WO2018189355A1

WO2018189355A1 - Conveyor furnace for heating material by means of microwaves

Info

Publication number: WO2018189355A1
Application number: PCT/EP2018/059492
Authority: WO
Inventors: Thilo Solawa
Original assignee: Dieffenbacher GmbH Maschinen- und Anlagenbau
Priority date: 2017-04-13
Filing date: 2018-04-13
Publication date: 2018-10-18
Also published as: DE102017108087A1

Abstract

The invention relates to a conveyor furnace (4) for heating material (2) by means of microwaves, comprising a treatment chamber (7) for heating the material (2), wherein one or more openings (6) are arranged in the treatment chamber (7) in order to introduce radiation (5) into the treatment chamber (7) via waveguides and/or the microwave generators are arranged directly in the treatment chamber (7), at least one endlessly circulating transport belt (1, 8) for transporting the material (2) through the conveyor furnace (4), and a plate (10) over which the transport belt (1, 8) is drawn. The invention is characterized in that the transport belt (1, 8) and the plate (10) consist at least in part of materials that are close together or identical in a triboelectric series.

Description

Continuous furnace for heating material by means of microwaves

The invention relates to a continuous furnace for heating material by means of microwaves according to claim 1.

In the production of material plates, in particular wood-based panels of lignocellulosic material, it is known to preheat the material scattered to a non-woven before pressing in a press. Due to the higher heat at the beginning of the compression, the press needs less time to completely heat the fleece. Accordingly, the press can be made shorter or operated faster. Have proven particularly hot air or

Steam preheating or the use of high-frequency radiation, such as microwaves, for preheating in microwave continuous ovens, referred to in the following continuous furnace. The physical principle is based on the

Conversion of electromagnetic energy into thermal energy in the absorption of microwaves by the material to be heated.

For example, it is known from DE 197 18 772 A1 to expose the material scattered to a nonwoven fabric to microwaves before being introduced into a heated, preferably continuously operating press so as to accelerate a subsequent heating and pressing operation. The heating with microwaves has the advantage that the desired heat is generated directly in the product by the

Microwaves penetrate into the product, be absorbed and stimulate existing water molecules or other electric dipoles to vibrate. In contrast, when using hot plates or

Heißluftvorwärmsystemen or the like, the heat applied substantially from the outside, whereby a complete penetration of the product to be manufactured with this heat can not always be guaranteed. In the case of products preheated by means of microwaves, such a heat distribution is to be ascertained in the heated press in which the core of a product also reaches a desired temperature, without critical temperatures already being exceeded during pressing on the areas lying further outside. Compared to the use of steam preheating systems, the use of microwaves has the advantage that no additional moisture is introduced into the material to be compacted during preheating. Due to the additional moisture which is introduced with the Dampfvorwärmsystemen, the material is to be dried prior to application to the conveyor belt such that the maximum moisture content of the material before pressing by adding moisture, such as steam, is not exceeded. This leads already in the pretreatment of the material to an intensive drying of the material and a high

Power consumption.

When using microwaves or high frequency radiation in one

Continuous furnace for heating the material can be dispensed with intensive drying of the material under maximum moisture in advance, which has a positive effect on the energy balance.

In known microwave ovens, as they are used in the field of catering or in the household, is usually a hermetically demarcated

Treatment chamber is provided, which is to be sealed off to the outside with respect to the leakage of microwaves.

In contrast, in the continuous furnace described here, the material to be treated is irradiated to one for the radiation, in particular microwaves,

deposited permeable conveyor belt and transported by this through the treatment room, wherein the material to be treated is uniformly irradiated both from below and possibly from above with microwaves.

The problem is that the conveyor belt is due to the requirements of transparency for microwave radiation of plastic, such as polyester, so that it may possibly come to electrostatic charges during its movement over a wall chamber covering the bottom plate, as such plate also made a microwave transparent plastic,

For example, made of polypropylene, so that for a homogeneous heating of the material and radiation below the material and thus below the

Floor area can be introduced into the treatment room and absorbed by material. In the case of the relative movement of the conveyor belt relative to these floor areas, it may be due to triboelectric effects for the separation of charges and thus to an electrostatic charge. This transmits and also affects the material to be treated. As a result, individual charged particles of the material tend to be from the mat or fleece, in particular from the latter

Surface, during transport through the continuous furnace to solve.

