EP0562250A1 - Process and device for quenching of metal pieces - Google Patents

Abstract

For quenching heated metal workpieces (15) at a quenching intensity which is in a range typical for oil- or water-quenching with an H-value of 0.2 to 4, the quenching medium used is a cooling gas which is made to act in the form of discrete impingement jets issuing from a nozzle field onto the workpiece surface which is to be cooled. With a limitation of the delivery rate for the cooling gas to a preset maximum limit of about 1,000 kW/m<2> of nozzle field, the quenching intensity is brought to a value of between H = 0.2 and H = 4 by appropriate selection of gas jet parameters, in particular the gas velocity w, the gas pressure p, the gas jet cross-sectional area and the number of the impingement jets per unit area. <IMAGE>

Description

The invention relates to a method for quenching metallic workpieces with a quenching intensity which is in a range (H = 0.2 to 4) typical for oil or water quenching, in which a quenching medium is brought into effect on the surface of the workpieces to be cooled.

In addition, the invention relates to a device for performing this method, in particular for treating rotationally symmetrical workpieces, such as rings, gears, disks, shafts and the like, with a quenching chamber in which at least one, at least partially delimited by a nozzle field, is used to hold individual workpieces Space is provided.

Quenching systems for hardening workpieces made of steel and other metals are of great importance in technology because they significantly improve the performance properties of the workpieces. Quenching in water or oil, as well as in salt baths or in a fluidized bed, has long been known. Recently, the cooling of the workpieces in the gas flow has also been used, in which a heat-treated batch with cooling gas which is circulated via a heat exchanger is flowed into in a cooling chamber and is brought into effect in the form of discrete jets on the workpiece surface to be cooled. An industrial furnace equipped with such a quenching device is described in EP 0151 700 A2.

The increases in hardness and / or strength in the workpiece that can be achieved when the workpieces are quenched, that is to say when they cool rapidly from treatment to room temperature, crucially depend on the fact that the cooling process takes place at high speed according to a temperature-time profile appropriate for the respective material. For this purpose, it is necessary to dissipate the heat present in the workpiece with a correspondingly high heat flow density over the cooled surface during this cooling process. The size of the heat flow density that can be achieved depends, among other things, on the heat transfer coefficient α (W / m² K). In practice, a characteristic value, the so-called H value, is often used to describe the quenching effect or intensity according to Grossmann (MA Grossmann, M.Asimov, SF Urban "The Hardenability of Alloy Steel", ASM Cleveland, 1939, Pages 124 to 190) are used. This H value is Experience has shown that it is in a range from about 0.2 to 4, with the known quenching systems consistently using only salt baths, oil or, in the upper range of about H = 0.9, as the quenching medium in the H value range from 0.2 to 4 to 4, only water can be used. Gas quenching is only known in an H-value range from 0.1 to 0.2 (cf., for example, "Handbuch der Fabrication Technology", Carl Hansen Verlag Munich Vienna Volume 4/2, 1987, page 1014). Higher values of up to ≈ 0.2 can only be achieved with strong circulation and / or overpressure.

The use of the known quenching systems with liquid quenching agents in the H value range from 0.2 to 4 brings with it a number of fundamental difficulties which are well known in practice. Since using a liquid as a quenching medium, the quenching intensity can be changed practically only slightly during cooling, but this would often be desirable in order to avoid hardness cracks and dimensional changes of the workpiece, which often leads to quality problems, to which there are also cost problems because the lack of controllability of the Quenching process can only be compensated for by expensive alloying elements (oil-hardening steels are alloyed). The residues of quenching oil, salt or water additives adhering to the workpiece after cooling must be cleaned from the workpiece and then disposed of, which gives rise to environmental problems. Finally, the most common quenchant, oil, is flammable, with the result that safety problems still arise that require special precautions.

The above-mentioned environmental and safety problems occur with the known gas quenching, as for example in the EP 0151 700 A2 is not described, but because of the low quenching intensity (H <0.2), such known gas quenching systems can only be used for hardening higher alloyed steels, even in the case of overpressure operation.

The object of the invention is to remedy this and to provide a quenching method and a quenching device suitable for carrying out this method, which allow a quenching intensity in the H-value range of approximately 0.2 to 4 to be achieved without the having to accept the aforementioned problems.

To achieve this object, the quenching method according to the invention is characterized by the use of a cooling gas as the quenching medium, which is brought into effect in the form of discrete impingement jets emerging from a nozzle field on the workpiece surface to be cooled, with limitation of the delivery rate for the cooling gas to a predetermined maximum Limit value of approx. 1000 kW / m² nozzle field, the quenching intensity is brought to a value between H = 0.2 and H = 4 by appropriate selection of gas jet parameters, in particular the gas velocity w, the gas pressure p, the gas jet cross-sectional area and the number of impact jets per unit area becomes.

The invention is based on the surprising finding that it is possible, when using an appropriately selected nozzle pitch t Nozzle array with a relatively small effective nozzle diameter d and a small distance h from the nozzle array to the workpiece surface to be cooled with possibly increased gas pressure p in the impact jet field of a cooling gas to achieve a high heat transfer from the workpiece surface to be cooled to the cooling gas flow, without the need for the promotion of the the cooling gas acting on the nozzle field would have to be increased to a value which would make the whole process uneconomical.

From EP 0151 700 A2 it is known that a good convective heat transfer from the workpiece surface to be cooled to a gaseous medium can be achieved by the use of nozzle fields when cooling a workpiece, but so far it has appeared to be obviously impossible, in this way, for To achieve oil and water hardening typical high values of the quenching intensity with economically justifiable effort, because with an increase in the cooling gas speed the energy requirement for gas production increases with the third power of the gas speed and therefore an increase in the gas speed in the nozzle fields of known gas quenching systems is practically out of the question.

