11.2.3. Check of the bearing high-speed

Check of the bearing high-speed is carried out by the value of the race diameter product, which turns round, and the rotational speed. This value is called the number Dn. For modern bearings Dn = (1,6... 2,4)10⁶ mm(r/min).

Number Dn must be as great as possible, because the bearing unit is more compact then. However, excessive increase of the number Dn results in increase in centrifugal loads on bearing rotated elements. It negatively influences its work capacity (load-bearing capacity).

11.2.4. Check of the bearing static load-bearing capacity

The essence of the check consists in the following. The greatest possible bearing radial load at operating conditions R_max should not exceed marginal load Q_st. It can cause a residual strain marginal level of the balls, rollers and races, estimated by value _res=d₀10^-4 (d₀ is a diameter of the balls or rollers, mm).

The requirement of sufficient static load-bearing capacity looks like

R_max < Q_st.

For the standard bearings Q_st is selected with the help of the reference books.

For the GTE support bearings the marginal load Q_st can be estimated with the help of the empirical formulas:

- for the ball bearings

- for the roller bearings

11.2.5. Definition of the necessary oil circulation through the bearing

It is carried out on the basis of a bearing thermal rating calculation, as a result of which the quantity of heat selected during friction (internal heat-evolution) and heat supplied to the bearing from an engine ardent parts is determined.

Necessary oil circulation is determined by heat balance – requirement of heat removal by oil flow from the bearing in such a quantity, that its elements temperature was within the boundaries permitted by requirement of material strength.

According to the statistical data, obtained for maintenance of GTE designs, the necessary oil circulation through the roller bearings located in engine’s “cold” zones makes 1...3 l/min, and through the roller bearings located in “ardent” zones, and ball bearings – 4...12 l/min. Oil is supplied to bearings with the help of spray injectors.

Questions for self-check

1. Explain the GTE rotor supports designation.

2. What are the elements of rotor support casing? What they intended for?

3. What are the elements of support bearing unit?

4. What is the bearing durability and safe life?

5. What is the bearing high-speed and static load-bearing capacity?

6. What requirement is made to the necessary oil circulation through the bearing?