U.S. patent application number 10/485286 was filed with the patent office on 2004-09-30 for method for cooling work pieces especially shape-rolled products from rail steel.
Invention is credited to Kuppers, Klaus, Meyer, Meinert, Nerzak, Thomas, Plociennik, Uwe.
Application Number | 20040187974 10/485286 |
Document ID | / |
Family ID | 7693931 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040187974 |
Kind Code |
A1 |
Kuppers, Klaus ; et
al. |
September 30, 2004 |
Method for cooling work pieces especially shape-rolled products
from rail steel
Abstract
The invention relates to a method for producing especially
shape-rolled products from rail steels that have a finely perlitic
and/or ferritic/perlitic structure after cooling. The inventive
method is characterized by guiding the workpiece through a cooling
stretch that is composed of individual independent cooling modules
(2a-e) having independently adjustable cooling parameters. Between
said cooling modules (2a-e) intermediate zones (5a-e) are provided
for relieving the stress of the structure comprising means for
determining the actual temperature (T.sub.ACTUAL) of the respective
work piece in said intermediate zones (5a-e) Depending on the
respective actual temperature values (T.sub.ACTUAL) of the work
piece in an intermediate zone (5a-e) the specific cooling
parameters, especially the cooling intensity, of the respective
subsequent cooling module (2b-e) are controlled in order to
safeguard a defined temperature of the work piece during the entire
passage through the cooling stretch (1), the defined temperature
(T.sub.DESIRED) of the work piece being above a critical
temperature at which the bainitic portions of the structure are
formed.
Inventors: |
Kuppers, Klaus; (Erkrath,
DE) ; Meyer, Meinert; (Erkrath, DE) ; Nerzak,
Thomas; (Gelsenkirchen, DE) ; Plociennik, Uwe;
(Ratingen, DE) |
Correspondence
Address: |
THE FIRM OF KARL F ROSS
5676 RIVERDALE AVENUE
PO BOX 900
RIVERDALE (BRONX)
NY
10471-0900
US
|
Family ID: |
7693931 |
Appl. No.: |
10/485286 |
Filed: |
January 26, 2004 |
PCT Filed: |
July 25, 2002 |
PCT NO: |
PCT/EP02/08271 |
Current U.S.
Class: |
148/511 ;
148/664 |
Current CPC
Class: |
C21D 11/005 20130101;
C21D 9/04 20130101 |
Class at
Publication: |
148/511 ;
148/664 |
International
Class: |
C21D 009/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 1, 2001 |
DE |
10137596.4 |
Claims
1. A method of cooling workpieces, especially structural shape
rolled products, of rail steels with a fine perlitic or ferritic or
perlitic/ferritic structure, whereby the hot workpiece is guided
through a cooling stretch (1) with an inlet region (12) and an
outlet region and is subjected to a cooling process and whereby a
transformation into a perlitic or ferritic/perlitic structure is
effected, characterized in that the workpiece is passed through a
cooling stretch which is comprised of individual independent
cooling modules (2a-e) with independently adjustable cooling
parameters, whereby between the cooling modules (2a-e) intermediate
zones (5a-e) for structure destressing or stress relief are
provided with means for actual temperature measurement (T.sub.ACT)
of the respective workpieces in these intermediate zones (5a-e) and
whereby in dependence on the respective actual temperature value
(T.sub.ACT) of the workpiece in an intermediate zone (5a-e) the
specific cooling parameters, especially the cooling intensity), of
at least the respective subsequent cooling module (2b-e) are
controlled to ensure a defined temperature of the workpiece during
the complete passage through the cooling stretch (1), whereby the
defined temperature (T.sub.SET) of the workpiece respectively lies
above a critical temperature at which bainitic structure components
are formed.
2. The method of cooling according to claim 1 characterized in that
the cooling process is carried out in dependence upon the cooling
module traversed in individual cooling process steps and in
dependence upon the intermediate zones traversed for structure
stress relief in timed phases of reheating and/or timed phases of
retention of heat and/or in timed phases of slow cooling in
combination.
3. A method of cooling according to claim 1 characterized in that
in dependence upon the respective measured actual temperature value
(T.sub.ACT) of one or any intermediate zone (5a-e) the specific
cooling parameters of the respective subsequent cooling module
(2b-e) and simultaneously the cool parameters of a preceding
cooling module (2a-d) are controlled.
4. A method of cooling according to claim 1 characterized in that
the surface temperature of the workpiece at the end of the
intermediate zone (5a-e) is measured.
5. A method of cooling according to claim 1 characterized in that
the actual temperature measurement (T.sub.ACT) is carried out by
means of an optical and contactless measurement.
