VÖGELE screeds


The subassemblies of VÖGELE drums in detail

VÖGELE screeds are the hearts of all road pavers. The screed compacts the mix evenly across the entire paving width to create a uniformly sealed surface texture.

Grade the pavement exactly to your client’s specifications with reliable screeds from VÖGELE. Maximum precompaction guaranteed.

Screed types

The paving screed is the heart of every road paver. The tasks of the screed in the paving process are as follows:

  • The production of a uniformly sealed surface texture
  • The achievement of a high degree of precompaction
  • The grading of the pavement exactly to the client’s specifications

Generally speaking, there are two different screed types.

Extending screeds

Extending screeds (AB type) enable the realisation of varying paving widths between 1.1 m and 9,5 m. Their particular strength is their enormous flexibility when paving different working widths. The ability to pave precisely limited widths enables them to cater for an exceptionally broad spectrum of applications. Today, extending screeds are among the most typically used flexible screeds. They are predestined for paving jobs where versatility and adaptability are critical factors.

Fixed-width screeds

With additional bolt-on extensions, fixed-width screeds (SB-series) can be employed for paving widths from 2.5 m to 16 m. Thanks to a screed plate depth of 500 mm (330 mm in the case of extending screeds), these screed types react more slowly, which leads to a more even paving quality and higher profile precision. The continuous, mechanically-extended, construction of the screed leaves no marks whatsoever on the surface of the paved asphalt. Not even when the planing angle of the screed is changed.

Fixed-width screeds are employed predominantly on extensive construction projects with consistently broad paving widths and large radii. Hydraulic extensions make them especially versatile and suitable for a wide range of applications. With broad working widths, they deliver high profile precision and are also suitable for paving with high compaction, for example with CTB, RCC and PCC.

Screed components

The operating principle behind all paving screeds

The screed components shown here all have a direct or indirect influence on paving quality.

(1) Torque restraint system
(2) Single-tube telescoping system
(3) Hydraulic cylinder for width adjustment
(4) Hydraulic screed extension
(5) Screed plate with heating rod
(6) Screed base member
(7) Heating rod monitoring system
(8) Eccentric vibration
(9) Tamper bar with heating rod

The metering gates push the material placed in front of the screed forwards. The tamper at the front end of the screed strikes off the mix as it passes under the screed to create the necessary precompaction and essentially determines the ‘floating behaviour’ of the paving screed.

The screed plates are responsible for ensuring the evenness of the pavement surface.

The pressure bars are pressurised by pulsed-flow hydraulics, and are the final components of the VÖGELE high compaction screeds.

These components enable the screed to deliver a perfect paving result with extremely high precompaction that reduces subsequent final compaction with rollers to a minimum.

All compaction aggregates are fitted with heating rods that prevent the adhesion of asphalt and ensure the production of a faultlessly sealed surface.

Together with the guide strips and sliding blocks, the telescoping tubes and the torque restraint system guarantee the necessary rigidity of the extending screed.

Basic screed adjustments

Correct adjustment of the screed before paving begins prevents unnecessary wear.

Click on the gallery to see the procedures for the various screed components.

Setting the planing angle of the extending screed

The planing angle must be correctly set on both the inner and outer edges of the extending screed.

Setting the outer planing angle on the extending screed:
  • Retract the screed to its maximum extent.
  • Lay a ruler (4) under the screed plates at the height of the outer adjusting spindle.
  • Adjust the height of the screed extension so that the ruler lies on the points (1), (2) and (3).
  • Measure the gap: There must be a gap of approximately 1 mm between the ruler and the screed plates at a position around 30 mm behind the rear edge of the tamper.
  • Release the chains on the adjusting spindles.
  • Make the adjustments on the front adjusting spindle with appropriate tools.
  • Measure the gap and, if necessary, repeat the adjustment procedure.
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Setting the inner planing angle on the extending screed:
  • Extend the screed until the adjusting spindles are directly beneath the sliding blocks.
  • From here, repeat the adjustment procedure as before, from the second step of the setting procedure for the outer planing angle.
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After setting the planing angle, please tighten the clamping screw for height adjustment again. Now check the settings again.


Adjusting spindles

Before carrying out the adjustment of the adjusting spindle, the play of the threaded bush (5) should be checked with tightened locking nuts.

Height adjustment of the adjusting spindle:
  • Set the screed with extension units on wooden blocks.
  • Release the chain (1) with the aid of the shackle.
  • Turn the adjusting spindle (2) down so that the front face (3) comes to rest completely on the flange face on the screed frame.
  • Remove the internal hex bolt (4) from the flange.
  • Hand-tighten the threaded bush (5) with a suitable tool.
  • Remove the threaded bush (5) with a 45° twist to expose the hole for the locking bolt.
  • Tighten the internal hex bolt (4).
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Always adjust all four spindles of each extending screed.

