Heat chamber furnace for heat treatment with gaseous atmosphere quenching

Abstract

A furnace for thermal treatment with gaseous atmosphere quenching having a bell inside which there are provided a rotor regulating the gas atmosphere flow, a heat exchanger regulating the temperature of the gas atmosphere and a thermal chamber configured for thermal treatment and the following gaseous atmosphere quenching. The thermal chamber has at least a surface positioned on a side adjacent to the heat exchanger and at least a surface positioned on an opposed side to the adjacent one to the heat exchanger and wherein at least a surface has a plurality of screens which connect the inside of the thermal chamber with the inside of the bell to allow the passage of the gas atmosphere from the thermal chamber to the bell, wherein the screens are adjustable to modify the passage section and so the flow of the gas atmosphere in function of the temperature required by the thermal treatment.

Claims

1. Furnace for thermal treatment with gaseous atmosphere quenching consisting of a bell inside which there is provided a rotor regulating the gas atmosphere flow, a heat exchanger regulating the temperature of the gas atmosphere and a thermal chamber configured for thermal treatment and the following gaseous atmosphere quenching, said thermal chamber consisting of a surface positioned on a side adjacent to the heat exchanger and a surface positioned on an opposed side to the surface adjacent to the heat exchanger and wherein a surface consists of a plurality of screens which connect the inside of the thermal chamber with the inside of the bell to allow the passage of the gas atmosphere from the thermal chamber to the bell, wherein said screens are adjustable to modify the passage section and so the flow of the gas atmosphere in function of the temperature required by the thermal treatment, and wherein said screens are hinged to said surface of the thermal chamber positioned on a side adjacent to the heat exchanger.

2. Furnace according to claim 1, wherein said screens have a movement in a range of between 0 and 90 , wherein 0 corresponds to the position in which the screens are parallel to the wall of the thermal chamber, where the passage of the gas is completely closed; and wherein 90 corresponds to the position in which the screens are perpendicular to the wall of the thermal chamber, where the passage of the gas is maximum.

3. Furnace according to claim 1, wherein said screens are connected to a actuation system.

4. Furnace according to claim 3, wherein said actuation system comprises a plurality of levers controlled by a rod connected to a crankshaft, which is constrained to a rod integral to a bushing sliding on a worm screw.

5. Method for controlling the temperature in an furnace for thermal treatment with gaseous atmosphere quenching according to claim 1, by means of regulating the rotation angle of screens of the furnace and having the following steps: a) defining the map of the set points of the temperature of charge, measuring the effective temperature of charge detected by the charge thermocouples and defining the opening degree of the screens as detected by the encoder as input parameters of a controller (PLC); b) calculating the difference in temperature between the measured value and the set point value and carrying out the needed command of opening or closing of the screens to bring the system to the set value; c) receiving the command from the controller (PLC), regulating the speed of the rotor by means of the motor and consequent gas flow variation; d) receiving the command from the controller (PLC), actuating the screens by means of the actuation system and variation of the opening angle of the screen; e) reading the degree of the screens opening by means of the encoder; and f) feedback of the screens opening degree towards step b.

Description

(1) In the following, there are described various embodiments of the invention by means of examples with reference to the appended drawings, in which:

(2) FIG. 1 shows a scheme of the basic structure of a furnace for thermal treatment with gaseous atmosphere quenching.

(3) FIG. 2 shows a plant view of the rear surface of the thermal chamber, with screens in complete closing position, according to an embodiment of the present invention.

(4) FIG. 3 shows a plant view of the rear surface of the thermal chamber, with screens in complete opening position, according to an embodiment of the present invention.

(5) FIG. 4 shows an axonometric view of the rear surface of the thermal chamber, with screens in complete closing position, according to an embodiment of the present invention.

(6) FIG. 5 shows an axonometric view of the rear surface of the thermal chamber, with screens in complete closing position, according to an embodiment of the present invention.

(7) FIG. 6 shows an axonometric view of the thermal chamber, with screens in complete closing position, according to an embodiment of the present invention.

(8) FIG. 7 shows an axonometric view of the thermal chamber, with screens in complete opening position, according to an embodiment of the present invention.

(9) FIG. 8 shows an axonometric view of the screens in complete opening position, according to an embodiment of the present invention.

(10) FIG. 9 shows an axonometric view of the screens in complete closing position, according to an embodiment of the present invention.

(11) FIG. 10 shows an axonometric section of the movement system according to an embodiment of the present invention.

(12) FIG. 11 shows a flowchart of the control system of the opening angle of the screens, according to an embodiment of the present invention.

(13) As it is shown in FIG. 1, a type of known furnace 1 for thermal treatment with gaseous atmosphere quenching comprises a thermal chamber 2 therein, where it is positioned the charge of material to be treated 3. Said thermal chamber 2 is insulated and is provided on each surface 4, 4 with a series of circular apertures 5 or screens 100 which connect the inside of thermal chamber 2 with the inside of the bell 7 in order to allow the passage of the gas atmosphere from the thermal chamber to the bell.

(14) The screens 100, adjustable to modify the passage section of the gas atmosphere according to the temperature needed by the thermal treatment, and the circular apertures 5 are closed during the heating step in order to reduce the heat dispersions at minimum and to carry out the treatment with the maximum accuracy and to obtain temperature uniformity inside the thermal chamber 2. The furnace 1 comprises further a rotor 90, actuated by a motor 91 which has the function to circulate the gas homogeneously and according to predetermined speeds inside the bell 7.