6. The method of cooling according to claim 1 characterized in that
the control of the cooling parameters, especially the cooling
intensity is achieved by means of pressure control and/or
temperature control of the cooling medium.
7. A process for cooling according to claim 1 characterized in that
the cooling medium especially cooling water before impingement upon
the workpiece surfaces is so preheated that an undershoot of the
Leidenfrost temperature does not occur or occurs later than with
nonpreheated cooling medium.
8. A method of cooling according to claim 1 characterized in that
the temperature of the workpiece before entry or upon entry into
the cooling stretch (1) is measured and this temperature value is
used for presetting the cooling parameters of the individual
cooling modules.
Description
[0001] The invention relates to a method of cooling workpieces,
especially for the cooling of rolled products and here to a method
of cooling shape-rolled products [rolled structural shapes] of rail
steels with a fine perlitic or a ferritic/perlitic structure,
whereby the hot workpiece, that is a workpiece with an authentic
structure, is passed through a cooling stretch with an inlet region
and an outlet region and is subjected to a cooling process and as a
result a transformation is carried out into a perlitic or
ferritic/perlitic structure.
[0002] Rail steels are significant for the production of rails as
well as of their connection elements and their fastening elements.
The vertical and lateral forces which are applied by the wheel to
the rail, like normal forces, traveling forces, acceleration forces
and braking forces, give rise in the regions in which they are
directly effective to extremely high dynamic stresses and, as a
rule, to a plastic deformation of the steel. As a result of these
loads, wear effects arise in the form of ablation of material,
friction wear, material breakage, local workpiece fatigue or
cracking. An improvement in the resistance of a rail to these wear
effects can be achieved by increasing its elastic limit and tensile
strength as well as its fatigue limit in combination with the
provision of the finest possible striated perlitic structure.
[0003] Under normal cooling conditions using a cooling bed in
accordance with the state of the art, rail steels undergo a
transformation to a perlitic structure. In this manner rail steels
with a ferritic/perlitic structure can reach tensile strength
values in a range of 700 to 900 N/mm.sup.2 while steels with a
purely perlitic structure can achieve tensile strength values in
excess of 900 N/mm.sup.2. The significant properties of the rail
steels are determined by the proportion of the structure
constituted by ferrite/perlite as well as by its morphological
structure. Both in the case of ferritic/perlitic steels and in the
case of perlitic steels, the lamellae spacing plays a role.
[0004] The invention sets out as its object to provide a cooling
process for the production of workpieces, especially shape rolled
products from rail steel with improved properties and a fine
striated perlite or ferrite/perlite structure.
[0005] According to the invention it is proposed that the
workpiece, which is at its (rolling) heat, for example a rolled or
optionally an extruded structural-shape product, is passed through
a cooling stretch which is assembled from individual/independent
cooling modules with independently adjustable cooling parameters,
whereby between the cooling modules there are intermediate zones
for thermal equalization or thermal stress relief with means for an
actual temperature determination for the respective workpiece in
this intermediate zone and whereby, in dependence upon the
respective actual temperature value in the intermediate zone or in
one of the intermediate zones, the specific cooling parameters,
especially the cooling intensity, of the respective subsequent
cooling module, are controlled in order to maintain a defined
(surface) temperature during the entire passage along the cooling
stretch, whereby the defined temperatures of the workpieces
respectively each lie above a critical temperature at which the
bainitic portions of the structure are formed.
[0006] The basic concept is, therefore, the control of the cooling
of a workpiece of rail steel in a cooling stretch under the
condition that the surface temperature of the workpiece of rail
steel is so cooled that the desired perlitic or ferritic or
perlitic/ferlitic structure is established, whereby in the stress
relief phases there is both a continuous monitoring of the
temperature characteristics in preferably each intermediate zone
and optionally regulation of the cooling parameters of the
individual cooling modules to ensure that the temperature does not
fall below a critical temperature so that the under cooling cannot
result in a bainitic transformation which can give rise to
undesirable bainitic components in the structure.
[0007] The cooling process is carried out by the workpiece
traversing cooling modules in individual cooling process steps and
in dependence upon the conditions in the intermediate zones for
stress relief of the structure in timed phases which can include
reheating and/or timed phases in which thermal conditions are
maintained and/or timed phases provide a slower cooling, taken
together. The workpiece in all intermediate zones can be subjected
to the same stress relief phase or can be subjected to different
timed phases of stress relief in the various intermediate zones.
