Apparatus for making hot asphalt paving material

Abstract

Hot asphalt paving material is made in a rotary drum mixer which has a burner at the aggregate-introducing end and an interior transverse flame shield in the path of the burner to divide the rotary drum into a drying section and a mixing section. Means are provided in the mixing section for introducing asphalt cement into the dried aggregate material and for agitating the mix. Exhaust gases from the mixing section are passed through a heating and cooling heat exchanger and returned to the burner.

I claim: 
     
       1. Apparatus for making asphalt paving material from a particulate aggregate material and asphalt, comprising, a rotary drum having an inlet and an outlet end,   means for rotating the drum about its longitudinal axis,   said drum having a drying section extending inwardly from the inlet end thereof and a mixing section extending inwardly from the outlet end thereof,   burner means for directing a flame into the drying section,   means for lifting the aggregate material in the drying section and releasing the material so lifted downwardly through the area heated by the flame for removal of moisture,   a heat shield located within the drum in axial alignment with the flame,   said heat shield defining the downstream end of the drying section and the upstream end of the mixing section,   an opening in the plane of the shield permitting the flow of aggregate material from the drying section to the mixing section,   means in the mixing section for introducing hot asphalt into the aggregate material,   agitator means in the mixing section for agitating and mixing together the asphalt and aggregate material,   means for withdrawing exhaust gases from the mixing section, and   recirculation means for returning the exhaust gases and airborne solid particles therein to the drying section at the inlet end of the rotary drum whereby the heat and combustible constituents of the exhaust gases aid the combustion process in the drying section and the airborne solid particles are removed from the gases upon contact with the hot asphalt in the mixing section.   
     
     
       2. The apparatus of claim 1 wherein the means for withdrawing exhaust gases from the mixing chamber has an exhaust gas inlet pipe which projects inwardly into the mixing chamber toward the heat shield. 
     
     
       3. The apparatus of claim 1 having air conditioning means for heating and cooling the exhaust gases which are being returned to the drying chamber at the inlet end of the rotary drum. 
     
     
       4. Apparatus for making asphalt paving material from a particulate aggregate material and asphalt, comprising, a rotary drum having an inlet end and an outlet end,   means for rotating the drum about its longitudinal axis,   burner means for directing a flame into the rotary drum,   means for lifting the aggregate material in the drying section and releasing the material so lifted downwardly through the flame and in the vicinity thereof for removal of moisture,   means in the rotary drum for introducing hot asphalt into the aggregate material,   agitator means in the rotary drum for agitating and mixing together the asphalt and aggregate material,   means for withdrawing exhaust gases from the rotary drum, and   recirculation means for returning the exhaust gases and airborne solid particles therein to the inlet end of the rotary drum whereby the heat and combustible constituents of the exhaust gases and the combustion process and the airborne solid particles are removed from the gases upon contact with the hot asphalt in the rotary drum.   
     
     
       5. The apparatus of claim 4 having air conditioning means for heating and cooling the exhaust gases which are being returned to the drying chamber at the inlet and of the rotary drum. 
     
     
       6. Apparatus for making asphalt paving material from a particulate aggregate material and asphalt, comprising, a rotary drum having an inlet end and an outlet end,   means for rotating the drum about its longitudinal axis,   said drum having a drying section extending inwardly from the inlet end thereof and a mixing section extending inwardly from the outlet end thereof,   burner means for directing a flame onto the drying section,   means for lifting the aggregate material in the drying section and releasing the material so lifted downwardly through the area heated by the flame for removal of moisture,   a heat shield located within the drum in axial alignment with the flame, said shield being a body of refractory material which is concentric with and transverse to the rotational axis of the drum,   said heat shield defining the downstream end of the drying section and the upstream end of the mixing section,   an opening in the plane of the shield permitting the flow of aggregate material from the drying section to the mixing section, said opening being an annular space lying between the outer periphery of the shield and the interior wall of the drum,   means in the mixing section for introducing hot asphalt into the aggregate material,   agitator means in the mixing section for agitating and mixing together the asphalt and aggregate material.   
     
     
       7. Apparatus for making asphalt paving material from a particulate aggregate material and asphalt, comprising, a rotary drum having an inlet end and an outlet end,   means for rotating the drum about its longitudinal axis,   said drum having a drying section extending inwardly from the inlet end thereof and a mixing section extending inwardly from the outlet end thereof,   burner means for directing a flame into the drying section,   means for lifting the aggregate material in the drying section and releasing the material so lifted downwardly through the area heated by the flame for removal of moisture,   a heat shield located within the drum in axial alignment with the flame,   said heat shield defining the downstream end of the drying section and the upstream end of the mixing section,   an opening in the plane of the shield permitting the flow of aggregate material from the drying section to the mixing section,   means in the mixing section for introducing hot asphalt into the aggregate material,   agitator means in the mixing section for agitating and mixing together the asphalt and aggregate material,   said means for lifting the aggregate material in the drying section and the agitator means in the mixing section being flight bars attached to the interior of the drum, and   means for withdrawing exhaust gases from the mixing chamber, said means for withdrawing exhaust gases having an exhaust gas inlet pipe which projects inwardly beyond the flight bars.   
     
     
       8. Apparatus for making asphalt paving material from a particulate aggregate material and asphalt, comprising, a rotary drum having an inlet end and an outlet end,   means for rotating the drum about its longitudinal axis,   said drum having a drying section extending inwardly from the inlet end thereof and a mixing section extending inwardly from the outlet end thereof,   burner means for directing a flame into the drying section,   means for lifting the aggregate material in the drying section and releasing the material so lifted downwardly through the area heated by the flame for removal of moisture,   a heat shield located within the drum in axial alignment with the flame,   said heat shield defining the downstream end of the drying section and the upstream end of the mixing section,   an opening in the plane of the shield permitting the flow of aggregate material from the drying section to the mixing section,   means in the mixing section for introducing hot asphalt into the aggregate material,   agitator means in the mixing section for agitating and mixing together the asphalt and aggregate material,   said means for lifting the aggregate material in the drying section and the agitator means in the mixing section being flight bars attached to the interior of the drum, the flight bars in the mixing section being axially spaced from the flame shield to provide a settling area, said means for introducing hot asphalt into the aggregate material being constructed to direct hot asphalt into the settling area.   
     
     
       9. The apparatus of claim 8 having means for withdrawing exhaust gases from the mixing chamber, said means for withdrawing exhaust gases having an exhaust gas inlet pipe which projects inwardly beyond the flight bars. .Iadd. 10. Apparatus for making asphalt paving material from a particulate aggregate material and asphalt, comprising, a rotary drum having an inlet end and an outlet end, means for rotating the drum about its longitudinal axis,   said drum having a drying section extending inwardly from the inlet end thereof and a mixing section extending inwardly from the outlet end thereof,   burner means for directing a flame into the drying section,   means for lifting the aggregate material in the drying section and releasing the material so lifted downwardly through the area heated by the flame for removal of moisture,   a heat shield located within the drum in axial alignment with the flame, said shield being a body of material which is concentric with and transverse to the rotational axis of the drum,   said heat shield defining the downstream end of the drying section and the upstream end of the mixing section,   an opening in the plane of the shield permitting the flow of aggregate material from the drying section to the mixing section, and opening being an annular space lying between the outer periphery of the shield and the interior wall of the drum,   means in the mixing section for introducing hot asphalt into the aggregate material,   agitator means in the mixing section for agitating and mixing together the asphalt and aggregate material. .Iaddend.