EP3911905B1 - A pit type furnace for vacuum carburization of workpieces - Google Patents
A pit type furnace for vacuum carburization of workpieces Download PDFInfo
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- EP3911905B1 EP3911905B1 EP20708217.3A EP20708217A EP3911905B1 EP 3911905 B1 EP3911905 B1 EP 3911905B1 EP 20708217 A EP20708217 A EP 20708217A EP 3911905 B1 EP3911905 B1 EP 3911905B1
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- vacuum
- heating
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- furnace
- insulation
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- 238000010438 heat treatment Methods 0.000 claims description 99
- 238000009413 insulation Methods 0.000 claims description 25
- 239000000919 ceramic Substances 0.000 claims description 16
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 6
- 239000000395 magnesium oxide Substances 0.000 claims description 6
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 claims description 6
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 claims description 6
- 229910010293 ceramic material Inorganic materials 0.000 claims description 4
- -1 iron-chromium-aluminium Chemical compound 0.000 claims description 4
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 claims description 4
- 229910000838 Al alloy Inorganic materials 0.000 claims description 3
- ODINCKMPIJJUCX-UHFFFAOYSA-N Calcium oxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 claims description 3
- 229910052782 aluminium Inorganic materials 0.000 claims description 3
- 229910052804 chromium Inorganic materials 0.000 claims description 3
- 229910021485 fumed silica Inorganic materials 0.000 claims description 3
- 229910052742 iron Inorganic materials 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 2
- 238000005255 carburizing Methods 0.000 description 24
- 238000010791 quenching Methods 0.000 description 21
- 230000000171 quenching effect Effects 0.000 description 20
- 238000000034 method Methods 0.000 description 16
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 15
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 13
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 11
- 239000007789 gas Substances 0.000 description 9
- 229910052799 carbon Inorganic materials 0.000 description 8
- 238000011068 loading method Methods 0.000 description 8
- 230000003647 oxidation Effects 0.000 description 8
- 238000007254 oxidation reaction Methods 0.000 description 8
- 229910002804 graphite Inorganic materials 0.000 description 7
- 239000010439 graphite Substances 0.000 description 7
- 229910052751 metal Inorganic materials 0.000 description 7
- 239000002184 metal Substances 0.000 description 7
- 229910052757 nitrogen Inorganic materials 0.000 description 7
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 6
- 239000001301 oxygen Substances 0.000 description 6
- 229910052760 oxygen Inorganic materials 0.000 description 6
- 229910001562 pearlite Inorganic materials 0.000 description 6
- 230000009466 transformation Effects 0.000 description 6
- PNEYBMLMFCGWSK-UHFFFAOYSA-N Alumina Chemical compound [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 5
- 230000000452 restraining effect Effects 0.000 description 5
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 239000011651 chromium Substances 0.000 description 3
- 150000001934 cyclohexanes Chemical class 0.000 description 3
- 239000007770 graphite material Substances 0.000 description 3
- 239000000112 cooling gas Substances 0.000 description 2
- 239000000498 cooling water Substances 0.000 description 2
- 230000006378 damage Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 238000009421 internal insulation Methods 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 230000001681 protective effect Effects 0.000 description 2
- 230000005855 radiation Effects 0.000 description 2
- 239000004071 soot Substances 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 1
- 239000005977 Ethylene Substances 0.000 description 1
- 238000005273 aeration Methods 0.000 description 1
- 150000001338 aliphatic hydrocarbons Chemical class 0.000 description 1
- HSFWRNGVRCDJHI-UHFFFAOYSA-N alpha-acetylene Natural products C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 238000003421 catalytic decomposition reaction Methods 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000007859 condensation product Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 238000005553 drilling Methods 0.000 description 1
- 125000002534 ethynyl group Chemical group [H]C#C* 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
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- 238000011010 flushing procedure Methods 0.000 description 1
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Images
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
- F27B5/00—Muffle furnaces; Retort furnaces; Other furnaces in which the charge is held completely isolated
- F27B5/06—Details, accessories, or equipment peculiar to furnaces of these types
- F27B5/14—Arrangements of heating devices
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
- F27B5/00—Muffle furnaces; Retort furnaces; Other furnaces in which the charge is held completely isolated
- F27B5/06—Details, accessories, or equipment peculiar to furnaces of these types
- F27B5/16—Arrangements of air or gas supply devices
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
- F27D1/00—Casings; Linings; Walls; Roofs
- F27D1/0003—Linings or walls
- F27D1/0006—Linings or walls formed from bricks or layers with a particular composition or specific characteristics
- F27D1/0009—Comprising ceramic fibre elements
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
- F27D11/00—Arrangement of elements for electric heating in or on furnaces
- F27D11/02—Ohmic resistance heating
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Furnace Details (AREA)
- Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
- Muffle Furnaces And Rotary Kilns (AREA)
Description
- The subject of the invention is a pit-type vacuum furnace for carburization of elements, especially large-size elements.
