CS324991A3 - Vacuum furnace for heat treatment of metallic workpieces - Google Patents

Abstract

The vacuum furnace (1) contains a thermally insulated treatment chamber (5), in which the workpieces are arranged on a charge support (30) inside the useful space (27). Outside the treatment chamber, there is a blower (19) for gas circulation and a heat exchanger (26) for gas cooling. The workpieces are heated by heating pipes (31) which are arranged around the useful space inside the treatment chamber. The heating pipes serve simultaneously as gas supply pipes in the convective heating of the workpieces and the subsequent gas chilling. To this end, the gas supply pipes are provided in the region of the useful space with radial openings (32). The furnace guarantees a particularly homogeneous chilling of the workpieces in the entire useful space by an intermediate bottom (10) with a central gas passage opening (11) for optimising the flow conditions and by the possibility of blowing onto the workpieces simultaneously radially and axially, it being possible periodically to change the direction of the axial blowing. To this end, the gas supply pipes are equipped with additional gas outlet openings (34, 35) and closure elements (36, 37) and the walls of the treatment chamber are provided with closable gas outlet openings (13, 15). <IMAGE>

Description

MP-934-91-Ce

Vacuum Furnace for Heat Treatment of% &amp;amp;

Technical field i> O I! o <c-1 iS ^> l · Isra-Si o '«Α. ea i r. "V)

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a vacuum furnace for the treatment of suckling workpieces in a working chamber having heating-insulated walls with closable gas outlet openings and a useful space with a casing and faces surrounded by gas supply pipes that are parallel to the processing chambers and have in the area a shell of useful space-hole openings pointing radially inwardly, with a blower positioned outside the working chamber and with a heat exchanger, wherein the blower discharge side is connected via a gas distribution space to the gas supply tubes and the blower nozzle is connected directly to the working chamber during the heating phase and during the heating phase cooling phase with heat exchanger.

Background Art

A vacuum furnace of this type is described in German Pat. No. 28,398,807 and consists of a cylindrical pressure vessel in which a heat-insulated working chamber with heating devices is provided. For the heat treatment, the workpieces are placed in the utility chamber of the working chamber on the carrier and heated either in the vacuum or in the circulation of the working gas at the setting temperature. The circulation of the working gas is provided by the blower located outside the working chamber, which extracts the gas therefrom and blows it back through the gas distribution chamber and the gas supply pipes under pressure into the working chamber. The gas supply pipes are arranged parallel to the longitudinal axis of the working chamber and surround the workspace with the workpieces. In the working area, the gas supply pipes have nozzle openings for blowing the workpieces with working gas. To cool or quench workpieces, the blower suction branch is separated from the working chamber and connected to a heat exchanger 2 arranged outside the working chamber. At the same time, the gas outlet openings in the thermally insulated walls of the working chamber open so that the working gas can escape from the working chamber and, after passing through the heat exchanger, can be blown back by the fan as cooling gas back into the working chamber.

As an alternative to the radial blowing of workpieces described in the cited above. pat. in the prior art, one-sided axial blowing is known, followed by unilateral axial blowing combined with radial blowing as described in the German patent. 32 08 574, and blowing of workpieces from all sides. Vacuum furnaces of this type are mainly used for hardened tools and components of various kinds with different types of steels. However, they are also applicable to other heat treatments such as annealing and soldering.

The quality of the heat treatment depends to a large extent on the type of cooling operation. During the cooling of the workpieces in the gas stream, the greatest possible homogeneity, that is to say at least the thermal difference between the individual workpieces, is to be achieved. Especially in the case of large dimensions of the useful space, this is not sufficiently ensured in the known blowing processes. space. In addition, there is an influence of the shapes and sizes of the structural components on the processing result. It is an object of the invention to increase the uniformity of the treatment result for all components of a single batch by improving the gas flow during cooling and to allow optimum cooling adaptation to different shapes and sizes of chilled particles.

SUMMARY OF THE INVENTION

The essence of the vacuum furnace according to the invention is that, in the working chamber, an intermediate gas passage is disposed perpendicular to its axis, which separates the gas distribution chamber, which is returned to the blower and the gas distribution chamber, from each working chamber. the inlet pipe has two additional inward-facing gas outlet openings, one of which is located in the region of the gas distribution space and the second end of the gas supply pipe remote from the gas-evacuation space outside the useful space housing, the gas outlet openings of the gas supply pipe being closed by closing elements and closable the stage openings are arranged in the walls of the gas distribution chamber and in the bottom of the working chamber facing away from the separating gas space.

