PSI - Issue 82

Marko Katinić et al. / Procedia Structural Integrity 82 (2026) 220 – 226 M. Katinić, P. Konjatić/ Structural Integrity Procedia 00 (2026) 000–000

224

5

(

)(

)

( ! ! ! " " " " " " " " " " ! ! " ! ! # " ! ! " ! # )

!

!

(1)

#

=

$

The pressure p d for the achieved overlap of the connection is 76.89 MPa. The axial force F a that can be carried by the shrink fit connection is calculated using the following expression:

! # " ! " # $ ! µ = "

(2)

Assuming a friction factor of µ = 0.15, the axial force supported by the achieved overlap is 771 kN. Due to the rotation of the turbine rotor, the surface contact pressure pd decreases, and the bearing capacity of the axial force also decreases. However, since the maximum axial force that can occur is 300 kN, the shrink fit connection is considered safe for operation.

Fig. 4. New shrink-fitted thrust collar.

The contact pressure p d in the shrink fit joint generates radial and hoop stresses. The achieved overlap of the shaft thrust collar joint is usually between the minimum and maximum values. As previously mentioned, the achieved interference value is 0.2 mm and the stresses are calculated for this value. Table 1 shows the calculated hoop, radial and equivalent stress values for the shaft and collar diameters.

Table 1. Calculated stress values.

Inner shaft dia.

Outer shaft dia.

Inner collar dia.

Outer collar dia.

Hoop stress, MPa Radial stress, MPa

-201.46

-124.57 -76.89 108.87

102.46 -76.89 155.84

25.57

0

0

Equivalent stress, MPa

201.46

25.57

Along with the rotor repair, the sliding of the front bearing housing on the base plate surface was enhanced. Grooves were milled into the sliding surface of the bearing housing, into which graphite grease is injected, improving its anti friction properties (see Fig. 5). After the repair, the rotor was balanced and installed in the turbine. The turbine was commissioned at the end of June 1999. It has been operating with this rotor for over 25 years, accumulating more than 100,000 working hours. During overhauls, the rotor is regularly checked both dimensionally and using non-destructive methods.