Patent Grant
8694167
1. Field of the Invention
The invention relates to an intelligent control method for vacuum pumps used in an industrial furnace complex, particularly in vacuum furnace systems. The invention also relates to an industrial furnace complex associated therewith.
2. Description of the Related Art
According to DE 10152204 B4, the stated object is to improve a vacuum gas carburising complex so as to avoid the drawbacks of not being able to monitor and record data relating to a carburising atmosphere during the carburising process.
In this context, the following steps are carried out in a method for measuring and/or regulating the carburising atmosphere inside a carburising chamber of a vacuum gas carburising system:
With this method for controlling the process gas, it is only possible to measure the current state of the furnace atmosphere regularly during the carburising phase. However, with this method it is not possible to engage or disable the vacuum pumps throughout the entire process according to the status of the process concerned.
An automated system for monitoring operational safety and controlling the process cycle in a vacuum heat treatment furnace is also known from DE 41 21 277 C2, wherein a pressure sensor for measuring the pressure in the furnace housing and at least one gas sensor arranged in the immediate vicinity of the furnace are provided. Each sensor cooperates with a separate evaluation unit to initiate a safety program if a predetermined pressure is not reached in the interior of the housing and at the same time a given gas concentration is detected in the area surrounding the furnace. This immediately causes the cooling gas inlet valve to be closed, the gas outlet valve to be opened and a purge gas inlet valve to be opened. This safety program is activated in a line that connects a purge gas reservoir with the interior of the furnace housing. The pressure in a housing interior chamber and in the area surrounding the furnace is equalised depending on the coolant gas concentration at the gas outlet valve as recorded by a gas sensor that is integrated in a branch line to the gas outlet line.
This additional safety device in a vacuum furnace with high pressure hydrogen quenching guarantees that the furnace is flushed with an inert gas if a hydrogen leak is detected and a combustible/explosive gas mixture cannot be formed. However, it does not exercise any corresponding control/regulation of the vacuum pump.
A technical search for solution options must also include an examination of the device described in EP 0524 368 B1 (similar to DE 41 21 277 C2). In this case too, automated monitoring and control of the process sequence is provided in a vacuum heat treatment furnace, particularly a furnace that is operated for the purpose of annealing metal workpieces with hydrogen under overpressure as the coolant gas. In this case, a vacuum pump is connected to housing. Gas inlet and gas outlet apertures open into the heating chamber. The system includes a motor-fan unit, a coolant gas reservoir, a heater unit and a heat exchanger in the coolant gas circuit as well as a pressure sensor measuring the pressure in the furnace housing and at least one gas sensor arranged in the immediate vicinity of the furnace, and each of these components cooperates with an evaluation unit to initiate a safety program if a predetermined pressure is not reached in the interior of the housing and at the same time a given gas concentration is detected in the area surrounding the furnace.
As described in the preceding, this program immediately causes the coolant gas inlet valve to be closed and the gas outlet valve and a purge gas inlet valve to be opened. The purge gas inlet valve is integrated in a line that connects purge gas reservoir with an interior chamber of the furnace housing and so ultimately brings about pressure equalisation between the housing interior and area surrounding the furnace depending on the coolant gas concentration registered at the gas outlet valve by a gas sensor integrated in a branch line to the gas outlet line.
Accordingly, this solution returns full circle to the document DE 41 21 277 C2 examine previously with an additional safety device for a vacuum furnace with high pressure hydrogen quenching which ensures that the furnace is flushed with an inert gas if a hydrogen leak is measured, thus guaranteeing that a combustible or explosive gas mixture cannot form.
Accordingly, the general process sequence represented in both patents also does not disclose how the vacuum pump might be controlled or regulated.
A method for regulating the vacuum in a chamber that is connected to a pump device comprising several pumps arranged in series is disclosed in DE 100 43 783 A1. In this context, at least one suction parameter is modified depending on both the high vacuum pressure present in the chamber and a predefined setpoint pressure. The change to the suction parameter is effected by using at least one regulating parameter, the regulating parameter being determined according to the high vacuum pressure that is present inside the chamber.
While this regulation of the suction power of a pump is economical in terms of energy consumption, it is not able to isolate the pumps from the recipient by means of a valve if overpressure phases occur in the vacuum furnace during high pressure gas quenching or convection operation for example.
A diaphragm or piston pump, or a combined diaphragm/piston pump with a device for pressure-dependent reduction of the suction chamber expansion speed is also described in DE 198 16 241 C1. In this device, if the aspiration pressure or control signal falls below a certain value the speed of the drive unit is adjusted automatically, the pressure or control signal and speed value pairs in this range are measured and stored, and from this is calculated the minimum suction value with which the lowest final vacuum can be achieved. On this basis, the speed of the drive unit is set to the associated optimum speed.