The new method makes it possible to work with the high quenching intensity values known for salt, oil or water quenching in the quenching of metallic workpieces, without the disadvantages described at the outset, which are known when using non-gaseous quenching media to have to put up with. At the same time, there is the advantage that, particularly in the critical quenching phase of workpieces made of unalloyed and low-alloy steel, the quenching intensity can be reproducibly controlled within a few seconds.

The regulation can be carried out in a simple manner by an appropriate intervention on the cooling gas-promoting fan acting on the nozzle field and / or the cooling gas pressure in the system.

Practical experience has shown that with the new method a cooling gas velocity w of w = 40 to 200 m / sec. with an effective nozzle diameter d of d = 0.5 to 10 mm is used in the nozzle field, with a nozzle pitch of t of t = 4d to 8d being present in the nozzle field and the cooling gas pressure p in the system at p = 0.5 to Is 20 bar. The nozzle field is at a distance h of h = 2d to 8d from the surface to be cooled.

Air, nitrogen or a gas mixture can be used as the cooling gas, it being particularly expedient to use the protective gas as the cooling gas in cases in which the heat treatment preceding the quenching took place in a protective gas atmosphere.

To increase the cooling effect, if necessary the cooling gas contains hydrogen or another gas with increased thermal conductivity compared to air in a proportion of 0 to 100 vol.%. This hydrogen can also be added to the cooling gas. The addition simultaneously reduces the drive power of the fan that conveys the cooling gas.

Particularly in applications in which the workpieces are heated in a protective gas atmosphere, for example in a furnace chamber, it is expedient if the workpieces are heated and then quenched in a room which contains the essentially the same gas atmosphere for both processes, in which A gas overpressure can be maintained at least temporarily. This becomes more important when working with a cooling gas (e.g. protective gas) to which hydrogen is added to increase the cooling effect. Such addition of hydrogen means a certain risk of explosion, but this can be countered by keeping the gas spaces as small as possible, which is already favored by the system in the new method because the nozzle field is at a short distance from the workpiece surface to be cooled is arranged so that there are only small-volume gap spaces that are filled with the cooling gas. When the Workpieces in a protective gas atmosphere of a furnace chamber are therefore gas quenched directly at the outlet of the furnace chamber, ie in a space that is at least temporarily shared with the latter.

The new method can be used for quenching objects of any shape; if it is used for quenching hollow, in particular ring or tubular workpieces, then impact jets of the cooling gas are expediently brought into effect both on the outer and on the inner lateral surface and optionally on the end face of the workpiece from a nozzle field adapted to the shape of the workpiece . Finally, it can be advantageous if, during quenching, a relative movement between the workpiece surface to be cooled and the impact jets of the nozzle field is maintained at least temporarily, for example by rotating an annular or disk-shaped workpiece - or the nozzle field - while the other Part stands still.

A quenching device set up to carry out the new method has a quenching chamber in which at least one space, which is at least partially delimited by a nozzle field and is used to hold individual workpieces, is provided. According to the invention, this space is essentially designed to be closed, the nozzle field being designed to match the shape of the surface to be cooled of the introduced workpiece and being arranged and dimensioned such that the one to be cooled is in operation Surface of the workpiece is subjected essentially to discrete impingement jets of the cooling gas to produce a quenching intensity which is in a range typical for oil or water quenching (H = 0.2 to 4), the delivery rate of the blower means acting on the nozzle field reaching a maximum limit is limited by approx. 1000 kW / m² of the nozzle field.

At least some of the nozzles in the nozzle array can be provided with selectively operable throttling and / or closing means in order to influence, in particular to dampen, the quenching effect at certain points on the surface of the workpiece if necessary. The nozzle field can also be formed, at least in part, on an insert that can be interchangeably inserted into the quenching chamber, so that the quenching device can be easily adapted to any workpiece shape. As a rule, a special nozzle array is required for each workpiece shape.

Drive means for rotating the inserted, in particular rotationally symmetrical workpiece and / or at least a part of the nozzle field can be provided in the quenching chamber. These drive means can either be designed to act from outside the quenching chamber and / or have a turbine element to which cooling gas can be applied, which has the advantage that no additional drive source is necessary. Particularly in the case of lighter rotationally symmetrical workpieces, such as rings, gear wheels, disks, shafts and the like, can be achieve a very even cooling on the circumference. The space delimited by the nozzle field in the quenching chamber can also be designed as a pressure space, so that the pressure in the quenching system can be increased during the quenching process, which further increases the cooling effect.

One of the great advantages of the new quenching method and the quenching device operating according to this method is that the quenching intensity is controlled in its time course, and thus the temperature / time course of the cooling of the workpiece in accordance with the requirements of the respective workpiece and its material in a predetermined reproducible manner or can be regulated. For this purpose, the quenching device can have a process computer for controlling the chronological course of the cooling process, the process signals such as flow rate, pressure, temperature and composition of the cooling gas etc. and workpiece-specific data such as geometric shape and dimensions, material composition etc. and / or for the nozzle field as input signals characterizing data are supplied and the output signals calculated therefrom according to the program for influencing the cooling gas exposure to the nozzle field and / or the effective cooling gas passage cross section of at least some nozzles of the nozzle field and / or a relative movement between the workpiece and the nozzle field. Program control means can also improve the cooling effect on the workpiece surface to be cooled by correspondingly influencing the speed and / or pressure of the impact jets and / or the effective passage cross section of nozzles of the nozzle array in the sense of simulating the quenching effect of an oil or water bath hardening. In this way, by throttling the cooling effect according to a predetermined temperature / time curve by correspondingly reducing the cooling gas speed and / or the cooling gas pressure etc., the effect of oil or hot bath hardening in salt can be imitated.

