DE102017108092A1 - Continuous furnace for heating material by means of microwaves - Google Patents

Abstract

The invention relates to a continuous furnace (4) for heating material (2) by means of microwaves, comprising a treatment space (7) for heating the material (2), wherein in the treatment space (7) one or more openings (6) for the introduction of 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) in the treatment space (7) is pulled.

Description

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 made of lignocellulose-containing material, it is known to preheat the material scattered to a nonwoven 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. In particular, hot-air or steam preheating systems or the use of high-frequency radiation, for example microwaves, for preheating in microwave continuous furnaces, referred to below as the continuous furnace, have proven successful. The physical principle is based on the conversion of electromagnetic energy into heat energy in the absorption of microwaves by the material to be heated.

So it is for example from the DE 197 18 772 A1 It is known to expose the material scattered to a nonwoven fabric to microwaves prior to introduction 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, are absorbed and there to stimulate existing water molecules or other electric dipoles to vibrate. In contrast, when using hot plates or hot air preheating systems or the like, the heat is applied substantially from the outside, whereby a full 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 high energy consumption.

When using microwaves or high-frequency radiation in a continuous furnace to heat 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 used in the field of gastronomy or in the household, a hermetically delimited treatment chamber is usually 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 deposited on a for the radiation, especially microwaves, permeable conveyor belt and transported by this through the treatment room, the material to be treated both from below and possibly even from above evenly with microwaves is irradiated.

The problem here may be that the conveyor belt due to the requirements of transparency for microwave radiation consists 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 plates also made of a microwave transparent plastic, such as 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 the 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 dislodge from the mat, particularly from its surface, during transport through the continuous oven.

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, be it that they grow and detach from a certain size and fall back on the cake, which can lead to unwanted irregularities in this, or even that they ignite in unfavorable constellations.

It can also be problematic that the transparent to the radiation plate over which the conveyor belt runs, should be made particularly solid with a corresponding thickness due to the width of the continuous furnace of up to 3.5 m, so that they are the burden of the Material resting on the conveyor belt also withstands. In addition, the plate in the treatment room also heats up and may be subject to strong thermal expansion due to the material selected. This can lead to a deformation de plate, which in turn affects the conveyor belt running above it and the material lying thereon and there can lead to a deformation of the present in the form of a mat or nonwoven material.

Object of the present invention is therefore to overcome the disadvantages mentioned above.

Another object of the present invention is to improve the distribution of microwave radiation within the continuous furnace.

Yet another object of the present invention is to improve the transport of the material through the continuous furnace.

Yet another object of the present invention is to prevent such accumulation of electrostatically charged particles within the treatment space.

These and other objects are achieved by a continuous furnace for heating material by means of microwaves, comprising a treatment room for heating the material, wherein one or more openings for introducing the radiation via waveguide are arranged in the treatment room and / or the microwave generator in the treatment room in the treatment room are arranged directly, at least one endless circulating conveyor belt for transporting the material through the continuous furnace, and a plate over which the conveyor belt is pulled in the treatment room.

A further advantageous embodiment of the continuous furnace is characterized in that the plate is located on at least one or more carriers.

The invention is based on the finding that the support receives the support from the plate, as a result of which the plate can also be made thinner. By means of the carrier, sagging of the plate can be prevented, so that the material, preferably present as fleece or mat, can be transported more uniformly and without bending through the continuous furnace. By resting the plate on the carriers, there is also a thermal connection between the carriers and the plate, whereby any occurring heat distribution fluctuations can be dissipated and the heat distribution can be homogenized as a whole. By arranging the carriers between the microwave generators or the openings for the entry of the radiation into the treatment space and the plate, these can also influence and improve the distribution of the radiation in the treatment space, especially between the floor and the plate.

The invention is based on the recognition that, especially when using plastic plates which are microwave-transparent, the electrostatic charges are found essentially on their surfaces, i. on the top or bottom of each plate. By these plates lie on at least one carrying them and the charge-conducting carrier and thereby form a basically electrically conductive contact, these electrical charges can be compensated. Whether it be that excess charges are discharged, be it the missing charges are supplied. In this way, the electrostatic charges are largely compensated for and thus the above-mentioned problems can be effectively avoided.

The supports preferably extend substantially parallel to one another and are arranged parallel to one another. Preferably, at least a part of the carriers are aligned perpendicular and / or parallel to the production direction. The arrangement as well as orientation can be influenced by the width and the length of the continuous furnace.

