Riddle me this… what does a hopper and lampshade have in common?

The answer to this riddle may not be obvious, but, it is quite simple…the hopper and lampshade have the same angle!  This is shown in the graphic.Maynard_blog_8.28.13

As with a lampshade (see “A”), a hopper must be made economically.  Consequently, a 60º angle (see “B”) for a conical hopper is most commonly manufactured due to its simplicity, accuracy, and least amount of waste generated during fabrication.

The 60º cone for a silo or bin (see “C”) is derived from a semi-circle (see “D”) with a smaller cut-out for the required outlet; it is then rolled into a cone shape (see “E”).  With this, the fabricator can quickly make two identical hoppers at 60º with no scrap other than the outlet cut-outs!

Unfortunately, though the 60º cone is attractive economically to fabricate, it generally will not allow mass flow for most powders and bulk solids.  As a result, a Funnel flow discharge pattern will occur, often yielding flow problems such as arching, ratholing, powder flooding, and segregation.

If your material has any of these characteristics, then a mass flow hopper should be selected:

1)    fine powder (average size < 100 US mesh or 150 μm)

2)    prone to arching and ratholing

3)    prone to caking or spoilage

4)    segregation tendencies

If your material does not have any of these characteristics, then a funnel flow hopper may be acceptable.  Mass flow hopper angles can easily be determined through bulk material flow testing.  Additionally, cone shaped hoppers are not the only geometries that can provide mass flow.  Wedge shapes and transition hoppers can also be designed for mass flow provided the surface selected allows flow of the bulk material against the hopper walls.

At Jenike & Johanson, our responsibility is to assist you with selecting the most economical, practical, safe, and efficient storage and handling solution – we are not in business to sell you mass flow hoppers. Contact us  if you have a question about hopper application or whatever else may be on your mind.  Some “free” advice…leave the 60º angle selection for the lampshades!

2 Responses to Riddle me this… what does a hopper and lampshade have in common?

  1. Lyn Bates says:

    It is with great trepidation that I dare to extend comment on the contribution of Eric Maynard on hopper design.

    One could bicker that some lampshades differ in angle and there is nothing especially economical about choosing 60 degrees as a hopper angle. Other angles may better suit the aspect ratio of standard sheet sizes, in fact a cone that forms a wall angle of 63,4 degrees has minimum wastage from a sheet that has the common ratio of 2:1 between the length and breadth.

    However, a more important point, that Eric will be well aware of, is that the selection of an optimum hopper design is quite a bit more complicated than possible to condense in such a short article.

    Other fine details may be added to expand on his notes. The selection of mass flow for fine powders and material prone to segregation may not be essential unless these properties give problems. An ‘expanded flow’ construction, rather than total mass flow, may be appropriate for a material that tends to arch or rathole, unless other factors determine otherwise. A mass flow section at the outlet region is also favourable for passing lumps that tent to form structural arches. The significant flow benefits of wedge shape hoppers could also perhaps be more emphasised.

    Overall, I take my hat off to J & J for their invaluable service to the solids handling industry and would commend any with uncertainties to send bulk material for testing.

    Lyn Bates

    • Eric Maynard says:

      Hello Lyn,

      Thank you for your comments on my recent blog post. I fully agree with your statement that “selection of an optimum hopper design is quite a bit more complicated than possible to condense in such a short article”.

      The same thought applies when I say to my sons “be careful” when they go to play outside…for instance, “be careful” implies “watch out for cars while on your bikes”, “don’t jump off the swing set”, or “don’t hurt each-other when wrestling”!! A simple statement can often contain a wealth of instructions/guidance…and it is imperative that the end-user ask for further information if clarity is not achieved.

      Thanks for following our blog and providing pragmatic commentary.

      — Eric