POWER PACK USING MICROWAVE ENERGY FOR HEATING

Abstract: Apparatus for heating thermoplastics material or paper material covered with thermoplastics material, with the aid of microwave energy. The inventive apparatus comprises a power pack (1) formed as an individual aggregate including a microwave energy generating unit (2), a heating unit (3), an energy absorbing unit (4) and antennae (5-7) for transmitting microwave energy between the units (2-4), said heating unit (3) forming an elongate heating region for the materials which are to be heated and subsequently sealed, said unit substantially comprising an elongate hollow section (10) with a similarly elongate slot (11) in which the thermoplastics material which is to be sealed is arranged to move at a predetermined distance from a tongue formation (12) in the section (10) inwards of the wall thereof containing the slot. The heating unit (3) further includes at its end areas two antennae (6, 7) for transmitting microwave energy formed by the microwave energy generating unit (2) to the different units (2-4), unutilized microwave energy transferred to the heating unit (3) being transmittable via the antenna (7) at one end area of the heating unit (3) to the energy absorbing unit (4) and optionally also to the microwave energy generating unit (2), i.e. the heating unit (3) may function both as resonator and microwave transmission conductor.

Description: POWER PACK USING MICROWAVE ENERGY FOR HEATING The present invention relates to an apparatus for heat¬ ing, with the aid of microwave energy/ thermoplastics material or paper material coated with thermoplastics material/ while utilizing the dielectric losses occurr- ing in the material when it is subjected to a high- frequency electric field such as to generate heat re¬ quired in the material for a subsequent seal/ preferably over an elongate heating region. It is known to weld plastics, plastics-coated paper or carton and the like with the aid of microwave energy/ the heating required for welding taking place due to the dielectric ' losses in the material intended for welding. The method is particularly suitable for the tight seal¬ ing of packages made from thermoplastics, carton or paper coated with plastics, particularly in a continuous process where welding is continuous or stepwise/ so that an elongate weld seam or weld joint is not provided by welding the entire seam in one operation but gradually, and possibly stepwise. Microwave welding is of great interest in sealing packages by welding-on a lid, or possibly a folded-over portion/ of an integrally made package to obtain tight closure. The object of the present invention is to provide an apparatus of the kind mentioned in the introduction/ which comprises a more simplified and more operationally reliable system than used so far/ and which is further¬ more less sensitive to contaminants in the heating unit. Essentially distinguishing for the invention is that the apparatus comprises a power pack implemented as a complete aggregate/ which includes a microwave genera¬ ting unit and antennae for transmitting microwave energy between units, a heating unit forming the elongate heating region and substantially comprising an elongate hollow section with a similarly elongate slot, the thermoplastics material to be sealed being arranged to move in the slot at a predetermined distance from a tongue formation along the length of the section, the heating unit further being provided with at least two antennae,* preferably arranged at the end areas thereof, for transmitting microwave energy to the units from the microwave energy generating unit, unutilized microwave energy transmitted to the heating unit being trans¬ ferable by an antenna at one end area of the heating unit to an energy receiving unit and possibly to the microwave energy generating unit, i.e. the heating unit may function both as resonator and transmission con- ductor for microwaves. With the aid of the invention there is further achieved through the simplified system that circulators and long wave conductors previously necessary may now be ex¬ cluded. There is also obtained a sole unit/ a pack/ where the different units can be oriented such that the power pack will more readily fit in to the machine where it is to be used. The apparatus in accordance with the present invention is furthermore less sensitive to contaminating effects caused by so-called series applicators/ particularly since its field strength can be adjusted to obtain the greatest possible power in relation to flash-over in the heating unit. The field strength can be • regulated in the heating unit by a portion of the energy being taken up by the energy receiving unit and the remainder going back to the microwave energy generating unit. Finally, microwave leakage can also be prevented by the tongue configura¬ tion of the heating unit having been made shorter than the hollow section by an amount such as to ensure re- tention therein of the microwaves. The invention will now be described in detail below with reference to the accompanying drawing, on which Fig. 1 is a view from above of the apparatus in accordance with the invention, Fig. 2 is an end view of the apparatus illustrated in Fig. 1, with alternative placing of the microwave energy generating unit and Fig. 3 is a side view of the apparatus illustrated in Fig. 1 and 2. As will be seen from the drawing the apparatus in accordance with the invention is an individual complete power pack 1, including a microwave energy generating unit 2, a heating unit 3, an energy receiving unit 4, antennae 5/ 6/ 7 for transmitting the microwave energy between the units 2-4/ a casing 8 housing the units/ closed chambers 9 for transferring microwaves/ and unillustrated fastening means for the units 2-4. The heating unit 3 forms an elongate heating region within which the thermoplastics material to be sealed is heated/ the unit 3 including an elongate hollow section 10 provided with a slot 11 along one elongate face. The thermoplastics material which is to be heated and sub¬ sequently sealed is arranged to move in and along the slot 11 at a given distance from a tongue configuration 12 along the length of the section 10 and inwards of the slot 11. The heating unit 3 includes at least one antenna 6, 7 at either end area. One antenna 6 transmits microwave energy from the antenna 5 of the microwave energy generating unit 2 to the heating unit 3. The other antenna 7 of the heating unit 3 transmits un¬ utilized microwave energy from the heating unit 3 to the energy absorbing unit 4, and to attain the right field strength in the heating unit 3 only a portion of the energy in the energy absorbing unit 4 is absorbed the rest going back again for being taken up by the microwave energy generating unit 2, e.g. when the package or packages in the heating area cannot utilize the energy supplied. The energy receiving unit 4 may include an energy absorbing agent such as water or oil. To eliminate microwave energy leakage from the heating unit of the power pack 1 the longitudinal tongue forma¬ tion 12 included therein is made shorter by a multiple of half a wavelength than the hollow section 10 in¬ closing the tongue formation. As has been mentioned above, a closed chamber 9 is arranged between the antennae 5 and 6 on the microwave energy generating unit 2 and heating unit 3 for the microwaves transmitted between the antennae 5 and 6. There is also a closed chamber 9 between the other antenna 7 of the heating unit 3 and the energy absorbing unit 4. There are unillustrated air nozzles arranged along the heating unit 3, which are intended to be used for blow- ing off contaminants which can splash up from the packages on heating the thermoplastics material which are to be heated. These air nozzles may be adjusted to suitable spraying directions in relation to the heating unit -in order to provide the best effect. The power pack 1 also includes lifting means (unillustrated on the drawing) for lifting it from its normal working position, and it also has the heating unit 3 attached to it by quick release couplings (unillustrated on the drawing) . The heating unit 3 may be integrally formed, e.g. by extrusion. Upstream of the heating unit 3, seen in the advancing direction of the packages, there may be at least one (unillustrated) sensing means for regula¬ ting the microwave energy generated in the unit in response to the number of packages in the heating unit 3. The microwave energy generating unit 2 is a power source in the form of a magnetron or microwave generator in a semiconductor implementation.

