Pneumatic cylinder with safety device

[0008]Particularly dangerous are piston-rod breakages at the lower dead center point of the ram where the piston is at the greatest distance from the impact plate. The available cylinder stroke distance then becomes the acceleration distance of the piston. Thus, once the piston has completed the stroke distance, it has considerable kinetic energy. The impact plate is dimensioned so as to absorb this energy and to permit a safe catching of the piston, even if force-transmitting parts break off near the lower piston dead center, thus increasing the safety. The danger to personnel nearby or to other plant components can be minimized and / or eliminated.

[0009]The impact plate in the simplest form can be a flat plate that spans the pneumatic cylinder crosswise and projects with its edge over the cylinder wall. It can be frictionally clamped with a clamping device along the edge, for example, in the form of a clamping ring or rings. The clamping force is preferably adjusted such that during a piston-catching operation, which progresses in the manner of a deep-drawing operation, it permits a controlled subsequent sliding of the impact plate edge, so as to avoid the forming of folds in the pot-shaped part that forms and the forming of premature cracks. The clamping ring can be held in position with several screws which are pulled tight with a controlled torque and are secured in the tightened position, for example, with screw-securing shellac or varnish. The clamping ring and a counter surface assigned thereto are advantageously provided with flat contact surfaces for the impact plate. However, the contact surfaces can also be provided with ribs, burls as well as opposite-arranged associated recesses for influencing the sliding through and / or slipping through of the impact plate edge. In addition, it is possible to provide the impact plate with one or several recesses to influence the drawing behavior. In the same way, the impact plate can also be provided with ribs, local reinforcements or local weakened zones. The impact plate preferably has a uniform thickness. However, it is possible to impress a thickness profile designed to distribute the accumulating deformation energy evenly over the complete plate surface or over preferred deformation zones. For this, a rotation-symmetrical plate profile is preferred, meaning variations in the diameter relating to the radial direction, and not variations in the circumferential direction.

[0011]The piston and the clamping ring are preferably each provided with a rounded area along the respective edge facing the impact plate. This rounded area, preferably having a radius of 5 mm to 20 mm, makes it easier during the deformation to prevent the formation of cracks in the impact plate, and thus prematurely ending the energy absorption.

Particularly dangerous are piston-rod breakages at the lower dead center point of the ram where the piston is at the greatest distance from the impact plate.