- The furnace is designed for carrying out carburization processes of large-size massive and very massive elements, especially gear wheels, gears, power industry equipment and drilling tools used in the extractive industry, where the thickness of the carburized layers is above 2 mm, which involves sufficiently long heating times.
- Carburization of, for example, gear wheels for wind turbine gearboxes or other gearboxes is usually carried out in pit type retort furnaces normally using the gas carburization method. The carburization of such gearwheels is usually carried out at temperatures of about 900-930°C and with carburization thicknesses ranging from 2 to 5 mm, which requires very long process times and thus a long exposure of charge elements to a high carburization temperature. After carburization and precooling, the workpieces are usually transferred to a quenching tank, after fixing (restraining) them in the tooling to limit quenching deformations.
- There are single-chamber and multi-chamber vacuum furnaces designed for low-pressure carburizing (LPC), with spatial charge loading. The heating chamber equipment, i.e. insulation and heating elements, are usually made of graphite materials and CFC composites. Spatial charge loading means that the charge in the form of densely packed workpieces is loaded into a strictly separated space in the furnace heating chamber, called the usable space of the heating chamber. The usable space of the heating chamber is usually completely filled with workpieces arranged in many layers on special devices (multi-layered charge arrangement).
- Typical horizontal vacuum furnace for low-pressure carburizing (LPC), such as disclosed in patent documents
US 4 854 860 A ,US 8 636 946 B1 andUS2003/057615 A1 , has a graphite heating chamber installed in a vacuum-tight water-cooled outer furnace body. High treatment temperatures (up to 1300°C) can be achieved with the use of a graphite heating chamber and graphite heating elements. The carburizing gases that do not react with graphite and do not undergo catalytic decay on its surface are used during the process. The graphite heating chamber does not provide a sufficient barrier for heat transfer, therefore the outer furnace body is equipped with a water jacket through which cooling water flows. In the presence of oxygen, the heating chamber can only be opened when cold due to the fact that it is made of graphite. The presence of even small amounts of oxygen inside the heated furnace chamber may cause damage to the chamber and the heating elements as a result of oxidation. The limitation of such a design is the impossibility of loading and unloading hot charge in the presence of oxygen. - In high-volume production, modular furnaces and systems consisting of one functional quenching chamber are used. The chamber is usually made in such a way that it cooperates with up to ten low-pressure carburizing (LPC) process chambers in a mobile way. These are solutions that are used for high-volume treatment of small and medium-sized workpieces. Solutions of this type are not likely to be used for treatment of large-size workpieces.
- The pit type vacuum furnace is dedicated to a completely different type of charge, which until now could be treated mainly in pit type atmospheric furnaces.
- There are also in-line or rotary type vacuum carburizing furnaces with designs suitable for continuous operation including transport of workpieces. The graphite equipment in these furnaces is suitable for carrying out vacuum heat treatment over the entire cycle, from loading to unloading, and the graphite materials are characterized by a minimal impact on the catalytic decomposition of the carbon carrier, usually aliphatic hydrocarbons of the acetylene and / or ethylene type, which has a significant impact on control (simulation) of coal demand when processing densely arranged, spatial charges with a large surface of parts to be carburized.
- A design of vacuum carburizing furnaces using liquid organic compounds such as cyclohexanes [C6H12] is also known, in which a controllable method of vacuum carburizing is obtained, but the disadvantage of the process is the increased amount of undesirable deposits on the surfaces of insulation and heating elements. The deposits must be regularly removed. In order to ensure efficient removal of the deposits, the furnace is equipped with a heating chamber with ceramic insulation to enable cyclical, usually weekly, burning of deposits by, for example, controlled aeration. In the case of the furnaces in which cyclohexanes are used as carburizing gas, cyclical burning of deposits is necessary, which can only be done in a chamber with ceramic insulation. In the case of the pit type furnace, the use of ceramic insulation involves the need to open the hot chamber in the presence of oxygen.
