Microwave Heating Apparatus

Abstract

A microwave heating apparatus comprises a rotatable cylindrical heating chamber supplied with microwave energy, and means for feeding objects to be heated to said chamber and for taking out fully heated objects. Helically arranged, inwardly projecting metal strips are provided on the inner surface of the chamber for stirring and for successively forwarding the objects to be heated through the chamber to its outlet and for also agitating the microwaves so as to effect uniform application of microwave energy to the object.

Description

BACKGROUND OF THE INVENTION

This invention relates to a microwave heating apparatus arranged for continuous heating of an object which is in the form of powders, granules or strips.

Continuous heating of an object which is in the form of powders, granules or strips has heretofore been effected by introducing hot air into a rotatable heating furnace containing said object. However, this process had the drawbacks that it not only presented difficulties in maintaining the flow rate and temperature of hot air at prescribed levels, but also failed to uniformly heat an object, resulting in non-uniform qualities of the heated product.

It is accordingly the object of this invention to provide a microwave heating apparatus of simple construction capable of uniformly and continuously heating an object which is in the form of powders, granules or strips.

SUMMARY OF THE INVENTION

According to this invention, the above object is attained by providing a microwave heating apparatus comprising a cylindrical heating chamber; means for rotating said chamber about its axis; means supplying said chamber with microwave energy at the axial portion thereof; means for feeding objects to be heated to said chamber and taking same out when fully heated; and means for stirring and for successively forwarding the objects through the chamber to its outlet and for also agitating microwaves so as to effect the uniform application of microwave energy to the objects. The stirring means includes helically arranged, inwardly projecting metal strips on the inner surface of the heating chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a microwave heating apparatus according to an embodiment of this invention;

FIG. 2 is a schematic sectional view on line 2--2 of FIG. 1 taken in the direction of the indicated arrows;

FIG. 3 is a schematic sectional view of a microwave heating apparatus according to another embodiment of the invention; and

FIG. 4 is a schematic sectional view on line 4--4 of FIG. 3 taken in the direction of the indicated arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, there are laid two parallel metal rails 11 and 12 at a prescribed spacing around the outer peripheral wall of a cylindrical metal heating chamber 10. Against said rails 11 and 12 abut two pairs 18--18 and 19--19 of rollers respectively which are mounted on shafts 16 and 17 respectively, said shafts 16 and 17 being rotated by a motor 14 fixed on the floor 13 through a belt 15. The cylindrical heating chamber 10 is rotated about its axis by the motor 14 while being mounted on the rollers 18 and 19. On the outer peripheral wall of the cylindrical heating chamber 10, along lines which are spaced from both open ends thereof to an extent equal to 1/4 of the wave length of microwaves used in the subject heating apparatus, there are fixed metal flanges 20 and 21. The open ends of chamber 10 are closed by metal seal members 22 and 23 slidably engaging the flanges 20 and 21. At the joint of the heating chamber 10 with the seal members 22 and 23 is formed a so-called 1/4 wave length choke section so as to prevent microwaves from leaking outside from said joint. If neccessary, an interstice within the choke section is filled up by coating dielectric material such as Teflon on the outer wall of, for example, the heating chamber 10. This arrangement improves the choke properties and also prevents an object being heated from starting a fire by microwave discharge if it happens to be brought into said interstice. As described above, the heating chamber 10 is rotated while being mounted on the rollers 18 and 19 with the seal members 22 and 23 slidably engaged with the flanges 20 and 21.

To one seal member 22 is connected one end of a rectangular wave guide 24, the other end of which is connected to the antenna 26 of a magnetron 25 so as to introduce microwave energy having a prescribed frequency from the magnetron 25 into the heating chamber 10. Into the seal member 22 is inserted the lower end of an inlet pipe 27 which feeds objects to be heated into the heating chamber 10. The upper end of the inlet pipe 27 is connected to a hopper 29 through a motor-driven rotary valve 28. Thus an objects to be heated taking the form of powders, granules or strips (not shown) are successively brought into the heating chamber 10 through the inlet pipe 27. The rotary valve 28 includes four metal blades 30 spaced from each other at a peripheral angle of, for example, substantially 90.degree.. The interstices between the ends of the blades 30 and the inner wall of the casing of the rotary valve 28 are filled with dielectric material such as Teflon (not shown) so as to prevent microwaves from leaking outside through the valve 28. The other seal member 23 is provided with an outlet pipe 31 and a rotary valve 32, enabling fully heated objects to be successively drawn out through the outlet pipe 31 and rotary valve 32 in turn. Like the aforesaid rotary valve 28, the rotary valve 32 includes four metal blades 33. The interstices between the ends of the blades 33 and the inner wall of the casing of the rotary valve 32 are filled with Teflon (not shown) as in the preceding case so as to prevent microwaves from leaking outside through the rotary valve 32.

