RU2171960C2 - Furnace for thermal and chemical treatment of metalware in controlled atmosphere and method of its heating - Google Patents

Abstract

FIELD: metallurgy, mechanical engineering. SUBSTANCE: furnace for thermal and chemical treatment of metal-ware in controlled atmosphere and method of its heating can be utilized in production of various metal-ware, for instance, bolts, nuts, expansion anchors. Proposed furnace has zones of heating, precise heating and soaking. Each two adjacent radiation tubes in zone of precise heating are connected in pairs and in series by heat insulated goose-neck pipes brought outside limits of furnace to form common multibranch heater whose first branch is fitted on side of loading of metalware with gas burning unit and whose last branch is equipped with fume branch pipe linked to united outside recuperator. All radiation tubes in zones of heating and precise heating are mounted in horizontal planes parallel to transportation conveyer and in vertical plane in zone of soaking across exit from conveyer. Air collectors of upper and lower rows of radiation tubes are coaxially built in fume conduits and form outer recuperators united in rows and linked by flanges to fume branch pipe of radiation tubes with adjustable clearances. Method of heating of furnace lies in following: combustion products of each pair of adjacent radiation tubes of zone of precise heating are fed in sequence from first heaters into second heaters which are outside of limits of working space of furnace and its insulation and are removed from second heaters into united outside recuperators to ensure that pressure in points of their connection to fume branch pipes of radiation tubes is equal to atmospheric values of environment. EFFECT: improved quality of thermal and chemical treatment of metalware, raised efficiency of furnace and prolonged service life of radiation tubes. 4 cl, 3 dwg _

Description

 The present invention relates to metallurgical heat engineering and can be used in metallurgical and engineering plants for heat treatment of various metal products (hardware), such as bolts, nuts, washers, dowels, etc. in a variety of controlled atmospheres.

 Known furnace with radiation pipes (A.S.SSSR N 394646, class. F 27 B 17/00, publ. 11.01.74). The furnace contains gas, air collectors, chimneys, recuperators, radiation pipes (RT), transport mechanisms. RT are the main element of the furnace heating system. They burn fuel, muffling oxidative products of combustion from the working space of the furnace, filled with a controlled atmosphere with a given chemical composition and humidity. It conducts the full technological cycle of thermochemical processing of hardware, including their heating, precise heating and aging at given temperatures.

 The main distinguishing feature of this furnace is the installation of individual external heat exchangers connected to the chimney on the smoke pipes of the RT. These heat exchangers can be used for various technological functions, heating gas, air, steam, water.

 It should be noted that, in contrast to the analogue under consideration, on furnaces, as a rule, RTs are used with recuperators built into their bodies, designed to heat the air required for combustion in one heater. This with the horizontal installation of the RT leads to the deposition of soot carbon on relatively cold regenerative surfaces and a violation of the aerodynamic characteristics of the heaters. Burning soot carbon inside the RT is carried out by supplying large amounts of excess air to the combustion. In the same way, its formation in the Republic of Tajikistan is suppressed, which leads to wasteful use of fuel and a decrease in the efficiency of furnaces. In addition, burning is not an effective means of ensuring the reliability of the RT. The specified characteristics are ensured by periodically disassembling and revising the heaters, which, with a large number of RTs on furnaces, is associated with significant labor costs, so the vertical installation of recuperators on smoke pipes is preferable and allows for independent repair and revision of RTs and recuperators.

 Known closest to the proposed furnace with RT (US Patent N 3515380, CL F 23 B 5/14, publ. 04/27/71). This furnace contains a common external heat exchanger for the RT, designed to heat the air supplied to the combustion to all heaters. Here, an external recuperator is built into the furnace smoke path.

 This furnace has significant advantages over furnaces with individual heat exchangers, the maintenance and repair of which, in contrast to the general recuperator, is associated with significant labor and material costs. In addition, the intended use of the heat exchanger as a recuperator for heating the air necessary for combustion is preferable, since it improves the quality of fuel combustion in the Republic of Tatarstan, the uniformity of temperature distribution on the radiating surfaces and heating of the hardware, providing high efficiency and efficient operation of the invention directly.

