Originally Posted by MabriF

I have got the following situation regarding a troughed belt:

+1430 tph (metric)

+Iron ore (2400 t/m3)

+Maximum lump size: big: 300-350mm, however material is obtained by a jaw crusher with 7" CSS.

Given the fact that the tph is low,

Everything is matter of scale, to me 1430 tph is BIG ■

First, don't believe everything you read or hear. Do believe in experience and limitations of the rules.

Second, CEMA has been rewritten many times by different authors from different companies. Originally, CEMA was the work of three at Hewitt-Robins. They developed an in-house design standard/guide in 1953. Some of the criteria was not fully applied or described in the original "Blue Book" circa 1966. Since then, somethings get passed down and reprinted without anyone knowing the origins.

The bit of fact on the lumps size verses belt width had many caveats. First, it is a lump for all 3-Dimensions. Second, it assumes the belt is already fully charged such that the lump must be contained. Third, there is no orientation assumed nor change in crossection with the lump applied. As it has been shown, a 48" belt can carry lumps as large as 36" in the axial dimension, and is at the owners risk. If you take the large rocks into account in the bulk density calculation, you will usually find room for larger rocks. Problem with this criteria is pluggage. The rock can bridge the skirt or chute opening. Thus, the largest dimension must pass through the skirt opening or as CEMA says 2/3(w) where w = width of belt. Thus 48 inch belt might carry 32" rock in one dimension and smaller in other dimensions. The odd ocassional rock might pass provided the chute has no obstructions smaller than 32".

Tarbela dam in Pakistan, had 60" belt carrying close to 48" rock, in one dimension. The rocks were so large they mashed the idler roller shells. ■

A point not addressed in the CEMA criteria is the need for the lump not to bridge across the center roll. Thus, ~0.371(w) is yet another lump size limitation thought of by the original authors ala Tarbela (see references from old PHB publications)

Another serious problem arises with apron feeders. The pans discretize the discharge, as the pans mover over the head sprocket, with large flow and voids.

The Canadian oil sands see this problem today with slug-surge flow, large ice blocks, and binding cohesive ore. New methods are developed to handle these impediments using advance DEM methods and clear thinking to spread the consolidated into a uniform flow stream. Probably should pattent it. Some sod will likely come along and claim it. ■

Originally Posted by MabriF

Dear sirs,

This is my first message on this forum. Hello to everyone!

I have got the following situation regarding a troughed belt:

+1430 tph (metric)

+Iron ore (2400 t/m3)

+Maximum lump size: big: 300-350mm, however material is obtained by a jaw crusher with 7" CSS.

Given the fact that the tph is low, I have used the CEMA handbook to obtain the minimum belt width using the interpolation shown in chapter 4. The result is to use a very wide belt (e.g 72"), which for 1430 tph seems to be too much. Even more, is seems to be too much when compared to some existent 48" belts carrying aproximately the same TPH and material.

The question is: Are there aditional criteria or technological devices to handle this situation in order to not to use an excesively wide belt?

I have been trying to consider that the jaw crusher in fact yields some kind of sheet-shaped lumps instead of spherical or cubical ones, but I am not certain.

I would be grateful if someone can comment something on this.

Thanks in advance.

Mauricio Fuentes F.

JRI Ingeniera (Chile)

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another method of breakage is the belt feeder breaker of which there are at least five manufacturers of note in no particular order being;

WR STAMLER

LONG AIRDOX

METSO

MCLANAHAN

pennsylvanis crusher

All five have an international presence in the market place as well with excellent parts distribution.

Belt feeder breakers are available in many configurations for primary breakage, secondar breakage prior to entering the screening and secondary crushing-tertiary phase.

Between the five they have been in the breakage business with a combined amount of experience of almost two hundred years of experience in various company forms.

My expreince with WR STAMLER involved 22 years of underground mining with primary breakage and secondary breakage prior to entering the tertiary phase of crushing and screening.

The secondary breaker roll was a necessary unit as we had to deal with sedimentary shale that passed under the minus six inch breaker setting in the primary breaker at the mine face.

The secondary breaker roll breaks all over size(being rock salt-Halite and sedimentary shale)everything prior to entering the primary screen of the underground plant from the surge pile.

The WR STAMLER breaker roll uses a simple breakage principal using welded bit holders carrying large bits to break the ore by concentrating the rotating breaking force upon one point of the

rock entering the pick assembly and breaking it or pushing it back to be carried back into the breaker roll to be broken until it is finally broken and passes under the breaker roll assembly to the

conveyor carrying away to the belt conveyor.

A secondary breaker of any manufacure can reduce the ore size to below 2 inches after the jaw crusher and then to the belt conveyor.

An open chute drop gravity feed under a jaw crusher would entail the use of a double roll crusher assembly to break the ore with (twin active rolls-driven with a gear drive) to its final size prior to the exiting belt conveyor.

The installation of a secondary breaker would require a shut down period to remove the structure under the jaw crusher and install the breaker under or near the jaw crusher.

The breaker roll should be larger than the jaw crusher outfeed and the chutes exiting the breaker hopper assembly can be narrowed after the breaker roll as the ore is of course smaller in size. ■