Twenty years ago, researchers at Hüttenes-Albertus achieved a decisive break-through in improving the environmental properties of the cold box binder system. By using biodiesel as a solvent, benzene, toluene and xylene (BTX) emissions could be significantly reduced – an invention that is continuing its success in foundries to this day.
For some decades, the cold box system has been one of the most prevailing core production processes. It meets many key requirements that foundries have, particularly for automated series production: high productivity through quick curing, high strengths at a low dosage as well as high-quality castings due to good thermal resistance and good collapse behaviour.
Although the cold-box system offers many economic and manufacturing benefits, there is, however, one downside to it: emissions generated during core production and casting burden the natural and workplace environments.
Rapeseed oil reduces BTX emissions
Researchers at Hüttenes-Albertus (HA) successfully tackled this problem. 20 years ago, HA chemists, Dr. Marek Torbus and Gerard Ladégourdie, managed to improve the environmental compatibility of the Cold-Box binder system by substituting the aromatic solvents that were normally used with fatty acid methyl esters (biodiesel). This helped to reduce BTX emissions significantly – both during core production and also during casting.
The modified cold-box system with solvents on the basis of vegetable oil offered clear advantages and became a success story that still continues today. As the inventor of the environmentally friendly binder system, Hüttenes-Albertus can now look back on 20 years of experience and expertise.
Further benefits: less amine, less release agent
In addition to the clear benefit for the environment and work place, the system also offers a number of other advantages: the biodiesel-based cold-box variant is highly reactive, which reduces the consumption of amine as a catalyst.
Moreover, it has an excellent release effect, i.e. it has a lower tendency to stick to the core tool surface than a cold-box binder on the basis of aromatic solvents. For foundries, this means improved efficiency, since less release agent is needed. Plus, the cleaning intervals are longer, which contributes to higher productivity.
Aliphatic instead of aromatic solvents
The cold-box process is based on the formation of polyurethane from two components, which are added to the core sand: a phenolic resin (also called gas resin or part 1) and an activator (part 2, polyisocyanate). A tertiary amine is used to catalyse the polymerisation reaction of these two components.
The reactive components of part 1 and part 2 are available in dissolved form. The solvents contained in these components ensure sufficient liquidity of the product and serve as a carrier medium to provide good mixability with the sand. In addition, they control key properties, such as the sand bench life, feasibility of using water-based coatings, moisture resistance of the cores and collapse behaviour.
Traditionally, aromatic hydrocarbons were used as a solvent. As a result of the thermal load during the casting process, they have the disadvantage of producing undesired decomposition products (particularly BTX) that are emitted into the air. Aliphatic solvents based on fatty acid methyl esters (e.g. from rapeseed oil) considerably reduce the level of harmful emissions, both in iron and aluminium casting.
Biodiesel is made from renewable resources. Meeting all physical requirements for a solvent to be used in polyurethane binding systems, it is a starting product that is odourless and non-hazardous to health. Moreover, biodiesel is not classified as flammable, which simplifies transportation and storage.