Hopper Pull-out Forces

(not verified)
Posted in: , on 28. Jul. 2006 - 04:21

Hello all.

I've been working on a belt conveyor system which has a 22000m hopper, loading onto a feeder belt conveyor. we are in dispute over the required pull-out force to overcome material loading, and ways to reduce this loading.

the details are :-

hopper outlet size : 0.8 x 8m

bulk density : 2300kg/m

belt speed : 1.0m/s

belt width : 1200mm

angle of repose : 35°

surcharge angle : 25°

overall conveyor length : 120m

overall conveyor rise : 18m

using the bruff method i come up with 336kN (starting), 84kN (running).

I'm looking at incorporating a baffle/shedder plate system to reduce to load on the belt. has anyone had any experience with doing this, and what is the best method?



Re: Hopper Pull-Out Forces

Posted on 28. Jul. 2006 - 08:32

You need to specify more information including:

1. Tonnage

2. Idler trough angle

3. lump size and percentages of larger sizes

4. Belt feeder opening dimensions

5. Configuration of feeder side walls

6. Configuration of hopper bottom side walls

7. Internal friction angle of material

8. Maybe you could share how you were able to make this calc.

There are ways to significantly reduce the necessary belt feeder motor torque to initially move the load and then maintain its withdrawl.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: www.conveyor-dynamics.com nordell@conveyor-dynamics.com phone: USA 360-671-2200 fax: USA 360-671-8450

Extraction From Hopper

Posted on 28. Jul. 2006 - 01:39

The long outlet suggests that it is made to enhace the capacity of the hopper without consideration of the extraction profile. The likely result is that product is being taken from the back end and sheared under the full length of the dead contents under the remainder of the outlet slot. It would also seem probable that the width of opening is well in excess of the potential arching dimension and high overpressures are acting on the belt and the shear plane developed during feed-out.

As there is no information about the nature of the bulk material or geometry and construction of the hopper walls, it is not possible to advise on the best approach other than to say a crude solution is to fit intermediate baffles along the opening, provided these do not lead to arching on reduced slot lengths.

Were the hopper drawing, critical arching size, time consolidation characterists and wall friction details to be available, it may be practical to fit taper shedder plates along the slot and radiacally reduce the down pressure on the belt and provide a relaxed shear plane along the length of the discharge. Basically, the situation calls for a professional consultation, as the original design seems far from satisfactory and a detailed investigation is needed to secure the best solution.

Re: Hopper Pull-Out Forces

Posted on 28. Jul. 2006 - 04:34

Originally posted by anthonyc

Hello all.

... i come up with 336kN (starting),



Interesting, my 'rule of thumb' for this data indicates 231 kN. I'd normally have a drive giving 2 x FLT on startup (462 kN).

Lets see what others post.

Hopper ?

Posted on 28. Jul. 2006 - 04:46

Why is it that you are not using an apron feeder to solve the whole problem before it starts!!!!?, And eliminate any future problems?

You are adding huge stesses to the conveyor by not using even a small apron feeder. Its your money spent on additional repairs THAT CAN BE AVOIDED.

(not verified)

Re: Hopper Pull-Out Forces

Posted on 30. Jul. 2006 - 10:08

Hello again,

thanks for starting a dialogue on this. the design of this particular conveyor is quite political. Five engineers, and five vastly different opinions.

Here's some more info as requested.

1. Tonnage : 1000 T.P.H

2. Idler trough angle : 35°

3. lump size and percentages of larger sizes : 3mm

4. Belt feeder opening dimensions

5. Configuration of feeder side walls : 35°

6. Configuration of hopper bottom side walls : Vertical

7. Internal friction angle of material : Unknown. Client will not pay for a trest on the material.

8. Maybe you could share how you were able to make this calc : Using the formula F=(2cb/(c+b))*u*D*g*n/1000

b = width of hopper outlet (0.8)

c = length of hopper outlet (8.0)

D = Bulk density (2300kg/m)

g = 9.81m/s

n = material flow factor (4 - starting, 1 - running)

u = Co-efficient of friction (0.4)

The length of the hopper is chosen because it is filled by a 6m long side tipper truck. We don't have too much height to play with, so that's why the 8m can't be reduced. However, i could bring it in to about 6m long, but this does not solve the problem.