The reheating can be effected either from residual heat from the
interior of the workpiece and still present therein and/or from the
supply of heat to the workpiece from the exterior. In this manner a
somewhat sawtooth cooling pattern is established which has been
found to be particularly effective in establishing the desired
final internal structure of the workpiece and thus the mechanical
properties thereof. The bainitic formation is counteracted in that
the parameters of the cooling stretch are so set that at no point
in time during the cooling process can bainite formation take
place.
[0008] It is also provided by the invention that the intermediate
zones are utilized for a thermal equalization over the workpiece,
especially rolled products, or for the cooling thereof at slow
cooling speeds.
[0009] Preferably the respective measured actual temperature value
in each of the intermediate zones is utilized to control the
specific cooling parameters of the respective subsequent cooling
zone and simultaneously the cooling parameters of the respective
preceding cooling modules. This means that the workpiece or rolled
product to the extent that it deviates from a predetermined
setpoint temperature at a certain point in time or in a particular
intermediate zone, is brought back to the setpoint temperature by a
specific change in the cooling parameters of the subsequent cooling
module and at the same time the preceding cooling module is
adjusted for the next workpiece to follow in the sequence.
[0010] Advantageously, the surface temperature of the workpiece at
the end of the intermediate zone, i.e. following the end of the
region in which structure destressing occurs, is measured. The
temperature measurement in the intermediate zone can also be used
for quality monitoring.
[0011] According to a preferred embodiment, the surface temperature
measurement is effected by an optical and contactless measuring
device, that is by means of a pyrometer.
[0012] The control of the cooling parameters and here especially
the cooling intensity is effected preferably by means of control of
the pressure with which the cooling medium is directed onto the
surface of the workpiece and/or by means of regulation or regulated
adjustment of the temperature of the cooling medium and/or by means
of controlled adjustment of the volume rate of flow of the cooling
medium by selection of the cooling nozzle geometry. As the cooling
medium, preferably cooling water is used.
[0013] The pressure control is effected preferably by means of a
pressure control valve in the inlet to the nozzles and which may be
arranged on the cooling beams. The cooling intensity is also
controllable by utilizing different numbers of nozzles per cooling
beam or cooling beam arrangements.
[0014] According to an especially preferred embodiment of the
temperature control of the cooling medium it is proposed that the
cooling medium, that is especially cooling water, before its
impingement upon the workpiece surface, is preheated at least to
the extent that undershooting of the Leidenfrost temperature does
not occur or is very greatly delayed.
[0015] The Leidenfrost phenomenon is a nonwetting property of a
liquid when the temperature of the contacted body lies above the
boiling temperature of the liquid. Water, for example, is protected
by a gas skin of vaporized water from further evaporation and thus
loses for a certain time its cooling effectiveness. By preheating
the cooling water it is possible to influence the Leidenfrost
temperature. The Leidenfrost temperature increases with increasing
cooling water temperature at the inlet and the cooling effect is
weakened. So that an undershoot of the Leidenfrost temperature will
not occur or will be delayed significantly, it is proposed to
preheat the cooling water. This offers the possibility of weakening
the cooling and making it more reproducible.
[0016] According to a preferred method step, the temperature of the
workpiece before or upon entry into the cooling stretch is measured
and based upon this temperature measurement the cooling parameters
of the cooling line are preset especially in terms of the
adjustment of the pressure with which the cooling medium is
directed upon the workpiece surface.
[0017] Further details and advantages of the invention will be
obtained from the dependent claims and the following description in
which the embodiments of the invention illustrated in the FIGURES
are described in greater detail.
[0018] Apart from the previously described combinations of
features, features of the invention can be taken alone or can be
considered significant to others in other combinations.
[0019] The drawing shows:
[0020] FIG. 1 is a schematic overview of a coding stretch in which
the method of the invention is carried out;
[0021] FIG. 2 is a temperature-time diagram with the cooling curves
of five measurement points in or on the railhead of a usual rail
steel with about 0.8% C and 1.0% Mn which is subjected according to
the invention to such a cooling pattern in a cooling stretch
according to the invention in which the bainitic temperature is not
undershot;
[0022] FIG. 3 for comparison is a temperature-time diagram of the
five cooling curves of an unregulated course of cooling wherein the
bainite temperature is undershot.
[0023] The cooling stretch 1 illustrated in FIG. 1 is connected to
a structural shape rolling line (not illustrated), for example, a
rolling line for rail structural shapes of rail steels. The cooling
stretch 1 is comprised, in the illustrated embodiment, of five cool
modules 2a-e, but is not however limited to this number of cooling
modules. The individual cooling modules 2a-2e are for example so
constructed that they encompass one or more cooling beams or
cooling nozzle arrangements. The pressure with which the cooling
water emerges from the individual nozzles is adjustable by means of
the respective pressure control valves 2a- e. The actual pressure
is measured by means of the pressure measuring devices 4a-e.
