1000 x 1400 belt feeder are notorious for ratholes in iron and aggregate industry. It is obvious that the material is not flowing on the walls and the outlet is not big enough to break the stable rathole. Either you get the material test for a proper outlet size and get an appropriate size outlet / discharger or try using brut force techniques.!!!!! ■

I second what mantoo has said as unless you have mass flow you have no flow with anything that ratholes-I lost a close friend because of this.

After seeing the drawing it is no wonder you have problems- a quarter of the inverted cone should be removed and a sand hopper with an apron feeder should be installed in place of the belt feeder-in my opinion or at least the bottom quarter of the hopper should be removed and sides added to the belt feeder to allow easy flow of the material out of the bin to the belt. ■

The hopper seems to be of good construction but I suspect that there are some small adverse features in the detail that are sufficient to cause the problem described. The Iron ore concentrate with around 9% moisture will be quite strong and poor flowing. The slope of the conical walls shown is usually adequate to generate mass flow but this is clearly not taking place. I would enquire whether the design is based on measured wall friction values of the product and account taken of the worst slip conditions. I presume that the hopper wall surface may be warm and the contact layer may have dried out if the contents were not moved during the filling process. Ratholes are not stable in massflow hoppers or when the diameter exceeds a size relative to the strength of the bulk m aterial. It is therefore crucial to secure wall slip in the lower section of the hopper. A key region of this construction is the transformation from the circular section of the hopper to the interface at the extraction belt outlet. The drawing does not have sufficient detail to confirm the exact geometry, but the present fitting would appear to be a relatively elementary shape, rather than exploiting the benefits of flow technology. Other features that call for attention are: -

1.The surface finish, alignment and welding on the Hardex liner plates may be offering a rough surface to the material and detract from the theoretical or measured wall friction value on which the design was based.

2.Presumably there is a small step of the Hardex thickness at the top edge of the Hardex liners.

3.The ladder obviously presents a non-slip region in the periphery of the hopper.

4.The outlet show in View ‘A’ is parallel and presumably horizontal, whereas the interface should be tapered and inclined to generate a progressive extraction by the belt.

We are able to conduct wall friction tests, if these have not already been carried out, but the main retrofit requirements seem to lie in a redesign of the final transformation section and perhaps addressing some minor within the hopper. The fact that the material forms a rathole, rather than an arch and total blockage, indicates that the fundamental problem lies with the wall geometry and finish rather than the size of the outlet.

The time and detailed attention required to pay proper attention to the situation means that this would have to take the form of a consulting arrangement, with further detail drawings transmitted and correspondence exchanged. If you wish to pursue this route please respond to lyn@ajax.co.uk. I would expect that your situation demands early attention and would endeavour to deal with the position as a priority. ■

I have wondered in the past about those who ask for fixed internal ladders in hoppers, then wonder why they get poor flow! ■

Indeed ladders hinder material flow but saves a lot of time and money if one needs to visit the hopper with a pick axe etc. ■

Maybe if they didn't have the ladder they wouldn't need to visit the hopper with a pick axe ...... ■

Maybe ....... Maybe Not!!!!! million dollar question? ■

hopefully they are using a scaling bar before entering the bin and are tied off with a full body harness and a confined space retieval winch cable. ■

The simple answer is to fit a set of shedder plates in sections that overlap to rest on the ladder rungs and can be lifted out progressively. These will offer far less resistance than the ladder and, if slightly tapered in width around the ladder from top to bottom, will relieve the hoop stress and actually improve the flow characteristics of the silo, especially if the largest taper is on the bottom section.

However, the ladder is not thought to be the major problem in this instance, although it certainly is an adverse feature. I cannot emphasise enough the importance of detail around the outlet region where finish and geometry is concerned. ■

I note that you say that the ore moisture is 9%.

Disregarding design issues, I wonder how confident you are about your moisture levels?

I have seen havoc created in too many bins of various types by careless control of plant water. In the case of iron ore, this can lead to cemented bin contents that need to be blasted clear.

Tell tales signs of excessive water can often be seen by way of otherwise inexplicable splashes of mud around the conveying system.

It only takes one incursion of unplanned water to cause a major problem. Typical causes are:

-Hosing out a preceding unit, while continuing to run the conveyor into the bin.

-starting a conveyor with a pocket of water in it.

- leaving dust suppression water running when the belt is running, even if there is no ore on it.

- running wall lubrication water when it is not required.

No amount of measurement of ore properties will overcome this type of basic operating problem and I have seen it over and over again.

I suggest the issue of unplanned water is worth considering. ■

Interesting....

Def. the wall friction is high enough to prevent mass flow

The hopper outlet dims would seem to be OK otherwise U have have an arch and no flow at all.

In Aust..U can get testing and recc. done by TUNRA

They do the worst case moisture range checks and 48hr or more consolidations checks...ie design for worst case.

Have U done tests at differing fill levels??

Differing moisture levels

As other have alluded to:

The ladder is not nice for flow reasons - I do not like the safety aspects

The liners at the bottom could be the issue eg small step at the start of the liners.......U can try 3CR12 - polished etc.

