WO1996039791A1

WO1996039791A1 - Microwave oven

Info

Publication number: WO1996039791A1
Application number: PCT/SE1996/000733
Authority: WO
Inventors: Göran Öjelid
Original assignee: MIRATRON AG
Current assignee: MIRATRON AG
Priority date: 1995-06-03
Filing date: 1996-06-03
Publication date: 1996-12-12
Anticipated expiration: 1997-12-03
Also published as: AU6020996A

Abstract

A microwave oven for industrial application, in particular for drying objects in a continuous process, comprises a transport device for the objects inside an oven room as well as several microwave generators. The invention is primarily characterized in that each generator (10) is connected to the oven room through a separate impedance match element (7) and a separate directional coupler (12). In a preferred embodiment, the directional couplers are arranged such that their direction of radiation can be changed from the outside of the oven - also when the generators are in operation - and that this is also possible with the aid of electrical motors.

Description

MICROWAVE OVEN

Industrial microwave ovens have previously been specifically * constructed for specific applications. Change of shape or weight 5 of the object to be treated alone result in difficulties, such as fc lower efficiency and inho ogeneous treatment. This invention provides a solution which allows adjustment to quite different objects to be treated in the most simple way. The microwave oven according to the invention is above all characterized in that 10 each generator is connected to the oven room through a separate impedance match element and a separate directional coupler. In preferred embodiments the directional couplers are arranged such that they can be adjusted from the outside of the oven room with respect to their direction of radiation - also when the 15 generators are in operation, and that this is also possible with the aid of electric motors. The invention will now be described in greater detail with reference to the enclosed drawing wherein:

Fig. 1 shows an oven in a vertical section,

20

Fig. 2 shows an impedance match element in a side view,

Fig. 3 shows the element with a directional coupler.

25 According to Fig. 1 a microwave oven is constructed according to a tunnel having side walls 1, 2, bottom 3 and top wall 4. Several large venting openings 34 are provided in the top wall 4. At each end a large door 5 is provided which may be moved upwards in a vertical direction by means which are not further described here.

30 In order to obtain a seal without wear, the door is slightly- wedge-shaped. Just above the bottom 3 a roller way 6 is provided which may be driven from the outside in a per se known manner. Three rows of microwave generators 10 are provided on the walls 1, 2. The generators are of the per se known magnetron type and

35 operative in the dm-wave range and have an output of about 1 kW each. They are each air-cooled through one ventilator 15. The exhaust air from the ventilators find its way through a perforated area 16 into the oven room. Each generator is fed as usual trough a high-tension transformer, having a diode and a capacitor coupled thereafter, as well as a heating transformer with net energy. Their HF-output is transmitted by an antenna 11 from the magnetron to the element 7 for impedance matching. At the other end of the element 7 is placed a directional coupler 12 in the form of a metal rod 13 having a spiral element 14 connected to it, said rod 13 being parallel to the antenna 11. The directional antenna is supported by a shaft 18 of a ceramic material such as for example aluminium oxide. The shaft 18 extends outwards through the element and is at that location provided with an arm 19. The rod 13 extends through a sleeve 20 having about 2.5 times greater inside diameter, into the oven room where it supports the spiral 14. The sleeve 20 at the same time serves as a coupling between the element 11 and the oven wall 1 and is at the inside of the oven room fastened by a nut 21. The impedance match element functions according to a per se known principle such that it fixes the distance between the antenna 11 and the rod 13 as well as the distances to the respective surrounding and common metal walls. The device functions according to the following.

Objects 30 to be treated, such as for example mould cores made of sand and binding agent having paint thereon, are standing on a pallet 31 and are slowly moved through the oven by the roller way 6. In correspondence with the transport, a number of magnetrons are successively connected to the current net and transmit their HF-output through the directional couplers onto the objects. Because the directional couplers, which are comprised of spirals in per se known way, transmit their output in the form of unsymmetrically joumalled lobes, the output will meet the objects primary at different locations. By observing the objects over the areas 16 it may be decided at what extent these primary radiating areas complete each other. An adjustment in order to obtain an optimal completion may be achieved very simply by individually adjusting the directional coupler with the aid of the arm 19. This brings about several advantages.

Firstly, the efficiency is essentially higher because the treatment of the objects is based on primary radiation in stead of as to date, common distribution through reflections against the oven walls. Secondly, the radiation may be adjusted to the shape of the objects, such that thinner or otherwise sensitive parts are subject to less radiation. Thirdly, a standardised arrangement of the oven for a large pallet of objects may be optimized in the easiest way.

In operation, when objects of different kind are to be treated successively, it is preferred that the adjustment of the directional couplers is achieved by electrical so called step- motors which are connected to the shafts. To this end the motors are fed through a programmable device and particularly such, that the once determined adjustment is stored under a certain code number as a fixed part of a program. Alternatively, in an more uncomplicated arrangement, the code consists of a determined number for each directional coupler.

It is to be understood that the device on the outside of the oven is protected by walls provided with doors.

Claims

C A I M S

1. Microwave oven for industrial application, comprising an oven room, a transport device for the objects to be treated and several microwave generators which are connected to the oven room, c h a r a c t e r i z e d in that each generator (10) is connected to the oven room through a separate impedance match element (1) and a separate directional coupler (12) .

2. Microwave oven according to claim 1, c h a r a c t e r ¬ i z e d in that the directional couplers (12) are arranged such that they can be adjusted from the outside of the oven room with respect to their direction of radiation.

3. Microwave oven according to claim 2, c h a r a c t e r ¬ i z e d in that the directional couplers (12) are supported on shafts (18) of highly insulating material and are adjustable thereby, also when the generators are in operation.

4. Microwave oven according to claim 2 or 3, c h a r a c ¬ t e r i z e d in that the directional couplers (12) are connected to one or more electrical motors in such a way that they are adjustable in steps by the motors.

5. Microwave oven according to any of the claims 1 - 4, c h a r a c t e r i z e d in that the directional couplers (12) are arranged on two vertical oven walls (1,2) which are parallel to the direction of a movement of the transport device.

6. Microwave oven according to any of the claims 1 - 5, c h a r a c t e r i z e d in that the transport device (6) is placed within the oven room and includes parts of metal.