Title: Multi-cell thermal processing unit
Abstract: The present invention relates to a multi cell thermal processing unit. The thermal processing unit comprises an air tight common chamber containing an atmosphere other than ambient air. A loading cell is linked to the common chamber via a gas tight door for providing to and receiving from the common chamber a workpiece. Further, a preheating cell is linked to the common chamber via a heat insulating door. The preheating cell provides a substantially fixed temperature for activating the workpiece. Thermochemical processing of the workpiece is provided by a first and a second thermochemical processing cell each linked to the common chamber via a heat insulating door. The first thermochemical processing cell provides substantially fixed first thermochemical processing conditions for nitriding the workpiece. The second thermochemical processing cell provides substantially fixed second thermochemical processing conditions for post nitriding treatment of the workpiece. A cooling cell linked to the common chamber provides controlled cooling of the workpiece. The thermal processing unit according to the invention, wherein thermochemical processing cells are operated under substantially constant conditions considerably facilitates control functions for providing predetermined conditions. This allows a substantially more accurate control of the thermochemical processing conditions which is especially advantageous for reproducibly thermochemical processing workpieces using nitriding processes.
Patent Number: 6,902,635 Issued on 06/07/2005 to Korwin, et al.
| Inventors:
|
Korwin; Michel J. (Westmount, CA);
Szymborski; Janusz (Pointe Claire, CA)
|
| Assignee:
|
Nitrex Metal Inc. (St. Laurent, CA)
|
| Appl. No.:
|
025503 |
| Filed:
|
December 26, 2001 |
| Current U.S. Class: |
148/559; 266/78; 266/252 |
| Intern'l Class: |
C21D 010/00 |
| Field of Search: |
266/44,78,252,249
148/559
432/230,207
|
References Cited [Referenced By]
U.S. Patent Documents
| 2000664 | May., 1935 | Hayes.
| |
| 3598381 | Aug., 1971 | Schwalm et al.
| |
| 3662996 | May., 1972 | Schwalm et al.
| |
| 3926415 | Dec., 1975 | Konas et al.
| |
| 4653732 | Mar., 1987 | Wunning et al.
| |
| 4763880 | Aug., 1988 | Smith et al.
| |
| 4951601 | Aug., 1990 | Maydan et al.
| |
| 5052923 | Oct., 1991 | Peter et al.
| |
| 5868871 | Feb., 1999 | Yokose et al.
| |
| 6065964 | May., 2000 | Pelissier.
| |
| 2001/0015074 | Aug., 2001 | Hosokawa.
| |
| Foreign Patent Documents |
| 1 193 317 | Apr., 2002 | EP.
| |
| 1 229 137 | Aug., 2002 | EP.
| |
| 08 178 535 | Jul., 1996 | JP.
| |
Other References
English language translation of Japanese 08 178535, Dec. 7, 1996.
Czelusniak et al., "NITREG; NITREG-ONC; NITREG-S; advanced surface hardening
technologies for steel through nitrogen implantation", Nitrex Metal Inc., St-Laurent,
Quebec, Canada, no date.
|
Primary Examiner: Kastler; Scott
Attorney, Agent or Firm: Freedman & Associates
Claims
1. A multi cell thermal processing unit comprising:
an air tight expandable common chamber module for containing an atmosphere other
than ambient air, the chamber module comprising N ports;
a loading cell linked to the first port of the common chamber module via a gas
tight door for providing to and receiving from the common chamber module an iron-base
alloy workpiece;
a first thermochemical processing cell linked to the second port of the common
chamber module via a heat insulating door for thermochemical processing the workpiece,
the first thermochemical processing cell for providing substantially fixed first
thermochemical processing conditions of a thermochemical process for improving
material characteristics of the iron-base alloy material of the workpiece;
a second thermochemical processing cell linked to the third port of the common
chamber module via a heat insulating door for thermochemical processing the workpiece,
the second thermochemical processing cell for providing substantially fixed second
thermochemical processing conditions of the thermochemical process;
a transport mechanism disposed within the common chamber module for handling
and transporting the workpiece within the thermal processing unit;
at least a processor in control communication with the first thermochemical processing
cell, the second thermochemical processing cell, and the transport mechanism for:
processing data related to the thermochemical process in order to divide the
thermochemical process into at least two portions and to determine at least the
first and second thermochemical processing conditions based on operational ranges
of at least the first and second thermochemical processing cells for optimizing
operation of the multi cell thermal processing unit;
controlling provision of the first and the second thermochemical processing conditions;
and,
controlling handling and transportation of the workpiece within the thermal processing
unit; and,
N-3 sealing covers for airtightly sealing the remaining N-3 ports, the covers
being removable for mating the common chamber module to a processing cell or another
common chamber module.
2. A multi cell thermal processing unit as defined in claim 1, comprising:
a second common chamber module having N ports, the first port of the second chamber
module being connected to a fourth port of the common chamber module for providing
transport communication therebetween;
a third thermochemical processing cell linked to the second port of the second
common chamber module via a heat insulating door, the third thermochemical processing
cell for providing substantially fixed third thermochemical processing conditions;
and,
N-2 sealing covers for airtightly sealing the remaining N-2 ports, the covers
being removable for mating the second common chamber module to a processing cell
or another common chamber module.