In the vacuum furnace according to the invention, a very uniform cooling process is carried out for all workpieces of one batch due to the fact that the workpieces can be blown simultaneously radially and axially during the cooling phase. Alternate opening. and closing the locking elements of the outlet openings to ground the axial blowing direction several times during the cooling operation.

In a vacuum furnace, it is particularly advantageous if the gas supply pipes are simultaneously designed as a heating element. For this purpose, these tubes are made in a space of thermally conductive material and bonded to external current sources. The heating tubes are separated by ceramic insulating parts from other parts of the gas supply tubes.

The problem associated with adapting the cooling conditions to the individual shapes and sizes of the workpieces is simply solved in the vacuum oven according to the invention in that the axial-radial volume flow ratio can be set to any value during the heat treatment only by partial closing and opening of the gas outlet openings. supply pipes. This is made possible by the fact that the seal elements for the two gas outlet openings of each gas supply pipe are designed as sliding tubes arranged in a gas supply pipe and connected by a rigid rod. 4 With the appropriate length of the sliding tubes and their distance, the two gas outlet openings in the gas supply pipe can be alternately opened and closed by axial displacement through two end positions. This makes it possible to change the direction of the axial blowing. According to this direction, there are two different cooling phases: in the cooling phase 1, an axial blowing of the gas distribution space takes place through the central outlet opening of the intermediate bottom. In the cooling phase 2, the workpieces are axially blown in the opposite direction, whereby the working gas is sucked out of the useful space through the central opening inserted. Thus, the inserted bottom provides optimum gas flow in the useful space, thereby achieving a homogeneous temperature throughout the cooling operation.

In addition, such a locking device allows the axial volumetric flow rates to be continuously adjusted during operation, while simultaneously closing the two outlet openings to completely disengage the axial blowing, with the appropriate length and distance of the slide tubes.

The adjustment of the closing devices is preferably carried out by "adjusting devices which can move the sliding tubes in axial direction. It is particularly advantageous to close the tube which is at the end of the closing device away from the distribution gas chamber in the axial direction. In this constructional measure, the working gas pressed into the gas supply pipes acts by permanently axial force on the closing device and their adjusting device, in which case the adjusting device can be arranged so that the axial screen acts as The tensioning device can then be connected to the closing devices by simple cables or chains, and the same applies to the connection of the two slide tubes of the closing device. 200 C. 5

According to an alternative embodiment of the invention, the seal elements of the two gas outlet openings of one gas supply pipe are formed by a barrier tube which slides through the gas supply pipe, has two openings that have an axial longitudinal opening that is disposed in the nozzle area of the gas supply pipe and between the flow tubes. the gas inlet openings and whose width corresponds to the diameter of the nozzle openings.

This stop tube is oriented in the gas supply pipe so that the axial longitudinal opening does not cover the nozzle openings of the gas supply pipe.

As in the aforementioned locking device of the two sliding tubular sections with the connecting rod, the two gas outlet openings of the gas supply pipes can be alternately opened and closed by this closing tube by axially moving it.

In this case, the working gas volume during axial blowing can be adjusted during the operation of the furnace by suitable shifting of the chute. In addition, the sliding tube can be adjusted. change the volume of radial flow. For this purpose, the openings of the closing tubes corresponding to the nozzle openings of the gas supply pipe are enlarged in the tangential direction by the width of the axial longitudinal opening. Consequently, by rotating the stop tube about its axis, the volume of the radial flow can be regulated from a maximum value to zero. The adjustment of the shut-off tubes is carried out with the advantage of the positioning devices which move the shut-off tubes one-way and turn the angle around the longitudinal axis corresponding to the radial opening angle of the nozzle openings. 1 in these stop tubes it is advantageous to be closed at the end facing away from the gas distribution space. 6 Overview of Drawings

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a longitudinal section through a vacuum furnace according to the invention during a heating phase, analogous to a baking section during cooling phase 2, FIG. Fig. 4 shows a gas supply pipe and a closing device, in various positions, and Fig. 5 a gas supply pipe and a stop tube in various positions. EXAMPLES OF THE INVENTION

FIG. 1 shows a longitudinal section through a vacuum furnace according to the invention in a vertical position, but in other embodiments it may be a horizontal vacuum furnace.

