U.S. patent application number 14/416280 was filed with the patent office on 2015-06-25 for method for producing at least one component and open-loop and/or closed-loop control device.
The applicant listed for this patent is Robert Bosch GmbH. Invention is credited to Siegfried Bajohr, Dominic Buchholz, Laszlo Hagymasi, David Koch, Rainer Reimert, Thomas Waldenmaier.
Application Number | 20150176114 14/416280 |
Document ID | / |
Family ID | 48875018 |
Filed Date | 2015-06-25 |
United States Patent
Application |
20150176114 |
Kind Code |
A1 |
Koch; David ; et
al. |
June 25, 2015 |
Method for Producing at least One Component and Open-Loop and/or
Closed-Loop Control Device
Abstract
The disclosure relates to a method for producing at least one,
in particular metal, component, preferably a cylinder head, a
nozzle body for a high-pressure injection pump, a component of a
diesel injection engine, or a throttle disk, by means of
low-pressure carbonitriding in at least one treatment chamber,
which preferably can be evacuated, and an open-loop and/or
closed-loop control device, which enables the setting of a
specified ratio between a carbon concentration and a nitrogen
concentration in a surface layer of the at least one component. In
at least one treatment phase, a carbon-providing gas and a
nitrogen-providing gas are simultaneously introduced into the
treatment chamber. Based on a specified ratio between a carbon
concentration and a nitrogen concentration to be absorbed by the at
least one component in a surface layer of the component, a target
value for the temperature and/or the pressure to be set in the
treatment chamber is determined and is set in the treatment chamber
for a specified time.
Inventors: |
Koch; David; (Karlsruhe,
DE) ; Bajohr; Siegfried; (Wiesloch, DE) ;
Hagymasi; Laszlo; (Gerlingen, DE) ; Buchholz;
Dominic; (Walzbachtal, DE) ; Reimert; Rainer;
(Idstein, DE) ; Waldenmaier; Thomas;
(Freiberg/Neckar, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Robert Bosch GmbH |
Stuttgart |
|
DE |
|
|
Family ID: |
48875018 |
Appl. No.: |
14/416280 |
Filed: |
July 22, 2013 |
PCT Filed: |
July 22, 2013 |
PCT NO: |
PCT/EP2013/065420 |
371 Date: |
January 22, 2015 |
Current U.S.
Class: |
148/215 ;
118/708; 148/218 |
Current CPC
Class: |
C23C 8/02 20130101; C23C
8/30 20130101; C23C 8/32 20130101; C23C 8/00 20130101; C23C 8/34
20130101; C23C 8/80 20130101 |
International
Class: |
C23C 8/30 20060101
C23C008/30 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 24, 2012 |
DE |
10 2012 212 918.9 |
Claims
1. A method for producing at least one metallic component in at
least one treatment chamber, the method comprising: introducing, in
at least one treatment phase, a carbon-emitting gas and a
nitrogen-emitting gas simultaneously into the at least one
treatment chamber determining, in the at least one treatment phase,
a target value for at least one of a temperature and a pressure to
be set in the at least one treatment chamber, the target value
depending on a specified ratio between a carbon concentration and a
nitrogen concentration to be taken up by the at least one metallic
component in an outer layer of the at least one metallic component;
and adjusting, in the at least one treatment phase, the target
value in the at least one treatment chamber for a specified
time.
2. The method as claimed in claim 1, wherein the carbon-emitting
gas is a first gas and the nitrogen-emitting gas is the first
gas.
3. The method as claimed in claim 2, wherein the first gas is an
amine compound.
4. The method as claimed in claim 2, wherein the first gas emits
carbon and nitrogen in a ratio of less than or equal to three.
5. The method as claimed in claim 1, wherein a ratio between a
volumetric flow of the carbon-emitting gas introduced into the at
least one treatment chamber and a volumetric flow of the
nitrogen-emitting gas introduced into the at least one treatment
chamber is less than three.
6. The method as claimed in claim 1, further comprising: measuring
the at least one of the temperature and the pressure in the at
least one treatment chamber; and correcting the at least one of the
temperature and the pressure to match the target value.
7. The method as claimed in claim 1, further comprising: activating
a heating device in the treatment chamber to adjust the temperature
to match the target value for the temperature the activating
comprising: increasing the temperature of the heating device in
response to the temperature being less than the target value for
the temperature; and decreasing the temperature of the heating
device in response to the temperature being greater than the target
value for the temperature.
8. The method as claimed in claim 1, further comprising: setting a
volumetric flow discharged from the at least one treatment chamber
to adjust the pressure to match the target value for the pressure,
the setting comprising: decreasing the volumetric flow in response
to the pressure being less than the target value for the pressure;
and increasing the volumetric flow in response to the pressure
being greater than the target value for the pressure.
9. The method as claimed in claim 1, further comprising: changing
the target value for the temperature in the treatment chamber at
least once.
10. The method as claimed in claim 1, further comprising: at least
one of heating up the temperature and cooling down the temperature;
and equalizing the temperature after the at least one of the
heating up and cooling down.
11. The method as claimed in claim 1, further comprising: changing
the target value for the pressure in the treatment chamber at least
once.
12. The method as claimed in claim 1, wherein the target value for
the pressure in the treatment chamber is less than or equal to 100
millibar.
