Re: Fines Control In Chutes
DEM and its derivatives can give you the formulae you seek.
The same question and answer has been offered many times in this forum. Discrete Element Method (DEM), Smooth Particle Hydrodynamics (SPH), Discrete Finite Element or Discrete Grain Breakage (DGB), and many similar applied mechanics procedures can and have been solved for granular flow physics in most applications.
Graunular flow physics is the study of contact mechanics, rheology, attraction and repulsion, agglomeration, from macro to ab-initio particle sizes for:
a) accoutability with particles of all sizes and shapes,
b) particle breakage interactions,
c) particle flotation in a turbulent gas or fluid multi-physics field,
d) particle-to wall and particle-to-particle interactions such as friction, cohesion, adhesion, magnetism, Van der Waal electrostatic influence, Einstonian attraction, et al.
e) particle shape variations
f) time based relaxation for elastic, viscoelastic, plastic, interactions
g) flow fields in, transfer chutes, with many types of storage devices, feeders, stockpiles, reclaim devices,
h) many industries from material handling, comminution, chemical building and mixing, from cosmetics, paints, medicines, mining et. al.
There are commercial codes that can do many of the noted physics. The codes should be able to render behavioral conditions as measured in laboratory tests and field measured behaviors. Millions of particles need to be rendered to define a flow field's physics to simulate observations. Give it a try. ■
Re: Fines Control In Chutes
I've always understood that a crash/stone/dead/whatever box was simply a ledge in the chute which became overlaid with material in such a manner as to separate the platework from an abrasive feed and so obviate wear. Surely then the issue is simplistic; with a box no wear, without a box as you were.
Regarding box separation the gravity of the situation 
is not to be overlooked. The material should not be allowed to re-accelerate beyond the velocity which you first arrested and also bear in mind the allowable exit fall velocity. ■
Fines Control in Chutes
In sponge iron plants fines generation is to be avoided to have better control in the process and also to avoid financial losses in the raw material handling system. We are having stone boxes inside the chute. Having more number of chutes may lead to jamming and less number of stone boxes may lead to fines generation and chute wear outs.
What should be the formala to know the distances between successive stone boxes - both to avoid fines generation and to protect the mother plate? ■