Tubular electric heater

Abstract

FIELD: electrical engineering.SUBSTANCE: invention relates to devices used in electrotechnological installations, in particular to metal rod electric heaters of furnaces for performing processes of melting or heating various materials or products made thereof. The tubular electric heater includes a heating element, heating wires, which form a long hot zone, placed in the holes of support disc insulators installed coaxially between spacer sleeves on a central rod along the longitudinal axis of a protective tube, and the hot zone is divided into two parts with free ends by a common fastening unit relative to the central rod and two end support insulators having the ability to move freely when the heating wires elongate during heating in both directions from the fastening unit, according to the new technical solution, the fastening unit divides the hot zone of the heating element into two parts, determined by the established dependencies.EFFECT: increasing the operational reliability of electric heaters with a long hot zone of the heating element located at an angle relative to the horizontal.1 cl, 2 dwg

Description

[0001] The present invention relates to devices used in electrical engineering installations, in particular to metal rod electric heaters of furnaces for performing processes of melting or heating various materials or products made from them.

[0002] Rod tubular electric heaters, which melt or heat various materials by radiation, are widely known. They are made of alloys with high electrical resistance (fechrals Kh23U5T, GS23-5, etc.). The heating wires of the heating elements are connected to current leads for supplying voltage from a power source and are separately placed around the circumference in holes in support disk insulators, separated by spacer bushings. They are mounted on a central rod and are stationary relative to it, thus forming a hot zone. To protect the heating elements from the aggressive furnace atmosphere, they are placed in a protective device made in the form of a tube made of heat-resistant material [1, 2, 3, 5].

[0003] A common and fundamental drawback of known rod-type tubular electric heaters, in which the heating wires of the heating elements are made of fechrals, is their low creep resistance and heat resistance [4]. This results in both significant wire elongation and their warping (sagging) at high temperatures, even under their own weight. This results in short circuits between the wires or between the wires and the protective tube, leading to heater failure. Therefore, given these properties of fechrals, design constraints are imposed on both the heating element design and the fechrals' possible applications.

[0004] In a rod heating element, the heating wires extend along the axis of the heating element toward the unsecured (free) end of the hot zone on the central rod. To compensate for this wire elongation, a movable end insulator is installed at the free (unsecured) end of the hot zone, allowing for free wire extension and preventing short circuits. The use of a movable insulator ensures trouble-free operation of the electric heater only with relatively short (approximately up to 2000 mm) hot zones of the heating elements. This is explained by the fact that, firstly, the permissible distance between the pre-end support insulator of the hot zone and the movable insulator should not exceed the accepted distance between the support insulators [4], which prevents the sagging of the wires due to their own weight at permissible temperatures.Calculations and practical experience show that this distance should not exceed 40-80 mm, depending on the material grade and wire diameter at temperatures up to 1000°C, and this does not take into account the low creep resistance of fechral. Secondly, the mechanical resistance (external friction) to wire movement through the openings of the support insulators increases with the number of insulators, i.e., the length of the heating element's hot zone (power). This additional mechanical resistance is accompanied by a radial component of the force, which, combined with gravity, causes the wires to sag between the support insulators. This sagging, in turn, can lead to wire jamming in the openings of the support insulators as the wires extend further, resulting in short-circuit failure of the electric heater.

[0005] For furnaces with high electrical power and, consequently, large internal furnace dimensions, it is advisable to use tubular electric heaters with an enlarged hot zone (up to 4000 mm or more). However, due to the above-described disadvantages and to ensure the required furnace power, short electric heaters are also used, which are installed on the vault on both sides of the furnace space or placed opposite each other in a single protective tube [6]. This significantly increases the cost and is not always feasible due to the furnace design or its location within the production area.

[0006] The closest to the claimed technical solution is a tubular electric heater [7], which includes a heating element, the heating wires of which are connected to current leads for supplying voltage from an electrical power source and are placed radially around the circumference in the openings of support insulators installed coaxially between spacer bushings on a central rod along the longitudinal axis of a protective device in the form of a pipe made of heat-resistant material, and the hot zone is divided by a common fastening unit relative to the central rod into two parts with unfastened ends and two end insulators that have the ability to move freely in both directions from the fastening unit.