13. The method as claimed in claim 1, wherein the target value for
the temperature is between 650 degrees Celsius and 1050 degrees
Celsius.
14. The method as claimed in claim 1, wherein a plurality of
treatment phases are performed, the plurality of treatment phases
each being respectively separated from one another by a diffusion
phase.
15. The method as claimed in claim 14, wherein a specified ratio
between a carbon concentration and a nitrogen concentration to be
taken up by the at least one metallic component in an outer layer
of the at least one metallic component is different in at least two
of the plurality of treatment phases, depending on a specified
carbon and nitrogen depth profile in the outer layer of the at
least one metallic component.
16. At least one of an open-loop control device and a closed loop
control device for producing at least one metallic component in at
least one treatment chamber, comprising: a controller configured
to: introduce, in at least on treatment phase, a carbon-emitting
gas and a nitrogen-emitting gas simultaneously into the treatment
chamber; determine, in at least one treatment phase, a target value
for at least one of a temperature and a pressure in the at least
one treatment chamber, the target value depending on a specified
ratio between a carbon concentration and a nitrogen concentration
to be taken up by the at least one metallic component in an outer
layer of the at least one metallic component; and adjust, in at
least one treatment phase, the target value in the at least one
treatment chamber for a specified time.
17. The method as claimed in claim 1, wherein the at least one
metallic component is at least one of a cylinder head, a nozzle
body for a injection pump, a component of a diesel injection engine
and a throttle plate.
18. The method as claimed in claim 3, wherein the amine compound is
at least one of an aliphatic monoamine, as primary, secondary and
tertiary compounds, an aliphatic diamine, and a mixture of an
aliphatic monoamine and an aliphatic diamine.
19. The method as claimed in claim 12, wherein the target value for
the pressure in the treatment chamber is between 2 millibar and 30
millibar.
20. The method as claimed in claim 13, wherein the target value for
the temperature is between 650 degrees Celsius and 960 degrees
Celsius.
Description
[0001] The present invention relates to a method for producing at
least one component and to an open-loop and/or closed-loop control
device of the generic type of the independent claims.
PRIOR ART
[0002] The document DE 199 09 694 A1 describes a carbonitriding
process in which the inward diffusion of the nitrogen takes place
during the entire process or, if elemental nitrogen is used as the
donor gas, preferably only in the last process phase. Molecular
nitrogen, ammonia and other nitrogen-containing compounds are
mentioned in particular as nitrogen donors. Carbon donors are not
specified.
[0003] The document DE 101 18 494 C2 describes a low-pressure
carbonitriding process in which steel parts are first carburized
and subsequently nitrogenized with a nitrogen-donor gas. Acetylene,
propane and ethylene are specified as carbon donors. A donor gas
that contains ammonia is mentioned as the nitrogen donor. Nothing
further is specified about the nitrogen donor.
[0004] The document DE 103 22 255 A1 describes a process for
carburizing steel parts in which nitrogen-emitting gas is fed in
both during the heating-up phase and during the diffusion phase.
Ammonia and nitrous oxide are specified as nitrogen donors and
acetylene, propane and ethylene are specified as carbon donors.
[0005] The mentioned documents DE 101 18 494 C2 and DE 103 22 255
A1 describe low-pressure carbonitriding processes in the pulsed
mode, in which nitrogen compounds, such as for example ammonia or
nitrous oxide, are used as the nitrogen donor gas and are
introduced into the treatment chamber in the offering phases
between the offers of carburization and/or when heating up the
charge and/or in the final carbon diffusion phase, in order to
introduce the nitrogen into the surface of the component.
[0006] Due to the alternating carbon and nitrogen offering phases,
caused as a result of the process, it is not possible to ensure a
continuous uptake of carbon and nitrogen. As a result of this, the
process times become longer, since allowance has to be made for
diffusion phases between the carbon and nitrogen offering phases in
order to speed up the uptake of carbon or nitrogen in a subsequent
offering phase.
[0007] Russian patent 1680798 describes a process for
carbonitriding metallic components in which amine compounds, such
as for example methyl amine, diethyl amine and dibutyl amine, are
used as carbon and nitrogen donors, in order to introduce carbon
and nitrogen simultaneously into the surface of the component. In
the case of this process, amines are introduced into the treatment
chamber at high temperatures (T=1100.degree. C. to 1200.degree. C.)
in order to produce a carbon- and nitrogen-rich atmosphere. This
process proceeds under atmospheric pressure.
[0008] In the case of this carbonitriding process, the high
treatment temperatures of 1100 to 1200.degree. C. and the
atmospheric pressure are problematic. At these temperatures, the
conversion of the amine compounds in the gas phase and on the
surface of the component is so high that more complex geometries
with interior surfaces, such as for example bores, or closely
packed component charges are carbonitrided unevenly. In addition,
the process gas pressure of 1 bar makes the diffusion of the donor
gases within the charge and/or within interior geometries, such as
for example blind-hole bores, considerably more difficult.
[0009] In technical terms, this temperature range together with the
high process gas pressure must be rated as conditions necessitating
a very high-maintenance plant. Furthermore, at these temperatures,
low-cost metallic materials have a tendency to form coarse grains,
which can have adverse effects on the durability of the component,
as a result of which more expensive materials have to be used
and/or an additional heat treatment step has to be carried out to
make the grains fine.
