🔍 Key Concepts

• Behavior of a journal bearing as speed increases (rest, starting, accelerating, normal running) • How the oil wedge (hydrodynamic film) supports the shaft and shifts the journal away from the load • Relationship between journal position, clearance, and the amount of metal-to-metal contact

💭 Think About

• Look at Figure C: compared with the other figures, is the journal closer to the bearing shell in one area or more nearly centered all around? What does that tell you about the thickness of the oil film? • Under a steady vertical load (weight of the shaft), when would you expect the journal to sit almost directly at the bottom of the bearing, and when would you expect it to be lifted up and slightly offset by the oil wedge? • Think about the moment when the shaft is just starting to turn versus when it has built up full hydrodynamic pressure: in which case is the journal most squeezed to one side, and in which case is it better supported and more evenly separated from the bearing?

✅ Before You Answer

• Compare how uniform the clearance is between journal and bearing in all four sketches; more uniform clearance usually means more stable, fully developed lubrication. • Note the direction of rotation arrow and where the smallest clearance (tightest gap) is located relative to the direction of rotation and the vertical load. • Decide in which operating condition there is likely to be the thickest, most complete oil film around the journal, and match that to the figure that shows the journal most nearly centered.