Heat treatment furnace

Abstract

This invention comprises a heat treatment furnace comprising in its housing an insulated process chamber provided with thermal insulation and a heating element maintaining the processed material at a temperature set for the process carried out in the furnace, characterized in that in the process chamber of the furnace (1) in which the processed object is placed, there is an additional heating element (2) powered from an external energy source, on which dissociation of ammonia present in the furnace atmosphere takes place, and this heating element (2) is positioned in such a way that it is in direct contact with the atmosphere in the process chamber (1) of the furnace and when it is activated it reaches a temperature higher than the temperature set for the process in the furnace.

Description

[0001] Heat treatment furnace

[0002] This invention relates to a furnace for heat treatment, especially thermochemical treatment. The furnace is designed to carry out processes that require concentrations of nitrogen and hydrogen, generated from ammonia, in the working atmosphere that are specific to the process. These processes include nitriding, carbonitriding, and nitrocarburizing.

[0003] The furnace atmosphere typically derives atomic nitrogen from dissociated ammonia. The degree of ammonia dissociation, measured by the nitrogen potential of the working atmosphere, is determined by the ratio of partial pressures of ammonia and hydrogen, the atmosphere's active components.

[0004] Existing solutions typically involve rinsing the furnace with specific amounts of ammonia, followed by dissociated ammonia, to achieve the desired technological parameters for the process. Dissociated ammonia is obtained using an external ammonia dissociator. It is typically a tube furnace equipped with a catalytic filling. Ammonia decomposes thermally on the catalyst within this furnace. The dissociator is typically equipped with heaters, a temperature controller, overheating protection, insulation within a housing, and suitable gas fittings, including an ammonia flow regulator, usually a mass flow regulator. Dissociator is described in document CN106006577A. Known thermochemical treatment processes conducted in a dissociated ammonia atmosphere typically involve supplying dissociated ammonia to the furnace process chamber from an external ammonia dissociator.

[0005] Polish Patent PL215404B1 describes a method for producing rhenium metal powder from ammonium perrhenate (NH4ReO4) through reductive annealing in a dissociated ammonia atmosphere. This atmosphere is generated in an ammonia dissociator and then fed into a furnace where the reduction process takes place.

[0006] The nitriding furnace described in CN203419976U discloses a furnace equipped with a device for decomposing gaseous ammonia, mounted on the furnace cover.

[0007] Using an external dissociator necessitates the transfer of ammonia decomposition products, including highly flammable hydrogen, to the heat treatment furnace. This poses a risk of leaks in the transmission pipeline connections. Additionally, the thermal losses of the external dissociator significantly exceed the energy required for ammonia dissociation. The total heat energy loss comprises: the energy required to heat the device to its operating temperature (typically up to 950°C), maintain this temperature during the process and preparation periods, energy used to heat ammonia to its dissociation temperature, and heat losses in the pipeline transferring ammonia decomposition products to the heat treatment furnace. The gas produced in the dissociator cools during transmission and must be reheated to the process operating temperature. For instance, if the gas temperature at the dissociator outlet is 950°C, it may cool to 100°C during transmission and then require reheating in the furnace to the process temperature, such as 520°C. Another disadvantage of using an external dissociator is the significant loss of gases. Normative acts mandate that after the dissociation process, the dissociator must be purged with nitrogen, using a volume five times that of the dissociator. To reduce ammonia concentration in the heat treatment furnace's working chamber, a continuous supply of fresh ammonia to the dissociator is necessary.

[0008] The invention aimed to develop a heat treatment furnace that addresses the aforementioned shortcomings.

[0009] A heat treatment furnace comprising in its housing an insulated process chamber provided with thermal insulation, a heating element maintaining the processed material at a temperature set for the process carried out in the furnace, powered from an external power source via power cables routed to the heating element through passages in the furnace housing, characterized in that in the process chamber of the furnace in which the processed object is placed, there is an additional heating element powered from an external energy source, on which dissociation of ammonia present in the furnace atmosphere takes place, and this heating element is positioned in such a way that it is in direct contact with the atmosphere in the process chamber of the furnace and when it is activated it reaches a temperature higher than the temperature set for the process in the furnace.

[0010] Preferably, the additional heating element is an electric heater.

[0011] Preferably, the additional heating element is a heat radiating tube.

[0012] A more detailed explanation of the invention, along with a cross- sectional view of the furnace's interior, is provided in Figure 1 .

[0013] In the process chamber 1 of the metal heat treatment furnace P an electric heater 2 is installed, situated in the fan chamber 3 behind the atmosphere guide vane 4. The electric heater 2 is powered from an external energy source, with the power supply cables of the electric heater 2 are routed out of the furnace P through the bushing 5. The processed charge 7 is located in the process chamber 1 and the furnace heaters 6 are located outside the process chamber 1. Before activating the heater 2, furnace P is filled with ammonia. After switching on the electric heater 2 and reaching the temperature necessary for thermal dissociation of ammonia, the decomposition of ammonia present in the atmosphere of furnace P begins. When the electric heater 2 is activated, the power of the heaters 6 of furnace P is proportionally reduced. During the furnace P process, ammonia is not supplied to process chamber 1 , though this option remains available in specific circumstances. The furnace, as per the invention, in order to provide the required amount of dissociated ammonia in the furnace atmosphere, consumes energy solely for ammonia molecule decomposition, significantly reducing energy consumption compared to systems using external dissociators. When using an external dissociator, the total energy consumption also includes the energy required to heat the device to its operating temperature (typically up to 950°C), maintain this temperature during the process and preparation periods, heat the ammonia to its dissociation temperature, and reheat the dissociator's exhaust gases, which cool during transfer to the furnace's process chamber.

[0014] The furnace, as per the invention, also eliminates significant gas losses associated with purging the dissociator with nitrogen post-process. The furnace, as per the invention, utilizes ammonia introduced into the furnace atmosphere at the process initiation. Accelerating the reduction of nitrogen potential in the furnace does not necessitate additional fresh ammonia supply, unlike systems using an external dissociator.

[0015] The solution, as per the invention, also eliminates the ammonia and hydrogen transfer installations between the dissociator and the furnace, thereby reducing the overall installation cost. Additionally, the number of detachable connections in the gas installation is minimised, significantly reducing the risk of leaks at connection points. Testing of the furnace, as per the invention, demonstrated that a significant acceleration of ammonia dissociation is achieved in a furnace equipped with an additional heating element within the process chamber. Depending on the settings, the nitrogen potential has been significantly reduced compared to the natural potential decline. The test results are presented in a graph of nitrogen potential versus time. The dashed line illustrates the natural rate of ammonia decomposition within the process chamber, while the solid line shows the accelerated decomposition of ammonia in the process chamber equipped with an additional heating element, which facilitates the dissociation of ammonia present in the furnace atmosphere.

Claims

Patent claims1 . A heat treatment furnace comprising in its housing an insulated process chamber provided with thermal insulation and a heating element maintaining the processed material at a temperature set for the process carried out in the furnace, characterized in that in the process chamber of the furnace (1 ) in which the processed object is placed, there is an additional heating element (2) powered from an external energy source, on which dissociation of ammonia present in the furnace atmosphere takes place, and this heating element (2) is positioned in such a way that it is in direct contact with the atmosphere in the process chamber (1 ) of the furnace and when it is activated it reaches a temperature higher than the temperature set for the process in the furnace.

2. A heat treatment furnace according to claim 1 , characterized in that the additional heating element (2) is supplied with electrical energy.

3. A heat treatment furnace according to claim 1 , characterized in that the additional heating element (2) is a heat radiating tube.

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