[0010] A further important aspect is that, in the case of all the
low-pressure carbonitriding processes described, no closed-loop
control is provided for controlling the carbon and nitrogen uptake.
The ratio between the carbon and nitrogen introduced in the outer
layer is however decisive for the resultant properties of the
material and the component.
DISCLOSURE OF THE INVENTION
[0011] In comparison, the process according to the invention for
producing at least one component and the open-loop and/or
closed-loop control device according to the invention with the
features of the independent claims have the advantage that, in at
least one treatment phase, a carbon-emitting gas and a
nitrogen-emitting gas are introduced simultaneously into the
treatment chamber, that, depending on a specified ratio between a
carbon concentration and a nitrogen concentration to be taken up by
the at least one component in its outer layer, a target value for
the temperature and/or the pressure to be set in the treatment
chamber is determined and is adjusted in the treatment chamber for
a specified time. In this way it is possible to ensure continuous
carbon and nitrogen uptake. Carbon and nitrogen are offered
simultaneously, and consequently without a change of process gas or
diffusion phases between alternating carbon and nitrogen offering
phases. As a result, the process times become shorter. Low-pressure
carbonitriding additionally makes homogeneous carburizing and
nitrogenizing possible, even in the case of closely packed charges
or complex component geometries, such as for example bore
geometries. The closed-loop control of the temperature and/or
pressure allows a specified ratio between the carbon and nitrogen
concentrations introduced in the outer layer to be set, and
consequently the resultant properties of the material and component
to be influenced.
[0012] Advantageous developments and improvements of the method
specified in the main claim are possible by the measures presented
in the dependent claims.
[0013] It is particularly advantageous if one and the same gas is
introduced into the treatment chamber as the carbon-emitting gas
and as the nitrogen-emitting gas. This considerably simplifies the
method, since only one gas has to be introduced into the treatment
chamber.
[0014] Advantageously chosen as such a gas is an amine compound,
preferably aliphatic monoamine, as primary, secondary and tertiary
compounds, or aliphatic diamine or a mixture of the two.
[0015] A further advantage is obtained here if a gas that emits
carbon and nitrogen in a ratio of less than or equal to three is
chosen as the carbon- and nitrogen-emitting gas. In this way, the
desired ratios can be set in the carbon and nitrogen profiles while
at the same time reducing the formation of soot in the furnace
installation.
[0016] The same advantage is also obtained if, when using different
gases for the emission of carbon and nitrogen in the treatment
chamber, the amount, in particular the volumetric flow, of the
carbon-emitting gas fed into the treatment chamber and the amount,
in particular the volumetric flow, of the nitrogen-emitting gas fed
into the treatment chamber in the ratio of the emission of carbon
and nitrogen in the treatment chamber is chosen to be less than
three.
[0017] It is advantageous for the closed-loop control if the
pressure and/or the temperature in the treatment chamber is
measured and as an actual value is corrected to the target value
determined. This makes particularly simple and reliable closed-loop
control to the specified ratio between the carbon concentration and
the nitrogen concentration to be taken up by the at least one
component in its outer layer possible.
[0018] The closed-loop control is also made particularly simple and
convenient by the actual value for the temperature being corrected
to the target value for the temperature by activating a heating
device in the treatment chamber, the temperature of the heating
device being increased if the actual value for the temperature is
less than the target value for the temperature and the temperature
of the heating device being lowered if the actual value for the
temperature is greater than the target value for the
temperature.
[0019] The closed-loop control is made correspondingly simple and
convenient if the actual value for the pressure is corrected to the
target value for the pressure by setting an amount of gas, in
particular volumetric flow, discharged from the treatment chamber,
the discharged amount of gas being lowered if the actual value for
the pressure is less than the target value for the pressure and the
discharged amount of gas being increased if the actual value for
the pressure is greater than the target value for the pressure.
[0020] It is also advantageous if the target value for the
temperature in the treatment chamber is changed at least once. This
makes it possible to set different ratios between the carbon
concentration and the nitrogen concentration used in different
zones of depth of the outer layer.
[0021] A further advantage is obtained if a temperature-equalizing
phase is arranged downstream of at least one heating-up phase or at
least one cooling-down phase in the treatment chamber. In this way,
the target value for the temperature can be adjusted as exactly as
possible for all of the components within a charge.
[0022] It is advantageous that the target value for the pressure in
the treatment chamber is changed at least once. This makes it
possible to set different ratios between the carbon concentration
and the nitrogen concentration used in different zones of depth of
the outer layer.
[0023] A further advantage is that the target pressure in the
treatment chamber is less than or equal to 100 mbar, preferably
between two and 30 mbar. In this way, diffusion processes of the
corresponding gas within a charge or within interior geometries,
such as for example blind-hole bores, become considerably
easier.
[0024] It is also advantageous that the target value for the
temperature lies in a range from 650.degree. C. to 1050.degree. C.,
preferably in a range from 650.degree. C. to 960.degree. C. In this
way, homogeneous carbonitriding of closely packed component charges
or complex geometries with interior surfaces, such as for example
with bore geometries, can be ensured.
