired output of 7.5 m³ prepared molding material per hour, is installed on the second module frame. Combined with the vacuum peripherals, the mixer enables constant cooling to 40C while optimally processing the bentonite-bonded molding material. The electrical cabinets containing the power/control equipment of the system are mounted in the direct vicinity of the mixer. Beneath the mixer, a receiving hopper mounted on load cells is installed for the prepared molding material. It is equipped with a discharge belt conveyor. Behind it, an EIRICH QualiMaster AT1 ProfiPlus was installed above the belt conveyor. The quality system, an advancement of the QualiMaster AT1, offers new possibilities in addition to the measurement and control of compactability and shear strength. More reliability regarding the correction factor for evaporation is achieved by a second temperature measurement in the inline tester. In addition, the springback effect is measured in a tenth of a percent. The measured value informs on the springback effect during the molding process. The AT1 ProfiPlus also measures gas permeability as a reference value.

The QualiMaster SandExpert software solution not only continuously records, analyzes and displays batch data, but also performs preventive molding material management based on the company-specific mold database. Molding material preparation can be programmed for specific molds and carried out fully automatically.

Another belt conveyor feeds the processed and quality-tested molding material to the existing prepared-sand line. It distributes the material to the eight vibro-presses and the HWS molding line.

The key advantages of the new system are:

• Minimal space required for the three process steps: homogenizing, cooling, processing.
• Assurance of constant, reproducible molding material qualities in spite of fluctuating initial and environmental conditions.
• Optimal quantitative and qualitative disintegration of the bentonite in a technical vacuum.
• Systematic quality assurance through EIRICH’s control concept of seamless data integration, which ensures the networking of production and control parameters at all levels.
• Retention of reusable substances in the molding material system (fines) thanks to the closed water circuit.
• Reduction of the amount of dust-laden air to be extracted as no separate cooling unit is required.
• Assembly and installation, commissioning with material in less than 14 days.