The disadvantage of such economical regulation of a pump's suction power by varying its suction or speed is also that the system cannot determine when the pumps are isolated from the recipient by a valve. However, this is essential in the overpressure phases that occur in a vacuum furnace (high pressure gas quenching or convection operation).
DE 699 07 890 T2 also discloses a method and device for regulating pressure in vacuum systems, in which the following steps are carried out:
In this context, the readjustment is carried out using a proportional and integral regulator and the delay thereof for a specified period.
With this method and device for pressure regulation in vacuum systems, it is possible to regulate the suction power, but the “intelligence” of the system is limited by the fact that a switch-off function is not triggered in the process phases that are performed without a vacuum.
This shortcoming (no switch-off in the phases of the process that do not require a vacuum) is also not corrected by the solution suggested in JP 2008002274 A, which discloses an evacuation device for regulating the furnace pressure in the vacuum furnace by altering the speed of the vacuum pump. In order to carry out the evacuation, a first recirculation line between the pump outlet and the pump inlet is opened when the lowest speed for the vacuum pump is reached. A second recirculation line is opened if the lowest speed for the vacuum pump is reached again despite the first recirculation line being open. When the upper limit of the pump speed regulator is reached, the recirculation lines are closed. The recirculation lines are opened and closed by corresponding valves. The recirculation flow is adjusted using resistors.
A brief review of a different field such as is represented by JP 2001214868 A gives no hint as to how to ensure that the system switches off during the process phases where a vacuum does not occur. In this case, only one vacuum control unit in one furnace is provided for simply adapting the vacuum level in the furnace without increasing the size of the device and raising the vacuum pump output while the vacuum arc furnace is operating. In this case, the vacuum arc furnace is equipped with a vacuum pump that is connected to the interior of the furnace via a suction line. A vacuum atmosphere is created in the furnace housing with the shared use of a mechanical booster pump and a rotary pump. When the smelting furnace is in use, the rotating speed of the pumps is controlled by an inverter. When the suction power is altered, the vacuum is adjusted in the furnace. When the vacuum display signal reaches the controller, the inverter automatically initiates control of the pump speed.
A further consideration of U.S. Pat. No. 3,736,360 instructs one skilled in the art with control system for an electrically heated vacuum furnace. Among other devices, this system is equipped with a vacuum pump that is connected to the interior of the furnace via a suction line, and also with a plurality of heating elements for various zones and with a temperature measuring device for each zone, and with a controlled measuring instrument for the master zone. These instruments are connected to a primary furnace regulator and secondary regulators for the individual zone. A control valve in the vacuum line or a controlled cock, connected to the vacuum line, make it possible to keep the pressure in the furnace constant while the pump operates at constant speed. A pressure gauge connected to the vacuum line is also connected to the heater elements.
After evaluating this intelligent system for regulating the suction power, no provision was found for a switch-off capability for the phases without vacuum.
Based on a general survey of the evaluated prior art and practical experience in process operation of vacuum systems, “emergency devices” and “pressure regulating devices” are known that primarily use safety or pressure as a “regulating parameter. But more stringent requirements are applied to vacuum heat treatment in a modern vacuum furnace to ensure that besides the existing temperature-time sequences it is able to respond flexibly in anticipation of the pressure-time sequences.
In view of the above, it may be concluded that the problem of obtaining information about when the vacuum pumps can be shut off entirely after a certain point in time while process gas is being evacuated at certain times in a given process has not yet been solved.
The object of the invention is to provide an intelligent method for controlling vacuum pumps used in an industrial furnace complex, particularly in vacuum furnace systems, in which the incremental deactivation or activation of the pumps throughout the entire process exerts an influence on a corresponding controller/regulator for the vacuum pump in such manner that the vacuum pumps are switched off as a function of the pressure-time sequences in the process phases in which a vacuum is not present, thus enabling the overall workflow of the treatment process to be operated as economically as possible in terms of energy consumption.
This stated object takes into account the fact that certain types of vacuum pumps require a lead time before they are ready to operate for their intended application.
According to the invention, this is solved with a method for controlling at least one vacuum pump used in an industrial furnace complex, particularly in vacuum furnace systems, and a vacuum pump controller that is integrated in a control and regulation device, in which
The incremental deactivation or activation of the vacuum pump using the program in the process controller with the four logically linked program steps makes it possible to control the vacuum pumps economically in terms of energy and without extensive investment according to the features of the claims.
If the query in the first step, as to whether the process is active in the industrial furnace complex, is answered with no, the pump controller is not started, if it is answered with yes, a test of the current process phase is performed.
