It is normal to have some device at the outlet of the box hopper to give some degree of volumetric control.

Here's one option -

http://www.saxlund.se/eng/stang.html

and here's another -

http://v3.espacenet.com/publicationD...C&locale=enGB

Enjoy

PS, you can also have vertical rotors

http://www.richard-western.co.uk/tra...ders/index.htm ■

Marco,

I worked on a similar system that blends shreaded tires with coal at a power plant.

The walking floor discharges into an open screw feeder. The screw is supported on loadcells. The actual weight doesnt matter as long as the screw has product to feed. The screw feeder discharges onto a conveyor belt.

The feed of the walking floor is a straight setpoint. If the screw is light, the floor kicks on. When the screw is at weight, it shuts off.

The control of the screw feeder is the cool part.

The process runs in a PID loop. The Process Variable is the shreaded tire belt scale rate, the Control is the speed of the screw, and the Setpoint Variable is the rate of flow of Coal.

More coal raises the setpoint, speeds up the screw and is monitored by the tire feed belt scale. ■

The flow properties of the bulk material are the key to the features needed in the handling system. Non-cohesive material with reasonably constant angles of repose discharge with little short time variation in rate. Cohesive, "birds nesting" materials can have very high short time variations in discharge rate which needs smoothing out with systems in my previous post. ■

I'm working with Marco on this issue, unfortunately the material is really difficult to classify ! In general shred cotton stalk and vineyard stalk are shred in a mixer wagon for 15 min, in order to achieve at least a 90% less than 45 mm.

The material so shred is in a fibrous form rather than granulated. But we have made a compromise between size/form and diesel consumption!

So the cohesion of the material is generally high but with a sufficient cycle time in the mixer wagon the fiber size is controlled, hence tangling occurs at local scale (i.e. there is a formation of short radius agglomerates).

We have contacted saxlund for an offer... they were really expensive!! So we (unfortunately) did ourselves by design and construct such system. Indeed the system is analog to a Saxlund ZB push floor (http://www.saxlund.se/eng/stang.html )

It is really interesting the idea of Todd to decouple the extraction from the walking floor from the dosing function of the screw feeder.

So the walking floor will be in on/off mode filling the screw , than the screw speed increase or decrease according to flowrate needs in the utility.

Unfortunately, our screw feeder is rigidly flanged to the discharge flange of the ram feeder and also the material is airlike! (i.e. specific gravity close to 0,1 ton/m3 !!) Hence the delta weight is really small even if we managed to put flexible joint between flanges.

the idea of our german consultants on the pellettizers is to continuously control speed of the two screws as well as cycles/min of the ram feeder. Frankly speaking I'm not confident this approach will work!, I'm attracted instead by the experience of Todd ,but we have to puzzle out how to adapt this to a very light material!

Hope to have clarified some points.. ■

IMHO the material you are describing will "birdsnest" very easily. You do need to consider some features to volumetrically smooth out the dIscharge. ■

Definetely you're right!

we are thinking abt. an horizontal small screw that will even the height of the material falling down into the conveying screw .

What do you think?

For sure we will make a lot of test and adjustment!! ■

Dear All,

As we are the producer of the WALKING FLOOR® system, we can advice you in different ways how handle difficult bulky material (metering and storing). The floors you are talking about are typical wedge floors. Some big advantage of the WALKING FLOOR® system; low in power consumption and low in maintenances.

If you have questions do not hesitate to contact me.

Adelbert Regeling

KEITH WALKING FLOOR Europe

Harselaarseweg 113

3771 MA Barneveld

The Netherlands

+31 (0)342-422007

+31 (0)342-422180

+31 (0)6-50641187

aregeling@keithwalkingfloor.com ■

[QUOTE=Adelbert Regeling;55175]Some big advantage of the WALKING FLOOR® system; low in power consumption and low in maintenances.

/QUOTE]

Lower than push floors/ladder frames? ■

Yes, lower than push floor/ ladder frames.

Contact me if you need more information. ■