EP0422353A2 - Furnace for the partial thermic treatment of tools - Google Patents

Abstract

An oven for the partial heat treatment of tools, for example, twist drills, comprises a first section, which contains the heating chamber that is constantly at the desired operating temperature. A second section for the loading and unloading and the quenching is provided. Between the two sections there is arranged a transport device for the charges of tools. The oven may be in the form of a one-chamber or three-chamber vacuum oven. The oven provides a high heat transfer rate, because the heating chamber is constantly at the desired operating temperature and the heat transfer by heat radiation under vacuum is started immediately when the charge is at its final position inside the heating chamber.

Description

The invention relates to a furnace for the partial heat treatment of tools having a clamping area and a working area, in particular drills, with a heating chamber which receives the batches for the tools and has a door in which heating elements which emit heat radiation for curing under vacuum conditions are arranged, with an evacuation device , with a quenching device and with a charging frame for receiving the tools to be treated, the clamping area not to be heated being arranged inside and the working area to be heated being arranged outside the charging frame.

Furnaces for the partial heat treatment of tools, for example of twist drill blanks made of high-speed steel, are known. Such twist drills should be fully hardened in the cutting area, while on the other hand they should remain soft in the shank area, ie on the clamping side. One requirement is that the transition from one area to the other should be as small as possible. This is achieved by austenitizing the cutting area at temperatures between 1140 and 1300 ° C and then quenching it, depending on the HSS grade, while the shaft area must not be warmer than 850 ° C.

A known furnace for partial heat treatment provides for curing in a vacuum. The tools, for example in the form of the spiral drill blanks, are inserted into a massive receptacle, which is usually made of steel, with a high heat storage capacity and are placed in a vacuum oven. This is followed by evacuation and heating of the furnace with the batch inside. The parts of the workpieces protruding from the holder, namely the cutting part of the drill, are heated to the austenitizing temperature by the heat radiation emitted by the heating elements, while the part located in the charging plate, namely the shaft of the drill bit blank, is shielded from the heat radiation. The large mass of the receiving device for the tools prevents them from heating up to temperatures above 850 ° C.

A disadvantage of such a furnace for the partial heat treatment of workpieces is the very long heating and cooling time, which causes an extensive transition zone from the hard to the soft area. In addition to the workpieces, all furnace parts located in the heating chamber, namely the heating, heating connection, insulation, batch pick-up, must be warmed up and cooled again in the subsequent quenching process. This disadvantageously results in a high expenditure of time, high heat losses and a low "efficiency" with regard to the ratio of usable mass to empty mass. In addition, such a furnace can only achieve low productivity, i.e. the number of pieces per hour is low in relation to the operating and plant costs, which results in high unit costs.

Proceeding from this, the object of the invention is an efficient furnace for partial heat treatment to create tools in a vacuum, in particular the transition zone from the hard to the soft area should be small.

As a technical solution it is proposed with the invention that the furnace has a first area in which the heating chamber which is always at the working temperature is arranged, that the furnace further has a second area for loading and unloading and for quenching, and that between these two A transport device for the batches is arranged in areas.

With such a furnace for the partial heat treatment of tools, very short transition zones from the hard to the soft section can be achieved economically. The tools are moved under vacuum from the cold area of the furnace into the warm area, ie into the heating chamber, which is already at the working temperature. As soon as the batch arrives in this heating chamber, full heat transfer by radiation from the warm heating chamber to the workpieces to be partially hardened takes place without delay. This ensures a high heat transfer capacity, so that the sections of the workpiece to be hardened are heated to the working temperature within a few minutes up to the core. The workpieces can then leave the warm heating chamber and be quenched in the cold area of the furnace. The short time required for the heat transfer ensures that the amount of heat dissipated in the case of twist drill blanks by heat conduction along the drill axis in the shielded section of the workpiece, namely in the shank of the drill, is very small and therefore this section is cold and in the original state, i.e. soft remains.

In a first embodiment, the furnace is a single-chamber vacuum furnace. This then has two places, namely a cold place for the one area on which the batch stands during evacuation and quenching and which is also used for loading and unloading, and a warm place for the other area with the heating chamber.

As an alternative to the single-chamber vacuum furnace, a multi-chamber vacuum furnace can also be provided as the furnace for the partial heat treatment, the two regions being provided in one chamber each and the chambers being separated from one another by vacuum-tight and thermally insulating intermediate doors. The two areas for the partial heat treatment are thus formed by independent chambers.

