Dear Sir:

As Mr. Blakely points out, more information is needed. Rock boxes in succesion are a very effective way to control wear because the material builds up avoiding the need to install liners on the area covered by the buildup. However, the design could be complicated. The boxes plus the build up reduce the crossflow area of the chute and possible backflows could occur if high flow rates are to be expected. In addition to that, the angle of buildup would depend on the particular characteristics of the ore you process such as the particle size and the percentage of clay present.

Boxes too far appart could leave portions of the chute unprotected. Boxes too close together could prove to be more expensive than lining the whole chute (it greatly depends on the geometry).

Regards, ■

We use step chutes (rock boxes) all the time. We use them with furnace coke, cinter, ore, slag, clinker etc.. Can't use where there are alot of fines present or high moisture. We use them with the clinker that is high in fines but has almost no moisture. For furnace coke we found that lining our chutes with Wearmax was a better solution lasting 5-10x longer than stainless, rockboxes slowed down the material too much even on a steep incline. ■

In its ultimate form what you are describing is the Weba chute. They do work well in some applications but they also require rebuilds. The frequency depends on the ore, with -150mm iron ore my guess is every 12 months. If you want to avoid such re-builds but use the same consept to control the material speed then you have to have your trajectoiries done accurately, there must be no cohesive material (eg wet fines) to consider and you basically have each step set up as a mini autogeneous rock box.

The concepts have merit but also have their downsides as far as expense in building plus life cycle costs. Material flow control can be very good.

Regards

Col Benjamin

Gulf Conveyor Systems Pty Ltd ■

At Dos Santos International we had the pleasure of selling the first WEBA chute in North America, a cascade type. The cascade design uses closely spaced internal shelves, or terraces, that fill with the transferred material. In a short time the material compacts between the shelves and serves as the wear surface.

The Weba chute, installed in the USA Gulf Coast handles coal at very high volumetric rates, to 9000 t/h. The material varied from dry to wet, depending on the conditions at the open reclaim yard or at the bottom of the barges that are continuously unloaded. There is no shortage of fines. This transfer is very successful.

Joe Dos Santos ■

Dear Sir,

I did linerless chute in coke handling system. I did stone box system for all the chutes, coke being very abrasive material.

Regards.

A.Banerjee ■

Mr. Banerjee,

I too had used rock box transfers to reduce wear. A WEBA Cascade chute is much more sophisticated in controlling the material flow through the chute so that the material will neither speed up nor slow down excessively. The terraces are closely spaced and, when packed, the chute behaves like a rough lined chute. The shelves have provision for initial field adjustment. The material flow is so well controlled onto the outgoing belt that typical transfers are without skirts.

Joe Dos santos ■