DE2224503A1 - Heating element - Google Patents

Description

The invention relates to a heating element made of a refractory, oxidation-resistant material with a melting point above 2500 ^° C., which is generally referred to as "resistance".

Lei known heating elements of this type, whether they are through their Shaping individually delimit a boiler room or put together to form boiler rooms of any shape and size bulky and occasionally cumbersome protection devices must be provided. ■

The invention is based on the object, while avoiding this disadvantage, a heating element of the type described at the outset To create art that better meets the various requirements of the practice than the known ones.

BATH ORIGINAL

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This is achieved with a heating element according to the invention achieves that it is roughly the general shape of a parallelepiped and in a direction perpendicular to two opposite one another Sides has a non-homogeneous structure, which when one of these two sides is heated to one for whose electrical conductivity is sufficiently high, the other side at a sufficiently low temperature! holds, which practically does not allow electrical conductivity, this structure being due to expansion | different resulting movements.

Examples of embodiments according to the invention are grounded explained in more detail below with reference to the drawings, in which

1 in a perspective view and FIGS. 2 and 3 in a side view show three variants of a first embodiment of a heating element designed according to the invention. 2a and 3a represent views along the arrows Ha-IIa and Illa-IIIa 'in FIGS. 2 and 3.

4, 5 and 6 show a side view of three variants of a second embodiment of this heating element, the 4a, 5a and 6a represent views along the arrows IVa-IVa, Va-Va u, VIa-VIa in FIGS.

7 to 10 show in perspective the assembly of several j heating elements according to the invention.

! 11 shows a fourth variant in a side view

of the first embodiment.

j Figs. 12 and 13 show in a side view and in one

Partial section along the line XIII-XIII in FIG. 12 is another

[ Variant of the first embodiment.

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The general shape of a heating element according to the invention, made of a fireproof, oxidation-resistant material as it is used for "the manufacture of resistors, is parallelepipedic or roughly that of a parallelepiped. It thus has the general shape of a block,. Its Length L is greater than height H, which in turn is greater than the thickness E (Fig. 1),

The structure of the heating element is not homogeneous in this way between two opposing sides designated F 1 and F ₂ (generally those which are separated from one another by a distance equal to the height H of the element) and essentially perpendicular to these two sides designed that when one of the two sides F ,, and Fp, here the side F ,,, is heated sufficiently high that it becomes electrically conductive, the other side remains sufficiently cold and thus practically non-conductive. Due to its side Fp and the _{material present between the sides F ^ and F 2} , the heating element itself forms a suitable thermal protection. . ,; In addition, this structure is designed so that it absorbs the movements that result from the expansion differences. ·

In practice, the structure of the heating element is designed in such a way that

• that the temperature difference between the two sides F ,,

• and F _{2 is} in a range in which the resistance of the

': cold side is at least a hundred times greater than the resistance the warm side.

! The heating element is at the level of the two ends lying in the longitudinal direction, for example by means of platinum contacts ! powered by electricity.

: In general, the material from which the erfindungsge-ι if heating elements exist, 'partially or completely "stabilized" zirconium oxide in its high temperature

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BATH ORIGINAL

stable shape, d. H. in its cubic form. It is believed that this stabilization can be achieved through additives of lime, xttrium oxide, rare earth oxides, magnesium oxide or obtained by other additions.

The heating elements according to the invention can also consist of a certain composition of the pyrochloride type on the basis of zirconium oxide of the formula Zr ₉ T ₂ Oj-, where T is a metal, preferably a rare earth.

":.. The non-homogeneous structure of the heating element can be designed in various ways. According to a first embodiment, this non-homogeneous structure is obtained by which the heat transfer from the side F. to the side F ₂ is limited to a sufficient extent so that the Side F _{? Maintains} a temperature at which it is non-conductive, through holes and cutouts which are continuous in the body of the heating element and substantially perpendicular to that side which connects the sides F. and F ₂ with each other, the ratio of Void to compact body of the order of 0.1-0.2 to 3 is chosen when the material from which the element is made is partially or fully stabilized zirconia.

