INCLINED SCREEN

What is an inclined vibrating screen?

Inclined vibrating screens have no horizontal layers, being designed at a certain angle. The screen sits on springs mounted at the four corners of the chassis. The screen body is driven by the vibration system.

For which processes/applications are inclined vibrating screens used?

Inclined vibrating screens are used for sizing rocks of a wide range of sizes when high capacity is needed. In these screens, the material to be screened moves across the screen surface due to the inclination and vibration of the screen. During this movement, smaller particles pass through the screen opening while the larger particles move across the screen surface and are discharged at the end of the screen.

Inclined screens are the most popular screen type, and can have up to four layers. The angle of the inclined screen is between 15° and 30°, and the vibration stroke can be adjusted between 6 mm and 12 mm, depending on the application and speed.

Inclined vibrating screens are used in various industries, for aggregate production, mining operations, industrial mineral production and agriculture, and in the chemical and food sectors. The popularity of inclined vibrating screens is due to the high capacity and high screening efficiency they offer, if selected correctly.

What materials can inclined vibrating screens process?

Inclined vibrating screens can be used to separate all kinds of materials, as long as the size, screen type, screen mesh opening, screen sieve slope, vibration direction, frequency and amplitude are selected correctly. When screening moist, clayey or muddy materials, screening efficiency can be increased through a wet screening approach.

Useful tips for the maintenance and operation of vibrating inclined screens.

-        The main parts of the screens:

-        Main chassis and connections

-        Screen sieves

-        Drive system

-        Springs

Feed and discharge zones

·        The number of pieces is not high in vibrating screens. 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.

·        In vibrating screens, the inclination of the screen, the vibration rate of the screen and the direction of the screen should be set to ensure the material remains on the screen for a sufficient amount of time, and moves across the screen, thus preventing 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.

·        As the angle of descent of the material over the inclined screen increases, the likelihood that material of appropriate size will pass through the screen increases. In such cases, the vibration amplitude must be low and the amplitude angle and frequency must be high. In other words, the material should pass over the screen as perpendicularly as possible, should not rise too high above the screen and should strike the screen surface many times before leaving the screen surface. A large amplitude angle facilitates screening by loosening the bed of material being screened. Under such conditions, the likelihood that particles will pass through the screen increases.

·        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.

·        The screen frame surface, size and tensioning system should be suitable for the screen sieves commonly available on the market. Taking a positive approach, it should be possible to adapt it to different screens with small changes to the chassis. The side tensioning systems of polyurethane screens are often similar to those of steel mesh screens.

·        The material to be sieved should not come into contact the main chassis of the screen. Side edges that come into contact with the material on the screen will wear, and any worn parts should be easily replaced with spares. If necessary, tension plates that come into contact with the screened material should be covered with polyurethane or rubber.

·        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.

·        In cases where screening efficiency is not important, small holes in the screens may be temporarily patched using the same screen material if necessary, and the screen can continue to be used for a while.

·        For efficient screening, the material to be sieved must be properly distributed over the screen. For this reason, the material should not be fed to the screen from a single point, but should be properly fed transversally.

·        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 multi-layer screens, the selection of appropriate screen sieve is important. The material to be sieved should be evenly distributed over the screen. This is very important for the full use of screen sieve capacity.

·        In general, “the screen opening of a lower screen should be half that of the upper screen, or smaller.” For example, if the upper sieve is 4.75 mm, the lower sieves 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. Sometimes, the vibration may result in oversize materials mixing with undersize materials from the sides. Holes or tears in the screen sieve should be investigated if large materials are noted on the conveyor belt carrying undersize materials.

·        When using screens with two or three sieves, it is important to replace the screen sieves when they become punctured or torn.

·        The number of screen layers and screen sieve openings are determined depending on the size distribution in material to be sieved and the purpose of use of the material separated according to the resulting size.

·        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.

·        Screens work through vibration. Vibration causes bolt and nut connections to loosen. There should be no loose bolts in the body of the screen. A counter nut or knurled washer 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 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.

·        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.

·        No time should be spent repairing cracked bodies. The cracked part should be replaced as a whole. The screen body should not be repaired by welding.

·        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 sieves of appropriate sizes in the stocks for use in trials.

·        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.