EP0621344B1 - Flexible adaptive quenching - Google Patents

Abstract

To obtain a defined quenching profile in the quenching of metallic workpieces in a liquid bath after a heat treatment, a process is suggested in which the flow velocity of the liquid is adjusted in the region of the workpieces to 10 to 30 m/sec, 0.5 to 1.5 m/sec or 0 m/sec, while at the same time, on the other hand, the liquid volume available for heat exchange is variably adjusted. <IMAGE>

Description

The invention relates to a method for quenching metallic workpieces in a liquid bath after a Heat treatment and a device for performing the Procedure. In particular, the invention relates to a method for quenching batches of material after a heat treatment be quenched in an oil bath.

It is known, for example for hardening steel parts, metallic workpieces after heat treatment in Dip quenching liquid baths, causing the immersed Workpieces are cooled to a predetermined temperature. The properties of the materials thus obtained, for example their surface hardness, brittleness etc. depend on the Quenching essentially depends on which Temperature difference between the workpiece surface and the Cooling medium in which time unit is achieved. This Quenching or cooling rate is essentially depending on the medium used for deterrence. As liquid media come with, for example, water, water dissolved salts, water with polymers, different oil qualities as well as salt baths in question.

For a given quench liquid, the rate of cooling can in the quench bath only by the initial temperature and be influenced by the selected circulation rate. So it is known in the prior art, for example from EP-A-0 049 339, by varying the circulation rate Oil quenching baths the cooling speeds and thus the Workpiece properties vary. For example known to constantly circulate the oil in an oil quenching bath, usually flow velocities of about 1 m / sec to get voted. Because of the supposedly high power requirement and due to the lack of clear control parameters are up to date Technology only extremely brief increases in flow velocities, for example in the range of 2 m / sec, known with which at the beginning of the quenching process on the Workpiece surface achieved very high cooling speeds become.

However, these changes are very limited possible so that a single liquid bath is not a large one Variation of the cooling rate allows.

One way to increase the range of variation is in using multiple quench baths with different Liquids, which is very expensive. In addition, the Materials from the heat treatment chamber to the individual Quench baths and between each of the quench baths an atmosphere that may have to be exposed to protective gas, transported to undesirable oxidation prevent. This increases the effort even more.

Nevertheless, the different hardness properties of the Quench baths desirable. The fastest cooling is in Water quench baths reached, the slowest in salt baths. The cooling rate of oil baths lies between the two. While desirable by water quenching Hardness can be achieved, the disadvantage of water quenching however, in that during the further cooling martensitic transformation of the temperature gradient taking place very large between surface and core of the respective workpiece is, so that it either leads to workpiece cracks or very high Tensions can come. These tensions can warp of the workpiece.

In contrast, salt bath quenching offers depending on the temperature of the salt bath used the possibility in the area of Martensite transformation to slow down the cooling and one To generate temperature compensation between the edge and core, so that the martensitic transformation takes place without thermal stresses can.

In between is the oil deterrent, which is in the upper one Temperature range, especially during the cooking phase relatively high quenching intensity, in the lower Temperature range, however, has a medium.

The desire for many workpieces is the high Quenching intensity of water quenching in the medium temperature range obtained properties combined with the low warpage martensite conversion caused by a slow Cooling rate reached in the lower temperature range becomes.

The state of the art only offers timely implementation from a water bath to a salt bath, which is extremely difficult is because the right time to take the batch out the water bath and the implementation in the salt bath hardly determined and the necessary short conversion times for thin ones Workpieces can hardly be reached in practice. Also have to there are two quenching baths and the batch may have to be replaced by one Protective gas atmosphere can be transported.

Proceeding from this, the object of the present invention is to specify a method for quenching metallic workpieces, in which a very high cooling rate is achieved by quenching in a single liquid medium in the medium temperature range, while a very slow cooling rate is set in the lower temperature range.

Furthermore, the invention is intended to be a device for Implementation of the method according to the invention can be specified.

To achieve this object it is stated that in order to achieve a predeterminable Abschreckprofils a workpiece, the flow rate of the liquid in the region of the work piece one after the other in any order to 10 to 30 m / sec, 0.5 to 1.5 m / sec or 0 m / sec is set, the setting of this flow rate in terms of time and sequence depending on the given quenching profile and in that at the same time with each change in the flow rate, the liquid volume available for heat exchange is changed depending on the given quenching profile.

At the same time means that the adjustment of the volume in each case when the speed change takes place. Variable means that the volume with each change depending on the desired quenching profile regardless of speed is adjusted.

