I claim the ornamental design for a sintering furnace, as shown.
FIG. 1 shows a perspective view of the sintering furnace in a closed state;
FIG. 2 shows a perspective view of the sintering furnace in the open state, portions of the furnace shown in broken lines forming no part of the claimed design.
FIG. 3 is a front elevational view of the sintering furnace according to FIG; 1;
FIG. 4 shows a back view of the sintering furnace according the FIG. 1, portions of the furnace shown in broken lines forming no part of the claimed design.
FIG. 5 shows a right side view of the sintering furnace according to FIG. 1;
FIG. 6 shows a left side view of the sintering furnace according to FIG. 1;
FIG. 7 shows a bottom view of the sintering furnace according to FIG. 1, portions of the furnace shown in broken lines forming no part of the claimed design; and,
FIG. 8 shows a top view of the sintering furnace according to FIG. 1.