3. A multi cell thermal processing unit as defined in claim 2, comprising a control
communication link between the third thermochemical processing cell and the at
least a processor, the at least a processor for controlling provision of the third
thermochemical processing conditions, wherein the substantially fixed third thermochemical
processing conditions are a third portion of the thermochemical process.
4. A multi cell thermal processing unit as defined in claim 2, comprising a fourth
thermochemical processing cell linked to the third port of the second common chamber
module via a heat insulating door, the fourth thermochemical processing cell for
providing substantially fixed fourth thermochemical processing conditions.
5. A multi cell thermal processing unit comprising:
an air tight common chamber for containing an atmosphere other than ambient air;
a loading cell linked to the common chamber via a gas tight door for providing
to and receiving from the common chamber an iron-base alloy workpiece;
a first thermochemical processing cell linked to the common chamber via a heat
insulating door for thermochemical processing the workpiece, the first thermochemical
processing cell for providing substantially fixed first thermochemical processing
conditions of a thermochemical process for improving material characteristics of
the iron-base alloy material of the workpiece;
a second thermochemical processing cell linked to the common chamber via a heat
insulating door for thermochemical processing the workpiece, the second thermochemical
processing cell for providing substantially fixed second thermochemical processing
conditions of the thermochemical process;
a transport mechanism disposed within the common chamber for handling and transporting
the workpiece within the thermal processing unit; and,
at least a processor in control communication with the first thermochemical processing
cell, the second thermochemical processing cell, and the transport mechanism for:
processing data related to the thermochemical process in order to divide the
thermochemical process into at least two portions and to determine at least the
first and second thennochemical processing conditions based on operational ranges
of at least the first and second thermochemical processing cells for optimizing
operation of the multi cell thermal processing unit;
controlling provision of the first and the second thermochemical processing conditions;
and,
controlling handling and transportation of the workpiece within the thermal processing
unit.
6. A multi cell thermal processing unit as defined in claim 5, comprising a control
communication link between the air tight common chamber and the at least a processor,
the at least a processor for controlling provision of the atmosphere within the
common chamber, the atmosphere substantially comprising an inert gas.
7. A multi cell thermal processing unit comprising:
an air tight common chamber for containing an atmosphere other than ambient air;
a loading cell linked to the common chamber via a gas tight door for providing
to and receiving from the common chamber an iron-base alloy workpiece;
a first thermochemical processing cell linked to the common chamber via a heat
insulating door for thermochemical processing the workpiece, the first thermochemical
processing cell for providing substantially fixed first thermochemical processing
conditions of a thermochemical process for improving material characteristics of
the iron-base alloy material of the workpiece;
a second thermochemical processing cell linked to the common chamber via a heat
insulating door for thermochemical processing the workpiece, the second thermochemical
processing cell for providing substantially fixed second thermochemical processing
conditions of the thermochemical process;
a transport mechanism disposed within the common chamber for handling and transporting
the workpiece within the thermal processing unit; and,
at least a processor in control communication with the first thermochemical processing
cell, the second thermochemical processing cell, and the transport mechanism for:
processing data related to the thermochemical process in order to divide the
thermochemical process into at least two portions and to determine at least the
first and second thermochemical processing conditions based on operational ranges
of at least the first and second thermochemical processing cells for optimizing
operation of the multi cell thermal processing unit;
controlling provision of a first atmosphere composition and a first temperature
of the first thermochemical processing conditions, and a second atmosphere composition
and a second temperature of the second thermochemical processing conditions; and,
controlling handling and transportation of the workpiece within the thermal processing
unit.
8. A multi cell thermal processing unit as defined in claim 7, comprising a control
communication link between the air tight common chamber and the at least a processor,
the at least a processor for controlling provision of the atmosphere within the
common chamber, the atmosphere substantially comprising an inert gas.
9. A multi cell thermal processing unit as defined in claim 8, comprising a third
thermochemical processing cell linked to the common chamber via a heat insulating
door, the third thermochemical processing cell for providing third thermochemical
processing conditions of the thermochemical process.
10. A multi cell thermal processing unit as defined in claim 9, wherein the heat
insulating door of at least one of the thermochemical processing cells is also
a gas tight door.
11. A multi cell thermal processing unit as defined in claim 8, comprising a
preheating cell linked to the common chamber via a heat insulating door, the preheating
cell for providing a substantially fixed temperature for heating the workpiece
to a predetermined temperature.
12. A multi cell thermal processing unit as defined in claim 11, comprising a
second other preheating cell linked to the common chamber via a heat insulating
door, the second other preheating cell for providing a substantially fixed second
other temperature for heating the workpiece to a predetermined second other temperature.
13. A multi cell thermal processing unit as defined in claim 11, comprising a
quenching cell linked to the common chamber via a gas tight door, the quenching
cell for providing a predetermined quenching operation for the workpiece.
14. A multi cell thermal processing unit as defined in claim 13, comprising a
second other quenching cell linked to the common chamber via a gas tight door,
the second other quenching cell for providing a second other predetermined quenching operation.
15. A multi cell thermal processing unit as defined in claim 11, comprising a
heating cell linked to the common chamber via a heat insulating door, the heating
cell for providing heating of the workpiece to a predetermined temperature after quenching.
16. A multi cell thermal processing unit as defined in claim 15, comprising a
cooling cell linked to the common chamber, the cooling cell for cooling the workpiece.
