I'm happy to be told U'm wrong, but I don't believe bike chain lubricants are anywhere close to a mixed-regime, and are instead always in a boundary regime. For sure, suspension oils will be in mixed and hydrodynamic regimes, but chains are very very different as far as speeds are concerned.
For the Hersey number, the speed is the speed at which the pin is rotating against the roller. I think this should be somewhere on the order of 0.01m/s (this assumes the link is rotating at one full rotation/s)
The dynamic viscosity is a difficult parameter to estimate, especially when dealing with solid additives in lubes, but for the sake of argument, assume you are using WPLs 2.5wt suspension oil. The viscosity will be ~0.02Pa*s
With these two numbers, to enter the mixed regime (lambda=1.2) the load would need to be less than 0.001N/m. Now, I don't have the biggest legs out there, but even I am putting significantly more load onto the chain than that.
So my question is this, is the Hersey number even worth considering when thinking about chain lube, or are there far more important considerations to be accounted for?
Aug. 27, 2021, 7:55 a.m. - mvigers
I'm happy to be told U'm wrong, but I don't believe bike chain lubricants are anywhere close to a mixed-regime, and are instead always in a boundary regime. For sure, suspension oils will be in mixed and hydrodynamic regimes, but chains are very very different as far as speeds are concerned. For the Hersey number, the speed is the speed at which the pin is rotating against the roller. I think this should be somewhere on the order of 0.01m/s (this assumes the link is rotating at one full rotation/s) The dynamic viscosity is a difficult parameter to estimate, especially when dealing with solid additives in lubes, but for the sake of argument, assume you are using WPLs 2.5wt suspension oil. The viscosity will be ~0.02Pa*s With these two numbers, to enter the mixed regime (lambda=1.2) the load would need to be less than 0.001N/m. Now, I don't have the biggest legs out there, but even I am putting significantly more load onto the chain than that. So my question is this, is the Hersey number even worth considering when thinking about chain lube, or are there far more important considerations to be accounted for?