The arrangement and shape of these holes and cutouts is chosen so that the electric current is only close the side F ^ can flow when that is near that side F ^ existing material of the element brought to a temperature becomes, in which it becomes conductive.

1, 2 and 3 are three variants of this first embodiment shown.

In the exemplary embodiment according to FIG. 1, the heating element designated as a whole by 1 - as shown - is a number of holes or bores 2 and cutouts 3, which the

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Have the form of a slot located along a broken - extends \ line portions 3a, which extend over a certain longitudinal dimension parallel to Seite.F ^, as well as portions 3b and 3c of general shape extending in sentlichen we perpendicular to the side F . extend. This structure \ is designed so that this side F. is connected to the cold side Γ Fp via sections 4 of the element, which have a relatively small cross-section due to the shape of the cutouts 3. Because of this configuration, the transmission of noise from the side F. to the side Fp is greatly reduced.

The sections 3a are formed so that the thickness of the Element at the level of the side F ^ is relatively small, with through the section with this thickness dimension of the electrical; tric current flows. In practice, this is in Fig. 1; Thickness dimension marked with D ^ as well as that of the section te 4, which is denoted by Dp, on the order of 1-3 to 5-10 mm.-. .

Advantageously, at the ends (in the longitudinal direction of the Element considered) large recesses 5 are provided, which can have a shape as can be seen from Fig. 1, and which can serve on the one hand to suspend the element and on the other hand for the arrangement of the power supply lines 6, which, as shown in FIG. 1, are advantageously set at the level of those edges or sides of the recesses 5 which '' are closest to the F ^ side. These power supplies can ■! consist of platinum plates that are glued on under pressure: or are cast on.

It may be advantageous to design the heating element 1 so that the temperature on the side F ^ at least on one Part of their longitudinal measurement increases. For example, it can be the embodiment of FIG. 1 it may be desirable that the

BATH ORIGINAL

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Temperature along the arrow f ,, becomes higher.

To achieve this, it is sufficient to choose the size and arrangement of the holes and cutouts so that they are in the area of the Page F> | in the direction of arrow f ,, a progressively larger increasing resistance results. For example, like Pig.1 shows, in the first section 3, starting from the left, form a section 3d between section 3b and your Section 3a lies and is inclined so that the cross section of the conductive portion during operation of the element decreased as shown.

This means that a heating element is damaged and out of operation 1 is avoided due to the formation of a crack interrupting the flow of electrical current, which could form in the area of the side F ^, this is advantageous by incisions 7b, which run perpendicular to the side F ^, divided into several parallel lamellae 7a, such as .es is shown in FIG.

In the design modifications according to FIGS. 2 and 3 is In principle the same structure as in the one based on FIG. 1! described embodiment provided, but the ! Holes and cutouts have different shapes.

Through the rectangular holes 8 and the cutouts 9 in the form of a U or I in the embodiment of FIG. 2 and through the circular holes 10 in the embodiment of FIG. 3, the heating elements in question are designed so that the sides F ₁ and F _{p are} only connected to one another by relatively narrow bridges P, which reduce the heat transfer from side F ^ to side Fp to a sufficient extent. In addition, these holes and cutouts are designed in such a way that the electric current can only flow through the side F ^, a special, elongated and inclined cutout 11 is provided in the heating elements according to FIGS Dimensions can be seen from these figures.

209852/0625 bad original

As in the embodiment of FIG. 1, the holes and Cutouts 8, 9 and 10 are arranged between two recesses 5. In the area of which the power supply lines (not shown) are provided. Furthermore, as in the embodiment according to FIG. 1, the distribution of the Holes and cutouts 8, 9 and 10 advantageously, as shown, chosen so that a temperature gradient in the direction of the arrow f ^, as shown in FIG was explained in more detail. . . -

The cross-sectional shapes of the elements 1 according to FIGS. 2 and 3 are shown in Figs. 2a and 3a.

