HORIZONTAL SCREEN

What is an horizontal screen?

In horizontal screen systems, the screens are positioned horizontally. The descent angle of particles is different in horizontal and inclined screens under equal vibration, and the screen openings are wider than in the horizontal sieves used in inclined screens. This reduces the efficiency of screening in terms of size in inclined screens.

To achieve high screen efficiency, the screen sieve should be horizontal and the drop angle should be as high as possible. In horizontal vibrating screens, three vibration motion systems are used to increase screening efficiency and capacity. This movement system is placed at the center of gravity of the horizontal screen, providing the screen with elliptical movement.

For which applications are horizontal vibrating screens used?

Horizontal vibrating screens are used when the precise sorting of crushed rocks in a narrow range is required. Although they are widely used in crushing and screening plants where precision screening and sorting is preferred in the 3rd  Stage (tertiary), they are also used in the 2nd Stage (secondary) and 1st Stage.

Besides the operating speed, the stroke length and angle of horizontal screens can be adjusted to suit the application.

Horizontal vibrating screens can be used under the most challenging of operating conditions with the use of a wet screening system.

Horizontal screens are used in ore preparation and enrichment, in aggregate crushing and screening plants, in the construction and agriculture sectors, and in any sector requiring materials to be sorted according to size. These are the most common type of screen and offer high screening efficiency.

What materials can be processed with horizontal screens?

Horizontal vibrating screens can be used for sorting all kinds of materials as long as the size, screen type, screen sieve opening and screen sieve incline, as well as the direction, frequency and amplitude of vibration, are selected correctly. Wet screening is used for screening moist, clayey and muddy materials, and increases screening efficiency.

Horizontal screens are widely used in aggregate, concrete and asphalt recycling plants, and for a wide range of applications in the mining sector due to the very good results they achieve in screening. Horizontal screens are also used for wet screening and for screening fine materials of similar sizes, as well as in general usage areas.

In horizontal screens, the screened material remains on the screen surface for a long time. The screening efficiency of such screens when used to screen materials of similar sizes is quite high.

Useful tips for the maintenance and operation of horizontal screens.

·        The number of pieces in these screens is not high. When selecting a screen, the appropriate screen movement system, screen opening and screen opening ratio should be selected for the type, size and capacity of the material to be screened and for the desired screen efficiency.

·        The material fed to the screen should be of a suitable size and amount for the screen capacity. Materials smaller than the screen opening will not pass through the screen if fed above capacity, if the rock does not stay on the screen for enough time and if the vibration of the screen is inappropriate.

·        The inclination of the screen sieve, the vibration rate of the screen and the direction of the screen should ensure the material remains on the screen sieve for sufficient time and moves in the required direction, with features to prevent the holes from clogging. If the vibration is too high, the material will be thrown forward across the screen and the desired screening will not be achieved. Under low amplitude vibration, agglomerations will occur on the screen and the capacity will decrease. For this reason, the selection of a suitable vibration system is of vital importance when selecting a screen.

·        Screens with square openings are widely used in ore preparation and aggregate production. In such screens, the open area on the screen surface is larger. When high capacity is required, square screens with wide openings are used, while small elliptical screens or thin long-range screens are used in dewatering processes. If flat pieces are not desired in material after screening, screen sieves with rectangular openings oriented in the flow direction, perpendicular to the flow direction, should be selected.

·        Balance-weighted systems are connected to the screens individually or together with a cardan shaft or coupling, depending on the desired vibration amplitude. Care should be taken to ensure that the weights are symmetrical to each other in a connection.

·        Screens are produced with various qualities, suitable for light, medium-light, medium, medium-heavy, and demanding operating conditions, with steel wire mesh screens being particularly popular due to their low price.

·        Screen sieves must be made from quality materials. The screen surface should not sag and or become stretched due to side tensioners, and should remain tight. The steel wire used in screen production must be strong enough to support the material passing over it, and should be resistant to tension and abrasion. All these features should be considered when selecting screen sieves – price should not be the only determinant.

