Erosion of the strip seal slots in the NGV segments of low pressure turbines (LPT)

Industria de Turbo Propulsores S.A. (ITP) trusts in the power of 12 die sinking EDM machines to erode the strip seal slots in the NGV segments of low-pressure turbines.

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.

• Company: Industria de Turbo Propulsores S.A. (ITP)

• Address: Headquarters: Zamudio – Bizkaia – Spain. The ITP group has 17 centres located in Europe, America and Asia.

• Employees: 3.000

• Activity: ITP is a leader in engineering, research and development, manufacturing and casting, and the assembly and testing of aeronautical engines and gas turbines. ITP is the official maintenance service provider for most of the current aircraft engine manufacturers in the world. Sener Aeronáutica (53.12%) and Rolls Royce Aviation (46.87%) are shareholders in the ITP Group.

• Customers: Major manufacturers in the aeronautical sector (Rolls Royce, Honeywell, Pratt & Whitney, Eurojet …)

• Equipment: Die sinking EDM equipment for manufacturing NGVs at the production plant in Zamudio (Spain): 12 ONA die-sinking EDM machines.

An NGV segment. The turbines consist of several stages of NGVs and blades. Each stage of NGVs is made up of between 18 and 38 NGV segments.

Detail of the slots (strip seal slots) machined by EDM in an NGV segment.

ITP has exclusively designed and manufactured the low pressure turbine for the Rolls Royce Trent 900 engine used in the Airbus A380, which is the world’s largest passenger aircraft, and the Trent 1000 that is used in the Boeing 787 Dreamliner.