For ultrasonic screening Allgaier has come up with a new, further developed ultrasonic system for its tumbler and vibrating screens (Fig.). That means increased throughput rates and higher screening efficiency as well as longer cleaning intervals. For a wide range of powders, the screen throughput for cut-points ≤ 300 μm can be improved by up to 30 % with much better screening efficiency. For instance, colour powders with a low melting point can be effectively screened on a screen diameter of 1200 mm with low-watt energy input. Melting of the powder caused by heating owing to excessive energy input is then reliably avoided.
These advantages are achieved by a generator, in which product-specific working programmes can be stored and which searches for and selectively excites the best resonance points during screening. Thanks to the flexible adjustment of the system, the lifetime of the screening surfaces is lengthened, the input energy can be used more efficiently and the screen cleaning intervals lengthened considerably. At the beginning of the screening process, the ultrasonic system searches for the three best resonance points for selective excitation. If conditions change during the screening process on account of weight or temperature of the screen feed, the optimal operating points are also adapted to the changes.
The system constantly records the changing vibration situation and adapts the process to optimal screening at short intervals. The screening surface is effectively vibrated over its entire area. Depending on the size of the screening surface, the number of ring resonators varies. A relatively small ultrasonic screen manages with a single ring resonator and the large-area screens are equipped with two or four independently operating resonators. This ensures uniform distribution of the ultrasound and excitation of the screening surface. Decoupling bars between the resonators and screen frame avoid vibration of the screen frame, which could lead to unwanted heating. The ultrasonic system is suitable for a screen diameter from 600 mm to 2900 mm. The screen inserts can be supplied in a continuous or a segmented version. With a special twin generator, two screen inserts can be operated by one generator.
Companies already using screens supplied by the German screen manufacturer can retrofit the new system and profit from the improvements. The ultrasonic system can also be used in hazardous areas with risk of explosion. For dust, inside the machine Zone 20 and outside the machine Zone 21 are permitted. For gas, the screen insert is certified inside and outside for Zone 1.
ALLGAIER WERKE GmbH, Uhingen (D), Tel.: +49 7161 301-0,