Claims: CLAIMS 1. Apparatus for heating thermoplastics material or paper material coated with thermoplastics with the aid of microwave energy while utilizing the dielectric losses occurring in the material when it is subjected to 5 a high-frequency electric field for generating heat required in the material for a subsequent seal, pre¬ ferably over an elongate heating region, c h a r a c t ¬ e r i z e d i n that the apparatus, comprises a power pack (1) formed as an individual aggregate and including 10 a microwave energy generating unit (2), a heating unit (3), an energy receiving unit (4), antennae (5-7) for transmitting the microwave energy between the units (2-4), said heating unit (3) forming the elongate heating region and substantially comprising an elongate, 1 . 5 hollow section (10) with a similarly elongate slot (11) in which the thermoplastics material which is to be sealed is arranged to be moved at a predetermined distance from a longitudinal tongue formation (12) situated inside the section (10) and inwards of the slot 20 (11), said heating unit (3) being further provided with at least two antennae (6, 7), preferably arranged at the end areas of the heating unit (3) for transmitting microwave energy generated in the microwave energy generating unit (2) to the different units (2-4), un- 25 utilized microwave energy transmitted to the heating unit (3) being transmitted via an antenna (7) at one end area of the heating unit (3) to the energy receiving unit (4) and optionally also to the microwave energy generating unit (2), i.e. the heating unit (3) may 30 function both as resonator and transmission conductor for microwaves. 2. Apparatus as claimed in claim 1, c h a r a c t - . e r i z e d i n that the longitudinal tongue formation (12) in the heating unit (3) is shorter than the hollow section (10) containing said tongue formation/ by an amount such as to ensure the elimination of microwave 5 energy leakage to the outside of the heating unit (3). 3. Apparatus as claimed in claim 1 or 2/ c h a r - a c t e r i z e d i n that the spaces between the microwave energy generating unit (2) and the heating unit (3) as well as between the heating unit (3) and 10 the energy absorbing unit (4) are taken up by closed chambers (9) which transmit the microwaves. 4. Apparatus as claimed in any one of claims 1-3/ c h a r a c t e r i z e d i n that the heating unit (3) includes at least one nozzle placed along it for 15 blowing away contaminants. 5. Apparatus as claimed in any one of the preceding claims/ c h a r a c t e r i z e d i n that the power pack (1) is provided with a lifting means for raising it from a normal working position and that the heating 20 unit (3) is attached to the power pack (1) with the aid of quick release coupling. 6. Apparatus as claimed in any one of the preceding claims/ c h a r a c t e r i z e d i n that the heating unit (3) is made in one piece e.g. by extrusion. 25 7. Apparatus as claimed in claim 1/ c h a r a c t¬ e r i z e d i n that at least one sensing means is situated upstream of the heating unit (3) in the convey¬ ing direction of the thermoplastics material/ said sensing means being adapted to regulate the microwave 30 energy generated in the microwave energy generating unit (2) in response to the number of packages in the heating unit (3). 8. Apparatus as claimed in any one of the preceding claims/ c h a r a c t e r i z e d i n that the micro¬ wave energy generating unit (2) is a power source comprising a magnetron or a microwave generator in semiconductor implementation.

Inventors: JACOBSON BENGT, NILSSON INGEMAR, WALLIN KAY, JACOBSON, BENGT, NILSSON, INGEMAR, WALLIN, KAY
Applicants: SPRINTER SYSTEM AB
Application year: 1985
Main classification: H05B6
IPC codes: H05B6