Apparatus and method for controlled hardening of parts

Abstract

The invention relates to a hardening chamber comprising a heating element (9) and a temperature sensor (10), and between the heat exchanger (6) and the blower assembly (7) there is a bypass channel (14) with its inlet comprising tilting or sliding shutters (11). When the shutters open the entrance to the bypass channel (14), they at least partially close the entrance to the heat exchanger zone (6). The invention also relates to a method of controlled hardening of parts that periodically omits the passage of cooling gas through the heat exchanger (6) by directing the cooling gas through the bypass channel (14) using shutters (11).

Description

[0001] Apparatus and method for controlled hardening of parts

[0002] The invention relates to an apparatus and method for controlled, deformationminimizing hardening of components using a cooling medium with a regulated temperature.

[0003] The invention may find application in industry.

[0004] Polish Patent Description No. PL228193B1 discloses a device for individually hardening parts of technical devices. This device is a component of a vacuum furnace assembly, where the assembly’s hardening chamber is equipped with a sealed door for loading and unloading parts. The device is characterized by the following components located inside the hardening chamber: a replaceable table and a system of replaceable nozzles surrounding it, while a tank for the supplied cooling medium is connected to the hardening chamber's inlet, and the hardening chamber's outlet is connected to a tank for the received cooling medium. A compressor connects both tanks, and the hardening chamber is connected to a system of vacuum pumps. Advantageously, the known device includes a supply gas flow rate controller and a shut-off valve connected between the tank's outlet and the hardening chamber's inlet. Additionally, a shut-off valve, a discharge gas flow rate controller, and a heat exchanger are connected between the hardening chamber's outlet and the tank's inlet. It is also advantageous when the tank outlet is connected to the compressor inlet via a shut-off valve, and the compressor outlet is connected to the tank via a shut-off valve and a heat exchanger.

[0005] Polish patent description PL238181 discloses a device for continuously heat treating steel, metal, and alloy parts. This device is an integrated set of process chambers, where a horizontally oriented heating chamber, enclosed in a vacuum housing, is positioned between two vertical reloading chambers. A loading chamber is connected to the first reloading chamber's inlet, while at least one cooling chamber is connected to the second reloading chamber's outlet. The cooling chamber is equipped with a movable shaft in the form of a rotating table and cooling gas nozzles mounted on two movable and replaceable collectors. The device is characterised in that the heating chamber features a movable shaft containing 2 to 50 processing stations with a cylindrical outline, up to 1000 mm in diameter and 1000 mm in height. The shaft drive and the drives of the reloading chambers' loading and unloading mechanisms are equipped with a mutual synchronization system. The cooling chamber is equipped with at least one fan assembly with a heat exchanger. The cooling chamber contains two oppositely positioned fan units, each equipped with a heat exchanger. The cooling chamber is equipped with an external fan assembly with a heat exchanger and pipes for the supply and discharge of cooling gas.

[0006] The same Polish Patent Description PL238181 discloses a device for gas cooling heat- treated parts under overpressure, especially for hardening. This device is an autonomous cooling chamber equipped with a movable shaft in the form of a rotating table and cooling gas nozzles mounted on two movable and replaceable collectors, arranged directly around the stations of the parts being cooled. The device is characterised in that the cooling chamber is equipped with an externally located fan assembly with a heat exchanger and pipelines for supplying and discharging the cooling gas.

[0007] A significant drawback of current state of the art is that gas cooling systems do not have the ability to regulate the temperature of the cooling medium and thus control the cooling process of the hardened parts. Cooling in known systems takes place at a gas temperature close to the ambient temperature. The proposed solution, according to the invention, enables controlled cooling of hardened parts by regulating the cooling medium's temperature during the initial cooling phase, followed by subsequent cooling phases under different flow and pressure conditions, allowing for multiple repetitions.

[0008] The invention's core is a hardening chamber, a component of a vacuum furnace assembly, equipped with a sealed door for loading and unloading parts. Inside, it houses a replaceable table surrounded by a system of replaceable nozzles. It also includes at least one fan assembly and at least one heat exchanger. The hardening chamber is characterised by the inclusion of a heating element and a temperature sensor. A bypass channel, positioned between the heat exchanger and the fan assembly, features an entrance equipped with shutters that can tilt or slide. When the shutters open the entrance to the bypass channel, they at least partially close the entrance to the heat exchanger zone.