17. A multi cell thermal processing unit comprising:
an air tight common chamber for containing an atmosphere substantially comprising
an inert gas;
a loading cell linked to the common chamber via a gas tight door for providing
to and receiving from the common chamber an iron-base alloy workpiece;
a first thermochemical processing cell linked to the common chamber for thermochemical
processing the workpiece, the first thermochemical processing cell for providing
first thermochemical processing conditions of a thermochemical process for improving
material characteristics of the iron-base alloy material of the workpiece;
a second thermochemical processing cell linked to the common chamber for thermochemical
processing the workpiece, the second thermochemical processing cell for providing
second thermochemical processing conditions of the thermochemical process;
a transport mechanism disposed within the common chamber for handling and transporting
the workpiece within the thermal processing unit; and,
at least a processor in control communication with the first thermochemical processing
cell, the second thermochemical processing cell, and the transport mechanism for:
processing data related to the thermochemical process in order to divide the
thermochemical process into at least two portions and to determine at least the
first and second thermochemical processing conditions based on operational ranges
of at least the first and second thermochemical processing cells for optimizing
operation of the multi cell thermal processing unit, wherein the at least first
and second thermochemical processing conditions are variable within ranges smaller
than total ranges of the processing conditions of the thermochemical process;
controlling provision of the first and the second thermochemical processing conditions;
and,
controlling handling and transportation of the workpiece within the thermal processing
unit.
18. A multi cell thermal processing unit as defined in claim 17, comprising a
preheating cell linked to the common chamber via a heat insulating door, the preheating
cell for providing a substantially fixed temperature for heating the workpiece.
19. A method for thermal processing a workpiece comprising:
dividing a thermochemical process for improving material characteristics of an
iron-base alloy material of the workpiece into at least two portions and determining
corresponding thermochemical processing conditions based on operational ranges
of at least two thermochemical processing cells, wherein the determined corresponding
thermochemical processing conditions are variable within ranges smaller than total
ranges of the processing conditions of the thermochemical process;
providing the workpiece to a first thermochemical processing cell linked to a
common chamber containing an atmosphere other than ambient air;
thermochemical processing the workpiece by providing first thermochemical processing
conditions of the thermochemical process;
transferring via the common chamber the workpiece from the first thermochemical
processing cell to a second thermochemical processing cell linked to the common
chamber after elapse of a first predetermined time interval;
thermochemical processing the workpiece by providing second thermochemical processing
conditions of the thermochemical process; and,
removing the workpiece from the second thermochemical processing cell after elapse
of a second predetermined time interval.
20. A method for thermal processing a workpiece as defined in claim 19, comprising:
providing a second workpiece to the first thermochemical processing cell after
transferring the workpiece to the second thermochemical processing cell; and,
thermochemical processing the second workpiece by providing the first thermochemical
processing conditions of the thermochemical process.
21. A method for thermal processing a workpiece as defined in claim 19, comprising:
transferring via the common chamber the workpiece from the second thermochemical
processing cell to a third thermochemical processing cell linked to the common
chamber;
thermochemical processing the workpiece by providing third thermochemical processing
conditions of the thermochemical process; and,
removing the workpiece from the third thermochemical processing cell after elapse
of a third predetermined time interval.
22. A method for thermal processing a workpiece as defined in claim 21, wherein
at least one of the determined thermochemical processing conditions is substantially fixed.
23. A method for thermal processing a workpieee as defined in claim 21, comprising:
providing the workpiece to a preheating cell linked to the common chamber; and,
preheating the workpiece to a predetermined temperature.
24. A method for thermal processing a workpiece as defined in claim 23, comprising:
transferring via the common chamber the workpiece from the preheating cell to
a second preheating cell linked to the common chamber; and,
preheating the workpiece to a second predetermined temperature.
25. A multi cell thermal processing unit comprising:
an air tight common chamber for containing an atmosphere other than ambient air;
a loading cell linked to the common chamber via a gas tight door for providing
to and receiving from the common chamber an iron-base alloy workpiece;
a first thermochemical processing cell linked to the common chamber via a heat
insulating door for thermochemical processing the workpiece, the first thermochemical
processing cell for providing substantially fixed first thermochemical processing
conditions of a thermochemical process for improving material characteristics of
the iron-base alloy material of the workpiece;
a second thermochemical processing cell linked to the common chamber via a heat
insulating door for thermochemical processing the workpiece, the second thermochemical
processing cell for providing substantially fixed second thermochemical processing
conditions of the thermochemical process;
a transport mechanism disposed within the common chamber for handling and transporting
the workpiece within the thermal processing unit; and,
at least a processor in control communication with the first thermochemical processing
cell, the second thermochemical processing cell, and the transport mechanism for:
processing data related to the thermochemical process in order to divide the
thermochemical process into at least two portions and to determine at least the
first and second thermochemical processing conditions based on operational ranges
of at least the first and second thermochemical processing cells for optimizing
operation of the multi cell thermal processing unit, wherein the at least first
and second thermochemical processing conditions are variable within ranges smaller
than total ranges of the processing conditions of the thermochemical process;
controlling provision of the first and the second thermochemical processing conditions,
wherein at least one of the first and the second thermochemical processing conditions
comprises a predetermined potential corresponding to the thermochemical process;
and,
controlling handling and transportation of the workpiece within the thermal processing
unit.