To the inner peripheral wall of the heating chamber 10 are fitted a plurality of metal strips 34 in a helical form so as to be inclined downward from the seal member 22 to the seal member 23 at an angle of .theta.. The helical metal strips 34 transfer an object of heating with a stirring action toward the outlet pipe 31 as the result of the rotation of the heating chamber 10. The helical metal strips 34 also agitate microwaves introduced into the chamber 10 from the magnetron 25 through the rectangular wave guide 24 to prevent standing waves of the microwaves from appearing in the heating chamber 10, thereby uniformly applying the microwave energy to the objects. When the heating chamber 10 rotates, the seal members 22 and 23 slidably engage the flanges 20 and 21. Since, however, the seal members and flanges are joined, as previously described, with the 1/4 wave length choke section formed therebetween, there occurs substantially no electric field on their sliding surfaces, eliminating discharge therebetween and resultant seizure, and consequently ensuring the smooth rotation of the heating chamber 10 at all times.

It will be apparent that in the foregoing embodiment, the number of rotations of the heating chamber and the number, size and angle .theta. of inclination of the metal strips 34 may be suitably chosen according to the properties and quality of an object of heating.

FIGS. 3 and 4 show a microwave heating apparatus according to another embodiment of this invention. The parts of FIGS. 3 and 4 which are the same as those of FIGS. 1 and 2 are denoted by the same numerals and description thereof is omitted. In FIGS. 1 and 2, the movement and stirring of an object of heating in the heating chamber 10 were effected by the metal strips 34 disposed therein. In the embodiment of FIGS. 3 and 4, however, the passage of the object through the heating chamber 10 is attained by inclining said chamber 10 downward toward the outlet side 31 with respect to the floor 13. Agitation of microwaves is carried out by a microwave agitating member 40 comprised of a plurality of metal plates convergently projecting from the inner wall of the heating chamber 10 to its center. Further, the object of heating is stirred by a stirring means 43 which comprises a plurality of dielectric members provided with a recess 41 on that side which faces the direction indicated by the arrow in which the heating chamber 10 rotates and further separated from each other by a plurality of partition walls 42 which are also made of dielectric material Said partition walls 42 are arranged at a prescribed spacing so as to enable the object of heating to be gradually carried to the outlet 31 as the result of the rotation of the heating chamber 10.

According to the embodiment of FIGS. 3 and 4, the heating chamber 10 is rotated by a gear means 44 connecting the motor 14 and shaft 16. The heating chamber 10 has an inlet 45 and an outlet 46 after air dry hot air thereby enabling it to pass therethrough. This hot dry air acts as a supplemental heating means to the main microwave heating system and also plays the part of quickly drawing off steam evolving from, for example, a wet object when it is heated. The inlet 45 and outlet 46 have a sufficiently small inner diameter to prevent microwaves from leaking outside, or may be fitted with a mesh like metal shield (not shown). Further, the interstice of the 1/4 wave length choke section formed at the joint of the heating chamber 10 with the seal members 22 and 23 is sealed with dielectric packing 47. According to the embodiment of FIGS. 3 and 4, the interstice between the heating chamber 10 and seal member 23 which is sealed with the packing 47 is inclined downward toward the outlet 31, to reduce the possibility of an object of heating to be brought thereinto by chance, thus offering great convenience.

Claims

What is claimed is:

1. A microwave heating apparatus comprising:

a cylindrical metal heating chamber provided with an inlet and outlet for objects which are to be heated;

means for rotating the heating chamber about its axis;

means for supplying microwave energy, to the heating chamber at the axial portion of the heating chamber;

means for successively introducing the objects to be heated into the heating chamber through the inlet and for successively drawing off the heated objects through the outlet; and

a plurality of inwardly projecting helically arranged metal strips provided on the inner wall of the heating chamber for stirring and gradually forwarding the objects through the heating chamber to the outlet of the heating chamber and for also agitating the microwaves in said heating chamber.

2. The microwave heating apparatus according to claim 1 wherein the heating chamber comprises a cylindrical metal member open at both thereof; flanges projecting from the peripheral wall of the open ends of the cylindrical member; and two metal seal members having an engagement portion engageable with the flanges, thereby closing both open ends of the cylindrical member; said flanges being spaced from the edges of said open ends to an extent equal to one-fourth of the wave length of the microwaves, and the joint of the cylindrical metal member and the two seal members being provided with a 1/4 wave length choke section.

3. The microwave heating apparatus according to claim 2 wherein the 1/4 wave length choke section has dielectric material filled into the interstice between the cylindrical member and seal members.

4. The microwave heating apparatus according to claim 3 wherein the dielectric material is used as a packing for keeping said interstice airtight.

5. The microwave heating apparatus according to claim 1 wherein the heating chamber has an outer peripheral wall and wherein the means for rotating the heating chamber comprises rails mounted on the outer peripheral wall of the heating chamber and rollers rotatably mounted on shafts disposed below the heating chamber so as to rotate in abutment against the rails.

6. The microwave heating apparatus according to claim 1 wherein the means for successively introducing the objects to be heated and means for drawing off same respectively have a rotary valve which includes a plurality of metal blades movably mounted in a valve casing and dielectric material filled into the interstice between the ends of the blades and the inner wall of the valve casing, said dielectric material preventing microwaves from leaking outside through said interstice.

7. The microwave heating apparatus acording to claim 1 wherein the heating chamber is provided with an inlet and outlet for dry hot air so as to conduct hot dry air therethrough.

8. The microwave heating apparatus according to claim 1 wherein said metal strips extend in substantially the axial direction of said heating chamber.