[0007] This well-known electric heater completely solves the problem of short-circuiting heating wires in heating elements with a long hot zone only when installed horizontally in a stationary furnace. When the electric heater is installed horizontally, the heating wire extensions on both sides of the mounting point will be equal only when the hot zone is divided into two equal parts, as these extensions depend on identical conditions for all wires in both parts of the hot zone. However, when using heating elements with a hot zone divided into two equal sections by a common mounting point for inclined (rotary) furnaces, the conditions for wire extension will differ due to the additional force—the force of gravity on the wires—which may result in exceeding the permissible distance between the pre-terminal support insulator and the movable insulator on the inclined side.

[0008] The problem solved by the proposed technical solution is to increase the operational reliability of electric heaters with a long hot zone of the heating element exceeding 2000 mm and located at an angle relative to the horizontal.

[0009] The stated problem is solved in that in a tubular electric heater, including heating wires that form a hot zone of the heating element and are placed in the holes of the support disk insulators, which are installed coaxially between the spacer bushings on the central rod along the longitudinal axis of the protective tube, and the hot zone is divided into two parts with both ends unfastened by a common fastening unit relative to the central rod and two end support insulators that have the ability to move freely along the axis of the central rod in both directions from the fastening unit, according to a new technical solution, the fastening unit divides the hot zone of the heating element into two parts, determined by the following dependencies:

[0010]

[0011]

[0012] where - the length of the hot zone of the heating element; β - the angle between the position of the longitudinal axis of the heating element in the working space of the furnace relative to the horizontal; - the length of the hot zone part from the fastening unit in the direction of its inclination; - the length of the second part of the hot zone. Dividing the heating element's hot zone into two parts, depending on the angle between its position in the furnace's working space relative to the horizontal, allows for the effect of gravity on the heating wires' elongation between the pre-end support insulators and the movable insulators to be taken into account. This, in turn, eliminates the permissible distance between the pre-end support insulators and the movable insulators, and, consequently, eliminates the permissible distance between the pre-end support insulator and the movable insulator on the tilted side. The use of this technical solution for rotary furnaces, in which the process is carried out at an inclined position for long periods (for example, when casting aluminum alloys into a mold), will prevent distortion and jamming of the movable insulators and, consequently, warping of the heating wires, leading to short circuits.

[0013] The invention is illustrated by drawings, where Fig. 1 shows a tubular electric heater in which the hot zone of the heating element is located in the working space of the furnace at an angle relative to the horizontal; Fig. 2 shows a vector diagram of the main forces in relative units that affect the elongation of heating wires.

[0014] In Fig. 1, 2 positions correspond to:

[0015] 1 - current lead;

[0016] 2 - heating wires;

[0017] 3 - protective pipe;

[0018] 4 - mounting unit;

[0019] 5, 6 - movable insulators;

[0020] 7 - central rod;

[0021] - length of the hot zone;

[0022] - the length of the hot zone part in the direction of the slope;

[0023] - the length of the second part of the hot zone;

[0024] β- tilt angle;

[0025] , -thermal force vectors;

[0026] , -gravity force vectors;

[0027] , -gravity force vectors acting along the hot zone axis;

[0028] , - directions of extension of heating wires.

[0029] The tubular electric heater operates as follows. When the power source connected to the current leads 1 is turned on, the heating wires 2, located in the protective tube 3, heat up to a predetermined temperature and begin to extend in different directions from the fastening unit 4. The magnitude of their extension will mainly depend on the lengths of the hot zone parts ( ), the coefficient of thermal expansion of the wire material, the temperature of the wires, the gravity forces from the weight of the wires of the corresponding part and the vectors of the acting forces from the fastening unit to the sides And movable insulators 5 and 6, located on the central rod 7.

[0030] Thermal Force Vectors And , directed in opposite directions from the fastening unit 4, cause the heating wires to lengthen according to a known relationship , Where -change in length, - coefficient of linear thermal expansion of the material, -initial length, - temperature change. Thermal forces are the result of intermolecular forces and depend on the number of molecules at a given length and temperature. Thus, at the same temperature of the heating wires, they are proportional to the lengths of the hot zone segments.