26. A multi cell thermal processing unit as defined in claim 25, comprising:
a third thermochemical processing cell linked to the common chamber via a heat
insulating door, the third thermochemical processing cell for providing third thermochemical
processing conditions of the thermochemical process.
27. A multi cell thermal processing unit as defined in claim 26, wherein the
heat insulating door of at least one of the thermochemical processing cells is
also a gas tight door.
28. A multi cell thermal processing unit as defined in claim 5, wherein the thermochemical
process is one of nitriding, carburizing, carbo-nitriding, and nitro-carburizing.
29. A multi cell thermal processing unit as defined in claim 17, wherein the
thermochemical process is one of nitriding, carburizing, carbo-nitriding, and nitro-carburizing.
30. A multi cell thermal processing unit as defined in claim 19, wherein the
thermochemical process is one of nitriding, carburizing, carbo-nitriding, and nitro-carburizing.
Description
FIELD OF THE INVENTION
This invention relates to thermal processing of workpieces and in particular
to a multi-cell thermal processing unit comprising a plurality of thermochemical
processing cells, wherein each cell is operated at a substantially fixed predetermined
atmosphere and temperature.
BACKGROUND OF THE INVENTION
Heat treating of metal is a commonly used technique to improve material characteristics
of a workpiece for specific applications. For example, surface hardening involving
a change in the composition of the outer layer of an iron-base alloy through application
of an appropriate thermal treatment. Typical processes are carburizing carbo-nitriding
and nitriding. Application of such processes enhances wear resistance, corrosion
resistance, and fatigue strength of such treated workpieces. Other heat treatment
processes involve annealing and aging.
However, in order to reproducibly obtain predetermined results using these
surface hardening processes control of operating parameters such as composition
of the atmosphere, temperature, and pressure during the hardening process is required.
This is particularly necessary for nitriding processes. From the control point
of view nitriding is a very complex process influenced by thermodynamic relations
at the gas/metal interface during breakup of the atmosphere's components. The exact
nature of the reactions taking place, i.e. mass transport of the gaseous phase,
adsorption, diffusion and nitride phase formation is determined by the kinetics
of this process. In order to control this process accurate provision of the atmosphere's
components as well as temperature and pressure are essential.
Normally, a heat treating process of a workpiece comprises a number of
processing steps such as preheating, carburizing or nitriding, and cooling or quenching.
Numerous prior art systems have been disclosed teaching cascading of various chambers
for preheating, thermal treating and cooling in order to avoid, for example, cooling
of the nitriding furnace for loading and unloading of a batch of workpieces. Such
systems are disclosed, for example, in U.S. Pat. No. 3,598,381 issued to Schwalm
et al. in Aug. 10, 1971, U.S. Pat. No. 3,662,996 issued to Schwalm et al. in May
16, 1972, U.S. Pat. No. 4,653,732 issued to Wunning et al. in Mar. 31, 1987, U.S.
Pat. No. 4,763,880 issued to Smith et al. in Aug. 16, 1988, and U.S. Pat. No. 5,052,923
issued to Peter et al. in Oct. 1, 1991, which are incorporated hereby for reference.
However, these systems are very inefficient for modern applications. Nowadays,
use of thermal processing of metal workpieces in order to improve their material
characteristics is numerous. This results in an increasing demand of a plurality
of differently treated workpieces meeting different material characteristic requirements.
The above mentioned heat treating systems only allow treatment of workpieces using
a same process. Furthermore, change of thermochemical processing parameters such
as atmosphere composition or temperature for different workpieces requires change
of the operating parameters of the heat treating cell of the system. Therefore,
a complex heat treating cell being able to provide numerous different heat treating
parameters is required. Additionally, change of the heat treating parameters requires
a substantial amount of time for adjusting the heat treating cell, which is not
acceptable in modern manufacturing processes. Another disadvantage of these prior
art systems is the inefficient use of the various system components through the
cascading of these components. For example, the thermochemical processing step
requires substantially more time than the cooling or quenching step. Thus, during
the thermochemical processing step the cooling or quenching cell is sitting idle.
However, it would be advantageous for modern manufacturing applications
to divide the thermal process into steps performed under substantially fixed conditions
or performed within a narrow range of conditions based on the different processing
steps required for the different heat treating of workpieces. Manufacturing and
operating costs would be substantially reduced if each of the processing modules
is operated at substantially fixed parameters such as atmosphere composition and temperature.
It is, therefore, an object of the invention to provide a method for thermal
processing
workpieces by dividing the thermal process into steps performed under substantially
fixed conditions or performed within a narrow range of conditions based on the
different processing steps required for the different heat treating of workpieces.
It is further an object of the invention to provide a multi-cell thermal processing
unit wherein each of the processing cells is operated at substantially fixed operating parameters.
SUMMARY OF THE INVENTION
The multi-cell thermal processing units according to the invention are highly
advantageous for modem thermochemical processing applications. For example, keeping
the operating conditions in each of the thermochemical processing cells constant
or varying these conditions only within a range smaller than the range required
for a complete thermochemical processing process provides considerable time as
well as energy savings. Furthermore, operating a thermochemical processing cell
under substantially constant conditions considerably facilitates control functions
for providing predetermined conditions. This allows a substantially more accurate
control of the heat thermochemical processing conditions which is especially advantageous
for reproducibly thermochemical processing workpieces using nitriding processes
such as the NITREG® process.
