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Thread: Idler Trough Angles

  1. #1
    Kinder Guest

    Idler Trough Angles

    To increase trough angle from 20 to 45 degrees , does this consistantly provide greater belt capacity. (for given belt width) If 45 degrees provides the advantages of capacity and containment of material why is it not the most popular trough angle? Does 45 degrees provide all round advantages? Is is depenendant on material conveyed or other factors........Thanks in anticipation

  2. Neil,

    45 degree trough angle idlers are capable of handling a higher capacity of product for a given belt width -- BUT -- the higher angle also requires longer transition lengths at all pulleys in order to prevent belt damage (longitudinal cracks at the trough junction points). This does not present a problem except at the discharge pulley, where it makes little sense to carry a greater amount of material on the carry run and then have it overflow the belt just prior to discharge. All belts, regardless of the idler troughing angle must be able to support the conveyed material while essentially flat (i.e. -- while going to the discharge pulley).

    In my opinion, the real advantage of the higher angled troughing idlers is with their ability to contain material (less spillage potential) at the load point (allows some bounce room) and along the carry run (minimizes wind influence on the material and bounce effect of the idlers).

    The disadvantages of the steeper idlers include the increased transition zones, increased chance for belt damage, and increased mistracking susceptibility (the wing idlers have a greater effect on tracking and the belt is affected by wind to a greater degree).

    Like most conveyor components, steep trough idlers have their place and offer advantages when used judiciously. Any system should be designed with the needs of the end user in mind (even if the end user doesn't really know what those needs are) and it is incumbent on the system designer to offer the most economical system possible -- taking into account all costs, including maintenance and operational ones.

    If you have specific systems to discuss, I would be willing to help as necessary (especially if I can get a trip to Australia out of it - you pay for time, my frequent flier mileage account pays for air travel).

    Regards,
    Dave Miller
    ADM Consulting
    10668 Newbury Ave., N.W.,
    Uniontown, Ohio 44685 USA
    Tel: 001 330 265 5881
    FAX: 001 330 494 1704
    E-mail: admconsulting@cs.com

  3. #3
    Lawrence K. Nordell

    Lawrence K. Nordell

    President and CEO

    Conveyor Dynamics Inc. [eDir]

    Conveyor Dynamics Inc.

    Professional Experience 57 Years / 11 Month Lawrence K. Nordell has 57 Years and 11 Month professional experience

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    45 degree troughing roll assy use

    Dear Sir

    High trough angles (40-45) are often used today due to better knowledge of the applications:

    1. They consume more power due to the higher compound bending of the belt at the idler junction and higher pressure on the center roll - published in Bulk Solids Handling Power of Rubber Part I.

    2. The high stress at the idler junction must consider the belt construction and its adequate fatigue resistance to junction failure. Thin belts tend to have inadequate resistance to troughing load support - steel cord or fabric. Thus, idler spacing also plays an important role in defining the use of high angle troughs.

    3. They track better than 20-35 degree trough belts due to the increase force differential from lateral displacement - ie horizontal curve design technology.

    4. Often 40-45 degree idler trough designs use a shortened center roll which yields 3 important features: a) it decreases the pressure on the center roll = lower power and junction stress,
    b) balances the idler bearing loads, c) increases the cross-sectional capacity = 28% of belt width for center roll length has about 10% better capacity than the standard CEMA/DIN/ISO 37% of belt center roll length ( 3-equal roll lengths)

    Lawrence Nordell
    Conveyor Dynamics, Inc.
    1111 wesst Holly St.
    Bellingham, WA 98225
    USA
    ph 360/671-2200
    fx 360/671-8450
    email nordell@conveyor-dynamics.com
    website www.conveyor-dynamics.com

  4. Hello Kinder,

    Earlier respondents have already provided adequate information on the subject. In general, 40 / 45 degree trough idler will be difficult to use in layout of short length conveyors (less than 15m subject to belt width) due to transition length. For longer conveyors, its use will depend upon various considerations as mentioned by earlier respondents.
    One will observe from many installations that troughing angle up to 30 degree is quite common for belt width up to 1000mm. 35 degree trough idlers are quite common for belt width from 1200 mm to 1600 mm. 40 / 45 degree trough idlers are quite common for belts 1800 mm and wider. These are generally used combinations of belt width and troughing angles, as guidance and not rigid rules.

    Regards,
    Ishwar G Mulani.
    Author of Book : Engineering Science and Application Design for Belt Conveyor.
    Email : parimul@pn2.vsnl.net.in
    Tel.: 0091 (0)20 5882916

  5. #5
    David Beckley Guest
    Hello Neil,

    Inspite of the fact that this is now quite an old request, I feel I should add a few comments to the above. The increase in cross sectional area of the material is dependant on the burden surcharge angle. The following numbers are applicable for a 1500 mm wide belt. For three equal length idlers and a burden surcharge angle of 20, the difference in material cross sectional area will be 8% and at 5 surcharge, the difference will be 15%. There are however some disadvantages that include:

    The material load acting on the centre roll bearings will be 13% higher with 45 idlers with a 20 surcharge and 20% higher with a 5 surcharge. This increase in load on the bearings could increase the capital cost of the idlers if larger bearings have to be used.

    The height of the troughed belt will increase by 25% between 35 and 45 three equal length idlers. The length of transitions and the radius of convex curves is directly proportional to the trough height. This fact will mean longer transitions and larger vertical curves and this could impact on real estate requirements for the conveyor.

    The width between the skirt plates at the loading point will have to be less for 45 idlers if the same amount of belt is to project from the skirts. If handling large lumps, this reduction in skirt width could be a problem

    As mentioned by others above, the power demand will be greater with 45 idlers

    Inspite of the popularity of the 45 idlers, all of the above should be considered before selecting the troughing angle.

