Photo: Michael Schwarzenberger
Butterfly valves are used to control air flow in bleed air systems and for environmental control systems. A typical butterfly valve includes a housing that defines an air flow passage. A shaft is mounted in a housing and supports a butterfly disk that incorporate a sealing ring and a stiffer. An actuator rotates the shaft to selectively open or close the butterfly disk to control the air flow through the passage in the housing. In this type of configuration, leakage is generated mainly by the wear of the sealing elements. Thus, the wear rate is the main parameter to be considered, and the well understanding of the high temperature wear behaviour of the materials used in these components under extreme conditions is essential.
Nowadays, cobalt alloy like Stellite 6 is used for the manufacturing of the butterfly sealing rings. High temperature wear of sealing rings and stiffness under complex thermomechanical stresses leads to bleed valve internal leakage increase. The limitation of leakage through the correct selection of materials, the design of the sealing rings and housings, adequate manufacturing routes and the correct assembly between the stiffener and the butterfly will ensure a perfect seal avoiding possible leaks during operation, what will lead to a reduction of fuel consumption of about 1.8 kg/h for small-medium range aircraft. Furthermore, the avoidance of cobalt oxidized wear particles in the airflow will result on an improved cabin air quality.
Photo: Courtesy of Liebherr
Nickel-based alloys like NiCrSiFeB Self-Fluxing alloys exhibit excellent corrosion and are reported to be wear-resistance up to 600 oC. They also demonstrate an excellent oxidation resistance up to melting range, and satisfactory resistance to some organic acids. Nowadays, these materials are mainly used as coatings. So, the project will identify and define the critical process parameters to manufacture the Nickel based self-fluxing alloys by Centrifugal Casting (CC) and Laser Metal Deposition (LMD).
The project will go a step forward in the processing of Nickel Self-fluxing alloys by two new manufacturing routes oriented to replace Cobalt parts considering Eco Design process optimization approach based in LCA analysis for the development and future industrialization of sealing rings
of aero engine components. The manufacturing process development and the selection of the best NiCrSiFeB alloy and associated process parameters set will be supported with data analytics and validation testing, including metallurgical and mechanical characterization, tribological studies at high temperature, toxicity analysis and LCA & LCC analysis.
New manufacturing routes for Ni Based self-fluxing alloys
It will be possible to manufacture bulk parts of NiCrSiFeB alloys. Control of solidification ranges to avoid microshrinkage problems will be key in CC process, together with process modelling to reduce setting up times. Specific process conditions such as thermal gradients and fine powder stream will be combined with a melt- pool size monitoring system and a multivariate process control system in LMD process. The development of robust manufacturing study will be supported by advanced data analytics.
How to determine the best NiCrSiFeB alloy as Cobalt alloy replacement
- Extensive tribological studies at high temperature
- High temperature mechanical properties (hot hardness) Advanced Microstructural analysis
- Toxicity analysis
- LCA & LCC analysis
Firstly, the best combination of process parameters for both CC and LMD and chemical composition will be selected. Afterwards, 8 sealing rings will be manufactured, 4 by CC and 4 by LMD, including post-processing operations for endurance test. A complete characterization of the worn surfaces of the tested rings
will be carried out by electron microscopy and non-destructive testing. These results together with outcomes from toxicity analysis and LCA/LCC will define the potential substitution of current Cobalt rings by the developed alternative ones.
- To reduce the overall manufacturing cost of sealing rings >30% for both CC and LMD process maintaining or increasing the wear resistance as compared to Stellite 6.
- For LMD process, to reduce time- to-market from several months to one month.
- To obtain viable solutions to replace Cobalt in future aero components.
- Reduce EU dependence on critical raw materials like Cobalt.
- To reduce material waste and scraps by 12% per component for CC and 25% per component for LMD.
- To reduce CO2 emissions, perceived noise and fuel consumption due to the expected limitation of leakage and the suppression of pressure relief holes per valve leading to a reduction of fuel consumption of 1.8 kg/h for small-medium range aircraft.
- To contribute to the development of next generation of High Performance and Energy Efficient systems, such as for new Environmental Control Systems (ECS) to be incorporated in the Ultra High By-pass Ratio (UHBR) engine of future aircraft.
- To improve aircraft cabin air reducing the potentially contaminated bleed air.
Reduction of scrap
- In the case of CC, the tighter cooking control by the refrigeration of the mold and the selection of adequate coatings will lead to a reduction of scrap rate due to microshrinkage of around 60% and additional material for pre-machining of 30%.
- LMD, being an additive manufacturing technology, will allow to reduce both production time and waste generation, and thus, less energy consumption will be necessary. It is expected a reduction in material waste and scrap of >50% compared to conventional manufacturing routes like machining.
Reduction of dependence on critical raw materials
Cobalt is one of the 27 critical raw materials for the EU, being mainly used as battery chemicals (49%) and superalloys (18%). The Cobalt demand in EU is about nine times higher than the supply, so EU strongly depends on imports. Substitution of Cobalt with other more common metals will reduce EU’s demand on this critical raw material.
Reduction of potential hazadous materials
Cobalt has some hazardous properties. The wear of Cobalt alloy particles can end up in the cabin air, what supposes a potential health concern. The substitution of Cobalt by Nickel self-fluxing alloys together with the increase of the wear resistance will reduce the presence of debris in cabin air.
The work plan is divided into 7 WPs – 2cross-cutting WPs (dedicated
to Project Management and to Dissemination and Exploitation), and 5 technical WPs – with a duration of 24 months (from 1st January 2021 to 31st December 2022).
- WP1 is dedicated to the definition of the requirements and specifications for the sealing rings, study of the self-fluxing nickel alloys to be used and definition of the test plan.
- WP2 will address the manufacturing process study, including the obtaining of the best parameters to manufacture NiCrSiFeB alloys by both CC and LMD together with the use of advance data analytics methodologies.
- WP3 will be focused on the metallurgical and tribological characterization of the best candidates selected in the previous WP. Wear rate evolution of the selected Ni-alloys will be compared to Stellite 6.
- WP4 will be focused on environmental aspects. Thus, wear particles will be analysed and the toxicity of debris particles will be assessed. Additionally, the environmental impact and life cycle cost of the sealing rings obtained by CC and LMD will be obtained and compared to current product.
- After selecting the most promising Ni-alloy solutions for both processes, WP5 will address the manufacturing of the sealing rings and their final testing.
Project launched at Kick-off meeting
15 January 2021
The project was launched during the kick-off meeting that was held on-line, due to the pandemic, on the 15th of January 2021. All partners, the topic manager LIEBHERR and the Project officer, who represented the Clean Sky Joint Undertaking, participated in the meeting.
The participants shared a common vision of the project, including the objectives, the planning and the required activities to achieve the expected results. The working plan was set up and validated.
NEMARCO project is composed of 5 partners from 2 different countries (Spain and France), with complementary skills and experience, covering the whole project value chain. The partners are referent entities in their fields at European level and have collaborated together in previous projects.
LORTEK is the project coordinator. LORTEK and AZTERLAN will be focused on manufacturing, specifically the former on LMD and the later on CC, both for the process study as well as the manufacturing of the demonstration rings. CIDETEC and LTDS will deal with the metallurgical and tribological characterization, while CTME will address the toxicity assessment and the life cycle cost analysis. LORTEK will be responsible of exploitation and dissemination.