The invention relates to a process of crosslinking a polymer material with silane by means of heat, in which process a polymer, a grafting agent, an initiator and a crosslinking catalyst and optional additives are fed into an extruder and extruded to a homogenous mass by keeping the process temperature so low that the initiator used does not degrade during the extrusion and the optional additives do not react or degrade in the extruder, and, after the extrusion, the extruded mass is grafted and crosslinked. After the extrusion, the process of the invention comprises a step of heating the initiator, mixed homogenously with the polymer material, by means of infared radiation in a wavelength range absorbed by the initiator. |