[0031] When the hot zone is positioned at an angle to the horizontal (axis ) projections of gravity vectors , on the axis of the hot zone will be equal to the forces And , constantly acting along its axis. In this case, the force is the main force causing the elongation of the section at high temperatures due to creep (low creep resistance of wires made of fechral), and the force counteracts the forces that cause the section to elongate due to creep. Gravity And as well as thermal forces And proportional to the lengths of the hot zone.

[0032] Thus, with a long hot zone, the heating element, in terms of the nature and magnitude of the extension of the heating wires, works like two short ones, but with different lengths of parts of their hot zones, depending on the angle The coordinated movement of the wires ensures normal operation without distortion or jamming of the movable insulators and maintains the permissible distance between the penultimate support insulators of the 8 free ends of the hot zone and the movable insulators, preventing wire sagging and possible short circuits. This is especially important when using fechral heating wires, which have very low heat resistance and cryptographic resistance at high temperatures.

[0033] Implementation example:

[0034] Rotary mixer oven with tubular electric heaters fixed on the roof, long hot zone of the heating element, The maximum tilt angle β during casting into a crystallizer is 25°. In this case, the hot zone of the heating element is divided by a common mounting unit into two unequal parts according to the proposed relationship. , , .

[0035] Limits of application of the proposed technical solution.

[0036] 1. Stationary furnace - mixer with tubular electric heaters fixed on the arch, a long hot zone of the heating element, In this case, the electric heaters are located horizontally ( ) And , i.e., the hot zone is divided by the mounting angle into two equal parts; the gravitational forces from the weight of the wires do not contribute to their elongation. Therefore, dividing the hot zone into two equal parts is justified by the equality of the forces acting on the wires and applying the dependence of the lengths of the parts on the angle. no need (for a parent application for an invention).

[0037] 2. Furnace with vertical arrangement of tubular electric heaters ( ) and a long hot zone. In this case, , , i.e. this technical solution is not applicable to furnaces with vertically positioned electric heaters.

[0038] Sources of information:

[0039] 1. Research and Production Center of Magnetohydrodynamics. Heating elements [electronic resource]. URL: https: / / www.npcmgd.com / catalog / products / nagrevatelnye-elementy, free (last accessed: 06.05.2025).

[0040] 2. Kanthal. Powder metallurgy. High-temperature tubes [electronic resource]. URL: https: / / www.kanthal.com / globalassets / kanthal-global / downloads / powder-metallurgy-high-temperature-tubes.pdf, free (last accessed: 06.05.2025).

[0041] 3. Electrothermal equipment: Handbook / Edited by A.P. Altgauzen. - M.: Energia, 1980. - 416 p.

[0042] 4. Svenchansky A.D. Electric industrial furnaces. Textbook for universities / A.D. Svenchansky. - M .: Energy, 1975 .-- 384 p.

[0043] 5. Patent. RF No. 133675 - Protected type heater / M.A. Zorin. - Published. 10.20.2013.

[0044] 6. Pat. RF No. 2846066 - Tubular electric heater / A.A. Temerov, V.N. Timofeev, S.N. Perfilyev [and others]. - Publ. 08 / 29 / 2025.

[0045] 7. Patent application No. 2025120563 - Tubular electric heater / A.A. Temerov, V.N. Timofeev, A.N. Openyshev [and others]. - Application 07 / 25 / 2025.

Claims

A tubular electric heater including heating wires that form a hot zone of the heating element, placed in the openings of the support disk insulators installed coaxially between the spacer bushings on the central rod along the longitudinal axis of the protective tube, and the hot zone is divided by a common fastening unit relative to the central rod into two parts with unfastened ends and two end insulators that have the ability to move freely in both directions from the fastening unit, characterized in that the fastening unit divides the hot zone of the heating element into two parts determined by the following dependencies: Where - the length of the hot zone of the heating element; β - the angle between the position of the longitudinal axis of the heating element in the working space of the furnace relative to the horizontal; - the length of the hot zone part from the fastening unit in the direction of its inclination; - the length of the second part of the hot zone.

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