Can you be more specific or gime more details of hopper size, type of chute / feeder under hopper, properties of material to be handled? ■

Googling "hopper valley angle"

led me immediately to

http://www.bulksolidsflow.com/freep...eyangles.html

Such a wonderful thing is Google ........................ ■

Originally Posted by shri12p

Dear All,

Can any body eleborate the formula for caclulating the Valley angle for the hopper.

Should the chute angle be miniumn or the valley angle???

Kindly guide me on this topic

Regards

Shrinivas Bartakke

Namaskar Shrinivas Batakke,

The steeper the valley angle the less bridging will occur and the faster the material will discharge;

what is more important is the opening of the hopper at the base.

The wider the discharge opening the better the discharge feed as it will not allow bridging and rat holing to occur.

Settling for a 45 degree valley angle and a discharge opening six times the size of the run of mine material works well as the material cannot hang up.

Smaller material always benefits from a very wide discharge opening at the base of the hopper to create mass flow conditions from the rear to the front of the hopper. ■

If an understanding of flow from hoppers/bunkers/silos is required then a good starting place is the work originated by Andrew Jenike. This brings together hopper flank angles and outlet dimensions with the properties of the material being stored. ■

I think that the comments of Mr. Batakke should be expanded, as they may give a false impression.

A wide opening will be less likely to bridge, but will not of itself generate mass flow, neither will a steeper valley angle reduce the probability of bridging unless it exceeds the critical value to induce slip on the all the contact surfaces. Some materials will certainly hang up on a 45 degree valley angle and steeper walls can in fact reduce the discharge rate, as flow from a mass flow hopper is generally less than that from a non-mass flow hopper that does not bridge or rathole.

The size of opening required to pass lumps depends on many factors, such as the shape of opening, whether mass flow or not and the flow velocity of the material. Guide figures for these varying conditions are given in a table from www.ajax.co.uk.

It is generally taken that the valley angle of a pyramid shape hopper should be as steep as that of a cone to secure mass flow and the probability of securing mass flow has been assessed for a wide range of common bulk materials for differing degrees of wall inclinations as shown in graphs prepared by ter Borg, E.MeGee and D.McGlinchey, available from lyn@ajax.co.uk. From this is will be clear that very few pyramid hoppers are likely to mass flow, even if the corners are radiused, which helps significantly in affecting clearance and slip.

The note about extracting from ‘front to rear’ of a hopper to create mass flow conditions, presumably one served by a feeder, is dependent on the extraction profile generated by the feeder and the wall inclination of the hopper, rather than the size of opening. With screw feeders this is dependent on the screw geometry, whereas with belt feeders the shape of the hopper interface is critical. Typical shapes for belt interfaces for poor flow and easy flow materials are also available from lyn@ajax.co.uk.

Whereas pyramid shaped hoppers offer poor prospects for mass flow, ‘V’ shaped hoppers are better than cones and some variations on these better still. Their design always depends on the specific bulk material properties, so there is no substitute for securing measured values, of which bulk density and wall friction are the most basic. ■

True on all counts Lyn,

As long as he does not pull my deceased

uncles trick and clear a 12 by 12 surge bin

draw chute with A 12 inch stick of

Hercules Brand Dynamite

and blow the entire chute of its rails when

the chutes were clogged in the surge bin.

Its been 32 years and I still laugh and laugh;

lots of noise and dust other wise and a

geyser of Halite from what I remember.

Happy holidays to all. ■