If the query in the second step, as to whether the vacuum pump is required in the current process phase, is answered with yes, the vacuum pump is switched on and the process query starts as described in the first step. If the query is answered with no, a test of all future process phases is performed.
If the query in the third step, as to whether the respective vacuum pump will be required in the future process phases is answered with no, the vacuum pump is switched off in order to save energy and the query is started again as described in the first step. If the query is answered with yes, the time until the pump will be required to operate is calculated and a required lead time for flawless functioning of the vacuum pump, as a warming up time so to speak, is determined immediately.
Finally, in a fourth step it is queried whether the time until the next required operation of the vacuum pump is greater than the required lead time for the pump. If the query is answered with yes, the vacuum pump is switched off to save energy, if the answer is no, the vacuum pump is switched on and the process query is restarted as described in the second step.
The sequence of the stepped queries may be integrated in a controlling and regulating device in the form of a control loop in such manner that the switching of the vacuum pump is controlled according to the relationship Pa=S1S2(
S3
(S4(T1>T2))).
The industrial furnace complex, particularly the vacuum furnace system, for performing the method, comprises a heating chamber, at least one vacuum pump and a vacuum pump controller integrated in a controlling and regulating device, wherein at least one pressure sensor, at least one gas inlet, and a pump valve are provided and are connected with the vacuum pump controller having a logic circuit to enable the steps of
Species-related industrial furnace complexes, which in certain cases comprise at least one gas discharge means, may also be operated in accordance with the method of the invention.
The invention will be described on the basis of an exemplary embodiment and with reference to the drawing.
In the drawing
In an industrial furnace complex 1, shown in
According to the method, a method for switching vacuum pump 3 off or on in steps depending on whether a vacuum is needed or not is carried out on the basis of pressure-time sequences in order to control vacuum pump 3. As shown in
Referring now to the flowchart of
In a second program step, vacuum pump 3 is switched on and the firth query S1 is restarted as described in the first program step if the second query S2 is answered with “yes” (S2=1). Also in the second program step a check of all future process steps is performed and a third query S3 of all future process phases is made if the second query S2 is answered with “no” (S2=0).
In a third program step, if the third query S3 is answered with “no” (S3=0), the vacuum pump 3 is switched off in order to save energy and the first query S1 is restarted as described in the first program step. Also in the third program step if the third query S3 is answered with “yes” (S3=1), a time T1 until the next required operation of vacuum pump 3 is calculated and a necessary lead time T2 is determined as the effective warming up time to enable vacuum pump 3 to function flawlessly and a fourth query S4 whether T1 is greater than T2 is performed.
In a fourth program step, if the answer to the fourth query S4 is “no” (i.e., T1≦T2) vacuum pump 3 is switched on and the query S1 is restarted as described in the first program step. However, if the answer to the fourth query S4 is “yes” (i.e., T1>T2), then the vacuum pump 3 is switched off and the query S1 is restarted.
The flowchart shows that at least one of these steps, or several of these steps, or the entire process are able to determine the control, depending on the existing condition, whether a heat treatment process is active in industrial furnace complex 1, whether vacuum pump 3 is required in a current phase of the heat treatment process, whether vacuum pump 3 will be required in a future phase of the heat treatment phase, or if time T1 until the next time vacuum pump 3 is required to operate is greater than an essential lead time T2 for vacuum pump 3.
The control of vacuum pump 3 may then be adjusted and operated in accordance with the relationship Pa=S1S2(
S3
(S4(T1>T2))) in pump controller 11.
In industrial furnace complex 1, in order to carry out the method according to the invention, vacuum pump controller 11 is advantageously includes a logic circuit in a control and regulating device that is present as part of the furnace equipment. The logic circuit is programmed to execute query S1 regarding the status of vacuum pump 3 in the heat treatment process, query S2 as to whether its operation is required in the current phase of the heat treatment process, query S3 as to whether its operation will be required in a future phase of the heat treatment process and/or query S4 regarding required lead time T2 for vacuum pump 3. A pressure sensor 7, a gas inlet valve 8, and a vacuum pump valve 10 are connected with vacuum pump controller 11 to form a circuit for controlling the furnace complex 1. If necessary, industrial furnace complex 1 may also comprise a gas outlet valve 9 which is connected to the vacuum pump controller 11.
Since the invention enables the incremental deactivation or activation of pumps throughout the entire process via intelligent controlling/regulation as a function of the pressure-time sequences, the entire heat treatment process cycle may be operated economically in terms of energy and existing systems may be retrofitted very inexpensively.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2011 103 748 | May 2011 | DE | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5734856 | Wang | Mar 1998 | A |
| 20040013531 | Curry et al. | Jan 2004 | A1 |
| 20090112370 | Tanaka et al. | Apr 2009 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20120310421 A1 | Dec 2012 | US |
