US3736360A - Control system for vacuum furnaces - Google Patents

Control system for vacuum furnaces Download PDF

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Publication number
US3736360A
US3736360A US00192999A US3736360DA US3736360A US 3736360 A US3736360 A US 3736360A US 00192999 A US00192999 A US 00192999A US 3736360D A US3736360D A US 3736360DA US 3736360 A US3736360 A US 3736360A
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United States
Prior art keywords
furnace
vacuum
pressure
suction conduit
setting
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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US00192999A
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English (en)
Inventor
C Bergman
P Larsson
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ABB Norden Holding AB
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ASEA AB
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Publication date
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/1003—Use of special medium during sintering, e.g. sintering aid
    • B22F3/1007—Atmosphere
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D16/00—Control of fluid pressure
    • G05D16/20—Control of fluid pressure characterised by the use of electric means
    • G05D16/2006—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means
    • G05D16/2013—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means using throttling means as controlling means
    • G05D16/202—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means using throttling means as controlling means actuated by an electric motor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2201/00—Treatment under specific atmosphere
    • B22F2201/20—Use of vacuum
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2203/00—Controlling
    • B22F2203/03—Controlling for feed-back

Definitions

  • ABSTRACT A control system for an electrically heated furnace for sintering powder bodies, especially bodies of hard metal, has a vacuum pump connected to the interior of the furnace chamber by a suction conduit.
  • the furnace includes a plurality of heating elements for different zones, a temperature sensitive instrument for each zone and a controlled measuring instrument for one of the zones which is the master zone. These instruments are connected to a master regulator for the furnace and slave regulators for the individual zones.
  • a throttle valve in the vacuum conduit, or a controlled tap connected to the vacuum conduit make it possible to keep the pressure in the furnace constant despite the fact that the pump runs at a constant speed.
  • a pressure-sensing member connected to the vacuum conduit is also connected to the regulators for the heating elements.
  • the present invention relates to a control system for a vacuum furnace for sintering powder bodies, preferably bodies of hard metal.
  • the control system regulates the heating of the furnace during that part of the heating process when degassing takes place.
  • the control system can be used in furnaces of the type described in Swedish published specification No. 333,437.
  • the Prior Art Bodies of hard metal are manufactured of powder containing carbides of tungsten, tantalium, titanium or vanadium or a mixture of two or more carbides of these substances and a binder which may consist of cobalt and/or nickel, or possibly iron.
  • the total carbide content is usually 70-99 percent and the content of binder 1-30 percent.
  • the powder has a great tendency to absorb or react with the gases in the atmosphere, mainly oxygen and water vapor. These substances are removed by degassing during heating, by performing the heating under vacuum. When hard metal is being degassed it is desirable to keep the pressure below a certain level during the entire degassing process.
  • the heating is usually carried out as quickly as possibly, i.e., the heating is performed with the highest power or with the highest permissible temperature gradient tolerated by the furnace or and workpiece.
  • the gas emission is usually very irregular, however, for hard metal and it has a pronounced maximum which for many composites is at about 700C. If, as is desirable, the gases are to be removed without the pressure rising above a certain level, an extremely large and expensive vacuum equipment is necessary with a' constant temperature gradient. Too much gas emission may also cause cracks in the workpiece due to the explosive action of the gases. In certain cases, therefore, the power supply has been controlled in accordance with the temperature.
  • the heating is controlled depending on the pressure in the furnace equipment is provided with pressure-sensing members to sense the pressure in the furnace or in a suction conduit and power, regulating members which, in accordance with the output signal fromsaid pressure sensing member, regulate the power supply to the heating element in the furnace.
  • Further characteristics of the invention include a control system for an electrically heated furnace for sintering powder bodies, especially bodies of hard metal, has a vacuum pump connected to the interior of the furnace chamber by a suction conduit.
  • the furnace includes a plurality of heating elements for different zones, a temperature sensitive instrument for each zone and a controlled measuring instrument for one of the zones which is the master zone.