 An object of the invention is to improve the quality of thermochemical processing of hardware, increase the efficiency of the furnace and the life of the RT.

 The solution to this problem is achieved by the fact that in the furnace for the heat treatment of hardware in a controlled atmosphere, containing heating zones, precise heating and soaking, a conveyor installed in them, a heating system consisting of gas and air collectors, chimneys, combined external recuperators and rows of radiation pipes placed in zones above and below the conveyor, in the zone of precise heating, every two adjacent radiation pipes are connected in pairs in series connected to the insulated elbows removed from the furnace and, forming a multi-branch heater, the first branch of which on the metalware loading side has a gas burner device, and the last branch is a smoke pipe connected to a combined external recuperator. Such a design of the precise heating zone allows more accurately heating the hardware to predetermined process temperatures and using the physical heat of the flue gases at the first recovery stage to directly heat the hardware itself, and during repairs, perform pairwise rearrangement of the heating and regenerative parts of the common heater.

 The solution to this problem is also achieved by the fact that in the heating and precise heating zones, radiation pipes are installed in horizontal planes parallel to the conveyor, and in the holding zone at the exit from the conveyor - in a vertical plane. This allows you to exclude podstovanie hardware at the exit from the conveyor before unloading.

 The solution to this problem is also achieved by the fact that the air collectors of the upper and lower radiation pipes are coaxially integrated in the chimneys and form external recuperators combined in rows, connected by means of flanges to the smoke pipes of the radiation pipes with adjustable gaps. This embodiment of flange connections allows the adjustment means to align the work of radiation pipes along the smoke path.

 The solution of this problem is achieved by the fact that in the method of heating the furnace, which includes the supply of gas and air, heating the air in external heat exchangers, the formation of a gas-air mixture and its burning in radiation pipes located above and below the heated metalware moving with a conveyor, in each pair of adjacent radiation pipes of the zone of precise heating, the combustion products are sequentially fed from the first branches of the heater to the second outside the working space of the furnace and its insulation and removed from them into the combined external recuperation tors provide a pressure at the connection with the flue pipes radiant tubes value equal to the atmospheric environment.

 The drawings show: FIG. 1 - furnace for heat treatment of hardware in a controlled atmosphere, a longitudinal longitudinal section; FIG. 2 - the same, transverse section of the furnace in the zone of precise heating; FIG. 3 - the same, a longitudinal section of the furnace along the installation axis of the upper row of the RT. Drawings are made on the example of a furnace with a U-shaped RT.

 The furnace contains a heating system with the upper 1 and lower 2 rows of the RT, separated by the height of the transport conveyor 3, gas 4 and air collectors 5, chimneys 6.

 The conveyor 3 is driven by shafts 7 and supported by support rollers 8. The furnace is equipped with loading 9 and unloading 10 windows and is divided along the length into zones of heating 11, precise heating 12 and soaking of hardware 13 at a given temperature in a controlled atmosphere, which filled its working space. The furnace is equipped with a removable vault 14. In the heating and precise heating zones, all RTs are installed in horizontal, parallel 3, planes (pos. 1, 2), and in the holding zone at the exit from 3 in a vertical plane (pos. 15). In contrast to the heating and holding zones in the zone of precise heating, every two neighboring RTs are pairwise connected in series by heat-insulated elbows 16 that are extended outside the furnace and form a common multi-branch heater. The first branches of the RT of all zones of the furnace contain gas burner devices 17, and the last (exhaust) - smoke pipes 18. Air collectors 5 are coaxially integrated into the chimneys 6 and form external recuperators 19 connected in series, connected by flanges 20 to smoke pipes with adjustable gaps.

 The furnace operates as follows. The hardware is loaded through the window 9 onto the cargo belt of the transport conveyor 3, where they sequentially pass through the heating zones 11, precise reheating 12 and holding 13, filled with a controlled atmosphere with the specified physicochemical properties and unloaded into the window 10. Heating of the hardware is carried out by RT, installed in rows above and below the hardware parallel to the conveyor in the heating and fine heating zones and perpendicularly (pos. 15) in the holding zone directly at the outlet of the hardware from the conveyor above window 10. Such a RT installation allows you to organize dimensional heating of products and to exclude them podstyvaniya at the exit of the furnace. As an example, a furnace with U-shaped RTs operating on natural gas was taken.

