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INNOVATIVE SAND CORES WITH WATERSOLUBLE BINDER SYSTEMS FOR THE NON FERROUS SECTOR

Issued at 2022-06-20



A key limit on the high pressure die casting process (HPDC) is the inability to produce complex, hollow castings at high volume and in a cost-effective and sustainable way, due to the difficulty in producing suitable cores. Standard sand cores made with common organic or inorganic binders cannot be used for HPDC, as they are difficult to remove after casting and do not provide adequate surface finish. Salt cores are more suitable, but can be expensive to produce, whilst presenting other operational limitations. In response to this challenge, the Foseco Foundry R&D Centre in Enschede, the Netherlands, has developed a new type of sand core, using an innovative Water-Soluble Binder (WSB) and sealant, which offers competitive strength and manufacturability, whilst enabling easy removal after casting.

HPDC offers a range of advantages, such as higher production rates and good surface finish; as a result, is the process of choice for many of the new, lightweight parts needed by the growing e-mobility and 5G markets. However, it is also not without its challenges. One significant limitation is the ability to produce complex internal cavity shapes. In order to overcome that obstacle, it is necessary to develop disposable cores that must be able to tolerate the high pressures, temperatures and speeds involved in the HPDC process.

A new type of sand core, developed by the Foseco Foundry R&D Centre, provides a solution to these challenges. These cores are made with an innovative Water-Soluble Binder and sealant using standard sand core production equipment. They therefore offer a more cost-effective and sustainable option for HPDC of complex, hollow shapes at high volume and are equally suitable for use in liquid HPDC or also in semi-solid (Rheocasting) process.

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

MECHANICAL STRENGTH

The ECORES06* liquid binder was set at 6.0wt% of the sand. Depending on the casting process and the related requirements, the exact strength values can be selected

The strength values of samples without the additive were relatively low (low compaction (low sample weight)); the average value was about 100N/ cm². However, the addition of only a small amount of the additive, in this case 2.0wt%, resulted in a significant improvement in the mechanical properties: strength values were around 700N/cm². A further increase of the concentration resulted in strength values higher than 1200N/cm² (high compaction (high sample weight)).

MANUFACTURING SAND CORES

All sand cores are produced using a standard core shooter equipped with a hot box system. For the new HPDCsuitable 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

WATER-SOLUBILITY OF THE BINDER

Irrespective of the mechanical strength of the sand cores, the water solubility of the binder was excellent with full dissolution feasible 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. This makes these cores very promising candidates for slow and fast solidifying casting processes. 

 


Source: Foundry Planet



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