RU2207474C1 - Facility or shf thermal treatment of large dielectric articles - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: invention deals with SHF treatment of large-size dielectric articles such as high-voltage porcelain insulator and other articles. Multimode chamber of SHF heating has internal dimensions ( 4.59 x 4.5 x 4.27 ) λ₀, where λ₀ is length of wave in free space, is mounted on rigid platform and includes outer rigid framework. Doorway is limited by flat frame. Half-wave radiation traps and contact seal arranged around edges provide for snug door fitting. Upper wall carries L-shaped slotted guide exciter with two groups of mutually perpendicular half-wave slots above two communication windows made in upper wall of heating chamber. SHF energy reflectors are positioned opposite to communication windows close to bottom wall at angle of 45 degrees to incident beam. Chamber has dielectric supports with height h≥λ₀/4, resting on three-four dielectric columns. Each column has rectangular seat with metal ball placed in it which partially protrudes downwards and leans against bottom of chamber. EFFECT: raised efficiency of SHF thermal treatment of large dielectric articles. 1 cl, 2 dwg _

Description

 A device for microwave heat treatment of large dielectric products, such as porcelain insulators and other products and materials, is intended for use mainly in the electrical industry, but can also be used in other sectors of the economy, for example, in construction and food processing.

 Known microwave oven [1], containing a metal casing, inside which there is a heating chamber, magnetron, an electrolyte source and a waveguide-slot exciter, consisting of two branches: one branch is located on the upper wall of the chamber, the second on the bottom. The heated product is located on a dielectric shelf, under which there is a lower branch of the waveguide-slot pathogen that radiates energy upward to the product and to the sides. In this case, the lower wall of the chamber has limbs that act as reflectors of microwave energy to the product. The distance from the upper slots of the lower waveguide to the dielectric shelf is not more than the wavelength.

 The described oven relates to domestic microwave ovens, which, as a rule, contain a smaller heating chamber than is required for the formation of a multimode field that provides uniform heating in horizontal and vertical planes. In addition, the division of the microwave power input from the magnetron by simple branching cannot be uniform and varies systematically depending on the coordination with the load (product). The bends of the lower wall as reflectors work only partially due to the side lobes of the incident energy, since its main flow falls directly on the product. Thus, it can be noted that the product is heated not due to the field generated in the heating chamber, but due to direct irradiation. Therefore, in general, this furnace does not provide uniform heating, which is not very important for food products, but it is necessary for the heat treatment of technical products made of ceramics, rubber, plastics, etc.

These disadvantages are eliminated in the proposed invention, "Device for microwave heat treatment of large dielectric products", for example, for drying semi-finished porcelain high-voltage insulators, ceramic building blocks and other products. This is achieved by the fact that the device contains a multimode resonator heating chamber with internal dimensions (4.59 × 4.5 × 4.27) λ ₀ , where λ ₀ is the wavelength in free space, mounted on a rigid metal platform and containing a stiffening frame, adjacent to the outer walls of the heating chamber.

 The doorway is limited by a rigid flat frame on which the door is mounted and a snug fit of half-wave radiation traps made around the perimeter of the door is ensured. For a more reliable sealing of the door at its edges around the perimeter, a groove is made for laying, for example, a metal cable braid, worn on a soft rubber tube. The internal height of the frame is equal to the height of the heating chamber, which ensures the convenience of loading the heating chamber.

 An L-shaped waveguide-slot exciter with two groups of mutually perpendicular slots is installed on the upper wall, each of which is in different arms and is located above its communication window. One communication window is adjacent to one of the side walls, the second to the rear wall of the camera.

Opposite the communication windows on the bottom wall of the camera, microwave reflectors are installed at an angle of 45 ^° to the incident beam. Thus, direct irradiation of the processed products is excluded, and they are heated by the multimode field formed in the chamber. Some part of the microwave energy is reflected on the lower parts of the heated products. However, the main purpose of the reflectors is to exclude direct reflection of microwave energy to the pathogen, and through it to the generator.

Products subject to microwave heat treatment are installed on a dielectric stand, supported by three or four dielectric racks, each of which has a rectangular socket in which a metal ball is placed, partially protruding from the socket and resting on the bottom of the heating chamber. The minimum stand height is λ / 4.
For microwave heat treatment of products and materials of smaller sizes, it is advisable to provide a continuous process using a conveyor belt. With periodic loading of the camera, it is possible to provide technological heating with different modes by regulating the microwave power supplied to the products (materials). If there is one resonator chamber through which the conveyor passes, regulation is excluded. Therefore, it is advisable to use several resonator chambers, in each of which you can enter the power of the level required for the implementation of the process. To do this, it is enough to use a waveguide-slot exciter that branches the necessary power into each resonator chamber.

