Abstract: An improved L-sealing apparatus providing an L-shaped sealing bed assembly mounted at its ends and corner on three piston-and-cylinder assemblies operable upon closing of the sealing arm into adjacency with the sealing bed assembly to translatorily move the sealing bed assembly into uniform and continuous surface contact and pressure with the heating wire arrangement of the sealing arm. In another embodiment, the sealing bed assembly is fixed to the machine frame and a pair of pneumatic-electromagnetic latching assemblies are provided to magnetically engage the sealing arm at its opposite ends in its sealing disposition adjacent the sealing bed assembly to torsionally distort the sealing arm if and as necessary to bring its wire heating assemblies into parallel continuous and uniform surface contact and pressure with the sealing bed assembly.