Particularly with a view to reducing the risk of explosion when using an addition of hydrogen to the cooling gas, and with a view to reducing the blower output for conveying the cooling gas, it is often advantageous if the quenching device is located directly at the outlet of the furnace chamber containing a protective gas atmosphere of a continuous continuous furnace , in particular a roller hearth furnace, is connected essentially gas-tight. For this purpose, the quenching device can have a loading and unloading chamber which is connected to the furnace chamber and which is closed to the outside by an optionally operable door. The loading and unloading chamber can also be connected to the space delimited by the nozzle field by means of selectively operable closure means which allow the quenching process to be carried out under cooling gas pressure, at least temporarily.

In the case of smaller quantities of the workpieces to be treated, these are generally introduced one after the other into the quenching chamber, quenched there and then reused fed. In order to increase the throughput, the quenching device can also have a plurality of quenching chambers arranged next to one another and operable in parallel with one another. Finally, the arrangement can be such that the quenching device has a plurality of quenching chambers arranged one behind the other, which are optionally connected to one another by a transport device with the interposition of other treatment stations, for example for calibrating the workpieces, the quenching chambers being set up for operation with different quenching effects. This makes it possible, for example, to achieve step cooling with different cooling gas inlet temperatures.

Fig. 1

ein Diagramm zur Veranschaulichung der erfindungsgemäß erreichbaren Abschreckintensitäten für verschiedene Gasdüsenfelder im Vergleich mit herkömmlichen Abschrecksystemen,

Fig. 2

eine Abschreckvorrichtung gemäß der Erfindung, im axialen Schnitt, in einer Seitenansicht, in schematischer Darstellung und angebaut an den Ausgang der Ofenkammer eines Rollenherdofens,

Fig. 3

das Düsenfeld der Abschreckvorrichtung nach Fig. 2, im axialen Schnitt, in einer Prinzipdarstellung und in einem anderen Maßstab,

Fig. 4

die Anordnung nach Fig. 3, geschnitten längs der Linie A-A der Fig.3, in einer Draufsicht,

Fig. 5

die Kühlgasversorgungseinrichtung der Abschreckvorrichtung nach Fig. 1, zusammen mit der zugehörigen Steuerungseinrichtung, in einer schematischen Darstellung,

Fig. 6

eine Ringhärteanlage mit zwei hintereinander geschalteten Abschreckvorrichtungen gemäß der Erfindung, in einer schematischen Teildarstellung und in der Draufsicht, und

Fig. 7

ein Diagramm zur Veranschaulichung des Temperatur-Zeit-Verlaufs bei der erfindungsgemäßen Abkühlung eines Ringes in einem Gasdüsenfeld, mit einem Düsendurchmesser von d = 2 mm.

Exemplary embodiments of the subject matter of the invention are shown in the drawing. Show it:

Fig. 1

2 shows a diagram to illustrate the quenching intensities that can be achieved according to the invention for different gas nozzle fields in comparison with conventional quenching systems,

Fig. 2

1 a quenching device according to the invention, in axial section, in a side view, in a schematic representation and attached to the exit of the furnace chamber of a roller hearth furnace,

Fig. 3

2, in axial section, in a schematic diagram and on a different scale,

Fig. 4

3, cut along the line AA of Figure 3, in a plan view,

Fig. 5

1, together with the associated control device, in a schematic representation,

Fig. 6

a ring hardening plant with two series quenching devices according to the invention, in a schematic partial view and in plan view, and

Fig. 7

a diagram to illustrate the temperature-time curve in the cooling of a ring according to the invention in a gas nozzle field, with a nozzle diameter of d = 2 mm.

The quenching effect, known as the quenching intensity, which can be achieved on the workpiece with known quenching systems, which use gas, salts, oil or water in particular, is described by the so-called H value in the left part of the diagram in FIG. 1. It follows that in the practical H-value range of about 0.05 to 4, the greatest quenching intensity, i.e. the most abrupt cooling, previously only achieved using water as a quenching medium. The H value for a water quenching system is approx. 0.8 to 4. With oil as the quenching medium, depending on whether the quenching is mild or abrupt, H values of approx. 0.3 to 1 can be achieved, while hot bath quenching systems work in salt with an H value of approx. 0.2 to 0.4. The quenching intensity achievable with known gas quenching systems is relatively low; it is in an H value range of up to max. approx. H = 0.2. For the gas quenching of workpieces in the stack through which it flows, it is known that the H value has hitherto been on the order of 0.1.

The invention is based on the finding that it is surprisingly possible to carry out gas quenching in the case of workpieces consisting of steel in such a way that a quenching intensity in a range of H = 0.2 to 4 typical for oil or water quenching is achieved, and although without the gas velocity having to be brought to practically unrealizable high values or uneconomically large amounts of gas having to be circulated, ie without the delivery rate for the cooling gas exceeding a predetermined economically justifiable upper limit.

In order to achieve the high quenching intensity corresponding to the high H-value range of 0.2 to 4 when using cooling gas as the quenching medium, the cooling gas is applied to the workpiece surface to be cooled in the form of discrete impingement jets emerging from a nozzle field Brought into action, the quenching intensity being regulated in a controllable manner by appropriate selection of gas jet parameters, in particular the gas velocity W, the gas pressure P, the gas jet cross-sectional area and the number of impact jets per unit area.

