Vertical screw conveyors

A vertical screw conveyor conveys material upward in a vertical path. It requires less space than some other types of elevating conveyors. Vertical screw conveyor can handle most of the bulk materials provided there is no large lump. The maximum height is usually limited to 30m.

A vertical screw conveyor consists of a screw rotating in a vertical casing. The top bearing for the screw shaft must be designed to stand against radial and thrust loads. A suitable inlet port at the lower end and a discharge port at the upper end of the casing are provided. Feeding a vertical screw conveyor deserves careful consideration. Most materials are fed to the vertical conveyor by a straight or offset horizontal feeder conveyor. The ideal operation of a vertical screw conveyor is to have a controlled and uniform volume of material feeding.

Uneven feeding and start stop operation may adversely affect the performance of the vertical screw conveyor in terms of speed, capacity and horse power.

Average capacities and speeds of vertical conveyor

Nominal diameter of screw in mm	Capacities in m3/hr	Speed of screw
150	10	Up to 400 RPM
250	35	300 RPM
300	75	250 RPM
400	170	200 RPM

Vertical screw conveyors or some special design of vertical screw conveyor finds wide application in ship unloading.

Practical experience with these conveyors has shown that the resistance factor for vertical conveyors is higher than those of the horizontal conveyors. Resistance factor λ may be taken as 5.5 to 7.5 for grains. 6.5 to 8.3 for salt.

The driving power of the loaded screw conveyor is given by:

P = P_H + P_N + P_st

Where,

P_H = Power necessary for the progress of the material

P_N = Driving power of the screw conveyor at no load

P_st = Power requirement for the inclination of the conveyor

Power necessary for the progress of the material P_H:

For a length L of the screw conveyor (feeder), the power PH in kilo watts is the product of the mass flow rate of the material by the length L and an artificial friction coefficient λ, also called the progress resistance coefficient.

P_H = I_m.L. λ.g / 3600 (kilowatt)

= I_m.L. λ / 367 (kilowatt)

Where,

I_m = Mass flow rate in t/hr

λ = Progress resistance coefficient

Each material has its own coefficient λ. It is generally of the order of 2 to 4. For materials like rock salt etc, the mean value of λ is 2.5. For gypsum, lumpy or dry fine clay, foundry sand, cement, ash, lime, large grain ordinary sand, the mean value of λ is 4.0.

In this connection it should be noted that the sliding of the material particles against each other gives rise to internal friction. Other resistance due to grading or shape of the output discharge pattern contributes to the resistance factor. That is why the parameter λ is always higher than that due to pure friction.

Drive power of the screw conveyor at no load, P_N:

This power requirement is very low and is proportional to the nominal diameter and length of the screw.

P_N = D.L / 20 (Kilowatt)

Where,

D = Nominal diameter of screw in meter

L = Length of screw conveyor in meter

Power due to inclination: P_st

This power requirement will be the product of the mass flow rate by the height H and the acceleration due to gravity g.

P_st = I_m.H.g / 3600

= I_m.H / 367

H should be taken positive for ascending screws and will be negative for descending screws.

Total power requirement:

The total power requirement is the sum total of the above items

P = (I_m (λ.L + H) / 367) + (D.L /20) (Kilowatt)

Vibratory conveyor / Oscillating Conveyor

A vibratory conveyor essentially consists of an open or closed trough or pipe, generally horizontal but not always so, and which is elastically supported on a base structure or suspended from an overhead structure by springs. The trough or pipe is caused to oscillate at high frequency and small amplitude by an appropriate drive mechanism. Vibratory conveyors are commonly employed in industry to carry a wide variety of particulate and granular types of bulk materials. The fundamental action of the vibrating troughs on the bulk material loaded on it is to throw the particles upward in the forward direction so that the material performs series of short hopping movement and propagates at a certain speed.

Oscillating conveyors are utilized to convey sand or other granular particles at a desired rate. The conveyor is generally placed under a vibrating shakeout or a grid to eliminate direct handling of hot sand by the belt conveyor. In the process of reciprocation, the oscillating conveyor cools the hot sand to some extent which increases the life of the return sand conveyor belt.

An important characteristic of vibratory conveyor is the ease with which the flow rate of the conveyed material can be controlled by adjusting the amplitude and or frequency of the vibration. This particular aspects of such conveyor has led to the wide spread application of vibrating trough as feeders employed to supply material in controlled amount to various machines. When the trough is replaced by a screen, the vibratory conveyor may serve as vibrating screen, which has wide application in various industries. A distinction must be made between feeders and conveyors. A feeder is used as a discharge device under a storage hopper or bin and is subjected to varying head loads. A conveyor requires regulated feed rate and must not operate under varying head load conditions.

Construction details of Oscillating Conveyor:

CONVEYOR LAYOUT

Conveyor layouts:

Belt conveyors can be designed for practically any desired path of travel. It should be noted that transfer between conveyors should be avoided where possible due to additional wear on the belts at the loading points. Some of the profiles shown below:

Horizontal Conveyor

 

 

Decline Conveyor

Inclined Conveyor

Overland Conveyor

CONVEYOR LAYOUT

Conveyor layouts:

Belt conveyors can be designed for practically any desired path of travel. It should be noted that transfer between conveyors should be avoided where possible due to additional wear on the belts at the loading points. Some of the profiles shown below:

Horizontal Conveyor

 

 

Decline Conveyor

Inclined Conveyor

Overland Conveyor