[0009] Preferably, the hardening chamber is equipped with a heat accumulator comprising a housing with thermal insulation and a connecting pipe. Located inside the housing are a heating element with a heat-accumulating insert and a temperature sensor for monitoring the insert's temperature.

[0010] Preferably, the heat-accumulating insert is made of copper or its alloys, in particular in the form of tubes or balls or sinters.

[0011] Preferably, the temperature sensor is placed near the heating elements.

[0012] It is also preferred that the hardening chamber is connected to a heating chamber and a transport mechanism transferring parts between the chambers.

[0013] It is also preferred that the fan assembly and / or the heat exchanger are located inside the hardening chamber.

[0014] It is also preferred when the fan assembly and / or the heat exchanger is located outside the hardening chamber and includes a conduit system for supplying and removing cooling gas.

[0015] A method of controlled hardening of parts using a cooling gas with an adjustable temperature, comprising a step of heating the hardening chamber internally, in gas, to a set temperature and a step of lowering the temperature of the gas on a heat exchanger, characterized in that after placing the part to be hardened in the chamber, the circulation of the cooling gas in the hardening chamber, forced by a fan assembly, is carried out in such a way that the passage of the cooling gas through the heat exchanger is periodically omitted using shitters directing the cooling gas to a bypass channel, where it is subsequently returned to the hardening chamber.

[0016] Preferably, after heating the hardening chamber to the set temperature in gas, the chamber is filled with cooling gas at a pressure of 0.01 to 4 MPa absolute, flowing from the supply tank through the heat accumulator. The heat accumulator heats the cooling gas to a temperature exceeding the onset of the martensitic transformation of the steel used in the part.

[0017] Preferably, the step of heating the hardening chamber to the set temperature is carried out using air or nitrogen.

[0018] Preferably, the cooling gas is nitrogen and / or argon and / or helium and / or hydrogen or air or a mixture of air with nitrogen or with argon or with helium.

[0019] Preferably, the cooling gas temperature is regulated in the range from -200 to

[0020] 600°C. Preferably, the hardening process is carried out in a cooling gas at a pressure ranging from 0.01 to 4 MPa. abs.

[0021] The proposed solution enables the temperature of the machined parts to be equalized before the martensitic transformation begins, which should result in reduced stress in the parts and reduced deformations.

[0022] The device, according to the invention, enables controlled cooling of hardened parts by regulating the cooling medium's temperature during the initial cooling phase, followed by subsequent cooling phases under different flow and pressure conditions, allowing for multiple repetitions. This allows for any shaping of the cooling curve, achieving optimal steel microstructure and mechanical properties. The use of the controlled hardening method on parts minimizes deformation compared to single-part processing and ensures full repeatability of deformation across all identical parts, while maintaining identical mechanical properties.

[0023] The invention in the embodiments is presented in the drawing, in which fig. 1 shows a side view of the cooling chamber without an accumulator in a longitudinal section, showing the components of the chamber, fig. 2 shows the front view crosssection of the cooling chamber without an accumulator , fig. 3 shows a side view longitudinal section of the cooling chamber with an accumulator, showing the component elements of the chamber, fig. 4 shows a front view cross-section of the cooling chamber with an accumulator, fig. 5 shows a cross-section of the cooling chamber, showing the shutters in a state of preparing the chamber for work with an increased temperature of the cooling medium, fig. 6 shows a cross-section of the cooling chamber, showing the shutters in a state of cooling with cold gas, fig. 7 shows a cross-section of the cooling chamber, showing the shutters in a state of maintaining the temperature of the cooling chamber, fig. 8 shows a a longitudinal section of the multi-chamber furnace with a connected cooling chamber with an accumulator, fig. 9 shows a a longitudinal section of the heat accumulator in a version with copper pipes as heating elements, fig. 10 shows a view of the accumulator from the side of the heating element, fig. 11 shows a longitudinal cross-section of the heat accumulator with the heated gas circulation marked, fig. 12 shows cross-sections A-A, B-B, C-C of the heat accumulator, marked in fig. 11 , wherein A-A shows the gas inflow and outflow zone, B-B the heating element zone, and C-C the gas return zone, fig. 13 shows a longitudinal cross-section of the heat accumulator in the version with the heating element being copper balls, fig. 14 shows the heat accumulator as in fig. 13, in cross- sections D-D, E-E, F-F, marked in fig. 13, wherein D-D shows the gas inflow and outflow zone, E-E the heating element zone, and F-F the gas return zone, fig. 15 shows a longitudinal cross-section of the heat accumulator in the version with the copper sinters as the heating element, fig. 16 shows the heat accumulator as in Fig. 15, in cross-sections G-G, H-H, l-l, marked in Fig. 15, where G-G shows the gas inflow and outflow zone, H-H the zone of heating elements, and l-l the gas recirculation zone.