 In the heating and holding zones, gas burner devices are installed in the first branches of the Republic of Tatarstan, and smoke pipes are installed in the second. Combustion is stretched along the entire length of the U-shaped heater, which makes it possible to intensify the heating of the hardware at the initial stage and to exclude the possibility of them catching up at the outlet of the furnace. In the heating zone, it is necessary to carry out precise heating of the products to a predetermined temperature. This is achieved by the fact that the combustion products of the Republic of Tatarstan are not immediately removed from the furnace, but are directed by rotary elbows 16 to neighboring heaters, which allows for a more smooth heating of the products and to prevent their overheating. Such a heating system for the zone of precise preheating of the furnace also provides an increase in its efficiency, since the secondary use of the physical heat of the exhaust gases makes it possible to heat up the hardware, and lengthening the smoke path ensures the completeness of natural gas combustion in the heaters with a proportionality close to stoichiometric values (L = 1,1 - 1.3). In addition, the removal of the rotary elbows 16 beyond the working space of the furnace and its insulation increases the life of the RT, since when the first of the pairwise connected heaters is burned (burnout of the second, ceteris paribus, is excluded) after its restoration, it is possible to rearrange the neighboring heaters and reuse them use in less intense temperature conditions.

 To ensure high-quality combustion of natural gas, air is supplied to the RT furnace heated to a temperature of 473 - 673 K. Air is heated in external heat exchangers 19, which are coaxially installed pipes, connected in a series of RTs. The internal pipes of these recuperators are the air collectors 5 of the furnace, and the external ones are its chimneys 6. At the junction of the combined recuperators 19 with the smoke pipes of the RT, by regulating the gaps between the flanges 20, they provide a pressure equal to the atmospheric pressure of the environment, which makes it possible to equalize the work of the RT along the smoke path .

 The proposed furnace for thermochemical processing of hardware in a controlled atmosphere and a method for heating it are introduced on two quenching and tempering lines for the production of high-strength fasteners of the calibration workshop of the plant. The operation of the furnaces showed that they are characterized by increased efficiency and fully meet the specified technological requirements.

Claims (4)

 1. An oven for heat treatment of hardware in a controlled atmosphere, containing heating, precision heating and holding zones, a conveyor installed in them, a heating system consisting of gas and air collectors, chimneys, combined external heat exchangers and rows of radiation pipes located in zones above and under the conveyor, characterized in that in the zone of precise heating every two adjacent radiation pipes are paired in series connected by thermally insulated elbows extended outside the furnace, forming a common multi-branch second heater, the first branch of which by the load of hardware is gas-burning apparatus, and the latter - a smoke pipe connected to the joint outer recuperator.  2. The furnace according to claim 1, characterized in that in the zones of heating and precise heating, the radiation pipes are installed in horizontal planes parallel to the conveyor, and in the holding zone at the exit of the conveyor in a vertical plane.  3. The furnace according to claims 1 and 2, characterized in that the air collectors of the upper and lower rows of radiation pipes are coaxially integrated into the chimneys and form external recuperators combined in rows, connected by means of flanges to the smoke pipes of the radiation pipes with adjustable gaps.  4. A method of heating a furnace for the heat treatment of hardware in a controlled atmosphere, including the supply of gas and air, heating the air in external heat exchangers, the formation of a gas-air mixture and its combustion in radiation pipes located above and below the heated hardware moving in the heating zones, using an conveyor heating and aging, removal of combustion products, characterized in that in each pair of adjacent radiation pipes of the zone of precise heating, the combustion products are sequentially fed from the first branches of the heaters into orye, outside the working space of the furnace and its insulation, and removed from the second in the combined external recuperators provide a pressure at the connection with the flue pipes radiant tubes value equal to the atmospheric environment.

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