Re: "Fluff" Bunker Design.
Questions:
-what is the size of bin or hopper you are looking at
-what is the discharge rate required
-how uniform must the discharge rate be
-any process requirement for the hopper to be completely sealed
We have successfully handled chopped polyester fibres and shredded paper (also called fluffs) which are around 3 PPCF from hoppers, and fed them at a relatively uniform rate.
Trying to shear the material out of a closed hopper will not work as the material is too elastic (compressible) and will make a nice tight jam up at the outlet. ■
Re: "Fluff" Bunker Design.
Some materials are best never put in a storage bin with a converging section.
An alternative from the past comes to mind -
A long rectangular bin with a conveyor in the base so the whole bin is live and the contents are fed to one end where it discharges. To avoid a mass discharging in one 'lump' the end is provided with a series of rotating shafts with prongs that pick away at the material and control the discharge. The discharge rate is controlled by the speed of the conveyor. The bin can be fed by a conveyor mounted over the bin and feeding in the opposite direction to the discharging mass so you always get 'first in first out'. ■
Re: "Fluff" Bunker Design.
JD:
Our existing fluff hoppers are 1400 ft3 but we only fill them 50% to avoid having the sweep arm motor tripping out, due to over load. We are looking at 2,000 lbs per hour discharge rate, but since there is another smaller fluff hopper above the extruder throat, the consistency is not super critical.
The hopper needs to accept material at a rate 2-3 times the discharge rate. We have drum filters or bin vents removing the conveying air and the goal is to keep the pressure in the bunker ambient pressure or 1” wc below ambient.
Designer:
Agreed on the no storage ideal but size reduction is a batch operation and pelletizing is continuous. We have about 15 of these bunkers and if the material is discharged at the same rate as the bunker is filled there are no discharge problems.
If the bunker is filled and left for 2-3 day, the fluff de-aerates and packs. The sweep arms are used to stir the fluff and move it into a screw conveyer, which meters into the extruder feedthroat.
We also have three vee-shaped bunkers along the lines of your long rectangular bin / conveyer suggestion. That’s where we needed flow aids.
Thanks for the responses, people.
Any other suggestions?
I’ll keep this thread updated with my progress.
Regards,
Bob ■
Re: "Fluff" Bunker Design.
Bob
Your hoppers are fairly large for this kind of product. The discharge rate is average. We usually use an inclined cleated belt at around 45-50 degrees to draw out of the hopper and let gravity shear the material out. Without knowing the hopper shape & dimensions it is difficult to say whether it would work for you. The hopper walls should also be near vertical.
It may be difficult to maintain the seal for your pneumatic conveyor/dust collector discharging this way. A rubber curtain at the exit may do the job.
Designer: Your idea is good, in fact there are thousands of bins as you describe around here, except they are filled with hay, towed behind tractors and called forage wagons. I have actually suggested to a frugal customer once that this was the only thing he could buy for the price he wanted to pay. ■
'Fluff' Bunker
As you say the equipment works well unless left to stand for an extended period, and then the material settles to a firmer condition it may be questioned whether the hopper walls are too smooth. It is indicated that the critical depth of product to leave the material sufficiently loose to allow the discharger to work is about half the bin depth. Fixing some expamet or other non-slip materialt to the walls will help support the mass and reduce the compacting overpressures, without requiring the product to converge. If this is not enough, a vertical sheet of similar material fixed across the diameter of the bin should help to restrain the mass further, yet allow the contents to collapse to the discharger. ■
Re: "Fluff" Bunker Design.
Quote: 'If the bunker is filled and left for 2-3 day, the fluff de-aerates and packs".
Correctly diagnosing the problem is 90% of the solution. PP fluff will indeed deaerate in the bottom of the hopper with time and compression from headload. Vibrators will do a great job of eliminating what little air is left. Stirring devices can also work entrained air from the material.
I recommend gas permeation (NOT fluidization) pads to keep a SLIGHT airflow into the bottom of the hopper, intended to only replace the air that is released from the product. However you must use extreme caution when adding air, too much and you can empty the hopper out of any small orifice before you can shutoff the air flow.
You can go to Diamondback Technology diamondbacktechnology.com who specializes in the interaction of entrained air within the product voids. They will provide you with an engineered solution showing exactly where and how much air to add. I have had the good fortune to work with Dr. Jerry Johanson, although I’m not worthy to carry his laptop bag I have learned a small amount from his experience. Following is my fluff hopper retrofit at a PP resin producer in Texas. Note the permeation nozzles at the top of the Diamondback hopper.
Otherwise you can do the trial-and-error method, arbitrarily locating air pads into the cone, starting with almost no air and sneaking up to the required amount. Best of luck with your project.
Delmar Schmdt
Melfi Technologies
www.melfitechnologies.com
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"Fluff" Bunker design.
We are Polypropylene web film manufacturers (BOPP) and reclaim everything in sight. Most of our reclaim is in the form of 0.001” (or less) thick continuous film which has been ground through a small screen. This “fluff” (1-3 lbs/ft3) is easy to pneumatically convey but difficult to dispense from storage bins.
We have tried vee-bottomed bins with agitator bars. Flow aids like air cannons, shakers & vibrators only pack the material tighter. We have had some success with air sweeps, on flat surfaces.
Our most robust bunkers are cylindrical, with a rotating sweep arm to keep the fluff aerated and feed a screw conveyer discharge. These work fine unless the fluff is allowed to settle and then sweep motor trips and bridging rear their ugly heads.
So, who out there has a solid “fluff” hopper design we could consider?????
Thanks, ■