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Replace your screw classifier

Sand screw replaced with CDE EvoWashThe use of wet processing technology for sand production is an established process across the world as it allows you to increase the efficiency of concrete production by giving you a sand product with greatly reduced volumes of material in the minus 200 mesh range.

In the US the most common equipment applied in sand washing operations are classifying tanks and sand screws.

If you are currently operating a sand screw or a classifying tank for your sand washing operations then there are a number of issues that you will be familiar with.

The problem with classifying tanks

sand classifying tankThere are a number of limitations with classifying tanks when employed on sand classification projects:

  • Require large volumes of water to ensure the continuous overflow required to remove your minus 200 mesh material.
  • Significant space required on site and can take a long time to install and commission.
  • The use of gravity as the means of separation is not an accurate process and means you will sacrifice some of your plus 200 mesh material in order to ensure removal of unwanted fines.
  • Adds significant cost to your operation as quality sand lost during the process has to be extracted from your ponds and reprocessed.
  • Health & Safety risks - these are open top tanks filled with large volumes of water to which your site personnel require access to maintain the tanks mechanical elements and seals. The poses an unnecessary risk to your people.

Want to increase your sand production?


Have a look at our tried and tested system for maximizing sand production & eliminating loss of quality fines

The problem with sand screws

sand screw on sand washing plant in USAThere are 2 issues that those operating sand screws will be familiar with:

  1. The loss of quality fines to your settling ponds
  2. The high and variable moisture content of the final sand product - compromising product quality in readymix concrete, precast concrete and asphalt.

There are also additional health & safety risks associated with the fact that the screw mechanism is uncovered - posing an unnecessary risk to the health & safety of your site personnel.

Why do sand screws lose quality material to the ponds?

inefficient overflow weir on sand screw in USASand screws will accept material either directly from your aggregates screening operation or will be fed from your classification tank.

The sand screw is equipped with an overflow weir at the feed point which provides the mechanism for fines removal.

The limited capacity at the feed point means that control over the volumes of water required for accurate material classification is very limited.

The result of this is that quality sand is lost over the overflow weir and is sent to your settling ponds or water treatment phase.

This has a number of negative impacts on the efficiency of your sand washing operations:

  1. You are missing out on revenue by sacrificing good material in order to maximise removal of minus 200 mesh fines.
  2. This process typically requires the reprocessing of your waste material – introducing significant operational costs through the unnecessary double handling of material.
  3. The time required for clearing out your settling ponds to recover lost material requires unnecessary plant downtime – harming the overall productivity, efficiency and profitability of your  operations.
  4. By sending excess material to your settling ponds you require considerably more space to accommodate them – and the classification inefficiencies increase as the proportion of fines in your feed material increases.

The problem of high moisture content in your sand

wet sand from sand screw or bucket wheelSand screws employ the Archimedes screw principle to achieve dewatering of your sand product.

The operation of the screw pushes the sand fraction up the elevated chamber while the water and the finer particles fall to the overflow weir.

The sand product is typically discharged with between 23% to 25% moisture content – when processing finer material this number can be significantly higher.

This causes a number of problems:

  1. Your sand product needs to be stockpiled for a considerable amount of time before it can be sold.
  2. Unnecessary double handling of this material as it needs to be moved to a separate stockpile area.
  3. You are not able to turn your final products into revenue as quickly as you would like.
  4. As a result of not using sufficient volumes of water, fines are not efficiently removed

Find out more about CDE in the US


Improving the efficiency of your sand washing plant

EvoWaah sand washing plant in TexasOver the last two decades CDE has designed and delivered hundreds of global projects to increase the efficiency of sand washing operations.

Our success has been down to our capability to address the efficiency issues from traditional sand washing technologies and employ our EvoWash sand washing plant to:

  1. Guarantee removal of the minus 200 mesh fraction while retaining all quality fines in your final sand product.
  2. Maximise sand dewatering to between 12% and 15% moisture - ensuring it is ready for market as soon as it hits your stockpile.

The solution to losing quality fines

hydrocyclones on EvoWash sand washing plantThe solution to this problem is to use mechanical separation as the means of classification rather than gravity.

This involves using a hydrocyclone based system like our EvoWash sand washing plant.

This gives you unrivalled control over your silt cut point - the specification of your cyclone set up is determined after extensive material testing to determine the proportion of minus 200 mesh material to be removed.

The minus 200 mesh material exits the overflow at the top of the cyclone with the waste water and this is sent to your settling ponds. The sand fraction exits the cyclone at the bottom, ready for dewatering and stockpiling.

This has a number of benefits:

  1. Eliminate the loss of quality fines to your settling ponds, maximizing your product yield and minimizing operational costs .
  2. The space required to accommodate your settling ponds is reduced 
  3. Guarantee production of sand specifications in line with the requirements of your customers or your downstream processes.
  4. Reduced health & safety risks on site thanks to the removal of the requirement to regularly clean out your ponds for reprocessing.
  5. By reducing the requirement for large settling ponds you are also reducing health & safety risks for your neighbours, inquisitive youth and wildlife.


The solution to high moisture content

dry washed sand from CDE EvoWashThe inability of the screw classifier to effectively dewater your sand product requires unnecessary double handling of your product.

The solution to this problem is to employ a high frequency dewatering screen to dewater your sand product.

Once your sand slurry with the minus 200 mesh material removed is discharged from your hydrocyclones it should be delivered to a dewatering screen which is sized according to your specific capacity requirements.

This allows for the production of a sand product with moisture content typically in the 12% to 15% range.

The net result of this is that the product is ready for market straight from the belt – which has a number of benefits:

  1. You are able to sell your product immediately – turning your sand into revenue in the shortest possible time.
  2. You are able to use your sand product immediately in downstream processes such as concrete production.
  3. You can eliminate the area required to stockpile your sand product for further dewatering.
  4. You can remove the unnecessary double handling of your material.
  5. The reduced vehicle movements that this allows not only reduces your operational costs but reduces health & safety risks on site.

EvoWash sand washing plant

Find Out More


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