Originally Posted by nikhilmohite2010

Dear Sir,

I am a mechanical design engineer for material handling equipments. I want to know whether U trough screw conveyors can carry material at 45 deg. inclination ? material is DDGS with B.D.0.45 g/cc .capacity required is 9 tph

or whether pipe will be suitable for this application?

Please reply.

Well it certainly won't carry much, if any, in a gravity flow mode of axial transfer and it is rarely recommended because of the low capacity efficiency. Transfer up the slope depends on the material sliding down the face of the screw flight in this manner of conveying so relate the contact friction value of the material on the screw flight surface to the effective inclination of the flight tip to the horizontal and you will see little, if any, margin for a repose condition to develop. Short pitch construction helps in marginal cases and some benefit can be given by a relatively high screw speed and co-axial restraining angles above the 'rising' side of the screw but you would be better seeking the advice of a specialist if the decision is important as many things can go wrong with inadequate design experience. ■

Hello,

An important American source (LB) provides following information about screw conveyor constructional features with respect to screw conveyor inclination to horizontal.

1) For inclination upto 20 degree: Regular pitch screw (i.e. Diameter = Pitch) operating in U-Trough.

2) For inclination more than 20 degree and upto 45 degree: Short pitch screw in U-Trough but with shroud cover. Short pitch screw implies that Pitch = Half the diameter.

3) For inclination more than 45 degree and upto 60 degree: Short pitch screw in split type tubular casing.

It seems the arrangement-2 has ease of providing hanger bearing and ease of access for maintenance compared to tubular type. Otherwise one can also use construction-3 for application-2. The split type tubular casing together with hanger bearing will require somewhat complex construction considering erection, maintenance, etc.

Short pitch (half pitch) results into more (approximately double) pushing force per unit length of screw conveyor, on material being conveyed. So screw has short pitch for higher inclined screw conveyors. As said earlier, regular pitch is OK upto 20 degree, as per the said information.

Ishwar G. Mulani

Author of Book: ‘Engineering Science And Application Design For Belt Conveyors’. Conveyor design basis ISO (thereby book is helpful to design conveyors as per national standards of most of the countries across world). New print Nov., 2012.

Author of Book: ‘Belt Feeder Design And Hopper Bin Silo’

Advisor / Consultant for Bulk Material Handling

System & Issues.

Pune, India. Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

Fitting a shroud will help to reduce fallback, but increases cost somewhat. intermediate bearings on inclined conveyors will offer more obstruction and should be used with considerable discretion and attention to detail. Ultimately, much depends on the nature of the bulk arterial, that has not been mentioned. Overall, I would suggest that the design of screw conveyors inclined at more than 30 degrees would be best left to specialists because it is not only the conveying aspect that is important, but the pick-up characteristics at the inlet, where the feed hopper or inlet chute design, inlet form and length and the distance along the casing from end plate are of large significance.. ■

Hello,

To understand the influence of inclination on ‘conveying ability’ of screw conveyor, it is worthwhile to analyse the phenomenon from basic principles. Some information given below will be useful for the readers who are not so expert on screw conveyor design:

1) Take a ordinary screw (bolt) with a loose nut. When we rotate the screw, the nut will have a linear motion, forward or backward if nut is prevented from rotation. The nut will not move forward or backward if nut is also rotating with the screw at same rotational speed. To be precise, the nut linear motion will depend upon rotational speed difference between the screw and the nut. The maximum linear speed will be when nut rotation speed is zero (we are discounting negative rotation of nut). Forward or backward linear motion will be according to the helix type left or right, and direction of rotation (clockwise or anti-clockwise).

2) Now consider the case of horizontal screw conveyor. Suppose material mass is ‘M’ in a one pitch length. The friction coefficient is ‘mue’ between material and screw flight, as well as material and trough, say 0.4.

The material friction grip on trough = (mue).M.gwhere ‘g’ is gravitational acceleration constant. Also above is the resistance to motion, any direction tangent to trough.

The material is pushed forward (axially) by the flight. Therefore the flight pushing force will be also equal to resistance to motion.

Hence pushing force by flight = (mue).M.g

Now the rotating screw will also tend to rotate the material which will be corresponding to above value (perpendicular force to flight surface).

Hence material rotational force = (mue).(mue).M.g

Thus the material rotational force is less and so it will not rotate and will remain stand still. This is evident by (mue).(mue).M.g < (mue).M.g

Thus in this case material (nut) will not rotate and hence material will have a linear motion when screw is rotating. The flight helix angle is very shallow (9 degree for half pitch and about 17.5 degree for regular pitch) and its cosine influence effect is neglected.

3) Now the other limiting case is 90 degree vertical screw in a cylindrical trough.

Here, the material is resting on flight surface which is nearly horizontal.

Hence friction grip on flight face = (mue).M.gThe flight will tend to rotate the material by this force.

The force resisting rotary motion of material is by material spreading force by Rankine factor, against trough. So resisting force by trough surface to material will be (mue) x (Material side spread force as per Rankine formula). This will be quite low.

Thus the material rotational resistance is less than the rotating impelling force. So material will freely rotate with the screw and will not move forward.

The only solution would be is to increase material fiction grip with the trough by introducing centrifugal force. By choosing the screw rotational speed (having ‘G’ effect of adequate value acting on material in trough), it would be possible to create situation where material rotation impelling force arising from flight surface is less than the material rotational resistance force arising from trough. In this situation the material will not be rotating (i.e. being bulk material, the bulk material average rotating speed is less than the screw rotational speed). This will result into material being moving upward (into being conveyed).

The information is for primary understanding. The concerned application engineer is to develop the exact calculation procedure, befitting to the need.

The write-up mentions 2 limiting cases of inclination. The information can be applied to conveyor of other inclinations wherein force perpendicular to trough will be M.g.cos(theta) and force along trough will be M.g.sin(theta).

Ishwar G. Mulani

Author of Book: ‘Engineering Science And Application Design For Belt Conveyors’. Conveyor design basis ISO (thereby book is helpful to design conveyors as per national standards of most of the countries across world). New print Nov., 2012.

Author of Book: ‘Belt Feeder Design And Hopper Bin Silo’

Advisor / Consultant for Bulk Material Handling

System & Issues.

Pune, India. Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

If the thread starter is still interested I would suggest that he constructs the auger which would be very cheap Then he could try a pipe casing. If that didn't work for him neither would any sort of trough. Or what?

Then perhaps he might care to present his results...for his unspecified conveying distance. Just a thought.

Roland's suggestion to find out what the manufacturer comes up with is best: if the material was available.

American manufacturers of this equipment carry plenty of very comprehensive literature on the subject. It is mainly in N. American units and the situation is hardly likely to improve after 20th January inst. ■