the mould parts are represented by the slope of the curves the flatter the slope the greater is the speed the steeper the slope the smaller is the speed fig5 shows a cycle of movement which is typical for known blowing machines the two mould parts are moved in the closing direction initially at a relatively high normally constant speed vn until they have reached approximately the position s 1 until about this point in time the only thing that matters is that the two mould parts should be moved in the closing direction as rapidly as possible in order to keep the amount of time required as small as possible at the latest at the point s 2 at which the partly finished product 15 is squeezed flat in the regions of the pinch edges as shown in the illustration of fig4 the reduction of the closing speed to the lower value vv has been completed the reduction to the speed vv can for example be effected by bringing into action a throttle which is built into the hydraulic drive circuit for the two mould parts after reaching the retarded closure speed vv the two regions 15a 15b fig4 of the intermediate product 15 are pressed against one another and with the formation of the above mentioned welded seam are connected to one another until as a result the components take up the positions shown.