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Thread: Soft Chutes Hard Rocks Combination

  1. #1
    Join Date
    Aug 03

    Soft Chutes Hard Rocks Combination


    As usually, I would request some help:
    The topic is tightly connected to my previous post on chute design, where I got great help from this estimated forum. However, I would like to go a step further.
    We have a customer, a fairly big mining company that wants us to redesign a transfer chute in between 2 conveyors. It is a mine extension project, so that feeding conveyor still does not exist. Receiving conveyor is in place, and has been in use for many years. Conveying material on existing conveyor and on one to be put in place is hard rocks (Zink ore) up to 20" dia. approx. in size. The design capacity is 650t/h @ 200ft/min, belt width 60”. The chute that was designed for this application by another company was a conventional one that, in my opinion would work pretty well. However, prior to my employment at this company, soft chute design (by a prominent soft chute design preacher from Australia) was proposed as a better solution.
    Since I have some concern regarding the particular application, and since I have received some invaluable advice from Lawrence Nordell regarding my previous post, I would like to have your input regarding soft chute in combination with transferring hard rocks.
    Simply I have no experience regarding the particular combination. However I have some trepidation that proposed design cannot accommodate hard rocks of given size in an acceptable way. Namely, I am scared that the wear is going to be so high that even CHT 475 or 500 liners would not be able to provide reasonable long life.
    Your thoughts would be highly appreciated. To make it more clear; I am looking for some information on existing chutes of the same design with the same ore if available. If they do exist, what is your experience with them?

    Best regards.

    Mike Nemet

  2. #2
    Join Date
    Aug 03
    I forgot to mention the transfer height. it is 6.5'



  3. #3
    Lawrence K. Nordell

    Lawrence K. Nordell

    President and CEO

    Conveyor Dynamics Inc.

    Conveyor Dynamics Inc.

    Professional Experience 59 Years / 11 Month Lawrence K. Nordell has 59 Years and 11 Month professional experience

    Discussions 304 Lawrence K. Nordell acceded to 304 discussions, Publications 0 Lawrence K. Nordell Nordell released 0 publications

    Know-How Design (1524) Lawrence K. Nordell used this tag 1524 times, Pipe Conveyor (239) Lawrence K. Nordell used this tag 239 times, Chutes (119) Lawrence K. Nordell used this tag 119 times

    Dear Mike,

    I assume you are defining "soft chute" as a curved hood & spoon type chute?

    To paraphrase your question:

    1. belt width = 60 in. (1524 mm)
    2. capacity = 650 t/h ( assumed metric)
    3. belt speed = 200 fpm (1.02 m/s)
    4. largest lump = 20 in. (508 mm)
    5. drop height = 6.5 ft. (1.98 m)

    Things I would ask that you have not given:
    1. transfer angle between conveyors
    2. discharging and receiving conveyors are the same width
    3. slope angle at discharge and receiving conveyors
    4. rock hardness index
    5. size distribution P80, and P20 in particular
    6. surface moisture content
    7. pulley diameter of discharge
    8. idler transition geometry at discharge
    9. idler trough at receiving station
    10 ore bulk density

    Opinions on your quest:
    1. drop height may be a problem to skrt transit. from 60 to 40 in.
    2. don't need a hood
    3. don't need a curved spoon only a gouge resist. lined kick board
    4. the 60 inch disch. belt may create more problems if in-line xfr
    5. how do you contain the 20 in. round lump at the discharge?
    6. spoon or kick board cannot protect belt at 90 deg xfr @ 6.5ft
    7. 500 brinnel might be a little light but maybe made up by thick.
    8. short height won't give adequate protection against punctures
    9. most likely you have a large granular product that flows well so the sliding angle may be closer to 45 degrees
    10. I recommend the skirt width be on the order of 50 not 40 in.
    11. you seemed to be worried abt liner life - try belt damage

    I would assume you have read the ref. papers published on:
    1. Palabora - Bulk Solids, Beltcon -- see our website references
    2. Los Pelambres - SME authored by CDI's David Kruse

    The design is mostly intuitive, but they say the devil is in the details.

    Others will have more to say I am sure.

    Much Luck,

    Lawrence Nordell
    Conveyor Dynamics, Inc.

  4. #4
    Mick Wordsworth Guest
    A bit late in the day to respond but this may interest you. Tasman-Warajay has had some direct experience with this particular problem in the past. The answer is that the wear mechanism in soft loading / hood spoon type chutes is straight sliding abrasion in sized material, and when larger particle are contained within a range of smaller particles (in what could be still termed as free flowing material). Larger particles behaving indepenently are not suitable for this type of system, they should be contained and put on, rather than launched onto, the recieving belt.

    Within a transfer system of this type material velocity is typically much higher than a conventional design and in harder materials (i.e. iron as opposed to coal) substantial increases in liner wear rates is the norm. Tasman-Warajay in conjuntion with Dr Jeffory Gates (University of Queensland Materials Performance Dept) undertook an R&D exersize at Finnican Island in Western Australia several years ago to establish the suitability of our transfer system designs in hard rock mining. The results were that they work well, but wear is a major issue. The other thing was that our real life in the field testing results were nothing like the results generated by the accepted laboratory type abrasion tests (i.e. sand and rubber wheel) which Jeff had himself participated in at various stages during his career. (Incidently the department run by Jeff speciallises in liner materials mostly in industrial applications, his personal specialty being bulk white iron castings)

    The bottom line is that if you have blockage / bridging problems and this is causing production downtime then a soft-loading transfer will substantially eliminate or help overcome this problem. The down side is that while plant availability is going to increase, so are your liner costs (not a little bit but substantially).
    A variety of liners were used in the experiment including Ni-hard 4, Domite, and chromium carbide overlayed plate. The surprising thing was that the various types all performed well in different locations within the transfer system and dreadfully in others. This of course adds a new dimension to the detailed design of the system as well as the expense of carrying a range of replacement items in your stores inventory. Another problem is that due to the geometry in this type of transfer it is nearly impossible to use standard off the shelf liners (More expense and long delivery lead times).

    I am not trying to be negative, however I would caution you to be sure that the pain is worth the payback before you start, the first step being undertake some in the field testing. This is as simple as positioning a sample of liner material (or several types) in the material stream (possibly the trajectory from the head pulley) where you can acurately measure velocity, remove it after a measured material throughput and weigh it against its original weight. You will then be able to calculate material loss versus tonnage throughput and depending on the selected thickness, calculate liner changeout fequency and expected cost. After that it becomes a simple current costs verses expected costs and what if any resultant benefit exersize.

    The other thing you should be mindful of is that the fundamental design principles of a system of this type are to gather and control the material discharging from a head pulley and then redirect it so that it loads centrally and softly onto the recieving belt at a similar velocity. This means turning the material and you need a certain amount of belt separation to do this (dependant on belt width, velocity, and relationship between the belts). In some cases there is not enough separation to do this and thats that. There are a few tricks that can be done to achieve an acceptable material flowpath in low headroom transfer applications, but after 10 years the best we have been able to achieve is about 8 feet and this is on a small belt.

    Given the belt widths you mentioned, the material size and type, and the separation, my response to you if asked to provide a transfer system of the type that we specialise in would be - Sorry we cant help you. If you have been given differing advice, I would suggest that you ask to be shown one that's operating in the field.

    Regards Mick

    Regards Mick

  5. #5
    Join Date
    Aug 03
    I want to thank to everyone of you on your kind responses.



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