·        The durability of the screen sieve is determined by the amount of material it screens. Although the cost of synthetic screen sieves may seem high due to its resistance to abrasion, the unit screening cost per ton is low.

·        Records should be kept of when the sieve of a screen is replaced and the screen operating hours, and the type and amount of sieved rock, the feed rate and the output rock dimensions should be recorded. Screening hours should be recorded, and screen sieves should be replaced before they become pierced during sensitive screening applications.

·        Having a feeding chute with a width close to that of the screen feeding chamber (up to 70%) will increase efficiency.

·        Screen frames are usually positioned on springs at the four corners. Spring quality is highly important. All springs should be replaced together when they lose their flexibility.

·        Depending on the application, screens may also be set on screws or reinforced rubber springs. These springs provide a lower operating noise, a safe sieving environment, and smoother start and stop operations.

·        Coil springs are used in non-corrosive and non-abrasive environments. These springs are easy to acquire, maintain and replace.

·        Reinforced rubber springs are used in abrasive and corrosive environments. Reinforced rubber springs are relatively harder to maintain than coil springs. These springs also have an additional cost.

·        In wet screening, the screened material passes through the screen with water and is carried by the water through channels. These channels are prone to abrasion. Abrasion problems can be resolved with rubber coatings.

·        In general, “the lower mesh opening should be half that of the upper mesh or smaller.” For example, if the upper sieve is 4.75 mm, the lower one can be 2.36 mm, 1.7 mm or 850 µ.

·        The passaged of larger pieces through the screen can only occur through tears, perforations or abrasions to the screen sieve.

·        After sieving, the material should be checked for conformity with the intended purpose. Material samples should be taken from before the screen, below the screen and above the screen for screen analysis in a laboratory. Based on the results of the screen analysis, sieves with different openings may be used and crusher mouth settings may be adjusted.

·        In aggregate production, screens are usually located after the crusher. Sieve openings can be adjusted to suit the aggregate requirement, and closed circuits must be created in which coarse material on the screen is returned to the crusher when fine aggregates are required.

·        The amount of material fed to the screen must be equal to the total quantity of material of different sizes produced by the screening. The automatic band scales on belts carrying materials should be checked for correct measurement, and the belt scales should be checked at regular intervals.

·        There should be no belts missing from the pulley systems used in the drive system to provide vibration to the screens, and all belts should be replaced with new ones when necessary.

·        Loose belts produce heat as they pass over the pulley, while over-tensioned belts put unnecessary pressure on the drive system. When pressed with the finger, the belt should only stretch about the thickness of the finger.

·        The side plates of the body of the screen should be made of high quality steel, holes should be drilled properly using a laser or drill, and any internal stresses on the body should be relieved.

·        Screens work through vibration. Vibration causes bolt and nut connections to loosen. There should be no loose bolts in the body of the screen. Counter nuts or knurled washers should be used to prevent nuts from loosening. A special bolt-nut connection called a “huck-bolt” should be used to prevent loosening. The best guarantee against loosening is this fastening system.

·        The side plates and frame of the screen should be connected to each other with huck-bolts or bolts with locking nuts. Connections to the screen must be made with bolts; connections should not be welded. Welds to the screen body do not last long, and will crack in a short time.

·        Regular daily and periodical maintenance should be carried out, all equipment in a crushing and screening plant should be subjected to regular checks, and maintenance should not be delayed. The daily lubrication of moving parts must be carried out regularly.

·        Sufficient sieves, spare parts and consumables should be kept in stock.

·        Aggregate production facilities must produce aggregates of suitable sizes to meet market demand. If necessary, there should be a sufficient number of screen sieve panels of the appropriate size kept in stock for trial use.

·        The measures to be taken in the event of equipment failure in facilities should be planned. When necessary, a guide to feeding and loading from intermediate stocks and from loaders and trucks should be provided, along with any possible changes that may be required in the flow process to ensure the continued operation of the facility.

·        Occupational health and safety precautions should be taken in crushing, screening and sizing facilities, and employees should be provided with continuous training in this area and in technical matters.