[0025] In the case of the process gas being continuously offered,
precipitates such as carbides, nitrides and carbonitrides may form
in an unwanted and uncontrolled manner in the outer layer of the at
least one component, in dependence on the temperature and the
carbon and nitrogen depth profiles developing. It is therefore
particularly advantageous in the case of the method according to
the invention that a number of treatment phases are provided,
respectively separated from one another by a diffusion phase. In
this way, unwanted precipitates such as carbides, nitrides and
carbonitrides in the outer layer of the at least one component can
be avoided, and also a desired or specified carbon and nitrogen
depth profile can be set in the outer layer of the at least one
component.
[0026] Such a specified carbon and nitrogen depth profile can be
produced particularly simply by the specified ratio between the
carbon concentration and the nitrogen concentration to be taken up
by the at least one component in its outer layer being chosen to be
different in at least two of the treatment phases, depending on the
specified carbon and nitrogen depth profile in the outer layer of
the at least one component.
DRAWING
[0027] An exemplary embodiment of the invention is represented in
the drawing and explained in more detail in the description that
follows.
[0028] FIG. 1 shows a schematic representation of a plant for the
low-pressure carbonitriding of at least one component,
[0029] FIG. 2 shows the influence of the temperature on the ratio
between carbon and nitrogen set in the outer layer of a
component,
[0030] FIG. 3 schematically shows a way of conducting a
low-pressure carbonitriding process with a controlled
temperature,
[0031] FIG. 4 schematically shows the buildup of the outer layer of
the treated components that is achieved by the way in which the
process is conducted as shown in FIG. 3 and
[0032] FIG. 5 shows a block diagram of an open-loop and/or
closed-loop control device used for conducting the process.
DESCRIPTION OF THE EXEMPLARY EMBODIMENT
[0033] FIG. 1 shows a schematic representation of a plant 1 for the
low-pressure carbonitriding of one or more components 2. In FIG. 1,
five components 2 are represented by way of example. The components
2 are arranged on a support 3 in a treatment chamber 4. The
components 2 can be heated by means of a heating device 5
represented in the lower region of the drawing. An inlet 6 with an
associated flow control valve 7 allows the introduction of a
carbon- and nitrogen-donor gas 8. A temperature sensor 9 and a
pressure sensor 10 are arranged in the upper region of the drawing
of the treatment chamber 4. An open-loop and/or closed-loop control
device 11 shown above them receives the signals coming from the
temperature sensor 9 and the pressure sensor 10. An outlet 12 of
the treatment chamber 4 leads to the input of a pump 13, which may
be formed for example as a vacuum pump. Arranged upstream of the
pump 13 is a throttle 14, in particular for controlling the
pressure.
[0034] During the operation of the plant 1, the carbon- and
nitrogen-donor gas 8 is introduced simultaneously into the
treatment chamber 4 in various process phases by means of the flow
control valve 7. The open-loop and/or closed-loop control device 11
monitors and controls the process or the individual process phases,
inter alia by means of the temperature sensor 9 and the pressure
sensor 10. Of importance in particular is the temperature recorded
by the temperature sensor 9, which is also referred to hereinafter
as the treatment temperature. The treatment temperature is obtained
in the atmosphere of the treatment chamber 4, as still to be
explained in relation to the subsequent FIGS. 2 and 3. The pump 13
acts at the outlet 12 together with the throttle 14 like a valve.
The degree of opening of the throttle 14 is controlled
process-dependently by the open-loop and/or closed-loop control
device 11, inter alia depending on the pressure recorded by the
pressure sensor 10, which is also referred to hereinafter as the
treatment pressure, in order to set the required treatment pressure
in the treatment chamber 4, partially evacuate the treatment
chamber 4 or let out or exchange the gases located in it. The
heating device 5 is controlled by the open-loop and/or closed-loop
control device 11, inter alia depending on the treatment
temperature recorded by the temperature sensor 9. The flow control
valve 7 is managed by the open-loop and/or closed-loop control
device 11 in order to control the process-dependent throughputs of
the process gas.
[0035] The carbon-donor gas, also referred to as the
carbon-emitting gas, and the nitrogen-donor gas, also referred to
as the nitrogen-emitting gas, may be different from one another. In
this case, the different gases can be fed into the treatment
chamber 4 in a desired mixing ratio in a mixing chamber (not
represented in the drawing) upstream of the flow control valve 7 or
by means of in each case a separate flow control valve. In this
case, known gases can be chosen. For example, acetylene, propane or
ethylene for the carbon-donor gas. For example, ammonia or nitrous
oxide for the nitrogen-donor gas. The composition of the process
gas for the treatment chamber 4 is set by way of the amounts of gas
of the carbon-emitting gas and the nitrogen-emitting gas.
[0036] However, it has been found to be particularly advantageous
if one and the same gas is chosen for the carbon-donor gas and for
the nitrogen-donor gas, for example an amine compound, preferably
aliphatic monoamine, as primary, secondary and tertiary compounds,
or aliphatic diamine or a mixture of the two. This makes it
considerably easier to conduct the process. A mixing chamber
upstream of the flow control valve 7 or an additional flow control
valve is not required in this case.
[0037] Instead of the way described on a temperature and pressure
basis, the closed-loop control or open-loop control may
alternatively be performed only on a temperature basis or only on a
pressure basis, so that only one of the two sensors is required. In
the case of temperature-based closed-loop control, only the
temperature sensor is required, and in the case of pressure-based
closed-loop control only the pressure sensor is required.
