English
 Supplier sign in
Home
STAY INFORMED
Subscribe to our monthly newsletter.
Your email address will never be disclosed to any third party.
Read our privacy notice.

       

Specialist article
01.09.2021  |  2547x
Share this item
Gully or valley angle of a rectangular hopper

About the gully angle of pyramid shaped hoppers

Recommendations for proper flow from rectangular or pyramid shaped hoppers, in view of the corners of the hopper that are less steep.
Rectangular hoppers are widely used to store bulk solids. Although convenient to fabricate they have process drawbacks in that large flat sides are prone to deflection, so often require stiffening, and the converging faces form gully angles that offer poor flow and self-clearing properties. Some small compensation is given by the rectangular outlets being somewhat easier to fit with slide valves. ​​

Gully angle

The gully angle of a symmetrical, pyramid shaped hopper is roughly 10 degrees less steep than sides and is prone to retention of product unless it is radiused.

Flow pattern

For mass flow design purposes, the inclination of the gullies should be considered as a cone. For funnel flow hoppers the gully angle should exceed the wall friction angle by at least 10 degrees. Some product retention in the corners is almost inevitable unless the corner is radiused or significantly increased in inclination.

Mass flow in two steps

Mass flow is much more practical and residue much less likely if the end walls are made vertical. This can be done in two stages to transform to a square outlet. Both stages could be inclined for mass or funnel flow, or the first stage funnel flow and the second mass flow, to produce a form of expanded flow, with the slot transition giving compensating flow benefits, compared with the final square outlet in mass flow.

The ratio of length to width of an outlet must exceed 3:1 to secure the full flow benefits of a slot outlet and provide reliable discharge similar to a circular outlet diameter that is twice the slot width.

Two opposing walls must be longer than the ‘critical rathole diameter’ and sufficiently steep to permit mass flow to ensure that the hopper will not ‘rathole’. The ends must still be considered as parts of a cone to guarantee mass flow, otherwise the end sections will only self-clear according to the ‘drained repose’ angle.

Calculation
Gully or valley angle c = arctan [ ( tan(a)^2 + tan(b)^2 )^0.5 ]
Where a and b are the inclination of the two sides of the hopper.
Follow the link to find a practical tool to calculate the volume, surface area and weight of a pyramid shaped hopper.

Company information

Related articles

Hopper inserts, an approach to solving poor flow Enhanced hopper performance through sustained examination of  materials, hopper geometries and influence of insert design.
Hopper inserts, an approach to solving poor flow
Enhanced hopper performance through sustained examination of materials, hopper geometries and influence of insert design. The enormous volume of bulk materials handled every year means solids must be stored in hoppers, intermediate bulk containers, silos and other storage devices, often several times before being processed. However, storage can result in a number of handling issues including erratic surges, arching, ratholes, packing, flushing, dead regions, feed upsets, and in some cases can reduce the suitability of the product for the next process stage [IMG02**R45] Although it is seemingly counterintuitive to introduce an obstacle into the storage container as a solution to these problems, the use of inserts can enhance storage container performance. An insert is usually a static fitting on the inside of a bulk storage container, including liners and other modifications that alter the internal space of a vessel. Flow regimes are determined by how the individual particles in a bulk solid respond to local forces at contact points. An insert alters the flow regime of a material
02.10.2021  |  2294x  |  Specialist article  | 
Improving flow in hoppers with Sigma2-relaxation Plane flow is less troublesome as axisymmetric flow. Sigma2-relaxation will show even less flow problems. By: Lyn Bates
Improving flow in hoppers with Sigma2-relaxation
Plane flow is less troublesome as axisymmetric flow. Sigma2-relaxation will show even less flow problems. By: Lyn Bates Stresses on bulk materials can be applied as compressive, tensile or in shear. Whatever combination is applied can be resolved into principle stresses by means of Mohr’s circles. i.e, stresses acting normal to surfaces at right angles to each other without shear stresses. Stresses applied on a sample in one principle plane induce a deformation, creating a reduced stress at 90° according to the Poisson’s ratio of the material (See fig. 2a). That is the change in the width per unit width of a material relative to its change in its length as a result of strain. Bulk material flowing down a conical converging channel has to deform in two planes under the compressive stresses of reducing diameter. Product in a plane flow channel only converges is one plane so, despite being confined, it will flow down walls about 10° less steep that in a cone. A plane flow channel that widens slightly at 90° to the converging plane will allow a larger degree of relaxation to
28.01.2021  |  1024x  |  Specialist article  | 
How to increase capacity of an inclined screw conveyor When the axis of a screw conveyor is inclined, the capacity falls off progressively. Changing the arrangement of the casing can help.
How to increase capacity of an inclined screw conveyor
When the axis of a screw conveyor is inclined, the capacity falls off progressively. Changing the arrangement of the casing can help. The capacity of a screw conveyor falls off progressively as the axis of the casing is inclined. This is mainly because the dynamic repose slope surface of the material is unchanged and is limited by material carrying over the centre shaft by its rotation to fall back into the prior pitch space so the inclination of the screw flight cuts off an underside section of the material in transit. There is also a small degree of back leakage from the upper region, where the radius of the screw separates from the vertical wall of the casing above the centre shaft level. This effect increases with inclination as gravity supplements the force of the friction of the casing wall restraining the contact layer of the material. Moreover, when the axis of the conveyor is inclined, not only is the geometry of the screw affected, but the sliding angle of material on the flight surface is reduced. The inner region of a screw flight face has a much coarser inclination than at the tip
14.12.2020  |  2406x  |  Specialist article  | 

More items

Related categories

PORTALS
BulkSolids-Portal Schuettgut-Portal Recycling-Portal
Related
Bulkgids.nl
SIGN UP FOR OUR NEWSLETTER
Newsletter archive
Service and contact
ContactDisclaimerPrivacyAdvertising
FOLLOW US
Linked