Sandeep,

MAIN ADVANTAGES OF CIRCULAR MOTION SCREENS

1.Lower price

2.Better anti blinding and anti pegging ability than low angle linear motion screens

3.Better able to be “fine tuned” to suit changed or unexpected conditions. ie: easier in the field adjustment of throw and frequency, plus the ability to change the direction of rotation

MAIN ADVANTAGES OF LOW ANGLE LINEAR MOTION SCREENS

1.Less head room when installed with horizontal or near horizontal decks

2.No water run off into the “overs” product in the case of wet screening

3.The mechanism is a self contained easily removable module

The Circular Motion Screen is the ideal and generally preferred machine for general sizing and classification applications. Their only real disadvantage is increased head height requirements over the low angle linear motion screen.

For wet screening applications where a general sizing or classification duty is required, the circular motion screen will perform in an effective manner, but because of the declined deck surface, care should be taken to ensure that water in the feed and from spray bars is passed through the deck - and not carried down the underside of the screen body to discharge with the oversize. Where such a water carry over would be detrimental, the low angle linear motion screen should be selected.

The Low Angle Linear Motion Screen is widely used in the mining industry for the washing process. Large screening areas are available with this type of machine which enables thin bed depths resulting in better washing. Furthermore the gentle slope and high acceleration forces tend to give more effective dewatering after washing.

Although the initial cost of a linear motion screen will always be greater than an equivalent circular motion type, the low angle allows simplified structural support requirements with less head room, and particularly for multiple screen arrangements will allow smaller buildings, simplified flow of material with simpler chutes, less conveyors and subsequent cost savings.

For general sizing and classification requirements many operators hold the opinion that the low angle linear motion screens will achieve a higher efficiency because the particles present themselves normal to the apertures. Specific tests over many years removes credence from this argument. It is true that the horizontal projection of the aperture gets smaller as the deck angle increases, but this is only one consideration in the sizing process, and this effect is outweighed by the beneficial effect of counterflow rotation alone.

Another commonly held fallacy is that screening quality is dependent upon retention time on the screen deck, and that the slower velocity of the low angle screen makes it easier for a particle to find its way through a limited opening. What is not being considered here is that the coarser material remaining on the screen deck forms a dense layer which acts like a filter obstructing the finer material.

For general sizing requirements there will be no significant difference in the efficiency of a linear motion verses a circular motion screen, however provided that head room or water run off is not a determining factor, the circular motion screen should be selected because it is better able to be “fine tuned” to best possible efficiency, at a lesser machine cost ■

Sandeep,

MAIN ADVANTAGES OF CIRCULAR MOTION SCREENS

1.Lower price

2.Better anti blinding and anti pegging ability than low angle linear motion screens

3.Better able to be “fine tuned” to suit changed or unexpected conditions. ie: easier in the field adjustment of throw and frequency, plus the ability to change the direction of rotation

MAIN ADVANTAGES OF LOW ANGLE LINEAR MOTION SCREENS

1.Less head room when installed with horizontal or near horizontal decks

2.No water run off into the “overs” product in the case of wet screening

3.The mechanism is a self contained easily removable module

The Circular Motion Screen is generally preferred normal sizing applications. Their only real disadvantage is increased head height requirements over the low angle linear motion screen.

For wet screening, the circular motion screen will perform effectively, but because of the declined deck surface, care needs to be taken that water is passed through the deck - and not carried down the underside of the meshes to discharge with the oversize. Where water carry over would be detrimental, the low angle linear motion screen should be selected.

The Low Angle Linear Motion Screen is widely used in the mining industry and for washing processes. Large screening areas are available with this type of machine which enables thin bed depths resulting in better washing. Furthermore the gentle slope and high acceleration forces tend to give more effective dewatering after washing.

Although the initial cost of a linear motion screen will always be greater than an equivalent circular motion type, the low angle allows a simplified support structure with less head room, and particularly for multiple screen arrangements will allow smaller buildings, simplified flow with simpler chutes, less conveyors and subsequent cost savings.

For general sizing requirements there will be no significant difference in the efficiency of a linear motion verses a circular motion screen, however provided that head room or water run off is not a determining factor, the circular motion screen is normally selected because it is better able to be “fine tuned” to best possible efficiency, at a lesser original machine cost. ■

JOHN: an excellent reply, my apologies but, for some reason I have not been able to access the forum website for about 2 weeks.

.......................

The reason these units are NOT used as a "standard" are many:

- More expensive capital cost

- More expensive to maintain

- More complicated drive systems (typically gear driven)

- Bigger motors needed, more energy consumed

- Lower working clearances between decks

- Higher operating inertias needing stronger structures

- Gravity is free (inclined) Mechanically moving is NOT

- Operating in cramped quarters around unit undesirable

- Nastier working conditions for Maintenance Men

- Harder to install screen sections due to limited space

- Given a choice inclined much simplier device

Having said all of the above, If you were to ask 10 users their preferred choice.....half would say inclined, half horizontal and all would be right. It is PERSONAL PREFERENCE. But, usually driven by the amount of space that is available to install.

Example: If I was doing a simple job, say......changing 3 decks of wirecloth on a lowhead horizontal. I would basically have to remove the top deck first, pull the second deck wirecloth sections up thru the first deck and same with the 3 assuming I did not have removable chutework. Nasty, time consuming and expensive.

LOWHEADS are excellent on dewatering jobs for a whole bunch of known reasons.

Keep Shaking out there......... George Baker, Mod ■

Sandeep,

Depending upon the screen size and duty, either twin unbalanced electric motors or a single mechanical unbalanced exciter may be used.

Unbalance motors are usually not available with as large a dynamic moment as the exciters, and so are typically more suitable for the smaller and/or lighter screens.

However there is some degree of overlap between the two, and where this is the case unbalanced motors are generally (but not always) the more economical.

Refurbished exciters are often available from the original manufacturers. I am not overly familiar with Indian suppliers, but “IC” India - Mr. I Sen (www.intcomb.com) may be able to help, or another reputable supplier would be “Joest Australia” (www.joest.com.au), Mr. Ian Laws. ■