Water-Soluble Binder for HPDC Sand Cores

FOSECO has developed a new type of sand core using a novel, water-soluble binder and sealant that offers competitive strength and manufacturability, plus easy removal after casting. Standard sand cores made with organic or inorganic binders cannot be used for high-pressure diecasting (HPDC) as they are difficult to remove after casting and do not provide adequate surface finish. Salt cores are a better option, but can be expensive to produce, and present other operational limitations.

HPDC is an increasingly important metalcasting option, offering advantages like high production rates and good surface finishes. It’s particularly valuable in producing lightweight parts for automotive, e-mobility, and high-tech (5G) markets. A significant limitation for HPDC is the ability to produce complex internal cavity shapes. Diecasting operations need to have available disposable cores that can tolerate the high pressures, temperatures, and speeds involved in the HPDC process.

Cores formed with the Foseco Foundry R&D Centre’s water-soluble binder and sealant are produced using standard sand core production equipment, and offer a cost-effective, high volume, and sustainable option for HPDC of complex, hollow shapes and are equally suitable for use in liquid HPDC or semi-solid (rheocasting) process.

For high-pressure casting processes, a sealant may be necessary to avoid penetration of the liquid metal into the pores of the sand, which results in casting-surface roughness. Different techniques can be used to apply a sealant, such as dipping or spraying.

All sand cores are produced using a standard core shooter equipped with a hot box system. For the new, HPDC-suitable cores, the sand mixture is prepared using the ECORES06* liquid binder and ECOSOL01 additive (powder). It is then automatically injected at high speed into a specially designed core box using compressed air, and cured.

In testing, and irrespective of the mechanical strength of the sand cores, the binder’s water solubility was demonstrated in less than 5 seconds. It is interesting to note that the new water-soluble binders showed excellent solubility after the casting trials in multiple processes – from liquid HPDC, rheocasting, gravity and LPDC processes, indicating that the application temperature of such a type of binder is at least 750°C.