Composite impeller of a centrifugal compressor

The impeller is the most loaded element of the centrifugal compressor rotor. In the impeller mounted on the rotor shaft with tension, when the wheel rotates at a high rotational speed under the action of centrifugal forces, large internal stresses arise. In addition, the impeller is exposed to pressure, temperature, aggressive working environment, as well as vibration. To ensure reliable operation of the compressor, the impeller must have sufficient fatigue strength, corrosion and erosion resistance, as well as a perfect flow part to obtain high compressor efficiency.

TRIZ specialists have developed a composite impeller design that meets such requirements as:

• -high efficiency;
• -the possibility of choosing the material according to the conditions of use;
• -technology;
• -construction without using the welding-soldering method;
• -reduction of the volume of mechanical and thermal treatments;
• -cost reduction.

The composite impeller consists of three parts: the main disk with milled blades and the covering ring element 1, disk 2 and neck 3. The working wheel with an outer diameter of D₂ = 397 mm and an operating frequency of 10850 rpm was selected as a prototype. The components of the wheel are made of alloyed corrosion-resistant steel 34CrNi3Mo, yield strength of the material σ_0.2 = 800 MPa.

Parts of composite impeller

Disc 2 and neck 3 are connected to the annular covering element of the integrally milled main disc 1 by means of a fit with tension. The cylindrical surfaces of the constituent parts of the wheel are divided into two belts: inner 4 and outer 5. The tension is provided by the outer belt 5.

Neck of the composite impeller

Such a constructive implementation allows:

• 1) perform milling of the main disk with blades with a cover ring element from a single workpiece;

• 2) use non-weldable materials;

• 3) to reduce the centrifugal load acting on the main disk and blades, due to the reduction of the mass of the integrally milled main disk and the elastic connection of the tension of the component parts 2 and 3 with the latter (centrifugal force acts on each part separately according to its mass);

• 4) to ensure the pressing of component parts 2 and 3 to the blades of the main disk due to landing with tension on the outer belts 5;

• 5) eliminate the slippage of component parts 2 and 3 on the seats, due to the lack of transmission of torque by the latter;

• 6) to provide compensation for the displacement of the center of mass of the main disk with blades by the force of landing with the tension of the disk and neck, which allows to reduce the deflection of the main disk in the direction of injection during the operation of the impeller;

• 7) eliminate the main stress concentrator at the joints of the neck and blades due to the lack of a rigid connection (soldering, welding, milling) between the elements;

• 8) reduce the level of tension in the connection points of the main disk with the blades by reducing the centrifugal force acting on the main disk;

• 9) exclude deformation of channels and covering discs.

After the manufacturing of the component parts, assembly of the impeller, static and dynamic balancing, tests were carried out at working revolutions with simulation of the landing of the impeller on the rotor with tension.

One-piece milled main disc with blades and cover ring element

Composite impeller

The impeller in the housing of the stand for overclocking