  • a throttle valve in the vacuum conduit, or a controlled tap connected to the vacuum conduit, make it possible to keep the pressure in the furnace constant despite the fact that the pump runs at a constant speed.
  • a pressuresensing member connected to the vacuum conduit is also connected to the regulators for the heating elements.
  • the invention offers several advantages.
  • the gas emission within the temperature range where it is maximum can be limited to a maximum value adapted to a vacuum equipment and the size of the equipment can be considerably reduced, often to only 25 percent of what was previously considered suitable.
  • the control also makes it possible to very accurately determine the pressure within the temperature ranges where the gas emission is slight, so that the pressure can be held permanently above the level at which damaging gasification of components forming the hard metal is obtained, for example cobalt. In many cases it is suitable to keep a pressure of 1.10 torr in the furnace. The loss of cobalt is then negligible.
  • the control system also makes it possible in a controlled manner to regulate the pressure according to the temperature.
  • FIG. 1 shows schematically one embodiment of the invention
  • FIG. 2 a variant of a regulating means included in the means shown in FIG. 1,
  • FIG. 3 gas emission from a hard metal body weighing kg when heated with constant supply of power, i.e., with an approximately constant temperature gradient and
  • FIG. 4 shows the temperature of the workpiece as a function of the time when using the invention.
  • FIGS. 1 and 2 designates a sintering furnace which is sealed with respect to the surroundings so that a vacuum can be maintained therein.
  • the furnace is connected by a conduit 2 to a pump 3.
  • a workpiece 4 which has been formed by compacting powder.
  • the furnace is a l is divided into four different zones, each with its own heating element 5a, 5b, 5c and 5d which through a cable 6 are supplied with electric power from a current source, not shown, by way of regulators 7a, 7b, 7c and 7d.
  • the cable contains conductor pairs 6a, 6b, 6c and 6d for the elements in each of the heating zones.
  • the regulators may be constructed of AC regulators with thyristors, for example ASEA type YQNA and of power regulators comprising Pl regulators, multipliers and summating means made by ASEA and designated QRTN 201, QRTF 205 and QRTF 201 and measuring units for voltage and current to the heating elements.
  • ASEA thyristors
  • Pl regulators multipliers and summating means made by ASEA and designated QRTN 201, QRTF 205 and QRTF 201 and measuring units for voltage and current to the heating elements.
  • thermoelements 8a, 8b, 8c and'8d whichgive the real value to the control equipment for the temperature in the four zones of the furnace.
  • thermoelement 9 which sets the desired value for the temperature in the slave zones, which is equal to the real value in the master zone.
  • a temperature regulator 11 which is a master regulator and temperature regulators 12a, 12b and 12c which regulate the temperatures in the different zones of the furnace.
  • a regulator can be used which has a scale 13 on which a desired value can be set for the final sintering temperature to be reached.
  • the real value is obtained from the thermoelement 8d in the master zone in the furnace.
  • a regulator of the make Eurotherm O-l 800C type PID can be used.
  • Temperature regulators of the make Eurotherm 3 3mV type PID can be used as slave regulators.
  • the slave regulators regulate the temperature in the respective slave zones so that it is as close to the temperature in the master zone as possible.
  • the desired value for the slave regulators comes from the thermoelement 9 in the master zone and the real value from the thermoelements 8a, 8b and 8c in each zone.
  • a pressure gauge 15, for example of a type having a logarithmic scale, is connected to theconduit 2 and emits a signal dependent on the value shown on the indicator. The signal is supplied to a vacuum regulator 16.
  • a PI regulator sold by ASEA under the designation QALB may be used.
  • the regulator 16 activates a servomotor 17 in FIG. 1 to set a throttle valve 18 in the vacuum conduit 2 so that the pressure in the furnace 1 can be kept constant in spite of a constant speed of the pump 3.
  • the equipment also includes a regulator 19 which can either be directly actuated by the output signal from the regulator or by a member which senses the position of the valve 18. In this way the regulator senses how much of the pump capacity is being used and delivers a signal dependent on this, this signal being delivered through the conduit 20 to the regulators 7a, 7b, 7c and 7d so that these increase the power supply to the furnace when the pump capacity is not fully exploited.
  • the regulator 19 may be a PI regulator, make ASEA, type QALB 210.
  • a power limiter 21 which senses the temperature derivative. This may be provided with a setting device for the desired value. The real value can be obtained by measuring the alteration of resistance in the heat coils in the master zone. When the real value exceeds the desired value the power limiter emits an output signal which is supplied to the regulators 7a, 7b, 7c and 7d so that they decrease the power supplied to the furnace.
