EP0487504A1 - Arrangement for heating an elongated piece of electrically conductive material - Google Patents

Abstract

The pairs of electrodes (30,31) are coupled to a high frequency generator (23) to provide the heating effect. The elecrodes form capacitor plates, electrically insulated from the strip material. Smaller plates (32) are positioned on the sides of the strip where there are no main and are similarly linked to the generator. The overall heating effect from the different paris of electrodes an even heating pattern without forming any localised discontinuities, especially for heat setting materials.

Description

The invention relates to a device for heating a strand of electrically conductive material, preferably solidified by the heating, in a channel which is delimited by walls made of electrically insulating material, adjacent to which a capacitor plate arrangement, which is connected to a high-frequency generator, is provided.

Such a device is known from EU-B-0085318, in which two capacitor plates are arranged on two opposite sides of the channel offset by approximately their length from one another, which are connected to a non-potential-free connection of the high-frequency generator, while on both sides adjacent to the two capacitor plates In each case two further capacitor plates are arranged, which are connected to the potential-free connection of the high-frequency generator and extend along the channel to such an extent that the strand is no longer at potential outside the heating range. However, as has been shown, the heating of the strand is not sufficiently uniform and, as a result, can lead to shell formation within the strand, which causes the homogeneity of the end product and thus its strength, if it is, for example building materials to be hardened by heating is impaired. This may be due to the fact that the fields in the middle of the strand can compensate approximately, while very strong fields occur between adjacent capacitor plates of different polarity in the edge region of the strand, so that the field distribution with respect to the axis of symmetry in the longitudinal direction of the strand is highly asymmetrical. Because of the relatively uneven heating, a very large heating section is also required.

The object of the invention is therefore to provide a device of the type mentioned at the outset which enables more uniform heating of the strand and prevents shell formation within the strand.

This object is achieved in that the four middle capacitor plates - on two opposite sides of the strand, two adjacent in the longitudinal direction of the strand - are all connected to the non-potential-free connection of the high-frequency generator and additionally to the two remaining sides of the strand in the middle region of the strand and the extension of these capacitor plates, an auxiliary capacitor plate, which is also connected to the non-potential-free connection of the high-frequency generator, is provided.

The object is further achieved in that the four middle capacitor plates - each arranged on two opposite sides of the string - are connected to two uncorrelated high-frequency generators. This also ensures that the field inside the strand becomes more homogeneous and concentrated.

The object is also achieved in that the distance between the capacitor plates arranged adjacent in the longitudinal direction of the strand is at least equal to the distance between the capacitor plates opposite each other with respect to the strand.

If you use two uncorrelated high frequency generators, the distance between the floating outer capacitor plates is and to select the adjacent, middle, non-potential-free capacitor plates at least equal to the distance of the capacitor plates opposite one another with respect to the strand, while the distance between the middle neighboring capacitor plates can be narrower.

The object is also achieved in that, in the case of a high-frequency generator, the distance between the potential-free outer capacitor plates and the adjacent middle capacitor plates is at least equal to the distance between the capacitor plates opposite one another with respect to the strand, while the distance between the middle neighboring capacitor plates is narrower and in each case on one side of the line has potentials applied symmetrically to the zero potential.

In addition, the object is achieved in that a cylindrical capacitor consisting of a capacitor electrode surrounding the strand and at least one capacitor electrode located in the interior of the strand, which is arranged in the area of the surrounding capacitor electrode and has a different polarity than the surrounding capacitor electrode, is provided, which at least when the surrounding capacitor electrode is not potential-free, it is expediently arranged between outer capacitor plates which are adjacent in the strand direction and are at zero potential.

Although the skin effect in heating devices using high-frequency electrical energy is normally a second-order disturbance, it can become a dominant effect depending on the size of the capacitor plate. In order to keep its impact as low as possible, it is therefore expedient to construct the capacitor plates each from several, preferably two partial plates, which are at the same potential and whose adjacent edges are separated by a slot, which is preferably kept as small as possible.

Further embodiments of the invention can be found in the following description and the claims.

The invention is explained in more detail below on the basis of the exemplary embodiments illustrated in the attached figures.

1 shows an essentially schematic and perspective view of a strip strand system with a device for heating the strand.

2 to 10 show essentially schematic embodiments of capacitor arrangements.

