Furnace for heating a preform, provided with two cooling fans

A furnace (22) for heating a preform (10), which comprises:

• a longitudinal heating tunnel (24) bounded transversely by mutually parallel longitudinal vertical internal faces (36, 38) of two walls (40, 42), one a heating wall (40), being equipped with a heating system (46), and the other an aerated wall (42), having aeration orifices (50), and in the heating tunnel (24), a first portion (12, 14) of the preform (10) is heated, while a second portion (16) of the preform (10) is held outside the heating tunnel (24) through a longitudinal opening (41) made between longitudinal edges of the walls (40, 42) of the heating tunnel (24);
• a blower (52) which includes a first fan (54a) and a second fan (54b)
• said first fan (54a) delivers a first air stream transversely in a first delivery duct (60a) from an upstream, outside the heating tunnel (24), to a downstream, inside the latter, in a direction of the first portion (12, 14) of the preform (10), by passing through the aerated wall (42);
• said second fan (54b) delivers a second air stream transversely which is parallel to the first air stream, in a second delivery duct (60b) from the upstream, outside the heating tunnel (24), to the downstream, directly to the second portion (16) of the preform (10), so as to keep the constituent material of this second portion (16) of the preform (10) at a temperature below its softening point;
• and
• the two separate air delivery ducts (60a, 60b) being adjacent and formed by the upper and lower compartments of a common box (66) having a dividing partition (68).