American Aerospace Turbine Blade Restorer-Shroud Furnace
Used Blade Remanufacturing Thermal Deformation Excess and Vacuum Furnace Cooling Rate Insufficiency
Aero-turbine blades are the core components of aero-engines, which work under extreme environments of high temperature, high pressure, and high speed, and long-term service will lead to various kinds of damages of the blades, such as cracks, abrasion, and deformation. In order to reduce the cost and prolong the life of the component, the remanufacturing (MRO, Maintenance, Repair, and Overhaul) of used turbine blades is particularly important. However, one of the biggest challenges in the remanufacturing of turbine blades is excessive heat distortion. During high-temperature heat treatments (e.g., solution, aging), the blade is subjected to a wide range of thermal deformation due to material properties, complexity, and
During high-temperature heat treatments (e.g., solution, aging), blades are susceptible to deformation due to material properties, complex geometry, residual stress release, and uneven heating and cooling. The original scrap rate of 25% and thermal deformation of 0.15mm, seriously affecting the repair qualification rate and production efficiency.
In addition, the traditional vacuum furnace in the heat treatment of high temperature alloys, there is often a cooling rate is not enough. High-temperature alloys in solid solution treatment requires rapid cooling to maintain a supersaturated solid solution state, inhibit the precipitation of harmful phases, so as to obtain the best mechanical properties. If the cooling rate is too slow, this can lead to coarsening of the precipitated phases at the grain boundaries, which reduces the plasticity and toughness of the material, and even affects the fatigue life of the blades. A single batch took 14 hours to process, reflecting the inefficiency of the original equipment and its inability to meet the fast turnaround requirements of the aerospace MRO industry.
Customised Shroud Furnace (10-⁴Pa Vacuum)
In response to the high-precision requirements of aerospace turbine blade remanufacturing, a customised shroud furnace with an ultra-high vacuum of 10-⁴Pa was adopted. The hood furnace is a cyclic furnace featuring a liftable body for easy loading and unloading of workpieces. Ultra-high vacuum is essential for heat treatment of aerospace high-temperature alloys:
1. Prevention of oxidation and contamination: Aerospace high-temperature alloys are very sensitive to oxidation and contamination. At high temperatures, even a small amount of oxygen can cause oxidation of the blade surface, resulting in the formation of an oxide film that can affect the adhesion of subsequent coatings or lead to a direct loss of performance.
The ultra-high vacuum environment of 10-⁴Pa can eliminate the residual gas in the furnace to the maximum extent, effectively preventing the workpiece from oxidation and contamination at high temperatures, ensuring the surface quality of the blades and the purity of the material. 2.
2. Residual stress release and organisation homogenization: Vacuum environment is conducive to the full release of residual stress inside the workpiece, reducing the tendency of thermal deformation. At the same time, heat treatment in vacuum can promote the uniform diffusion of alloying elements, so that the internal organisation of the blade is more homogeneous, thus improving the overall performance of the material. 3.
3. Heating Uniformity Control: The design of the customised hood furnace pays special attention to the layout and power control of the heating elements to ensure the uniformity of the temperature field inside the furnace. Precise heating of complex blade geometries is achieved through multi-zone temperature control and precise temperature sensors to further minimise thermal distortion.
Helium fast cooling system (200 °C/min)
In order to solve the problem of insufficient cooling rate in vacuum furnaces, the solution introduces an advanced helium fast cooling system, which achieves a very high cooling rate of 200 °C/min. Helium as a cooling medium has the following significant advantages.
1. Excellent thermal conductivity: Helium has the highest thermal conductivity of the noble gases, much higher than nitrogen or argon. This means that helium is able to carry heat away from the blade surface more efficiently, resulting in rapid cooling.
2. High-pressure circulating systems: Helium fast cooling systems are typically equipped with high-pressure circulating fans and highly efficient heat exchangers capable of blowing helium at very high flow rates to the surface of the workpiece. Optimisation of the nozzle design and airflow organisation ensures that the cooling medium covers all surfaces of the blades uniformly and avoids localised uneven cooling.
3. Preventing precipitation of harmful phases: The cooling rate of 200℃/min enables the high temperature alloy to pass through the temperature range of harmful phase precipitation quickly after solid solution treatment, and effectively inhibits the formation of brittle phases such as grain boundary carbide and σ-phase, so as to maintain good plasticity and toughness of the material, and improve the mechanical properties and fatigue life of the blade.
4. Improve production efficiency: Rapid cooling significantly reduces the heat treatment cycle time, shortening the single batch processing time from 14 hours to 5.2 hours, which significantly improves the production efficiency and capacity, and meets the demand for fast turnaround in the aerospace MRO industry.
3D Temperature Field Simulation Calibration
In order to further accurately control thermal deformation, the solution employs advanced 3D temperature field simulation calibration technology. This technology plays a key role in the optimisation of the thermal treatment process:
1. Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD): The finite element analysis (FEA) software is used to simulate the temperature distribution, stress-strain and deformation of the blades during the heating and cooling process by building a three-dimensional model of the blades and the furnace chamber. At the same time, combined with the computational fluid dynamics (CFD) simulation of the gas flow and heat transfer process in the furnace, optimising the nozzle layout and airflow organisation of the helium cooling system. 2.
2. Optimisation of process parameters: Based on the simulation results, we can accurately predict the effects of different heating profiles, cooling rates and atmosphere flow on the deformation of the blades. Through repeated simulation and optimisation, the optimal heat treatment process parameters are determined, including heating rate, holding temperature, cooling rate, helium flow rate and pressure, etc., so that the blade deformation can be controlled within a very small range.
3. Real-time calibration and feedback: In actual production, temperature data are monitored in real time by multi-point temperature sensors in the furnace and compared with the simulation results. If deviations occur, the system can be adjusted and calibrated to ensure that the actual process is consistent with the simulated optimisation results. This calibration method combining simulation and reality is the key technology to achieve the deformation amount <0.03mm, which ensures that 100% of the repaired blades can be directly installed and qualified.