The invention relates to a melter, comprising a block (2) having a detachable shell (6), in which there is housed a melting chamber (3) provided with an upper opening that is closed with a hinged and detachable lid (11), the chamber (3) being arranged on lower supports (7), with the freedom to expand upwards, the opening of said chamber (3) incorporating a gasket (8) having an upwardly inclined flexible lip in the outer part on which the shell (6) rests, establishing sealed closure with respect to the chamber (3), whereas on the gasket (8) there is arranged a frame (9) having an upward vertical flange, with respect to which the lid (11) that closes on the gasket (8) is assembled, such that when the chamber (3) expands due to the temperature, the flexible lip allows the expansion maintaining leak-tightness.