EROSION OF THE STRIP SEAL SLOTS IN THE NGV SEGMENTS OF LOW PRESSURE TURBINES (LPT)
The initials NGV stand for ‘Nozzle Guide Vane’. Its purpose is to set up and redirect the flow of gas so that it strikes the moving blades in the best possible conditions for work to take place. Low pressure turbines have several stages of NGVs and blades. Each set of NGVs consists of between 18 and 38 NGV segments which are mounted in the engine in rings. To maintain the seal between the different segments, the lateral faces of the segments (wedge faces) have slots (strip seal slots) where strips can be inserted to produce a labyrinth seal. These strip seal slots are machined using EDM.
Erosion de las strip seal slots:
- The strip seal slots have different shapes and depths depending on the stage where they are located, but they can essentially be summarised in the following table:
- Component material: nickel based alloys.
- Depth: from 3.50 to 5.50 mm.
- Width: 0.74 +/- 0.10 mm.
- Cross section: from 40 to 80 mm2.
- Other: high precision requirements in the bottom radius.
- Electrode material: ultra-fine graphite.