suction line 28 to a source of vacuum 29 with that the ambient air outside the cooling drum 26 is used as medium for cooling the cooling groove 26 formed on the circumference of the cooling drum 25 has a width b the width b of the cooling groove 26 is dimensioned in relation to the yarn plug 13 such that the width b is preferably greater than twice the amount of the yarn plug diameter d i e b gt 2d between the plug outlet 24 and the cooling groove 26 a free spacing a extends to permit an unobstructed deposit of the yarn plug 13 in the cooling groove 26 during the crimping process the spacing a remains unchanged in the crimping device 7 a heated conveying fluid enters the yarn feed channel 20 via the injector 19 this causes a suction effect to develop at the upper end of the yarn feed channel 20 which sucks the filament bundle 10 into the crimping device 7 the conveying fluid advances the filament bundle 10 through the yarn feed channel 20 into the stuffer box chamber 22 in the stuffer box chamber 22 the filament bundle 10 compacts to a yarn plug 13 in so doing the filament bundle 10 opens up and the individual filaments come to lie on top of one.