[0024] Embodiment 1 :

[0025] The hardening chamber A according to the invention as shown in fig. 1 , 2, 5, 6, 7 operates in a multi-chamber furnace assembly with a vacuum heating chamber C for heating and with a transport mechanism B for transporting parts copper sinters. The multi-chamber furnace is equipped with oppositely located tight loading doors 2 and unloading doors 3 for loading and unloading the hardened part 12. Inside the hardening chamber A there are: a table 4 on which the part 12 is placed, a system of replaceable nozzles 5 (adapted to the shape of the part), heat exchangers 6 for cooling the cooling gas heated during hardening, a set of blowers 7 forcing the circulation of the cooling gas, heating elements 9 for maintaining the temperature of the cooling gas, a PT100 temperature sensor 10 for controlling the temperature of both the gas filling the chamber before the part 12 is placed in it (air or nitrogen) and the cooling gas (the upper part of the chamber), and shutters 11 for regulating the temperature of the cooling gas. The housing 1 of the hardening chamber is fitted with thermal insulation 13.

[0026] In hardening chamber A made of structural steel, part 12, made of H13 tool steel, is heat treated, with nitrogen used as the cooling gas. After prior heating of part 12 in heating chamber C at a temperature above the austenitizing temperature , e.g. 1030°C, part 12 is conveyed by transport mechanism B, under vacuum conditions, to hardening chamber A. A nitrogen-filled hardening chamber A is preheated by means of heating elements 9 to the set te perature of 345°C, a temperature above the onset of the martensitic transformation. To reload parts 12 from heating chamber C, hardening chamber A is pumped out by a vacuum system until a vacuum of at least 0.1 hPa is obtained. Then, after opening the loading door 2, part 12 is transferred by means of the transport mechanism B into the hardening chamber A and placed on the table 4. Loading door 2 and the vacuum valve close.

[0027] The hardening process takes place in two stages. First, the valve at the cooling gas inlet to the hardening chamber A is opened. The cooling gas from the supply tank enters the system at a pressure of 0.2 MPa. The temperature of the cooling gas is close to the temperature of the hardening chamber A. Once atmospheric pressure is reached within the chamber, a set of blowers is activated to force cooling gas through nozzles 5 onto the hardened part 12. The gas absorbs heat from part 12, cooling it. If the temperature sensor 10 indicates a temperature below the set point, the gas is redirected back to the blower, bypassing the heat exchanger 6 (shutters 11 open). Cold gas supply is used for large, heavy parts when cooling with a regulated medium temperature. The gas temperature is measured by temperature sensor 10. The gas temperature is monitored by the controller, which also controls the operation (opening / closing) of shutter 11. If the temperature sensor

[0028] 10 indicates excessive gas temperature, the controller signals shutter 11 to close, directing the gas to the exchanger zone 15 on the heat exchanger 6 for cooling. When the temperature sensor 10 indicates an excessively low temperature, the controller signals shutter 11 to open, directing the gas through the bypass channel 14 to the blower assembly 7, which then directs the gas to the nozzles 5, which in turn direct the gas onto the hardened part 12.

[0029] In the second stage, cold gas at ambient temperature is replenished in the chamber to a pressure of 1.5 MPa to further cool part 12 to ambient temperature. At this point, shutters 11 close the bypass channel 14, directing the gas heated by part 12 to the heat exchanger 6 for cooling. After part 12 cools to ambient temperature, the gas is released to atmospheric pressure. The unloading door 3 opens, allowing part 12 to be removed from the hardening chamber A using the transport mechanism or manipulator located in the transport chamber B.

[0030] The hardening chamber operates in 3 stages.

