The demands on castings are constantly increasing. Molding material of reproducible quality, tailored to the specific requirements, is consequently getting more and more important. This is why today already more than 50 foundries all over the world rely on the EVACTHERM® process from EIRICH for their molding material preparation. Vacuum mixing guarantees constant cooling to 40 °C with optimum preparation of the bentonite-bonded molding material - even under varying initial and environmental conditions. In the past only available for an output in the range of 60 m3/h and above, EIRICH now offers EVACTHERM® technology starting at an output of 7.5 m³/h. The first small vacuum mixer will be commissioned at ZMM Stomana in Bulgaria in July 2019.
ZMM Stomana, formerly one of the largest machine tool manufacturers in Bulgaria, is now specializing in the manufacture of woodworking machines. The company also has a foundry. The production facilities are technologically no longer state of the art and are now undergoing thorough modernization. Maximum system availability and consistent first-class quality of their castings - these are the ambitious goals the Silistra-based company now wants to achieve with its foundry. 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.
For the highest level of economic efficiency
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 that 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 40 °C
- 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 has developed a new concept.
A worldwide novelty: EVACTHERM® technology of modular design
The desired integration of the new preparation system for molding material into the constructional situation on site meant 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 40 °C. 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 process is therefore cost-effective.
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. In combination with the vacuum peripherals, the mixer enables constant cooling to 40 °C 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 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.
A milestone in molding material preparation
With the newly developed system, EIRICH is setting new standards in the field of molding material preparation - especially for systems with comparatively small outputs.
The key advantages 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.
The system, which is customized to the individual requirements of ZMM Stomana, is currently being commissioned in Hardheim at the main factory of Maschinenfabrik Gustav EIRICH. This is possible due to the modular design. Assembly / installation and commissioning of the equipment in the foundry of the Bulgarian company is scheduled for July 2019.
