Design estimate work done to find load carrying capacity and rate of load of a simple hydrostatics step bearing
Answers
Dry bearings :
These bearings are made of self lubricated solid lubricant materials. Bearings operate dry or with limited lubrication and experience solid to solid contact, which means relatively high friction compared to full fluid film bearings..
For low temperature application, following materials can be utilized.
• Polymers: Thermoplastics --> PTFE, nylon, acetal resin.
• Thermosetting --> Phenolics, polyesters, and polyimides.
Following four material parameters/properties play important role in choosing material for dry bearings.
• Maximum Temperature – Softening.
• PV limit– Heat generation, Wear rate.
• Maximum Pressure(P)
• Maximum velocity (V)
EX : Estimate wear of 10mm long Nylon bushing supporting a 10-mm diameter and 5 kg shaft running at 900 rpm.
Wear factors for polymeric bearings :
Velocity, V = Π * D * N/60 => V = 0.47124 m/s.
Pressure, p = W/(L * D) => 490500(N/m2).
Wear volume as per Archard`s equation
On substituting values of k for Nylon material
This value is too high. Wear can be reduced by appropriate filler in nylon with such material wear thickness.
h = (0.24/4)0.32 ≈ 0.2 mm it is acceptable.