APPARATUS FOR HEAT-SEALING PLASTIC PACKAGINGS OR WRAPPING, FOR EXAMPLE PACKAGINGS WITH SETS OF ROLLS OF PAPER

摘要

The heat sources which act in conjunction with the active runs of the vertical-axis conveyors (T1, T1') which keep the side flaps of the packagings folded down, comprise bodies (2) of any mechanically strong material, whether made in one piece or composite equipped with a plurality of electrical strip resistors (1) laid parallel with each other in the direction of the length of the said conveyors and operating in contact with the active runs of these conveyers. The strips, heated by the Joule effect and temperature-controlled by continuous electronic monitoring of their resistances, are quantitatively involved in the sealing process in direct proportion to the dimensions of the packagings to be sealed. This system has practically zero thermal inertia and therefore quickly reaches operating temperatures and equally quickly becomes inactive, thereby avoiding the dangerous problems of known radiant-mass systems, compared with which it also has the advantage of using much less electrical power.