In accordance with the present invention there is provided a multi cell thermal
processing unit comprising:
an air tight expandable common chamber module for containing an atmosphere other
than ambient air, the chamber module comprising N ports;
a loading cell linked to the first port of the common chamber module via a gas
tight door for providing to and receiving from the common chamber module a first
and a second workpiece;
a first thermochemical processing cell linked to the second port of the common
chamber module via a heat insulating door, the first thermochemical processing
cell for providing substantially fixed first thermochemical processing conditions
for thermochemical processing the first workpiece;
a second thermochemical processing cell linked to the third port of the common
chamber module via a heat insulating door, the second thermochemical processing
cell for providing substantially fixed second thermochemical processing conditions
for thermochemical processing the second workpiece;
a transport mechanism disposed within the common chamber module for handling
and
transporting the first and the second workpiece within the thermal processing unit; and,
N-3 sealing covers for airtightly sealing the remaining N-3 ports, the covers
being removable for mating the common chamber module to a processing cell or another
common chamber module.
In accordance with the present invention there is further provided a multi cell
thermal processing unit comprising:
an air tight common chamber for containing an atmosphere other than ambient air;
a loading cell linked to the common chamber via a gas tight door for providing
to and receiving from the common chamber a workpiece;
a first thermochemical processing cell linked to the common chamber via a heat
insulating door, the first thermochemical processing cell for providing substantially
fixed first thermochemical processing conditions for nitriding the workpiece;
a second thermochemical processing cell linked to the common chamber via a heat
insulating door, the second thermochemical processing cell for providing substantially
fixed second thermochemical processing conditions for second nitriding treatment
of the workpiece;
a cooling cell linked to the common chamber for controllably cooling the workpiece; and,
a transport mechanism disposed within the common chamber for handling and transporting
the first and the second workpiece within the thermal processing unit.
In accordance with the present invention there is yet further provided a multi
cell thermal processing unit comprising:
an air tight common chamber for containing an atmosphere other than ambient air;
a loading cell linked to the common chamber via a gas tight door for providing
to and receiving from the common chamber a first and a second workpiece;
a preheating cell linked to the common chamber via a heat insulating door, the
preheating cell for providing a substantially fixed temperature for activating
the workpiece;
a first thermochemical processing cell linked to the common chamber via a heat
insulating door, the first thermochemical processing cell for providing substantially
fixed first thermochemical processing conditions for thermochemical processing
the first workpiece;
a second thermochemical processing cell linked to the common chamber via a heat
insulating door, the second thermochemical processing cell for providing substantially
fixed second thermochemical processing conditions for thermochemical processing
the second workpiece; and,
a transport mechanism disposed within the common chamber for handling and transporting
the first and the second workpiece within the thermal processing unit.
In accordance with the present invention there is yet further provided a multi
cell thermal processing unit comprising:
an air tight common chamber for containing an atmosphere substantially comprising
an inert gas;
a loading cell linked to the common chamber via a gas tight door for providing
to and receiving from the common chamber a workpiece;
a preheating cell linked to the common chamber via a heat insulating door, the
preheating cell for providing a substantially fixed temperature for heating the
workpiece to a predetermined temperature;
a first thermochemical processing cell linked to the common chamber, the first
thermochemical processing cell for providing a first portion of thermochemical
processing conditions of a thermochemical processing process for thermochemical
processing the workpiece;
a second thermochemical processing cell linked to the common chamber, the second
thermochemical processing cell for providing a second portion of the thermochemical
processing conditions of the thermochemical processing process for thermochemical
processing the workpiece; and,
a transport mechanism disposed within the common chamber for handling and transporting
the workpiece within the thermal processing unit.
In accordance with an aspect of the present invention there is provided a method
for thermal processing a workpiece comprising the steps of:
providing a first workpiece to a first thermochemical processing cell linked
to a common chamber containing an atmosphere other than ambient air;
thermochemical processing the first workpiece by providing a first
portion of thermochemical processing conditions of a first thermochemical process;
transferring via the common chamber the first workpiece from the first
thermochemical processing cell to a second thermochemical processing cell linked
to the common chamber after elapse of a first predetermined time interval;
thermochemical processing the first workpiece by providing a second
portion of the thermochemical processing conditions of the first thermochemical
processing process; and,
removing the first workpiece from the second thermochemical processing cell
after elapse of a second predetermined time interval.
BRIEF DESCRIPTION OF THE FIGURES
Exemplary embodiments of the invention will now be described in conjunction
with the following drawings, in which:
FIG. 1 is a simplified flow diagram illustrating a processing flow for prior
art thermal processing systems;
FIG. 2 is a simplified flow diagram illustrating a processing flow for prior
art thermal processing systems;
FIG. 3
a is a simplified flow diagram of a method for thermal processing
according to the invention;
FIG. 3
b is a simplified flow diagram illustrating a comparison of the
timing of a simple process flow divided into three processing steps;
FIG. 3
c is a simplified flow diagram illustrating a comparison of the
timing of a simple process flow divided into three processing steps;
FIG. 4 is a simplified flow diagram of a method for thermal processing according
to the invention;
FIG. 5 is a simplified flow diagram of a method for thermal processing according
to the invention;
FIG. 6 is a simplified flow diagram of a method for thermal processing according
to the invention;
FIG. 7 is a simplified block diagram of a multi-cell thermal processing unit
according to the invention;
FIG. 8 is a simplified block diagram of another embodiment of a multi-cell thermal
processing unit according to the invention; and,
FIG. 9 is a simplified block diagram of yet another embodiment of a multi-cell
thermal processing unit according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
In the following description the expression workpiece is used to refer to any
kind of manufactured metallic component such as springs, valves, piston rings,
etc. for thermal processing. Furthermore, the expression workpiece also includes
a batch of components, which are treated together and are provided, for example,
in a racking. Moreover, a complete process including steps such as preheating,
thermochemical processing, quenching etc. is called thermal processing. Whereas,
the expression thermochemical processing includes only operations combining the
effects of heat and of an active atmosphere such as nitriding, carburizing, nitro-carburizing,
or comparable processing steps.
