The device has an elastic unit connected to a support (5) of an arm and placed near an exit point of a load strip beyond the support. The unit has elastic tongues (7) arranged above the exit point of the load strip, where the tongues are made of spring steel. The tongues are pushed by an exit point of one link (M1) against the action of a torsion spring and are cooperated with a rear edge of a body of the link for pivoting the link with respect to another link (M2) to unhook the links.
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