Would help to know the following data for the application -

1) capacity in tonne/hr (as tonne/hr does not always equal tonnes/day divided by 24)

2) density in kg/m3

3) rough particle size distribution of the coal and moisture content. ■

Hi fredericktan75,

If you don't mind a bit of global warming here and there, a 35 m vertical screw for uplift seems a great theory.

1 - What sort of frictional resistance do you expect with a shaft full to bursting with coal?

2 - How many bearings are you planning to have in 35 m? What sort of horizontal deflections would be acceptable in the shaft?

3 - How do you debog? What do you do with the waste product when you want to get to an intermediate bearing.

4 - With vertical lifting you must be looking at 100% full flooded screw. How else would you get the product to rise?

5 - How will you deal with an emergency plant shut while you sort out a bearing failure?

6 - What does your maintenance department think of screw conveyors? The Geraldton Port Authority has banned them on their ship loading facilities.

7 - Has anybody else tried it?

One way to handle a maintenance issue is to strip the lot out and replace it with a brand new technology. While every problem has a solution, every solution brings new problems.

Has anyone done a thorough, rational Failure Mode & Effects Analysis (you can google that)? If you are short on information you can email us at the Bionic Research Institute.

Regards - Sgt John Rozentals

Director Bionic Research Institute

john.bionic@yahoo.com.au

www.latviantourists.com.au ■

Re item (4)

On the basis of past experience I would not agree with that statement.

Re item (7)

http://www.bmhmarine.se/images/BMHpd...%20Rev%203.pdf ■

Dear Mr. Frederick,

You have not mentioned the coal size. But I am presuming it might be less than 10 mm or may be less than 25 mm. Coal is a very sober / noble material for handling coal by elevators. Therefore, as an equipment, there is nothing wrong with the selection of elevator. Please try to correct your elevators with reference to quality of design, type, fabrication and finally installation. If everything is good but installation is faulty, even then elevator may not perform properly. Generally I have not come across the difficulty of handling such coal by elevators. The only point is that coal dust within the elevator should not result in to the explosive / combustible situation. This is a precautionary condition to prevent sparking, short circuit etc within the elevator. But you have not mentioned such difficulty in your installation.

Screw conveyor would not be a better choice for elevating the material by 35 m height. If you have money, and want to opt for alternative type of equipment, then you can think of using Contiwell / Flexowell / etc. type of conveyor-cum-elevator, wherein material is conveyed by the formation of buckets integral to the belt. The conveying route is horizontal for few meters at loading point, then it becomes vertical and again it is horizontal at discharge end.

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 ■

fredericktan75 has yet to respond to my first post.

From past experience with bucket elevators and sidewall elevators handling coal the particle size distribution and moisture content are critical.

If the coal has a high fines content and moisture content it will adhere to the elevator buckets slowly building up if there is no regular maintenance regime. This can reduce the effective capacity and result in overloading.

In a sidewall elevator it will adhere to the corrugated sidewalls and to the cross cleats. Then it will fall off in the most inaccessible places (in accordance with the the law of Arkwright Sod) making cleaning difficult.

Regarding the possibility of an internal explosion, this will require a density of dust in air not normally seen in bucket elevators. Take note of the possibility but don't panic about it. ■

If your bucket elevator is so bad that you are considering replacing it rather than repairing it then you are a candidate for a much better system. Our DSI Snake Sandwich High-Angle Conveyor system uses all conventional conveyor equipment and smooth surfaced rubber belts that can be continuously scraped clean. The coal load is sandwiched between smooth belts that impart a continuous hugging pressure along the carrying path, developing the material's own internal friction to firmly contain and positively elevate the material. Such a system, operating at a Steel Mill in Northern Spain, since 2003, elevates coal to the new pulverizing plant and to the old pulverizing plant. The pocket belt (system with corrugated side walls) that previously elevated to the old pulverizing plant has been abandoned in favor of the DSI Snake Sandwich system.

We would like to know what the hourly design rate is to determine the proper belt width.

Joseph a. Dos Santos, PE ■

What is the available footprint for new machine installation?

How many bins are involved?

Are the bins clustered or single file?

What is the present high level distribution regime?

What is going wrong with the existing gear?