In the case of the multi-chamber vacuum furnace, this is preferably a three-chamber vacuum furnace in which a prechamber, a heating chamber and a quenching chamber are arranged one after the other, each of the chambers being assigned an evacuation device. The three chambers are also separated from each other by thermal and vacuum-tight intermediate doors. The prechamber serves exclusively as an evacuable rinsing chamber, in that this prechamber is evacuated to the same working pressure as it prevails in the heating chamber before the batch is transported into the subsequent heating chamber. The heating chamber remains constantly under vacuum in the warm state, so that the materials for insulation and heating need not be resistant to oxidation at high temperatures. Graphite material or molybdenum is therefore mainly used in the heating chamber. The quenching chamber contains, for example, a blower and a heat exchanger for recooling the gas, these two Components can also be designed as an external unit. There is also a transport system in the quenching chamber that is the same as that in the antechamber.

In a preferred development of the heating chamber, its housing has high-temperature-resistant and, if it is not constantly under vacuum at the high temperatures, oxidation-resistant insulation, on the inside of which also high-temperature-resistant and possibly oxidation-resistant, heat-storing plates with high heat emission behavior are arranged. Optimal heat behavior is ensured by such a heating chamber. While the insulation, which consists, for example, of aluminum oxide fibers, provides thermal insulation of the heating chamber from the outside, the heat-storing plates, which can be silicon carbide plates, for example, provide the necessary immediate heat radiation when the batch is in the housing of the heating chamber has been transported. The insulation and the heat-storing plates only need to be made of an oxidation-resistant material if they come into contact with air. This is the case, for example, with the single-chamber vacuum furnace, but not with the three-chamber vacuum furnace, in which the chambers can be evacuated separately from one another. The heating elements can be arranged on the ceiling or on the ceiling and on the side and also consist of high-temperature-resistant and possibly oxidation-resistant and also vacuum-resistant heating conductor material, for example Kanthal.

In a preferred development of the heating chamber, this has a lowerable bottom hatch made of insulation material and the charging frame consists of an insulating plate on which a Radiation screen is arranged, wherein the charging frame can be moved under the heating chamber by means of the transport device and thereby replaces the lowered floor hatch in its working position. The lowerable floor hatch preferably consists of the same insulation material as the housing of the heating chamber. However, it is equipped without a heat-storing plate, since in the lowered state the floor hatch would otherwise give off heat radiation without any useful value, since the floor hatch is then outside the heating chamber and has been replaced by the charging frame. The insulating plate of the floor hatch can consist, for example, of ceramic fibers. As a further movable element, the heating chamber has an insulated door for moving the batch in and out, which, in contrast to the lowerable floor hatch, can be provided with heat-storing plates on the inside. The radiation shield arranged on the insulating plate of the charging frame reduces heat transfer to the charging frame by reflection.

The charging frame is additionally provided with a lifting and lowering device, so that the charging frame, after it has been positioned below the heating chamber, can be pressed against the housing of the heating chamber, thus avoiding radiant heat flowing through gaps into the cold furnace chamber.

In a further development of the charging frame, the insulating plate with its radiation shield is arranged on a base plate, which improves the overall stability of the charging frame.

In a further development of the charging frame, the radiation shield and the insulating plate and, if necessary, the reason plate with through bores for receiving the tools and below it a base plate is arranged at a distance, this distance being adjustable with an adjusting device. This creates a possibility to vary the "immersion depth" of the workpiece according to the needs.

Finally, it is proposed in a further development of the charging frame that the base plate for the height adjustment has a radiation shield on its outside. This reduces the heat transfer from the underlying warm floor hatch to the floor slab.

Finally, it is proposed in a further development that heat exchanger elements are arranged in the cold region of the furnace. These serve to re-cool the gases.

• Fig. 1 einen Längsschnitt durch eine erste Ausfüh­rungsform eines Ofens in Form eines Einkam­mer-Vakuumofens;
• Fig. 2 einen Schnitt entlang der Linie II-II in Fig. 1 durch den kalten Bereich des Ofens;
• Fig. 3 einen Schnitt entlang der Linie III-III in Fig. 1 durch die Heizkammer des Ofens;
• Fig. 4 eine Einzelheit in Fig. 3;
• Fig. 5 einen Schnitt durch das Chargiergestell des Ofens;
• Fig. 6 einen Längsschnitt durch eine zweite Ausfüh­rungsform in Form eines Dreikammer-Vakuum­ofens;
• Fig. 7 einen Schnitt entlang der Linie VII-VII in Fig. 6 durch die Heizkammer;
• Fig. 8 einen Schnitt entlang der Linie VIII-VIII in Fig. 6 durch die Abschreckkammer;
• Fig. 9 einen Schnitt durch das Chargiergestell für den Dreikammer-Vakuumofen.