- The use of typical, known heating chamber designs suitable for the low-pressure carburizing (LPC) technology and based on graphite materials, although it is effective because much higher carburizing process temperatures can be used, even up to 1100°C, however, it does not make it possible to introduce gas into the furnace and open the furnace after precooling to a direct quenching temperature or after pearlite transformation, to enable the transfer of the workpiece to the quenching tooling and, after appropriate fixing (restraining), the transfer of the workpiece to oil quenching, because each opening of the heating chamber at a quenching temperature and in the presence of oxygen will cause its destruction due to intensive oxidation.
- The purpose of the invention is to develop a new design of vacuum carburizing furnace for, especially, large-size massive and very massive elements, whose chamber should make it possible to introduce gas into the furnace and open the furnace after precooling to a quenching temperature or after pearlite transformation, to enable the transfer of the workpiece to the quenching tooling and, after appropriate fixing (restraining), the transfer of the workpiece to oil quenching.
- A pit type furnace for vacuum carburization of workpieces, equipped with a vacuum-tight cylindrical outer furnace body with a sliding cover embedded on it, wherein in the outer furnace body there is a heating chamber equipped with the insulation with a multi-layered structure with at least three layers made of ceramic materials and there are heating elements inside the chamber, characterised in that, the heating chamber insulation is multi-layered and contains at least three different layers made of ceramic materials and an external layer in the form of microporous elements made of pyrogenic silica, a middle layer in the form of a high-temperature fibrous ceramic mat is made of silica (SiO2), calcium oxide (CaO) and magnesium oxide (MgO) and an internal layer in the form of vacuum-moulded fibrous ceramic modules resistant, located on the hot heating chamber side, made of aluminium oxide (Al2O3) and silica (SiO2), while the heating elements are made of heat-resistant iron-chromium-aluminium alloys with the following composition: 4-7 wt. % Al, 20-30 wt. % Cr, and 63-76 wt. % Fe, and are located, divided into heating zones, along the heating chamber height (2).
- The layer of microporous elements (3a) has a thickness of 20mm.
- The layer of fibrous ceramic mat has a thickness of 155 mm.
- The layer of vacuum-moulded fibrous ceramic elements has a thickness 125 mm.
- The furnace according to the invention enables vacuum carburization of massive and very massive workpieces, where the thickness of the carburized layers normally exceeds 2 mm, which involves sufficiently long heating times. Its design makes it possible to use suitably thick layers of thermal insulation, for which in the phase of convection heating and vacuum heating and heat treating prior to the low-pressure carburizing (LPC) process, adequate time is provided for cleaning it from air residues after the previous furnace opening phase, after unloading and loading the charge. Due to the working characteristics of the pit-type vacuum furnace (opening the heating chamber when the furnace is hot), a thermal insulation liner with a relatively large total thickness (approx. 300 mm) can be used, because the moisture contained in the insulation escapes to the environment as a result of evaporation, which makes it possible to achieve the required vacuum inside the heating chamber. The increased thickness of the heating chamber insulation, as compared to the typical vacuum carburizing designs, and the thermal insulation materials used in the multi-layered insulation of the heating chamber reduce heat loss during the process and make it possible to obtain a sufficiently low heat transfer coefficient. Consequently, an alternative design of the furnace, without the water jacket, can be used. The water jacket is the space between the internal wall and the external wall of the outer furnace body, in which the flowing water absorbs heat, so that the temperature of the external wall of the outer furnace body of a typical vacuum furnace usually does not exceed 40°C. In addition, this type of vacuum carburizing naturally allows the use of significantly higher carburizing temperatures (even up to 1050°C) compared to typical gas carburizing carried out in retort furnaces or even retortless furnaces (usually in the range of 900-930°C). Higher temperatures produce significantly higher carbon diffusion coefficients, which results in effective reduction of the carburizing time and the entire heating cycle. Therefore, the furnace is highly efficient.
