Circular-motion vibrating screen with many innovative features

For many years now, screens of the CK line have already been successfully used worldwide for screening of aggregates, gravel, ore and coal as well as in the recycling industry. They have impressed with their strong reliability and screening efficiency. With screening areas up to 17 m², in models with two or three screening decks, they are ideally tailored to meet the requirements of customers in the aggregates and mining industries. They can be integrated in stationary (Fig. 2), semi-mobile and mobile plants (Fig. 1).

1 Previous design

Circular-motion vibrating screens are of simple and rugged design. The sidewalls consist of standard steel sheets that can be laser-cut to any size and shape. Attachments and crossbeams are all bolted to the screen to maximize vibration resistance and lifetime. The screen tray is generally supported on steel springs, which stand on a steel structure.

The screen decks can be supplied in various versions with perforated plates, polyurethane surfaces or woven wire cloth or a combination of these, in line with customer requirements. The screen linings can be changed easily and quickly with clamping and tensioning devices. In the feed area, the screens are fitted with a dummy floor to absorb impact forces. The screens of the CK line can be optionally fitted with a water-spraying system and/or dust cover.

The circular vibration is usually generated by shafts with unbalance discs fixed on both sides, the shaft bearings being integrated in the sidewalls of the screen. Depending on the size of the screen, one or two drive shafts are used, which are individually driven by a separate motor. For twin-shaft drives (Fig. 1), the two drives are synchronized by means of a toothed belt. The motors are mounted outside the screen tray on small platforms in the steel structure and are connected to the drive shafts by means of  V-belts. To adapt screening performance and for optimum screen settings, the vibration amplitude can be adjusted by increasing or decreasing the unbalance weights. The speed can be varied just by changing the V-belt pulley.

2 CK+ innovative concept

thyssenkrupp has now upgraded the existing CK line of circular-motion vibrating screens to the state of the art. Focuses of this development were the drive concept, support of the screens and easy maintenance. The new line has been designed to offer a substantial plus with regard to reducing production costs, installation effort and maintenance for the operators, so that logically the name CK+ was chosen.

2.1 Drive

As mentioned earlier, conventional screen drives consist of diverse rotating and connecting parts, e.g. motors, V-belts, shafts and unbalance exciters (Fig. 3a). All these parts are subject to wear and must therefore be regularly maintained. Some of them must be anchored in the steel structure (motor), be safeguarded against manual interference (V-belts, toothed belts) or protected against wear caused by material falling down on them (shaft). A simplification of this system therefore offers interesting advantages with regard to installation, function and maintenance requirement.

The solution to this complex problem was already on hand at thyssenkrupp: in its newly developed goovi^® screen, which has already been featured in several published reports, a novel, revolutionary drive concept has been introduced. This concept has now been transferred in a simplified form to the CK line of circular-motion vibrating screens. For this reason, compact, lifetime-lubricated standard unbalance motors are used, which are flanged symmetrically and directly to the sidewalls; these are synchronized by means of a connecting rod (Fig. 3b). This rod and the inner drive components are protected against falling screening material by a protective pipe with rubber coating.

The advantages of this compact solution with direct drive compared to a conventional drive are clearly shown in Fig. 3. The number of rotating and moving parts has been drastically cut, as a result of which maintenance requirement, failure probability and accordingly downtime are automatically reduced. Belt guards and motor platforms in the steel structure are not necessary at all with this concept. Accordingly, a lighter and less complex steel structure can be designed and the installation time is shortened significantly.

2.2 Support

In the design of the screen support, a completely new direction has been taken. Instead of the conventional screen support with steel springs (Fig. 4a), now rubber spring elements are used (Fig. 4b), which are supplied as standard components by speciality manufacturers. In comparison with steel springs, they offer very effective vibration dampening and low residual force transmission into the foundations. In addition, they boast a long lifetime, zero maintenance and low noise generation.

Another feature is the innovative adjustment mechanism that enables different settings for the screen inclination. Accordingly, the screen inclination can be adapted to the specific screening material and application so that optimum screening performance is ensured at all times.

For the fitting and removal of the rubber spring elements, the screen tray can be lifted by means of hydraulic cylinders so that the springs can be comfortably fitted under zero load.

2.3 Easy maintenance

A special feature of the new CK+ circular-motion vibrating screens from thyssenkrupp is their very easy maintenance. Of course, during reworking of the screen design, provision was made to meet the new stipulations in the recently revised EN 1009 with regard to the space requirement for maintenance work on machines for mechanical processing of minerals (Fig. 6). The distances between the screen decks and to the obstacles at different points have been increased considerably. The screen decks are therefore easily accessible and the screen linings can be quickly changed. For the fitting and removal of wear and replacement parts, no special tools are needed.

Another plus in respect of easy servicing is the optionally available mobile chute cart which diverts the material flows from the different screen decks on the discharge side in the desired directions to the downstream conveying elements (Fig. 5). During operation, it offers the possibility to control the function of the screen at any time by means of a platform and inspection flaps. For service work, the entire chute cart including platform can be moved back by means of a handwheel and a simple rail track. A movable service platform can be folded down over the space between screen and chute cart so that this area can be safely accessed. Now it is possible for the service workers to comfortably enter the area of the screen tray and to carry out any necessary maintenance work. Once servicing has been completed, the platform is folded back up and the chute cart moved back to the screen and locked into place. With this practical device, maintenance work can be performed safely and in a comfortable position with minimized effort to enable walk-on access.

2.4 Sizes and possible applications

Particle sizes up to 200 mm can be fed to thyssenkrupp’s new CK+ screens and screened at a minimum cut-point of around 1.5 mm. For this, a series with screening areas from 4 – 17 m² per screen deck is available, see Table 1. While the first two digits of the nomenclature specify the effective screening area, the number of screen decks is indicated by the last two digits. For example, a CK+ 1002 screen is a machine with a screening area of 10 m² and 2 screen decks.

As the connection dimensions are identical, CK screens of the previous generation can be easily replaced with CK+ screens with direct drive. This means that screen replacement can be carried out in the shortest possible time with extremely little effort.

3 Summary

In comparison with conventional circular-motion vibrating screens, the new line of CK+ circular motion vibrating screens from thyssenkrupp Mining Technologies offers operators considerable advantages with regard to acquisition, installation and operation thanks to a host of innovative detail solutions.

Thanks to the compact drive with standard unbalance motors, many rotating and moving parts are no longer necessary. The same goes for all belt guards and motor platforms in the steel structure. This reduces the installation and maintenance requirements as well as machine failure and downtime, adding up to a significant cost saving both for screen acquisition and operation.

The screen support with rubber spring elements and an adjustment option for the inclination of the screen ensures quiet and safe operation and enables, thanks to adjustment of the screen inclination, optimization of the product quality.

Generous spacing between the screen decks in compliance with EN 1009 facilitates maintenance work in these areas so that screen linings can be changed quickly and safely. Access to the screening areas is enabled by a moveable chute cart and a fold-down service platform in a very short time.

Overall, the new CK+ circular motion vibrating screens from thyssenkrupp Mining Technologies impress with their compact design, high availability, low installation and maintenance requirement, and at the same time they enable very high throughput rates with excellent separation sharpness.