Abstract: The disclosure relates to a mold for aluminothermic welding without preheating of two metal parts, said mold being composed of two mold parts and two sets of cores and having internally employed a mold cavity and two mold channels with cross-sections of elongated shape, extending from underneath the base portion of said mold cavity to the upper side of said mold, said mold channels and the extremities of said base portion being connected together through two connecting ducts with cross-sections of elongated shape on the vertical, the rising channels being employed from recesses of mold channels or cores and complementary channel portions determined by positions of said cores inserted into said mold channels onto positioning means, said mold in which closing gates connecting the upper side of rising channels directly to the atmosphere or to the upper side of head portion of said mold cavity, the invention further relating to a process in which a liquid bath of constant height is created in the welding cavity,