- The subject of the invention is presented in the embodiment shown in the figures,
fig.1 shows the vertical cross-section of the furnace with the water jacketed outer furnace body, equipped with a blower, heat exchanger and convective mixer as well as upper and lower hatches, and a schematically shown cooling gas circuit,fig. 2 shows the cross-section of the furnace with the heating chamber with the convection heating system and the possibility of cooling the charge inside the heating chamber in a closed gas circulation system,fig.3 is a view showing the heating chamber built into the vacuum-tight outer furnace body with a convective mixer,fig.4 shows the cross-section of the heating chamber with the heating elements in the furnace without water jacket, blower, heat exchanger and hatches, which shows the heating chamber design and the insulation layers,fig.5 schematically shows the outer furnace body with a water jacket and the heating chamber wall layers with installed heating elements,fig.6 schematically shows the outer furnace body without a water jacket and the heating chamber wall layers with installed heating elements,fig.7 is a view showing the furnace closed by means of a vacuum cover and a vacuum pump system connected to the vacuum outer furnace body,fig.8 shows a top view of the furnace with an open vacuum cover and a view of the internal part of the heating chamber and insulation structure and metal heating elements,fig.9 is a side view of the vacuum furnace in the pit, with all accessories such as a vacuum pump system, pneumatic system, and a carburizing cabinet for LPC processes,fig.10 shows loading of the furnace charge with the furnace cover open. - The pit-type vacuum furnace for vacuum carburization of workpieces, especially large-size workpieces, is equipped with a vacuum-tight cylindrical
outer furnace body 1 that is closed or opened withcover 8 during charge loading and unloading,heating chamber 2 located in thisouter furnace body 1, equipped with insulation andheating elements 4 installed inside the chamber. The heating chamber in the embodiment is made of metal plate, e.g. 5 mm thick metal plate. - In the embodiment shown in
Figs. 1 ,2 and5 , the vacuum-tightouter furnace body 1 has a water jacket formed between the outerfurnace body wall 1 and the additionalexternal wall 1a of the outer furnace body. - In the embodiment shown in
Figs. 3, 4 and6 , theouter furnace body 1 does not have a water jacket and has no additionalexternal wall 1a. - The
heating chamber insulation 2 is multi-layered and contains the external layer in the form ofmicroporous elements 3a with the extremely low thermal conductivity, themiddle layer 3b in the form of a high-temperature fibrous ceramic mat and theinternal layer 3c in the form of ceramic modules resistant to high temperatures and oxidation in air, located on the hot heating chamber side. - In the present invention,
external layer 3a of theheating chamber insulation 2 in the form of microporous plates made on the basis of pyrogenic silica with extremely low thermal conductivity (about 0.025 W/(m·K)) is 20 mm thick. Themiddle insulation layer 3b is a 155mm thick high-temperature (1300°) fibrous ceramic mat made on the basis of silica (SiO2), calcium oxide (CaO) and magnesium oxide (MgO). The average thermal conductivity of such a liner at working temperature is about 0.1 W/(m·K). Theinternal insulation layer 3c, installed on the hot heating chamber side, is in the form of 125 mm thick vacuum-moulded fibrous ceramic modules / elements made on the basis of aluminium oxide (Al2O3) and silica (SiO2), resistant to high temperatures (1350°C) and oxidation in air. The average thermal conductivity of such a liner at working temperature is about 0.2 W/(m·K). - The insulation is secured to the heating chamber structure by means of metal bars.
- The
heating elements 4 arranged inside theheating chamber 2 are made of heat-resistant ferritic resistance alloys of the iron-chromium-aluminium type and contain from 4 to 7 % of Al and from 20 to 30 % of Cr, the remaining content is Fe. - Ferritic alloys show high resistance in an oxidizing and carburizing environment and are characterized by high resistance to carbon corrosion, which makes it possible, after the heating and heat treating cycle, to carry out the vacuum low-pressure carburizing (LPC) phase, preferably of the impulse type with controlled diffusion phases and, after precooling for direct quenching (or after heating to a quenching temperature after prior pearlite transformation), to introduce nitrogen into the furnace to achieve ambient pressure and, after sliding the door (cover) of the outer furnace body, to quickly transfer the workpiece to a quenching tank, e.g. oil quenching tank or to quench it after prior setting and fixing (restraining) in appropriate tooling. Ferritic alloys (iron, chromium, aluminium) owe their high heat resistance mainly to the fact that at a sufficiently high temperature (over 800°C), they produce a thin, dense, several microns thick layer of aluminium oxide (Al2O3) on the surface in the presence of even a very small amount of oxygen. In practice, as a result of intensive low-pressure carburizing processes, carbon deposit settles on the surfaces of metal heating elements and carbon penetrates into the metal structure. In order to extend the life of heating elements, they should be subjected to cyclic oxidation processes to renew the protective Al2O3 layer. In the pit-type vacuum furnace, each opening of the heating chamber at the quenching temperature causes favourable oxidation of the surface of the heating elements. In addition, the oxidation of the heating elements can be carried out in a controlled manner by aerating the heating chamber at a sufficiently high temperature.
