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Thread: Silo Honking

  1. #1
    Stef R. Guest

    Silo Honking

    Dear forum

    I have to design 650 m3 Aluminium Silos for the storage of PET-granules.
    These products are known to induce the famous "Silo honking".
    I know this phenomena can be counteracted by building in internals in the silos to create a "first in - last out" flow. However these internals are quit expensive and often cause problems for the stability of the silos.

    Please let me know if there are any other solutions to prevent the silos from honking.

    All help will be much appreciated.

    Many thanks


  2. Silo Honking is due to the slip-stick behaviour of the granular material between the material itself and the silo wall. For smooth wall, thin tall silos pulsations occur mostly in mass and mixed flow patterns but some core flow silos have also been known to honk. The pulsations occur up to a certain height known as critical height and below that they stop. Since you are designing aluminium silos there are severe structural implications and also variable discharge rate issues. There are a number of ways to address this issue easiest remedy is to roughen the cone wall surface up to critical region. Silo cone inserts work also.

  3. #3
    Stef R. Guest
    Thanks for the information Mantoo.

    Is there a way to determine the critical height of the product up to where honking can occur?

    We are also considering to add small internal cones at certain heights of the cylinder, thus reducing the pressure in the cylindrical shell in order to avoid the slip-stick behaviour.
    This in case roughening up the cone (and part of the cylinder) is rejected by the client. (These silos need to have mass flow at any time as the product stored comes from a mixing blender, and need to be withdrawn from the silo in a "first in first out" sequence.)

  4. If mass flow is required then wall roughening is not an option. Only method I am aware of measuring this critical height is experimental maybe there is a way of calculating it also.

    Since silo cone insert is an art rather then a science be very careful in its designing. There are few manufactures who sell these cones under various trade names. Normally single cone of suitable diameter is fitted at appropriate vertical distance from the silo outlet. I would prefer the cone angle to be similar to the silo cone angle so that there is no preferential flow either on the insert or silo cone.

  5. #5
    Stef R. Guest
    Thanks Mantoo for your reply. This is very helpfull.

    By the way, I am aware of the "art" of inserts in silos. We have learned from years of experience that the design loads on these inserts should be taken very conservative.
    Simple assumptions combined with increased safety factors do the job, rather than trying to figure out what really happens in the silo with inserts.
    The disadvantage of this "state of the art" engineering is that when whe have to compete with other firms, that do not have this experience, we often loose the project. But this is an other discussion.

    Kind regards

    Stef. R.

  6. #6
    RPD - Invista (UK) Ltd., U.K. Guest
    Edinburgh University led a research project into this a couple of years ago and produced quite a good report on the causes and looked at some alternative solutions.

    The contact at Edinburgh is Dr Jin Ooi (, it may be worth making contact with him.

  7. #7
    Stef R. Guest
    Thanks RPD

    I will contact him immediately.


  8. #8
    We have been very successful in designing anti-dynamic tubes in our aluminum welded silos to prevent honking and quaking. They are simple and inexpensive, and they work. Please e-mail our company for more information.

    Keith McGuire, PE
    Columbian TecTank

  9. Dear Sir

    the University of Karlsruhe in Germany has done quite good research in that field under a special research program SFB219. There is a doctorial thesis of Dr. Tejchman. He is now Professor in Polen (Katedra Podstaw Budownictwa i In¿ynierii Materia³owej
    Wydzia Inynierii Ldowej i Œrodowiska
    Politechnika Gdañska
    tel: (058) 347-14-81
    You may ask him or the University of Karlsruhe about this matter. Tell him you got his contact data through me.

    Best of luck

    Dr. Tarek Nasr
    Scherr+Klimke AG
    Ulm, Germany

  10. Thumbs up Silo Honking

    Although the term 'silo honking' is new to me the problem is not! There is a safe, remove and effective method to prevent this occuring with any dry material, powders, ash, granuals etc., within silos and hoppers. Primasonics Acoustic Cleaners have been installed on hoppers and silos in a wide range of industries in over 40 countries worldwide with excellent results By installing the correct model of sonic horn and sounding it for a few seconds at pre-determined intervals, both ratholing and bridging of material within silos and hoppers is eliminated and mass flow at maximum output is the result.

    Can I suggest that you visit one of the following web sites to gain a better insight into how these acoustic cleaners are designed and operate. There is a US web site - - which contains 'An Irishman's Guide to Acoustic Cleaning' along with specific information on their application within silos & hoppers. There is also a silo questionnaire which can either be filled in on line or downloaded. The other web site worth visiting is - - which is a little bit more technical.

    If you prefer you can e-mail me directly on -

    The end of your problem is in sight!

    Donald F Cameron
    Managing Director
    Primasonics International Limited

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