  • the power limiter may be built up of resistance measuring units, a motor operating device for reference comparison and a PI regulator, make ASEA, type QALB 210.
  • the equipment If the equipment is to operate at different pressures at different furnace temperatures it may be provided with a program mechanism 24 into which the desired value for the pressure is programmed.
  • This program mechanism delivers an output signal dependent on the program, this signal being supplied to the vacuum regulator 16.
  • the pressure in thefurnace l is regulated when the quantity of gas emitted is less than the pump capacity at the desired pressure, by letting air into the conduit 2 through a controllable valve 25.
  • This valve is operated by means of a servomotor 26 of the same type as the servomotor l7. Otherwise the equipment is in agreement with that shown in FIG. 1 and the function is the same.
  • the curve 30 in FIG. 3 shows the relationship between the quantity of gas emitted from workpiece per time unit and the temperature upon heating with constant temperature increase per time unit.
  • the time t hours and the temperature TC are indicated along the abscissa. while along the ordinate the gas quantity emitted Q torrl/sec is indicated.
  • the workpiece is being heated C/h.
  • the curve 30 shows that the gas emission has a pronounced maximum at about 750C.
  • the gases emitted are mainly carbon monoxide (CO), carbon dioxide (CO water vapor (H 0) and hydrogen (H
  • the heating of the furnace is dependent on the furnace pressure in such a way that the temperature gradient in the range 600C to 850C is limited to such a value that the gas emission corresponds to the maximum capacity of the vacuum pump at the furnace pressure selected.
  • FIG. 4 shows an example of the relationship between the time t in hours and the temperature T in C.
  • the curve representing the temperature gradient is extremely flat in the range between 600C and 800C.
  • Method of controlling a vacuum furnace system comprising a vacuum furnace having an electrical heating element, regulating means between said element and an electric power source controlling the heating effect of said elements, a vacuum pump, and a suction conduit element having a gas flow regulating means therein joining the furnace to the vacuum pump, which method comprises sensing the vacuum in said suction conduit element and controlling said gas flow regulating means in response to variations of such vacuum to maintain the pressure in the furnace substantially constant.
  • Method according to claim 1 which comprises controlling the heating effect of the furnace elements in response to variations of said vacuum.
  • Method according to claim 1 which comprises supplying gas from a gas source to the conduit element between the furnace and the vacuum pump by a gas flow regulating means, said supplying of gas maintaining the vacuum pressure level within the preselected level.
  • Method according to claim 1 which comprises controlling the heating effect of the furnace elements in response to the setting of the gas flow regulating means.
  • Vacuum furnace equipment which comprises an electrically heated furnace element, a vacuum pump, a suction conduit element joining the furnace to the vacuum pump, heating means in said furnace, a current source, power control equipment arranged between the current source and the furnace element to regulate the heat supplied to the furnace, which includes a pressure sensing member, which senses the pressure in the furnace or conduit element and includes means to deliver an output signal dependent on the pressure, and a gas flow regulating member, and means connected to said pressure sensing member for setting the flow regulating member in a position in accordance with said pressure dependent signal to maintain the vacuum in said suction conduit element substantially constant.
  • Vacuum furnace equipment including means responsive to said pressure sensing member to control the heat supplied to the furnace.
  • said gas flow regulating member comprises a throttling member in the suction conduit, and means setting said throttling member in response to the output tween the furnace element and the vacuum pump, and means responsive to the output signal of the pressure sensing member to control said throttling member to supply gas to the suction conduit when the pressure in this conduit falls below a minimum preselected value.
  • Vacuum furnace equipment which comprises a unit which senses-the setting of the throttling member and includes means to emit an output signal dependent on the setting of said member, which influences the power control equipment regulating the heat effect supplied to the furnace.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical & Material Sciences (AREA)
  • Fluid Mechanics (AREA)
  • Mechanical Engineering (AREA)
  • Ceramic Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Materials Engineering (AREA)
  • General Physics & Mathematics (AREA)
  • Automation & Control Theory (AREA)
  • Furnace Details (AREA)
  • Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)
  • Powder Metallurgy (AREA)
US00192999A 1970-10-27 1971-10-27 Control system for vacuum furnaces Expired - Lifetime US3736360A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
SE14477/70A SE349858B (enrdf_load_stackoverflow) 1970-10-27 1970-10-27

