Re: Friction Coefficient Calculation
I don’t think so it is possible to link Wall friction with internal friction angle they are measured by separate tests. But if you find a solution it will save everybody loads of time especially if one uses Jenike shear cell to measure internal friction. ■
Re: Friction Coefficient Calculation
Dear Mr. Alex,
The friction coefficient between material and wall is a separate characteristic from material internal friction coefficient. For example if material is limestone then its internal friction coefficient could be around 0.6. Now, the friction coefficient between this material and steel wall or steel skirt plate could be say 0.42 for fairly even surface of steel without protruding edges (say flush and welded reasonably good welded steel surface would be of this type). However, if the steel surface is flush welded but of poor quality with reference to surface finish or it has protruding edges, bolt heads, rivets, etc. then the friction coefficient between material and the steel wall of the skirt plate could be 0.5. The above values are mentioned by making reference to DIN.
Regards,
Ishwar G Mulani.
Author of Book : Engineering Science and Application Design for Belt Conveyors.
Author of Book : Belt Feeder Design and Hopper Bin Silo
Advisor / Consultant for Bulk Material Handling System & Issues.
Email : parimul@pn2.vsnl.net.in
Tel.: 0091 (0)20 25882916 ■
Coefficient Of Friction
Sir,
Will it depend on the moisture content also????
can u tell me from where will i get the frictional coefficient values of limestone on steel plates in relation with moisture content..
It will be very useful in determining the discharge chute angles. ■
Re: Friction Coefficient Calculation
Yes moisture content will have an influence.
It is not advisable to use generic values for designing purposes. Wall friction angle varies from 15- 30 degrees for carbon – stainless steel. Best option is to test your materials on a wall friction tester. ■
Re: Friction Coefficient Calculation
Originally posted by Mantoo
Best option is to test your materials on a wall friction tester.
Exactly! ■
Re: Friction Coefficient Calculation
Addressing the original post, as I understand, Alex was seeking a relationship between friction angle and coefficient of friction.
We could consider tan (theta) = u, hence u = atan (theta) (consider f=uN, rearranging for u =f/F or shear stress / normal stress as Alex suggested earlier), where theta is the angle of the graph of f (shear stress) vrs N (normal stress).
Suggest the K is to account for head, or lack there of, (note that the relationship is not really hydrostatic is often assumed, and the K accounts for this).
I am not aware of a relationship between internal friction and wall friction.
Material moisture may affect the properties. There is some guidance in various sources (AS 3774 for one) or you could get someone like TUNRA to do a test of your material / wall liner.
Regards,
Lyle ■
Re: Friction Coefficient Calculation
Stumbled across my TUNRA notes, they use sin of theta for their Apron Feeder calculations, I guess this has something to do with the failure plane (others may know). The K factor appears to be a shape factor.
The understerding I presented earlier was based on my understanding of TUNRAs chute notes.
Regards,
Lyle ■
Re: Friction Coefficient Calculation
I don't know if this is what you want, but I have some notes copied from a publication (whose reference I've lost) which states :
Flank angles for mass flow -
Pyramid Bunker 50 degrees + 1.2*WFA
Conical Bunker 45 degrees + 1.2*WFA
V/Wedge Bunker 35 degrees + 1.2*WFA
(WFA = Wall Friction Angle in degrees)
NOTE, I make no comment on their accuracy!! ■
Re: Friction Coefficient Calculation
Eurocode ENV 1991 and AS3774 also have graphs relating hopper half angle and wall friction for mass flow and core flow. ■
Friction Coefficient Calculation
Dear All
I was wondering if it is possible to obtain the friction coefficient (or equivalent friction coefficient) merely from knowing the wall friction angle.
By definition
Tan (Friction Angle) = Shear Stress / Normal Stress
how could I work with this and establish a formulae to give me the friction coefficient?
I have found a formulae which states
Equivalent Friction Coefficient = K * sin (Effective Angle of Internal Friction)
where K is an empiracle constant of 0.8
thanks in advance! ■