Tunnel furnace for the heat treatment of articles

A tunnel furnace composed of individual sections for the heat treatment of articles which are transported through said tunnel comprising:

• a rotating, endless, air permeable conveyor belt for carrying said article through a main heating space;
• means for separating each said section into said main heating space and outer spaces on either side of said main space in communication with said heating space at the top thereof and below said belt;
• circulation fans within said furnace for circulating air in a continuous path upwards through said conveyor belt and then downwards through said outer spaces;
• a heater disposed in each said outer space comprising a vertically extending burner pipe and a pipe section extending therefrom in a vertical plane in said outer space for conducting the flame and combustion gases, said section having an S-shaped configuration with vertically spaced horizontal portions connected by U-shaped portions so that the combustion gases flow upward during a portion of their travel within said section and for heating said circulating air which moves past said burner pipe and said section, said section terminating in a mouth exposed to the circulating air flow.