In particular, the carriers do not run only at the edge of the floor areas, but in particular over the central areas bounded by the edges.

Alternatively or in combination, the carriers include a spacer and a rail, the rail being in contact with the plate. As a result, the carriers are on the one hand not solid, whereby a better distribution of the radiation, in particular the microwaves, is achieved in the treatment room.

Preferably, the spacers and the rails are of the same material or of different materials. The distribution of radiation in the treatment room can be influenced by the choice of materials. Alternatively, the materials can also be selected so that they specifically influence the distribution of the radiation in the treatment room.

Preferably, the carriers do not cover the openings, so that they can release the radiation freely into the treatment room. Direct reflection of the radiation in the opening is thus avoided. The said openings for microwaves are preferably arranged in the areas between the above-mentioned parallel rails.

Preferably, the carriers are equidistant and thus arranged distributed in the treatment space. This can be advantageous in particular for the distribution of the radiation in the treatment room.

A further embodiment provides that the carriers are formed from a material with low thermal expansion. Low thermal expansion in the present case means that the material of the carrier by direct heating by absorption of the radiation as well as by indirect heating via contact heat and / or heat radiation only slightly, preferably less than 5%, especially less than 3%, highest preferably by less than 2% over the size at room temperature.

The supports are preferably constructed of a material which is transparent to the radiation or of a metallic material, for example of aluminum or steel. Transparent materials for the radiation offer the advantage that they do not affect the distribution of the radiation in the treatment room, but, because they are mostly plastics, difficult to connect to the wall, in particular to the bottom of the continuous furnace. Metallic materials can influence the radiation distribution, also positively.

A further embodiment is characterized in that the contact surface of the plate on the carriers is less than 20%, preferably less than 12%, particularly preferably less than 8%, most preferably less than 5%. By a small contact surface the largest possible area is available through which the radiation can penetrate into the material and heats the material, in particular if the carriers are constructed of a material which is not transparent to the radiation.

Preferably, the plate is overlapped or encompassed by a holder at its edges. By the holder bending of the plate, for example by thermal expansion or the like, is avoided. The bracket, which are usually made of steel or aluminum, also serves as a guide device for the plate. In addition, these holders make it possible to compensate for electrostatic charges on the side of the plate facing the conveyor belt, ie to supply or remove these charges causing electrons.

Alternatively or in combination, the holder forms with the plate an overlap region of 2 cm to 20 cm, preferably from 5 to 15 cm, whereby a secure guidance of the plate through the holder, which is preferably arranged completely circumferentially around the plate is guaranteed. By the brackets thereby overlap the edges of the plate, joints are also avoided at the edges, in which otherwise could accumulate particles and as pollution etc. can lead to malfunction.

Preferably, the holder tapers in a wedge shape from the housing of the continuous furnace to the plate. The running over the plate and the bracket conveyor belt can thus conform to the shape and angular transitions, which could lead to damage to the conveyor belt can be avoided.

A further embodiment is characterized in that the plate is mounted floating between the carrier and the holder. Thus, the plate is free to expand, for example when heated by the material being heated and heated above it.

Preferably, the plate is connected at a fixed point with the support or the holder or the housing of the continuous furnace. The fixed point allows targeted control of the thermal expansion of the plate in one or more specific directions.

A further embodiment of the invention provides that the plate is constructed of segments. Especially when building the system or even when changing the plate provides a segmented plate has the advantage that the individual segments can be removed and replaced separately.

The segments of the plate preferably overlap and preferably have overlapping segment noses. Due to the overlap, the space between the wall or the bottom of the continuous furnace and the plate is closed and there are no openings in the plate, through which material can penetrate into the area below the plate and ignite there.

Alternatively or in combination, the segments of the plate are interconnected, preferably about tongue and groove. On the one hand, a kind of overlap of the individual segments takes place through the connection, on the other hand, the stability of the plate is improved overall by the connection of the segments. Preferably, the segments of the plate can also be welded.

Preferably, expansion joints are arranged between the segments.

In particular, the plate has a thickness of less than 30 mm, preferably less than 20 mm, particularly preferably less than 15 mm. A thinner plate also allows for easier handling due to its lower weight.

A further embodiment of the invention provides that the plate comprises a base plate and a wear plate, which rests on the base plate. Due to the transport belt running over the plate, wear can occur on this plate. By the execution of the plate as a split plate comprising a base plate and a wear plate can be changed in a visible wear only the wear plate, wherein the base plate is arranged in a continuous furnace. The change of the plate can thus be done faster, reducing the downtime for such a change is shortened.