The deterrent method according to the invention is preferably carried out only in oil instead, and it can by the invention possible control measures the desired cooling rates can be set.

Should a batch of workpieces after the heat treatment in Art are ironed to achieve a defined quenching profile that is, the cooling operations of a given curve can be followed by varying the flow velocities the one available for heat exchange Liquid and through simultaneous volume variation the Set the desired cooling process.

A method is advantageously specified in which in one first process step the workpieces after a Heat treatment in a given volume of liquid, in particular Oil volume, are used, being in the volume a flow speed of 10 to 30 m / sec is set becomes. This initially results in a very high cooling rate achieved. At the desired time, a second Process step the flow rate to zero be reduced, i.e. the quench liquid is at rest. At the same time, the volume of liquid is limited. At this Cooling the batch in the limited oil volume is about is a quasi adiabatic cooling, which is beneficial Way by the ratio of the batch mass and the batch temperature the oil mass and oil temperature is determined. The thermal data can be used in the case of quasi Easily calculate adiabatic cooling and as control variables use for cooling the batch. Then in a third process step again the volume restriction canceled and the flow rate to 0.5 to 1.5 m / sec, resulting in a medium cooling rate results.

In an advantageous manner, the Temperature distribution determined and as a control parameter used.

Preferred features of the method can be found in the dependent claims.

With controlled cooling at a high cooling rate in the medium temperature range and a low cooling rate in the lower temperature range is the time where to reduce the flow velocity and that Restricting fluid volume is of great importance. This point in time can be determined using the temperature values in the Determine the area of the batches and ideally corresponds to that Time shortly before the martensite start temperature is reached Batch.

On the one hand, there are advantages to this new quenching process in that the batches are no longer in different quench baths have to be implemented. By using appropriately higher Flow velocities can also be purely water-hardening Steels to be deeply hardened. At the same time, the procedure can be set as desired, i.e. it is also possible with this Process from the start batches that have a low quenching rate need with only minor Cool down oil flow rate and end up with limited Cool the liquid volume very slowly. The The method according to the invention is therefore extremely broad Spectrum can be used very flexibly. For example, even low-warpage, very deeply hardened workpieces easy adjustment of flow velocities and volumes produce.

US-A-2 639 047 discloses an apparatus for heat treatment a quench basin, which facilities to carry the batch to be deterred and a liquid bath comprises, and at least one oil circulation pump for moving the Liquid bath, the quenching basin directly on one Heat treatment furnace is arranged and located above the Quenching tank is a prechamber in which a Lifting device for lifting and lowering the batch from or is arranged in the quenching basin. Such a device is in accordance with the invention characterized in that a lifting and lowering cover device in the furnace antechamber is arranged, the liquid volume of the liquid bath in the lowered state limited that the batch is available for heat exchange.

This cover device is advantageously a hood, which also advantageously has a flap.

The fact that the hood has a flap, the Cooling over the batch defined with a certain Perform temperature gradients. In combination with one Temperature sensor within the batch can measure the temperature in the Workpiece area by temporarily opening or closing the Flap in the hood can be controlled.

A particular advantage is in the quenching pool Nozzle system arranged, through which in connection with a Circulation pump the liquid with very high flow rate can be directed to the batch.

It is stated in a particularly advantageous manner that the Nozzle system consists of nozzles that run around the batch and between the batch parts can be arranged.

To monitor the individual process steps is the Temperature sensor connected to a control unit.

Fig. 1a, 1b und 1c

eine schematische Darstellung einer Vorrichtung zur Durchführung des erfindungsgemäßen Abschreckverfahrens in verschiedenen Verfahrenszuständen;

Fig. 2

ein Diagramm des Temperaturverlaufes über die Zeit bei der Abschreckung eines Werkstückes nach dem erfindungsgemäßen Verfahren;

Fig. 3

ein Diagramm des Temperaturverlaufes über der Zeit zur Ermittlung der Umschaltzeitpunkte für die Durchführung des erfindungsgemäßen Verfahrens;

Fig. 4

ein Ausführungsbeispiel für die Düsenanordnung in einer Abschreckkammer; und

Fig. 5

eine schematische Schnittdarstellung an der Stelle A-A gemäß Fig. 4.

Further advantages and features of the invention result from the following description with reference to the figures. Show:

1a, 1b and 1c

a schematic representation of a device for performing the quenching method according to the invention in different process states;

Fig. 2

a diagram of the temperature profile over time in the quenching of a workpiece according to the inventive method;

Fig. 3

a diagram of the temperature curve over time to determine the switching times for performing the method according to the invention;

Fig. 4

an embodiment of the nozzle arrangement in a quenching chamber; and

Fig. 5

3 shows a schematic sectional illustration at position AA in FIG. 4.

