Gas turbines feature a set of discs, with spacers that create space between each pair of discs that carry the blades.
Spacer discs are generally made of Inconel 706 or alloyed steel, depending on where they’re located in the turbine. This web cast showcases the best machining practices and solutions for spacer discs of gas turbines.

If you have trouble viewing the video posted above, please watch on the Sandvik Coromant YouTube Page.

Video Transcription:

Hello, and welcome to our webinar about machining processes for a spacer discs for land-based gas turbines.

Gas turbines usually feature a set of discs, with spacers that create space between each pair of discs that carry the blades.

Spacer discs are generally made of Inconel 706 or alloyed steel, depending on where they’re located in the turbine. The blank typically weighs about 6,600 lbs, but after machining, the weight goes down to about 3,900 lbs.

This slide shows some of the typical features, operations and solutions for spacer-disc machining.

Most spacer-disc machining can be performed on a vertical turning lathe.

We’ve developed some unique tooling solutions, which you see here, to make some of the most difficult aspects of machining the turbine a lot easier.

Now we’ll review the steps of operation for machining spacer discs.

The first step of operation is rough turning of the outer diameter and the face. For this, we recommend a square insert because the 45-degree angle helps to thin out the chips and spread out wear on the cutting edge. This can greatly increase tool life by reducing the hammering effect from the chips. The tool also has our HP technology, which directs coolant through the nozzle and straight to the cutting zone.

The next operation involves generating the pockets in the face. We usually use a round insert such as an RCGX in a Sialon grade 6060. This type of insert offers strength and sturdiness.

We also have a process we call trochoidal turning that can be a very helpful technique when generating deep pockets.

We’ve developed a unique solution specifically for generating the radial grooves in the spacer-disc face. As you can see in the picture, this feature is one of most difficult to generate. For a proven method that offers the greatest efficiency and ease, use a long dampened SL blade, mounted on an SL adapter, and orient the insert at 90 degrees.

Another unique solution is used to rough the seal fin grooves. In this case we use our CoroCut 2 edged RO geometry insert with a blade that can cope with thin walls, and trochoidal turning. The same setup can be used for finishing the seal fin grooves.

Now we can finish turn the outer diameter and the faces. We use our new SF geometry and try to keep the depth of cut around 1/3 the size of the nose radius to get the best results. Also, the HP tool directs the coolant across the top face of the insert to help with chip control.

The same setup and process recommendations apply to finish turning of the inner diameter.

For drilling holes, the 17-millimeter CoroDrill 880 is a very effective tool.

The last step is to apply a CoroMill 327 with a chamfering insert to chamfer the front and back sides of the holes.

At this point, let’s touch on some of the tools that help create these unique machining solutions that dramatically reduce cycle time on spacer-disc production. On this slide you’ll see some of our Coromant Capto Machine Adapted Clamping Units for vertical lathes. These units are designed to bolt directly to the ram on a vertical turning lathe for easy installation. Different configurations offer flexibility, and the units provide access to the wide-ranging and highly effective Coromant Capto tooling line.

Here is a Coromant Capto C8-sized adapter with our SL 100 coupling on the front. SL stands for “Serration Lock” and the SL 100 uses serrations and bolts to attach to our assortment of SL 100 blades. Blades come in several configurations and can position inserts in different ways to machine a wide variety of component features.

Here is one of the blades that attaches to the SL 100 adapter from the previous slide. This particular blade holds a round RCGX insert at a right angle to the component’s centerline. It is extra long to reach inside a component and generate pockets. The round yellow piece you see in the model is a carbide slug that helps to prevent vibration.

This slide shows our WCMX grooving insert mounted in another dampened blade with a carbide slug. The WCMX insert was designed specifically for roughing out deep grooves on components for the power generation industry.

This concludes our Web Cast about spacer-disc production. Thanks for spending a few minutes with us. For more information, call 1-800-SANDVIK.