Two exemplary embodiments of an oven according to the invention for partial heat treatment of tools in the form of twist drills are described below with reference to the drawings. In these shows:

• 1 shows a longitudinal section through a first embodiment of a furnace in the form of a single-chamber vacuum furnace.
• FIG. 2 shows a section along the line II-II in FIG. 1 through the cold region of the furnace;
• 3 shows a section along the line III-III in Figure 1 through the heating chamber of the furnace.
• Fig. 4 shows a detail in Fig. 3;
• 5 shows a section through the charging frame of the furnace.
• 6 shows a longitudinal section through a second embodiment in the form of a three-chamber vacuum furnace;
• 7 shows a section along the line VII-VII in FIG. 6 through the heating chamber;
• 8 shows a section along the line VIII-VIII in FIG. 6 through the quenching chamber;
• Fig. 9 shows a section through the charging frame for the three-chamber vacuum furnace.

1 to 5 show a first embodiment of a furnace for the partial heat treatment of tools in the form of a single-chamber vacuum furnace 1 and FIGS. 6 to 9 show a second embodiment in the form of a three-chamber vacuum furnace 2.

The single-chamber vacuum furnace 1 of the first embodiment consists of a furnace housing 3, which defines a furnace chamber 4. This forms two places, namely a cold place (on the left in FIG. 1) and a warm place (on the right in FIG. 1), a heating chamber 5 being arranged in the warm place, in which the partial heat treatment is carried out. The two places are connected by a roller table 6, which defines a transport device and which in the area of the warm plat zes with the heating chamber 5 can be raised and lowered by means of an eccentric drive 7. This is indicated by the double arrow D in Fig. 1. Two cross-flow fans 8 are arranged between the two places. Furthermore, the cold area of the single-chamber vacuum furnace 1 has lateral heat exchanger elements 9. Finally, a buffer container 10 and an evacuation device 11 can also be seen in FIG. 3.

The heating chamber 5 has a housing with an insulation 12, which consists of a high-temperature and oxidation-resistant insulating material, for example aluminum oxide fibers. High-temperature and oxidation-resistant and heat-storing plates 13 made of a material with high heat emission behavior, for example silicon carbide plates, are likewise arranged on the inside of the insulation 12. The heating chamber 5 has a door 14 facing the cold place of the single-chamber vacuum furnace 1, which door can either be folded up or moved to the side and also has insulation 12 and heat-storing plates 13 like the rest of the heating chamber 5. The bottom of the heating chamber 5 is formed by a bottom hatch 15, which is made of the same insulation material as the insulation 12, but which has no heat-storing plates 13 like the rest of the heating chamber 5. By means of a lifting and lowering direction 16, this floor hatch 15 can be lowered below the roller table 6, as can be seen in dashed lines in FIG. 4 on the right side.

Within the heating chamber 5, this has heating elements 17 on the ceiling and on the side, which are made of high-temperature-resistant, oxidation-resistant and vacuum-proof heating conductor material, for example Kanthal.

A charging frame 19, which is shown in detail in FIG. 5, is used to hold the tools 18 provided for the heat treatment. This charging frame 19 initially consists of a rectangular transport frame 20. A base plate 21, for example made of steel, is mounted on this. The base plate 21 receives an insulating plate 22, for example an aluminum oxide fiber plate, which is intended to reduce the heat transfer to the base plate 21. Finally, a radiation shield 23 is applied to the insulating plate 22, for example in the form of a polished sheet or a film with a low heat emission value, i.e. high reflection. For example, NiCr material can be used as the material. The composite formed in this way from base plate 21, insulating plate 22 and radiation shield 23 has bores 24 for receiving tools 18 in the form of spiral drill blanks. A base plate 25 is arranged at a distance below the composite, which base plate is provided with a radiation shield 26 on its underside. The base plate 25 with its radiation shield 26, which can also be made of the same material as the radiation shield 23, is height-adjustable via threaded bolts 27, which are fastened in the base plate 21 and which define an adjusting device 28, in such a way that the immersion depth of the tools 18 can be varied.