The outlet hopper/feeder geometry is also critical - they are all ONE and can not be designed independently. The hopper has to be tapered in both directions

When U empty the bin...U may be able to see tell tale signs of the flow and no flow regions...also...may even be buildup in places...

Just where is the rat hole - towards the back of the feeder??? This suggests poor draw down by the feeder.

I will be interested in where this issue ends up

Cheers

James ■

You have not mentioed grade of concentrate. +67% Fe conentrate with low Al2O3, should normallt flow properly.

I see following possible reasons.

1. Ladder. Ladder should be removed. If you require a ladder for clean-up or inspection, use rope ladder,

2. The Hardox lined surface may not be smooth. We have used Ultra high density polymer liners. They have worked well. Try to romove 90 deg corners in the lowest 4 m zone where liners are installed by installing moulded UHDP sections to get a rounded corner.

3. A round conical bin with a table feeder is ideal for this application. ■

The Design of Bin for Iron Ore is not good sufficiently.Because of that,inclination of bin must be at least 80º in any case of iron ore get %8-9 moisture.I know it is midly that you have to change conical part of bin.It is not possible I absuletly know.So that,Maybe You can add a few shock blaster or vibrator on above outlet part at conical surface.In addition to these,you have to cover inside of the conical part with as teflon or alpolen1000.I hope it is useful for you. ■

using Ultra high density polymer liners + air cannon better ■

We can supply pneumatic piston vibrators to improve flow in bins and hoppers. Installation does not penetrate the bin wall like air cannons and blasters do.

Read more about the comparison of vibrators and cannons here:

href="http://www.navco.org/pneumaticvscannon.html" target="blank">http://www.navco.org/pneumaticvscannon.html

Although the above article is geared to power plants some issues ring true for all types of material, not just coal.

We can design a Bin Map Solution which is a unique scientific approach that virtually gaurantees material flow. Our Engineers will consider aspects such as material bulk density, moisture content, and construction of the hopper, along with bulk flow theory concepts, to provide you with an CAD drawing like the one below, designed for your specific application, that recommends placement, sizing, and control patterns to optimize area of influence and produce reliable material flow.

Learn more or Request a Bin Map here:

href="http://www.navco.org/industrial-bin-vibrators/bhbinmap.htm" target="blank">http://www.navco.org/industrial-bin-...s/bhbinmap.htm

Attachments

bin map cad dwg example (GIF)

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you are true that wear have to be.But it will get minor cost to you.Sure Material flow is more important than minor cost,isn't it? ■

If you want a safe way to remove the initial hang up of material, try contacting Pneumat Systems Europe Ltd.

We offer a non-man entry system that can safely remove hang ups and blockages in silos, hoppers, bins etc.

Contact us here:

http://www.pneumat-europe.com/ ■

We also offer brute force feeders that can discharge difficult even sticky material up to 3500 TPH.

See a video of a small demo here with some pictures of larger feeders at the end.

http://video.google.com/videoplay?do...42947253651151

We'd be happy to provide you with a quote for an engineered solution. ■

The article published by Navco on the use of vibrators for stimulating flow is an excellent review of the mechanical aspects of vibration. It also indicates the difference between well established structural considerations and the more awkward understanding of transmitting vibration though bulk solids and the dangers of misapplication consolidating the product to a stronger state, instead of loosening it for flow. Vibration has a valuable contribution to make in respect of aiding flow. Obviously, it has to be employed with understanding and in conjunction with best practice in hopper design and consideration of aeration techniques, where appropriate, rather than as a brute force substitute. With other technical publications by the company enlarging the scope of this subject, it illustrates the value of dealing with an enightened supplier, rather than a supplier of stock i tems. ■

Here is link to the PDF White Paper Lyn mentions above:

(thanks Lyn!)

Its posted here in another forum on this site:

https://forum.bulk-online.com/showth...ighlight=navco ■

Here is an informative article about table feeders for difficult applications as someone mentioned above: I have no affiliation, I just found it when researching the topic myself out of curiosity

http://www.powderandbulk.com/pbserv...plications.htm ■

I can offer a simple, effective solution to cure your 'ratholing' problem with the ore in the silo. I have looked at your dimensional drawing and provided the top of the silo is enclosed you could install a Primasonics Acoustic Cleaner Model PAS - 60 on top of the silo. This acoustic cleaner would be sounded for a few seconds at periodic intervals during material discharge and it would prevent any material build up on the side walls. Please have a look at this link for further information (

href="http://www.primasonics.com/silosapplications.htm0" target="blank">http://www.primasonics.com/silosapplications.htm0

I also attach a photograph of such an installation.

Should you wish to discuss it further or require a quotation please contact me on - +441768866648 or e-mail us at

href="mailto:sound@primasonics.com">sound@primasonics.com.

Our Irinian agent will also be pleased to help:-

Mojtaba Malayeri

Commercial Manager

Petro Artiman Pars

E-mail:

href="mailto:mojtaba.malayeri@petroartiman.com">mojtaba.malayeri@petroartiman.com

Regards

Donald F Cameron

Primasonics International Limited

Attachments

grassim (JPG)

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