Like all equipment used in materials handling the choices are dictated by the application.

Having logs impact on idler rolls is not a good idea. Neither belt nor rolls would last very long.

Similarly having large crushed rock fall onto impact beds would result in the belt getting cut to shreds.

At the other end of the scale if the material is light a fluffy there is no need for either.

What kind of impact bed were you contemplating? Fixed rows, rubber mounted etc… ■

Kayem,

One function of impact bars is to maintain the skirt seal with the belt during heavy impact between skirts that would otherwise force an opening between idler spacing’s. I do not know about logs but have reasonable knowledge about large rocks.

We and others have developed special impact beds placed longitudinal/parallel to the belt axis just/only under the skirts to maintain free in-plane motion of the belt during heavy rock impacts, without allowing the belt plane to move/dilate away from under the skirt seal. The belt is supported by impact rolls between skirts. Special spring dampened beds are engineered to support the impact idler and impact bar kinetic energy forces according the rock size and drop distance in concert with the idler roll rubber configuration.

This system was successfully commissioned at the Palabora (RSA) underground block cave mining expansion project. The impact table was/is subjected to dire (+1000mm) primary jaw crusher rocks. To my knowledge is has been used now for many years since its installation. ■

Impact bars do serve to minimize critical lateral tensile tearing of the rubber between steel cords during extreme large object impacts. Transverse deflection is minimized that would otherwise occur with idler rolls.

This is the case, with frozen lumps, at the Oil Sands in Canada.

However, the belt cover must take added punishment of abrasive shear action between belt and impact bar during this action. This shear work is amplified by foreign small hard particle materials caught in this intense zone of work. ■

Lyle,

For really big lumps, there is a fair amount published years ago (late 1960's?) about Tarbela Dam, I believe, in Pakistan. The conveyor system handled larger lumps. The conveyor was designed by PWH of Bad Oeynhausen, then in West Germany. PWH is now Krupp.

There were many photos of this very big material handling system. The large lumps destroyed the idler barrels with the huge impact. PWH made PR publications of this system with its record breaking dam ballast haulage. Some lumps were up to 1600mm and weighed close to a ton in the photos. I am sure Krupp has publications of this system. I believe they hauled river run rock.

The Russians had designed special rail/belt carts for even bigger lumps.

Japan (Bando, I believe) handled the world's largest lumps on a special crusher feed system from a rail(?) side dump. This was documented with the Japanese PR film of the action. Some rock weighed well over a ton. I saw this in the mid 1970's film. Ask Bando.

Palabora's (Rio Tinto) conveyor was treated to the large lumps by an underground jaw crusher system that were opened to pass the large rock from the initial block cave mining action. The jaw crushers made large spears that had to pass through modified chutes.

The conveyor chutes were designed to handle up to 300mm lump in a 90 degree tranfer from the jaw crushers. Some lumps ranged closer to 1200mm. The belt was/is 1050mm wide. It was designed to handle 2500 t/h in the initial case and ultimaltely 3600 t/h. It was/is running about 4.3 m/s at 2500 t/h and could run to 5.6 m/s at 3600 t/h from memory. The idlers were 45 degree with shortened center rolls. The conveyor could transport the rock, the chutes were the bottle-neck.

The impact idlers/bars refered to earlier were for this system. It was very successful, including the special impact assy. removal system. This was a take-off of David Beckley's iron ore impact roller design. We have not published its details. I believe David might have done so in his design/maintenance school.

The belt was all underground. It hand a 560m straight section for loading the belt from the four jaw crushers and about an 800m long 9 degree slope prior to the head station.

This underground conveyor used the first wine glass pipe frame with a single support post anchored to the 9 degree sloped tunnel floor. This was designed for vehicle and operator clearance until the sparks pasted their conduit along it and safety pasted bumpers to protect against runaway vehicles. Idler spacing was 4 x 8 m

The chute top surface had to be remover along with the skirt system top during commissioning to pass the lumps. There were four separate jaw crusher loading points at about 176 m centers.

This system was commissioned in 2001-2002 again from memory. Mr. Johann Van Heerden was my site mentor at Palabora. He is still there. Mr. Dave Lunderstedt was the underground design manager manager. He now works for another firm in RSA.

What else can I say. ■

Hi Kayem

I only use impact beds where I am stuck for access.

For example, if you have a bifurcated chute then there is sometimes poor access to the impact idler wing rolls on the inside.

There I have used impact beds, as they help solve this problem.

Otherwise I avoid them, especially after I saw how much damage they can cause to the belt with big lumps with too much impact energy (i.e. more than 1000 Joules)

Where we have 2000 Joules or more, we have designed and used special feed point arrangements, and have been quite successful. Normal impact idlers are also a waste of time, in my opinion, for high impact.

Cheers

LSL Tekpro ■

We use the Brelco "Key-skirt" instead of the normal rubber skirting.

This moves with the belt and works very well on normal idler type loading areas.

LSL Tekpro ■

Hello Lyle,

Checking how far you are off the subject.

I assume that you are comparing suspended idlers (garlands or using teh nomenclature is SANS1313 part 2 - Link Suspended idlers) to standard foot mounted idlers. as mentioned by Larry one of the problems associated with suspended systems is the loss of sealing effect.

There is another form of idler base construction which has been proven to operate better in hard rock environment than the standard foot mounted idler. This is the 'catenary' base or, again as per SANS 1313 part2 Fixed Form suspended Idler. In this case the centre roll position is below the stringer level and the typical long and thin outer wing roll support bracket, prone to bending due to impact of large rocks, becomes a short sturdy element.

The concept is not new and was used extensively in coal mining - possibly because it tends to allow for shorter support structure, which is god for accomodating in shallow seam conditions.

Use this format in an offset roll configuration with a tubular cross-piece and you can achieve a 'belt friendly' idler base design.

An element such as this formed the basis for Larry's Palabora impact point design, although I believe that these had some additional 'quick release' facilities.

Again some of the concepts were discsussed in BELTCON 13 in a paper by Simon Curry.

Suitably off the topic?

FORUM USERS - REMEMBER BELTCON 14 - 1/2 AUGUST 2007 JOHANNESBURG SOUTH AFRICA

Regards,

Adi Frittella ■

Adi

I did 2 papers for Beltcon 13, but heard nothing about Beltcon 14 until very recently. I actually did not think there was to be one..(why are you guys being so quiet?)

LSL Tekpro ■

Hi Graham,

Definitely something wrong with our PR if you've heard nothing yet. Your contributions have always been appreciated.

Possibly a sign of the times and how busy we all are these days?.

Certainly hope to see you at BELTCON 14.

Regards,

Adi ■