 The number of resonator chambers in a multi-chamber line is determined based on the power of the microwave generator, the heat treatment time, and the heating mode. In most cases, three to five cameras are sufficient. At the above resonator chamber, the right wall is removed, and it is installed first on the left. In the other, the left wall is removed, and it becomes the extreme right. Two side walls are removed from the chambers installed between the first and the last, and large flanges are welded to the ends of the formed tunnel sections with the preservation of all internal dimensions. The same flanges are welded from the open walls of the first and last sections (chambers). Between the flanges of each section, metal partitions are inserted that limit the size of the chambers in which the windows for the passage of the conveyor with materials are cut. Partitions can be removed for access inside the heating chambers. Thus, a multi-chamber production line was obtained.

 On the upper or rear wall, flange communication windows are made for attaching a waveguide-slot exciter. To increase the multimode nature of oscillations, two branches of waveguide-slot exciters can be used, for example, installed on the upper and rear walls of the chambers.

 In FIG. 1 shows a general view of a heating chamber with an open door and product stands placed inside.

 In FIG. 2 shows a fragment of a stand for products with a stand and a metal ball.

 Figure 3 presents schematically a General view of a multi-chamber production line (secondary elements not shown).

A device for microwave heat treatment of large products, such as porcelain high-voltage insulators, is made in the form of a multimode resonator chamber 1 with internal dimensions (4.59 × 4.5 × 4.27) λ ₀ , where λ ₀ is the wavelength in free space. The camera is mounted on a rigid metal platform 2. The frame 3 is attached to the outer walls of the camera. On the upper wall there is a L-shaped waveguide-slot exciter 4 containing two groups of half-wave slots (not shown, since they can be either longitudinal, transverse or even at an angle) located above the communication windows 5. Inside the camera opposite the communication windows on Microwave energy reflectors 6 are installed at an angle of ~ 45 ^° to the vertically incident central beam, eliminating direct reflection of energy to the pathogen and generator and directing it to the lower parts of the heated products.

 The processed products are placed in the chamber on special dielectric supports 7 (Fig. 2), which are supported by 3-4 dielectric racks 8, into which metal balls 9 are supported from below, resting on the bottom of the chamber.

 The doorway of the chamber is made in the form of a rigid frame 10, which adjoins when closing the door 11. To prevent leakage of microwave energy through possible gaps between the frame of the opening and the door, half-wave barriers 12 and a groove 17 with contact seal are made around the door.

 Platform 2 is made of channel and has a number of crossbars 13, eliminating the deflection of the bottom wall under a significant load of products.

 The cap 14 of the pathogen is sealed after its adjustment.

 Two holes 15 are made on the upper wall of the heating chamber for connecting exhaust fans, and lattice windows 16 are made in the lower part of the side walls of the chamber for air intake from the surrounding space.

 A device for microwave heat treatment of large dielectric products works as follows.

 Since the semi-finished products of wet products subject to heat treatment, such as high-voltage porcelain insulators, have a weight of 80 to 140 kg, a height of 1000-1200 mm and diameters of 400 to 550 mm, they are installed on supports 7 (Fig. 2) outside the heating chamber . Then the door of the heating chamber is opened and with the help of the elevator, 3-5 products are placed in turn with the stands in turn. Stands based on metal balls 9 can be moved manually in any direction in the heating chamber, which allows you to install the product as the operator sees fit. After loading is completed, the chamber door is closed with clamping handles and the generator is turned on (started). Turning on the generator high voltage is possible only with a tightly closed door equipped with a high voltage interlock.

 At the same time as the generator is turned on, exhaust fans are connected to the windows 15 (fans not shown). Then set the required level of output power of the generator. Microwave energy is introduced into the heating chamber using the L-shaped waveguide-slot exciter 4, in which there are two groups of half-wave slots located above the communication windows 5. Half-wave slots can be either longitudinal or transverse, but necessarily either one or the other, because taking into account the rotation, they turn out to be mutually perpendicular, which reduces the electrical connection between them.

 Under each communication window, microwave energy reflectors 6 are installed at the bottom wall, i.e. that part which falls vertically in order to direct it to the lower parts of the heated products and exclude its reflection from the lower wall back to the generator. Thus, the matching of the generator with the heating chamber is improved.

A heating chamber with dimensions (4.59 × 4.5 × 4.27) λ ₀ , or 1505 • 1480 • 1400 mm, for a frequency of 915 MHz, allows to obtain 20 or more types of oscillations, which ensures the formation of a total field of standing waves sufficient for uniform heating of products. Moreover, the dimensions expressed in terms of wavelength λ ₀ are valid for any other frequency when high uniformity of heating is required.

 The heating process can be controlled by an infrared pyrometer through the pipe 18.

The microwave energy consumption is calculated from the drying requirement of 50 W / kg. Therefore, for drying 1000 kg of loaded products, the input power is 30 kW. In this case, until the end of drying, it is not necessary to regulate the generator output power. To speed up the process in the initial period, the output power of the microwave generator can be increased by 20-25% in order to quickly raise the temperature of products to 60-70 ^o C. Then the power decreases to normal, i.e. up to 30 kW.

Drying takes place at a temperature not exceeding 75 ^o C.