[0031] I - preparing the chamber for operation with increased cooling gas temperature. This is the stage in which the chamber is heated internally to the set temperature. At this time, the heating elements 9 and the blower unit 7, which forces gas movement within the chamber, are switched on. The temperature is monitored by temperature sensor 10, and shutters 11 remain open as shown in Figure 5.

[0032] 11 - maintaining the temperature of the cooling chamber. This stage involves the control system using temperature sensor 10 to control the opening / closing of shutters 11 , maintaining the set temperature. Ill - cold gas cooling. During this stage shutters 11 are closed, with the gas circulating in the circuit: part 12 - heat exchanger 6 - blower assembly 7 - nozzles 5, as shown in Fig. 7.

[0033] Wherein:

[0034] • When the shutters are closed, they close the gas flow through the bypass channel and direct it to the heat exchanger

[0035] • When the shutters are open, they open the bypass channel Embodiment 2:

[0036] The hardening chamber A according to the invention as shown in fig. 3, 4, 5, 6, 7 operates in a multi-chamber furnace assembly as shown in fig. 8 with a vacuum heating chamber C for heating and carburizing, and with a transport mechanism B for transporting parts 12. Further as in embodiment 1 , but the chamber comprises a heat accumulator 8 mounted in the upper part of the housing 1 , which heats the cooling gas while it is being fed into the chamber. At the inlet of the heat accumulator 8, the temperature of the cooling gas is close to the ambient temperature, it is not heated in the buffer tank, and at the outlet it is heated to the set temperature. The heat accumulator 8 is equipped with a housing made of structural steel together with a connecting pipe 19 and thermal insulation 20. Inside the housing there is a heating element 16 of the accumulator surrounded by a heat accumulating insert 17 and the accumulator 18 temperature sensor for monitoring the temperature of the heat accumulating insert 17. The heat accumulating insert 17 may be a copper tube arrangement as in Figs. 11 , 12, 13, 14.

[0037] The heat accumulating insert 17 may also be a bed of copper balls as in Figs. 15, 16. The heat accumulating insert 17 may also be a bed of copper sinter as in Figs. 17, 18. In hardening chamber A made of structural steel, part 12 made of carburizing steel 20MnCr5 is heat treated, with argon used as the cooling medium (gas). After preheating and carburizing of part 12 in heating chamber C to the required layer thickness, at a temperature above the austenitizing temperature , e.g. 950°C, part 12 is transported under vacuum to hardening chamber A. The hardening chamber A is preheated to a temperature of 400°C by means of heating elements 9 and circulating air remaining after unloading the part from the hardening chamber in the previous hardening cycle, and then the air is pumped out of the chamber by a vacuum system until a vacuum of at least 0.1 hPa is obtained. Then, after opening the loading door 2, part 12 is transferred by means of a transport mechanism or manipulator into the hardening chamber A and placed on the table 4. Loading door 2 and the vacuum valve close.

[0038] The hardening process takes place in two stages.

[0039] First, the valve at the gas inlet to the hardening chamber A is opened. Cooling gas from the pressurized supply tank enters the system via heat accumulator 8, which heats the gas to the set temperature of 400°C, which corresponds to the temperature above the onset of the martensitic transformation, to a pressure of 0.2 MPa. The blower assembly 7 forces hot gas through the nozzles 5, which direct the gas onto the hardened part 12. The gas removes heat from part 12, cooling it. Temperature sensor

[0040] 10, connected to the controller, monitors the heated cooling gas temperature. The controller signals shutters 11 to open or close, maintaining the gas temperature by directing it to heat exchanger 6 when too hot or through bypass channel 14 when too cold.

[0041] In the second stage, the gas is injected to a set pressure of 1 .0 MPa to further cool the part 12 to ambient temperature. At this point, shutters 11 close the bypass channel 14, directing the gas heated by part 12 to the heat exchanger 6 for cooling. After part 12 cools to ambient temperature, the gas is released to atmospheric pressure. The unloading door 3 opens, allowing part 12 to be removed from the hardening chamber A using the transport mechanism or manipulator.

[0042] The chamber operates in 4 stages.

[0043] I - preparing the chamber for operation with increased cooling medium temperature. This is the stage in which the chamber is heated internally by gas to the set temperature. At this time, the heating elements 9 and the blower unit 7, which forces air movement within the chamber, are switched on. The temperature is monitored by temperature sensor 10 and the shutters 11 are closed.

