When discussing screw conveyors, it is important to know the difference between shafted and shaftless screw conveyors and their respective applications. You will find a simple explanation below telling you a bit more about it.
Because of the nature of the dewatered biosolids present in the wastewater treatment industry, a more efficient solution than the shafted screw conveyor had to be developed. This was done in the early 1940s in Europe with the development of the shaftless screw conveyor, also known as the centreless screw conveyor.
The main issue with these bio solids is that they can be very sticky and sluggish, depending on solids content and the amount of polymer needed in the dewatering process. If we take a look at the characteristics of the sludge, we can see that solids and polymer only account for 20 to 30 percent of their content, with the balance being moisture contained in the solids. The result of the sludge stickiness is solids have a tendency to continually build up on the shaft, until it was not able to convey any material at all.
By removing the shaft and increasing the strength of the spiral, the shaftless screw is able to convey more material and prevents the solids from building up on the screw.
The shaftless screw conveyor is known to be the solution for waste water treatment plants, it has also been proven to be the best option for conveying difficult bulk solids.
Because of its efficiency in handling these solids, the shaftless screw use has been promoted within many other industries such as chemical, food, and minerals processing. Nowadays, shaftless screws are also used in different applications other than conveyors, for instance screw feeders, screw presses, screw classifiers...