As in the exemplary embodiments according to FIGS. 2 and 3, in the modified embodiment according to FIG. 11 there are at least certain features that are also present in the embodiment according to FIG. 1. In this case it is not intended to obtain a temperature increasing along the side F ^. On the contrary, the cutouts are practically symmetrical too. the center line XX arranged and formed. Even if the general shape differs according to the illustration, the holes 2, the cutouts 3a and 3b and the recesses 5 of the embodiments described above are found again. Likewise, in a special shape, as shown in FIG. 11, the sections 4 are present which connect the sides F .. and F _{2 to} one another. The thickness D ^ of the element in the area of the side F ₁ and the sections 3a and the thickness D _{2 of} the sections 4 correspond to the dimensions given above.

According to FIG. 11, incisions 20 are provided which, as shown, _{extend perpendicular to the side F 1} and have a length h of 0.5 to 3 cm. These incisions 20 are formed at the level of the sections 4.

The heating element formed in this way, as shown in FIG. 11 shows, provides good thermal and electrical insulation, '

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a good power-temperature ratio, a favorable one
Possibility for suspension, especially in the area of the
Recesses 5, good elasticity, good capacity for stretching forces and finally a considerable heating surface.

During the operating state of an element 1, the
Elongations through the sections 4, which the rare F ^ and
Fp of the embodiment according to FIGS. 1 and 11 with one another
connect, and in the embodiment according to FIGS
absorbed by the bridges P.

While in the embodiments according to FIGS
and 11 the ratio of cavity to compact body is in the vicinity of 1, this ratio of the embodiment according to FIG. 12 is in the range of the lower limit given above!

i ze at about 0.1. This element according to FIG. 12, like the j according to FIG. 11, has a side F ^ provided for the heating,
whose temperature is constant on the useful section. ', \

This heating element is provided with two large cutouts 20, which extend approximately parallel to the side F .., whereby 'there is a thickness dimension D ^ of the warm side F ^' (D ^ corresponding to the dimensions given above), and the one with the Side F_ are connected by two incisions 21, ^l which are essentially perpendicular to side F,. run until ι on a section 21a, which is in the vicinity of the cutouts 20! is formed and extends at an angle of about 45 °. The incisions 21 are open _{on the F 0 side.} On this ■

C. I.

On the side F ₂ , the element thus consists of three parts 22, 23
and 24, which each have recesses 25, 26 and 27, \ of which the first and third recess for the arrangement ■: serve the power supply lines (which are not shown and are very easily accessible due to this design), where-
the purpose of the second recess is to obtain a lighter structure.

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In the legs 25a, 25b; 26a, 26b and 27a, 27b, which j enclose the relevant recesses are for the! Suspension of the heating element holes 28 to 33 provided

see. . ^!

The section 21a of the incisions, which runs obliquely at an angle of approximately 45 °, forms a protective device! and it ensures thermal protection. from the warm side ■ j

- ■ ■ * - j

In addition to the cutouts 20 and 21, cutouts 34 are provided which are generally perpendicular to the side F ₁
extend and arranged in the body of the element between the cutouts 20 and the recesses 25, 26 and 27
are. Due to their design and arrangement, as emerges from FIG. 12, these cutouts 34 ensure
good management of the current flow and localization
possible cracks caused by mechanical forces
can be caused on thermal shocks and on
burnout of the material can be attributed to it. Further
are notches 35 in the vicinity of the ends of the element provided, which run perpendicular to the side F ₁ and are open to this ί. These incisions serve as thermal protection and to relieve stretching forces.

So that you get an approximately constant thickness of the warm section
or the heating section in the area of side F ₁ ,
is a through hole 3 <S between the cutouts 20
preέβηβη.

Finally, in addition to the. ι slot-shaped incisions 7b, which those in the execution! shape according to FIG. 1 and for the heating section | serve as thermal insulation, the side F ₁ with for example
two recesses 37 and 38 provided through which they a T-
and U-profile is obtained, as shown in FIG. This gives you

209852/0625

a "better creep behavior.