    Regards,

    Dave Beckley
    Conveyor Design Consultants of WA
    Perth, Western Australia.
    Last edited by David Beckley; 2nd March 2004 at 6:57.

  6. Kinder,
    My opinion is that speaking about the angle of the angled idlers without considering the lenght proportion of the same in relation to the center ones will always be somewhat vague.
    We also must consider the density of the material, the velocity of the system, duty cycle etc.

    It takes more power and the transition lenghts are longer. It may damage the belt if not properly selected etc. All those are important facts but if you tansporting cotton, fibers, wood chips...
    Can one maintain the same capacity by subtitution of loaded weight with belt speed?

    In short, I believe that one needs to look at the whole system to realize if 45 deg. is more advantageous than 30 deg.


    Antonio Reis
    Vitrom Mfg Consultants
    Your Process and Manufacturing Solutions
    Phone: 209.834.1900
    Fax: 209.834.1039
    www.vitrom.com

  7. Please keep in mind that as the belt trough angle is increased, the distance across the top edge of the belt decreases. This can be a major problem in the load zone as the cross sectional area of the chute will need to be decreased to allow sufficient edge distance for sealing

    A couple of ways to overcome this is to use a smaller trough angle in the load zone, and increase the angle after the load zone, Keep in mind transition distances for the belt used must be maintained.

    Another approach is to gradually make the transition form flat to full trough over the full length of the designed load zone using adjustable idlers.
    Larry J. Goldbeck
    Martin Engineering

  8. Thats an amazing quantum of information !

    I still have two specific questions and would appreciate replies / opinions -

    1. In any given deep troughing application, would a steel cord belt be a preferred selection, or a textile reinforced belt ? For example, would a ST 630 belt be preferred over a EP 800/4 belt ? Why (or why not) ? Would not the presence of a weft member cause greater problems (bottom cover wear, higher idle power consumption etc.) in a multi-ply EP belt than in a weft-free steel cord belt ?

    2. In a deep troughing application, how EXACTLY would one select the lengths of the wing idlers vis-a-vis the central idler in a 3-roll carrying idler arrangement (ref : Mr. Nordell's #4)? Instinctively, it seems that a belt would be most 'comfortable' on equal length idlers. Would this not be a over-riding consideration considering the extra load on the center roller could be taken care of with heavier bearings and that the replacement costs of belt are normally greater than that of idlers ?

    Thanks in anticipation.

    Kayem

  9. Again these are only opinions and should be treated as such.
    First I agree with Mr. Nordell that the effort of modeling and carrying finite analyses on a full system is the most efficient path for large projects. Of course the finite analyzes package as to meet certain criteria to be of use.
    As for question #1, my opinion is that the choice of belting is most related to the required forces to move the load and not so much to the type of idler arrangement one decides to use.
    In short one is exchanging thickness of belting and weight in some instances for less cross section flexibility.
    In my opinion, the flexibility required to accommodate the throughing arrangement is in a different plane than the flexibility required to perform around pulleys and tensioning systems.
    The types of materials that are used in the bottom cover are important in this manner:
    If the material is compliant as to provide good grip at the drive system, it will resist lateral movement along the idlers and the belt will track poorly or the cover will have high wear. Certainly the alignment of the idlers and the layout structure of the conveyor have some impact on this.
    If the material is less compliant as to better slide on the idlers, one can have slippage on the drive and a mess in control.

    With respect to question #2, I think that the length of the belt and the alignment of the path are the main parameters determining the idler configuration.
    In my opinion, as one folds the belt to form a "U" it looses its ability to accommodate changes in the following stages:
    1- when it is flat or close to flat. Fortunately it slides along the idlers relatively well but it tolerates little center misalignment between drive and tail pulleys.
    2- With equal length idlers, or close to that, around the 45 deg. the belt will have difficulties managing turns and the friction of the bottom cover is a significant player determining the life of the bearings on the angle idlers, much more so than if those idlers are relatively short in comparison with the center idler.
    Here is where some claim that a textile-reinforced belt will stretch and perform better than a steel belt.
    3- after a certain angle the belt easily manages the turns but most of the load is in the center idler.

    Again as I stated above, without all the requirements it is difficult to state the benefits of some specific component arrangement. Every conveyor is a different system and must be treated as a system.

    Antonio Reis

  10. #10
    David Beckley Guest
    To all the above correspondents,

    As this discussion has now included the length of the centre roll I have run some figures that may be of interest. For this example I used a 1500 mm wide belt, 45 wing rolls, the CEMA burden edge distance and (a) three equal length (549 mm long) rolls and (b) a short centre roll 420 mm long with 614 mm long wing rolls.

    The increase in the troughed height of the belt with the short centre roll is 13%, this will increase transition length and vertical curve size.

    The burden cross sectional area increases by 5% for a 5 burden surcharge angle and 2.5% for a 20 surcharge. This is a small increase for the added complication of two roll types.

    The burden height increases by 16% for a 5 burden surcharge angle and 12% for a 20 surcharge. This increase in burden height will increase the pressure on the belt at the intersection point of the rolls where belt damage can occur.

    The load on the centre roll bearings reduces on the short centre roll by 10% for a 5 surcharge angle and 13% for a 20 surcharge. This reduction in bearing load can also be achieved by using three equal length rolls and 35 wing rolls.

    If the conveyor is fitted with a travelling tripper, I would definitely avoid the use of short centre rolls and 45 troughing angles generally, as the deeper trough will increase belt edge buckling problems in the tripper approach curve.

    Finally, from a purely practical point of view, maintenance workers do not like having to carry two different trough roll types when maintaining elevated conveyors.

    As you may now have concluded, I believe there are many advantages of the 35 three equal length roll idler.

    David Beckley.

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