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Thread: Crowned Tail Pulley

  1. Crowned Tail Pulley

    I realise crowning a tail pulley on a steel cord belt is not recommended practice.

    Can someone please explain to me why, and the possible consequences.

    Regards
    Shane

  2. #2
    David Beckley Guest
    Shane,

    If you use a crown faced pulley, the differential diameters will cause an increase in the tension in the centre of the belt and a reduction in tension at the edges. As steel cord belts have a high elastic modulus, these changes in tension will be significant. If you look at the relative path lengths around the pulley and consider the induced strain, you will see why crown pulleys are not normally recommended for use with steel cord belts.

    Regards,

    David Beckley,
    Conveyor Design Consultants of WA
    Perth, Western Austrailia.

  3. Dear Mr. Shane,

    Mr. David Beckley has given the engineering reason for unsuitability of crowned pulley with steel cord belts. I am putting the same thing in a simplistic manner as below.

    The textile fabric is comparatively stretchable, so, it can accept differential elongation easily and set properly on the crowned pulley, with lesser value of stress related to strain. However, steel cord belt is less stretchable and it will not easily accept the differential elongation between belt edges and belt center, easily. This will cause large difference in stresses at the belt center and stresses at the belt edges, which is objectionable.

    Regards,
    Ishwar G Mulani.
    Author of Book : Engineering Science and Application Design for Belt Conveyors.
    Email : parimul@pn2.vsnl.net.in
    Tel.: 0091 (0)20 25882916

  4. #4
    Horacio Guest
    As said in the replies the center of the belt will be subject to stronger tensions in Steel cord conveyor.

    If the belt may resist , the weakest point is always the splice will not, in the center of the belts if later you Xray the splice you for sure will observe cord end pull and destroy adhesion between Cord and rubber in the center cables of the splice.

    Later you will see some protuberance on the surface and any time your splice is gone

  5. crowned tail pulley

    OK....this is clear, but bucket elevators supplier crown both the drive and tail pulleys so that they track well.

    Why is this not detrimental??

    Thanks


    James

  6. Yes, as Mr. R J Morrish says, the crowning is used for steel cord belts in bucket elevators. In this case also, the phenomenon as mentioned earlier holds good. However, this is countered by higher safety factor somewhere around 9 to 10 instead of 8.
    The crowning used for steel cord belt in case of bucket elevators, is possible less sharp than conventional values.

    Above information is as per published literature of the belt manufacturers.

    Regards,
    Ishwar G Mulani.
    Author of Book : Engineering Science and Application Design for Belt Conveyors.
    Email : parimul@pn2.vsnl.net.in
    Tel.: 0091 (0)20 25882916

  7. Why crown pulleys?

    Dear Shane
    I believe that the issue should be viewed from the point that since crowning is intended for better belt tracking but that it is bad for the belt, you are still left with the issue that the belt is still running off centre or theat the possibility exsists that it will.
    One therefore has to find products that can steer a belt back to centre but the product should be belt friendly.
    Take a moment to view the products at www.waloni.com and see what we have to offer. Waloni has made belt tracking there core business and concern and have solved thousands of belt tracking problems since 1992.
    Hope we can help you.
    Regards
    Mark Hupertz

  8. I don't believe the added fatigue on the splices and belt is worth the minimal belt training effect of a crowned pulley. This is true for fabric or steel belt and for elevators and conveyors.

    If properly designed, manufactured and installed you don't need crowned pulleys. I would not use a crowed pulley on any high belt tension application especially steel cord.
    Loeffler Engineering Group

  9. Crowned pulley

    Dear Mr. Shane,
    Crowining means you are providing different diameter at centre & at edge.Due to this, belt speed will be different & lead to tension difference & hence shotter belt life.
    Regards.
    A.Banerjee

  10. Strange concerns

    Gentlemen,
    I am quite surprised about these arguments. A standard tail pulley, 1600 mm wide for instance, has a difference in diameter between centre and side of about 2,4 mm. The additional tension we are talking about is just enough to centre the belt properly and reliable.

    The additional belt tensions in the centre are much less than those caused by the troughing of the belt in front of that pulley even if the standard length of the troughing area is kept as per the belt suppliers specifications (which is at least on mobile machines quite often not possible).

    So I see in the crowned pulley one of the cheapest and most reliable solutions to keep the belt on track.

    Holger
    Dr. Holger Lieberwirth
    TAKRAF
    E-mail: holger.lieberwirth@takraf.com
    Internet: www.takraf.com

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