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US3736360A true US3736360A (en) 1973-05-29

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US00192999A Expired - Lifetime US3736360A (en) 1970-10-27 1971-10-27 Control system for vacuum furnaces

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US (1) US3736360A (enrdf_load_stackoverflow)
AT (1) AT311689B (enrdf_load_stackoverflow)
BE (1) BE774266A (enrdf_load_stackoverflow)
CA (1) CA957001A (enrdf_load_stackoverflow)
CH (1) CH542675A (enrdf_load_stackoverflow)
DE (1) DE2152489B2 (enrdf_load_stackoverflow)
FR (1) FR2113295A5 (enrdf_load_stackoverflow)
GB (1) GB1357580A (enrdf_load_stackoverflow)
IT (1) IT940043B (enrdf_load_stackoverflow)
LU (1) LU64131A1 (enrdf_load_stackoverflow)
NL (1) NL7114654A (enrdf_load_stackoverflow)
SE (1) SE349858B (enrdf_load_stackoverflow)
SU (1) SU566510A3 (enrdf_load_stackoverflow)

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4011430A (en) * 1975-05-06 1977-03-08 National Forge Company Multizone electrical furnace methods and apparatus
US4066868A (en) * 1974-12-26 1978-01-03 National Forge Company Temperature control method and apparatus
US4158742A (en) * 1976-11-30 1979-06-19 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration General purpose rocket furnace
US4179618A (en) * 1976-12-01 1979-12-18 Kawasaki Jukogyo Kabushiki Kaisha Apparatus for ion-nitriding treatment
US4195820A (en) * 1978-04-10 1980-04-01 Pyreflex Corporation Precise thermal processing apparatus
US4205631A (en) * 1978-10-11 1980-06-03 Westinghouse Electric Corp. Pressure limiting control for an inlet draft fan in an electric power plant
US4321457A (en) * 1979-02-21 1982-03-23 Klockner-Humboldt-Deutz Ag Method and device for the burning of an artificial carbon body, especially of an anode for the aluminum fusion electrolysis
WO1997017583A1 (en) * 1995-11-07 1997-05-15 Sandvik Aktiebolag (Publ) Power control for furnace
US20100173470A1 (en) * 2009-01-08 2010-07-08 Samsung Electronics Co., Ltd. Methods of forming a silicon oxide layer and methods of forming an isolation layer
EP2530416A1 (de) 2011-05-31 2012-12-05 Ipsen International GmbH Verfahren zur Steuerung von Vakuumpumpen in einer Industrieofenanlage
US20130175256A1 (en) * 2011-12-29 2013-07-11 Ipsen, Inc. Heating Element Arrangement for a Vacuum Heat Treating Furnace
JP2017036483A (ja) * 2015-08-11 2017-02-16 セイコーエプソン株式会社 焼結体の製造方法、脱脂体の製造方法および加熱炉
CN108253780A (zh) * 2018-04-02 2018-07-06 宁波恒普真空技术有限公司 一种实现四区域控温的真空烧结炉
CN113606949A (zh) * 2021-07-29 2021-11-05 北京北方华创真空技术有限公司 多工位除气炉的抽真空系统

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4305756A (en) * 1980-01-14 1981-12-15 Witec Cayman Patents, Ltd. Method and means for removing binder from a green body
NL8800074A (nl) * 1988-01-14 1989-08-01 Philips Nv Inrichting en werkwijze voor het verwijderen van een organisch bindmiddel uit een pasta.
DE3910777C2 (de) * 1989-04-04 2001-08-09 Ald Vacuum Techn Ag Induktionsofen mit einem metallischen Tiegel
GB8907994D0 (en) * 1989-04-10 1989-05-24 Torvac Furnaces Ltd Vacuum furnace
EP2610354A1 (en) * 2011-12-29 2013-07-03 Ipsen, Inc. Compensating heating element arrangement for a vacuum heat treating furnace

