a device for controlling the sealing of thermoplastic overwraps , particularly sealing end flaps of the overwraps on packets of cigarettes . at various speed levels of the overwrapping machine the time devoted to this sealing operation is kept constant . this is achieved by providing a plurality of control cams , the number of which corresponds to the number of speed levels there are on the machine . each control cam operates at one of the speed levels , to periodically activate and deactivate sealing contrivances which operate on the ends of the packet .