Manufacturing technology of steam turbine blades

In the process of manufacturing blades, one of the main conditions is strict adherence to the production algorithm

There is a list of methods for processing products, the most popular of which at the moment are milling, planing or turning of products.

Machine turning of blades

The shape of the manufactured blades, cut with a milling cutter, is often selected in such a way that the outer and inner surfaces of the parts have the shape of a cylinder or cone. This condition makes it possible to turn the contours of the product with a single profile cutter. The longitudinal blades of the lower stages can also be turned with a milling cutter. Both the outer and inner profiles of such products have a complex structure and their turning is performed by profile cutters using specially selected templates.

The methods of manufacturing turbine blades by planing or turning using a template do not oblige the engineer to observe the contour radii along the height of the product, which is necessary in the case of the milling method. The contours of the product designed according to these methods are planned on the drawing by points and radii shifting from cut to cut. Here, the stated criteria for aerodynamic operating conditions are achieved.

Light-rolled profiles are used everywhere, implying the lowest steel costs. The manufacture of products in a light-rolled contour is more accessible than those turned with a cutter. The contours of the blades do not require lengthy additional turning due to the fact that the external structure has a high purity of turning and is carried out with a high level of accuracy.

The negative qualities of manufacturing working blades from a light-rolled profile are manifested in the comparatively low strength of the tail joints, which is why they are more often used for low-weight products. An additional disadvantage is the reduction of the fatigue limits, determined by the acting pressure and erosive destruction at the joints of the product and the intermediate body.

Casting of working blades

Accurate and high-strength shapes of working blades are also obtained by casting. The most common is casting using high pressure and using product models, casting in a shell and a chill mold, depending on the required dimensions.

For the production of blades using investment patterns, small-sized castings are prepared from alloys with fixed dimensions without subsequent additional mechanical processing. If it is necessary to adjust the surfaces and achieve maximum accuracy, grinding and subsequent polishing of the model is performed.

The manufacturing process includes several stages:

1. Manufacturing a model from steel or copper alloys, subsequently processed to maximum compliance with the specified dimensions.
2. Manufacturing a mold from light, non-refractory metal alloys.
3. Wax models of future parts are cast in smelted molds. Artificial wax substitutes, such as paraffin, are most often used.

Then the resulting model of the product is painted and covered with a thin layer of calcined quartz or corundum powder and dried for several hours. Then additional wax models are smelted with an exposure of 1.5-2 hours and calcination of the models at a temperature of 800-850C. After the molds are fully prepared, pouring is carried out. To fill the blade shape with molten metal as accurately as possible, press pressure or centrifugal force is used.

Material for manufacturing

Strip, rolled or stamped blanks are used in the production of turbine blades. In the production of products using strip steel, the metal utilization rate is low and ranges from 10% to 25%, and the remainder of the metal mass is converted into shavings. Products made from rolled and stamped steel have a higher coefficient and are used with the least effort when turning the product. Blade turning is performed using milling, planing and turning machines.

Quality standards for steam turbine blades

• Absence of external damage - cracks, chips on the product, traces of exposure to chemically active substances, significant corrosion damage.
• Compliance of product dimensions with those specified in the relevant regulatory documentation.
• Successful passage of vibration tests, resistance of the product to the influence of permissible deforming effects.

Current design and production methods make it possible to produce blades of various sizes and designs, both cylindrical in shape with dimensions from 15 to 20 mm, and complex, with a helical shape, up to 1000-1100 mm.