[0044] II - preparing the accumulator for operation - this is the stage in which the accumulator is heated to the set temperature using the heating element 16. This step is executed during the heating of part 12 in heating chamber C.

[0045] III - maintaining the temperature of the hardening chamber. This stage involves the control system using temperature sensor 10 to control the opening / closing of shutters

[0046] 11 , maintaining the set temperature.

[0047] IV - cold gas cooling. During this stage shutters 11 are closed, with the gas circulating in the circuit: part 12 - heat exchanger 6 - blower assembly 7 - nozzles 5.

Claims

Claims1 . A hardening chamber, a component of a vacuum furnace assembly, equipped with a sealed door for loading and unloading parts. Inside, it houses a replaceable table surrounded by a system of replaceable nozzles. It also includes at least one fan assembly and at least one heat exchanger. The hardening chamber is characterised by the inclusion of a heating element (9) and a temperature sensor (10). A bypass channel (14), positioned between the heat exchanger (6) and the fan assembly (7), features an entrance equipped with shutters (11 ) that can tilt or slide. When the shutters open the entrance to the bypass channel (14), they at least partially close the entrance to the heat exchanger zone (6).

2. A hardening chamber according to claim 1 , characterized in that it is equipped with a heat accumulator (8) comprising a housing with thermal insulation (20), together with a connecting pipe (19). Located inside the housing are a heating element (16) with a heat-accumulating insert (17) and a temperature sensor (18) for monitoring the insert's temperature.

3. A hardening chamber according to claim 2, characterized in that the heat accumulating insert (17) is made of copper or its alloys.

4. A hardening chamber according to claim 3, characterized in that the heat accumulating insert (17) is in the form of pipes or a bed of balls or sinters.

5. A hardening chamber according to claim 1 or 2, characterized in that the temperature sensor (10) is located near the heating elements (9).

6. A hardening chamber according to claim 1 or 2, characterized in that it is connected to a heating chamber (C) and a transport mechanism (B) for transferring parts between the chambers.

7. A hardening chamber according to claim 1 or 2, characterized in that the fan unit (7) and / or the heat exchanger (6) are located inside the hardening chamber (A).

8. A hardening chamber according to claim 1 or 2, characterized in that the fan unit (7) and / or the heat exchanger (6) is located outside the hardening chamber (A) and comprises a conduit system for supplying and removing cooling gas.

9. A method of controlled hardening of parts using a cooling gas with an adjustable temperature, comprising a step of heating the hardening chamber internally, in gas, to a set temperature and a step of lowering the temperature of the gas on aheat exchanger, characterized in that after placing the part (12) in the chamber, the circulation of the cooling gas in the hardening chamber (A) forced by a fan assembly (7) is carried out in such a way that the passage of the cooling gas through the heat exchanger (6) is periodically omitted, wherein this omission is carried out using shutters (11 ) directing the cooling gas to a bypass channel (14), and the gas is subsequently returned to the space around the hardened part (12).

10. A method according to claim 9, characterized in that after the step of heating the hardening chamber (A) to the set temperature, the hardening chamber (A) is filled with cooling gas under pressure from 0.01 to 4 MPa abs, flowing from the supply tank through the heat accumulator (8). The heat accumulator heats the cooling gas to a temperature exceeding the onset of the martensitic transformation of the steel used in the part (12).11 .The method according to claim 9 or 10, characterized in that the step of heating the hardening chamber to a set temperature is carried out with air or nitrogen.1 . A method according to claim 9 or 10, characterized in that the cooling gas is nitrogen and / or argon and / or helium and / or hydrogen or air or a mixture of air with nitrogen or with argon or with helium.

13. A method according to claim 9 or 10, characterized in that the temperature of the cooling gas is regulated in the range from -200 to 600°C.

14. A method according to claim 9 or 10, characterized in that the hardening process is carried out in a cooling gas at a pressure of 0.01 to 4 MPa abs .List of symbols:

1. cooling chamber housing2. loading door3. unloading door4. table5. replaceable cooling nozzles6. heat exchanger7. blower unit (with fan)8. heat accumulator9. heating element10. temperature sensor11 . shutter12. hardened part13. thermal insulation14. bypass channel15. exchanger zone16. accumulator heating element17. heat accumulating insert18. gas temperature sensor19. connecting pipe20. thermal insulation of the accumulatorA. hardening chamberB. transport mechanismC. heating chamber

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