US20070068606A1 - Single-chamber vacuum furnace with hydrogen quenching - Google Patents

Single-chamber vacuum furnace with hydrogen quenching Download PDF

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Publication number
US20070068606A1
US20070068606A1 US11/526,209 US52620906A US2007068606A1 US 20070068606 A1 US20070068606 A1 US 20070068606A1 US 52620906 A US52620906 A US 52620906A US 2007068606 A1 US2007068606 A1 US 2007068606A1
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Prior art keywords
furnace
interior
workpieces
hydrogen
filling
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Abandoned
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US11/526,209
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English (en)
Inventor
Peter Schmetz
Mehmet Ozdeslik
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SISTERN TEKNIK ENDUSTRIYEL ELEKTRONIK
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SISTERN TEKNIK ENDUSTRIYEL ELEKTRONIK
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Assigned to SISTERN TEKNIK ENDUSTRIYEL ELEKTRONIK reassignment SISTERN TEKNIK ENDUSTRIYEL ELEKTRONIK ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: OZDESLIK, MEHMET, SCHMETZ, PETER
Publication of US20070068606A1 publication Critical patent/US20070068606A1/en
Abandoned legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material

Definitions

  • This invention relates to a method for operating a heat treatment plant with a single-chamber vacuum furnace, and to a single-chamber vacuum furnace.
  • Low alloy steels have hitherto mainly been hardened in controlled atmosphere furnaces with oil quenching (so-called sealed quenching).
  • the vacuum gas carburization is carried out in special multi-chamber systems in which oil baths or high pressure quenching stations with nitrogen or helium are used for quenching.
  • Gas quenching is preferred because there is less distortion on the hardened material when quenching in gas, and because no subsequent cleaning is required.
  • the multi-chamber furnaces normally used for this, in the prior art, are very expensive and have been developed specially for the mass production of automotive supplier parts or similar parts. They lack the flexibility to be adaptable to changing objectives and tasks imposed on them. Moreover, the process must be controlled and monitored much better in the case of single chamber furnaces because during the process the workpieces must not be moved and it must therefore be possible to arrange measurement sensors directly on or in the workpiece capable of recording its actual temperature.
  • Lambda 0.35 for bolts 20 mm ⁇ 40 mm long
  • Lambda 0.65 for bolts 40 mm ⁇ 80 mm long
  • Lambda 1.50 for bolts 80 mm ⁇ 160 mm long
  • Lambda 2.35 for bolts 120 mm ⁇ 240 mm long
  • lambda value is the cooling time from 800° C. to 500° C., measured in seconds, divided by 100. These values for the cooling rate are much slower than those that can be achieved when quenching in the oil bath.
  • This object is realized by a method for operating a single-chamber vacuum hardening furnace, including the steps of filling the interior of the furnace with workpieces, sealing the interior of the furnace and evacuating the same, heating the workpieces and maintaining a theoretical temperature, filling the interior of the furnace with hydrogen under high pressure, switching off the heating and circulating the hydrogen for cooling the workpieces, discharging the hydrogen and evacuating the interior of the furnace, filling the interior of the furnace with an inert protective gas up to approximately atmospheric pressure, and opening the furnace and unloading the workpieces.
  • a single-chamber vacuum furnace for carrying out such method, and including a safety zone that surrounds the furnace and which prevents walking or travelling in the immediate vicinity of the furnace, with the exception of the front side thereof, which is adapted to be opened by mechanical or electrical means.
  • FIG. 1 shows the basic time curve of temperature and pressure, and the type of gas supplied in the gas carburization of workpieces
  • FIG. 2 shows the spatial arrangement of the essential plant components in an operation in a diagrammatic representation
  • FIG. 3 shows a hardening furnace suitable for the method according to FIG. 1 in a cross-section from the side.
  • FIG. 1 the time curve of the temperature inside a hardening furnace when a method according to the invention is carried out is plotted in curve 1 .
  • Curve 2 shows the progress of the pressure inside the hardening furnace over the time during which the method is carried out.
  • the time scale which generally represents a period of five hours from the beginning to the end of the process, is arranged on the horizontal X-axis.
  • the temperature scale covers a temperature range from 0° C. to 1,200° C.
  • the pressure scale is arranged on the right-hand side of the graph and indicates the pressure in bars absolute, going from 0 bar to 10 bars, 0 bar being the vacuum.