- Metal
resistance heating elements 4, made of iron-chromium-aluminium alloys, are arranged on the internal insulation walls. They can be made in the form of tapes to ensure low surface load at full power. The heating elements are arranged circumferentially around the internal surface of the heating chamber, divided into heating zones at the height of theheating chamber 2. The terminals of the heating elements are led to the outside of the vacuumouter furnace body 1 and theheating chamber insulation 2 through electrically and vacuum insulated water-cooled terminals 5 in the side wall of theouter furnace body 1. - The furnace is equipped with a
mixer 9, built into thefurnace cover 8 on theheating chamber side 2, to make it possible to carry out convection heating by providing the atmosphere-nitrogen circulation in the phase of convection heating and/or convection precooling for quenching. Thecover 8 is slid away for the time of unloading and loading with the use of jacks,e.g. screw jacks 10 and a horizontal sliding drive using a gear-motor 11. The vacuum cover is equipped with a vacuum sealing, preferably with alip seal 12. - The furnace with the water jacket is equipped with a
blower 14 with aheat exchanger 13 installed in the upper insulating wall 7 of theheating chamber 2 suspended in thefurnace cover 8 and with the gas circulation hatches 6 located in the upper insulating wall 7 of thecover 8 of theheating chamber 2 and in thebottom insulating wall 17 of theheating chamber 2, which makes it possible to carry out accelerated pearlitic precooling to a temperature of about 550-650°C. The hatches 6, driven by pneumatic cylinders, are opened in the phase of precooling to a temperature of pearlite transformation or quenching. Pearlitic precooling of the charge convective precooling system is carried out by nitrogen circulation through the following route: charge - upper hatches 6 - heat exchanger 13 - blower 14 - lower hatches 6 - charge/heating chamber 2. - The thermal insulation in this furnace, designed for carburizing thick layers, will be built in layers of ceramic mats, ceramic modules and / or ceramic plates with a thickness giving heat loss below 1 kWh/m2 of insulation at a temperature of 1000°C of vacuum (radiation) heating at a LPC cycle pressure of about 5-15 mbar.
- Workpieces in the tooling or single large-size workpieces are placed in the heating chamber on the charge supports 16 fixed in the
lower wall 17 of theheating chamber 2 and in the bottom of the lower vacuum outer furnace body. - The example of the operation of the furnace according to the invention is as follows. A workpiece, e.g. a large-size gear wheel, is introduced into the furnace by an external transport system and placed on the charge supports 16 . The
furnace cover 8 is moved over theouter furnace body 1 and is lowered to the closed and vacuum sealed position. The pump system removes air to reach a pressure of approx. 5×10-2mbar and after adequate holding and heating the system to a temperature of e.g. 400°C, nitrogen is introduced into the outer furnace body to reach a pressure of 900mbar and further heating is carried out in a convective manner to a temperature of e.g. 800°C with the possibility of nitrogen flow (flushing with nitrogen) to remove condensation products and impurities after a previous process / opening the furnace. In this heating phase, the convectivegas circuit mixer 9 is working. In the furnace equipped with a blower and hatches, thehatches 6 are closed. After adequate holding to equalize the temperature of the workpiece and the heating chamber, the outer furnace body is pumped down to a pressure of approx. 5×10-2 mbar and further heating to a carburizing temperature is carried out by radiation in a vacuum. When the set charge temperature is reached, the programmatic low-pressure carburizing (LPC) cycle is carried out, e.g. using FineCarb technology. After completion of the dosing phase and the diffusive holding cycles, in the furnaces equipped with ablower 14, the workpiece temperature is programmatically reduced to a temperature of quenching or pearlite transformation by precooling the system after introducing nitrogen into the outer furnace body to a pressure of approx. 900mbar and starting theblower 14, opening the hatches 6for cooling gas inflow and outflow from the heating chamber and starting the cooling water inflow to theheat exchanger 13. If a cycle with the pearlite transformation phase is carried out, after the time of holding / temperature equalization, thehatches 6 are closed and theblower 14 and theexchanger 13 are turned off. Convection heating is started to reach the quenching temperature, and, after proper equalization of the workpiece temperature, the heating is stopped, the furnace is filled to reach the ambient pressure and thefurnace cover 8 with the equipment is raised and moved away. The workpiece is removed from the furnace by means of an external transport device, e.g. an overhead crane with suitable handles, and transferred to the appropriate restraining tooling and then to a quenching tank, together with the tooling. - In the vacuum furnace according to the invention, as a result of cyclical opening the