A screw will tend to buckle under the intended duty & you must ensure that the buckling deflection does not exceed the casing clearances which you will need to drive the coal skywards. The necessary intermediate bearings then restrict flow. Consider using 6 screws each 7 metres lift, plus discharge end requirements, keeping one for spare duty. That way you'll have more than half a chance. ■

There are a few misconceptions about vertical screw elevators in these replies that require much too detailed explanations to deal with here. Suffice to say that screw elevators are considerably more difficult to design than screw conveyors or screw feeders. These various modes of screw handling are described in my book - 'Guide to the Design, Selection and Application of Screw Feeders'.

I would not recommend a conventional screw elevator for the duty described because of the length, power requirements, product breakage and difficulty of restarting if stopped under load for any reason. The new static screw elevator patented by Olds Engineering in Australia is a far better bet because of various advantageous features, but even that is unproven on such extended lifts and although considerably more efficient than a rotating screw elevator is still less mechanically efficient than a bucket elevator

I would advise the user to examine in more detail the reasons why his bucket elevators are experiencing frequent breakdowns as this machine would seem to be the most appropriate for this particular duty. The lifting part is not usually a problem, so the inlet and discharge should be reviewed, unless specific features pinpoint a particular problem. Most discharge problems of wear and re-circulation of product arise because the bucket speed is too fast and material is thrown against the roof to fall back down the casing. Inlet feed should be properly directed and high enough to be picked up by the buckets instead of dredged from the boot. A good fitting liner can also help to minimise bucket tip wear by grinding away through a rough bed. Do not jump from the frying pan to the fire. ■

From fredericktan75's latest post it would appear that the equipment supplied is unsuited to the duty. Go back the equipment supplier and get them to fix the problems and make the elevators "fit for purpose".

Lyn says "Suffice to say that screw elevators are considerably more difficult to design than screw conveyors or screw feeders. Do not jump from the frying pan to the fire."

HOW VERY TRUE! ■

Dear Sirs

please let us know the main problems you have at the bucket

elevators .

As a company specialised in the engineering and supply of

bucket elevators we can submit a proposal for solving

the problems .

Best regards

F.Gambarotta ■

We go from 3 to both. What's the 3rd elevating?

You bought a cat in a bag before. What makes you think your evaluation process has got any better now?

This is clearly a hardware quality issue. Get some good chain & try again. Its cheaper than buying probably dodgey drums & a poorly spliced belt.

Would you crown the drums? (another post)

If one side is consistently wearing out faster then perhaps it is leading due to sprocket mounting error. Have you checked it? Did the cattle herding supplier provide a dimensional record with the QA documentation/ ■

Dear Sirs

in case you are interested to we can submit a offer for

modification of existing bucket elevators with

new chains and sprockets , probably keeping the casing.

Please send us the main data : capacity, specific weight in bulk ,

elevation hight , size of material etc .

Please be informed that we already supplied several

central chain bucket elevators for coal , with center

distances up to 59 mt .

Best regards

F.Gambarotta ■

We now know that your machines are Chain & Bucket elevators, and are of the twin chain type.

Since bucket elevators are simple machines to size, the fact that your supplier undersized the machines must cast doubt on his ability to design such machines.

When using twin chains it is important that the chains are matched lengths and that they elongate evenly each side. Quite clearly one problem you have is differential elongation side to side. This is a common problem with twin chain bucket elevators.

Firstly is the chain physically suitable for the loads being imposed on it?

You are handling coal. Is it wet, as it is well known that wet coal is corrosive and will eat away chains. Even if the chain components are hardened steel they will still suffer from corrosion leading to premature elongation.

Belt & bucket machines do not suffer from these problems, but you will need to ensure the head and boot pulleys and the back of the belt are provided with scrapers to keep them clean. By the way, it is not normal practice to splice bucket elevator belts (as is done with belt conveyors) but to use a mechanical joint. ■

Dear Sir,

I fully agree with the point of view that a belt bucket elevator with wear resistant buckets and a speed just enough for centrifugal discharge is the best solution. We can supply such.

Please have a look at www.jh.nl.

Kind regards,

Jur Lommerts

Jansen & Heuning Bulk Handling Systems

www.jh.nl ■

WRONG!

In bulk materials handling there is not one perfect piece of equipment. ALL machines have their advantages and disadvantages the trick is to select the most suitable machine for the job at hand, and even then it is likely to be a compromise. Many people who have problems have them because the machine sold to them was not the most suitable for the application.

I know of many dozens (and more) of bucket elevators that run happily and cause the operators no problems whatso ever!

While not wanting to get into a slanging match I also know of a couple of sandwich belt elevators that were taken out and replaced by alternative pieces of equipment (bucket elevators and zig-zag inclined belt conveyors) because operationally they were not suitable.

