Production
Click on the picture to learn more about the production process.
Production is divided into several stages:
- sand quarrying/pre-sorting
- washing
- wet classification
- drying
- cooling
- sieving
- packing
- storage
Quarrying of sand
At Råda, the sand is quarried with a wheeled loader which excavates the sand from different parts of the filter bed so that the raw material yielded may have as even a composition as possible. Stones larger than 150 mm in diameter are removed. The sand is transported by a conveyor belt with a capacity of 200 tonnes/hour to a sieve where stones larger than 25 mm are sifted out. The sand is then stored in a stockpile.
Washing
The sand is then discharged into a sand washing tower with a capacity of around 70 tonnes an hour. In the tower, all the contaminants (clay in particular) are washed out of the sand and the sand is then classified by particle size by three hydrosizers. The sand subsequently discharges onto several dewatering screens and drops into silos for check tests. It is then loaded on a dumper and transported to a depot for storage and drainage so that the water content becomes as low as possible before the sand goes for drying. The reject from the washing unit is led to a cleaning plant. Using two lamella separators, two fractions are obtained, one fraction in fine sand and one containing clay particles less than 50µ. The cleaned water is fed back to the treatment pond to be recycled and used for washing the sand again.
Drying
From the depots, the sand is transported to the kiln, into which it is loaded and the moisture content is continuously measured for optimal efficiency.
Sorted by the granular size
Before the sand is unloaded into a silo, it is cooled down from a temperature of approx. 100ºC to 30-40ºC. Sand with a granular size larger than 0.7 mm is loaded into a sand filtration facility and separated into several, very narrow, fractions by cylinder screens with a diameter of 2.6 metres and a capacity of 15 tonnes/hour.