Preferably, the wear plate is made thinner than the base plate. The change of the wear plate can thus be done without large equipment and fast.

In a preferred embodiment, the wear plate has a thickness of less than 8 mm, preferably less than 5 mm, particularly preferably less than 3 mm.

• 1 die Prinzipskizze einer erfindungsgemäßen Vorrichtung;
• 3 eine Teilansicht des Durchlaufofens im Bereich des Transportbandes; und
• 2 eine Teilansicht des Behandlungsraumes perspektivischer Darstellung;
• 4 eine Teilansicht einer aus Segmenten aufgebauten Platte.

Further advantages and features of the invention will become apparent from the dependent claims, which can be combined with each other in any combination, as well as the following description. Showing:

• 1 the schematic diagram of a device according to the invention;
• 3 a partial view of the continuous furnace in the region of the conveyor belt; and
• 2 a partial view of the treatment room perspective view;
• 4 a partial view of a constructed of segments plate.

In the 1 can be seen a schematic diagram of a continuous furnace 4 for heating material 2 , in particular of lignocellulosic material 2 , as used for example in the wood-based panel industry for the production of wood-based panels. Lignocellulosic material 2 , such as chips or fibers, is placed on an endlessly circulating conveyor belt 1 scattered to a mat or a nonwoven and in the production direction 3 a continuous furnace only symbolically represented here 4 fed. The continuous furnace 4 includes a treatment room 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, it can be the top of the material 2 by means of another conveyor belt 8th be covered at the same speed as the material 2 through the treatment room 7 starts to rotate. The upper conveyor belt 8th that on the material 2 rests on the one hand has the function of the surface of the material present as a mat 2 Protect if this by the continuous furnace 4 and, on the other hand, it also prevents particles, such as product fibers, dust, etc., from easily separating from the surface of the material 2 to solve.

In the treatment room 7 becomes the radiation 5 preferably above and / or below the material 2 introduced to a uniform heating of the material 2 to ensure. The radiation 5 can by means of microwave generators (not shown) outside the continuous furnace 4 be generated and waveguide via openings 6 in the treatment room 7 of the continuous furnace 4 be coupled. Alternative may be the radiation 5 also within the treatment room 7 generated, resulting in waveguides and the corresponding openings 6 can be waived. The radiation generator for generating the radiation 5 within the treatment room 7 or the openings 6 for the entry of radiation 5 in the treatment room 7 are preferably at a distance from the material 2 arranged around a spatial, in particular even propagation of the radiation 5 in the complete treatment room 7 to enable.

In production direction 3 before and / or after the treatment room 7 are in the example shown here absorption chambers 9 arranged, which prevents that in the treatment room 7 introduced radiation 5 , In particular microwave radiation, in an undesirable manner from the continuous furnace shown here 4 can escape. In the absorption chambers 9 will the residual radiation, which is not from the material 2 was absorbed on absorption elements 17 , For example, water storage or plates made of ceramic materials, passed to which the residual radiation is converted into heat and destroyed.

In the area of the treatment room 7 runs the lower conveyor belt 1 with its bottom over one for the radiation 5 or microwave permeable plate 7 so that the lower conveyor belt 1 , which is loaded with the weight of the mat, does not sag. The distance between the openings 6 or the microwave generators and the passing material 2 ensures that the radiation 5 in the treatment room 7 spread and distribute.

Because the conveyor belt 1 . 8th and the plate 10 consist of different plastics, it comes due to triboelectric effects to an electrostatic charge. The case on the conveyor belt 1 . 8th Charges arising from this are partly due to the material 2 which thus also charges electrostatically or already, for example due to the scattering of the material 2 to a mat, has an electrostatic charge. Individual particles of the material 2 , in particular if they are arranged on the edge, detach from the material due to this electrostatic charge or by the electric field generated by the charge separation 2 and then fly especially into the treatment room 7 , There, these particles can accumulate and thus lead to significant malfunctions.