  • Curve 1 commences at room temperature, which is section 1 a on temperature curve 1 .
  • the heating is then switched on and brings the furnace to a temperature of approx. 1,050° along section 1 b .
  • the required temperature range in the different carburization applications for which the furnace will be suitable is 800° C. to 1,100° C.
  • the furnace temperature is kept constant in section 1 c.
  • Section 1 c is approximately one hour long.
  • the furnace is cooled quickly, approximately within 20 minutes, from 1,050° to room temperature. There the temperature is then kept constant until the end of the process, i.e. until the workpieces are unloaded. This section is denoted by 1 e.
  • the pressure curve which is illustrated in curve 2 , initially commences at 1 bar, i.e. at ambient pressure. This corresponds to the air which is present inside the furnace when the hardening furnace is loaded.
  • section 2 a of the graph the furnace space is evacuated for a period of approx. 20 minutes. The air in the furnace space is removed before the heating is switched on so that no oxidation can take place. Instead the furnace space is flooded with approx. 2 bars of nitrogen, as protective gas, when the heating is switched on, i.e. in the transition from 1 a to 1 b on the temperature curve. The pressure is maintained for a period of approx. 2 hours, which corresponds to section 2 b on the pressure curve.
  • the nitrogen filling of the furnace is maintained up to a temperature of 700° C. Up to this temperature range the workpieces in the furnace are heated by convection heating. The furnace interior is then evacuated by the application of vacuum. The associated pressure reduction from 2 bars to 0 bar is identified by section 2 c . Further heating of the workpieces from 700° to the final temperature of 1,050° is achieved by radiant heating.
  • a gas containing carbon is repeatedly introduced into the furnace space at a pressure of approx. 30 mbars for a short time.
  • This gas e.g. acetylene
  • This carbon diffuses from the surface into the workpiece.
  • so-called diffusion phases 2 f are provided between carburization phases 2 e , in which diffusion phases the gas is removed from the furnace space by applying vacuum. Carbon absorbed by the workpiece surface until that time can then diffuse into the workpiece without additional carbon.
  • Phases 2 e and 2 f can be repeated according to the desired carbon distribution.
  • This exemplary embodiment contains process steps that would be suitable for thin-walled workpieces, where a relatively small carburization depth is aimed for.
  • the interior is flooded with nitrogen from 0 bar to ambient pressure to unload the inner furnace space, which is illustrated by curve section 2 i . If the furnace is then opened, air enters the inner space, and the pressure is set to atmospheric pressure. This section of the pressure curve is denoted by 2 k.
  • the method described offers the possibility, in a single chamber vacuum furnace, to achieve cooling rates which otherwise would only be attainable during oil quenching or water quenching.
  • the cooling rate depends on the slope steepness of curve 1 in section 1 d .
  • section 2 g If in section 2 g the hydrogen is then fed into the interior, there will no longer be any oxygen there. This therefore totally eliminates the risk of explosion. No oxygen enters the furnace interior during the cooling phase either.
  • the hydrogen is then discharged off into the flue by means of discharge valves, and when atmospheric pressure is reached the remaining hydrogen is pumped out of the furnace interior by means of vacuum pumps (section 2 h ). Any residual hydrogen present is then diluted by flooding with nitrogen in section 2 i until no further ignitable mixture can be formed in any case. At that time there is also an absence of ignition source in the furnace interior because the entire content of the furnace has been cooled to approximately room temperature.
  • the drive motors of the fans and the heating are without power.
  • the opening of the furnace in section 2 k for unloading the inventory contained in it, is then entirely non-critical. The air entering during opening finds neither an ignition source nor an adequate concentration of hydrogen to create explosive conditions.
  • the hydrogen pumped off in section 2 h is discharged through gas tight pipes and vacuum pipes via a flue into the atmosphere outside the operating building. After the hydrogen is pumped off, flue 17 ( FIG. 2 ) is fully flushed with nitrogen to ensure that no hydrogen that could form an ignitable mixture remains in it.
  • the operating building is shown in more detail in FIG. 2 .
  • FIG. 2 shows, in a diagrammatic representation, an operating building 10 for carrying out the method described above.
  • the operating building is designed as a shop in which a hardening furnace 11 is installed by an intrinsically known method.
  • a storage tank 12 for hydrogen is provided outside the building.