The single-chamber vacuum furnace 1 works as follows:

After opening the oven door 29, the batch 30 is given to the cold place of the single-chamber vacuum oven 1 by the transport frame 20 of the charging frame 19, which has guide strips with machined underside on the long sides and is made of cast iron, for example, on the roller table 6 comes into circulation, as can be seen for example in FIG. 2. When loading the single-chamber vacuum furnace 1, the heating chamber 5 is already at the prescribed working temperature, the bottom hatch 15 being closed, as shown in FIG. 3 by means of the solid lines. On the right side of this Fig. 3, the heating chamber 5 is also shown without charge 30.

After closing the oven door 29, the oven chamber 4 is evacuated and then the charging frame 19 on the roller table 6 by means of a push-pull chain unit 31 by latching into the heating chamber 5, after the door 14 has been opened and the floor hatch 15 by means of the lifting and Lowering device 16 has been lowered. After the charging frame 19 has reached its position within the heating chamber 5, the door 14 is closed and by means of the eccentric drive 7 the roller table 6 is moved upwards in such a way that the charging frame 19 closes the heating chamber 5 at the bottom and thereby replaces the floor hatch 15. The heat treatment can then take place in this state, which occurs immediately since the heating chamber 5 is already at the working temperature.

After the heat treatment has ended, the door 14 is opened and the roller table 6 is moved down again and the charging frame 19 is moved out again by means of the push-pull chain unit 31. Immediately afterwards, the door 14 is closed again and the floor hatch 15 is raised so that the heating chamber 5 is closed on all sides and no heat escapes. By actuating the cross-flow fans 8, the batch 30 is then quenched in the left region of the furnace chamber 4. After the quenching has taken place and after the furnace housing 3 has been flooded, the batch 30 can then be removed after the furnace door 29 has been opened.

The three-chamber vacuum furnace 2 of the second embodiment shown in FIGS. 6 to 9 consists of three chambers, namely a prechamber 32, a heating chamber 33 arranged downstream of this, and finally a quenching chamber 34 is arranged downstream. These three chambers 32, 33, 34 are each separated from one another by vacuum-tight and thermally insulating intermediate doors 35, with each of the chambers 32, 33, 34 also being assigned an evacuation device.

The pre-chamber 32 has an oven door 36. In addition, a telescopic loading system 37 is arranged in it.

The heating chamber 33 is formed in accordance with that of the first embodiment with the single-chamber vacuum furnace 1. Deviating from this, however, the materials for insulation and heating do not need to be resistant to oxidation at high temperatures, since the heating chamber 33 remains constantly under vacuum in the warm state. Graphite material or molybdenum is therefore mainly used here. The transport into the heating chamber 33 takes place by means of the telescopic loading system 37, i.e. via a combined lifting and moving device, which is installed in a frame that can be raised and lowered. Instead of the heating chamber in Fig. 5, the heating chamber 33 in this embodiment still has a second door 14 'to the quenching chamber 34 located behind it.

Finally, the quenching chamber 34 also has a telescopic loading system 37 'and, above all, a cooling fan 38 and lateral heat exchanger elements 9. In order to be able to remove the batches 30 from the quenching chamber 34, this still has an oven door 36'.

The three-chamber vacuum furnace 2 works as follows:

First, the batch 30 to be treated is fed to the pre-chamber 32 by the charging rack 19 being introduced accordingly. This charging frame shown in Fig. 9 differs from that of the first embodiment only in that no transport frame 20 is provided due to the telescopic loading system 37, 37 'used here. Otherwise the structure is identical. After the charging rack 19 has been introduced via an external transport system, the oven door 36 is closed in a vacuum-tight manner. The intermediate doors 35 between the chambers 32, 33, 34 are also closed, so that there is a vacuum in particular in the central heating chamber 33 and is above all at working temperature. The prechamber 32 is then evacuated to the working pressure of the heating chamber 33. Before the batch 30 is transported into the heating chamber 33, the intermediate vacuum-tight and thermal intermediate door 35 is opened and the bottom hatch 15 of the heating chamber 33 moves down. The charging rack 19 is now transported into the heating chamber 33 by means of the telescopic loading system 37 after the left door 14 of the heating chamber 5 has been opened. After the charging frame 19 has reached its final place, the door 14 and the intermediate door 35 are closed again. After the charging frame 19 has assumed the position of the bottom hatch 15 of the heating chamber 33 and this has been hermetically sealed, the tools 18 which protrude from the charging frame 19 are now heated.