Such dissolved particles then settle within the treatment room, especially at exposed locations. Here form corresponding agglomerates. These can lead to malfunctions of various kinds, be it that they disturb a uniform distribution of microwaves within the treatment room, whether they grow and detach from a certain size and fall back on the material cake, what in this undesirable

Irregularities, or even cause them to ignite in unfavorable constellations.

Object of the present invention is therefore to prevent such accumulation of electrostatically charged particles within the treatment room.

This object is achieved for the continuous furnace according to the invention in that the conveyor belt and the plate at least partially made of materials that are close to each other or identical in a triboelectric series.

The invention is based on the finding that the undesirable electrostatic charges occur, in particular, when two different, initially electrically neutral materials are brought into contact, rubbed against each other and separated again. In this case, some materials emit electrons and are thereby positively charged, while other materials absorb electrons and thereby receive a negative charge surplus.

A preferred triboelectric series consists in particular of the materials latex-asbestos-glass-mica-nylon-wool-lead-silk-aluminum-paper-cotton-steel-wood-hard-rubber-nickel / copper-brass / silver-acetate-silk-polyester-polyurethane -polyethylene polypropylene PVC silicone-polytetrafluoroethylene Teflon. In this triboelectric series, the first-mentioned materials are positively charged by a contact partner mentioned below, while partners from the rear region of the aforementioned contact partners receive an excess of electrons. The further away a pair of materials for the conveyor belt and the plate in the list are from each other, the stronger is the formation of electrostatic charges and the more preferably the materials absorb the charges and the materials release the charges, respectively.

In order to prevent this, according to the invention, a pairing of within the listed range close together or identical materials are selected.

Particularly preferred are the conveyor belt and / or the plate of a permeable to the radiation, in particular microwaves, material.

Especially if one of the mentioned materials is not

is microwave permeable, can be formed from this a grid or a fabric or network, their respective free spaces due to their dimensions for

Radiation, in particular microwave radiation are permeable. This grid, fabric or net is then used as a conveyor belt and / or for the plate over which the conveyor belt is moved. So on the one hand, an electrostatic

Charging can be prevented and on the other hand, the radiation, in particular the microwave radiation, pass through the conveyor belt and the plate and heat the material resting on the conveyor belt.

In a further development of the invention, it is proposed to provide the conveyor belt and / or the plate, which consist of basic materials spaced apart from one another within the triboelectric series, on the side or sides facing one another with a coating of a material which is in the

triboelectric series is closer to the material of the counterpart than the base material and / or coincides with the material of the counterpart.

Basically, such a coating over the entire surface, but also be carried out only lattice, tissue or net shape, to prevent direct frictional contact between the base materials of conveyor belt and plate. A preferred embodiment is characterized in that before and / or after the

Treatment room an absorption chamber is arranged. In this way it can be ensured that radiation which is not absorbed by the material can not escape from the continuous furnace either.

Alternatively or in combination, the plate is arranged in the treatment space and / or in the absorption chamber. The, in particular microwave transparent plate is preferably arranged in the treatment room, if the material is preferably to be irradiated from both sides of the surface with microwaves. The use of plates in the absorption chamber can on the one hand serve to transport the material via an absorption chamber arranged below the material, but also to shield the absorption chambers from dust and other interfering particles.

Preferably Deionisationselemente for discharging charge from

Conveyor belt and / or arranged from the plate. Thus, charges which produce charges despite the choice of conveyor belt and plate materials after the triboelectric series can be withdrawn from the conveyor belt and / or the plate.

An alternative embodiment provides that the conveyor belt is at least partially antistatic. This can be achieved, for example, in that metal or carbon fiber threads are embedded in the plastic of the conveyor belt or that fabric chains for guiding the charge are present in the conveyor belt.

Further advantages and features of the invention will become apparent from the following description of an embodiment. Showing:

Fig. 1 is a schematic diagram of a device according to the invention.