This is explained below with reference to a quenching device for rolling bearing rings which operates according to the new quenching method and which is shown in FIGS. 2 to 5:
The quenching device 1 (FIG. 2) has a housing 2 which carries an all-round connecting flange 3 with which it is attached in a gas-tight manner to the outer wall of a roller hearth furnace 4, the furnace chamber of which is designated 5 and the roller hearth is indicated at 6. The essentially box-shaped housing 2 forms the actual quenching chamber. In it a pot-shaped cylindrical insert 5 is inserted from above, with an edge Flange 6 is sealed onto a corresponding annular shoulder 7 of a housing wall 8 enclosing it at a lateral distance.

The insert 5 is formed with a hollow cylindrical middle part 9, which is closed on the upper end by an integrally formed end wall 10 and which on the opposite end connects to a likewise integrally formed, radially outwardly extending circular ring surface 11, which is formed into an integrally formed outer cylindrical Wall 12 merges, which is arranged coaxially to the inner cylinder wall 13 of the middle part 9. The outer and inner cylinder walls 12, 13 together with the annular wall 11 enclose a cylindrical annular space 14, the size of which is dimensioned in the axial and radial directions such that it can just accommodate a roller bearing ring 15 which forms the workpiece to be cooled. Upwards, the annular space 14 is closed during the quenching process by an optionally operable cover 16 which, in the closed position shown in FIG. 2, rests on the edge of the insert 5 in a sealed manner by means of a seal 17. The cover 16 is connected to the piston rod 18 of a pneumatic lifting cylinder 19, which is attached to a hood 20 forming part of the housing 2, which together with the insert 5 and the housing side wall 8 delimits a loading and unloading space 21. The loading and unloading space 21 is directly connected to the furnace chamber 5 via the furnace outlet 22, ie without an interposed lock. It is closed on the opposite side by a door 23, which can optionally be opened and closed.

Below the door, a tray 24 is placed flush with the housing side wall 8 with the top of the insert 5.

The inner and outer cylinder walls 12, 13 of the insert 5 are provided with radial cylindrical nozzle bores 25 which are arranged essentially horizontally parallel to one another. Each of the nozzle bores 25 is formed on the outside of the outer cylinder wall 12 and on the inside of the inner cylinder wall 13 with a funnel-shaped countersink 26.

The nozzle bores 25 opening into the annular space 14 from both sides form a nozzle field which, over its axial height, laterally delimits the annular space 14 both on the inside and on the outside.

In operation, the nozzle bores 25 are acted upon by a cooling gas which is fed via a line connection 27 to a pressure chamber 28 formed in the housing 2, which is closed at the top by the insert 5 in the manner shown in FIG. 2 and which seals the inner and the outer Cylinder wall 12, 13 and the annular wall 11 surrounds one side. The cooling gas flowing through the nozzle bores 25 of the nozzle field into the annular space 14 is passed via at least two line stubs 30, which pass through the annular wall 11 and the bottom wall 29 of the pressure chamber 28, into a collecting space 31 of the housing 2, which is connected to a line connection 32 and below of the pressure chamber 28 is arranged.

Support means for the roller bearing ring 15 to be quenched are arranged in the annular space 14, each holding the ring at the correct height and at the correct distance with respect to the nozzle bores 25 of the nozzle field. These support means are designed in the described embodiment such that they coaxially to the insert 5 and radially centrally between the nozzle section sections in the outer and inner cylinder walls 12, 13 held rolling bearing ring 15 during the quenching process by the indicated at 33 (Fig. 2) Can set axis of insert 5 in rotation.

To achieve this, differently designed drive means can be used, two embodiments of which are illustrated in FIG. 2:
On the left of the axis 33 side drive and support means are shown, which consist of a number of side-by-side arranged rollers 34, the length of which is slightly shorter than the radial width of the annular space 14 accommodating them and which sit on radial shafts 35, which are sealed in corresponding bearings of the inner and outer cylinder walls 14 are mounted. Each shaft 35 carries on its end part lying in the cavity of the inner part 9 a wedged bevel gear 36 which is in engagement with a common ring gear 37. The ring gear 37 is in turn seated on a drive shaft 38 which is rotatably mounted coaxially to the axis 33 in a corresponding bearing bore 39 of the housing 2. The shaft 38 is set in rotation by a drive source, not shown, in the sense of the arrow indicated at 40 in FIG. 2. In the area of their Implementation through the pressure chamber 28, it is sealed at 41.

An alternative embodiment is shown in FIG. 2 to the right of axis 33. The drive and support means are formed by a turbine ring 42 which is rotatably mounted in the annular space 14 on the annular wall 11 and the inner cylinder wall 13. The turbine ring 42 has a blading indicated at 43 on which the roller bearing ring 15 rests. It is driven during operation via nozzle bores 25, which are arranged in the region of the ring wall 11 below the turbine ring 43 and can be acted upon by cooling gas from the pressure chamber 28.

The structure of the nozzle field formed by the nozzle bores 25 is illustrated in detail in FIGS. 3, 4 on the basis of a schematic model of the insert 5 and the housing 2 surrounding it. In this model representation, the same parts are provided with the same reference symbols in FIG. 2.

The cylindrical nozzle bores 25 with the same diameter d and the same nozzle pitch t are arranged in the nozzle field. In this exemplary embodiment, the nozzle array comprises three rows of nozzle bores arranged at equal intervals t, ie corresponding to the lateral nozzle pitch t (see FIG. 3). The roller bearing ring 15 to be deterred is only in the annular space 14 by the support edges 44 indicated drive and support means are arranged at such a height coaxially to the axis 33 that it lies in the axial direction symmetrically to the three rows of nozzle holes one above the other (see Fig. 3). In addition, the roller bearing ring 15 is seated radially in the center in the annular chamber 14, which means that the radial distance h between the nozzle field and the outer or inner peripheral surface of the roller bearing ring is the same. Since the nozzle bores 25 of the nozzle array are oriented at right angles to the axis 33, they are also directed at right angles to the inner and outer peripheral surface of the roller bearing ring 15. Gas jets emerging from the nozzle bores 25 therefore strike the outer and inner circumferential surface of the roller bearing ring 15 in the form of discrete impact jets.