1 comprises four belts 10, 11, 12 and 13, which are arranged such that they form a rectangular channel 14 between them. The belts 10 to 13 are guided around rollers 15 and driven synchronously by means of a drive, not shown. The tapes 10 to 13 are, if necessary, also supported adjacent to the channel 14 by support gratings, not shown, while the vertical tapes 12 and 13 can additionally be guided at their edges via slide rails. The lower horizontal belt 10 is extended beyond the outlet end of the channel 14 and guided to the belt running control via a dancer roller 16.

Between the belts 10 to 13, a filling device, e.g. a filling funnel 17 which is expediently arranged such that it can be moved out of the inlet region of the channel 14 by means of a piston-cylinder unit for the purpose of cleaning. The outlet opening of the filling funnel 17 is located in the inlet area of the channel 14.

At the outlet end of the channel 14, a cutting device 18 is provided, which can be moved in the feed direction of the strip 10 from an initial position synchronously with the feed speed of the strip 10 and can be returned to the initial position after the cutting process has been carried out. In the embodiment shown, the cutting device 18 has a bracket 19, which receives a cutting wire 19a to and fro and is adjustable in the vertical direction in accordance with the cutting progress and can be moved with a carriage 20.

A belt weighing section can follow the cutting device 18 be provided.

The tapes 10 to 13 consist of an electrically non-conductive plastic, while adjacent to the tapes 12 and 13, namely on the outside of the tape parts, which form the entrance area of the channel 14, a schematically illustrated capacitor plate arrangement 21 is provided, which is connected via corresponding lines 22 a high frequency generator 23 are connected.

If a raw mixture, for example consisting of quartz sand, lime, water, cement with an accelerator / retarder system and foam for the production of lime silicate stones, is filled into the filling funnel 17, the raw mixture passes into the channel 14 and is conveyed through the belts 10 to 13 on the predetermined channel cross section kept. The raw mixture in the duct 14 is heated, for example, to a temperature of 50 ° C. via the capacitor plate arrangement 21, so that the raw mixture solidifies due to the strengthening reactions of the cement that are set in motion.

The solidifying strand of raw mixture in channel 14 is conveyed through belts 10 to 13 to the outlet end of channel 14. A relative movement between the strand and the tapes 10 to 13 and between the tapes 10 to 13 does not take place here, so that the wear problems are minimal.

In order to achieve a slight detachment of the tapes 10 to 13 from the solidified strand at the exit end of the channel 14, the tapes 10 to 13 are sprayed with a separating agent by spray devices 24 before they are deflected to the channel 14. In addition, scrapers 25 are provided, which remove any adhering material from the belts 10 to 13.

After the solidified strand emerges from the channel 14, it is transported further through the lower belt 10 and divided into individual stone blanks 26 by means of the cutting device 18. The separated stone blanks 26 can then optionally be weighed on a belt weighing line in order to be able to readjust the composition of the raw mixture in this way in order to ensure that the blends are as uniform as possible To achieve cullet bulk density of the stone blanks 26.

Furthermore, the waste heat of the high-frequency generator 23 can be used by blowing warm air generated by the generator cooling, for example by means of a hood, onto the stone blanks 26 in order to harden them, so that these have a sufficiently high strength for subsequent transport to an autoclave, but they do not must be fully generated by the heating in the region of the capacitor plate assembly 21. The length of the channel 14 is dimensioned such that the emerging strand has a desired strength, which may be increased to the necessary value by reheating with warm air from the generator cooling or another heat source.

The area of the channel 14 is expediently accommodated in a housing (not shown) which is at ground potential and which extends from the filling funnel 17 to the cutting device 18.

In order to be able to produce other formats, it is expedient if the belts 10 to 13 with their rollers 15 as well as support grids and sliding guides can be adjusted with respect to their belt levels so that the cross section of the channel 14 can be changed. The length of the blanks 26 can be changed by the cycle of the cutting device 18.

The feed rate of the belts 10 to 13 is expediently adjustable, in particular continuously adjustable, in order to be able to adapt the feed rate to the heating rate and the size of the capacitor plate arrangement 21 accordingly.

The belt strand system is suitable, for example, for the production of blanks for wall blocks, in particular lightweight blocks, for example based on lime silicate, gas or foam concrete or from coarse-ceramic material, the raw mixture containing large proportions of foam and water, so that cullet densities down to 0.2 g / cm³ can be achieved.

