Manufactured Sand: A Two-Pronged Approach – the Ortner®
If you’re not one of the lucky few who can still pull perfectly in-spec sand directly from your pit, then you’re going to have to make it for yourself.
Sand is a key component of many stone mixes, but especially paving mixes such as asphalt and concrete. Paving mixes require a specific range of stone sizes, which is usually accomplished by screening to produce specific size fractions that are then blended together to meet specifications.
Stone that has been crushed and screened in order to meet the specifications for various grades of sand is called manufactured sand (mansand). One of the more common grades produced by many quarries has a nominal top size of 1/4″ or 3/16″, which is the smallest cut-point that most conventional vibrating screens can efficiently make. The problem is that all of the dust and fines produced by the crusher and subsequent processing ends up in the 1/4″ x 0″ screenings. This concentration of fines usually exceeds the allowable percentages for mansand, and so the screenings must be further processed.
A common solution is to wash the fines out of the sand. This works well because the fines that are throwing off the sand gradations are typically minus #200mesh (<0.75 microns), and this size range easily floats in water. Maybe float isn’t the right word. The larger the particle, the more quickly it will settle to the bottom when placed in water, such as in the weir section of a piece of washing equipment. The smallest particles stay suspended the longest, and a properly designed fines-removal system is able to take advantage of this property. The Ortner® Washing System has been specifically designed for this task.
The Ortner®, a low-water, low-maintenance machine, has been around since the 1980’s. Screenings and water are mixed together in a feed-box and then introduced to an inclined rotating pan. The water and suspended fines flow over the lowest point of the pan, while the washed mansand is conveyed on the pan to a central discharge point. This is the simplest and most efficient way to remove unwanted fines from sand, which explains why it is also the most popular method.
Because the washed mansand is conveyed by the rotating pan, there is very little wear on the components of the Ortner®. The pan is vibrated, which allows excess water to drain from the washed sand and flow back down into the weir.
The manufactured sand from an Ortner® is much drier than you would expect from a typical wash-plant. This is important because it eliminates or drastically reduces the time required for the material to drain before it can be sold. All of the water that is removed from the washed mansand can be recirculated to wash more sand. The Ortner® is economical and environmentally friendly at the same time.
The second of AEI’s one-two punch for making mansand is the BIVITEC® screen.
In part two of this post, we show you how to produce mansand without any water at all using the BIVITEC®!