The vacuum furnace 1 consists of a pressure cylinder 2, which is closed from the top and bottom by the bottom, and the bottom bottom serves as a door and can be lowered to feed the charge. In the furnace 1 there is a working chamber 5, a blower 19 with a separating gas space space located above the working chamber 5, and a heat exchanger 26 between the upper side of the working chamber 5 and the distribution gas space 21 for cooling the furnace. gas during the cooling process. The furnace 11 has off-sliding sliding bushings 17, 18, 40 for controlling the shutter valves and sliders to control the flow of gas. The main osapracní chambers coincide with the longitudinal axis, 4 furnaces 1.

The working chamber 5 is formed by the walls 6, the bottom 2 and the cover plate T, which are all made of a highly heat-resistant and heat-insulating material. In the working chamber 5 there is a useful space 27 for heat treatment of the workpieces, which is a limiting skirt 28 and faces 29 which are parallel to each other.

V perpendicular to the main axis 4 of the working chamber 5, In order to optimize the flow conditions in the working chamber 5, an intermediate bottom 10 according to the invention is inserted above the useful space 27 according to the invention with a central gas passage 7 through the opening 11, which is perpendicular to the main axis 4. distribution space 12,.

At the same time, the cover plate 7 of the working chamber 2 forms the cover plate of the gas distribution chamber 12 and has a central suction opening 8 which can be closed by the slide valve 22 or connected to the suction nozzle 20 of the blower 19. In the walls 6 of the working chamber 2 are arranged according to the invention the gas outlet openings 13 and the central outlet opening 15 at the bottom. These openings 13, 15 can be closed by flaps 14, 16. Fig. 2 shows the connection between the gas distribution chamber 12 and the heat exchanger 26, or, as shown in Fig. 3, between the service space 27 around the working chamber 5 to the heat exchanger 26. Slide gate 22 in the suction opening covering it 2 of the working chamber 5 consists of two coaxial cylinders 23, 24 and has two switching positions I and II. In the I-position (Fig. 1) the inner cylinder 23 is connected to the suction branch 20 of the blower 19, while in the position II of Figs. is located in the gas distribution space (d) of the separating chamber (12) in this switching position (II) of the slide (22), the suction opening (2) in the cover plate (T) is closed and at the same time the suction branch (20) of the blower (19) is connected with a heat exchanger 26 arranged between the working chamber 2 and the gas distribution space 22 ''

In the switching position I of the slide valve 22, the blower 19 presses the working gas drawn from the working chamber into the distribution gas space.21a and from there into the gas supply pipes 32 · The gas feed pipes 22 'extend parallel to the longitudinal axis 6 into the working chamber 2a. between the sheath 28 of the useful space 27a and the walls 2 of the working chamber 5 up to the vicinity of 9. The gas supply pipes 32 surround the useful space 27 in a regular arrangement. 8 The gas supply pipes 31 are provided with nozzle openings for radially blowing the workpieces stored in the useful space 27 32 which extend radially inwardly and lie in the area of the useful space shell 28.

In the embodiment shown, the gas supply pipes 31 in the area of the useful space 27 are formed simultaneously as a heating device. For this purpose, in this part of the working chamber 5, they are made of a thermally conductive material and electrically insulated against the remaining length of the gas supply pipes 31 beneath the inserted bottom 10 by ceramic insulating tubes 33. According to the invention, an additional, axial blowing of the workpieces is provided. radial gas outlet openings 34, 35 in each gas supply pipe 31. These gas outlet openings 34, 35 lie above and below the useful surface 29 of the upstream space. The distribution space 12, while still the gas outlet openings 34 of the gas supply tubes 31, lies at the level of the charge carrier 30. From these gas outlet openings 34, 35, the workpieces 27 can be blown alternately axially. For this purpose, the upper and lower gas outlet openings 34, 35 are opened and closed alternately by closing elements. 2 The working gas coming out of the gas outlet openings 34, 15 flows radially below and above the adjacent surface 29 of the useful space 27. , inward, is then inverted by the action of a pressure gradient directed toward the opposed face 29 of the useful space 27 and blowing the adjacent face 29 in the axial direction. In order to prevent the charge carrier 30 from axially blowing the lower face 29, it is formed from radial beams and thus transmits gas. The closing elements of the gas outlet openings 34, 35 are formed in the illustrated embodiment of the vacuum furnace by two sliding tubes 36, 37 which slide in the gas supply tubes 31 and are connected to each other by a rod 38. 9

The rigid connecting rod and sliding tubes 36, 37 extend to the gas distribution chamber 21, where all the shut-off devices of all gas supply tubes 31 are interconnected by a common frame 22 · The shut-off devices 40 are also connected to the tube 39 for closing and opening gas outlet openings 34, 35.