It is always important with any materials handling system to ensure that the correct machines are selected for the duty, material and layout. Companies with only one product to sell sometimes do their equipment no favours selling it into unsuitable applications. ■

Thanks frederick, for asking the question.

You've given us all lots to think about - Sgt John.rz ■

Designer is RIGHT. I've nowt more to add except "Very well said lad." ■

Mr. Designer,

Sandwich belt conveyors have replaced existing bucket elevators and pocket belts in many cases. Until very recently the reverse had not happened.

I am very familiar with your first case, a single case where a HAC is being replaced with a bucket elevator. That was never a case of mis-application but rather a case of mis-use as the years progressed. The HAC unit, a 36" belt-width system, replaced a very troublesome bucket elevator and was designed to elevate a 3" minus material. It was celebrated by all at start-up and through the first several years. It was shown to many prospective customers. Years Later I became aware of the systems troubles and I offered to correct these, not kowing at that time the nature of the problems. Ultimately it was revealed that the material now handled was much larger, typically 10" to 12" and even larger. We can build a sandwich belt system to handle 12" minus material but this requires a 96" (2438mm) belt width not a 36" (914mm) belt width.

With the new bucket elevator the customer has pledged to reduce the material size to 6" minus. A few years from now we may again be discussing the problems with this new bucket elevator system.

I am not aware of the second case that you mention where a sandwich belt system was replaced by conveyors in switch back arrangement. I am curious to know what system this is and I invite you to advise the forum readers or to advise me via my Email address listed below.

Joseph A. Dos Santos, PE ■

I don't think so.

But I'm not entering into a discussion on the subject. ■

Mr. Designer,

It is of no value if you throw out claims and then don't back them. If this is not the appropriate thread then start another for that purpose.

Joseph A. Dos Santos ■

I know what I know.

I know what I have seen.

I have no axe to grind, I just call it as I know it.

If it suits you to doubt my honesty, such is life. ■

There are two sides to any issue. In fairness to the reader both sides must be aired for fair evaluation.

I certainly don't question your honesty. I am sure that you believe what you say. We all do. That is why it is important to back it up, for fairness sake.

Joseph A. Dos Santos, PE ■

This thread started out because some young lad in the Philippines has really dodgey bucket elevators. It is not fair to slam all bucket elevators as a result.

Vertical lifting, regardless of the hardware involved, is a bit like hydraulics: you only have consider it when you've landed yourself in a corner & there's no other way out. ■

I certainly agree, that if you already own the equipment and it is not working properly then the best path is to determine why it is not working properly, then to correct the problems. The original supplier should provide the answers and the help. If that fails then it is proper to turn to other suppliers/ experts in that same type of equipment for help.

In his very first post, that began this thread, fredericktan75 expressed such dissatisfaction as to consider replacing the bucket elevator with a vertical screw. Does anyone here consider this to be a better solution for 35 meters of lift?

Joseph A. Dos Santos ■

Lets send this thread in an entirely new direction.

Perhaps a skip hoist is in order here, particularly if the material can be bone dry one day & sopping wet the next. One large bucket with radiused corners can handle this change in material properties better than a lot of small ones.

When I look back in my Link Belt catalogues from the 40's to the 60's, skip hoists were not uncommon when every industrial plant had a coal fired boiler and a silo up in the air. (Am I the only one here old enough to remember this?)

35m is a tall bucket elevator particularly if not well built to start with. The feed will interrupted when the skip is lifting but it is better than not lifting for days if the bucket elevator breaks down. ■

A skip hoist is simply another name for a bucket elevator. It just has less & bigger buckets often riding tracks because the chain cannot stabilise the catenary resulting from the vertical offset of the end stations. It is not a realistic option unless there is a very hot product nearby.

Is a screw conveyor a realistic, never mind better, solution either? No. ■

Thank you for the last two posts. If the bucket elevator can be repaired, great. If it must be replaced then Dos Santos Sandwich Belts make the best sense.

Joseph A. Dos Santos ■

Oh I like that! We've done a few over the years and all things considered they have worked well.

One skip with tapered sides and filleted corners, fitted with four simple wheels.

One motorised winch with "off the shelf" steel cable.

One track for the skip wheels to run in.

A couple of switches/sensors to control the winch.

A load sensor to tell you when the skip is full.

Easy, simple and no special parts. A lot to commend it. ■