The opening at the bottom will taper outwards towards the exiting end. ie. be approx 400mm at one end and 800mm at the outlet. The side walls are at 35° and the end walls are vertical. The entire outlet has vertical walls. I've attached a sketch

I'm now pushing for this to be a short low speed feeder conveyor that transfers onto a high speed conveyor. Though i really would like to reduce the dead weight on the belt by the use of baffles or shedders.



Belt Feeder

Posted on 31. Jul. 2006 - 10:18

If you do not have the measured properties of the bulk material it is not possible to establish the overpressures or shear strength. The pull out force is that required to shear the material and this is related to the down force acting on the shear plane, so what's the use of a formula that doesn't have this information. The reluctance of a client to pay for testing is irrelevant. He has to pay, one way or the other, for the job to be properly undertaken and the price quoted should reflect this. The fact that companies will supply equipment without adequate information is endemic in the industry and indicates why things have not radically improved since the publication of the Rand reports in the 1980's. Can you imagine a bridge being built without knowing the strength of the steel used?

However, the situation can always be addressed by basic principles and brute force. There is obviously a massive surge load as the waggon tips, so the best, crude solution is to fit a heavry duty grid along the length of the hopper spaced sufficient to prevent arching. If there is no flow problem with the 400 mm wide opening at the start of the hopper it would seem that baffles at 1000 mm centres would be effective.

It is not clear how the hopper configuration tapers from 400 to 800 wide over the length and it is important that the baffles should not introduce adverse gully angles. I would suggest that deep, vertical flats be welded across about a meter above the belt that have 200 x 200 rolled steep angles welded on, point up, that end about 300 mm from each wall. Pads may be needed at the end of the flats to spread the impact load on the hopper walls. This is a basic structural problem that usually well dealt with by engineering companies.

Re: Hopper Pull-Out Forces

Posted on 31. Jul. 2006 - 12:20


Are U with Kockums or just next door??

Some general comments.

Hopper looks too small for trucks...

Belt trough of 35deg is OK for belts but not for feeders., Belt feeders are typ flat belts or use picking type carry idlers.

Belt speed is typ 0.3m/sec to 0.5m/sec depending on materials characteristics.

With the tapered slot..need to think of skirt configurations with the belt trough line > hence, use flat of picking type is common.

With belt feeders - spillage is issue - even with close spacer idlers etc..dump load will cause belt deflection between idlers and spillage from skirts.

Skirt design is critical to prevent leakage.

With a tapered slot....presume that the skirt just above are vertical > hence, your sketch is not quite right - will see 2 diff. wall angles for front and back.

Suggest installing fillet plates in the corners to reduce build up in the corners - say 200mm wide minimu.

Belt feeders are heavyily dependant upon belt tensions > U show a screw TU unit > with fabric belt > will get stretch and loss of tensions.

Also....do U want a variable rate of fixed at 1000tph > can vary rate by gate height or variable speed. Gate height adjustment needs to consider material lump size/even feeding etc. Variable speed needs to consider pull out/starting torque for the feeder esp after consolidations.

If material can get polished by the belt > apron feeders are a better choise for extraction.

There is an article by Rademacher - Netherlands Uni (?) - on feeder pull out forces > it is several years old now but the formulas do not change.

For internal baffles....what U are doing is making your long slot hopper a series of smaller hoppers. The general rule of thumb for the slot hopper is 3:1 ie lenght is 3 x slot width typ. Refer articles by Aussie Uni experts. Hence, to do what U ask...break it down into hoppers of this proportion. The partitions need to have sloping walls > these walls then meet the existing side sloping walls > hence, U will have valleys > U can calculate the "valley" angle and need to cross check with the material charteristics > angle should be 5deg steeper than the friction angle (need to also get the worst case eg moisture content/size range etc). The new sloping walls should then go vertical to match the vertical skirt walls. This then creates a small housing underneath the new sloping walls. The front wall height (above the belt)...should be LESS ie LOWER than the height of the front vertical wall > and each sub hopper downstream of this needs to be the same > or U will get reducing height and material choking.

To reduce build up in the corners of these new walls > add fillter plates as well.

The whole idea of tapered skirts etc etc is to provide an even draw down of the material > this then reduces the shear friction case where the material is fed from the rear only and shears its way across to the front.

