Force of rotating blade needed to shear a material

[LeviV]

I need to calculate the force needed to shear a material with a device consisting of blades attached to the outer diameter of a rotating shaft. This is what I have tried but the result I am getting gives very high torque and power values so I'm forced to select a massive motor to power a fairly little device, which seems like it should not be the case.

Shear area A: 0.0002m^2 (2cm x 1cm)
Material tensile strength tau: 241MPa
Cutter radius r: 0.12m
rpm N: 1500 rpm (157 rad/sec)

F_tensile = tau*A = 48200N
F_shear = F_tensile*0.6 = 28920N (approximately)
Torque = F_shear*r = 3470Nm
Power = Torque*N = 545100W

I would like to take the rpm of the machine, angle of the cutting blade, sharpness of the blade, etc into account to lower the torque and power required because it seems to me that these parameters would affect the force needed for shear. Is there a way to do this?

Any help would be appreciated.

Thanks,

 

[BrianPetersen]

Can't help with the specifics, but this is what flywheels are for.

 

[IRstuff]

Sounds like a really large blender of some sort. If so, it seems like you're ignoring the fact that the material is not fixed, i.e., when the blade hits the material, the material moves away from the blade. One thing that modern blenders seem to have evolved to are blunt blades, because the blades don't need to be maintained for sharpness, and the basic objective is to break things into tiny pieces. Whether the tiny pieces are achieved by classical mincing, or brute force smashing, machts nichts for the end product.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com:

http://www.engineering.com/AskForum/aff/32.aspx

 

[IRstuff]

One other thing, modern blenders only have a radius of about and inch and a half, which allows for much higher speeds, and the rest is accomplished by the solid/fluid dynamics design of the container and how the mixture is put together, to ensure that the material stays in contact with the blades and circulates enough to assure complete pulverization.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com:

http://www.engineering.com/AskForum/aff/32.aspx

 

[LeviV]

Thanks guys, yes you're right, it's basically a large blender, are there any simple techniques to take into account that the material is not fixed? My design ensures the material will for the most part be in contact with the blades as there is a fairly cutting volume, just a larger diameter shaft/blade.

 

[LeviV]

*Fairly small cutting volume

 

[desertfox]

try this link, it gives the force for cutting from which I guess you can work backward for the torque.

https://books.google.co.uk/books?id...lculation force for a rotary shearing&f=false

 

[LeviV]

Thanks, everyone, I ended up using the shearing with rotary cutters formula in desertfox's link.

 

[desertfox]

Hi

Your welcome