[0038] FIG. 2 shows the influence of the treatment temperature on
the carbon and nitrogen introduced in the outer zone of the
components 2, at a distance from the component surface of 50 .mu.m
after a carbonitriding period of 20 minutes at a set treatment
pressure of the donor gas dimethyl amine (C.sub.2H.sub.6NH) of 10
mbar. In this case, FIG. 2 shows by way of example the
experimentally determined influence of the treatment temperature on
the ratio of the carbon concentration and the nitrogen
concentration set in the outer zone of the components 2 for the two
temperatures 800.degree. C. and 850.degree. C. The two temperatures
were chosen for the representation in order to illustrate the
change of the ratios of the amount of carbon and the amount of
nitrogen taken up. At 800.degree. C., the amount of nitrogen taken
up predominates, whereas with a process of the same duration and a
temperature of 850.degree. C. more carbon is taken up. Generally,
with increasing treatment temperature, it can be assumed that the
ratio of the amount of carbon and the amount of nitrogen taken up
is shifted toward higher carbon uptakes. With knowledge of the
temperature influence on the ratio of the amount of carbon and the
amount of nitrogen taken up, a controlled temperature regime can be
followed, which, depending on the specified ratio between a carbon
concentration and a nitrogen concentration to be taken up by the
components 2 in their outer layer, necessitates a constantly
controlled temperature and/or a lowering or raising of the
treatment temperature.
[0039] It has also been experimentally demonstrated that, by
increasing the treatment pressure, the ratio between carbon and
nitrogen is shifted in favor of carbon.
[0040] Represented by way of example in FIG. 3 is a progression
over time of the treatment temperature and the treatment pressure,
also referred to as the process gas pressure, in the case of
low-pressure carbonitriding. Schematically represented for purposes
of illustration is the conduction of a low-pressure carbonitriding
process with a controlled temperature, which is used for example in
the case of the plant 1 shown in FIG. 1. The duration of the
process t is represented on the x axis of the diagram, the
temperature T is represented on the left-hand y axis and the
pressure p of the atmosphere in the treatment chamber 4 is
represented on the right-hand y axis. The low-pressure
carbonitriding comprises a heating-up phase A, two
temperature-equalizing phases B1, B2, two carbonitriding phases C1,
C2, two diffusion phases D1, D2, a temperature change E and a
cooling-off phase F.
[0041] An interruption on the x axis indicates that the process
phases represented do not have to last for the periods of time
respectively shown, but may also deviate from the representation of
FIG. 3.
[0042] FIG. 3 shows that, during a heating-up phase A, the
temperature is continuously increased with an approximately
constant heating-up rate up to a treatment temperature of
approximately 950.degree. C. by means of the heating device 5. For
this purpose, the heating device 5 is correspondingly activated by
the open-loop and/or closed-loop control device 11 and the
heating-up rate .DELTA.T/.DELTA.t is controlled.
[0043] In a first temperature-equalizing phase B1, following the
heating-up phase A, the treatment temperature is adjusted
constantly to a first target value for the temperature of
approximately 950.degree. C. by the open-loop and/or closed-loop
control device 11, by comparison of the temperature measured by
means of the temperature sensor 9 with the first target value for
the temperature of 950.degree. C., by corresponding activation of
the heating device 5. During the heating-up phase A and the first
temperature-equalizing phase B, no carbon- or nitrogen-emitting gas
is fed into the treatment chamber 4.
[0044] In a first treatment phase, following the first
temperature-equalizing phase B1 and also referred to as the first
carbonitriding phase C1, the treatment temperature continues to
remain adjusted to its first target value. In addition, a carbon-
and nitrogen-emitting gas, also referred to as the carbon- and
nitrogen-donor gas, for example methyl amine, is fed into the
treatment chamber 4 by way of the flow control valve 7. In this
case, the treatment pressure, also referred to as the process gas
pressure or donor gas pressure or partial pressure of the donor
gas, is adjusted constantly to a first target value for the
pressure of approximately 15 mbar by the open-loop and/or
closed-loop control device 11, by comparison of the pressure
measured by means of the pressure sensor 10 with the first target
value for the pressure of 15 mbar, by corresponding activation of
the degree of opening of the throttle 14.
[0045] The first target value for the treatment temperature and the
first target value for the treatment pressure are determined in the
open-loop and/or closed-loop control device 11, depending on the
experimentally determined relationships described above, by means
of correspondingly stored characteristic diagrams in order to
obtain a first specified ratio between the amount of carbon and the
amount of nitrogen taken up for the components 2 in their outer
zone. The amount or depth of penetration of the carbon and nitrogen
introduced into the components 2 according to the first specified
ratio is determined by the chosen first treatment period .DELTA.t1
of the first carbonitriding phase C1. In this respect, a first
treatment-period characteristic diagram is stored in the open-loop
and/or closed-loop control device 11 and, for the chosen target
value of the treatment temperature and the chosen target value for
the treatment pressure and also the material composition of the
components 2, describes an--experimentally or
computationally--determined relationship between the treatment
period and the amount of carbon and/or amount of nitrogen
introduced into the components 2 or depth of penetration of the
carbon and nitrogen into the outer layer. All of the components 2
treated in the treatment chamber should in this case have an
identical material composition, in order that the desired result
with respect to the carbon concentration and the nitrogen
concentration to be introduced is achieved.
