Re: Horizontal Screw With End Hanger And End Discharge?
No problem; in fact an improvement which I use all the time. ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com
Re: Horizontal Screw With End Hanger And End Discharge?
thanks for the reply. another question:
for this configuration, is there any need to have a larger pitch of the flighting near the discharge in order to allow the material to leave the screw more easily? ■
End Discharge From Screw
If the conveyor is not of an extended length it is much better to adopt a cantilever design from double bearings at the drive end. Pushing sand past a hanger bearing may cause contamination and wear if the material has to be expressed horizontally. If a bearing is essential it would be useful to extend it beyond the casing to allow the material to fall clear, unless this exposes it to other hazards. An expedient is to double flight the last section of screw before the hanger bearing to reduce the level of material transferred.
If the screw has to press the bulk horizontally forward at the end of the casing, it would be better to move the hanger bearing back along the trough and fit double flights before and after the bearing, so that the final axial load is on flights, rather than pushing past the obstruction of the bearing and its supports. ■
Re: Horizontal Screw With End Hanger And End Discharge?
Thanks Lyn. I will follow your advice and go with the cantilevered design. Here's another question.
If I use a tubular trough, am I guaranteed to get 95% loading? That is what is stated in one of my reference books (Sullivan Strong Scott). If that is the case, why would anybody even consider using a U-trough design? If one can get 95% loading with any type of bulk material, one would only need to spin their screw at a lower rate to acheive any rate capable with a U-shaped trough.
I am trying to run my calculations using the equation in CEMA 350 for capacity. And I am uncertain what my percentage trough loading for tubular casings... does it depend at all on the bulk material properties? Does varying the angle of inclination also affect the percentage trough loading?
Thank-you all for your responses! ■
Fill Level Of Screw
The fill level depends on infeed conditions. With a Feeder from a hopper, material falls into the screw to virtually fill the cross section. The volumetric fill is usually about 95%, depending on the screw speed but the density is also dependent on how the material flows from the hopper, so don't rely on settled density measurments for rating the mass occupying the screw volume. The axial movement of the screw contents then depends on the friction between the material and the face of the screw flight. A full screw does not move material forward one pitch space per revolution but rotated the mass in a helical manner according to the face angle and contact friction.
Conveyor loadings are below 45% of cross sectional fill to avoid back spill inefficiency and allow material to pass intermediate bearings. There are various recommendations in CEMA to allow for abrasive and poor flow materials. Also, allowance has tro be made for variable infeed rates, where appropriate.
Crudely speaking, inclination of the screw axis results in reduced transfer capacity. Slowly, at first, then down to about 30% of the horizontal capacity at 30 degrees, falling off rapidly above this angle because fall back over the centre shaft and in the gap between the flight and the falt side of a 'U' trough that becomes more exposed. The various modes of handling bulk material by screw are described in my book - 'Guide to the Design, Selection and Application of Screw Feeders'. ■
Re: Horizontal Screw With End Hanger And End Discharge?
Okay one small question that I am being held up on:
CEMA 350, Page 24. Equation for the capacity per minute per rpm:
C/rpm = 0.7854 (Ds^2 - Dp^2)*PK 60 / 1728
For all you screw conveyor guru's out there, how often do you actually use this equation to help you determine capacity?
And if you do... for quantity "K", do you put the percentage trough loading as a whole number? I.e. for 45%, do you insert .45 or just 45?
Thanks for your help! ■
Horizontal Screw with End Hanger and End Discharge?
Hi all,
I am designing a screw conveyor that will be moving Dry silica-like sand horizontally into a cross-flowing fluid stream which will carry the sand away. The sand is gravity fed into one end of the auger, but because of space constraints, the discharge must be in-line out of the top end of the auger.
My question is, has anybody done this before? As far as I've seen in design booklets, discharge outlets are usually perpendicular to the axis of the screw... I have not yet seen discharges out the top end of the auger. Since the screw is moving the sand in that direction anyway, my assumption is that this would NOT be a problem. The only challenge i see is being able to maintain an even and steady flow out of the discharge end.
Also, at the discharge end, I would simply put a mid-hanger bearing which would not obstruct flow, to support the other end of the screw.
Thoughts & ideas are greatly appreciated! ■