After the end of austenitization, the right door 14 'of the heating chamber 5 and the vacuum-tight and thermal intermediate door 35 to the quenching chamber 34 are opened. By means of the telescopic loading system 37 'of the quenching chamber 34, the batch 30 is transported into the quenching chamber 34. Both the door 14 'of the heater Chamber and the intermediate door 35 close again and the bottom hatch 15 of the heating chamber 5 moves upwards. The quenching chamber is now filled with gas, the pressure being adjustable and overpressure possible, the cooling fan 38 is switched on and cools the batch 30, for example to temperatures of less than 150 ° C. The furnace door 36 of the quenching chamber 34 is then opened and the charge 30 is then removed from the quenching chamber 34 by an external transport system.

During the entire treatment process, the heating chamber 33 remains under vacuum and above all at the working temperature, so that rapid heat transfer to the tools 18 to be treated is possible.

Reference symbol list

• 1 single-chamber vacuum oven
• 2 three-chamber vacuum furnace
• 3 furnace housings
• 4 furnace chamber
• 5 heating chamber
• 6 roller table
• 7 eccentric drive
• 8 cross flow fan
• 9 heat exchanger element
• 10 buffer tanks
• 11 evacuation device
• 12 insulation
• 13 plate
• 14 door
• 14 ′ door
• 15 floor hatch
• 16 lifting and lowering device
• 17 heating element
• 18 tools
• 19 charging rack
• 20 transport frames
• 21 base plate
• 22 insulating plate
• 23 radiation shield
• 24 hole
• 25 base plate
• 26 radiation shield
• 27 threaded bolts
• 28 adjustment device
• 29 oven door
• 30 batch
• 31 push-pull chain unit
• 32 antechamber
• 33 heating chamber
• 34 quenching chamber
• 35 intermediate door
• 36 oven door
• 36 ′ oven door
• 37 Telescopic loading system
• 37 ′ telescopic loading system
• 38 cooling fans
• D double arrow

Claims (11)

1. Furnace for partial heat treatment of tools (18), in particular drills, having a clamping area and a working area,
with a heating chamber (5, 33) receiving the batches (30) for the tools (18) and a door (14, 14 ′), in which heating elements (17) which emit heat radiation are arranged for curing under vacuum conditions,
with an evacuation device (11),
with a quenching device
and with a charging frame (19) for receiving the tools (18) to be treated, the area of use not to be heated being arranged inside and the working area to be heated being arranged outside the charging frame (19),
characterized,
that the furnace has a first area in which the heating chamber (5, 33), which is constantly at the working temperature, is arranged,
that the furnace further has a second area for loading, unloading and quenching, and
that a transport device for the batches (30) is arranged between these two areas. 2. Furnace according to claim 1, characterized in that the furnace is a single-chamber vacuum furnace (1). 3. Furnace according to claim 1, characterized in that the furnace is a multi-chamber vacuum furnace, the two areas being provided in one chamber (32, 33, 34) and the chambers (32, 33, 34) each being vacuum-tight and thermally insulating intermediate doors (35) are separated from one another. 4. Furnace according to claim 3, characterized in that the furnace is a three-chamber vacuum furnace (2), in which a prechamber (32), a heating chamber (33) and a quenching chamber (34) are arranged in succession, each of the chambers ( 32, 33, 34) an evacuation device is assigned. 5. Oven according to one of claims 1 to 4, characterized in that the housing of the heating chamber (5,33) has a high temperature resistant and, if it is not constantly under vacuum at the high temperatures, oxidation-resistant insulation (12) on the inside high temperature-resistant and possibly oxidation-resistant, heat-storing plates (13) with high thermal insulation behavior are also arranged. 6. Oven according to claim 5, characterized in that the heating chamber (5,33) has a lowerable bottom hatch (15) made of insulation material and that the charging frame (19) consists of an insulating plate (22) on which a radiation shield (23) is arranged The charging frame (19) can be moved under the heating chamber (5, 33) by means of the transport device and thereby replaces the lowered floor hatch (15) in its working position. 7. Oven according to claim 6, characterized in that the charging frame (19) is additionally provided with a lifting and lowering device (16). 8. Oven according to claim 6 or 7, characterized in that the insulating plate (22) with its radiation shield (23) on a base plate, (21) is arranged. 9. Oven according to one of claims 6 to 8, characterized in that the radiation shield (23) and the insulating plate (22) and optionally the base plate (21) are provided with through bores (24) for receiving the tools (18) and that a bottom plate (25) is arranged at a distance below it, this distance being adjustable with an adjusting device (28). 10. Oven according to claim 9, characterized in that the base plate (25) has a radiation screen (26) on its outside. 11. Oven according to one of claims 1 to 10, characterized in that heat exchanger elements (9) are arranged in the cold region of the furnace.

Images