In the area of the EV> side, there is advantageously one in the longitudinal direction extending incision 39 is provided, as shown in FIG.

The heating element according to this embodiment is not as light as the previously described embodiments, because of the ratio of cavity to compact body is much smaller. On the other hand, by reducing the cutouts that are designed so that the occurrence of Cracks are avoided, faster and easier manufacture. Due to the greater weight, there are also several suspension points intended.

As can be seen from the above description and the figures, in the embodiments according to FIGS. 11 and 12, the electrical current flow is to be conducted in such a way that it must flow _{through the side F 1.}

To illustrate, it is stated that in an embodiment in which the material of the heating element with zirconium oxide. 4 % lime is, the temperature of the side F ₂ is 1200 ⁰ K when the side F ^ has a temperature of 2200 ⁰ K.

According to a second embodiment, the non-homogeneous structure of the heating element 1 perpendicular to the sides F ^ and Fp is obtained in that a section A with low porosity, in the order of magnitude of less than 10 %, is formed on this element, in particular the side F ^, which is to become conductive, this section with low porosity is connected to a section B which has an increased porosity of over 30 % and in particular comprises _{the side F 2.} This structure is designed in such a way that the side F ₀ , when the side F .. is heated to a sufficiently high temperature at which it is electrically conductive, remains sufficiently cold that it is practically non-conductive.

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The section with lower porosity can be replaced by stable! -, ized zirconium oxide are formed, corresponding to the material from which the heating elements 1 of the embodiments according to FIGS. 1 to 3 exist.

The section with increased porosity, in which the pores take over the task of the cutouts in the exemplary embodiments according to the embodiment described above, can consist of the same material as the section with dense or low porosity or of a more economical material such as eutectic in ZrO ₂ - AIpO ₇ , aluminum oxide or another heat-resistant material that does not chemically react with the zirconium oxide.

In practice, the weakly porous section _{comprising the side F 1} will have a density of the order of 4.5 and the _{porous section comprising the side F 2 will have} a density of about 2.

To produce a heat-resistant body with the specified porosity, which is necessary for the formation of the side Fp comprehensive section B is required, one can fall back on known ceramic methods, in particular on forming, pressing and sintering (see, for example, "Ceramic Fabrication Processes" by W.D. Kingery, 1958, ' John Wiley).

After section B has been formed, this becomes with the section A connected, for example, by a spraying process, - in which one uses a gas burner in a known manner ■ Plasma used.

As an example, it should be mentioned that for the production of an element 1, in which the distance between the sides F ₁ and F _{2 is} 110 mm and whose _{section comprising the side F 1 is} made of stabilized zirconium oxide with a porosity '

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of 6%, there is, which side is to be heated to a temperature of 2200 ⁰ K for which the page F ₂ comprehensive portion on which the temperature in the area of this page Fp should not exceed 1200 ⁰ K, a porous material made of zirconia or another mixture of refractory oxides with a porosity of 35 % is used.

4, 5 and 6 are three possible variants for the Embodiment of the heating element 1 shown, which is formed according to this second embodiment.

The embodiments according to FIGS. 4 and 6 are in the longitudinal direction of the element formed symmetrically to a plane passing through the center. According to FIG. 4, there are recesses 5 parts 13 are provided corresponding to those in FIGS. 1 to 3 and according to FIG. 6, which likewise have recesses 5 form. As with the previously described embodiment the current leads, not shown, on the relevant surfaces of the sections A in the area of the recesses 5, arranged. Due to the symmetrical design of these embodiments according to FIGS. 4 and 6 is in the area of Side F ^ no temperature gradient available.

In order to obtain a temperature gradient, section A can be designed as shown in FIG. 5, where 'he in the direction of the arrow f ^, which shows the course of increasing temperatures indicates a decreasing cross-section. The element shown in FIG. 5 is used for the suspension provided with a hole T.

FIGS. 4a, 5a and 6a show the cross-sectional shapes of the elements according to FIGS. 4 to 6.

