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17.07.2018

Screen meets screw
Coil drum screening machines: careful screening for delicate products

The precision of a centrifugal screening machine and the careful product treatment of a screw conveyor – these properties are combined into one machine by the coil drum screen JEL WTS. Unlike with a centrifugal screening machine, the product to be screened is not flung through the screen cloth of the drum screen, rather it is guided slowly through the machine, along the lines of the screw conveyor. Due to this special type of screening movement, the coil drum screen is best suited for the screening of bulk materials prone to breaking. Even coated products are screened without damaging the delicate coating.

Design and operating modes

The coil drum screen has a similar design to a centrifugal screening machine and consists of a machine frame as well as screen housing with the internal rotating screen basket. The screen basket is divided into individual drum screen segments, each of which is covered with a different mesh size depending on the desired size of grain. The area underneath the drum screen is divided into compartments so that the different screened material grain sizes cannot be mixed together.

The greatest difference to centrifugal screens is that coil drum screens move and filter the product very carefully through the machine. The reason for that can be found inside the screen basket: the screen basket is fitted with a screw coil instead of blades. At the start of the screening process, the screen basket and screw slowly begin to turn on their own axis. When the product is fed sideways into the machine, it falls first into the screen cloth at the bottom of the screen basket. The slow rotation moves the product lying on the cloth up until gravity causes it to glide back down to the screen cloth. At the same time, the turning of the screw coil feeds the material in a horizontal direction through the individual drum screens. Throughout the whole screening process, the product never loses contact with the screen cloth so that it can be screened especially carefully and with absolute accuracy. The screening result can be regulated and suited to the product to be screened thanks to the option to adjust the RPM and the incline. With centrifugal screens, only the blades move, rotating very quickly on their own axis and flinging the product through the drum and against the screen cloth; the screen drum itself doesn’t move. That screening process is therefore rather unsuited for coated products or products generally prone to breaking.

A cleaning system can also be integrated into the coil drum screen to clear the screen cloth of clogged material. Good results are achieved with brush cleaning, for example. With this type of cleaning, directly above the screen cloth is a rotating shaft with brushes that brush the screen cloth in a spiral motion. So the cloth mesh stays free of clogged material, and the screen achieves its maximal throughput performance.

Operation and maintenance

The operation of the coil drum screen is also uncomplicated. A large pane of Makrolon glass at operating height doesn’t just enable the inspection of the screening machine while it is in use, but it also serves as a maintenance hatch for direct access to the screen basket. To completely remove it, you only have to detach the wing nut at the top of the shaft. The basket can then be easily taken out of the machine housing: to cover it with a new screen cloth, for example. Downtime is mostly avoided due to the machine’s low maintenance construction and the low number of parts subject to wear and tear.

Conclusion: The coil drum screen JEL WTS can be used for all screening tasks: from protective screening and separating the fine and coarse to grading screening of up to five different grain sizes. In cases with large quantities of a product and less delicate bulk goods, we recommend using a vibrating or oscillating screening machine. With products prone to breaking or small quantities, however, the coil drum screen convinces with its extreme accuracy and minimal production waste through its particularly careful product treatment.