Solid thermal heating block from refractory phosphate concrete

FIELD: heating.

SUBSTANCE: invention relates to the field of resistive heating in industrial resistance furnaces, namely, to solid metal ceramic thermal heating blocks. The solid thermal heating block is made of a non-electroconductive heat-conductive refractory phosphate concrete, in which the heating element is poured, made of a wire heater in the form of a zigzag and belt current leads, besides, the area and the perimeter of the wire section and the area and the perimeter of the current lead section are at the ratio of at least 1:4, axes of symmetry of the heating element match axes of symmetry of the thermal heating block, and areas of connection of the wire heater with current leads in the thermal block are made in the form of cone-shaped grooves.

EFFECT: production of a solid non-electroconductive heating block combining high efficiency, reliability and simplicity of manufacturing.

2 dwg

The invention relates to the field of resistive heating in industrial furnaces of the resistance, namely, the monolithic ceramic-thermal heating units.

Practice design and operation of industrial furnaces resistance determined the requirements of the heating elements, the main of which are the following: high efficiency and reliability, durability, and lack of electrical conductivity.

It is known that the most effective process of heat transfer from hot to cold body in comparison with heating by radiation and other heat transfer is the method of contact conductivity. (Maechee, Immideate, "fundamentals of heat transfer", Moscow, Energy, 1977).

Known most effective form of heater (resistive element)made of round wire in the form of a zigzag, grounded in the works of I.A. Feldman, for example, "Calculation and design of heaters electric resistance furnace", "Energy", Moscow-Leningrad, 1966.

The closest is the heating element, patent RU No. 2311742 from 02.01.2003,, IPC H05B 3/14, selected as a prototype, made of iron material with a resistive element located in the insulating layer, covered with a composite insulating and protective layers, where the heat transfer from the resistive element n of the surface is realized through the insulating composite structure, made of several ceramic and organic substances. Insulating composite structure is designed to smooth out differences in the resistive element and the material of the heating element of thermal expansion coefficient - KTR. The resistive element is covered with insulating layer from oxidation. The heating element is performed by the sequential steps of pressing a few molds and final firing. The disadvantages of this heating element are:

- high conductivity of the working surface of the element is made of ferrous material (not less than 75%), which is unacceptable according to the electrical safety requirements of the work performed in industrial furnaces of the resistance during tempering, quenching and heating of metal products of various configurations;

- the presence of a phased technology heating element a few molds and pressing equipment greatly complicates and increases the cost of the manufacturing process.

The present invention is the creation of a monolithic electroconductive heating unit that combines high performance, reliability and ease of manufacture.

Monolithic thermal heating unit is made of electroconductive heat-conducting refractory phosphate is on concrete. It flooded the heating element is made of wire of a heater in the form of a zigzag ribbon of current terminals. Area and perimeter of the cross section of the wire and the area and perimeter of the cross section of the current terminals are correlated not less than 1:4. The symmetry axis of the heating element coincide with the axes of symmetry of the heat of the heating unit. The junction of the wire heater and the current terminals to heat the heating unit is made in the form of a conical fill.

Figure 1 - the construction of the heat of the heating unit.

Figure 2 - heating element.

Monolithic thermal heater unit (1) is made in the form of a monolithic plate 1. The linear dimensions of the block are the linear dimensions of the heating element 2, made of wire of the heater 3 (figure 2) in the form of a zigzag, as the most efficient type of heater, and a band of current terminals 4.

The heating element 2 (figure 1), is located inside the heat block 1, and the symmetry axis of the heating element 2 coincide with the axes of symmetry of the heat block 1. Heat transfer from the heating element with all of its area to the phosphate material of concrete is the contact thermal conductivity, the density of the concrete provides virtually no oxidation of the metal heater. In the heating element 2 (Figure 2) brings the e, the length of the wire and the step zigzag wire heater 3 are required calculated value of electric resistance of the heating element 2, i.e. the required capacity of the heat block. The area and perimeter of the cross section of the wire and the area and perimeter of the cross section of the current leading correlate of not less than 1:4. The length of the cold end is determined by the method of attaching the power cord and the thickness of the concrete lining of the furnace.

These conditions eliminate operational deficiencies furnace has a blown heating element at the junction of the heater with the current terminals and the emergence of a high temperature at the cold end, leading to blown fasteners power cable power supply with current terminals, namely:

- fold increase in the perimeter of the cross section of the cold end toward the perimeter of the cross section of the wire of the heater leads to the decrease in current density with the same multiplicity on the surface of the cold end, with a corresponding decrease in the electrical resistance of the cold end and the decrease of temperature upon him;

- fold increase of the sectional area of the cold end to the cross-sectional area of the wire heater leads to a short-term decrease in density of the heat flux at the cold end with a corresponding increase in thermal resistance of the cold end, the heat dissipation is th energy and

the decrease of temperature;

- the achievement of this goal is the minimum required length of the cold end, providing an additional increase of thermal resistance and the decrease in temperature along the axis of the cold end connecting the heater with the cold end to cold end connecting with the power cord.

Figure 1 shows the connection of the wire heater 3 with the cold end 4, made in the heat block in the form of a conical recess 5 to prevent energy transfer from the material of thermal block on the current terminals of the contact conductivity.

Monolithic phosphate concrete block is homogeneous, has the same conductivity on all three axis, which provides, with regard to the coincidence of the axes of symmetry of the heating element with the axes of symmetry of thermal block, a uniform temperature distribution throughout the volume, and for each plane of the block, including the alignment of the temperature at the working surface of the block. Thermal blocks are freely joined in a panel of any size for resistance furnaces required power.

The relative porosity of up to 20% crystalline phosphate concrete, on the one hand, and high strength up to 70 MPa, on the other hand, provide damping of thermal expansion of the metal of the heating element, which increases the feeling of ductility with increasing temperature, without destroying the actual heat block.

The strength and hardness of the heat of the heating unit of the phosphate concrete can be used in the furnace of resistance, which reduces energy consumption up to 35%.

The technical result of the invention is obtaining a monolithic electroconductive heating unit that combines high performance, reliability and ease of manufacture.

The practical implementation of the proposed invention is executed on resistance furnace bogie hearth furnaces and a working volume of 1.2 cubic meters, operating temperature +1150°C. the Heating furnace 28 is a monolithic thermal heating blocks of size 400×400×30 mm with a resistance of 1.5 Ω each, collected in 5 panels that allows you to organize power 3-phase power supply power up to 30 kW.

Monolithic thermal heating unit is made of electroconductive thermal conductivity of concrete, which flooded the heating element is made of wire heater with current terminals, the symmetry axis of the heating element coincide with the axes of symmetry of the heat of the heating unit, characterized in that as an electroconductive heat-conductive concrete is used refractory phosphate concrete, and area and perimeter of the cross section of the wire is the area and perimeter of the cross section of the current leading correlate of not less than 1:4, and the junction of the wire heater and the current terminals in thermal block is made in the form of a conical recesses.