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Plastic Recycling

Due to the condition of the recyclable plastics received at recycling plants (being contaminated with various other none recyclable products and dirt), new product washing and cleansing processes have been developed.

Their goal is to remove as much of the contaminants as possible without taking out any recyclable products prior to the actual recycling process.


This pre-cleansing process is designed to remove the non-floatable plastics and contaminants, by sinking this material to the bottom of a vessel and transport the rejected material via shaftless screw conveyors.

This may sound simple enough, though several other local suppliers have tried and failed.

Even after several attempted modification to the original design, it still failed. Everything from drive shafts wearing out prematurely, spiral deformation, spirals snapping, exits blinding with material, changing gear drive positions pushing to pulling, all came to no avail.

So what could be the cause of all these significant problems?

After a thorough investigation by the Atara Equipment team, several of the more obvious issues came to light:

  • Premature wearing of the drive shaft: in all type of applications it is important material to select a drive shaft quality steel (cold rolled steel)

  • Packing gland needs to be designed for abrasive application, once grit enters the packing gland it gets imbedded into the packing material and acts like sand paper on the drive shaft

  • Spiral design: has to take into account, axial loading from the material being transported, plus the added axial loading from material being transferred from a horizontal screw to a vertical screw through an axial connection. Where the spiral design is too weak: the spiral will have a tendency to compress beyond it elasticity point and deform or bend. This can be avoided by designing a spiral: with the heaviest cross section running along the centre axis of the spiral and by adding an abrasive resistant ware resistant material on the peripheral. Where a single spiral is being used: it is important to have a cross section thicker running along the axial length of the spiral and the thinner along the peripheral edge, this can be formed during the manufacturing process of the spiral. It is important to not only know which type of steel is being supplied for your spiral, take HTMAS steel for instance: High Tensile Micro Alloyed Steel, , you will also need to know the actual Grade Designation of the steel, as within each grade designation the Brinell hardness of the steel changes. There is a direct link between the higher Brinell hardness of steel and the longer life expectancy of the spiral.

  • Performance: the storage hopper design. It is important to take into account the characteristics of the material:

    • What is the standard particle size?

    • Will the material be uniform in size?

    • What is the material angle of repose?

    • Are there any long stringy types of material?

    • Is the material prone to bridging?

    • Is the conveyor wide enough to allow the material to enter easily?

    • Will the spiral be able to remove enough material to allow more material to flow easily into the trough?

    • Are the slopped walls at a min of 60° angle?

Atara Equipment team solved all of the above issues on this particular project and a few others.

We installed:

  • New drive shaft and coupling disc

  • New packing gland

  • New spiral

  • Complete new vertical conveyor

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