  • a storage tank 13 for gaseous nitrogen is arranged next to a further storage tank 14 for liquid nitrogen. Both storage tanks 12 and 13 for the gaseous supply are connected by connecting pipes 15 , 16 to hardening furnace 11 .
  • Hardening furnace 11 is also provided with a flue 17 , which leads from the building into the atmosphere. Flue 17 is in this case designed higher than the ridge line of building 10 .
  • hardening furnace 11 On its left front side, hardening furnace 11 has a sealing or closure cover 18 which can be opened for loading and unloading hardening furnace 11 .
  • a shaded region 20 in which special precautions are taken against mechanical damage to the outer added components and the pipes, is illustrated behind the plane of sealing cover 18 .
  • This region 20 is mechanically protected so that it is not possible to pass through this region in the vicinity of hardening furnace 11 with machines such as fork lift trucks and the like. It is also not possible to pass through region 20 with a gantry crane due to the installation of suitable mechanical devices or electrical precautionary measures which influence the control of the crane. Barriers, guide planks, or even a cage may be provided for this purpose. These safety precautions prevent pipes 15 carrying hydrogen, the associated valve means and pumps, and the hardening furnace itself, from being damaged so that hydrogen can escape inside operating building 10 .
  • Sealing cover 18 of hardening furnace 11 is also provided with a peripheral seal which is sealed safely and hermetically by excess pressure from a protective gas during operation. This prevents leakages from occurring during the transition from vacuum to excess pressure that takes place during operation, as illustrated in curve 2 of FIG. 1 .
  • FIG. 3 shows hardening furnace 11 in an enlarged representation.
  • the furnace is designed as a single-chamber vacuum furnace with a fan whose axis of rotation is identical to the central axis of the furnace.
  • Furnace door or cover 18 is specially equipped to protect against leaks occurring during the transition between vacuum and excess pressure. This is described in more detail in laid-open specification WO 2004/096427A1, which originates from the same applicant. It should also be mentioned that vertical single-chamber furnaces are being built and that the cooling fan and heat exchanger can also be installed in an external housing which is then connected to the furnace housing.
  • Lambda 0.10 for bolts 20 mm ⁇ 40 mm long
  • Lambda 0.26 for bolts 40 mm ⁇ 80 mm long
  • Lambda 0.72 for bolts 80 mm ⁇ 160 mm long
  • Lambda 1.30 for bolts 120 mm ⁇ 240 mm long
  • a cold water store of several cubic meters of cooling water may be kept at a low temperature of approx. 3° C. - 5° C. for feeding into the heat exchanger for the first 30-60 seconds of the cooling process.
  • This favorably influences the extremely critical time phase of initial quenching from holding temperature 1 c.
  • the quality of the workpieces is also determined by the distortion that takes place during the hardening process.
  • the gas flow has been introduced successfully in vacuum furnaces several years ago. Now, this invention provides a new, supplementary solution to this problem.
  • the full hydrogen gas pressure is introduced into the furnace for quenching.
  • this pressure may be 10 bars but may also be 20 bars or 40 bars.
  • the cooling rate which must be set to achieve a certain lambda value is controlled by the gas flow rate and ultimately by the rate of circulation inside the furnace.
  • the circulating fan is speed controlled, a control range of 10% of the maximum speed being provided until the full maximum speed is reached.
  • the technical effect of this means that there are three factors of influence for the cooling rate, namely the type of gas, the gas pressure and the gas flow rate. Hitherto, the technical world was of the opinion that these three components were of equal importance. This may be true in terms of the hardness that can be achieved.
  • the type of cooling gas used affects all surfaces of the workpieces exposed to the cooling gas. The same applies to the gas pressure, which is the same throughout the treatment area of the furnace. However, the flow rate of the cooling gas has different effects on the workpiece surfaces according to how the gas flow is obtained.
  • a twist throttle or similar means may also be used to influence the flow rate.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Furnace Details (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Heat Treatment Of Articles (AREA)
  • Muffle Furnaces And Rotary Kilns (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)
US11/526,209 2005-09-23 2006-09-22 Single-chamber vacuum furnace with hydrogen quenching Abandoned US20070068606A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102005045783A DE102005045783A1 (de) 2005-09-23 2005-09-23 Einkammer-Vakuumofen mit Wasserstoffabschreckung
DE102005045783.5 2005-09-23