The nozzle field described has the following characteristic dimensions:
Nozzle bore diameter d = 0.5 to 10 mm
Nozzle bore pitch t = 4 d to 8 d
Distance of the nozzle field from the workpiece surface to be cooled h = 2d to 8d.

In operation, the pressure chamber 28 is acted upon by a fan 45 (FIG. 5) with a cooling gas via the line connection 27, the total pressure in the system, i.e. in the pressure chamber 28 P = 0.5 to 20 bar.

The gas velocity w = 40 to 200 m / sec. at the outlet of the nozzle bores 25.

Since the insert 5 carrying the nozzle field is removably inserted into the housing 8, the nozzle field can easily be adapted to different dimensions and sizes of the roller bearing rings 15 or other ring-shaped workpieces to be quenched by exchanging the inserts 5. It is important in any case that the nozzle field follows the shape of the workpiece to be cooled as closely as possible in order to ensure that the workpiece surface to be cooled is acted upon as uniformly as possible by impact jets of the cooling gas emerging from the nozzle bores 25 of the nozzle field. In the treatment of ring-shaped or disk-shaped workpieces, gear wheels and the like, different designs of the insert 5 and its parts carrying the nozzle field result in accordance with the workpiece shape. As in the present case, the nozzle field can consist of several sections that cool workpiece surfaces inside and outside or above and below. The nozzle bore diameter d and the distance h to the workpiece surface to be cooled are always relatively small.

In the described embodiment, the quenching device 1 is connected directly to the outlet of the roller hearth furnace 4, the basic structure of which is described, for example, in DE-PS 38 16 503. When the cover 16 is open, the annular space 14 is therefore in direct connection with the furnace chamber 5, which contains a protective gas atmosphere. Thus, the heating of the rolling bearing rings 15 and their subsequent quenching in the nozzle field of the quenching device 1 are common Shielding gas space instead of what allows shielding gas to be saved and the time that would otherwise be required for any lock operations to be avoided. The explosion risk associated with the addition of hydrogen to the protective gas is reduced to a minimum at the same time.

In principle, the cover 16 (FIG. 2) can also be omitted if, given the shape and the material of the workpiece to be cooled, it is possible to find the deliveries in the annular space 14 with a relatively low cooling gas pressure. It is also possible to carry out the heating and the quenching in the nozzle field of the quenching device 1 in a common overpressure space formed by the furnace chamber 5 and the annular space 14 if the walls of these spaces are designed to be overpressure-resistant. This also eliminates the pressure lock formed by the cover 16.

The cooling gas supply of the quenching device 1 is illustrated in FIG. 5:
The blower 45, which acts on the pressure side 28 with cooling gas via the line connection 27, is connected on the suction side via a gas cooler 46 with a coolant actuator 47 to the line connection 32 of the housing 2. To the cooling gas line piece 48 lying between the gas cooler 46 and the line connection 32, a gas expansion tank 50 is connected via a control valve 49, from which a waste gas line 52 branches off via a pressure regulator 51, which leads back into the furnace chamber 5 if necessary. On the pressure side of the blower 45 are connected to its pressure line 53 via control valves 54, 55, two compressed gas cylinders 56, 57, which contain additional gas, for example, hydrogen and / or nitrogen. In addition, there are 53 sensors 58, 59, 60, 61 in the pressure line for the mass flow, the temperature, the pressure and the composition of the cooling gas fed into the pressure chamber 28.

On the output side, these sensors are connected to a process computer 62, to which they transmit signals characteristic of the parameters they monitor. In addition, the process computer 62 receives signals characterizing the actual temperature of the roller bearing ring 15 to be quenched, which signals are supplied by a temperature sensor 63 which senses the outer peripheral surface of the roller bearing ring via a window 64 inserted pressure-tightly into the housing side wall 8 and the insert 5.

The process computer 62 calculates from the process-specific signals received by the sensors 58 to 61 (mass flow, temperature, pressure and composition of the cooling gas) and from previously entered data which are characteristic of the workpiece 15 to be treated (geometry and material values) and the nozzle field Output signals for controlling the blower 45, the control valves 54, 55 of the coolant control valve 47 influencing the additional gas quantity and the control valve 49 leading into the expansion tank 50. Together with the signals received from the temperature sensor 63 for the actual temperature of the workpiece 15, the process computer 62 regulates this way automatically the quenching process the workpiece located in the annular space 14, whereby it can largely regulate each predetermined temperature-time profile on the surface of the workpiece 15 to be cooled.

During the operation of the system described, the workpieces in the form of the roller bearing rings 15 on the roller hearth 6 are continuously guided through the furnace chamber 5 and heated to hardening temperature in the protective gas atmosphere contained therein. After this heating has been completed, the roller bearing rings 15 pass one after the other through the furnace outlet 22 (FIG. 2) into the loading and unloading space 21 of the quenching device 1, the cover 16 of which is in the open upper position when the door 23 is closed. The roller bearing ring 15 arriving in the loading and unloading chamber 21 falls into the annular chamber 14, in which it comes to lie in the correct position on the drive and / or support means, for example on the collar rollers 35 or the turbine ring 42. Then the lid 16 is closed; the fan 45 (FIG. 5) is switched on, and the pressure chamber 28 is acted upon by cooling gas, which is the same protective gas as is contained in the furnace chamber 5.