The heating elements designed according to the invention stand out characterized by excellent behavior over a long period of operation. So an element worked according to the in

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Fig. 1 illustrated embodiment, the side F ^

the heating wall of a furnace formed, for 500 hours trouble ^l

free. At the end of this test, an exam!

the element neither damage nor any changes i

change in its properties. The data '

of the experiment were as follows: - j

Temperature in the furnace chamber. 2073 ⁰ K "'■

Dimensions of the chamber 110 χ 25 x 16 ram

Dimensions of the element 220 x110 χ 30 mm ^!

Thickness of the heating section (D ^, Fig. 1) 3.5 mm '

Length of the heating section 120 mm

Width of the heating section 30 mm

Applied voltage 167 V

Amperage 8.7 A.

Power consumption 1.45 kW

On the surface of this element, after the connection

«ΙίλΙί 7nnoii lir \ t.or>Of> hi oril 1 c >>io?> WSr * Trvtir \ eraY \ foe + rrao + an + μοτιγΙουί

such areas of different colors are found v / ground, i

; which are delimited in Fig. 1 by the curves C ^, C ₂ , C and C. These curves represent the isotherms, each corresponding to a temperature of 1400 ⁰ K, 16oo ° K, 190O ⁰ K and 2025 K ^0.

With heating elements according to the invention, it is possible to produce ovens to train any design and dimensions. 7-10, several embodiments of ovens are shown shown.

Fig. 7 shows a furnace in the form of a vault with horizontal Axis composed of elements 1 with a trapezoidal cross-section, corresponding to that shown in FIG. The various elements 1 lie against one another without any special connecting elements being required. that are. The power supply lines 6 are arranged as in the exemplary embodiment according to FIG. 1 ″.

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wires denotes, which the power supply lines 6 with the Connect power source.

The elements 1 which are used in the construction of one shown in FIG Furnace with a rectangular cross-section are used, correspond to that shown in FIG. The power supplies are in turn denoted by 6 and the lead wires by 15. The three elements 1 that make up the ceiling of the furnace are held in place by a mechanical suspension, preferably by a heat-resistant fastening Stole.

As Fig. 9 shows, a furnace with a trapezoidal vault be formed when using elements 1 according to FIG. 3 and spacers 16, which are not electrically conductive are and for example consist of porous zirconium oxide or aluminum oxide, each between two elements 1 are used. The elements 1 and 16 can be mechanically suspended in their relative position to one another (you can just as easily let them rest on top of each other as with a kit).

The three ovens described each have a boiler room with a horizontal axis. In contrast, FIG. 10 shows | an embodiment with a vertical axis. There are 4 egg ' mentθ 1 provided according to Fig. 1, between which spacers 17, are arranged. The connection of the elements 1 and 17 to one another is formed by an enclosure of the mold, which holds and guides the entire structure in its position.

So that the elements forming a furnace 1 in the for the beginning Conductivity required dimensions are preheated, one can in anishe known ¥ ice a not shown Insert the preheating element into the boiler room to open the sides F ^ of the elements forming the furnace to the minimum temperature at which the material of these elements becomes conductive.

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Heating elements designed according to the invention have a number of advantages. They themselves ensure a suitable ι thermal protection and enable the construction of ovens with horizontal ■ j zontal or vertical axis, and they can have any desired temperature gradient in the heating room. Since there is no mechanical stress, an element has a very long service life of several thousand hours continuously at a temperature of 2200 ^° K. The heating elements ensure reliable operation even if cracks appear on the heating surface, they enable the design of ovens to a great extent numerous geometrical shapes and with different capacities and they can finally be used in an oxidizing atmosphere.

