Germany's top automotive bearing manufacturer-annealing furnace
Annealing of carburised bearing steels
Carburised bearing steels are usually carburised to form a high-carbon hardened layer on the surface in order to achieve excellent wear resistance and fatigue life during the manufacturing process. However, the carburised steel is subjected to high internal stresses and uneven hardness, and annealing is required to optimise the microstructure, remove internal stresses and provide a good organisational basis for subsequent machining (e.g. grinding). In this case, an advanced annealing process is used to control the hardness fluctuation of ±3 HRC after annealing of carburised bearing steel. Annealing of carburised bearing steels usually refers to spheroidal annealing, the purpose of which is to convert the flaky carburite in the steel into spherical carburite, thereby reducing hardness, increasing plasticity, improving machinability and providing uniform austenite grains for final hardening. For high carbon chromium bearing steels (e.g. GCr15), a typical process for spheroidal annealing consists of heating to the two-phase zone of austenite and carburite (between Ac1-Accm), holding for a period of time, and then cooling slowly through the pearlitic transformation zone to spheroidise the carburite. Large fluctuations in hardness can be caused by imprecise control of the annealing temperature, insufficient holding time or inappropriate cooling rate, resulting in incomplete or uneven spheroidisation of the carbides, formation of flaky pearlite or reticulated carburite residues, and thus affecting the final hardness.
Fully-automatic Bogie Carbide Furnace (1200℃)
Traditional industrial furnaces have limitations in temperature control and automation, making it difficult to meet the demands of high-precision heat treatment. The fully-automated bogie hearth furnace adopted in this case can be used up to a maximum temperature of 1200°C, which is able to meet the annealing temperature requirements of carburised bearing steel. The furnace has the following technical features:
1. Furnace structure and heating zone division: Bogie hearth furnaces are usually of box-type structure, where the workpieces are placed on movable bogies, which are moved in and out of the furnace chamber. In order to achieve precise temperature control and uniformity, the furnace chamber is usually divided into several independent heating zones, each equipped with a separate heating element (e.g. resistance wire or gas burner) and a temperature sensor. This multi-zone design compensates for temperature gradients and ensures that the workpiece is heated uniformly throughout the entire annealing process. The furnace lining is made of full-fibre structure with good heat preservation and energy-saving effect.
2. Furnace atmosphere control: For the annealing of carburised bearing steel, the control of the furnace atmosphere is crucial. In order to prevent oxidation and decarburisation of the workpiece surface, a protective atmosphere such as nitrogen, hydrogen or a mixture of nitrogen and hydrogen is usually introduced. In some cases, traces of reactive atmosphere may also be introduced to promote carbide spheroidisation. Precise control of the atmosphere ensures that the surface quality of the annealed workpiece is maintained, avoiding the need for subsequent cleaning processes and further improving hardness consistency.
3. Automated charging and operation: The fully automated Bogie Hearth Furnace is equipped with a motorised trolley and guideway system, which enables automatic charging and discharging of the workpieces into and out of the furnace chamber, reducing the need for manual intervention, and improving production efficiency and safety. The whole annealing process can be run automatically according to the preset programme, including heating, holding, cooling and other phases, without manual guarding, reducing operating costs and human error.
AI temperature control system (±1.5℃ accuracy)
AI temperature control system is one of the core technologies to solve the hardness fluctuation problem. Traditional PID control may be difficult to achieve extremely high control accuracy when facing the complex heat treatment process. By integrating advanced sensor technology, data acquisition system and machine learning algorithms, the AI temperature control system achieves an ultra-high temperature control accuracy of ±1.5℃. Its specific implementation includes:
1. High-precision Sensors and Data Acquisition: Multi-point high-precision thermocouple sensors are arranged in the furnace to collect real-time temperature data from all areas of the furnace. The high frequency of data acquisition ensures that small temperature fluctuations can be captured. The data is transmitted to the central control system via a high-speed data bus.
2. Machine Learning Models: The AI temperature control system uses historical heat treatment data and real-time temperature data to train machine learning models. These models learn the optimal heating and cooling profiles for different workpiece types, furnace loads, and environmental conditions, and predict temperature trends. Fine control of the temperature profiles prevents overshoots and undershoots and ensures that the workpiece follows the preset temperature profile throughout the annealing cycle.
3. Predictive control and adaptive adjustment: Based on the prediction ability of machine learning model, the AI system is able to achieve predictive control, adjusting the heating power and atmosphere flow in advance to cope with the upcoming temperature changes. At the same time, the system is also equipped with an adaptive adjustment function, which can optimise the control parameters in real time according to the actual operating conditions and feedback from the workpiece to further improve the control accuracy and stability. This intelligent control method is significantly better than the traditional fixed-parameter PID control and solves the problem of hardness fluctuations effectively.
Integrated Waste Heat Recovery Module
The problems of the old furnace with gas consumption exceeding the standard by 42% and an annual carbon penalty of € 280 K have been effectively solved by the integrated waste heat recovery module. Industrial furnaces generate a large amount of waste heat from the flue gas during operation, which, if emitted directly into the atmosphere, would not only result in a waste of energy, but also increase carbon emissions. The technical principle of the waste heat recovery module is to recover the heat from the high temperature flue gases by means of a heat exchange device and use it to preheat the combustion air, to heat the water used in production or to generate steam. In this case, one or more of the following waste heat recovery technologies may be employed:
1. Flue gas waste heat boiler: High temperature flue gases are introduced into a waste heat boiler and the heat is transferred to water through the heating surfaces of the boiler to produce steam or hot water for use in other parts of the plant or for heating. 2.
2. Air preheater: Transferring the heat from the high temperature flue gas to the combustion air entering the burner, increasing the temperature of the combustion air and thus reducing fuel consumption. This directly improves combustion efficiency and reduces gas consumption. 3. Heat pipe heat exchanger
3. Heat pipe heat exchanger: Using the high efficiency heat transfer characteristics of the heat pipe, the heat from the flue gas is transferred to other media, with a compact structure and high heat transfer efficiency.
The integrated waste heat recovery module not only significantly reduces gas consumption and energy costs, but also directly reduces CO2 emissions, thus avoiding high carbon fines and complying with the increasingly stringent environmental regulations in Europe. The synergy of these technologies has enabled the German automotive bearing manufacturer to achieve industry-leading product quality and environmental efficiency.