Some of these drawbacks of the prior art are overcome by the thermal processing
installation disclosed by Pelissier in U.S. Pat. No. 6,065,964 issued in May 23,
2000. Pelissier teaches a vaccum thermal processing installation for use under
a rarefied atmosphere including several processing cells linked to a common air-tight
vacuum chamber. By feeding all workpieces through a common vaccum chamber, improved
vaccum conditions are achievable within each oven chamber. This has specific advantages
to vacuum thermochemical processes, but is of little or no advantage to a nitriding
process wherein increased vacuum quality of successive chambers is not necessary.
Though, the system of Pelissier, appears similar to the system described herein,
it is a system that would not have been considered with foresight in looking toward
the inventive solution since, nitriding does not require improved vacuum atmosphere
quality. That said, Pelissier does teach a single common low pressure atmosphere
chamber for use in loading and unloading of workpieces into ovens for independent
processing therein. The main advantage of this installation is the use of only
two air-tight doors for operating a plurality of processing cells and a gas quenching
cell linked to the common chamber, thus reducing manufacturing costs and improving
manufacturing quality.
In order to provide a better understanding of the invention, flow diagrams illustrating
processing steps and their possible interconnection during operation of prior art
systems will be described first, followed by a comparison with flow diagrams illustrating
possible processing flows using the thermal processing unit according to the invention.
Referring to FIG. 1 a processing flow for prior art thermal processing
systems having a cascaded arrangement of a loading cell, a preheat cell, a thermochemical
processing cell, and a cooling or quenching cell is shown. Such systems are now
widely used in the industry for the thermal processing of workpieces. As shown
in the diagram these systems are very inflexible in their operation. For example,
they allow application of only one process having one set of predetermined operating
conditions such as atmosphere composition, temperature, pressure. For thermally
processing a workpiece requiring a process with a different set of parameters the
whole system has to be adapted for this process. This is especially inefficient
if the number of workpieces requiring this set of parameters is small. Furthermore,
use of some components of the system is always inefficient. For example, the step
of thermochemical processing requires substantially more time than the step of
quenching. Therefore, due to the cascading of the system components the quenching
cell is not in use most of the time. Another disadvantage of such systems is an
insufficient adaptability to the amount of workpieces to be processed. If the amount
exceeds the capacity of such a system a whole system comprising all the components
has to be installed.
An improvement of the above prior art systems is obtained using the system disclosed
by Pelissier in U.S. Pat. No. 6,065,964 and shown in the flow diagram of FIG.
2.
Linking a plurality of thermochemical processing cells, a loading cell and a quenching
cell to common chamber provides increased flexibility. Here, one loading cell and
one quenching cell are used to serve a plurality of thermochemical processing cells
resulting in a more efficient use of the loading and the quenching cell. It allows
parallel operation of the thermochemical processing cells and, for example, use
of the loading cell and the quenching cell while at a same time workpieces are
processed in some of the thermochemical processing cells. Furthermore, it allows
expansion of the system by just adding the required components.
Referring to FIG. 3
a a simplified flow diagram of a method for thermal
processing according to the invention is shown. Here, as compared to the diagram
shown in FIG. 2 the processing flow is divided into a preheat step and a plurality
of parallel thermochemical processing steps. Workpieces are preheated in a preheat
cell and then transferred into one of a plurality of thermochemical processing
cells. Each of the thermochemical processing steps is conducted using a thermochemical
processing cell having a substantially fixed predetermined atmosphere composition,
temperature and pressure. Alternatively, atmosphere composition, temperature and/or
pressure are changed within a predetermined range being a portion of the range
of operating conditions for a complete thermochemical processing process. If a
process requires changes exceeding these predetermined limits or the fixed predetermined
conditions of a given thermochemical processing cell the workpiece is transferred
to another thermochemical processing cell providing these conditions, e.g. from
thermochemical processing
1 to thermochemical processing
2 as shown
in FIG. 3
a. Dividing the thermochemical process into a plurality of steps
performed under substantially constant conditions or under conditions which are
only changed within a portion of the range of operating conditions for a complete
thermochemical process has numerous advantages for modern thermochemical processing
applications. Firstly, the combination of various different thermochemical processing
steps into one set of thermochemical processing conditions for processing a workpiece
allows implementation of a large number of different sets of thermochemical processing
conditions using a fixed number of thermochemical processing cells being smaller
than the number of sets of thermochemical processing conditions realized. Secondly,
numerous sets of different thermochemical processing conditions are provided in
parallel without changing operating conditions in each of the thermochemical processing
cells. Thirdly, changing the operating conditions within a thermochemical processing
cell requires a substantial amount of time and energy. Therefore, keeping the operating
conditions in each of the thermochemical processing cells constant or varying these
conditions only within a portion of the range of operating conditions for a complete
thermochemical process provides considerable time as well as energy savings. Fourthly,
it allows use of thermochemical processing cells, which are operable within a narrow
operating range considerably reducing manufacturing costs of each of the thermochemical
processing cells. Additionally, operating a thermochemical processing cell under
substantially constant conditions reduces material fatigue prolonging its lifetime.
