Screening machines for processing plastics

Polymer processing with highly efficient screening technology

In the production of plastic pellets, the previously polymerized pellets are usually screened to lengths. In this process, the pellets are extruded in a water bath for cooling and solidification. The liquid is then separated from the solids and the granules are screened to specified sizes. Common sizes of "on-size" pellets range from 1.6 mm to 6.0 mm. The screening machines are often made of stainless steel, and the pellets are screened on perforated plates. In some cases, screening is performed under exclusion of oxygen. Accordingly, the screening machines at RHEWUM are manufactured gas-tight and flooded with an inert gas, such as nitrogen. The surface can be polished.

For precise dry screening of polymers the vibration screening machine RHEmoto^® is the perfect solution. External low-maintenance unbalance motors generate a high-frequency vibration directly at the screen mesh without the need for the screen housing to vibrate. This efficient vibration transmission enables highest accelerations of the plastic granulate and thus exact separations.

For wet processing of plastic granules, the RHEhydra^® wet screening machine is the right choice. It offers a unique extremely advantageous combination of the vibration types linear vibration and direct excitation. The RHEhydra^® is the ultimate dewatering screen for fine and ultra-fine solids, achieving a dewatering rate and optimized residual moisture content that is about half that of a conventional linear vibrating screen.

Screening of polymers in biogenic wastes

RHEWUM screening machines are not only used in the production of synthetic granules, but also in the separation of plastics from biogenic waste. Such waste is fermented in biomass centers and resold as the resulting quality compost. Agricultural quality compost requires a particle size of 0 mm to 25 mm, while horticultural quality compost requires a particle size of 0 mm to 12 mm. However, if the quality compost contains plastics, this can become a problem. The reason is their additives, such as plasticizers, dyes or flame retardants. In its dry matter, quality compost must not contain more than 0.1 percent by weight of flat plastics larger than 2 mm. Flat plastics are plastic nets, foils, bags, strings or similar. A screening machine is used to separate the biogenic fraction from the plastic fraction.

For this screening task, the RHEsonox^® high-performance screen is the right choice. A screening machine for separating cuts from 50 µm to 6 mm, in which two counter-rotating unbalanced motors generate a linear motion, while an additional excitation of the screen cloth ensures maximum acceleration, thus enabling precise screening and at the same time preventing clogging of the screen cloth by stuck grain. This combination of linear drive and direct excitation allows difficult-to-screen material to be screened accurately and with high throughput.