With long hoppers > U are never going to get this anyway > the taperd needs to be from zero to full width > so material will shear anyway. This requires force and power to do so...your calcs. do not seem to count for this.

Also...with the low speed > the bed depth will be quite high > so U need high side boards > this will also add friction.

On the belt arrangement > U show a zero lift tail pulley transition and a half height lift from the head end > with the low speed and high forces > the belt will lift off the idlers and into the skirts > use a flat ie no LIFT transition at the head end. This is almost a mute point if U use a flat belt or picking idlers.

Cheers for now


(not verified)

Re: Hopper Pull-Out Forces

Posted on 1. Aug. 2006 - 01:05

Hello again,

Thanks for the guidance on this issue. we're all starting to find some common ground on the issues. James - i was with Kockums until recently. basically had learnt as much as i could / was allowed to, and had to move on. that's why i'm relatively new belt conveyors.

A few questions and points.

- Why is a belt trough on a feeder not acceptable? if we were to go flat, we would lose capacity and either have to increase the belt width substantially (to 3600mm), or have it running at 5.0m/s.

- Drive will have a VSD.

- Hopper valley angles have been checked and are o.k. material angle of repose is 30-35°.

- I've checked the calcs on the transitions, and have allowed enough length + some more.

- I don't believe the material can get "polished".

below is a link to a new sketch i did. the hopper now slopes back to front, both in the horizontal and veritcal planes.

thanks again to everyone giving advice.




Re: Hopper Pull-Out Forces

Posted on 1. Aug. 2006 - 01:58


The front wall should be vertical > good heopper design practise.

There should also be an adjustable shear gate located right at the front wall...as close to the front vertical wall as U can.

If U look at the internal shedders / hoods > U can see that the "valley" angle in now lower than the minimum wall slope > resulting in hang ups. As a result, U need to design the valleys of the hood/wall interfaces with the minimum wall angle and then go from there.

The issue with troughed belts and feeders is the skirt design > the rear of the hopper is typ narrower than the flat botom section and then the skirts move outwards and then have to go up the slope of the 2 sloping walls.....becomes messy and interesting. Flat belts are used or picking idler sets (wide flat middle rollers and 2 small wing idlers rolls).

With the flat belt feeders > U need to design for a speed > this is for wear reasons. The minimum hopper size / opening width etc is a function of the material characteristics. Hence, the material bed depth on the belt will be high > so U need high skirting boards to suit > U have a rectangular cross section of material on the belt. U will have friction drag from the material on the walls of the skirts. As u can gather, there is head pressure on the skirt interface with the belt > this will be a sealing challenge and source of leakage.

At the head end/discharge > with a rectangular cross section of material >> U will have either chunks of material slabbing off or shearing off as it nears the head pulley > this may lead to surges of material falling down onto the next belt > something to consider.

U should re read my last post on other details.

With such a long hopper > there will be preferential feeding from the rear and the front will not discharge until the rear is empty...this may an issue with truck loading given the apparently small hopper size/capacity wrt truck tray.

Another alternative is to use several sideways located feeders eg vibratory electromagnetic pan feeders at 90deg to the truck/hopper line....feed across to a collection / accelerator belt and then onto your second belt (or just use one belt). This means that your long hopper becomes a series of smaller sub hoppers and with the feeders > U will get even draw down. This concept has been used in coal terminals in Qld. U will have to consider flooding risk when the hoppers are empty and a truck dumps > this can be catered for by pan length and/or gates at the hopper/feeder interface.

Good luck



Re: Hopper Pull-Out Forces

Posted on 2. Aug. 2006 - 12:04

22000 cubic metres at 2.3 tonnes per cubic metre is a lot of weight for a hopper. Hoppers are the tapering bits at the bottom of bins by the way. We defined that on these forums way back.

120 metres is a rather long feeder conveyor.

6.4 square metres is rather a large opening to pass 1000 tph of 3 mm grains.

What the others have been too polite to say is that this design is a right cock up from start to finish. eg although you seem fond of side tippers in the southern parts they are notorious for throwing excessive weight onto one chassis member during tipping. They are also frighteninlgy unstable. I designed some for Fruehauf Natal but in 30 years of part time HGV driving, when I get peed off by office work, I have never seen such a gadget in Europe. Never. Why? Well just make sure the raised empty body can fall back into place before the sidewind blows the truck into the hopper. That takes a previous recognition of surge forces from the waggon a bit further along the line. Like Lyn Bates said, get the professional help that should have been there at the beginning.