[0046] In the present example, the first carbonitriding phase C1 is
subsequently followed optionally by a first diffusion phase D1, in
which, by corresponding activation of the throttle 14 and the flow
control valve 7 by the open-loop and/or closed-loop control unit
11, the treatment chamber 4 is evacuated by means of the pump 13,
with the flow control valve 7 closed, or is purged with an inert
gas, for example nitrogen or argon, which then is fed into the
treatment chamber 4 instead of the carbon- and nitrogen-donor gas
by way of the flow control valve 7 and is pumped away again by the
pump 13.
[0047] This is followed by a temperature-changing phase E for
changing the treatment temperature to a second target value of
approximately 850.degree. C., by corresponding activation of the
heating device 5, in order in the case of this exemplary embodiment
to set the final ratio between the carbon and the nitrogen in the
outer layer of the components 2.
[0048] In a second temperature-equalizing phase B2, following the
temperature-changing phase E, the treatment temperature is adjusted
constantly to the second target value for the temperature of
approximately 850.degree. C. by the open-loop and/or closed-loop
control device 11, by comparison of the temperature measured by
means of the temperature sensor 9 with the second target value for
the temperature of 850.degree. C., by corresponding activation of
the heating device 5. During the temperature-changing phase E and
the second temperature-equalizing phase B2, no carbon- or
nitrogen-emitting gas is fed into the treatment chamber 4.
[0049] In a second treatment phase, following the second
temperature-equalizing phase B2 and also referred to as the second
carbonitriding phase C2, the treatment temperature continues to be
adjusted to its second target value. In addition, a carbon- and
nitrogen-emitting gas, for example methyl amine, is fed into the
treatment chamber 4 by way of the flow control valve 7. In this
case, the treatment pressure is adjusted constantly to a second
target value for the pressure of approximately 10 mbar by the
open-loop and/or closed-loop control device 11, by comparison of
the pressure measured by means of the pressure sensor 10 with the
second target value for the pressure of 10 mbar, by corresponding
activation of the flow control valve 7.
[0050] The second target value for the treatment temperature and
the second target value for the treatment pressure are determined
in the open-loop and/or closed-loop control device 11, depending on
the experimentally determined relationships described above, by
means of correspondingly stored characteristic diagrams in order to
obtain a second specified ratio between the amount of carbon and
the amount of nitrogen taken up for the components 2 in their outer
zone. The amount or depth of penetration of the carbon and nitrogen
introduced into the components 2 according to the second specified
ratio is determined by the chosen second treatment period .DELTA.t2
of the second carbonitriding phase C2. In this respect, a second
treatment-period characteristic diagram, which is stored in the
open-loop and/or closed-loop control device 11, is used and,
depending on the chosen target value of the treatment temperature
and the chosen target value for the treatment pressure and also the
material composition of the components 2, describes
the--experimentally or computationally --determined relationship
between the treatment period and the amount of carbon and/or amount
of nitrogen additionally introduced into the components 2 or, on
the basis of the depth of penetration achieved in the first
carbonitriding phase C1, the realizable additional depth of
penetration of the carbon and nitrogen into the outer layer. If the
treatment temperature and the treatment pressure of the second
carbonitriding phase are chosen to correspond to the first
carbonitriding phase, the first treatment-period characteristic
diagram may also be used instead of the second treatment-period
characteristic diagram.
[0051] In the case of the exemplary embodiment represented, the
lowered second target value for the treatment temperature in
comparison with the first carbonitriding phase C1 in the second
carbonitriding phase C2 has the effect that the treatment chamber
is adjusted to a temperature at which the nitrogen fraction taken
up by the components 2 becomes greater and the carbon fraction
taken up by the components 2 becomes less.
[0052] In the same way as the lowered treatment temperature, the
lower treatment pressure in the second carbonitriding phase C2 in
comparison with the first carbonitriding phase C1, represented in
the exemplary embodiment, likewise has the effect that the ratio
between the amount of carbon and the amount of nitrogen taken up by
the components 2 is shifted in favor of nitrogen.
[0053] The second carbonitriding phase C2 may alternatively also
follow on directly from the temperature-changing phase E, without a
second temperature-equalizing phase B2.
[0054] As can be seen from FIG. 4, the amount of carbon and the
amount of nitrogen taken up in the first carbonitriding phase C1
lies in a second zone 110 of the outer layer 125, which is at a
further distance from the surface of the components 2 than the
amount of carbon and the amount of nitrogen taken up during the
second carbonitriding phase C2, which is in a first zone 105 of the
outer layer 125, which on the one hand adjoins the second zone 110
and on the other hand is terminated by the surface 100 of the
respective component 2.
[0055] Consequently, a corresponding depth profile of the carbon
concentration and the nitrogen concentration taken up into the
outer layer 125 of the components 2 is produced. In the present
exemplary embodiment, the second treatment period .DELTA.t2 has
been chosen to be shorter than the first treatment period
.DELTA.t1. Therefore, the second zone 110 in the outer layer 125 of
the components 2 has been formed thicker than the first zone 105.
The first zone 105 has in this case a first thickness d1, which is
less than a second thickness d2 of the second zone 110. Then, away
from the first zone 105, the second zone 110 is adjoined by a core
115 of the respective component, into which no carbon or nitrogen
has been taken up as a result of the treatment. The transition
between the two zones 105, 110 is depicted in FIG. 4 in an ideally
abrupt form, but in reality a gradual transitional region develops
between the ratios of the corresponding carbon and nitrogen
concentrations of adjacent zones.