The cooling gas emerging from the nozzle bores 25 impinges in the form of impact jets on the outer and inner circumferential surface of the roller bearing ring 15 to be cooled, where it causes a rugged, uniform cooling of the rotating roller bearing ring 15. The cooling gas flowing out of the roller bearing ring 15 is discharged from the blower 45 via the line connection piece 30 sucked off, the amount of heat absorbed is withdrawn in the gas cooler 46. The temperature-time profile of the cooling is regulated by the process computer 62 in the manner already described. After cooling to the desired temperature has been achieved, the fan 45 is turned off, the cover 16 is opened and the cooled roller bearing ring 15 is removed from the annular space 14 by a manipulator (not shown) and placed on the storage table 24 with the door 23 open for a short time. After closing the door 23, the quenching device is ready for cooling the roller bearing ring 15 which is brought up next by the roller hearth.

The quenching intensity that can be achieved in the nozzle field by gas quenching in the manner described is illustrated in the diagram of FIG. 1 on the right in comparison with the quenching intensities that can be achieved in the known quenching systems. Four nozzle fields are shown, the nozzle bore diameter d of which is 1 in each case , 2.4 and 8 mm. The nozzle pitch t and the nozzle field distance h are 5 x d. The gas velocity w is 100 m / sec.

sie überschreitet in keinem Fall einen maximalen Grenzwert von 1000 kW je m² Düsenfeld.The power of the blower 45 required for gas production is approximately

$\text{N ≈ 50 xp. (1 -0.009. Vol\% H₂) in kW per m² nozzle field,}$

in no case does it exceed a maximum limit of 1000 kW per m² of nozzle area.

For each nozzle bore diameter d, the gas pressure is p entered on a scale between 1 and 8 bar.

It can be seen from the diagram that the quenching intensity increases as the nozzle bore diameter d becomes smaller. Therefore, from the four nozzle fields shown in Fig. 1 with d = 1, 2, 4 and 8, the smallest nozzle field, e.g. with d = 1 mm. The diagram shows that the quenching effect or intensity of a medium oil quenching (H = 0.4 to 0.7) can be achieved even without overpressure, and this with a blower output of 35 to 50 kW per m² of nozzle field.

Nozzle bore diameters <1 mm can only be used in special cases due to the risk of contamination and the small distance.

On the other hand, it may be necessary to increase the nozzle bore diameter d and thus the distance h of the nozzle field from the workpiece surface to be cooled if the workpieces to be quenched are larger or have a specially shaped surface, as is the case with gearwheels, for example. With the same H value, this must be compensated for by a higher pressure p and an equally higher fan output.

In general, the quenching intensity can be increased by increasing the pressure p of the cooling gas and by reducing the nozzle bore diameter d at a small distance h. A further increase can be compared by adding a gas to air of high thermal conductivity, especially hydrogen, which is often contained in protective gases from the furnace anyway. A helium additive would have a comparable effect, but is generally not an option for economic reasons. The diagram in FIG. 1 shows that with the addition of hydrogen, for example 40% by volume, with a nozzle bore diameter of 1 mm and a pressure of 8 bar, it is readily possible to achieve quenching intensities which are typical for water quenching (H. = 2).

The quenching device explained with reference to FIGS. 2 to 5 has been attached to a continuous continuous furnace, for example the roller hearth furnace 4, inter alia the advantage that it can be arranged together with the continuous furnace directly in a production line for workpieces which, prior to their further processing, undergo heat treatment and subsequent deterrence is required. In the case of oil quenching systems, for example, this is not readily possible due to the associated fire risk. The entire heat treatment process can be automated, whereby the workpiece throughput per unit of time can also be increased if necessary, while at the same time there is the option of cooling the workpieces, if necessary, with different gas inlet temperatures in the individual stages, possibly even with intermediate operations for calibrating the workpieces, etc. , to subjugate. This is briefly explained with reference to FIG. 6:
In this case, the roller bearing rings 15 in three rows on the roller hearth 6 of the roller hearth furnace 4 transported in parallel through the furnace chamber 5. As soon as the front row of the continuously transported roller bearing rings 15 interrupts a light barrier 65 arranged in the vicinity of the furnace outlet 22, a subsequent outlet-side section 66 of the roller hearth 6 leading to the quenching device is driven by an overdrive drive 67 which increases the distance to the roller bearing ring row the subsequent row of rolling bearings is transported through the furnace outlet 22 into a first cooling station A. In the cooling station A, three quenching devices 1 are accommodated in parallel next to one another in a common housing 68 which is flanged directly to the outlet side of the roller hearth furnace 4 and whose cooling gas inlets and outlets are indicated in FIG. 6 by two arrows 69, 70. Each of the quenching devices 1 is designed in accordance with FIG. 2.

After the roller bearing rings lying in parallel next to each other have simultaneously cooled in the three quenching devices 1 of the first cooling station A to a predetermined first temperature value, manipulators (not shown in any more detail) are transferred to the three downstream quenching devices 1 of a second cooling station B of the same design, in which the cooling takes place Room temperature takes place, whereupon the workpiece group consisting of three roller bearing rings 15 lying next to one another is transported away via the common storage table 24.

