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WALL FRICTION MEASUREMENT

 

Measurement of wall friction is similar to measurement of shear­stresses, the only difference is that the powder shares on a wall sample.

For measuring of the static friction we need several repeading steps of shearing until the static friction gets to maximum. The dynamic friction value follows the static peak. Usualy the friction is measured starting with the lowest pressure and increasing the pressure for furter steps.

It is important to simulate the roughness of the surface of the plate. Differences can be many hundreds of percent. A wrong choice of roughness can lead big mistakes, such as collapse of silos.

The test palte for the measurement can be round or hexagonal.

 

 

 

 

EXAMPLE FOR EVALUATION OF RESULTS OF MEASUREMENT OF WALL FRICTION

 


EVALUATION REPORT WALL FRICTION
file name WF1a.wf
date03 May 2016
material VA
operator MB
client SHEAR-TEST
device shear-test.com ST200AUTO
shear cellST30.cel
note 

 

WALL FRICTION STRESSES
σw ◯Τw, m μm φw,m ◻Τw, s μs φw,s
[Pa] [Pa] deg [Pa] deg

4982 882 0.177 10.2 807 0.162 9.4
             
...            
             
24596 4078 0.166 9.6 3804 0.155 8.9

linear approximation of static friction Τm(σ) = σ * μs + adhesions
φs 9.4 deg angle of static friction
Τs = 71 Pa adhesion of static friction
Rs = 0.999 coefficient of correlation static friction

linear approximation of kinetic friction Τs(σ) = σ * μk + adhesionk
φk = 8.7 deg angle of kinetic friction
Τk = 0 Pa adhesion of kinetic friction
Rk = 0.999 coefficient of correlation kinetic friction

 

Measurements and evaluations of physical properties of powders and bulk solids yield locus