Abstract: The invention relates to an automatic unplugging aluminothermic welding crucible comprising a crucible per se made of refractory material, shaped generally as a truncated cone with a vertical axis, said cone tapering inwardly to the lower base thereof and comprising a conical hole receiving a crown provided with a conical bore, said conical bore receiving a casting socket, the conduit thereof being sealed by sealing means before filling of said crucible, said sealing means comprising a plug made of an aluminothermic compound consisting of iron oxide and aluminum agglomerated with a suitable binder, said plug resting on a steel washer.According to the invention, said sealing means comprise a plug made of an aluminothermic compound consisting of iron oxide and aluminum agglomerated with a suitable binder, for example, made of silicate.