Material Bridging Problem...

[Bluenoser337]

I have square tapered hoppers that discharge a mixture of rock and fines through flat horizontal hydraulic "gates" with the full-stroke opening being about 48" x 36". The material tends to "bridge" across the opening and will not fall through sometimes. Aside from a vibrator unit, does anyone have any ideas for "knocking loose" this material...or preventing it from bridging in the first place. Part of the problem is sometimes caused by freezing temperatures (the material can be damp). Thanks!!

 

[nornrich]

Bluenoser337,

In terms of the problem with the material caused by freezing, you might consider a heating jacket for the vessel. In solving the bridging problem, you might want to take a look a a silo fluidizer. This is a piece of equipment that forces air along the sidewalls of the hopper and into the material being stored. This loosens up the material and hopefully starts the material flowing again. Check out Solimar Pnuematics at

http://www.solimarpneumatics.com.

Regards,

Rich

Richard Nornhold, PE
nornrich@redrose.net

 

[Luza]

Bluenoser337
You don't say any about the material`s size, and lumps/fines distribution, ... it's important to know this in order to reccomend anything. So, I'd saw some that cover the critical bridged zone inside the hopper (like a liner) with 3.0 to 6.0 mm (1/8 to 1/4&quot 304 stainless steel in order to minimize the material/steel friction. Due to SS cost is high, similar results may be obtained with UHMW abrasion resistant / low friction polyestyrene.
Good Luck!

 

[martindup]

Bluenosser337,
All the above suggestions could be correct. Also available is air cannons. Air is blown in short bursts at pressure (6 bar or so) onto the specific area of the hopper where the bridging starts. For this you can also install a air-lance or sword into the corners of the square hopper where the air burst in. The pressurized air comes from very small vessels with a electronic timed solenoid.
I would though suggest finding out from similar industries with similar materials if they have such problems and what they did. Maybe a combination of the methods are needed.
Talking about liners, I've once used glass liners for fine coal. Worked pretty well.
Martindup

 

[Backfill]

Bluenoser:

Do you have the flow and draw angles on the material (i.e. flow function behavior?) If a low friction liner in the hopper doesn't reduce or look like it will reduce hangups, can you:
1. Steepen the hopper angles at all?
2. Insert a vane above the opening. It may break the bridge of interlocked particles. May have to armor the top edge a bit, perhaps with rail or AR bar.

Let us know more about the material properties, also the hopper size, including height and height of material. There are tricks out there... .

Best of luck on this. Be safe in breaking (shooting?) those bridges.

Backfill

 

[mx2mx2]

I know of a coating material that you could use to prevent your gating problem. It will render the surface non-stick and is easy to apply. You can find it at

http://www.kiss-cote.com.

Good luck!