News Natural-frequency Conveyors

New concepts for building natural-frequency conveyors

In both the chemical and the food industries, vibrating conveyors are required to handle high conveying capacities - and often also considerable conveying distances - for logistical tasks between the production and packaging stages. Freely configurable branching devices in the form of remote-controlled gates, flaps or switches are necessary to achieve the desired distribution of the mass flows between various packaging lines. Right from the outset, a conveyor is expected to be sufficiently flexible to adapt to other conveying distances according to future requirements. The current trend towards simple-to-process, granulated and if possible dust-free products moreover means that the bulk material has to be conveyed gently. Conveying under absolutely hygienic, easy-to-clean and environmentally compatible conditions is today taken for granted. Figure 1 shows an example of a reference plant: two roughly 25 m long, natural-frequency trough conveyors with several remote-controllable, intermediate processes are used to convey a filler at a rate of 60 m³/h.

Figure 1: Two natural-frequency trough conveyors, each 25 m long, in a filling plant

The above-mentioned plethora of requirements specified for the conveying system is optimally complied with by the specially designed natural-frequency conveyors from VIBRA SCHULTHEIS. The well-known characteristics of these vibrating conveyors, which operate near the resonant frequency - such as conveying distances up to 30 m in a single unit, smooth running with only minimal vibration transferred to the supporting structure and simple control of the conveying capacity - are complemented by a set of unique design features that make natural-frequency conveyors the perfect answer when it comes to solving logistical problems. These features are described in brief below:

A self-synchronizing, twin motor vibrating unit acts as the vibrator (Figure 2). This vibrator is insulated against structure-borne noise and characterized by practically silent operation. It has no coupling and no belt drive, endures continuous operation and requires almost no maintenance.

The associated frequency converter permits the conveying capacity to be set or varied easily.

The working spring stations, which are designed as standard units, are mounted between the conveying trough and the countervibrating frame by means of bolt connections (Figure 3). The linkage is integrated in the working spring stations.

This concept allows the countervibrating frame to be arranged either above or below the conveying trough. Figure 4 shows a conveyor with a top-mounted countervibrating frame.

The conveyor itself, which can take the form of either a trough or a tube, consists of short pipe sections with machined flange joints, between which special elements fitted with a gate or a flap can be flanged as shown in Figure 5.

Figure 2: The self-synchronizing motor vibrator unit is equipped with two vibrating motors designed to endure continuous operation, with infinitely adjustable out-of-balance force and a frequency converter

Figure 3: The natural-frequency stations are designed as finished assembly units

Figure 4: Assembly line for natural-frequency trough conveyors with a top-mounted vibrator

Standardized flap and gate valve devices, selected according to individual operating conditions, are used as discharge elements. The various flap types are illustrated and explained in Figure 6a-c.

Figure 5: Flanged flap element

Figure 6a Flap type for granules, non-dustproof

Figure 6b Flap type for granules and powder, only fine dust is lost

Figure 6c Dustproof flap type

Conveying systems with the characteristics described here are used successfully by numerous big-name companies in the chemical and food industries. Particularly complex conveying tasks have to be handled, for instance, in cereal production plants. One plant delivered to an international customer is required to feed various cereal products to the individual packaging machines over a total conveying distance of approximately 100 m at a mass flow rate of 80 m³/h. The conveying distances are determined by the production process and the available space, with branches, intersections and discharge points, and the complete plant incorporates 33 pneumatically controlled discharge flaps. A total of 11 individual conveyors with a length of up to 17 m each are installed for this purpose. Figures 7 and 8 show a section of the plant.

Figure 7

Figure 8

Figure 9 depicts another reference plant. This plant, which consists of 9 separate, dustproof trough conveyors with a maximum length of 26 m, is used to feed filling stations with a powdery filler. The built-in discharge flaps are dust-tight and are identical to the type shown in Figure 6c.

Figure 9: Partial view of a vibrating conveyor plant with an overall length of 110 m used to convey silicic acid at a rate of 60 m³/h

In many applications, tubular natural-frequency conveyors of the kind shown in Figure 10 represent an attractive alternative to conveyors with a rectangular cross-section.

Figure 10: Natural-frequency tube conveyor, diameter 250 mm, 12 m long

The unique design features described here are of course not only used to convey and distribute bulk materials in natural-frequency conveyors. They are also an advantage in all fluid-bed dryers which are excited according to the natural-frequency principle.

Figure 11: Natural-frequency fluid-bed dryer with a fluidizing plate area of 10 m²