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3291969A (en) * 1963-10-18 1966-12-13 Electroglas Inc Temperature control system for a diffusion furnace
US3428250A (en) * 1967-05-23 1969-02-18 Gen Electric Furnace control system

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3291969A (en) * 1963-10-18 1966-12-13 Electroglas Inc Temperature control system for a diffusion furnace
US3428250A (en) * 1967-05-23 1969-02-18 Gen Electric Furnace control system

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4066868A (en) * 1974-12-26 1978-01-03 National Forge Company Temperature control method and apparatus
US4011430A (en) * 1975-05-06 1977-03-08 National Forge Company Multizone electrical furnace methods and apparatus
US4158742A (en) * 1976-11-30 1979-06-19 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration General purpose rocket furnace
US4179618A (en) * 1976-12-01 1979-12-18 Kawasaki Jukogyo Kabushiki Kaisha Apparatus for ion-nitriding treatment
US4195820A (en) * 1978-04-10 1980-04-01 Pyreflex Corporation Precise thermal processing apparatus
US4205631A (en) * 1978-10-11 1980-06-03 Westinghouse Electric Corp. Pressure limiting control for an inlet draft fan in an electric power plant
US4321457A (en) * 1979-02-21 1982-03-23 Klockner-Humboldt-Deutz Ag Method and device for the burning of an artificial carbon body, especially of an anode for the aluminum fusion electrolysis
US5870423A (en) * 1995-11-06 1999-02-09 Sandvik Ab Individual heating element power control for a furnace
WO1997017583A1 (en) * 1995-11-07 1997-05-15 Sandvik Aktiebolag (Publ) Power control for furnace
US20100173470A1 (en) * 2009-01-08 2010-07-08 Samsung Electronics Co., Ltd. Methods of forming a silicon oxide layer and methods of forming an isolation layer
EP2530416A1 (de) 2011-05-31 2012-12-05 Ipsen International GmbH Verfahren zur Steuerung von Vakuumpumpen in einer Industrieofenanlage
DE102011103748A1 (de) 2011-05-31 2012-12-06 Ipsen International Gmbh Verfahren zur Steuerung von Vakuumpumpen in einer Industrieofenanlage
US20130175256A1 (en) * 2011-12-29 2013-07-11 Ipsen, Inc. Heating Element Arrangement for a Vacuum Heat Treating Furnace
JP2017036483A (ja) * 2015-08-11 2017-02-16 セイコーエプソン株式会社 焼結体の製造方法、脱脂体の製造方法および加熱炉
US20170043400A1 (en) * 2015-08-11 2017-02-16 Seiko Epson Corporation Sintered body production method, degreased body production method, and heating furnace
CN106424721A (zh) * 2015-08-11 2017-02-22 精工爱普生株式会社 烧结体制造方法、脱脂体制造方法以及加热炉
CN108253780A (zh) * 2018-04-02 2018-07-06 宁波恒普真空技术有限公司 一种实现四区域控温的真空烧结炉
CN108253780B (zh) * 2018-04-02 2023-12-15 宁波恒普技术股份有限公司 一种实现四区域控温的真空烧结炉
CN113606949A (zh) * 2021-07-29 2021-11-05 北京北方华创真空技术有限公司 多工位除气炉的抽真空系统

Also Published As

Publication number Publication date
SU566510A3 (ru) 1977-07-25
AT311689B (de) 1973-11-26
DE2152489B2 (de) 1975-01-09
NL7114654A (enrdf_load_stackoverflow) 1972-05-02
GB1357580A (en) 1974-06-26
LU64131A1 (enrdf_load_stackoverflow) 1972-05-12
SE349858B (enrdf_load_stackoverflow) 1972-10-09
FR2113295A5 (enrdf_load_stackoverflow) 1972-06-23
DE2152489A1 (de) 1972-05-31
CA957001A (en) 1974-10-29
CH542675A (de) 1973-10-15
BE774266A (fr) 1972-02-14
IT940043B (it) 1973-02-10

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