New binder system

For manufacturing large manually shaped castings in the weight range between about 1 t and 280 t, the current practice is to use mainly resin-bonded moulding material systems, for example based on furan and phenolic resins. These moulding material systems, while characterized by very good technical properties, are critical in terms of occupational safety, health protection, and environmental protection and odour emissions. Although these binder systems are used today on orders of magnitude between 0.8 and 2% in the moulding material, their processing, casting and reprocessing or disposal of the used sands result in some cases in considerable problems due to harmful components.

This problem can be addressed by substituting inorganic hydraulic binders such as cement for the organic binders. The main advantage of these binder systems is their good environmental tolerability, since on the one hand mixing of the moulding material and pouring of the castings do not release any harmful emissions or cause outgassing and, secondly, if the materials are not to be reused, the resulting used sands can be deposited in landfills or used as fillers in other areas (road construction, backfilling, etc.).

A problem is presented in this respect, however, by the processing properties of conventional, commercially available cements, for instance excessively long setting times, insufficient compression properties and poor flowability. For efficient applicability in the foundry industry, a binder material must show adaptability to the requirements of each specific casting/moulding job.

The stated goal of this R & D project is development of a hydraulic binder system for foundry moulding materials in the field of manually shaped large-volume casting of cast iron as a substitute for health-damaging and environmentally harmful synthetic resin binders. In contrast to applications in construction materials, etc., where a sufficiently long processing time is necessary - in some cases several hours - desirable curing/hardening times for iron casting are in the range of 4 to a maximum of 24 hours. A reduced level of final strength after casting (residual strength) is not problematic, and actually simplifies regeneration of old sand moulds. A cement without any setting regulator would, however, harden and clump together within seconds. The precise adjustment of solidification behaviour to achieve the desired ideal in terms of processing and final properties is the main challenge of the project.

The objective is to develop a system that simplifies specific adaptation of the mould materials to the varying requirement profiles for the different casting sizes and shapes required in foundry applications. The findings from the project should lead to rejection of environmentally harmful synthetic resin binder systems in the foundries and their replacement by environmentally friendly inorganic binder systems.

Once the feasibility of such applications has been confirmed on a smaller industrial scale, the next step will be to demonstrate their general practical applicability on a larger industrial scale in projects realized in cooperation with foundries.

Our partners in this demanding research project are the University of Freiberg, Institute for Ceramics, Glass and Construction Materials, as well as the Foundry Institute.