Turbomachine shaft and journal bearing assembly
A turbomachine comprising a turbomachine shaft for rotation about an axis and for supporting a turbine wheel at one end of the turbomachine shaft; and a bearing housing having a wall defining a bore in which the turbomachine shaft is received with a substantially annular clearance, the turbomachine shaft being supported for rotation in the bore by at least one journal bearing located within the annular clearance. A surface of the turbomachine shaft which radially underlies the or each journal bearing has a surface roughness (Ra) of less than 0.15 microns and the or each journal bearing comprises a bronze alloy incorporating bismuth in an amount of up to around 6 wt %.
1. A turbomachine comprising:
a turbomachine shaft for rotation about an axis and for supporting a turbine wheel at one end of the turbomachine shaft; and
a bearing housing defining a bore in which the turbomachine shaft is received with a substantially annular clearance, the turbomachine shaft being supported for rotation in the bore by at least one journal bearing located within the annular clearance;
wherein a surface of the turbomachine shaft which radially underlies the at least one journal bearing has a surface roughness (Ra) of less than 0.15 microns and the at least one journal bearing comprises a bronze alloy incorporating bismuth in an amount of at least 1 wt % and up to 4 wt %.
2. A turbomachine according to claim 1 , wherein the surface of the turbomachine shaft which radially underlies the at least one journal bearing has a surface roughness (Ra) of at least 0.02 microns.
3. A turbomachine according to claim 1 , wherein the surface of the turbomachine shaft which radially underlies the at least one journal bearing has a surface roughness (Ra) of 0.06 to 0.08 microns.
4. A turbomachine according to claim 1 , wherein the bronze alloy incorporates 2.0 to 3.9 wt % bismuth.
5. A turbomachine according to claim 1 , wherein the bronze alloy incorporates 2.7 to 3.7 wt % bismuth.
6. A turbomachine according to claim 1 , wherein the bronze alloy incorporates at least 80 wt % copper.
7. A turbomachine according to claim 1 , wherein the bronze alloy incorporates 84 to 92 wt % copper.
8. A turbomachine according to claim 1 , wherein the bronze alloy incorporates at least 5 wt % tin.
9. A turbomachine according to claim 1 , wherein the bronze alloy incorporates 9 to 11 wt % tin.
10. A shaft and journal bearing assembly comprising:
a shaft for rotation about an axis; and
at least one journal bearing to be mounted on the shaft;
wherein a surface of the shaft which will radially underlies the at least one journal bearing when mounted on the shaft has a surface roughness (Ra) of less than 0.15 microns and the at least one journal bearing comprises a bronze alloy incorporating bismuth in an amount of at least 1 wt % and up to 4%.
11. A shaft and journal bearing assembly according to claim 8 , wherein the surface of the shaft which radially underlies the at least one journal bearing has a surface roughness (Ra) of at least 0.02 microns.