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)

Oscillating Conveyor System

Selection of vibratory conveyor:

The oscillating motion of the trough is achieved via specially designed inclined arms and an eccentric shaft driven by a motor through V-belts. The eccentric shaft is mounted on anti friction bearings and has V-pulleys at both ends with weights on them to counteract the unbalancing force. The rotation of the eccentric shaft provides a forward and backward motion to a connecting arm attached to the trough through a rubberized pin. The trough motion is predominantly horizontal with some vertical component, which causes it to oscillate with a pattern conductive to conveying material. A retaining spring assembly at the back of the trough absorbs shock load. All components including drive motor are mounted on a rigidly constructed base frame.

Advantages:

· Hot and abrasive materials can be handled

· Cooling, drying and de-watering operation can be done during transport

· Scalping, screening or picking can be done

· Units can be covered and made dust tight

· Simple construction and low head room

· Can be made leak proof

Disadvantages:

· Relatively short length of conveying ( about 50m Maximum)

· Limited capacity, about 350 tons per hour for length of conveying of 30 m.

· Some degradation of material takes place.

Applications:

Vibratory conveyors find wide spread application in the transportation of dusty, hot, toxic, and chemically aggressive bulk material through a closed trough or pipe in chemical, metallurgical, mining industries and manufacturing of building materials.

Vibratory conveyors are also employed for transportation of steel chips in machine shop, hot knocked out sand, wastes and small castings in foundry shop. Vibratory feeders are also in use for delivery of small machine parts like screws, rivets etc.

Sticky materials like wet clay or sand are unsuitable for vibratory conveyors. In handling finely pulverized materials, like cement etc., the performance of such conveyors are reported to be poor.

Vibratory conveyors are hardly employed for handling common bulk loads, such as sand, gravel, coal etc as the same can be done more efficiency by belt conveyors.

CASTING

Methods are:

1. Pressing
2. Centrifugal Casting
3. Slip Casting
4. Extruding
5. Gravity Casting
6. Rolling
7. Iso-static Moulding
8. Explosive Compacting
9. Fibre Metal processes

Pressing:

The function principles of the mechanic press machines differ in how to ensure the upper punch main movement by cams, spindles and friction drives, eccentric, knuckle-joints or by the round table principle, independent if the die or lower punch movement is realized by cams  or eccentric systems or other mechanically or hydraulically combined systems. The executions of auxiliary movements are also not decisive for a term-classification. These auxiliary movements can also base on pneumatic and hydraulic principles. In comparison to hydraulic press machines the maximum compaction forces of mechanical powder presses are limited and are placed in the range </= 5000 kN. For the requirements of wet and dry pressing techniques in the field of Technical Ceramics cams, eccentric, knuckle joint as well as round table presses have proved and tested, whereas cam presses especially used for wet-press-techniques of pourable materials. The range of compaction force of mechanical presses for products of the Technical Ceramics is < 2500 kN, what is caused from the less density of the ceramic materials. Normally the upper punch, lower punch and die systems of mechanical presses don’t work on base of multi subdivided punches.

Centrifugal Casting:

It employed for compacting heavy metal powders such as Tungsten Carbide. The powder is twirled in a mould and packed uniformly with pressures up to 3 MPa. The uniform density is obtained as a result of centrifugal force, acting on each particle of powder.

Slip Casting:

Green compact of metal powder may be obtained by slip casting. The slurry, consisting of metal powder is poured in to porous mould. the free liquid in a slurry is absorbed by the mould tearing the solid layer of material on the surface of mould. The mould may be vibrated to increase the density of component. The Components are dried and sintered to provide sufficient strength.

Extruding:

It employed to produce the components with high density and excellent mechanical properties.

Both hot and cold extrusion processes are used for compacting special materials. In cold extrusion the powder is mixed with binder and the mixture is often compressed into billet before being extruded. The binder must be removed before or during sintering. In hot extrusion the powder is compacted in to billet and is then heated to extruding temperature in non oxidizing atmosphere.

Gravity Casting:

It used for making sheets having controlled porosity, the powder is poured on a ceramic tray to form a uniform layer and then sintered up to 48 hrs in Ammonia Gas at high temperature. The sheets are then rolled to desired thickness and to obtain a better surface finish. Porous sheets of stainless steel, made by this process are used for filters.

Rolling:

It employed for making continuous strips and rods having controlled porosity with uniform mechanical properties. In this method the metal powder is feed in to two rolls, which compress and interlock the powder particles to form a sheet of sufficient strength. It is then sintered, re-rolled and heat treated if necessary. Metal powders which can be compacted in to strips include Copper, Brass, Bronze, Nickel, Monel and Stainless Steel.

Iso Static Moulding:

It used to obtain the products having uniform density and uniform strength in all directions. metal powder is placed in elastic mould (Deformable Mould) which is subjected to Gas pressure (65 to 650 MPa). After pressing the compact is removed.

Explosive Compacting:

It employed for pressing hard particles. The metal powder are placed in water proof bags which are immersed in water. It contained in a cylinder having wall thickness. Due to sudden deformation of change at the end of cylinder the pressure in the cylinder increases. The pressure used to press the metal powders to form green compact.

Fibre Metal Processes:

In this process, the metal fibers (Fine wires of Convenient length) are mixed with a liquid slurry and poured over a porous bottom. The liquid is drawed off leaving the green mat of fibre. The mat in which the fibers are randomly distributed is pressed and sintered. The products are mainly used for Filters, Battery Plates and Damping’s.