in that several small sand grains join into a larger one fig4 shows the case where the discharged expanded material substantially consists of individual sand grains 15 with a spherical surface 7 fig5 shows in contrast an expanded granulate with larger sand grains 15 which have a rough surface 7 in order to enable rapid cooling of the expanded pearlite sand 1 a cooling air 16 is injected during the discharge from the furnace 2 see fig3 an outflow opening 29 for the cooling air 16 is provided for this purpose in the region of the discharge opening 20 the quantity of cooling air 16 can be regulated by a preferably controllable valve 28 the cooling air produces a cooling of the expanded pearlite sand 1 to a temperature of beneath 100 u00b0 c preferably beneath 80 u00b0 c a chute 8 is arranged as seen in the falling direction 23 after the discharge opening 20 directly adjacent to the outflow opening 29 for the cooling air 16 said chute is cooled by means of cooling water 30 the quantity of which is controlled by a preferably controllable valve 31 the expanded pearlite sand 1 is further cooled in this manner the expanded pearlite sand 1 finally reaches an entrained flow conveyance 17 via the chute 8 with.