The temperature-time profile for this step quenching is shown in FIG. 7 and on the basis of the following example of the method according to the invention explained:

Example:

A ring 15 of a roller bearing made of material 100 Cr6 is hardened in the nozzle field instead of the usual oil quenching. Workpiece data: Outer diameter: 140 mm Inside diameter: 116 mm Ring width: 40 mm Dimensions: 1.5 kg Surface (outside and inside): 0.032 m² Dimensions / surface: 47 kg / m²

Since the critical cooling time from 800 to 500 ° C for this steel is about 10 seconds, an H-value of 0.8 is required, corresponding to a rugged oil cooling. The nozzle area 2 (FIG. 1) is selected for the ring size and width. Nozzle array 2 Nozzle diameter d: 2 mm Nozzle pitch t: 10 mm Distance to the cooled surface h: 10 mm Number of nozzles outside: 200 Number of nozzles inside: 126 Total number of nozzles: 326 Nozzle area: 0.032 m² Total nozzle cross section: 0.001 m² Gas velocity: 100 m / s Gas flow: 360 m³ / h

The blower output in variant 1 is comparable to that of a circulation pump in an oil bath. With a cooling time of approx. 20 seconds per ring, the energy requirement per kg hardness is 0.01 kWh for variant 1 and 0.04 kWh for variant 2.

In the quenching phase, the temperature in the core of the rotating ring has cooled to 500 ° C after 10 seconds. After 18 seconds, 280 ° C is reached on the surface of the ring (optical control) and the cooling is switched off (cooling station A).

In phase II, the ring can be calibrated at a defined temperature before the formation of martensite.

In phase III, the ring is cooled in a further nozzle station with a supercooled circulating gas to about 0 ° C. for the complete formation of martensite (cooling station B).

The critical cooling time from 800 to 500 ° C, which in the example is about 10 seconds, can be even shorter for unalloyed and low-alloy steels. The very fast control of the quenching effect required for this and the very short movement sequences of the quenching device 1 required for this purpose, in contrast to the conditions in known gas cooling devices, can easily be achieved with the invention in a reproducible, economical manner. The necessary heat transfer between the workpiece surface to be cooled and the gas flow with high values of the heat transfer coefficient α can be achieved in the method according to the invention with the nozzle fields with a relatively small nozzle diameter d and small distance h to the workpiece surface to be cooled. As the heat flow densities on the workpiece surface reach the MW / m² range in the first seconds and there is considerable gas heating, it has been shown that the α values cannot correctly describe the process. It is therefore used to identify the quenching effect of the H-value used when hardening steel. The hardness result on the workpiece, ie the hardness curve over the cross section of the workpiece on the hardened surface, depends on the material, ie the steel alloy, on the cross section and on the quenching intensity (H value). The H value on a hardened steel workpiece can be determined from this known relationship. In practice, cylindrical specimens in particular are often used for this purpose (cf., for example, "Technology of heat treatment of steel", VEB German Publishing House for Basic Industry Leipzig, 2nd edition, page 604).

In the exemplary embodiment described, the nozzle field is equipped with cylindrical nozzle bores 25. In principle, it would also be conceivable to use other cross-sectional shapes, for example slot nozzles or the like, which is pointed out for the sake of order. All gases and gas mixtures which can be used for the respective purpose, including air, nitrogen and the like, can be used as the cooling gas.

In the new method, the workpieces 15 are quenched individually, because it is usually only possible in this way to adapt the nozzle field closely enough to the shape of the workpiece surface to be cooled and at a sufficiently small distance to arrange this. In certain cases, for example in the case of ring-shaped workpieces, it is also conceivable to introduce several workpieces approximately one above the other into a space delimited by nozzle fields and to treat them in this space, although precautions must then also be taken to adapt the nozzle fields to the workpiece surface remains guaranteed. A workpiece can also consist of several small individual parts, for example small screws, etc., which lie in a small, uniform bed height on a gas-permeable carrier, for example in a wire basket. The nozzle field then acts on the top and / or bottom of the bed, the dimensions and shape of which is adapted to the nozzle field.

Depending on the shape and shape of the workpieces to be treated, there may occasionally be a need to achieve a different, in particular lower, quenching intensity in certain areas of the workpiece surface to be cooled. This can be achieved, for example, by providing nozzle bores 25 of the nozzle array - individually or in groups - with closure or throttle devices. An example of this is illustrated in FIG. 3 in the form of an aperture ring 70 which is arranged on the outer cylinder wall 13 of the insert 5 so as to be longitudinally adjustable.

It was explained with reference to FIG. 2 that the roller bearing ring 15 is rotated relative to the stationary nozzle field during cooling. Alternatively, the arrangement could of course also be such that the roller bearing ring 15 is fixed while the insert 5 and thus the nozzle field execute a rotary movement. Axial up and down movements of the workpiece and / or the nozzle field are also conceivable and can be achieved with simple mechanical means.

A two-stage cooling of the roller bearing rings 15 in two cooling stations A and B connected in series was explained with reference to FIG. 7. Such a division into several cooling stations in series is often not necessary. By appropriate programming of the process computer 62 it can also be achieved that after a predetermined time by reducing the gas velocity w and / or the gas pressure p in accordance with the program, the cooling effect is throttled in order to imitate the effect of an oil or hot bath hardening in the salt.

Claims (30)