FIG. Fig. 4a shows the arrangement of the nozzle openings 32a of the gas outlet openings 34, 35 along the length of one gas supply pipe 32; 4b to 4d show a cross section of the gas supply pipe 31 with the shutter device, which consists of the two slide tubes 22 '37 and the connecting rod 38, in three different positions. The length of the two sliding tubes 22 * 37 is, in the example shown, equal to twice the diameter of the gas outlet apertures 21-35 and their distance is equal to the distance between the gas outlet apertures 21-22 '. From the following table, three states of gas can be found: "Open" 3'4T ^ -5 ^ -pl ^ new ^ -v -drain - tr-ub ^ ----c correspond to the three positions b, c, d of the shut-off device. 'upper gas outlet opening 35 nozzle lower gas outlet 32 openings 34 position b open open closed position c closed open closed position d closed open - open at appropriate intermediate positions the volume of the flowing out of the gas outlet openings 21 »22 'can be set to the desired value

According to a further embodiment of the vacuum furnace 1, according to the invention, the two separate sliding tubes 36, 32 ' are a long, long stop tube 41. The shut-off tube 41 has openings 41 for opening and closing the gas outlets 34, 35. 43, the distance of which is finer than the distance of the gas outlet openings 34, 35o is twice the diameter of the gas outlet openings 34, 35. To open the nozzle openings 32 of the gas supply pipe 31, the shut-off tube 41 between the two openings 42, 43 has an axial longitudinal opening 44, the width of which corresponds to the diameter of the nozzle openings 32 and whose length is equal to the distance of the outer nozzle openings 32 plus the diameter of one nozzle opening 32 plus twice the diameter of the gas outlet openings 34, 35 ''.

FIG. 5 shows one gas supply pipe 31

A and the associated shut-off tube 41 at the operating positions corresponding to FIG. 4 and for which Table 1 applies. To control the volume of the radial flow, the orifices 42, 43 of the shut-off tube 41 are enlarged in the tangential direction by the width of the longitudinal aperture 44. Axial rotation thus, the stop tubes 41 can close the nozzle openings 32 without affecting the size of the gas outlet openings 34, 35.

The heat treatment of the workpieces is carried out in the vacuum according to the invention in three stages, namely in the heating phase, the cooling phase 1 and the cooling phase 2. To introduce the charge into the furnace 1, the door 2 is lowered together with the charge carrier 30 and the bottom 9 the working chamber 2 downwards, and the workpiece 30 is placed on the workpieces to be heat treated.

After closing the door 2, the furnace X is pumped to a pressure of about 1 Paa and then filled with nitrogen. Then the heating phase begins. During the heating phase, the suction nozzle 20 of the blower 19 is connected to the working chamber 5, as shown in Fig. 1, which means that the slide valve 22 is in the switching position I. All gas outlet openings 13, 15 of the working chamber 2 are equally closed. as the upper gas outlet openings 35 in the gas distribution chamber 12.

The blower 19 induces circulation of the working gas heated by the heating pipes through the gas distribution space 21, the gas supply pipes 31, the useful space 21 and the gas distribution space 12 in the furnace 2 at a pressure of 0.2 to 0.3 MPa. The arrows 45, illustrating the flow in FIG. 1, indicate the working gas path during heating. After about one hour of heating, the austenitizing temperature of the workpieces is reached and cooling can begin. In cooling, the suction nozzle 20 of the blower 19 is connected by a heat exchanger 26 as shown in FIGS. 2 and 3: that is, the slide valve 22 is in the switching position II and closes the suction opening 8 in the cover plate 2 of the working chamber. alternately performs switching between the cooling phase 1 and the cooling phase 2. As shown in FIG. 2, during the cooling phase 2, the gas outlet openings 13 of the gas distribution chamber 12 are open while the outlet openings 35 and the outlet opening 15 at the bottom 8 are closed.

The workpieces are now blown off at a pressure of 0.6 to 1 MParadially and simultaneously axially from the lower gas outlet orifices 34 from the bottom up.

The working gas leaves the working chamber 5 through the gas passage opening 11 in the intermediate bottom 10 and the gas outlet openings 13 of the gas distribution chamber 12 and cools through the passage of the heat exchanger tubes 26, then is sucked in by the blower 19 and injected into the working chamber again 2 (as indicated by arrows 45 in FIG. 2).