Publications (1)

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US20070068606A1 true US20070068606A1 (en) 2007-03-29

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US11/526,209 Abandoned US20070068606A1 (en) 2005-09-23 2006-09-22 Single-chamber vacuum furnace with hydrogen quenching

Country Status (5)

Country Link
US (1) US20070068606A1 (fr)
EP (1) EP1767660B1 (fr)
CN (1) CN1936030A (fr)
AT (1) ATE504664T1 (fr)
DE (2) DE102005045783A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8820098B2 (en) 2011-05-17 2014-09-02 Air Products And Chemicals, Inc. Method and apparatus for quenching of materials in vacuum furnace
US20180187284A1 (en) * 2016-12-30 2018-07-05 Shanghai Yibai Industrial Furnaces Co., Ltd. High-pressure liquid-state or supercritical-state quenching apparatus

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102007029038A1 (de) * 2007-06-21 2009-01-02 Eliog-Kelvitherm Industrieofenbau Gmbh Vakuumofen zur Wärmebehandlung von metallischen Werkstücken und Verfahren zu dessen Betrieb
CN107560425A (zh) * 2017-09-30 2018-01-09 志圣科技（广州）有限公司 真空压力烤箱
CN111785445A (zh) * 2020-07-31 2020-10-16 浙江佳伟新材料科技有限责任公司 一种铜包钢同轴电缆的抗拉强度控制工艺
CN112853072A (zh) * 2020-12-31 2021-05-28 江苏华苏工业炉制造有限公司 一种方形单室卧式多区域加热高真空回火炉

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4278421A (en) * 1978-10-14 1981-07-14 Ipsen Industries International Gesellschaft Mit Beschrankter Haftung Industrial furnaces for the heat treatment of metallic workpieces
US4867808A (en) * 1987-10-28 1989-09-19 Degussa Aktiengesellschaft Heat treating a metallic workpiece by quenching under cooling gas under above atmospheric pressure and specified circulation rate
US20060180961A1 (en) * 2001-07-27 2006-08-17 Surface Combustion, Inc. Furnace for vacuum carburizing with unsaturated aromatic hydrocarbons

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Publication number Priority date Publication date Assignee Title
DE3416902A1 (de) * 1984-05-08 1985-11-14 Schmetz Industrieofenbau und Vakuum-Hartlöttechnik KG, 5750 Menden Verfahren und vakuumofen zur waermebehandlung einer charge
DE3819803C1 (fr) * 1988-06-10 1989-12-14 Ulrich 5810 Witten De Wingens
DE4034085C1 (fr) * 1990-10-26 1991-11-14 Degussa Ag, 6000 Frankfurt, De
DE4100989A1 (de) * 1991-01-15 1992-07-16 Linde Ag Verfahren zur waermebehandlung in vakuumoefen
DE4121277C2 (de) * 1991-06-27 2000-08-03 Ald Vacuum Techn Ag Vorrichtung und Verfahren zur selbsttätigen Überwachung der Betriebssicherheit und zur Steuerung des Prozeßablaufs bei einem Vakuum-Wärmebehandlungsofen
DE4312627A1 (de) * 1993-04-19 1994-10-20 Hauzer Holding Verfahren und Vorrichtung zur Wärmebehandlung von Gegenständen
FR2810340B1 (fr) * 2000-06-20 2003-03-14 Etudes Const Mecaniques Cellule de trempe au gaz
DE10108057A1 (de) * 2001-02-20 2002-08-22 Linde Ag Verfahren zum Abschrecken von metallischen Werkstücken
CN100434154C (zh) * 2003-04-30 2008-11-19 系统技术工业电子系统工贸有限公司 用于压力容器的速闭门

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4278421A (en) * 1978-10-14 1981-07-14 Ipsen Industries International Gesellschaft Mit Beschrankter Haftung Industrial furnaces for the heat treatment of metallic workpieces
US4867808A (en) * 1987-10-28 1989-09-19 Degussa Aktiengesellschaft Heat treating a metallic workpiece by quenching under cooling gas under above atmospheric pressure and specified circulation rate
US4867808B1 (fr) * 1987-10-28 1994-02-22 Leybold Durferrit Gmbh
US20060180961A1 (en) * 2001-07-27 2006-08-17 Surface Combustion, Inc. Furnace for vacuum carburizing with unsaturated aromatic hydrocarbons

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8820098B2 (en) 2011-05-17 2014-09-02 Air Products And Chemicals, Inc. Method and apparatus for quenching of materials in vacuum furnace
US20180187284A1 (en) * 2016-12-30 2018-07-05 Shanghai Yibai Industrial Furnaces Co., Ltd. High-pressure liquid-state or supercritical-state quenching apparatus
US10640845B2 (en) * 2016-12-30 2020-05-05 Shanghai Yibai Industrial Furnaces Co., Ltd. High-pressure liquid-state or supercritical-state quenching apparatus

Also Published As

Publication number Publication date
DE502006009240D1 (de) 2011-05-19
CN1936030A (zh) 2007-03-28
ATE504664T1 (de) 2011-04-15
DE102005045783A1 (de) 2007-03-29
EP1767660B1 (fr) 2011-04-06
EP1767660A1 (fr) 2007-03-28

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Effective date: 20060915

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