It is quite impossible to forget such binder for those who used to work with. Indeed, there was a time when all steel foundries used it. Not only. Its usage was widespread also in aluminum foundries, using very fine sands, when mirror-surfaces were required.
Later on, this resin has been superseded by furan and phenolic ones, considered more performant.
The alkyd resin – a complex oil-modified polyester – is used for the no-bake moulding process, especially where stripping times are long (i.e. min 1 hour).
Its percentage of use is about 0,8-0,6% on the sand weight, lower than traditional binding systems such as the phenolic and furan ones.
It is totally anhydrous, thus avoiding long and expensive drying processes, but also casting defects due to the high humidity, which is very difficult to eliminate with other binding systems.
Moreover, it is sulfur-free. This component is on the contrary present in acid hardening of no-bake systems, where acids such as the PTSA (i.e. p-Toluenesulfonic acid) bring to its accumulation in the sand.
The alkyd resin label is “white”, i.e. without any dangerous symbols. In fact, it reacts with a second component in a percentage of 20% composed by MDI (i.e. Diphenylmethane diisocyanate), similar to cold-box “dark” component.
The MDI is harmful, but it boils at 300°C therefore it does not remain in the air of the work environment.
A further advantage of such system is the absence of formaldehyde. Indeed, this toxic and volatile molecule is present in the other organic moulding systems, thus causing high level of toxicity.
Moreover, being totally organic, the alkyd resin burns without leaving residues. For this reason it can be completely reclaimed. This is not so easy to do with furan and phenolic systems.
A great number of steel foundries uses chromite sands on the model and silica one as filling. Chromite sand, once poured the metal and after the mechanical reclaiming process and its magnetic-gravimetric separation, results pretty much new, with neutral pH and without loss on ignition. Reclaim costs are consequently very low, if compared to the alkaline phenolic system.
From the metallurgic point of view, the alkyd resin creates a reducing atmosphere, thus giving good finishing results to metal surfaces. Moreover, cores easily collapse avoiding hot tears defects. Stripping of models is simple too, without any breaking or extraction problems.
In conclusion, we suggest testing this system using a little mixer for cores. Satisfaction is granted! Our technical team is always at your disposal in order to provide assistance and to give all the necessary information to achieve great performances.