Dear sir

impact bad reduces spillage at loading point and perfect skirt rubber sealing can be obtained.

In case of impact idlers when material wight comes on belt belt at the centre of two impact idlers sags and space for spillage is created.between fixed skirt rubber and belt . In addition to abve impact idler rubber also compresses and alow spacing between belt and skirt rubber sealing at roller top

A R SINGH ■

Impact beds are one of two types of belt support systems. Impact beds, as their implies, are placed under the belt in the load zone. These beds prevent the belt sag often seen with standard idler spacing in the load zone. It is recommended the impact beds be used to help idlers work, not in place of islers in the load zone.

Impact beds prevent belt sag in the load zone from impacting material, but they also absorb energy to protect the belt from impact damage. They do this by having a slick layer against the belt, and an absorbing layer between the belt and the impact bar support.

Another form of belt support is a seal support cradle. This type of belt support is also used with idlers and in the load zone when the conveyed material impact is somewhat lighter.

CEMA has a new standard for impact beds that rate them at light, medium, and heavy duty.

For further in formation on how to apply belt support systems please see Chapter 6, page 60 of Foundations III. A copy of this book can be obtaine dby contacting Martin Engineering at 309-594-2384 or visiting our website site at www.martin-eng.com. ■

Ozbos

Under heavy impact forces the impact idlers do get damaged or knocked off from their positions.

The impact beds are more robust and can absorb higher dynamic loads without damage - this is the reason they are used.



jbwala ■

Hello Ozbos..

It is interesting to note that when I was called in to advise at a Platinum mine on loading points that were getting smashed and were damaging the belts, the mine was actually busy removing impact beds, as they reckoned that they were useless.

I revised the chutes for them to reduce the impact energy, and put in garland impact idlers with Rosta suspensions. This, in conjunction with the flexible Brelco key-skirt rubbers solved the problems, and the belts now have a reasonable life, measured in years instead of weeks.

Regards

LSL Tekpro ■

As with any product, belt support systems do gave limitations. Intstallation is also extermely critical. High belt speeds (over 700 FPM) coupled with high impacts are the most difficult to handle for belt support systems. Redesigning a load zone is certainly the best solution but not always the most economical. ■

Hi Ozbos,

Coming in a bit late but impact beds are absolutely no substitute or solution to poor transfer chute design. Before you decide what you need work out why you have a spillage problem. The benefits that are ascribed to impact beds ie maintenance of an even profile so that you can maintain a better skirt rubber to belt interface can be achieved with an idler system as well. Remember if the impact belt does not solve your spillage problem then where will the spillage go now - between the belt and the impact bed? If this happens you wear out the bottom cover of the belt. Also for high impact I have found impact beds more likely to lead to belt damage.

Col Benjamin ■

Is it not obvious, eliminate impact and you have no need for impact tables as Colin suggested. Via la no-impact chutes.

A hybrid designed skirt system is catching on we implemented in Palabora's underground mine in 2001( sic). We designed a skirt seal using a longitudinal UHMW rub rail under the skirt position to controll dust and special impact idler rolls that were mounted on a elastomerically supported frame to minimize large rock damaging impact forces.

THis was very successful. Unfortunately others attempted to copy it on larger systems, without doing their sums, and ran into difficulty.

Weigh the cost verses the benefit and you will find that proper chute, skirt and receiving idler engineering has no substitute even as replacements. ■

Sometimes a picture is not worth a thousand words.

In the 70's Trelleborg used to throw about a leaflet showing a tree trunk dropping upright onto a conveyor with impact bars below. This served to show how outrageous some loading equipment is rather than how good an impact sustainment system is.

Which is just an example covered by Mr Nordell's reply. ■

heres a few picts, i don't know why the image tags on one pict dosen't work. i like the direction this thread is going ,, pictures always make it better.i will upload a few pictures of the slide beds we build . we have several hundred units in the field with great results. ■

Dear Mr. Ozbos,

Earlier respondents opinion provides good information about the impact beds and impact idlers. While comparing performance, one needs to see the absorption of impact energy also. The impact energy is due to material velocity component perpendicular to the belt, and this energy creates reaction pressure / force between lump and the belt.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■