After drying, determined according to the schedule, the products are calcined for one hour. In this case, the temperature gradually rises to 200-250 ^o C. Moreover, this happens automatically without power control. The fact is that while the humidity of the products is high enough, the quality factor of the resonator chamber drops to several units. When heating products to 70 ^o With the water contained in the products begins to absorb less microwave energy by about 2-2.5 times. The microwave energy released in this way provides heating of the mass of the product material (porcelain). The initial humidity of the products is 16-18%. As moisture is removed, the quality factor of the heating chamber rises and reaches 50 units by the end of drying. Due to this, the field strength in the chamber increases in proportion to the quality factor, which ensures an increase in temperature in the products without increasing the output power of the generator.

 Traditional drying of high-voltage porcelain insulators, for example, at Mosizolyator JSC lasts from 7 to 10 days, depending on size. The energy consumption in this case is 50-60 kW • h per product, per 1000 kg - 500-600 kW • h. When microwave drying, the consumption of microwave energy per 1000 kg is 220-240 kW • h. With a generator efficiency of 75%, the energy consumption will be about 320 kWh, i.e. almost double savings are achieved.

 But the main thing is the release of production space, significant time savings, since microwave drying does not last 200-240 hours, but only 8 hours. At the same time, the quality of the products increases.

 A device for continuous microwave heat treatment of products (materials), made by connecting several resonator chambers 1 (Fig. 3) into a production line, as shown above, is mounted on a common mounting base 18. Through all cameras and end devices for protection from microwave radiation 19 , 20 passes a dielectric conveyor 21 (for example, mesh from a mylar monofilament). Inside each chamber, dielectric rollers 28 are mounted to support the conveyor belt 21.

 The tunnel sections are divided into multimode resonator chambers by installing partitions 22 between the flanges 23 and 24. The partitions 22 can be removed for access inside the chambers.

 Communication windows 25 are made on the upper walls of the resonator chambers, to which waveguide-slot exciter 26 is connected using flanges.

 Since this device allows microwave heat treatment of relatively small products or materials in containers, there is no need for large doors. Therefore, hermetically sealed inspection windows 27 are made on the front walls.

 Exhaust fans (not shown) can be mounted on the top or rear wall.

Ha inlet and outlet chamber line established safety of microwave radiation device in combination the transition duct 19 having top and bottom by two transverse quarter protrusion spaced apart also at λ _0/4, and the cavity 20 connected to the transition channel , which contains inside the active absorbers of microwave energy.

 A transition channel with quarter-wave elements is designed to reflect microwave energy back into the camera, but there are no ideal reflectors. Therefore, to comply with sanitary standards for the level of microwave radiation into the surrounding space (SanPin 2.2.4./2.1.8.055-96), an additional volume resonator 20 is used, containing two cassettes 29 and 30 inside with winding of dielectric tubes through which running water is passed. The tube is wound in increments of 2-3 tube diameters. Continuous winding can turn into a conductive wall, and the effect of attenuation of microwave energy will be significantly reduced. Cassettes are installed: one 29 at the bottom under the conveyor belt 21, another 30 at the top above the processed material.

 The device operates as follows. Turn on the electric drive of the conveyor belt 21, on which products or containers with material are placed.

 When the products pass 2/3 of the length of the chamber line, they include a microwave generator and exhaust fans (the level of microwave energy introduced into the resonator chambers through the waveguide-slot exciter 26 must be determined before the microwave heat treatment of the product begins).

 Then they continue to lay products or containers on the conveyor, and part of the products installed at the beginning of the process as a load is passed again.

 At the output of the multi-chamber line, finished products are continuously removed from the conveyor, the quality of which, as a rule, is higher than with traditional heat treatments.

 Protective end devices ensure the safe operation of staff.

 The described device for microwave heat treatment of large-sized products was successfully tested at the FSUE NPP Toriy together with Mosizolyator CJSC.

 The multi-chamber line for continuous microwave heat treatment of materials in containers has been successfully tested at JSC Interkvarts (Vladimir).

Literature
1. US patent 4354083 from 12.10.1982, Cl. 219-10.55, H 05 V 6/72.

Claims (2)

1. Device for microwave heat treatment of large products, such as high-voltage porcelain insulators, or dielectric products in dielectric containers, containing a heating chamber, a microwave generator and a waveguide-slot exciter, characterized in that the multimode resonator heating chamber, having dimensions (4.6 × 4,5 × 4,3) λ ₀ ± 15%, where λ ₀ - wavelength in free space, mounted on a rigid platform, comprising an outer frame and a flat stiffening frame of the door opening, the inner height of which is equal to the inner height of the chamber a roar, and a hinged door containing perimeter half-wave radiation suppressors and a groove for accommodating a flexible contact seal is adjacent to the frame above and below the vertical size of the heating chamber, and a G-shaped waveguide-slot exciter is mounted on the upper or side wall of the chamber form a mutually perpendicular arrangement of half-wavelength slots and hence, communication windows, opposite which the opposite walls are set at an angle of 40-50 ^o for rays incident plane reflectors microwave energy .  2. The device according to claim 1, containing dielectric stands for installing workpieces and materials, characterized in that each stand is supported by 3-4 dielectric posts containing rectangular sockets with metal balls placed in them, partially protruding downward and resting on the bottom of the camera heating up.

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