In 2 shows a part of a cross section transverse to the production direction 3 through the treatment room 7 of the continuous furnace 4 , The present as a mat or fleece material 2 lies on the conveyor belt 1 on which in the treatment room 7 over the plate 10 in production direction 3 which moves into the image plane, is moved. The plate 10 which consists of one, for which in the treatment room 7 incoming radiation 5 transparent material, lies on the carriers 11 , which are at the bottom of the continuous furnace 4 brace on. The carriers 11 are in the present case of a spacer elements 13 and a rail 12 which is in contact with the plate 10 stands. Due to the design of the carrier 11 with spacer 13 and rail 12 results in a better propagation ability of the radiation 5 in the treatment room 7 and the radiation 5 is, for example, when using metallic carriers 11 , between the carriers 11 not channeled. The carriers 11 or the spacer elements 13 as well as the rails 12 can be made of a metallic material, such as steel or aluminum, which also by the movement of the conveyor belt 1 over the plate 10 resulting charges can be dissipated. Alternatively, the carriers can 11 or the rails 12 and the spacer elements 13 also from one for the radiation 5 transparent material, such as from a plastic such as polyethylene or polypropylene, be constructed. Especially when using spacers 13 from these materials, however, proves the connection of these to the wall of the continuous furnace 4 as difficult.

The peripheral edges of the plate 10 are each from a bracket 14 overrun, which has a section, which also serves as an overlap of the bracket 14 with the plate 10 can be seen, and which is on the top of said plate 10 firmly presses. Through this overlap area can on the top of the plate 10 accumulating electrostatic charges are compensated by supply or removal of electrons. At the same time these sections give the possibility that the plate 10 can expand heat-related and the resulting dimensional changes, in particular a length and width, can be compensated in located below the said sections joint areas. By making these joint areas below the sections of the bracket 14 they are also preserved from pollution. The plate 10 is thus floating between the straps 11 and the holder 14 stored and clamped and can expand freely here. The overlap area of bracket 14 and plate 10 is designed so that the plate 10 always from the holder 14 is overrun and the plate 10 below the bracket 14 can expand. Alternatively, the plate at a fixed point with the carrier 11 or the holder 14 be connected, so that the expansion preferably in one direction, for example, the production direction 3 , can be done. Due to the possibility of expansion of the plate 10 below the bracket 14 there is a change in the contact surface between plate 10 and conveyor belt 1 , In particular, tensions are within the plate 10 and bulges this avoided at a strong expansion.

In the 3 is a section of the treatment room 7 to see in perspective, which the bottom plate of the continuous furnace 4 with the openings 6 as well as the carriers 11 shows. On a presentation of the plate 10 which are on the straps 11 was waived for the sake of clarity. One recognizes in particular the transversely to the production direction 3 running, as rails 12 , which are on spacer elements 13 store, trained vehicles 11 , These rails 12 as well as the spacer elements 13 can be metallic and in direct, electrically conductive contact with the plate 10 stand. It is thus possible on this underside of the plate 10 accumulating electrostatic charges to compensate for an increase or decrease of electrons. The spacer elements 13 hold the parallel rails 12 of the carrier 11 in a distance between the bottom of the continuous furnace 4 and the plate 10 . so that the radiation 5 in this area can freely spread.

In the bottom plate of the continuous furnace 4 are preferably crosswise, in particular longitudinal or transverse to the direction of production 3 arranged openings 6 provided, passed through the waveguide and from outside of the continuous furnace 4 arranged magnetrons generated radiation 5 in the treatment room 7 is initiated. By the of the spacer elements 13 caused distance between the plate 10 and the bottom plate of the continuous furnace 4 can the radiation 5 distribute more evenly and thus occurs not only punctiform in one over the plate 10 guided material 2 one. By the arrangement of carriers shown here 11 In doing so, the least possible disturbance of the uniform introduction of radiation, in particular in the form of microwaves, is achieved, together with an optimized support of the plate 10 , The carriers 11 are preferably uniform, in particular arranged at an equal distance, wherein the openings 6 not from the carriers 11 be covered. Alternatively or in combination with the openings 6 can be arranged at provided points microwave generator, by means of which the radiation 5 directly in the treatment room 7 is produced.

In 4 is an embodiment of the plate 10 shown, which consists of segments 15 is constructed, which overlap in one area and a continuous support of the conveyor belt running above 1 allow. The individual segments 15 lie on carriers 11 on, which here again from distance elements 13 and rails 12 are constructed. The segments 15 have segment noses 16 on which the two segments 15 interlock with each other so that the individual segments 15 can expand to a certain extent when heated. In the area of the overlap of the segment noses 16 can also be introduced a sealing material, so that in the space below the plate 10 or the segments 15 no material can penetrate and possibly ignite. The sealing material should be compressible so that it expands the segments 15 can be compressed without the surface of the plate 10 to influence, for example by leaking sealing material. The plate 10 can be made up of multiple segments 15 be constructed. The segments 15 Depending on the size in and / or across the production direction 3 overlap.

