Abstract: Creep of foundry sand was observed at investigation on the influence of the duration of acting time of the compacting force on compaction of foundry sand. It was observed also, that the duration of force acting has significient influence on some important mould-forming properties, such as springback, pattern withdrawing force and reloading deformation etc. The mechanism of these mould-forming properties are analysed with theological principle or with considering the viske-elastic and viske-plastic behaviour of the bentonite-film between sand grains. Further the difference of the traditional high pressure squeezing and the newly developed air impulse compacting of foundry sand in compacting effect was discussed with above mentioned hypothesis. It follows that, it is necessary to consider the rhological behaviour of bentonite-film in research with high speed process of compacting foundry sand, such as air impulse compacting.

Key words: 紧实, 蠕变, 型砂, 铸造