1 shows a schematic diagram of a continuous furnace 4 for heating material 2, in particular lignocellulosic material 2, as it

for example, in the wood-based material industry for the production of

Wood-based panels is used. Lignocellulosic material 2, like

For example, chips or fibers ,, is scattered on an endlessly circulating conveyor belt 1 to a mat or a non-woven and fed in the direction of production 3 a here only symbolically shown continuous furnace 4. The continuous furnace 4 comprises a treatment space 7, in which the material 2, which is present here in the form of a mat or a fleece, with radiation 5, in particular with

Microwave radiation is irradiated from below and / or above.

If necessary, while the top of the material 2 by means of another

Conveyor belt 8 are covered, which runs at the same speed as the material 2 through the treatment chamber 7. The upper transport belt 8, which rests on the material 2, on the one hand has the function of protecting the surface of the mat material 2 as it passes through the continuous furnace 4, and on the other hand, it also prevents particles, such as product fibers, Dust etc., easily detach from the surface of the material 2.

In the treatment chamber 7, the radiation 5 is preferably introduced above and / or below the material 2 in order to ensure a uniform heating of the material 2. The radiation 5 can be generated by means of microwave generators (not shown) outside the continuous furnace 4 and by means of waveguides

Openings 6 are coupled into the treatment chamber 7 of the continuous furnace 4. Alternatively, the radiation 5 can also be generated within the treatment space 7, whereby waveguides and the corresponding openings 6 can be dispensed with. The radiation generator for generating the radiation 5 within the treatment chamber 7 or the openings 6 for the entry of the radiation 5 into the treatment chamber 7 are preferably arranged at a distance from the material 2 around a spatial, in particular even, propagation of the radiation 5 in the complete treatment chamber 7 to enable.

In the production direction 3 before and / or after the treatment chamber 7 absorption chambers 9 are arranged in the example shown here, which prevents that in the treatment chamber 7 introduced radiation 5, in particular

Microwave radiation, in an undesirable manner from the one shown here

Continuous furnace 4 can escape. In the absorption chambers 9, the residual radiation, which has not been absorbed by the material 2 on absorption elements 1 1, for example, water storage or plates of ceramic materials, passed to which the residual radiation is converted into heat and destroyed. In the region of the treatment chamber 7, the lower conveyor belt 1 runs with its underside over a plate 5 permeable to the radiation 5 or microwaves. Instead of a plate 7 made of material permeable to microwaves, it is also possible to use a plate

Grid structure or similar be provided, which can pass through the radiation 5 and at the same time can take a carrying function, so that the lower conveyor belt 1, which is loaded with the weight of the mat, does not sag.

Since the conveyor belt 1, 8 and the plate 10 made of different plastics, it comes due to triboelectric effects to an electrostatic charge. The thereby occurring on the conveyor belt 1, 8 charges are released from this part of the material 2, which thus also charges electrostatically or already, for example by the scattering, an electrostatic

Owns charge. Individual particles of the material 2, in particular as far as they are arranged on the edge, dissolve due to this electrostatic charge or by the electrical field generated by the charge separation of the material 2 and then fly in particular in the treatment room 7. There, these particles can accumulate and thus leading to significant disruption.

In order to reduce or avoid this, the material of the conveyor belt 1 and the material of the plate 10 are selected from a triboelectric series comprising the materials latex-asbestos-glass-mica-nylon-wool-lead-silk-aluminum-paper Cotton-steel-wood-hard-rubber-nickel / copper-brass / silver-acetate-silk-polyester-polyurethane-polyethylene-polypropylene-PVC-silicone-polytetrafluorethylene-Telfon contains. The choice is made in such a way that the two materials are close to each other in this list or, if possible, are identical. Below each other, a distance of zero to four intermediate materials is considered. Identical materials are also considered to be close together in the context of the present invention.

Furthermore, deionization elements for discharging charge from

Transport belt and / or be arranged by the plate. Thus, charges which produce charges despite the choice of conveyor belt and plate materials after the triboelectric series can be withdrawn from the conveyor belt and / or the plate. As Deionisationselemente example electrodes, pulleys or brushes can be used, which in the tape run of the conveyor belt 1, 8 or are arranged on the plate 10. Both surface sides of the

Conveyor belt 1, 8 and the surface side of the plate 10, over which the conveyor belt 1, 8 moves, guided over Deionisationselemente.

