Tumbler screens are widely used to screen powders at separation sizes from 20 to 400nm but suffer mesh aperture blockages from powder agglomeration due to high inter-particle attraction forces if effective cleaning aids are not used. Mesh wires also become coated with powder, reducing effective separation size and machine capacity.
Allgaier discovered that combining ultrasonic and air cleaning is much more effective than either method on its own, particularly towards the edge areas of the circular mesh panels. Small air jets from perforated arms rotating below the panels loosen the screened material and ultra-sound overcomes the adhesion between powder particles.
The combination system is applicable to machines of up to 2600mm diameter and is also simple to retro-fit to tumbler screens equipped with air cleaning. It gives the cost-effective sizing with precisely defined cut-points of materials previously requiring complex and expensive air separator processes and may be run continuously without any risk of overheating and the degradation or melting of heat-sensitive products.
Tests of the system with difficult-to-screen materials such as polyamide powders showed that yields improved by 65 per cent over ultra-sound alone and by 43 per cent against only air cleaning, while throughput increases were +68 per cent and +86 per cent respectively.
Main applications include plastics, cellulose, powder coatings, toners, metals, silicon, abrasives, coke, gypsum, enamel powder, starch, rice flour and pharmaceuticals.
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