Screed-tensioning device boosts paver efficiency
01 February 2000
Ingersoll-Rand ABG, a manufacturer of road construction machinery, has developed a new screed tensioning device for its range of pavers, which is said to boost paver efficiency and mat accuracy.
The new device, it adds, marks a further milestone in road construction.
A spokesman elaborates: ''This patented screed tensioning device achieves uniform pre-compaction and surface evenness even when paving at large widths.
''Paving without a screed tensioning device leads to a loss of paving quality, a fact which all manufacturers accept. The paver paves the mat with the screed in the so-called floating mode.
To ensure the floating behaviour of the screed, it is necessary to set the finishing plate on the screed to a positive angle of attack (a) as shown in Figure 1.
''When paving a mat with a uniform thickness, the angle of attack should be the same across the whole width of the screed.
''A positive angle of attack means that the front edge of the smoothing plate is higher than the rear edge.
''The angle of attack is determined by the parameters of the mix bearing capacity, compaction by the tampers, compaction by the screed vibration and weight, paving speed and mat thickness.
When paving without the screed tensioning device, the screed's lower area is subject to high torsional forces and tends to twist, as shown in Figure 2.
Due to these torsional forces, the twisting will increase to the outer edges the larger the paving width.This results in a smaller angle of attack (a1) in the outer areas of the screed than in the centre (a).
''By using the screed tensioning device, which is now offered as an option by ABG, the torsion and twisting on the screed is counteracted and the angle of attack (a) remains the same across the entire width of the screed (Pr by H), as shown in Figure 3. The screed tensioning device consists of a wire rope, hydraulic cylinder and pressure control valve.
''Another advantage is that the screed sections, screed guide cylinders and crown control adjustment are significantly relieved of their load.''
Ingersoll-Rand ABG recommends the application of the screed tensioning device on Variomatic screeds at paving widths of more than 7.00 m and on manually adjustable screeds beyond 10.00 m.
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