Fifthly, dividing the process flow into processing steps as shown provides the
means for maximizing efficiency. For example, for a given number of different thermochemical
processes and a given number of workpieces per process in a given time, the processes
are divided into a number of processing steps and according to the number of workpieces
per processing step and time required for each processing step the number of thermochemical
processing cells operating under the conditions required for each step is provided.
Based on this information and using network topology based on a flow diagram as
shown in FIG. 3
a it is possible to optimize the thermal processing with
respect to throughput of workpieces, efficient use of each component of the thermal
processing unit, processing time, and processing energy using a processor.
FIGS. 3
b and
3c illustrate a comparison of the timing
of a simple process flow divided into three processing steps, for example, a thermochemical
processing step
1 requiring 30 min, followed by a thermochemical processing
step
2 requiring 60 min and a thermochemical processing step
3 requiring
25 min. Provision of one thermochemical processing cell for step
1, two
cells for step
2 and one cell for step
3 instead of one cell for
all three steps results in considerable time savings as illustrated in FIGS. 3
b
and
3c. FIG. 3
b illustrates the timing in min for the
processing of two workpieces I and II. The total processing time for one workpiece
is 115 min. Therefore, two workpieces are processed in 230 min. For comparison,
the process flow shown in FIG. 3
c provides workpiece I after 115 and workpiece
II in 145 min, which amounts to a time saving of approximately 37%. Furthermore,
for more workpieces this arrangement provides one workpiece every 30 min resulting
in a substantially more constant processing flow having over twice the efficiency
as the number of workpieces increases toward infinity.
The diagram shown in FIG. 3
a is only a very simple example for the realization
of the processing flow according to the invention. Referring to FIG. 4 flexibility
is further increased by provision of different quenching steps Q
1 and Q
2
as well as a cooling step required for certain applications. Another option is
the division of the preheating step into a plurality of preheating steps with different
operating temperatures, as shown in FIG.
5. For example, workpieces requiring
different preheat temperatures are provided to different preheating cells operating
at different temperatures. Furthermore, it allows heating of a workpiece to a temperature
T
1 and then transferring the workpiece to another preheating cell for heating
to a higher temperature T
2. This has similar advantages as outlined above
for the preheating step. FIG. 6 illustrates the implementation of further processing
steps such as heating of a workpiece and slowly cooling of the workpiece after
quenching in order to remove stresses in the workpiece induced by the quenching
process. This treatment is referred to in the art as tempering.
Optionally, the method for thermal processing according to the invention
includes thermochemical processing steps for different thermochemical processing
processes combined in one processing unit and possible interconnection of same.
For example, a thermochemical processing cell for nitriding is used for performing
a step of a nitro-carburizing process.
Further optionally, the method for thermal processing according to the invention
includes other thermal processing steps such as annealing to relieve rolling, forging,
or machining strains in a workpiece before thermochemical processing and aging
to recover a workpiece from unstable conditions of its structure induced by quenching.
Referring to FIG. 7 a simplified block diagram of a multi-cell thermal
processing unit
100 according to the invention is shown. The thermal processing
unit
100 comprises a loading cell
102 for loading and unloading workpieces,
a preheating cell
104, a plurality of thermochemical processing cells—shown
are three cells
106,
108,
110 but the invention is not limited
thereto, and a quenching cell
112. The cells
102-
112 are linked
to a common gas tight chamber
120 comprising modules
120A,
120B,
and
120C. Preferably, the common chamber
120 is a gas tight chamber
for containing an atmosphere other than ambient air. For some applications operating
in a low pressure atmosphere or allowing for gas leakage of a gas other than air
an air tight common chamber
120 is sufficient. The workpieces are transferred
between the various cells via transport mechanism
140 disposed within the
common chamber
120. Such a transport mechanism comprises, for example, a
carriage for handling the workpieces in and out of the cells, which is moved along
a rail system to predetermined locations within the common chamber
120.
The common chamber comprises an atmosphere other than ambient air such as a low
pressure atmosphere or a high pressure atmosphere. For example, some thermochemical
processes operate at pressure of approximately 5-10 mbar. Preferably, the atmosphere
within the common chamber comprises substantially an inert gas such as Ar in order
to reduce interference with atmospheres in the thermochemical processing cells
106-
110 as well as to reduce reaction with hot surfaces of workpieces
during transfer in the common chamber
120. Each of the thermochemical processing
cells is operated under substantially fixed conditions for temperature, atmosphere
composition and pressure. Alternatively, at least some of the conditions in some
of the thermochemical processing cells
106-
110 are changed during
operation within a predetermined range covering only a portion of a total range
of conditions required for a complete thermochemical process. For example, some
nitriding processes require a gradual change of the atmosphere composition with
time in order to control the nitriding potential of the atmosphere. The loading
cell
102 and the quenching cell
112 are linked to the common chamber
120 via a gas tight door
122,
124 in order to avoid interaction
with the low pressure atmosphere of the common chamber
120 during operation.