1a, 1b and 1c schematically show a system with which the method according to the invention can be carried out.

In a known manner is a heating chamber 1 for heat treatment metallic workpieces closed with a door 2, which in shown embodiment in the direction of the arrow upwards can be opened. A pallet 3 is in the heating chamber Workpieces, one batch, arranged for heat treatment. A Temperature sensor 4 is in the form of a thermocouple probe also arranged on batch 3.

In addition to the heating chamber 1, a prechamber 5 is arranged, which has a device for raising and lowering batch 3, and also a hood 6 to cover the batch. The hood 6 is in Direction of the arrows can be lowered by the lifting device 7 or liftable.

This is in the lower part of the antechamber 5 Quenching basin 8, which is filled with oil.

The batch is located in the device shown in FIG. 1a 3 in the heating chamber 1 for heat treatment of the workpieces. After Completion of the heat treatment is the door 2 in a known manner raised and move the batch into prechamber 5. The Thermocouple probe 4 is then sent to a control unit 9 connected as seen in Fig. 1b. Then the batch is in the quenching basin lowered. The antechamber 5 can be known Way with protective gas. In the quench basin the oil by means of circulation pumps and nozzle arrangements, not shown to the desired flow rate brought what is controlled by the control unit 9. If necessary, the volume of liquid in the Quenching basin is limited in that the hood 6 by means of Lifting device 7, as shown in dashed lines in Fig. 1c, in the Quenching basin is lowered onto the batch.

The temperature course over time can be seen in FIG. 2 see where the time t on the abscissa and the time on the ordinate Temperature T are applied.

A -

Abkühlen in dem Abschreckbad bei hoher Strömungsgeschwindigkeit,

B -

Abkühlen im Abschreckbad in stehender Flüssigkeit oder bei sehr niedriger Strömungsgeschwindigkeit und beschränktem Flüssigkeitsvolumen,

C -

Abkühlen im Abschreckbad bei mittlerer Strömungsgeschwindigkeit und ohne Flüssigkeitsvolumeneinschränkung;

T_W-

Wendetemperatur

T_G-

Gleichgewichtstemperatur

t_A-

Anfang des Aufsetzens der Haube, und

t_E-

Ende der Bedeckung mit der Haube.

In Fig. 2 mean

A -

Cooling in the quench bath at high flow rate,

B -

Cooling in the quenching bath in standing liquid or at very low flow speed and limited liquid volume,

C -

Cooling in the quench bath at medium flow speed and without restriction of liquid volume;

T _W -

Turning temperature

T _G -

Equilibrium temperature

t _A -

Beginning of the hood, and

t _E -

End of the hood.

While the solid curve with the cooling process adiabatic cooling shows is dashed in area B of the Cooling process shown without adiabatic cooling.

After the heat treatment, the batch 3 is inserted into the quenching basin 8, in which the oil is directed onto the batches at high flow rates by means of circulation pumps. This is the area A in FIG. 2, in which, as shown, a very rapid cooling takes place. The flow rate is then reduced in the region of the temperature T _W by calming the oil and lowering the hood onto the workpiece. This results in a very slow cooling in area B. When the equilibrium temperature is reached at time t _E , the hood is raised again and the cooling process continues with a correspondingly low flow rate.

Without putting on the cap when the liquid is calm, the Area B the cooling curve take the broken line, which would lead to the undesirable tensions.

O -

Temperaturverlauf an der Dberfläche des Werkstücks,

C -

Temperaturverlauf in der Querschnittsmitte,

W -

Wendepunkt.

3 also shows a diagram in which the time t is plotted on the abscissa and the temperature T is plotted on the ordinate. It is a ZTU diagram (time-temperature conversion diagram) of the relevant steel quality. It means:

O -

Temperature curve on the surface of the workpiece,

C -

Temperature curve in the middle of the cross-section,

W -

Turning point.

Furthermore, the temperature profiles, here 1 / 2R and 3 / 4R, are given in different cross-sectional areas. If, for example, the temperature T _{W is} reached at point 1 / 2R on the cross section of a round bar, the circulation speed is automatically reduced. Direct switching points thus result from a ZTU diagram as shown in FIG. 3, with which the method according to the invention can be controlled by a control unit as a function of temperature measurements.

