Ten Key Steps for Achieving Reliable Flow from Hoppers
by Lyn Bates
1.Make sure that you know the full range of conditions of the material to be stored. Secure an officially verified, 'fully representative', sample and check that it is of consistent supply, from a homogeneous stock and stable in time and under the relevant operating conditions, - or know the reason why.
2.Measure wall friction every time with options, if any, of the wall contact material. Record the measurement for both design and reference. Remember, there is no ubiquitous 'Low Friction' contact material, it all depends upon both the product and the contact surface. Also, wall slip depends almost entirely on wall friction. It is much easier to do something about promoting flow than it is to generate wall slip if the slope of the hopper wall is inadequately steep getting the wall angle right is the most important design feature.
3.Establish, and allow for, any extended periods of storage. Not just in normal use, but for reasons of production campaigns, holidays, breakdowns, or irregular stoppages.
4.Check whether the ambient conditions alter according to production conditions, weather, season or events such as site wash-downs. Is there local vibration?
5.In the first instance, distinctly separate issues of Reliable Flow from Mass Flow of the whole hopper contents. Although a Mass Flow design helps material to flow through smaller outlets than a Non-Mass Flow pattern, it does not necessarily have to apply to the total contents. The choice for selecting Mass Flow is normally decided by how the nature of the product is affected by indefinitely extended storage or the need to counter segregation. An 'Expanded Flow' construction bestows the flow benefit of Mass Flow to the hopper outlet region. See Ajax notes on advantages and drawbacks of mass flow.
6.Ensure by design and fabrication that there are no surface impediments to smooth surface slip. Weld splatter or weld runs across the contact wall surface, offset flange joints, protruding gaskets, recessed ports and projecting intrusion near the outlet are highly effective at opposing the slip of material on the wall contact surfaces.
7.Allow a flanged joint well clear of the outlet, and a little spare headroom, so that access is available, or new outlet section can be retrofitted in the event of major flow difficulties.
8.Consider fitting a valve of a larger size than the final outlet, and converging below, to assist the commencement of flow. Materials will flow through a smaller opening that that required to start the material flowing, particularly if hopper contents are time consolidated.
9.Be aware that circular bins 'ring' like a bell when vibrated. They have inactive nodes at 45° to the initiating point. If fitting two vibrators, install them at 45° horizontal spacing, as near as practical to the outlet and activate them alternately, preferably only when flow is required and not occurring. Do not be bashful about considering flow assisting devices.
10.The most vital region for flow is the geometry of the outlet zone. Vee-shaped hoppers are twice as effective for outlet size than conical flow, and need lower wall angles for slip. For reliable flow when the final outlet size is limited, then use a planar transformation, preferably with * 'Sigma Two' relief ( * For an explanation of Sigma Two relief, and details how to use inserts to improve flow see Ajax technical article by Lyn Bates)
Too Late? - If you have to bang the hopper, it is not properly designed.
Fix it before it gets worse, as it will.
For any problem not covered, contact Ajax at:
http://www.ajax.co.uk/
PS: If you have questions, or want to discuss certain issues in more detail, copy/paste/quote the original text and your comment here:
Ten Key Steps for Achieving Reliable Flow from Hoppers
Ten Key Steps for Achieving Reliable Flow from Hoppers
by Lyn Bates
1.Make sure that you know the full range of conditions of the material to be stored. Secure an officially verified, 'fully representative', sample and check that it is of consistent supply, from a homogeneous stock and stable in time and under the relevant operating conditions, - or know the reason why.
2.Measure wall friction every time with options, if any, of the wall contact material. Record the measurement for both design and reference. Remember, there is no ubiquitous 'Low Friction' contact material, it all depends upon both the product and the contact surface. Also, wall slip depends almost entirely on wall friction. It is much easier to do something about promoting flow than it is to generate wall slip if the slope of the hopper wall is inadequately steep getting the wall angle right is the most important design feature.
3.Establish, and allow for, any extended periods of storage. Not just in normal use, but for reasons of production campaigns, holidays, breakdowns, or irregular stoppages.
4.Check whether the ambient conditions alter according to production conditions, weather, season or events such as site wash-downs. Is there local vibration?
5.In the first instance, distinctly separate issues of Reliable Flow from Mass Flow of the whole hopper contents. Although a Mass Flow design helps material to flow through smaller outlets than a Non-Mass Flow pattern, it does not necessarily have to apply to the total contents. The choice for selecting Mass Flow is normally decided by how the nature of the product is affected by indefinitely extended storage or the need to counter segregation. An 'Expanded Flow' construction bestows the flow benefit of Mass Flow to the hopper outlet region. See Ajax notes on advantages and drawbacks of mass flow.
6.Ensure by design and fabrication that there are no surface impediments to smooth surface slip. Weld splatter or weld runs across the contact wall surface, offset flange joints, protruding gaskets, recessed ports and projecting intrusion near the outlet are highly effective at opposing the slip of material on the wall contact surfaces.
7.Allow a flanged joint well clear of the outlet, and a little spare headroom, so that access is available, or new outlet section can be retrofitted in the event of major flow difficulties.
8.Consider fitting a valve of a larger size than the final outlet, and converging below, to assist the commencement of flow. Materials will flow through a smaller opening that that required to start the material flowing, particularly if hopper contents are time consolidated.
9.Be aware that circular bins 'ring' like a bell when vibrated. They have inactive nodes at 45° to the initiating point. If fitting two vibrators, install them at 45° horizontal spacing, as near as practical to the outlet and activate them alternately, preferably only when flow is required and not occurring. Do not be bashful about considering flow assisting devices.
10.The most vital region for flow is the geometry of the outlet zone. Vee-shaped hoppers are twice as effective for outlet size than conical flow, and need lower wall angles for slip. For reliable flow when the final outlet size is limited, then use a planar transformation, preferably with * 'Sigma Two' relief ( * For an explanation of Sigma Two relief, and details how to use inserts to improve flow see Ajax technical article by Lyn Bates)
Too Late? - If you have to bang the hopper, it is not properly designed.
Fix it before it gets worse, as it will.
For any problem not covered, contact Ajax at:
http://www.ajax.co.uk/
PS: If you have questions, or want to discuss certain issues in more detail, copy/paste/quote the original text and your comment here:
https://forum.bulk-online.com/forumd...-Ask-Lyn-Forumforumdisplay.php?59 Ask Lyn Forum
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