Impact nests are dependent on the loading severity. Any height difference is determined by the track discrepancies plus the passing roller clearances. Roller diameter is rather well known and track discrepancies should be small even allowing for eventual track settlement. In might be possible to replace the idlers in the nest with very shallow low-fric panels. I've never tried this. Maybe others can advise.

Mis-tracking is not the result of wind, rather to the contrary, but to the residual yawing between the rails and the main machine, maybe under wind. When the exigent rollers are loaded there is an overload due to the increased downstream burden length. This is the only topic of concern and easily remedied. ■

Dear all,

In our reclaimer , I removed all the impact table rollers. Extended the impact table receiving chute up to the main conveyor by an inclined chute towards the direction of the chute. Ensured that the material falls at the centre of main conveyor with very less impact. We are not facing any problem.

Thanks & many regards,

S.Ganesh ■

Impact tables can be dispensed with if the loading and material allow. Perhaps their origins were in high capacity operations and gained almost universal acceptance. I went along with the trend because it was routinely presented to me although I often privately questioned the necessity. It was easier to stand the cost, to the client, rather than risk multiple roller failures. The travel through the stockyard needs analysis and this can only be done after some considerable time. If the travel is over long distances which are consistently spaced then an impact nest might not be needed but if the machine often works repeatedly over short lengths an impact nest would be a necessity. For the cost of dozen idlers added to the full reclaim inventory it hardly seems important. Worrying about the life and geometry of a trailing impact roller seems even more trivial.

There is another situation where multiple machines work on the same belt. If impact nests are used disturbances will be imparted to downstream feeding points/impact nests which may/probably would demand a wider belt throughout. Fascinating stuff, isn't it just? ■

1.4 is too large a difference when the impact idlers are about 133mm. Use garlands. If an impact nest has been specified the easiest answer is compliance without further concern. ■

Dear Mr. Nimra,

Our reclaimer capacity is 1000 tph. We did based on our experience only.

Thanks and regards, ■

Yet again, some fundamental issues arise. It's like a breath of fresh air.

Mr Ganesh is probably talking about dispensing with the impact nest on a reasonably shortish belt. Because...referring to a recent/ongoing thread it is, should be, a preference that idler pitches can be progressively staggered along the belt path. Travelling trippers kick that idea into touch straight way. Accepting that and moving on: can we say that if an idler will withstand the loading from a correctly designed chute for 1000th^-1 of a given material then surely a correctly designed chute will enable, parametrically speaking, allow 3000th^-1 to also not require an impact nest? I started my conveying life in South Africa with very hard reef, worse than granite, and I never came across these fancy impact nests. When I returned to the UK all the Limey's were talking about impact nests for, can you believe, coal. Because I needed a job I went along but never really accepted the idea. Mr Ganesh has gone back to the roots of the situation. Elaborating:

So, spreading the wear over more idlers is no worse, better, than accepting concentrated intensified wear, fiscally or physically.

OPEX wise it doesn't matter and CAPEX wise the impact nests become a waste: expect that they propose a greater risk from spillage.

So, impact nests are a fallacy which implied that unionised workers could be convinced that the devil they know is better than the devil they don't know. The devil is still there, and as the Germans acknowledge, is hiding in the detail. Somebody thought impact nests were a good idea: it seemed reasonable. On later analysis it isn't but they are there to be replaced, or not, as any reader decides. Good design makes the devil smaller.

Another way to skin the cat:

Either way impact idler nests are for the bin! ■

Hello,

Linear travel stacker-reclaimer or reclaimer machine have to feed reclaimed material on to yard conveyor which passes through reclaiming machine. For this, there is a feed table, as an integral part of such mobile machine. The machine is moving on rail track. The feed table comprises of trough impact idlers plus troughing idlers. These idlers supporting frame is also of trough shape, just behind the idlers (instead of below the idlers). This arrangement enables to restrict belt lift just equal to impact idlers diameter + Clearance say 250 mm, etc. above the idlers of yard conveyor. So the belt is in trough shape on yard conveyor and also of the same troughing shape on feed table. The belt concave curvature is non-supported (occurring on its own).

As for the convex curve (rather hump) at table ends, one can have graded level difference for 1 or 2 idlers at belt entry and exit points. This can increase the height of feed table some what. Refer S/R manufacturers for specific information (if they happen to be supplier of the project).

Ishwar G. Mulani

Author of Book: ‘Engineering Science And Application Design For Belt Conveyors’. Conveyor design basis ISO (thereby book is helpful to design conveyors as per national standards of most of the countries across world). New print Nov., 2012.

Author of Book: ‘Belt Feeder Design And Hopper Bin Silo’

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India. Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■