In the capacitor plate arrangement 21 shown in FIG. 2, two pairs of mutually opposite capacitor plates 30 are provided adjacent to the belts 12 and 13 at a distance from one another, between which two further pairs of mutually opposite capacitor plates 31 are arranged, so that in the longitudinal direction of the channel 14 a capacitor plate 30, two capacitor plates 31 and a capacitor plate 30 follow one another in the longitudinal direction of the channel 14 on the two opposite sides. The outer capacitor plates 30 are connected to the potential-free connection (0) of the high-frequency generator 23 and extend so far along the channel 14 that the stray fields emanating from the inner capacitor plates 31 are picked up by the capacitor plates 30 on both sides, so that the strand inside of the channel 14 is free of contact voltage outside the heating region. The capacitor plates 31 are shorter than the capacitor plates 30 and connected to the other non-potential-free connection (+) of the high-frequency generator 23. In addition, two auxiliary capacitor plates 32, which are connected to the non-potential-free connection (+) of the high-frequency generator 23, are provided adjacent to the bands 10 and 11 opposite one another approximately in the middle between the four middle capacitor plates 31. The auxiliary capacitor plates 32 can be approximately as long as the capacitor plates 31, but are narrow in relation to the distance d between the capacitor plates 30 and 31 and are directed with their longitudinal axis in the direction of the longitudinal axis of the channel 14. The auxiliary capacitor plates 32 together with the same-polarized capacitor plates 31 lead between the outer, differently polarized capacitor plates 30 to a field line distribution which, in addition to the entire heating of the strand, particularly supports surface heating, which contributes to a shortening of the heating distance, the auxiliary capacitor plates 32 providing additional heating in the area of the adjacent strand. In the above-mentioned applications, this leads to an additional hardening in this area and thus to a better detachment of the hardened strand from the belts 10, 11.

In the embodiment shown in FIG. 3, two high-frequency generators 23 of half the total power are provided, which are uncorrelated are. A pair of mutually opposite middle capacitor plates 31 is connected to the potential-free and to the potential-free connection of one of the two high-frequency generators 23 (potential-free supply to the capacitor plates), the adjacent capacitor plates 31 being of opposite polarity in the longitudinal direction of the strand, but in each case to one other high frequency generator 23 are connected. As a result, a field which is quite homogeneous overall with respect to the strand cross section is generated, so that the interior of the strand is also warmed well and shell formation is avoided.

In the embodiment shown in FIG. 4, in order to generate a more homogeneous field, it is provided that a distance between the capacitor plates 30, 31 in the longitudinal direction of the strand is at least approximately equal to the distance d between capacitor plates 30 or 31 located opposite one another. The polarity of the capacitor plates 30, 31 is the same as in FIG. 3, but only one high-frequency generator 23 is used.

Auxiliary capacitor plates 32 can be provided in the middle between the four middle capacitor plates 31 as in FIG. 2, but in such a way that they are also approximately at a distance d from the adjacent capacitor plates 31. The auxiliary capacitor plates 32 can also be round or oval.

If two high-frequency generators 23 which are uncorrelated are used in the embodiment shown in FIG. 4, it is sufficient if only the distance between the capacitor plates 30 and 31, which are at different potential, is at least approximately equal to d , as shown in FIG. 5. The capacitor plates 30 are each connected to the floating output of the high-frequency generator 23, which is also connected to the adjacent floating capacitor plate 31.

If two high-frequency generators 23 are used, the outputs of which are symmetrical to the zero potential, the capacitor plates 30 adjacent to a pair of capacitor plates 31 are to be connected to the zero potential of the respective high-frequency generator 23 No contact voltage is guaranteed.

The distance between adjacent capacitor plates 30, 31 lying at zero potential can be chosen to be smaller than d , as shown in FIG. 5.

The auxiliary capacitor plates 32 of the embodiment of FIG. 4 can also be connected to a further non-correlated high-frequency generator 23, in which case the distance between the capacitor plates 31 and 32 can be chosen to be correspondingly small.

In the embodiment shown in FIG. 6, the capacitor plate arrangement is as in FIG. 5, but only one high-frequency generator 23 is used. For this purpose, however, the opposing pairs of capacitor plates 31 are subjected to voltage symmetrically with respect to the zero potential, in that a capacitor plate 31 is connected to an output connection of the high-frequency generator 23 and the opposite capacitor plate 31 is connected to the latter via a phase-shifting lambda / 2 bypass line 34 or a phase shifter network, which is a Phase shift caused by half a period.

