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Curved-screen Systems

Our non-oscillating systems for the preparation of suspensions

SIEBTECHNIK TEMA curved screen with brush

Due to its special mode of operation, the Curved-screen Systems is a universally applicable classifying and dewatering device. It can therefore be used in almost all branches of industry. For the pre-thickening of suspensions of all kinds, the curved screen is a highly economical preliminary stage before centrifuges and dryers. There is considerable potential for savings when removing crystalline or fibrous solids from process or waste water and when recovering valuable materials from aqueous media.

Function & design

SIEBTECHNIK Curved-screen Systems (type ZB or ZBB) are dynamic dewatering and classifying screens, although they do not contain any mechanically moving parts. It consists of a stationary housing which is fitted with a concave curved screen surface. These have been specially developed for the separation of solids from process or waste water and achieve optimum results at low cost.

Feeding takes place without pressure either via the static height or via an external sludge pump. The suspension is fed into the feed chamber in such a way that uniform feeding across the entire width of the curved screen is ensured. The slotted openings of the screen surface, which run at right angles to the transport direction, separate the liquid from the solids. Solids that are smaller than half the gap width mainly enter the underflow with the water, which results in classification. The dewatered solids are discharged at the end of the curved screen. Curved-screen Systems and screen linings are usually made of material 1.4301, but can also be made of material 1.4571 on special request.

Operating behavior & mechanical features

The profile bars of the wedge wire screen are arranged parallel to the curved screen plane. These screen linings are easy to replace and are selected according to the gap width (from 0.05 – 2 mm) depending on the specific problem. Due to the same radius of curvature and the same screen length, the screen linings can be rotated and therefore used for longer.

The device is equipped with an inlet housing for feeding the suspension to be dewatered or classified. A collection box with a nozzle in the bottom of the housing is used to discharge the screenings, while the dewatered solids fall off automatically at the end of the screen surface across the entire width.

Normally, the curved screen is operated without pressure or pressurized in such a way that the inlet is at a free gradient. For unpressurized operation, the inlet housing is fitted with overflow weirs or slotted nozzles. An inherently elastic flap enables automatic volume regulation in the simplest possible way.

In special cases (e.g. if the suspension has a high viscosity), designs with a pressure housing are used, whereby slotted or round nozzles are used to feed the suspension.

Depending on the feeding device, the suspension fed to the curved screen is directed via a weir or through nozzles in a tangential flow onto the upper part of the curved screen surface. As the flow continues over the screen surface, the boundary layer of the flow belt is deflected by the resulting angle of incidence between the profile bars and thus passes through the slot openings.

If the gap width is selected so that solids (fine fraction) can still pass through with the liquid, classification takes place. Quantitative separation or dewatering of the solids, on the other hand, takes place when the smallest solid particle in the suspension is larger than the separation particle size resulting from the choice of screen gap width. The largely dewatered solids or the coarse fraction is automatically discharged at the end of the screen surface due to the constant flow of material.

The constant overflow with relatively high flow velocity in conjunction with the shearing of the boundary layer produces a high self-cleaning effect, so that screen blockages are avoided. Screen wear is very low, as the boundary layer of the flow belt acts as a liquid film to counteract abrasion.

For classifying tasks, the gap width of the screen can be selected to be considerably larger (up to a multiple) than the desired separation particle size, which ensures a high throughput rate, a low level of faulty particle discharge and a screen surface that is always free and open.

Curved screen in special design
Curved screen ZB 1900 - SIEBTECHNIK TEMA

Cleaning device

SIEBTECHNIK Curved-screen Systems can optionally be equipped with an automatic cleaning device. This cleaning device moves cleaning brushes parallel to the gap openings across the entire width of the curved screen once during each cycle. By setting the time-controlled spindle drive for the cleaning brushes, optimum clearance of the curved screen is achieved. The cleaning device can also be extended with a spray system for removing grease. A control box with the necessary control technology completes our scope of delivery.

Areas of application

Chemical industry

  • Pre-dewatering of polystyrene upstream of a centrifuge
  • Classification of organic and inorganic intermediate and end products
  • Dewatering or pre-thickening of crystallizates and granulates
  • Clarification of solutions, alkaline solutions, process and waste water

Potash industry

  • Classification and thickening of salt suspensions, to relieve
    thickeners and centrifuges

Textile laundries

Pulp industry

  • Purification of wastewater with simultaneous fiber recovery

Slaughterhouses

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