Between the individual cooling modules 2a-e, intermediate zones
5a-e are arranged. At each end of an intermediate zone 5a-e a
pyrometer 6a-e is located for the contactless optical measurement
of the surface temperature of the rolled product found in this
intermediate zone, whereby in the case of a rail structure shape,
the surface temperature at the rail head is measured.
[0024] Upstream of the first cooling module 2a at the inlet region
or beginning 12 of the cooling stretch 1 an additional pyrometer 6f
is disposed. The individual pyrometers 6a-f are connected by means
of signal connectors 7a-g with a computer unit 8. The computer unit
8 is connected by corresponding control conductors 9a-e to the
individual control valves 2a-e for the cooling nozzles to vary the
settings of these control values. The cooling medium, especially
cooling water (cw) is supplied by a common feed pipe 10 with
branches 10a-e connected to the individual cooling modules
2a-e.
[0025] For regulating the pressure values, there is in addition a
control circuit of the pressure measurement devices 4a-e for the
computer 8 (signal conductors 11a-e). In the following, the process
is described. Prior to entry of the rolled structure shape of
steel, preferably a rail, into the cooling stretch by means of the
first pyrometer 6f, for example a two color pyrometer, an actual
surface temperature value is taken. This first surface temperature
value is fed to the computer unit 8 which has already been provided
with a presetting in response to this individual value. For the
individual control values for the setting of the cooling water
pressure as well as the cooling water temperature. After the
workpiece has traversed the first cooling module 2a it enters the
first intermediate zone 5a in which a relief or destressing phase
for the structure is effected. At the end of the first intermediate
zone 5a, by means of a second pyrometer 6a, for example a two color
pyrometer, a further surface temperature measurement (T.sub.ACT)
This actual value is transferred to the computer unit 8 over the
signal lines 7a and 7g and then a difference calculation is carried
out between a setpoint value T.sub.SET and the actual value
(T.sub.ACT). The setpoint value always lies immediately above a
workpiece-specific temperature at which bainite formation can
arise. The setpoint values are alloy--specific and can be obtained
by experiments. A determining factor for this critical temperature
below which the rail steel should not be cooled, is about 450 to
500.degree. C.
[0026] To the extent that there is a difference between the actual
value and the setpoint value, the subsequent or a plurality of
subsequent cooling modules have their cooling parameters adjusted,
here by varying the pressure control valves 2a-3e which regulate
the pressure of the cool water directly onto the workpieces. The
regulation of the pressure values in dependence upon a measure of
the actual pressure value is carried out continuously.
[0027] The described control is repeated in dependence upon the
respective temperature values detected in each further intermediate
zone. Preferably not only is each subsequent cooling module
adjusted but also the preceding cooling module is adjusted for each
measured value which then affects the subsequent rolled workpiece
to be cooled.
[0028] FIGS. 2 and 3 show with the aid of temperature-time diagrams
the cooling curves for the rail heads of a material with 0.8%
carbon with control and without control. The designation C80W60 or
C80W65 makes clear that the cooling speed in the core of the rail
head (for example a rail shape in accordance with AREA 136
[Standard of American Railway Engineering Association] is
significantly higher than in the boundary and that in the core
transformation of austenite to perlite or ferrite-perlite occurs at
elevated temperatures.
[0029] The temperature course over time was taken for five
different measurement points at the rail head At 1 the measurement
point was in the core of the rail head. 2 was a measurement point
which was located 5 mm below the surface 3 was a measurement point
which was located 5 mm below a lateral surface. 4 was a measurement
point on the lateral surface. 5 was a measurement point on the head
surface. It can be seen that at no time at any measurement point
did the structure of the rail head suffer an undercooling that
could have given rise to a bainite structure.
[0030] The simulated cool stretch had five modules which were
individually controllable. The individual cooling curves are
illustrated in FIG. 2 and in no case was the critical temperature
at which bainite formation could set in, undershot. On the cooling
curves 4 and 5 which indicate the cooling at the surface of the
rail head, the sawtooth cooling pattern is clearly shown and
involved reheating in the intermediate or equalization zones.
[0031] FIG. 3 shows by comparison a cooling stretch with five
cooling modules which are not individually controllable so that the
bainite temperature can be undershot in the regions close to the
surface (curves 4 and 5) of the rail head.
[0032] With the method proposed, a cooling of rail steels from the
rolling heat can be carried out to yield a fine perlitic or
ferlitic/perlitic structure without the mechanical properties and
especially the wear properties being negatively affected by
bainitic components.
* * * * *