Lumps can be large heavy and mainly related to your truck lading system . the larger the bucket the larger the lump.

the inpact force as DR Mulani pointed out is related to momentum , momentum is related to mass and velocity change , a vectorial answer for aceleration in base of change of velocity vector.

the larger the change the larger the impact, can you dump into a slide? with abouth the same angle as the truck max rise. or near. ■

Why design one when you can buy a prefabricated hopper?

And besides the point we have no idea what you are using under said hopper to move "Run of Mine" ores to the primary crusher and tertiary crusher.

Why not solve your problem and purchase a:

"WR Stamler Belt Feeder Breaker" or a Long Airdox Roscoe belt Feeder Breaker?,

and eliminate the need for a hopper all together and use the belt feeder to break and feed feed the primary and secondary crusher circuit?

They build them in many sizes including big ones for quarries etc., and they can be either stationary, skid, or crawler mounted.

Your dealing with gravity and mass against a stationary object with a volume of X and anything will wear out eventually and welds break eventually from the shock stress of the dumping etc.

With a "WR Stamler" or a "Long Airdox- Roscoe" belt feeder breaker you have a primary breaker and hopper all in one.

It all depends on your needs or what you think you need. ■

Phillip,

This is way off-the-beaten-track stuff. As suggested it's much easier if you can get someone else do the thinking for you - but let me try and talk you through it as best I can.

Impact forces are related to force = mass x accelleration.

When all else fails, mechanical engineers go back to that basic formula, try to quantify it, and thereby get some sort of design direction.

When I trod down the impact path it led to momentum and impulse. That was not very helpful to me. The other end of the coin was how quickly could the mass be decellerated - what was the elastic response of the material - be it steel plate or rock and soil. The deflection of steel plate can be calculated with great accuracy, but the response of rock and clay is not well documented in the handbooks.

I ended up dropping lumps of rock onto concrete and steel plate to get some idea of how much they would bounce back - ie how much energy would they absorb. Maybe you could try it on a scale? I'm not sure if that would help - but you could try on an empty scale, and then place a box full of ROM and clay, and see if it makes any difference (of course you may be getting a spring mass vibration thing going which would not be that helpful).

Then you have to allow for angular impact - not direct impact, but only the perpendicular component of impact.

Back at the steel face you are no longer concerned about plate deflection but only about stress. Structural engineers will add 100% to allow for impact, and even allow for some plastic yield under extreme cases. In some cases mechanical engineers may go as much as 5 times equivalent identifiable static forces, but usually this is to allow for other failure effects as well.

I hope all this gives you something to think about. ■

Tipping out of a Terex or Euclid haulpack simply involves brute force. The largest boulders will roll at frightening speed until something substantial stops them. Wear is not a problem. If the hopper can contain the avalanche it is not going to feel a few scratches. At the take out side of the box you will have to leave a gap for the stone to get onto & along the wobbler. This is the critical part because you have to stop the biggest boulders & then get them under the crossbar. If you are lucky the boulder can be caught while it is spinning & ascending so that it drops quiescently onto the bed of smaller material.

Use the heaviest steel sections that you can handle at the site. If you do calculations based on the deflection limit of half plate thickness you will get bogged down in the steel properties & anyway time is money.

The best mathematical treatise I ever saw was in a Swedish alloy design handbook which covered hoppers, truck bodies, digger shovels & the like.

Remember to consider I sections as channels bending in Iyy because after a week or so the exposed flange portions will have been deformed to suit. ■

Impact forces are a real pain. Here are a few threads that discuss them.

http://www.eng-tips.com/viewthread.cfm?qid=84200

http://www.eng-tips.com/viewthread.cfm?qid=74498

http://www.eng-tips.com/viewthread.cfm?qid=36240 ■

Our mining unit hoppers were fed from ROM dump trucks or belly scrapers. We handled coffee coloured rock, which is a ferrite - sandstone bonded with iron oxide. This would be similar to limestone in strength, carried in a matrix of sand and clay.

Our hoppers were steel plate, lined with UHMW Polyethylene. This works quite well. I would use a menu of steel plate 8,10 and 12 mm thick with stiffeners at 1200 mm down to 600 mm nominal. Assume the hopper is full, with a surcharge at about half the dump tray height. That will give you soil / rock forces to work with in terms of gravity load and active side pressure.

The highest pressures are at the bottom plates of the hopper - here the pressure is related to the head of ROM. The static loads give you one set of forces to work with. Double those for impact.

Impact velocity is also related to the drop height. But this will only come into play when the hopper is empty. The more ROM in the hopper, the less drop height, the less impact load.

As suggested use heavier sections on exposed steelwork - even a protective layer or liner plate would not go astray. Closed or boxed sections are much more robust in these applications.

Dump trucks are also notorious for side spillage. We build up volumes of spilled ROM each side of the roadway. This has to be cleaned away from time to time - and it impacts any nearby structures such as walkways, conveyor covers and equipment.

A related problem is how to clear the driveway of oversize boulders. We use a tilting grizzly which rolls everything into the hopper. This is nice, providing you don't get rocks larger than say 1 m cube. If you do, then you have to stop production and get into the hopper with jackhammers. It also means that the apron feeder and related equipment get hammered with oversize rock. It would be neater to cut the oversize with an inpit grizzly, but that means a second operation for the belly scrapers. With front end loaders in the pit it may be possible to avoid picking up the big plums. ■

Dear Mr. Phillip Bergmann,

I suggest you to mention the size of the boulder and its probable size shape, so that respondents will have some idea about the nature of the application. Also, the size and type of the truck and its falling level with reference to the hopper top mouth. The impact magnitude is also influenced by the hopper depth.

In general, such hoppers shape should be decided in such a manner that material falling from truck falls on the sloping edge of the hopper at upper zone. Then, the material should slide / roll down to the lower level. Also, the hopper should not be allowed to be completely empty to protect the underneath equipment and to enhance its life.

In an item like wagon tippler hopper, where the above mentioned arrangement is not feasible, then impact breaking beams are provided at spaced interval somewhere below the middle depth of the hopper.

The calculation of the impact force would be in accordance with the law of conservation of momentum, restitution coefficient, deformation of material, etc. However, worst case will be lump bouncing back from the hard surface or from the lump itself.

Choose the hopper angle, which is reasonably sufficient to create the desired flow. Do not opt for excessive slope because it will aggravate the situation.

The issue cannot be addressed without proper shape and size of the hopper to deal with the large size boulders.

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 ■