Force reactions of a cutting rotor

[jthorson]

I just joined this site and I was hoping some of you guys could help me out.

I'm working on conducting a bearing analysis on an attachment that mounts to an excavator that cuts off the top of a tree and then mulches up the standing trunk by a large spinning rotor with knives mounted on the circumference of the rotor, something similar to the picture I have attached. I'm working on putting together a loading duty cycle for the application but I'm struggling to come up with forces exerted on the cutting rotor when it is engaging the tree.

The cutting rotor weights 845 lbs, has a moment of inertia of 187.49 lb-ft^2, cutting diameter of Ø21.0 inches, and spins at various rpms (1000-1700rpm) pending on the load and hydraulic flow to the hydraulic motor that is driving this rotor.

I have a hydraulic pressure trace of this product while in action that plots the inlet line hydraulic pressure, return line hydraulic pressure, and hydraulic flow plotted versus time.

I think the only way I can determine the loads exerted on the cutting rotor while cutting is using the angular momentum formula which is:

(torque)x(time)=(moment of inertia)x(angular velocity final-angular velocity initial)

From the hydraulic pressure trace I can determine the rotor rpm's at various points of time from the hydraulic flow recording and time intervals in which the rotor speeds up or down, and using the above angular momentum formula, calculate the torque exerted on the rotor while cutting. From the torque exerted on the rotor while cutting, I can then use the radius of the cutting diameter to calculate the force on the rotor.

Does it sound like I'm on the right path? Thanks for any help you can give me

 

[hydtools]

I like the impulse momentum approach. But you have the torque profile by knowing the motor delta P profile vs. time. Knowing the motor displacement per rev, you can calculate the torque. Torque = disp per rev x deltaP / 2π.

Ted

 

[chicopee]

To add to Hydtools you also have the moment along the boom with possible jerks that should accounted in the bearing analysis. You probably should do research on hydraulic hammers/ breakers which are fitted on booms for the purpose of demolishing concrete pavement, piers etc...