Seeking: Innovative binder solutions to manufacture molds and cores for metal castings
We’re seeking a new, environmentally acceptable binder system. This could be based on inorganic, “clean” organic or hybrid derivatives, and should offer an immediate advantage over current systems, in terms of health, safety, and environmental issues.
Typically, silica sand is mixed with a small quantity (1–3%) of binder material, and then either rammed around a pattern (molding) or pneumatically forced into a pattern cavity (coremaking) and set. Molten metal is then poured into and around the resulting product to provide the desired shape of the metal part being cast. Binders used for molding are typically self-setting, in that after mixing two or more binder components onto the sand, there is a short delay before the mixture starts to set hard. Binders used for core making are typically gas-cured, in that a catalyzing/hardening gaseous component is forced through the sand/binder mixture to set it hard.
The molding and coremaking processes demand robust, environmentally acceptable binder systems with easy breakdown and removal after casting. While current organic systems (predominantly based around phenol formaldehyde base resins) provide exceptional performance, there are a number of issues surrounding their environmental profile, including health issues of users, volatile organic compounds, waste streams, odor, and thermal breakdown products. There is therefore a requirement to source a new, environmentally acceptable binder system. This could be based on inorganic, “clean” organic or hybrid derivatives, and should offer an immediate advantage over current systems, in terms of health, safety, and environmental issues. Key criteria include:
- Either a controllable self-setting system, where work-time could be varied by the use of different grades of hardener or different addition levels of hardener; OR a system that could achieve almost instantaneous cure through the application of a low-hazard gaseous hardener/catalyst (e.g. CO2).
- Low-toxicity/low-hazard material in terms of labeling and occupational exposure limits, and with zero or very low levels of free formaldehyde.
- High-strength development at low (<5%) addition levels.
- Chemical curing reaction, NOT a dehydration process. The curing mechanism should not be dependent on an external heat source and should take place under ambient conditions.
- Low-cost, high-volume product. Market volumes are measured in thousands of tonnes, but cost to the manufacturer (our client) would need to be <€2000 per tonne given volume production.
- No deterioration in strength on ambient storage for several days, and preferably an increase in strength.
- No adverse chemical reaction between the aggregate/binder and the metal during the casting process.
We know of the following binder systems and they are not currently of interest:
Organic: Amine-cured polyurethane, SO2-cured furan or epoxy, ester-cured alkaline phenolic, CO2-cured alkaline phenolic, acid-cured urea-formaldehyde/phenol formaldehyde/furan (by furan we mean polymers or blends with furfuryl alcohol).
Inorganic: CO2- or ester-cured sodium silicate, microwave-cured sodium silicate, machinable salt (sodium chloride) blocks.
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