Inductively heated extruder heater

1. A device for heating a feedstock of meltable or flowable material, comprising:

a) a heating body of electrically conductive material, with one or more inlet orifices where said feedstock is introduced, and one or more outlet orifices for said feedstock to exit after being heated, with one or more passages or mixing chambers connecting said inlet orifices and outlet orifices, comprising a nozzle, and

b) said nozzle sandwiched between the two ends of, or inserted through a hole or gap in, a continuous or segmented core of material having high magnetic permeability but low electrical conductivity, forming a complete magnetic loop, said nozzle fit in a gap in the magnetic loop, wherein the magnetic loop is oriented in a plane not substantially parallel with said nozzle, said core configured to support a loop or loops of magnetic flux lines of temporal alternating amplitude such that at least a portion of said temporal alternating magnetic flux lines interact with said nozzle resulting in heating of said nozzle due to eddy current effects, said core having at least some thermal conduction from said nozzle to said core, said eddy current heating limited by the Curie temperature property of material of said core, and

c) one or more coils of electrically conductive wire passing through the center of said loop and around the outside of said loop, and

d) one or more sources of high frequency alternating current connected to said coil or coils, inducing said magnetic flux lines and said eddy currents.

2. The device of claim 1 where said core is made of ferrite.

3. The device of claim 1 where said core is made of pressed iron powder.

4. The device of claim 1 where said heating body is made of steel.

5. The device of claim 1 where said heating body is tapered, and said core has a matching tapered gap or hole, such that no air gap exists between said heating body and said core.

6. The device of claim 1 where said feedstock is thermoplastic.

7. The device of claim 1 where said feedstock is aluminum.

8. The device of claim 1 where a flange or flanges comprising a heat sink are formed near said inlet orifice or said outlet orifice of said heating body.

9. The device of claim 2 , where said feedstock is thermoplastic and said heating body is steel.

10. The device of claim 2 , where said feedstock is aluminum and said heating body is steel.

11. A device for heating a feedstock of meltable or flowable material, comprising:

a) a heating body of electrically conductive material, with one or more inlet orifices where said feedstock is introduced, and one or more outlet orifices for said feedstock to exit after being heated, with one or more passages or mixing chambers connecting said inlet orifices and outlet orifices, comprising a nozzle, and

b) said nozzle sandwiched between the two ends of a continuous or segmented core of high magnetic permeability but low electrical conductivity, forming a complete magnetic loop at one point on said nozzle, and said nozzle fit in a gap in the magnetic loop, wherein the magnetic loop is oriented in a plane not substantially parallel with said nozzle said core configured to support a loop or loops of magnetic flux lines of temporal alternating amplitude such that at least a portion of said temporal alternating magnetic flux lines interact with said nozzle resulting in heating of said nozzle due to eddy current effects, said core having at least some thermal conduction from said nozzle to said core, said eddy current heating limited by the Curie temperature property of material of said core and one or more similar cores of magnetic material at additional points, to form additional heating zones in said heating body, and

c) a first coil of electrically conductive wire passing through the center of said first core and around the outside of said first core , and similar coils around said additional cores , and

d) a first source of high frequency alternating current connected to said first coil, and similar sources connected to each said additional coils, inducing said magnetic flux lines in said cores and said eddy currents in said nozzle.

12. The device of claim 11 , where said heating body is made of steel.

13. The device of claim 11 , where said core is made of ferrite.

14. The device of claim 11 , where said core is made of pressed powdered iron.

15. a device for melting and extruding filament or rod in a 3-D printer or other additive manufacturing system, comprising:

a) a heating body of electrically conductive material, with one or more inlet orifices, where a feedstock of meltable material is introduced, and one or more outlet orifices for said feedstock to exit after being heated, connected by one or more passages or mixing chambers, comprising a nozzle, and

b) said nozzle sandwiched between the two ends of, or inserted through a hole or gap in, a continuous or segmented core of material having high magnetic permeability but low electrical conductivity, forming a complete magnetic loop, and said nozzle fit in a gap in the magnetic loop, wherein the magnetic loop is oriented in a plane not substantially parallel with said nozzle said core configured to support a loop or loops of magnetic flux lines of temporal alternating amplitude such that at least a portion of said temporal alternating magnetic flux lines interact with said nozzle resulting in heating of said nozzle due to eddy current effects, said core having at least some thermal conduction from said nozzle to said core, said eddy current heating limited by the Curie temperature property of material of said core and

c) a coil of electrically conductive wire passing through the center of said core, and around the outside of said core, and

d) a source of high frequency alternating current connected to said coil, inducing said magnetic flux lines and said eddy currents.

16. The device of claim 15 , where said feedstock is thermoplastic.

17. The device of claim 15 , where said feedstock is metal.

18. The device of claim 17 , where said metal is aluminum.