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Claims (12)

Claims 1. Heating element made from a fire-proof, oücydation-resistant Material characterized in that it is approximately in the general shape of a parallelepiped and in a direction perpendicular to two opposite sides (F ^, Fp) has a non-homogeneous structure, when one of these two sides (F ,,) is heated a temperature high enough for their electrical conductivity, the other side (m.p.) to .ein sufficient holds low temperature, which practically does not allow electrical conductivity, with this structure changes due to differences in expansion absorbs resulting movements. 2. Heating element according to claim 1, characterized in that it consists of completely or partially stabilized zirconium oxide or of a certain composition of the pyrochloride type based on zirconium oxide of the formula Zr ^ T ₂ Op. is formed, where T is a metal, in particular a rare earth, and holes (2, 5, ü, 10) and cutouts (3, 9, 11, 20, 34) in the body of the element (1) in are formed essentially perpendicular to that surface which connects the two opposite sides (F .., F _? ), one of which can be heated to a temperature high enough for its electrical conductivity, the ratio of cavity to compact body in the range from about 0.1-0.2 to 3. 3. Heating element according to claim 2, characterized gekennzeichne ¹ 1, wherein the ratio of cavity is too compact body approximately at the first - 17 - 20 985 2/062 4. Heating element according to one of claims 2 and 3, characterized in that the holes (2, 5, 8, 10) and cutouts (3, 5, 9, 11, 20, 34) are designed and distributed so that on the one hand the two opposite sides (F ,,, F ^) ₁ of "which one can be heated to a temperature sufficiently high for its electrical conductivity, are connected to one another by sections (4) of relatively small cross-section and on the other hand the electrical current through that side (F ^) must flow, which has a sufficiently high temperature for its conductivity. 5. Heating element according to claim 4, characterized in that that the holes (2, 5, 8, 10) and the cutouts (3, 9, 11) are arranged so that the temperature the side (F ,,) through which the electric current flows, rises along this side. 6. Heating element according to claim 4, characterized in that that the holes (2, 36) and the cutouts (3, 20) are distributed so that the temperature of the side (F ,,) through which the electric current flows, is uniform along this side. 7. Heating element according to claim 1, characterized in that the ratio of cavity to compact body is approximately at the lower limit of the range from 0.1 to 3 and cutouts (20) are provided which are generally parallel to the heating side (F .) and are connected to the non-heating side (Fp) by incisions (21) which are generally perpendicular to the heating side, certain of which have a section (21a) inclined at an angle of about 45 ° and divide the element (1) into several parts (22, 23, 24) that further cutouts (34) are provided, which - 10 - 2 0 9 8 5 2/0675 BAD OR] QiNAL extend perpendicular to the side to be heated and in the body of the element between those to be heated Side (F ,,) parallel cutouts (20) and the non-heating side (Pp) are arranged, as well Incisions (35) perpendicular to the heating side and near the ends of the element are open to this, and recesses (25, 26, 27), which are to the non-heating side (Pp) are open. 8. Heating element according to claim 1, characterized in that substantially perpendicular to the arrangement of the two opposite sides (F. ,, Fp), one of which is provided for the electrical current conduction, the element (1) successively a first section (A) with low porosity of less than 10 ^c / o, which comprises the side (F.,) provided for the electrical line, and has a second section (B) with increased porosity of over 30 * / ■> . 9. Heating element according to claim 8, characterized in that the first section (A) made of stabilized zirconium oxide with a density of about h, 5 and the second portion (B) made of zirconium oxide, outectic Zirkonor.yd-Al ₂ O ^ or aluminum oxide alone exists, 'where the density of this second section is approximately 2. 10. Heating element according to claim 9, characterized in that the first section (A) has one in the longitudinal direction of the heating element (1) has a decreasing cross-section, 11. Heating element according to one of claims Ibis 10, characterized in that the side (F ₁ ) through which the electric current flows through incisions (7b) which extend perpendicular to this side (F ,,) in the longitudinal direction of the element , is divided into mutually parallel lamellae (7a). 20985? / 06? F 12. Heating element according to one of claims 1 Ms 11. characterized in that the heating side (F ^) has recesses (37, 38) through which them in a vertical section in the longitudinal direction receives a structure in the form of a T and U, 209857/0625 Blank page