Paver Set-Up

Mix Temperature

The mix temperature should be constant and high enough to prevent the mix from cooling before it is laid.

Paving material that has cooled is harder to compact.

The load bearing capacity of the mix, too, depends on its temperature. Feeding the paver with mix must be planned so as to ensure an optimum

temperature for paving. Grain Size

The maximum grain size should not exceed 1/3 of the layer thickness, otherwise the tamper will act directly on the underlying aggregate and shatter the grains.

Stiffness / Load Bearing Capacity

The composition of the mix should remain constant throughout the paving job.

Properties of the Mix

Properties of the mix have an influence on the screed’s floating behaviour. Paving materials with a high bearing capacity confront the screed

with a higher resistance than materials of poor bearing capacity. Conveying and compacting systems can be optimally set up to match

the type of mix.

Layer Thickness

The larger the layer thickness, the larger the screed planing angle.

Pave Width

The floating behaviour of the screed changes in accordance with the pave width.

Paver Stop

The longer the paver stops, the greater the irregularity to be expected in a longitudinal direction.

Ambient Conditions

Ambient conditions, such as temperature, can influence the mix and change the floating behaviour of the screed.

Head of Mix in Front of the Screed

If there is too large a head of mix in front of the screed, the mix may cool, thus having an adverse effect on both precompaction and the screed‘s floating behaviour.

A constant head of mix in front of the screed is a precondition for perfect floating of the screed.

The thicker the layer, the greater is the upward force exerted on the screed. Proportional control of conveyors and augers provides for an optimal head

Pave Speed

The pave speed determines the impact of the compacting systems on the pavement.

Pave speed and head of mix in front of the screed must be well adapted to each other.

When paving at a high speed, large quantities of paving material are consumed, which requires good job site logistics for supplying the paver with mix.

The pave speed must be selected so as to obtain as constant a supply of mix from the feed lorries as possible.

As the pave speed has a major influence on precompaction, it should be set so that the positive screed planing angle is not too large, as this would promote irregularities. The pave speed should, therefore, be set to a value ensuring good precompaction with the screed floating on the mix at a small planing angle.

Vibration Frequency

When paving thick layers, the vibration frequency has little influence on compaction. Vibration is far more important when paving wearing course, as it promotes the formation of a close-textured, even surface behind the screed.

Frequency / Pressure of Pressure Bar(s)

The pressure bar(s) are moved up and down by a pulsed hydraulic pressure. These pulses are generated by a rotary valve in the screed at a rate of between 58 and 68 Hz. Hydraulic rams press the pressure bar(s) downwards over the entire pave width. At the end of each pulse, the pressure bar(s) are returned to their original positions by springs acting against the force of the rams. The pressure applied to the pressure bar(s) changes the distance travelled by the pressure bar(s) with each pulse.

3.4

Paver Set-Up

Tamper Stroke / Tamper Speed

The length of the tamper stroke and the tamper speed are factors influencing precompaction of the mix and floating of the screed.

On VÖGELE screeds, the tamper stroke can be set to different lengths. The longer the tamper stroke, the higher the precompaction and the compaction depth. For this reason, the length of the tamper stroke should be set in accordance with the layer thickness in order to obtain the smallest possible, positive screed planing angle. A negative screed planing angle may result if the tamper stroke is too long for the layer thickness paved. This can lead to an open-textured, cracked surface structure and uncontrolled levelling resulting in irregularities.

Tamper Speed

Both the tamper speed and the pave speed have a major influence on precompaction of the mix. This means that the tamper speed must be adjusted in accordance with the pave speed or vice versa.

An optimal relationship has not yet been found. For this reason, the values must be individually adjusted until the smallest possible, positive screed planing angle is obtained and wear on the compacting systems is minimized.

Rigidity of the Screed

When making major changes or one-sided changes to the screed planing angle, torsion of the screed may result.

Screed Freeze

Screed Freeze is a briefly activated feature following a paver stop in Screed Float mode. A pressure of about 30 bar is applied to the piston side of the hydraulic rams for raising / lowering the screed in order to prevent it floating up when resuming paving.