New gas extraction system in sand moulds for steel and copper casting

The new technological development successfully transfers the experience of vacuum manufacturing, achieving a significant improvement in the quality of the castings. It is the result of the collaboration of AZTERLAN Metallurgy Research Centre with the companies ONDARLAN, MATERIART 2015 and CASTINOX.

Non-reusable casting moulds (those that are destroyed during demoulding of the parts once the metal is solidified) are the result of the agglomeration of different types of sand with organic and inorganic binders. In addition to shaping the mould, binders also provide moulds properties like: mechanical resistance at low and high temperatures, permeability to ensure a proper gas exit, reduced chemical reactivity with the molten metal and an adequate thermal conductivity to ensure the internal soundness of the cast components.

However, during the casting process, these binder elements suffer degradation and generate gases that mix with the liquid metal. In addition to having a negative impact on the environment and on the health&safety conditions, these gases also have a direct influence in the quality of castings, as they promote the generation of oxides and internal porosities in the components.

As explained by AZTERLAN researcher Fernando Santos, “when the metal is still in a liquid state, the reaction produced by the contact of the binders with the most oxidising alloying elements of the metal generates oxides inside the mould and on the surface of the melt, such as slags. In addition, a large part of the gases do not come out of the metal during solidification and generate pores and gas cavities that affect the soundness of the parts”.

With the aim of addressing gas extraction issues, different technologies related to vacuum generation can already be found in the market. In the case of steel manufacturing, secondary metallurgy integrates vacuuming to reduce the level of gases that remain in the final product. When it comes to superalloys transformed by the lost wax technology, fusion and casting are performed by means of vacuum furnaces to avoid generating reaction products that would then remain as inclusions within the components.

In order to transfer the vacuum experience to the manufacturing of aluminum or steel parts by means of lost wax process and to the production of steel parts by means of chemical sand moulding, AZTERLAN Technology Center has collaborated with ONDARLAN, MATERIART 2015 and CASTINOX in the development of a pioneering gas extraction system to improve the mould filling. Within the DESOX project these organisations have achieved significant accomplishments, such as manufacturing thinner wall components or reducing the presence of occluded gas and remnants of reaction products and inclusions within the parts.

“The new system consists of a gas extraction equipment, the adaptation of the moulding boxes and the incorporation of specific venting systems, which allow to extract not only the gases resulting from the decomposition of the sand binder, but also the air existing inside the mould”.

After pilot plant validations, the new system has been successfully transferred to industrial manufacturing conditions. “In both environments the results of the tests carried out have showed a 50% reduction of inclusions in the parts manufactured”.

The DESOX project has been funded by the Basque Government’s HAZITEK programme.

SEM image of oxides in a casting. The method developed within the DESOX project minimises pores, intermetallic compounds and oxides that affect the soundness of casted parts.