LIST OF REFERENCE NUMBERS

1

conveyor belt

2

material

3

production direction

4

Continuous furnace

5

radiation

6

opening

7

treatment room

8th

conveyor belt

9

absorption chamber

10

plate

11

carrier

12

rail

13

spacers

14

bracket

15

segment

16

segment nose

17

absorbing element

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19718772 A1 [0003]

Claims (24)

Continuous furnace (4) for heating material (2) by means of microwaves, comprising a treatment space (7) for heating the material (2), wherein in the treatment space (7) one or more openings (6) for introducing the radiation (5) via waveguides are arranged in the treatment chamber (7) 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) in the treatment chamber (7) is pulled. Continuous furnace (4) after Claim 1 , characterized in that the plate (10) lies on at least one or more carriers (11). Continuous furnace (4) according to one or more of the preceding claims, characterized in that the carriers (11) extend substantially parallel to one another. Continuous furnace (4) according to one or more of the preceding claims, characterized in that at least a part of the carrier (11) are aligned perpendicular and / or parallel to the production direction (3). Continuous furnace (4) according to one or more of the preceding claims, characterized in that the supports (11) comprise a spacer element (13) and a rail (12), the rail (12) being in contact with the plate (10). Continuous furnace (4) according to one or more of the preceding claims, characterized in that the spacer elements (13) and the rails (12) are made of the same material or of different materials. Continuous furnace (4) according to one or more of the preceding claims, characterized in that the carriers (11) do not cover the openings (6). Continuous furnace (4) according to one or more of the preceding claims, characterized in that the carriers (11) are arranged equidistantly. Continuous furnace (4) according to one or more of the preceding claims, characterized in that the carriers (11) are formed from a material with low thermal expansion. Continuous furnace (4) according to one or more of the preceding claims, characterized in that the carriers (11) are made of a material (5) transparent to the radiation or a metallic material, preferably aluminum or steel. Continuous furnace (4) according to one or more of the preceding claims, characterized in that the bearing surface of the plate (10) on the carriers (11) is less than 20%, preferably less than 12%, more preferably less than 8%, most preferably less than 5% , Continuous furnace (4) according to one or more of the preceding claims, characterized in that the plate (10) is overlapped or encompassed by a holder (14) at its edges. Continuous furnace (4) according to one or more of the preceding claims, characterized in that the holder (14) with the plate (10) forms an overlap region of 2 cm to 20 cm, preferably from 5 to 15 cm. Continuous furnace (4) according to one or more of the preceding claims, characterized in that the holder (14) tapers in a wedge shape from the housing of the continuous furnace (4) to the plate (10). Continuous furnace (4) according to one or more of the preceding claims, characterized in that the plate (10) between the carrier (11) and holder (14) is mounted floating. Continuous furnace (4) according to one or more of the preceding claims, characterized in that the plate (10) is connected at a fixed point to the carrier (11) or the holder (14) or the housing of the continuous furnace (4). Continuous furnace (4) according to one or more of the preceding claims, characterized in that the plate (10) is constructed from segments (15). Continuous furnace (4) according to one or more of the preceding claims, characterized in that the segments (15) of the plate (10) overlap and preferably have overlapping segment lugs (16). Continuous furnace (4) according to one or more of the preceding claims, characterized in that the segments (15) of the plate (10) are interconnected, preferably via tongue and groove. Continuous furnace (4) according to one or more of the preceding claims, characterized in that expansion joints are arranged between the segments (15). Continuous furnace (4) according to one or more of the preceding claims, characterized in that the plate (10) has a thickness of less than 30 mm, preferably less than 20 mm, particularly preferably less than 15 mm. Continuous furnace (4) according to one or more of the preceding claims, characterized in that the plate (10) comprises a base plate and a wear plate, which rests on the base plate comprises. Continuous furnace (4) according to one or more of the preceding claims, characterized in that the wear plate is made thinner than the base plate. Continuous furnace (4) according to one or more of the preceding claims, characterized in that the wear plate has a thickness of less than 8 mm, preferably less than 5 mm, more preferably less than 3 mm.

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