its inner surface on a pin 57 of the sliding piece 52 and the mobile hydraulic cylinder 23 being securely supported by this means as may also be seen from fig9 the two pressure arms 13a and 13b of the pressure beam 13 are also provided with support rails 58 and 59 in which the mobile hydraulic cylinder 23 can be inserted in the manner described and by virtue of the two rollers 56 can be displaced to any given position as required the straightening profiles can as described be loosely placed on the pressure arms 13a 13b and on the hydraulic cylinder 23 and are secured in this operating position by a spring loaded catch in view of the numerous profile dimensions of the container walls it is advisable to maintain a straightening profile store so that the necessary straightening profile is available when required the force transmission from the free stroke cylinder actuating the support beam to a sliding carriage carrying the support beam and being slidingly mounted on the sliding carriage support preferably takes place via a gear ratio transmission which can for example be designed in the form of at least one chain guided by means of toothed sprockets an embodiment example of such a force transmission is shown diagrammatically in fig1 in accordance with this arrangement the sliding carriage 14 is connected with an external cylinder 62 which can be hydraulically supplied by means of a chain drive 61 which.