(15) In case of furnaces with circular thermal chambers 2, the apertures 100 can be usually positioned at least on the rear wall 4, while the front wall 4, as well as the whole circumference of the thermal chamber 2, is provided with a series of circular apertures 5 together with groups of covers 5 which close the same. The covers 5 positioned on the circumference are held together by a shaft 50, while those positioned on the front wall 4 are held together by a disk 80; both the solutions are intended to carry out the opening of the covers 5 in synchronous. A ring 60 positioned on the circumference of the thermal chamber 2, by rotating, controls the synchronous movement of all the shafts 50 and as a consequence of the covers 5 which uncover the circular apertures 5. At the same time, the disk 80 of the front wall 4, hinged to the same, is rotated by a pneumatic cylinder 70 thus uncovering all the circular openings 5 provided. At the same time, it is carried out the opening of the screens 100 of the rear wall 4.

(16) In case of furnaces 1 with thermal chambers 2 of square shape, the apertures 100 are positioned on at least a surface, going from the one adjacent to the heat exchanger; the other surfaces are provided with mono-block screens.

(17) A first embodiment of the present invention is shown in FIGS. 2 and 3, in which the rear surface 4 of the thermal chamber 2, upwards of the heat exchanger 6 is provided with a plurality of screens 100, hinged both to the thermal chamber 2 and to a actuation system 8. The screens 100 are rotated by means of a system of levers 9, which act at the same time on all the apertures 100. Said levers 9 are controlled by a rod 10, connected to a suitably shaped crankshaft 11. The movement of the crankshaft 11 is carried out by a rod 12, integral to a bushing 15 sliding on a worm screw 14 coupled to the motor 13 (FIG. 10).

(18) According to a first embodiment of the invention, the screens 100 divide the gas passage area. In this way, they can work with a movement in a range between 0 and 90, wherein 0 corresponds to the position in which the screens 100 are parallel to the wall of the thermal chamber 2, where the gas passage is completely closed; while 90 corresponds to the position in which the screens 100 are perpendicular to the wall of the thermal chamber 2, where the passage gas is maximum.

(19) Moreover, since the screens 100 are little dimensioned, these need a smaller range and allow a greater area of the thermal chamber 2 to be covered. As a consequence, the gas quantity which can cross them and so the gas quantity passing in the heat exchanger 6 on the whole surface available for thermal exchange increases, thus increasing also the yield of the same furnace 1.

(20) Another embodiment of the present invention comprises also a control method of precision speed control cooling type (PSC), which allows an accurate regulation of the opening angle of the screens 100, thus allowing such a dissipation that the little temperature heads needed by the modern thermal treatments are respected.

(21) Such method can be in fact applied in some treatments which need to carry out little temperature variations during the cooling steps and in well determined time intervals.

(22) The temperature regulation during the cooling step, according to the desired cooling curve, is carried out as follows: the gases are first introduced from the circular apertures 5, then the temperature is regulated by controlling the gas flow (by acting on the speed of the rotor 90); in parallel a fine temperature regulation occurs, modulating further the gas flows through the angle opening of the screens 100.

(23) The traditional solution provides screens 100 which can carry out only a movement of the type opened-closed without any possibility of regulation. This implies that yet the opening of the screens causes a very high heat dispersion, i.e. the temperature can go down strongly in a short interval time in comparison with the values needed by thermal treatments. The control method, object of the present invention allows an accurate regulation of the opening angle of the screens, thus allowing such a dissipation that the little temperature heads are respected.

(24) The managing method, whose flowchart is shown in FIG. 11, comprises the following steps: a. defining S100 the map of set points of the temperature of charge, measuring S101 the effective temperature of charge detected by the charge thermocouples and defining S102 the opening degree of the screens as detected by the encoder as input parameters of a controller (PLC). b. calculating S110 the difference in temperature between the measured value and the set point value and carrying out the needed command (opening or closing of the screens) to bring the system to the set value; c. receiving S120 the command from the controller (PLC), regulating the speed of the rotor 90 by means of the motor 91 and consequent gas flow variation; d. receiving S130 the command from the controller (PLC), actuating the screens 100 by means of the actuation system 8 and variation of the opening angle of the screens; e. reading S140 the degree of the screens opening by means of the encoder; f. feedback S150 of the screens opening degree towards step b.

(25) The managing method regulating the system object of the present invention allows to vary the rotation angle of the screens 100 according to the particular thermal treatment desired. The method is carried out (FIG. 10) by an encoder 16 which reads the position of the bushing 15 and transmits the signal to the controller (PLC), which compares the measured value with the set value, i.e. the set-point input in defining step of the thermal cycle by means of the software interface provided in the operating panel (in the machine or in the control switchboard). After such comparison, in order to bring the system back to the set value, it is sent a command, both of opening or closing of the screens 100, to the inverter, which actuates the motor 13 in the same direction of the rotation direction needed. The coupling between the motor 13 and the worm screw 14 makes the bushing 15 slide which causes a movement of the integral rod 8, which leads to the variation of the opening angle of the screens 100.

(26) Moreover, the sliding of the bushing 15 modifies the position read by the encoder 16, which sends the datum to the controller (PLC) for recalculating a new command, thus creating a feedback cycle.

(27) In addition to the embodiments of the invention, as above described, it is to be intended that there exist many other variants. Further, it is to be intended that the embodiments are only example and do not limit the scope of the invention and its possible application or configurations. On the contrary, even if the above description gives the experts in the filed the possibility to realize the present invention at least according to one example configuration thereof, it is to be intended that many variations of the elements described can be made without departing from the scope of the invention encompassed by the appended claims, literally interpreted and/or legal equivalents thereof.