In this web cast, we look at the unique tooling solutions required to machine gas and steam turbine casings. Learn how to manage common problems associated with internal groove milling, large-hole rough and finish boring, and inner diameter groove finishing.

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VIDEO TRANSCRIPTION:

Hello, and welcome to our webcast that covers some of the machining processes for land-based gas and steam turbine casings.

Turbine casings require several machining operations. This presentation focuses on the operations that take the longest and often come with challenges, including internal groove milling, large-hole rough and finish boring, and inner-diameter groove generation.

Initial operations normally occur with the casing separated in two halves. This makes the machined features more accessible and allows the ram or quill of the machine to extend for the inner-diameter work. Semi-roughing and finishing operations often occur with the halves put together.

The first operation is rough milling of the internal grooves. Usually, this operation employs large-diameter side and face mills like the one on this slide. Turn-milling is an alternative concept that can save time and improve the security of the process.

Here we have a series of round insert cutters from our CoroMill 200 line. These cutters perform turn-milling operations, and are ideal for generating rough-form grooves.

This slide shows an example of the cutting results possible with a 75-millimeter diameter, five-tooth cutter for rough groove cutting.

While acquiring a variety of round insert cutters requires a higher initial investment compared to side and face cutters, the advantages with round cutters are significant. Round cutters can provide reduced cycle times, lower long-term tooling costs (thanks to longer tool life), better stability and security, easier tool handling, quicker insert indexing and changing and the elimination of presetting.

It is, however, important to keep in mind that round insert cutters result in a slightly concave surface, and are therefore best for roughing operations.

The next step in machining turbine castings is rough- and fine-boring operations. This image shows how big these parts can be relative to the size of a person.

Our CoroBore 820 XL—a large-diameter twin-bore platform—is ideal for rough boring operations. Made with aerospace-grade aluminum, the system is rigid, corrosion- and chip-resistant, flexible and light enough for easy handling.

For fine boring, we recommend the CoroBore 826 XL. This system features a unique dial-adjustment system that allows for easy adjustment for different tooling diameters. The system’s counterweight provides balanced, stable machining.

After the two halves of the turbine are mounted together, grooving and turning operations bring accessibility challenges.

The inner-diameter grooves of the turbine casing range in shape, depth and width.  Some of the deep and narrow grooves might require a long dampened blade like the one shown here, which features round carbide slugs for improved stability. Our SL 70 blades feature HP nozzles that direct the coolant in a tight stream toward the cutting zone to help break chips for better cutting performance.

This example shows how our Capto adapters can orient inserts at different angles to make challenging inner-diameter cutting operations easier and more effective.

The L-shaped inserts and blades from our CoroCut line can help when machining challenging forms, with customized modifications available.

This clip shows a process called “trochoidal grooving”—ideal for creating a recessed groove. It uses lower cutting forces and produces lighter and thinner chips, making it a good alternative to straight plunging.

Finally, finishing operations require turning tools like those seen on this slide. Our SL 70 couplings offer superior flexibility for turning and grooving operations. CoroTurn HP tooling combines with high-pressure coolant for ideal chip-breaking capability.

This concludes our webcast about turbine casing operations. Thanks for spending a few minutes with us. For more information, call 1-800-SANDVIK.