John Gateley johngateley@hotmail.com www.the-credible-bulk.com

Re: Hopper Pull-Out Forces

Posted on 3. Aug. 2006 - 09:21

Hello Anthonyc..

I have designed and built many such hoppers and conveyors, and have based my designs on the experiences of a super old materials handling engineer namely Len Barnish (long time retired) who gave me a massive founding in the right direction.

The way he configured the hoppers and especially the outlets gave rise to low belt loadings which I found most useful. For example, one similar to yours that I did, has a normal 45kW Fenner shaft mounted fixed speed drive. If you go by Bruff, J&J, Arnold, theoretical etc etc...you will end up with huge loads and massive drives.

The secret is to break the stress field and to configure the outlet to achieve this whilst at the same time ensuring you don't get spillage.

(Oh and NEVER use apron feeders when you can have a belt, especially for fine material.)


LSL Tekpro

Graham Spriggs

Hopping Hoppers

Posted on 3. Aug. 2006 - 01:41

Graham- he has not even bothered to tell us what he is moving through that hopper!!!!!!!!!.

Regarding apron feeders what is so bloody wrong with them in your opinion?, they are dumb and easy to repair and require minimal power in relation to load moved.

He is asking us for advice about fixing his problem with out even telling us what the material is!!!!!!!!!!!

There is no reason that the hopper in question could not have opposing flows from two smaller narrow apron feeders feeding directly into the center of that hopper to a lower drop point above the belt. this is done quite often in coal power plants with rotary car dumpers feeding a coal stock pile stacker delivery belt.

Its not our fault that his hopper is designed that way and has shock loading.

Regarding light materials if he maintains the steel skirting directly over the feeder pads properly by making sure flow does not come near the edge and stops moving due to the resistance of the steel skirt under the hopper by making sure the steel skirt is 2 inches above the feeder pads

and replaces it when it is worn out he will not have any spillage.

George and lynn- my apologies again if I missed something.


Still to bloody wet to do any thing here in the "Eastern Wilderness" @ 1140 feet above mean sea level.

Re: Hopper Pull-Out Forces

Posted on 3. Aug. 2006 - 02:57


I read the material is 3mm 2300t/m3

I am currently doing six belt feeders to feed -25mm 2300t/m3 on iron ore.

You could scarecly buy one apron feeder for the price of my six belt feeders.

Also apron feeders cause dribble through fines spillage and are big heavy horrible nasty things which wear out. We have proven that on fine material, apron feeders wear out far more quickly than belt feeders.

I have travelled from Arizona down through Mexico and through the length of Chile looking at Copper mines . In almost all cases there are belt feeders after the primarys.

I wonder why.

(Do you by any chance sell apron feeders?)


LSL Tekpro

Graham Spriggs


Posted on 3. Aug. 2006 - 06:35

Mr. Spriggs,

I do not sell apron feeders.

I was a maintenance mechanic in a salt mine for 22 years and we had an 24" by 72" apron feeder that worked tirelessly moving 6 inch ROM rock salt for 23 years until they built a new screening plant underground to replace the old screening plant.

(not verified)

Re: Hopper Pull-Out Forces

Posted on 3. Aug. 2006 - 11:53

thank-you for your responses.

to let you all know, this hopper has not been designed or built yet. it is just in calculation and concept stage. it doesn't take 30+ years of experience to know that you should make sure you have designed it correctly before making a fool out of yourself on commissioning. that's why i ask the questions now. i'm eager to learn about the concepts as there is a lot of opportunity for work coming up in this field.

particular thanks to james. i've managed to convince enough people that 24kW would not have been nearly enough power for this feeder!!!



Hopping Hoppers

Posted on 4. Aug. 2006 - 12:30

I wish you had told us that in the beginning.

If you use a twin apron feeder dumping into a central belt chute you will not have problems and you will have a smaller hopper even though it is taller with less steel and reduced angles for hang ups and spillage.

Apron feeders are dumb, basic, and stupid as they are either on or off and they are very easy to install and use with little trouble and the amount of power needed is low as it is powered through a reducing gear box.

The apron feeder I mentioned moved over 700,000 tons annually for 23 years under a 75 ton bin fed by a 36 inch conveyor.