cover 8 and/or aerating thecylindrical working chamber 1 at a process temperature of at least 800 °C, soot particles and other deposits / carbon deposits are oxidized on the internal surfaces of the thermal insulation liner of theheating chamber 2. - In the vacuum furnace according to the invention, as a result of cyclical opening the
cover 8 and/or aerating thecylindrical working chamber 1 at a process temperature of at least 800°C, soot particles and carbon deposits are oxidized on the surface of theheating elements 4 and an layer of aluminium oxides is formed or added to the surface of these elements. - Carbon-based impurities are removed and the protective oxide coating is reconstructed on the heating elements as a result of oxidation during convection heating in air.
Claims (1)
- A pit type furnace for vacuum carburization of workpieces, equipped with a vacuum-tight cylindrical outer furnace body with a sliding cover embedded on it, wherein in the outer furnace body there is a heating chamber equipped with the insulation with a multi-layered structure with at least three layers made of ceramic materials and there are heating elements inside the chamber, characterised in that, the heating chamber insulation (2) is multi-layered and contains at least three different layers made of ceramic materials and a 20 mm thick external layer (3a) in the form of microporous elements made of pyrogenic silica, a 155 mm thick middle layer (3b) in the form of a high-temperature fibrous ceramic mat is made of silica (SiO2), calcium oxide (CaO) and magnesium oxide (MgO) and a 125 mm thick internal layer (3c) in the form of vacuum-moulded fibrous ceramic modules resistant, located on the hot heating chamber side, made of aluminium oxide (Al2O3) and silica (SiO2), while the heating elements (4) are made of heat-resistant iron-chromium-aluminium alloys with the following composition: 4-7 wt. % Al, 20-30 wt. % Cr, and 63-76 wt. % Fe, and are located, divided into heating zones, along the heating chamber height (2).
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
PL428590A PL428590A1 (en) | 2019-01-15 | 2019-01-15 | Vacuum pit furnace for carburizing elements, in particular large-size elements |
PCT/PL2020/000001 WO2020149751A1 (en) | 2019-01-15 | 2020-01-10 | Pit type vacuum furnace for carburization of elements, especially large- size elements |
Publications (2)
Publication Number | Publication Date |
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EP3911905A1 EP3911905A1 (en) | 2021-11-24 |
EP3911905B1 true EP3911905B1 (en) | 2022-12-28 |
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ID=69726668
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP20708217.3A Active EP3911905B1 (en) | 2019-01-15 | 2020-01-10 | A pit type furnace for vacuum carburization of workpieces |
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Country | Link |
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EP (1) | EP3911905B1 (en) |
ES (1) | ES2938208T3 (en) |
PL (2) | PL428590A1 (en) |
WO (1) | WO2020149751A1 (en) |
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GB2621369A (en) * | 2022-08-10 | 2024-02-14 | Vacuum Furnace Eng Ltd | A vacuum furnace device |
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US4854860A (en) * | 1987-12-02 | 1989-08-08 | Gas Research Institute | Convective heat transfer within an industrial heat treating furnace |
US6585928B2 (en) * | 2001-09-07 | 2003-07-01 | C. Edward Eckert | Dispensing system for molten aluminum and method |
US8636946B1 (en) * | 2009-04-13 | 2014-01-28 | Emisshield, Inc. | Bell annealing furnace |
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2020
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PL428590A1 (en) | 2020-07-27 |
PL3911905T3 (en) | 2023-05-08 |
EP3911905A1 (en) | 2021-11-24 |
ES2938208T3 (en) | 2023-04-05 |
WO2020149751A1 (en) | 2020-07-23 |
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