The preheat cell
104 and the thermochemical processing cells
106-
110
are linked to the common chamber via heat insulating but not gas tight doors
126-
132.
This is possible if the steps of preheating and thermochemical processing are performed
at a same pressure, i. e. the pressure of the common chamber
120. In this
case interaction of the inert gas atmosphere in the common chamber
120 with
the atmospheres in the thermochemical processing cells is negligible. Use of only
heat insulating doors reduces manufacturing and operating costs of the thermal
processing unit
100. Optionally, some of the thermochemical processing cells
106-
110 are equipped with heat insulating as well as gas tight doors
if it is necessary to perform thermochemical processes at different pressures.
Further optionally, the preheat cell is equipped with a heat insulating as well
as gas tight door, for example, if in the preheating cell the function of activation
is performed requiring the preheating cell being at least partially filled with air.
The common chamber of the multi-cell thermal processing unit
100 shown
in FIG. 7 comprises 3 connected common chamber modules
120A-
120C.
In the example illustrated in FIG. 7 each module has 4 ports, but as is evident
the invention is not limited thereto. The ports provide communication to other
chamber modules as well as to the processing cells connected thereto, as shown
in FIG.
7. Ports not in use are sealed with a gas tight cover
150,
152. This modular structure of the common chamber substantially increases
flexibility of the multi-cell thermal processing unit
100. Firstly, it substantially
facilitates provision of the processing unit tailored to a customer's needs. Secondly,
it allows retrofitting of the unit in order to meet new demands, for example, adding
new processing cells for providing new operating conditions or adding more processing
cells operating under same conditions. New chamber modules are added to an end
module of an existing unit or, alternatively, interposed between two existing modules
if preferred, for example, to optimize workflow or to group similarly operating
processing cells.
Referring to FIG. 8 a more complex structure of a multi-cell thermal processing
unit
200 according to the invention is shown. In order to provide considerably
more processing flexibility more processing cells are added to the unit. Here,
the unit comprises, for example, three preheating cells
210-
214 operating
at different substantially fixed predetermined temperatures T
1-T
3.
This allows preheating of three workpieces at a time to different temperatures
for different thermochemical processing. Furthermore, it enables preheating of
workpieces in steps, for example, heating to a temperature T
1, transferring
to another thermochemical processing cell and heating then to a temperature T
2>T
1.
Thermochemical processing of the workpieces is performed in thermochemical processing
cells
216 to
222, similar to the unit
100 shown in FIG.
7.
The thermal processing unit
200 comprises two quenching cells
204
and
206 providing, for example, means for gas quenching in one cell and
oil quenching in another. Furthermore, a cooling cell
208 is provided for
slowly cooling a workpiece to room temperature. All processing cells as well as
loading cell
202 are linked to a common gas tight chamber
230. Optionally,
all cells are arranged in groups respective to their operation. For example, grouping
of thermochemical processing cells, preheat cells, quenching cells. Such grouping
facilitates provision of, for example, atmosphere components to the thermochemical
processing cells. Another aspect taken into consideration for the arrangement of
the processing cells is minimizing transfer distances of the workpieces during
thermal processing, which is, for example, achieved by locating the loading cell
202 between the quenching cells
204-
206 and the preheating
cells
210-
214 as shown in FIG.
8. Of course numerous other
arrangements as well as different numbers of cells are applicable depending upon
the various thermal processes performed and the amount of workpieces to be processed.
For example, if it is desired to temper some of the workpieces after quenching
these workpieces are transferred to one of the preheating cells
210-
214
or, alternatively, a heating cell
240 is added to the unit
200 as
shown in FIG.
8.
Optionally, sections of the common chamber are separated, for example,
by a gas tight door
250. For example, this allows separating the section
linked to the thermochemical processing cells
216-
222 from the rest
of the common chamber reducing the risk of contaminating the atmospheres in the
thermochemical processing cells.
Further optionally, the thermal processing unit according to invention comprises
a plurality of thermochemical processing cells for providing thermochemical processing
conditions for different thermochemical processing such as nitriding as well as
carburizing in one thermal processing unit.
Referring to FIG. 9 an automized thermal processing unit
300 according
to the invention is shown. Here, all cells
102-
112, transport mechanism
140 and provision of the atmosphere in the common chamber are controlled
by a computer
302. The computer control allows full integration of the thermal
processing unit into a computer aided manufacturing process. Based on network topology
as shown above, the available processing cells, the required thermal processes
and the number of workpieces per process it is possible to determine optimum use
of the thermal processing unit
300 and to control the unit accordingly using
computer
302. Furthermore, if some of the processing cells are operating
within a range of conditions, use of the computer
302 allows determining
optimum operating conditions for each of these cells in view of required thermal processes.
The multi-cell thermal processing units according to the invention are highly
advantageous for modern thermochemical processing applications. For example, changing
the operating conditions within a thermochemical processing cell requires a substantial
amount of time and energy. Therefore, keeping the operating conditions in each
of the thermochemical processing cells constant or varying these conditions only
within a range smaller than the range required for a complete thermochemical process
provides considerable time as well as energy savings. Moreover, it allows use of