If the selected material as such is not transmissive to the radiation 5, e.g. As metals (lead, aluminum, steel, nickel, copper, brass, silver, etc.), it may be designed for use as a conveyor belt 1, 8 or as a plate 10 lattice, mesh or fabric-like.

Through the gaps or holes in such grids, nets or tissues, the radiation 5, in particular the microwaves, then continue to pass, while between conveyor belt 1, 8 and plate 10, the triboelectric boundary conditions are changed so that no or only lower electrostatic charges be generated.

In embodiments not shown here, the conveyor belt 1, 8 on its plate 10 facing the bottom and / or the plate 10 on its the

Conveyor belt 1, 8 facing top provided with a coating. The material of the coating is chosen so that it in the o.g. triboelectric series closer to the base material of the counterpart is identical to the coated base material or with the material of the counterpart.

In this embodiment, the properties of the conveyor belt 1, 8 or the plate 10 in terms of flexural or bending stiffness, tensile strength, etc., are determined substantially by the base material being coated while determining the triboelectric conditions between the two passing elements by the coating.

In particular, such a coating can also consist of the same material as the base material of the counterpart, that is to say for a coating on the conveyor belt 1, 8 of the material of the plate 10 or for a coating on the plate 10 of the material of the conveyor belt 1, 8. Die Coating may be formed over the entire surface, as well as only grid, net or fabric-like. This is particularly advantageous if the selected material of the coating as such is not permeable to radiation 5, in particular microwaves, such. For example metals. Also in this way the formation of electrostatic charges is effectively prevented.

List of Reference P1550:

1 conveyor belt

2 material

3 production direction

4 continuous furnace

5 openings

6 radiation

7 treatment room

8 conveyor belt

9 absorption chamber

10 plate

1 1 absorption element

Claims

claims

1 . Continuous furnace (4) for heating material (2) by means of microwaves, comprising a treatment space (7) for heating the material (2), wherein in

Treatment chamber (7) one or more openings (6) for introducing the radiation (5) via waveguides in the treatment chamber (7) are arranged and / or the microwave generators in the treatment chamber (7) are arranged directly, at least one endless circulating conveyor belt (1, 8) for transporting the material (2) through the continuous furnace (4), and a plate (10) over which the conveyor belt (1, 8) is drawn, characterized in that the conveyor belt (1, 8) and the plate (10 ) consist at least partially of materials that are close to each other or identical in a triboelectric series.

2. continuous furnace (4) according to claim 1, characterized in that the

triboelectric series materials contains from the group of materials latex asbestos glass mica nylon wool wool lead silk aluminum paper cotton steel wood hard rubber nickel / copper brass / silver acetate silk polyester polyurethane Polyethylene-polypropylene-PVC-silicone-polytetrafluoroethylene-teflon.

3. continuous furnace (4) according to one or more of the preceding claims,

characterized in that the conveyor belt (1, 8) and / or the plate (10) are made of a for the radiation (5), in particular microwaves, permeable material.

4. continuous furnace (4) according to one or more of the preceding claims,

characterized in that at least one of the materials for the conveyor belt (1, 8) and / or the plate (10), a grid or a fabric or network is formed, each free spaces are permeable due to their dimensions for microwaves.

5. continuous furnace (4) according to one or more of the preceding claims,

characterized in that the conveyor belt (1, 8) and / or the plate (10) spaced from each other within the triboelectric series

Base materials consist, are provided on the or the mutually facing sides with a coating of a material which is closer to the material of the counterpart in the triboelectric series than the base material.

6. continuous furnace (4) according to claim 5, characterized in that the

Coating over the entire surface, grid, fabric or net shape is executed.

7. continuous furnace (4) according to one or more of the preceding claims,

characterized in that an absorption chamber (9) is arranged before and / or after the treatment space (7).

8. continuous furnace (4) according to one or more of the preceding claims,

characterized in that the plate (10) in the treatment chamber (7) and / or in the absorption chamber (9) is arranged.

9. continuous furnace (4) according to one or more of the preceding claims,

characterized in that Deionisationselemente for discharging cargo from the conveyor belt (1, 8) and / or from the plate (10) are arranged.

10. Continuous furnace (4) according to one or more of the preceding claims,

characterized in that the conveyor belt (1, 8) is at least partially antistatic.