[0056] There subsequently follows a further diffusion phase D2, in
which the treatment chamber 4 is evacuated or purged with an inert
gas, for example nitrogen or argon. There subsequently follows a
cooling-down phase F.
[0057] It goes without saying that numerous methods for
carbonitriding are possible in this way, and the invention is not
restricted to the sequence explained and the number of two
temperature-equalizing phases B1, B2, two carbonitriding phases C1,
C2, two diffusion phases D1, D2, one temperature change E and one
cooling-down phase F.
[0058] Depending on the desired properties of the material and the
component, such as for example the wear resistance and temperature
resistance, and the ferrous material used for the components 2, a
maximum outer concentration of carbon and nitrogen totalling 1.5
percent by mass should be maintained. It is desirable that the
outer carbon concentration should lie between 0.5 and 0.8 percent
by mass when there is an outer nitrogen concentration of between
0.2 and 0.7 percent by mass.
[0059] As described, to avoid unwanted precipitates of carbides,
nitrides and carbonitrides and/or to set a specified carbon and
nitrogen depth profile in the outer layer of the components 2,
optionally one or more diffusion phases may be introduced between
individual carbonitriding phases. The specified carbon and nitrogen
depth profile in this case indicates at which distances from the
surface of the components which ratio between the carbon
concentration and the nitrogen concentration to be taken up by the
component in its outer layer is intended to be present in the outer
layer of the components. As described above, a corresponding
carbonitriding phase is then provided for each of these zones of
the outer layer with an individually specified ratio between the
carbon concentration and the nitrogen concentration.
[0060] The desired distribution of the carbon concentration and the
nitrogen concentration in the outer layer of the components 2 is
consequently set by a controlled temperature regime and/or control
of the donor gas pressure during the low-pressure carbonitriding
and by suitable choice of the points in time and the treatment
periods of the carbonitriding phases. In the case of carbonitriding
phases in which the carbon- and nitrogen-donor gas is fed into the
treatment chamber 4, the treatment temperature of the components is
for this purpose advantageously controlled within a maximum
deviation of +/-15.degree. C., desirably within a maximum deviation
of +/-8.degree. C.
[0061] In addition, one advantage of the method according to the
invention is that the process is carried out at low pressures less
than or equal to 100 mbar, advantageously between 2 and 30 mbar,
whereby the accessibility of bore geometries for the uptake of
carbon and nitrogen increases. For this purpose, the process gas
pressure of the carbon- and nitrogen-donor gas is advantageously
controlled within a deviation of +/-8 mbar, even better within a
deviation of +/-3 mbar. Lower temperatures of less than or equal to
1050.degree. C., advantageously less than or equal to 960.degree.
C. and greater than or equal to 650.degree. C., allow homogeneous
carbonitriding of dense component charges or complex geometries,
such as for example with bore geometries, to be carried out.
[0062] The characteristic diagrams described are developed from a
simulation model, which calculates the diffusion of nitrogen and
carbon in dependence on time, temperature, pressure and material
composition.
[0063] FIG. 5 shows a block diagram of the open-loop and/or
closed-loop control device 11 with the components that are provided
for the activation of the flow control valve 7, the degree of
opening of the throttle 14 and the heating device 5 for setting the
carbonitriding phases. In this case, the degree of opening of the
throttle 14 is set during the carbonitriding phases, with the
vacuum pump 13 running, by the open-loop and/or closed-loop control
device 11 in such a way that the treatment pressure in the
treatment chamber 4 is controlled to the respective target value.
The control of the treatment pressure by means of corresponding
setting of the degree of opening of the throttle 14 takes place at
the gas outlet from the treatment chamber 4 upstream of the pump
13. If the actual value of the treatment pressure, measured by the
pressure sensor 10, exceeds the specified target value for the
treatment pressure, the throttle 14 is opened further by
corresponding activation on the part of the open-loop and/or
closed-loop control device 11, so that the pump 13 can remove a
greater volumetric flow from the treatment chamber 4 and the actual
value for the treatment pressure is lowered. If the actual value of
the treatment pressure, measured by the pressure sensor 10, does
not reach the specified target value for the treatment pressure,
the throttle 14 is closed further by corresponding activation on
the part of the open-loop and/or closed-loop control device 11,
whereby the volumetric flow that the pump 13 removes from the
treatment chamber 4 is reduced and an increase in the actual value
for the treatment pressure in the treatment chamber 4 is
achieved.
[0064] The other components of the open-loop and/or closed-loop
control device 11, as required for example for setting the
heating-up phase A or the diffusion phases D1, D2, are not
represented for reasons of overall clarity and can be formed in the
way known to a person skilled in the art.
[0065] At an input unit 200 of the open-loop and/or closed-loop
control device 11, a user can input a number of parameters for a
desired treatment of the components 2 in the treatment chamber 4.
