Skanska’s Hällevadsholm quarry has been supplying sized gneiss rock aggregate to the Swedish construction industry since its establishment in 1954, with demand for the material being in the region of 300 000 tons each year. Playing an increasingly vital role in the production of accurately sized material has been the WR modular screening media system from Sandvik Construction, which since its installation in 2012, has improved production efficiency of the quarry through its long lasting nature, accurate screening and flexibility of operation.
In Sweden, Skanska with its head-quarters in Stockholm is regarded as one of the largest building and civil construction firms, providing a cross section of services including road construction and civil engineering. Additionally Skanska in Sweden also includes a number of subsidiary operations, providing a range of services for the very largest projects, costing hundreds of millions of Euros, to smaller, localized concerns. Skanska also owns and operates the Hällevadsholm quarry, which was established in 1954. The operation quarries a gneiss deposit which has increasingly proved to be popular with concrete producers due to the gneiss, unlike granite, emitting no radon. Current production of this important resource is approximately 300 000 t each year.
Although the quarry has been able to operate highly efficiently, an increasing problem was found with regards to the screening media used. Due to the hard wearing nature of the gneiss, and the constant demands for accurate production, it was found that the traditional steel wire mesh screens needed to be replaced on a continual basis. Besides the cost of replacing the meshes, the process of replacing the meshes proved to be laborious, time consuming and at times involving risk of personal injury for the technicians involved.
A new solution for screening
The Site Manager of Hällevadsholm quarry, Stefan Abrahamsson, together with Operations Manager Björn Dahlung, contacted Sandvik for a solution. Sandvik’s Sales Manager, Mikael Sirenius, after assessing the problems encountered, suggested that the existing screen meshes be replaced with Sandvik’s WR modular screening media; a decision that they have not regretted in the year the system has been installed.
The basis of the WR screening media is its pioneering design, which provides users with an open production area greater than is found in traditional modular media. This is achieved through the use of cross-mounted flexible screen panels which generates a revolutionary wave like cascade effect in the material bed in order to improve stratification, and allow undersize material to find a more rapid path to the screening surface.
Additionally the system optimizes screening accuracy as the modular screening media utilizes a fibre reinforced rubber screen membrane, which enables the use of thinner panels, with closer aperture spacing, thus maximizing the open screening area. Other efficiencies are derived through the elevation of the screen panels from the longitudinal support bars, as well as the screen panels may be fully perforated from side liner to side liner. This absence of blind fields in the directional flow of material ensures maximum material separation, and minimizes the amount of undersized particles “carried-over” to the end product.
Minimising operational downtime
Use of the WR screening media ensures that operational downtime is minimized; this is due principally to the long lasting rubber and polyurethane materials which are used to make the screen panels, thereby extending the service intervals (Fig. 1). Additionally the WR screen panels possess a built-in cross beam protection lip which, together with support bar rubber capping, protects the adapter system against wear.
User friendly flexible use is ensured as replacing the screen panels, when the need arises, may be easily accomplished due to the wedge locking them into place may be quickly removed and reinstalled. This keeps change over time to a minimum, and as the absence of steel reinforcement makes the WR system light, which reduces the stress on the screen and bearings, there is a further reduction in the risk of unplanned production stops.
Rapid installation boosts production
The initial installation of the WR screening media at the Skanska Hällevadsholm quarry took two days. In effect this was a “retrofit”, where the previous screen was removed, and replaced by the modular media, on the existing VFS42/18-2 screen. This was due to the fact that the actual requirement was to enable the Hällevadsholm quarry to produce a 0-16 mm product off the second screen deck, but be able to further adjust separation when needed, depending on production demands. Due to the success of the WR media Skanska Hällevadsholm has further adjusted the production flow as the system is easy to use, and highly flexible. Hence the quarry now also uses the WR media for washing 16-22 mm aggregate to be used as macadam, with 1500-1600 tons of crushed rock now passing through the screen on a daily basis (Fig. 2).
Varied and unusual applications
As well as fulfilling a major role in concrete production, the material from the Hällevadsholm quarry is now also used for asphalt, house building, road building and general construction aggregate. The largest growing application however is quite surprising: wind power. The increasing emphasis placed on renewable energy resources in Sweden has seen a massive expansion in wind power. It has been calculated that each wind power turbine requires the use of between 7000-9000 tons of aggregates, arising principally from the need to build new roads to reach the often remote locations where the wind power stations are established.