Process for quenching metallic workpieces, with a quenching intensity which is in a range (H = 0.2 to 4) typical for oil or water quenching, in which a quenching medium is brought into action on the surface of the workpieces to be cooled, characterized by the Use of a cooling gas as a quenching medium, which is brought to bear on the workpiece surface to be cooled in the form of discrete impingement jets emerging from a nozzle field, with the quenching intensity being limited to a predetermined maximum limit of approx. 1000 kW / m² nozzle field for the cooling gas delivery rate is brought to a value between H = 0.2 and H = 4 by appropriate selection of gas jet parameters, in particular the gas velocity w, the gas pressure p, the gas jet cross-sectional area and the number of impact jets per unit area. A method according to claim 1, characterized in that the quenching intensity is regulated or controlled by influencing gas jet parameters and / or the effective nozzle cross section. Method according to one of the preceding claims, characterized in that a cooling gas velocity w of w = 40 to 200 m / sec. is used. Method according to one of the preceding claims, characterized in that a cooling gas pressure p of p = 0.5 to 20 bar is used. Method according to one of the preceding claims, characterized in that an effective nozzle diameter d of d = 0.5 to 10 mm is used in the nozzle field. Method according to one of the preceding claims, characterized in that a nozzle pitch t of t = 4 d to 8 d is used in the nozzle field, where d is the effective nozzle diameter. Method according to one of the preceding claims, characterized in that the nozzle field is arranged at a distance h from H = 2d to 8d from the surface to be cooled, d being the effective nozzle diameter. Method according to one of the preceding claims, characterized in that air, nitrogen or a gas mixture is used as the cooling gas. Method according to one of claims 1 to 7, characterized in that a protective gas is used as the cooling gas. Method according to one of the preceding claims, characterized in that the cooling gas contains hydrogen or another gas with increased thermal conductivity compared to air in a proportion of 0 to 100 vol.%. Method according to one of the preceding claims, characterized in that the workpieces are heated and then quenched in a room which contains the essentially same gas atmosphere for both processes. Method according to one of the preceding claims, characterized in that a gas overpressure is maintained at least temporarily in the space at least partially delimited by the nozzle field. Process according to claims 9 and 11 or 12, characterized in that the gas atmosphere consists of protective gas. Method according to one of the preceding claims, characterized in that it is used for quenching ring-shaped or tubular workpieces and that in this case, from a nozzle field adapted to the shape of the workpieces, impingement jets of the cooling gas onto both the outer and the inner lateral surface and optionally onto the End faces of the workpiece are brought into effect. Method according to one of the preceding claims, characterized in that a relative movement between the workpiece surface to be cooled and the impact beams is maintained at least temporarily during quenching. Quenching device for carrying out the method according to one of the preceding claims, in particular for treating rotationally symmetrical workpieces, such as rings, gearwheels, disks, shafts and the like, with a quenching chamber in which at least one space, which is at least partially delimited by a nozzle field and is used to accommodate individual workpieces, is provided characterized in that the space (14) is essentially closed, and that the nozzle field is designed to match the shape of the surface of the workpiece (15) to be cooled and is arranged and dimensioned such that the surface of the workpiece (15) to be cooled is essentially in operation with discrete impingement jets of the cooling gas is applied to produce a quenching intensity which is in a range of H = 0.2 to 4 typical for oil or water quenching, the delivery capacity of the cooling means conveying the cooling gas (45) to a maximum limit of approximately 1000 kW / m 2 nozzle field is limited. Apparatus according to claim 16, characterized in that the space (4) is designed as an overpressure space with a pressure-tight lockable loading and unloading opening. Apparatus according to claim 16 or 17, characterized in that at least some nozzles (25) of the nozzle array are provided with throttle and / or closure means (70) which can be actuated as desired. Device according to one of claims 16 to 18, characterized in that the nozzle field is at least partially formed on an insert part (5) which is interchangeably inserted into a housing (2). Device according to one of claims 16 to 19, characterized in that it has drive means (38) for rotating the workpiece (15) inserted into the space (14) and / or at least part of the nozzle field. Apparatus according to claim 20, characterized in that the drive means have a turbine element (42) which can be acted upon by cooling gas. Device according to one of claims 16 to 21, characterized in that a measuring device (63, 64) for the workpiece temperature during cooling is assigned to the space (14) at least partially delimited by the nozzle field. Device according to one of claims 16 to 22, characterized in that it has a process computer (62) for controlling the time course of the cooling process, the process data such as flow rate, pressure, temperature and composition of the cooling gas etc. and workpiece-specific data such as geometric data as input signals Shape and dimensions, material composition etc. and / or data characterizing the nozzle field are supplied, and the output signals calculated therefrom in accordance with the program for influencing the cooling gas admission to the nozzle field and / or the effective cooling gas passage cross section of at least some nozzles (25) of the nozzle field and / or a relative movement between the workpiece (15) and the nozzle field. Device according to one of claims 16 to 23, characterized in that it has program control means (62) through which the cooling effect of the impact jets on the workpiece surface to be cooled by correspondingly influencing the speed w and / or pressure p of the impact jets and / or the effective passage cross section can be influenced by nozzles (25) of the nozzle field in the sense of simulating the quenching effect of an oil or hot bath hardening in the salt. Device according to one of claims 16 to 24, characterized in that it is connected directly to the outlet of the furnace chamber (5) containing a protective gas atmosphere of a continuous continuous furnace, in particular a roller hearth furnace (4). Device according to Claim 25, characterized in that it has a loading and unloading chamber (21) which is connected to the furnace chamber (5) and which is closed to the outside by an optionally operable door (23). Device according to claims 16 and 26, characterized in that the loading and unloading chamber (21) is connected to the space (14) at least partially delimited by the nozzle field by means of optionally operable closure means (16). Device according to one of Claims 16 to 27, characterized in that it has a plurality of spaces (14) which are arranged next to one another and can be operated parallel to one another and are designed for simultaneous quenching and are at least partially delimited by a nozzle array. Device according to one of claims 16 to 28, characterized in that it comprises a plurality of one behind the other, each from a nozzle field Has at least partially delimited spaces (14), which can be passed through one after the other by the workpieces (15) to be treated, with the interposition of other treatment stations, and which are set up for operation with different cooling conditions. Quenching device according to one of claims 16 to 29, characterized in that the workpiece consists of small parts which are applied to a gas-permeable carrier with a low uniform bulk and that the nozzle field the dimensions and shape of the top and / or bottom of the bulk is adjusted.

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