If it is a food product and you don't want dead zones then the first option is better. The second option with higher partition wall can support the material and can support two small arches over both screws. You will have no advantage of using twin screws. Manufacturing cost of this design will be higher. If it is not a food product then I would not bother with any partition simple "U" trough will do. ■

Dear Designer,

You had phoned me today but did not leave your phone number to call you back. Please send me an email on the reason for your call.

Thanks,

Amrit Agarwal

Pneumatic Conveying Consulting

Email: polypcc@aol.com ■

Originally Posted by designer

Screw conveyors are not one of my strengths, so I'm seeking other opinions.

I've attached an outline sketch showing two styles of twin hopper discharger.

The top version is one I'm more used to where each of the twin troughs join at about the horizontal centreline of the screws.

The lower version has the screws spaced further apart so the twin troughs join above the centreline of the screws.

1) is there any practical difference in operation of the two styles?

1. more steel to wear prematurely with the center wedge between the augers

2. any oversize material may or may not travke and simply ride on the clearance

of the auger

3. more defined delivery volume with less bridging and less material not conveyed

provided it is less than the flight width spacing.

2) given that I'm using a twin screw because the material in the hopper has poor flow characteristics, is there likely to be a problem with material bridging the screws in the lower version by getting support from the centre piece between the screws?

Yes, that is entirely the issue with this dimension as it can reduce and block flow if the exit point

of the hopper is small in size( no larger than the augers.

You may be money and aggravation a head in using a walking floor or reciprocating ram boxes in lieu of the auger in thier place. ■

If your material is fibrous with a tendancy to interlock, the top option may tend to drag the entire hopper contents to the end all at once instead of shearing out.

I saw this happen with wood chips once, the partition between the screws was very low and it just dragged the bin contents en masse to the discharge end and plug solid. ■

Provided the central insert is sufficiently steep to induct slip, does not project more that 50% of the screw diameter above the centreline of the screws and the outer casing walls are vertical to above the screw diameters, the central region should not provide a foundation for an arch over the screws and are beneficial in widening the effective hopper outlet. Some casings are made with close screws, to fit an inverted ‘V’ on a flat bottom between the screws, to save forming a more awkward casing shape.

The screw geometry should provide progressive extraction over an axial length greater than three times the casing width in order to secure the maximum flow benefits of this twin-screw casing. Not mentioned is the direction of screw rotation, which is normally opposite hand for each screw, but this also has an influence over the extraction pattern. ■

Please expand upon “material in the hopper has poor flow characteristics”

If the material is adhesive it would benefit to push the screws even closer together. This will enable one screw to clean/wipe the other, and will require mechanical synchronizing of the screws. ■

Why not test the powder for wall and internal friction angle and then calculate the mass flow

cone angle and minimum outlet dimensions using Jenike method.

Lets not leave anything to chance. ■

Hello, I'm installing a feed hopper for a wood chip boiler system that is utilising very much the same design as described at the beginning of this thread. Currently the hopper has a high center v ridge between the 2 augers and both augers are turning the same direction.

If i understand alll of the comments i should cut down the center v section to the half way up the auger, and then replace the one auger with a reverse rotation so as it would turn into the other.

Thanks for any help.

Dave ■