Sink Float Tanks​

Rotajet sink-float tanks separate various types of plastics by density whilst removing contaminates prior to upstream processing.  Water is generally used in float sink tanks as the density media. 

Sink float tank for recycling and separation

Operation of Sink Float Tanks​

The gravity of water is 1000kgs / M3. This makes it ideal for the separation of polypropylene and polyethylene from PVC`s and ABS.

Other contaminants such as glass, grit and dirt will sink because of their denser structure. In some applications the water density can be increased by adding various chemicals. This will then  allow other material types to be separated using the same method.

Materials that are denser than the liquid will sink to the bottom 

Sinking Fraction Discharge

Sink float tank for recycling and separation

Floating Fraction Discharge

Materials with less density to the used liquid will float to the surface 

Sink float tank for plastic separation

Feeding material into a Rotajet float sink tank:

Rotajet float sink tanks are typically fed by a belt conveyor, screw auger or blower. Depending on the application the material can be discharged onto the surface of the tank, or fed by a screw feeder. 

The screw feeders, are mounted above the surface of the liquid and are submerged into the tank, this gives a uniform flow into the tank, breaks up any lumps, and ensures that all materials are fully submerged at the start of the process. This produces a high purity product as all particles are forced to either float or sink.

The floating fraction is driven along the surface of the float sink tank by a series of rotating paddles. Each paddle completely submerges the floating fraction as it is pushed along the surface of the float sink tank. The speed of the rotating paddles can be changed by the PLC, varying the agitation present and the discharge rate. The floating fraction is transferred into an incline discharge screw via a weir at the end of the float sink tank.

The incline discharge screw body is manufactured with easy to replace screens; these screens allow the water from the discharge weir to be screened from the floating fraction. The water is then fed by gravity into a Rotajet Vibratory Sieve, normally fitted with a 300-micron screen. The filtered water is then pumped into a holding tank, ready for reuse. We recommend that the floating fraction is discharged into a Rotajet Mechanical Dryer. The water removed during this process can also be recirculated through the vibratory sieve for filtering and reuse.

For optimum performance, the level of working fluid has to be maintained in the Rotajet float sink tank. This is done by reusing the filtered solution in the storage tanks and introducing fresh solution as required.

Plastic Type Density/g/cm3 Uses
Polypropylene 0.90 - 0.92 yogurt cups, plasticware
Low Density Polyethylene 0.91 - 0.93 squeezable bottles
High Density Polyethylene 0.94 - 0.96 milk bottles, bags
Polystyrene 1.03 - 1.06 egg cartons, packing peanuts
Polyethylene Terephthalate 1.35 - 1.38 water bottles
Polyvinyl Chloride 1.32 - 1.42 juice bottles, cling wrap

Contact Rotajet

We aim to get back to any enquiry within 12 hours, so please contact us if you are interested in a specific machine or would like to discuss an individual cleaning application. Our friendly team are happy to help via email at or by phone on +44 (0) 1924 271446.

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