As shown in FIG. 3, during the cooling phase 1, the gas outlet openings 13 of the gas distribution chamber 12, as well as the lower gas outlet openings 34 of the gas supply pipes 31, are closed while the upper gas outlets 35 of the gas supply pipes 31 and the outlet opening 15 at the bottom j) of the working chamber 5 are open. The workpieces in this cooling phase 1 are blown radially and simultaneously axially from top to bottom from the upper gas outlet ports 35, as shown by arrows 45 in Fig. 3.

The entire cooling, process takes on the size of the vacuumpec_1 and the type of workpieces between 30 and 60 minutes. During this time, it switches several times between cooling phase 1 and 2. The switching frequency is about one change-over-per-minute and the horizon is limited to two to three switches per minute due to gas mass inertia.

Simultaneous radial and switchable axial blowing of the workpieces is essential for a completely homogeneous temperature for all workpieces in the useful space 27 during the entire cooling operation in the vacuum furnace 1. The action of the bottom 10 of the present invention optimizes the flow of gas into the working chamber. ·> '

Experiments have shown that the optimum ratio of gaseous flow volumes between axial and radial blowing for a number of shapes and workpiece sizes lies between 20:80 and 80:20. The optimum ratio for the workpiece type currently being processed according to the invention is only adjusted by partial opening of the gas outlet openings during cooling. 34, 35.

Claims (9)

- 13 PATENT TJ31> o? . c 5 c: 3 S 3; m a-, Cl — 1 "<πN lUO ^ K ^ L-t n --------------- Mtn» X 55r -} -J A vacuum furnace for the heat treatment of metal workpieces in a work chamber having heating devices, heat insulated walls with closable gas outlets, and a useful space with a jacket and faces surrounded by gas supply tubes that are parallel to the working chamber axis and have a useful space in the shell region a nozzle orifice directed radially inward, with a blower disposed outside the heat exchanger working chamber, wherein the blower discharge side is connected via gas distribution pipes to the gas supply tubes and the blower suction nozzle is directly connected to the work chamber during the heating phase and during the heating phase a cooling phase with a heat exchanger, characterized in that an intermediate bottom (10) with a central gas through-hole (11) is disposed perpendicular to its axis by the worker (5) and separates the gas distributor (12) from the working chamber (5) returned , the blower (19) and the partitioning gas space (21), each gas feed pipe (31) having two additional inwardly directed gas outlet openings (34, 35), one of which (35) is located in the gas distribution area (12) and the second opening (34) at the end of the gas supply pipe (31) remote from the gas distribution space (12) outside the housing (28) of the useful space (27), the two additional outlet openings (34, 35) the gas supply pipes (31) are closable by closing elements (36, 37) and the closable outlet openings (13, 15) are arranged in the walls (6) of the gas distribution space (12) and in the working chamber bottom (9) (5) removed from the gas distribution space (21). 14 Vacuum furnace according to claim 1, characterized in that the gas supply pipes (31) are formed simultaneously as heating elements. Vacuum furnace according to claim 1 or 2, characterized in that the locking elements for the two gas outlet openings (34, 35) of one gas supply pipe (31) are formed by sliding tubes (36, 37) slidably mounted in the gas supply line. tube (31) and connected by a rigid rod. Vacuum furnace according to claim 3, characterized in that the sliding tubes (36, 37), which are interconnected, are provided with an axial displacement adjusting device. . and Vacuum furnace according to claim 4, characterized in that the end of the gas supply pipe (31) facing away from the gas distribution space (21) is axially closed by a sliding pipe (36). Vacuum furnace according to claim 1 or 2, characterized in that the locking elements for the two gas outlet openings (34, 35) of one gas supply tube (31) are formed by a sealing tube (41) which is sealed slidingly in the gas supply pipe (31) has two openings (42, 43) corresponding to and between the gas outlet openings (34, 35) in the region of the nozzle openings (32) of the gas supply pipe (31); whose width corresponds to the diameter of the nozzle openings (32). Vacuum furnace according to claim 6, characterized in that the openings (42, 43) of the barrier tube (41), corresponding to the gas outlet openings (34, 35) of the gas supply tube (31), are widened in width by a width axial longitudinal bore (44). 15 Vacuum oven according to claim 7, characterized in that the shut-off tubes (41) are provided with an adjusting device for their axial displacement and an angle corresponding to the radially angular opening of the nozzle openings (32) in the gas supply tubes (31) to the longitudinal axis of the longitudinal axis. Vacuum furnace according to claim 8, characterized in that the closing tubes (41) are closed at the end of the distribution gas space (21). 1