Fig. 4 shows, for example, the arrangement of jet nozzles in a quench basin. 8 are on the wall of a quenching basin a plurality of wall-side nozzles 10 are arranged. In the Quenching basins 8 are one above the other in a known manner stacked workpieces 12 introduced. Between the workpieces 12 middle nozzles 11 are set up. All nozzles are made using Circulation pumps 13 supplied with pressure. The wall-side nozzles 10 are over the entire height and along the entire circumference of the Quenching basin 8 arranged. The middle nozzles 11 can in Form so-called nozzle sticks can be arranged. Such Nozzle sticks do not have to be installed in a fixed location, but instead depending on the type of workpiece in the quenching basin 8 be positioned. Like the cut along the line A-A 5 shows, by the arrangement according to the invention the Nozzles allow the quench liquid to be directly in the area the workpieces have a corresponding flow velocity has, whereby the desired effect with the method according to the invention is achieved on all sides.

Reference list

1

Heating chamber

2nd

door

3rd

Batch

4th

Thermocouple probe

5

Antechamber

6

Hood

7

Lifting device

8th

Quenching pool

9

Control unit

10th

Nozzles

11

Nozzles

12th

Workpieces

13

Circulation pump

Claims (15)

1. Method of quenching metal workpieces in a liquid bath after a heat treatment, characterised in that, to obtain a presettable quenching profile of a workpiece, the flow rate of the quenching liquid in the region of the workpiece is adjusted successively in any order to

   a1) 10 to 30 m/s

   a2) 0.5 to 1.5 m/s or

   a3) 0 m/s,

   wherein this flow rate a1), a2), a3) is adjusted with respect to duration and sequence as a function of the quenching profile preset at any given time, and in that, simultaneously with every change of flow rate, the liquid volume available for heat exchange is varied as a function of the quenching profile preset at any given time.
2. Method according to claim 1, characterised in that the workpieces in a first step in a given liquid volume are subjected to a flow rate of 10 to 30 m/s, in a second step remain in a still liquid bath and with a limited liquid volume, and in a third step, with the restriction on liquid volume lifted, are subjected to a rate of 0.5 to 1.5 m/s.
3. Method according to claim 2, characterised in that switching from the first to the second step takes place shortly before reaching the martensitic transformation temperature.
4. Method according to either of claims 2 or 3, characterised in that switching from the second to the third step takes place when the temperature distribution over a workpiece cross-section has equalised.
5. Method according to any of the preceding claims, characterised in that quenching with a still liquid bath and limited liquid volume is determined by the ratio of charge mass and charge temperature to liquid mass and liquid temperature.
6. Method according to any of the preceding claims, characterised in that the temperature distribution is continuously determined in the workpieces to be quenched.
7. Method according to any of the preceding claims, characterised in that the restriction of liquid volume is determined as a function of the temperature values in the region of the workpieces to be quenched.
8. Apparatus for carrying out the methods according to one or more of claims 1 to 7, with a quenching tank (8) which includes means for carrying the charge (3) of metal workpieces (12) to be quenched and a liquid bath, in particular oil bath, as well as with at least one circulating pump (13) for moving the liquid bath, wherein the quenching tank (8) is arranged directly on a heat treatment furnace, over the quenching tank (8) is arranged a furnace pre-chamber (5) which is to be connected by a furnace door (2) to a furnace chamber (1) of the heat treatment furnace and wherein in the furnace pre-chamber (5) is arranged a lifting device (7) for lifting and lowering the charge (3) out of and into the quenching tank (8), characterised in that in the furnace pre-chamber (5) is arranged a covering device which can be lifted and lowered and which when lowered restricts the liquid volume of the liquid bath which is available to the charge (3) for heat exchange.
9. Apparatus according to claim 8, characterised in that the covering device is a hood (6).
10. Apparatus according to claim 9, characterised in that the hood (6) comprises a flap.
11. Apparatus according to any of claims 8 to 10, characterised in that in the quenching tank (8) is arranged a nozzle system (10, 11) which is connected to at least one circulating pump (13) for conducting the liquid at a high flow rate onto the charge (3).
12. Apparatus according to claim 11, characterised in that the nozzle system (10, 11) consists of nozzles (10, 11) arranged laterally around the charge (3) and between individual charge portions.
13. Apparatus according to any of claims 8, 11 or 12, characterised in that the covering device is a plate by means of which side walls of the nozzle system (10, 11) can be closed at the top.
14. Apparatus according to any of claims 8 to 13, characterised in that between the workpieces (12) ofthe charge (3) is arranged at least one temperature sensor (4).
15. Apparatus according to claim 14, characterised in that the temperature sensor (4) is connected to a regulating unit (9) for monitoring and regulating the individual steps of the method.

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