Sandvik’s QE341 scalping screen is a Carrara marble screening star for William Vennei

Sandvik’s latest premium screening plant, the QE341, is hard at work for a major company operating in Carrara, Italy’s white marble quarry province. Guy Woodford reports.

The quarries of Carrara marble spa in Vennai Guglielmo di Fantiscritti in the Italian Alps have long been the centre of producing marble that has formed some of the world’s greatest art works. Now, increasing use of modern equipment has helped improve operational efficiency, with a 460 Sandvik QE341 scalping screen among the highly-prized additions to the production process. The white marble quarries now operated by William Vennai S.p.A. (William Vennai) in the Italian Alps have proved to be a source of the highest quality material, providing marble for the statues of the great Michelangelo himself, amongst others. These are considered to be amongst the oldest and most prestigious in the entire area, with the company having quarried the marble since its incorporation in 1924. Located in the marble basin of Fantiscritti, they are capable of producing annually an amount equal to about 60,000tonnes of marble blocks, rising to 100,000tonnes through commercial connections with affiliated companies such as the Major Excavation Fantiscritti Marmi srl Scarl and E.T.A. Scarl.

In order to supply such a prestigious and valuable resource, the marble has to be extracted precisely. Although many techniques have remained the same, new technology is also playing its part. “Diamond wire saws have replaced the old helical wire ones allowing a radical lowering of work times, so much so that whereas to produce a block 10m x 10m it took three days of work it now takes only 4 hours,” explains Paulo Gianni, excavator operator at William Vennai.

After using horizontal and vertical drilling holes or joints with jackhammers, holes are screwed to the diamond wire which is connected to a powerful cutting machine. This scrolls down automatically during cutting phases or rotates the point of axis according to various requirements. When the marble block is separated from the mountain complete detachment is facilitated using special inflatable ‘pillows’ or hydraulic jacks using powerful excavators to a specially prepared ‘bed’ of debris to provide a safe resting place for the extremely valuable end product.

However, the marble is not all of a consistently high quality. The ‘perfect’ block represents only 20% of the production; the remaining 80% consists of semi-formed blocks as well as material that does not possess the desired homogeneous structure due to contamination with metamorphic rock, rubble and other materials. Earth and gravel are always present and need to be removed in order to preserve the quality of the marble.

In order to effectively and efficiently remove contaminants, which themselves are valuable products, from non-block marble production, the use of a mobile screen is advisable. In William Vennai’s case, this led to the firm purchasing a Sandvik QE341 scalping screen from the Swedish globally-headquartered OEM’s authorised Italian distributor, CGT (Compagnia Generale Trattori S.p.A.)

Erich Lucchetti, a partner of William Vennai, said of the new screen: “Acquiring the QE341 was a necessity in order to maximise and improve the quality of our end product. We could only really choose Sandvik, above all for the quality of the machines and then for our relationship with CGT, a relationship established over time and dating with me personally 30 years. We place so much emphasis on our relationship that our quarries only use CAT [block handling/hauling] machines. In future, if we require screening (or crushing equipment) we will put our faith in CGT again and also choose Sandvik.”

The QE341 is a heavy duty scalper said to have a class-leading open scalping area that delivers enormous rates of production. This means that production of even the most hard-wearing materials is facilitated through a wear-resistant steel apron feeder, with massive stockpiling capability with over-wide conveyors to maximise delivery. With a one piece wear-resistant rigid hopper it features a robust crusher-style chassis and has been designed to be compatible for 2-way or 3-way split configurations, as well as having the ability to interchange side conveyors thereby demonstrating the ultimate flexibility of the unit. The screen-box jack-up facility allows easier access to the bottom deck for maintenance and screen media changes.

Other key customer-focused features on the QE341 include an aggressive screenbox with 9mm of throw at over 1000 rpm which enables peak productivity; radio tracking and feeder control as standard to help ensure operator safety; unique colour-coded control panel with one touch start/stop enabling easy operation; optimum fuel economy at less than 15 litres/hour, reducing operating costs; and hydraulic folding maintenance platforms simplifying service and maintenance.