Abstract: For fixing electrostatically formed images of thermoplastic powder on copy sheets, an elastic roller and a heated rigid roller form a nip through which each sheet is passed with its image side engaged by the elastic roller, and the elastic roller has a pliable annular body formed with circumferential surface grooves or ribs which cooperate with organs of complementary form for separating each sheet from the roller surface behind the nip, yet which provide an even roller surface in the nip by being elastically deformed therein. The rigid roller is formed with circumferential surface grooves which also cooperate with complementary sheet separating organs. The separating organs cooperating with grooves may be blades extending into them behind the nip, or wires extending in them through the nip; those cooperating with ribs may be blades having profiled edges held almost in contact with ribbed regions of the elastic roller surface.