Thus, by corresponding input, the user can specify one or more
ratios between the carbon concentration and the nitrogen
concentration to be taken up by the components 2 in their outer
layer 125. A first ratio specified in this way is identified in
FIG. 5 as the first ratio data record 205; an nth specified ratio,
where n may be chosen as greater than or equal to one, is
identified as the nth ratio data record 215. If n=1, then there is
only one ratio data record for the specified ratio, which
corresponds to the first ratio data record 205. If more than one
ratio is specified, there is the corresponding number of ratio data
records. The entirety of all the specified ratio data records is
identified by 220. For each ratio data record, an assigned
carbonitriding phase is intended to be set here in order to
implement the specified ratio in the outer layer 125. If only one
ratio data record is specified here, there will also only be one
zone of the outer layer 125 with the corresponding specified ratio;
if there are a number of ratio data records, a carbonitriding phase
is set for each ratio data record, in the time sequence in which
they are input or in the sequence in which they are numbered. Then
there forms in the outer layer 125 a zone with the corresponding
ratio of the carbon concentration and the nitrogen concentration
for each ratio data record, and consequently for each
carbonitriding phase, the zones being formed in relation to the
surface 100 of the respective component 2 in accordance with the
time sequence of the input of the associated specified ratio, and
consequently in the sequence of their numbering. In this case, the
first ratio data record sets the carbon and nitrogen concentrations
at the greatest distance from the outer surface 100 of the
respective component 2 and the last data record used sets the
carbon and nitrogen concentrations nearest the surface. An example
of two such zones, and consequently two such specified ratios, has
been described with reference to FIG. 4. In this case, the second
zone 110 with the thickness d2 was set in the outer layer of the
component 2 with a first ratio data record and the first zone 105
with the thickness d1 was set with a second ratio data record.
[0066] For each specified ratio, a desired amount or depth of
penetration should also be indicated, in other words an associated
thickness of the assigned zone. Correspondingly, a first specified
thickness data record is identified in FIG. 5 by 225 and an nth
specified thickness data record is indicated by 235. The entirety
of the thickness data records is identified by 240. In the time
sequence in which they are input, for each required carbonitriding
phase, the corresponding ratio data record is fed as an input
variable to a temperature-pressure characteristic diagram 250 and
the assigned thickness data record is fed as an input variable to
the treatment-period characteristic diagram 255. The
temperature-pressure characteristic diagram was in this case
determined experimentally and, for each ratio between the carbon
concentration and the nitrogen concentration to be taken up by the
components 2 in their outer layer 125 that is specified at its
input, emits at its output a target value ST for the assigned
treatment temperature and a target value SD for the assigned
treatment pressure. The result of such an experimental evaluation
for the treatment temperature and the treatment pressure has been
stated by way of example with reference to FIG. 2. The target value
ST for the treatment temperature and the target value SD for the
treatment pressure are likewise fed as input variables to the
treatment-period characteristic diagram 255. The target value ST
for the treatment temperature is also fed as an input variable to a
first comparing element 265. The target value SD for the treatment
pressure is also fed as an input variable to a second comparing
element 260.
[0067] Furthermore, at the input unit 200, a material composition,
for example of the case-hardening steel 20MnCr5, is selected from a
proposed set that characterizes the material composition of the
components 2. In this case, a material-composition data record 245
is generated and likewise fed as an input variable to the
treatment-period characteristic diagram 255. The treatment-period
characteristic diagram 255 was in this case likewise determined
experimentally and indicates which treatment period is required in
order in the case of a component of the selected material
composition with the specified target value ST for the treatment
temperature and the specified target value SD for the treatment
pressure to form the specified thickness of the zone to be formed
with carbon and nitrogen taken up according to the specified ratio
of the carbon concentration and the nitrogen concentration in the
outer layer 125 of the respective component 2. For the treatment
period thus determined at the output of the treatment-period
characteristic diagram 255, a corresponding enabling signal is sent
to the flow control valve 7, so that this valve is open during the
determined treatment period for the assigned carbonitriding phase.
Outside the determined treatment period, the flow control valve 7
is closed or is only opened for purging with an inert gas, for
example nitrogen or argon, in a way known to a person skilled in
the art, for diffusion phases that are possibly provided.
[0068] As a further input variable, an actual value IT for the
treatment temperature, which is determined by the temperature
sensor 7, is fed to the first comparing element 265. The first
comparing element 265 compares the target value ST of the treatment
temperature with the actual value IT of the treatment temperature
and, depending on the difference between the target value ST for
the treatment temperature and the actual value IT for the treatment
temperature, emits a control signal to the heating device 5, in
order to minimize the control deviation and correct the actual
value IT for the treatment temperature to the target value ST for
the treatment temperature.
[0069] As a further input variable, an actual value ID for the
treatment pressure, which is determined by the pressure sensor 10,
is fed to the second comparing element 260. The second comparing
element 260 compares the target value SD of the treatment pressure
with the actual value ID of the treatment pressure and, depending
on the difference between the target value SD for the treatment
pressure and the actual value ID for the treatment pressure, emits
a control signal to the throttle 14, in order to minimize the
control deviation and correct the actual value ID for the treatment
pressure to the target value SD for the treatment pressure.
[0070] In this way, the respectively specified ratio between the
carbon concentration and the nitrogen concentration in the outer
layer 125 of the respective component 2 is set in the desired
thickness in the corresponding zone for the treatment period
determined. If a number of such ratios are specified, then a carbon
and nitrogen depth profile specified by the ratio data records 205,
. . . , 215 and the thickness data records 225, . . . , 235 is set
in the outer layer 125 by the carbonitriding phases that are
assigned and optionally separated from one another in each case by
a diffusion phase.
* * * * *