Heat treatment oven with inductive heating

1. A heat treatment oven comprising:

a loading or treatment zone having a longitudinally extending axis,

at least one gas inlet,

a gas preheater chamber situated in the oven between the gas inlet and the loading or treatment zone, above or below and in axial alignment along the axis with the loading or treatment zone, the gas preheater chamber having an axial height,

a susceptor comprising at least a side wall circumferentially surrounding the preheater chamber and the loading or treatment zone,

a field winding suitable for heating the side wall by induction, and

a gas distribution plate interposed between and separating the gas preheater chamber and the loading or treatment zone, the gas distribution plate extending transversely to the axis;

wherein the side wall of the susceptor terminates in an end portion having a ring that is situated around the preheater chamber, the ring comprising at least two recesses spaced apart circumferentially from one another so as to form portions of reduced thickness in said ring adjacent said preheater chamber, the recesses having an axially extending height less than the axial height of the gas preheater chamber and a radial dimension less than a thickness of said ring in a direction orthogonal to said axis.

2. An oven according to claim 1 , wherein the ring situated around the preheater chamber includes three recesses spaced apart uniformly from one another.

3. An oven according to claim 1 , wherein the recesses are formed in the inner or outer periphery of the ring.

4. An oven according to claim 1 , wherein the recesses are regularly spaced apart from one another.

5. An oven according to claim 1 , wherein the ring recesses have the axial dimension in the range of 30% to 60% of a radial thickness of the side wall.

6. An oven according to claim 1 , wherein the axial height of the recesses is less than the axial height of the preheater chamber.

7. An oven according to claim 1 , wherein the recesses have a width of at least 15 cm.

8. An oven according to claim 1 , wherein the side wall of the susceptor is made up of at least a top bushing surrounding the loading zone, and a bottom bushing surrounding the preheater chamber, the bottom bushing including said ring portion and recesses.

9. An oven according to claim 8 , wherein the bottom bushing confronts the side wall of the preheater chamber, and wherein said bottom bushing includes a shoulder for supporting the top plate of the preheater chamber.

10. An oven according to claim 1 , wherein the side wall of the susceptor is made of graphite.

11. An oven according to claim 1 , wherein the recesses are filled with an electrically insulating material.

12. An oven according to claim 11 , wherein the material is also thermally insulating.

13. An oven according to claim 1 , wherein the field winding is connected to an alternating voltage generator having a frequency lying in the range 50 Hz to 1000 Hz.