Inorganic binder technologies gain an increasing attention, not only in the European foundry industry. Does the global role-out of inorganic binder technologies determine the end for conventional shell sand processes?
Our US experts recommend:
A provocative question, I must admit, and the answer to this question is diversified in respect to the casting application. Of course, new technologies always threaten the existence of conventional technologies as far as they add performance value to the respective process itself. In case of aluminum casting applications, particularly in high productive segments such as the manufacture of aluminum engine blocks and cylinder heads in permanent mold casting, more and more foundries are converting from organic to inorganic binder systems – and there are several reasons for this trend.
Odorless core production, no harmful emissions during casting, less maintenance of machinery and tools, and the resulting higher productivity are well known economic and ecological benefits of the INOTECTM technology. Technological benefits rely on the faster solidification of the aluminum melt. Reduced die mold temperatures and the consumption of energy from the aluminum melt by water evaporation result in improved mechanic properties of the castings, e.g. reduced dendritic arm spacing.
The inorganic binder technology INOTECTM is described as a two component binder system including a liquid INOTECTM binder and a solid inorganic additive – the so-called INOTECTM Promotor. Shell sand is a phenolic resin coated sand with addition rates of 2,5 to 3,5% (based on sand). In terms of core manufacturing, both binder systems are cured in a hot core box. INOTECTM requires significantly lower core box temperatures (150 – 210 °C vs. 250 °C for shell sand) but also implies the necessity of hot-air purging that is missing in the shell sand process. Strength values (both hot and cold) of INOTECTM-bound cores are high enough for automatized handling. Care should be taken in regard of the brittleness which is typically higher than that of shell sand cores. Additionally, inorganic-bound cores have – by nature – a high affinity to water. Thus substantial technical adjustments (storage facilities with proper storing conditions to avoid exposure to high humidity) and continuous product development to improve humidity resistance are countermeasures.
A major disadvantage of shell sand cores are volatile emissions during core manufacturing as well as odor and smoke formation in the casting production process as a results of the thermal decomposition of the phenolic resin. As a consequence, condensate or tar build up reduce die mold lifetimes and imply continuous maintenance operations. Additionally measures, e.g. ventilation and air treatment systems, are mandatory. Higher risks for gas inclusions and casting defects are possible as shown by the difference in gas formation potential. The amount of condensate for INOTECTM is related to the amount of released water that contribute to the binding properties of the silicate gel structure during core manufacturing, storage and utilization.
INOTECTM Shell sand
Gas volume [ml]
Comparison of gas and condensate formation between shell sand and INOTECTM. Measurement was done using a COGAS apparatus in liquid aluminum.
Dimensional casting accuracy as a result of improved thermal stability is comparable for both binder systems. The INOTECTM tooling kit approach even enables tailor-made core property adjustments in respect to thermal strain and core geometry. Core collapse or shake-out processes for inorganic-bound cores require mechanic impact via hammering and vibrating systems. Continuous product development and process discipline enable reliable core collapse properties even of complex cores on serial production scale procedures.
In comparison to shell sand cores, the INOTECTM technology shows equal or even superior process properties during core manufacturing and aluminum casting production, if technical measures, process knowledge and process discipline are established.
So, consult with your ASK Chemicals contact for the best overall recommendation.