Instead, a high-frequency generator 23 with a symmetrical output can also be used. The opposing pairs of capacitor plates 31 are subjected to voltage symmetrically to the zero potential by connecting a capacitor plate 31 to one output connection of the high-frequency generator 23 and the capacitor plate 31 opposite with respect to the string to the other output connection of the high-frequency generator 23, which causes the opposite electrodes to be driven in phase . The capacitor plates 30 are then connected to the zero potential of the high-frequency generator 23.

According to FIG. 7, it can be provided that the capacitor plate 31 connected to the ungrounded connection of the high-frequency generator overlaps a small piece across the bands 10, 11 at both ends transversely to the longitudinal direction of the strand, either by means of a bend 35 or by its own narrow auxiliary capacitor plate 36 realized, whereby the field in the upper and lower region of the strand is slightly compressed for local surface heating. If this is followed by a further pair of capacitor plates 31 of reversed polarity, the more inhomogeneous field is located on the other side of the strand, so that overall good homogeneous surface heating results. One can work with one or two uncorrelated high-frequency generators 23 or with symmetrical or asymmetrical potential (with respect to the zero potential).

According to FIG. 8, the capacitor plates 31 (and possibly also 30) can consist of several partial plates 31a, 31b arranged adjacent to one another in order to keep the skin effect in the strand material as low as possible. The partial plates 31a, 31b are at the same potential and their adjacent edges are separated by a slot 37, which can be as narrow as possible due to the same potential.

In the embodiment shown in FIG. 9, a cylindrical capacitor is provided, in which the opposite capacitor plates 31 are closed to form a box 38 which surrounds the channel 14 and the bands 10, 11, 12, 13. Inside the channel 14 there is at least one capacitor electrode 39 in the area of the box 38, protected from the strand material in the channel 14 by a sleeve 40 made of insulating plastic, the outer box-shaped capacitor electrode 38 and the inner electrode (s) 39 being at different potentials , e.g. as indicated in Fig. 9.

As shown in FIG. 10, it is expedient to use somewhat concave capacitor plates 30, 31 with respect to the strand, which also contributes to the homogenization of the field. In addition, the concavity of the capacitor plate 30, 31 can be filled with a material 41 with the highest possible dielectric constant, so that its surface facing the corresponding band 10, 11, 12 or 13 is flat and abuts against it. While plastics have a dielectric constant of the order of about 2 to 4 (with a loss factor tg δ, which is extremely low, so that the plastic practically does not heat up), materials such as calcium titanate are provided here, the dielectric constant of which is very much greater than 1 is. Also show these materials have high dimensional stability and a low coefficient of thermal expansion. 11 shows the normalized potential curve between two opposing capacitor plates for a plastic layer between the strand and the capacitor plate (dashed) and for a material with a high dielectric constant between the strand and the capacitor plate (solid). Obviously there is a much smaller voltage drop across the capacitor plates in the latter case, which significantly increases operational reliability. At least in the above-mentioned applications, the continuous material has a dielectric constant of approximately 40 to 80 and a noteworthy loss factor tg δ, ie the continuous material can be heated particularly well by means of a high-frequency field.

In addition, it is expedient to provide the capacitor plates with a plastic layer on the sides facing the strips or to embed the capacitor plates in plastic in order to keep the wear on the strips moving along the capacitor plates low. However, this plastic coating should be as thin as possible so as not to influence the stress profile too much. For the same purpose, the material 41 can be ground and polished on the side facing the belt.

Claims (5)

Device for heating a strand made of an electrically conductive material, preferably solidified by the heating, in a channel (14), a capacitor plate arrangement (21), which is connected to a high-frequency generator (23), being arranged electrically insulated from the strand, and where appropriate the capacitor plate arrangement (21) has two pairs of capacitor plates (30) which are connected to the potential-free connection of the high-frequency generator (23), characterized in that a cylindrical capacitor consists of a capacitor electrode (38) enclosing the strand and at least one in There is a capacitor counterelectrode (39) located inside the strand, which is arranged in the area of the surrounding capacitor electrode (38). Device according to Claim 1, characterized in that the capacitor plates of the surrounding capacitor electrode (38) consist of at least two partial plates (31a, 31b) which are separated by a gap (37). Apparatus according to claim 1 or 2, characterized in that the capacitor plates of the surrounding capacitor electrode (38) are concave in the direction of the strand, the concavity being filled with an electrically insulating material. Device according to claim 3, characterized in that the electrically insulating material has a dielectric constant very much greater than 1, preferably greater than 100. Device according to one of claims 1 to 4, characterized in that the capacitor electrodes (38, 39) opposite each other with respect to the string can be applied symmetrically to the zero potential.

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