Tampers

The tamper must always have the same stroke across the entire paving width. The stroke can be altered by twisting the eccentric bush on the drive shaft of the tamper. This can be carried out easily from behind when the paver is being moved from one section to the next. In contrast, adjusting the lower reversal point of the tamper bar in relation to the screed plate, takes a little more time and effort. First of all, the metering gates must be removed to access the bolts that need to be removed from all the shaft mounting brackets. After removal of the locking nut (2), the tamper height can be altered with the bolt (1). The height to be set depends on the stroke setting of the tamper.

(1) Bolt
(2) Locking nut
(3) Eccentric shaft at the lower reversal point
(4) Tamper
(7) 1 mm at 4 mm stroke
(5) Chamfer
(6) Screed plate

The tamper should be set flush with the screed plate at a stroke of 2 mm (manual check by touch).

Tamper stroke 2 mm

The tamper is flush with the screed plate at the lower reversal point.

Tamper stroke 4 mm

The tamper is positioned at a maximum of 1 mm lower than the chamfer at the lower reversal point.

Tamper stroke 7 mm

The tamper position is 2.5 mm lower than the chamfer at the lower reversal point.

Setting up the pressure bars
  • Remove the twist lock (3) secured nut (2) from the pressure bar cylinder (1).
  • Turn the pressure bar cylinder (1) to adjust the height of the pressure bar(s). The clearance (7) between the pressure bar(s) and bottom edge of the screed plate should be at least 4 mm.
  • Check that the pressure bar cylinder makes contact with the metal plate (5) when retracted.
  • Set the pre-tensioning of the spring (6) to 5.5 mm with the nut (4). This sets the offset (8) to 59.5 mm.
  • Secure the pressure bar cylinder (3) again.
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Screed metering gate

The tamper (3) must be set to rest lightly over the entire length of the wear strip (1). Then adjust the spring steel bar (2) on the metering gate by means of the screw (4) from the rear of the screed until there is a gap of 0.5 to 1 mm between the tamper and the spring steel bar. By removing screws (6) and fitting various small shims (5), the metering gate should be aligned so that the spring steel bar (2) is at least parallel to the tamper or is preferably slightly inclined towards the front.

Finally, recheck the gap between the tamper and the spring steel bar and correct it if necessary.

Mechanical hydraulic side plates

Screed side plate height adjustment is a function often used during the paving process. As a user, you know from experience that this function is often needed when paving, for instance, along kerbs with high or low kerbstones or along gutters.

How side plates help to ensure perfect paving quality:

  • By preventing lateral spread of the mix during paving.
  • By producing clean joints and pavement edges.
  • By ensuring optimal compaction, also at the outer edges of the pavement.
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SUPER series USA

VÖGELE offers road pavers screeds designed especially for the American market that are particularly suitable for inner-city paving or paving at high speeds.

VF SCREEDS
VF extending screeds with front-mounted extensions for frequently varying paving widths:
  • Robust and smooth-running width adjustment system for precise paving at all widths
  • The paving width can be varied in a range from 3.05 m to 7.75 m (10 ft to 19 ft 8 in)
  • Crown profile adjustment and variable pitch extensions for numerous paving profiles; optionally available gutter profile
  • Extension cross-slope up to 10%
  • Innovative electric heating system
  • ErgoPlus operating concept for easy handling
  • Compact design for an outstanding overview of all parts of the machine
  • Ideal tool for paving with varying widths and the construction of major roads
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Main applications

Working at high paving speeds with varying paving widths requires a screed that can always be relied on to deliver precise paving results. The VF 600 from VÖGELE is such a screed.

Several constructional details enable fast and precise retraction of the screed. For instance, blockages are avoided, as the paving mix offers virtually no resistance at the chamfered leading edges of the extensions. The side plates of a screed with front-mounted extensions are only about half as long as those of one with rear-mounted extensions, an advantage that enables particularly precise paving. close to obstacles and involves less manual effort. A broad spectrum of possible pavement profiles makes the screed a particularly versatile tool. Due to these special features, the VF 600 is equally suitable for the paving of motorway intersections and surfacing main roads that require navigation around obstructions. This screed is an outstanding solution when it comes to the paving of car parks with pedestrian islands, lamp posts or manhole covers, residential streets or city streets with gas and water mains.

VR screed
VR extending screed with rear-mounted extensions for paving multi-lane roads:
  • Featuring large-sized and robustly-constructed telescoping tubes for high-precision paving. These guarantee the outstanding stability of the screed and enable the achievement of excellent paving results.
  • The telescoping tubes of the screed are located at a height that prevents any contact with the mix.
  • Even with the screed set to its maximum paving width, the telescoping tubes are extended by no more than half, which precludes undesirable sag.
  • Deep screed plates ensure excellent floating behaviour.
  • Together, the mountings of the telescoping tubes, the guide tube mounts and the torque restraint system constitute a sturdy 3-point suspension system that absorbs the forces exerted on the screed during paving and guarantees smooth variation of the paving width
  • in a range from 3.05 m to 6 m (9 ft 10 in to 19 ft 8 in)
  • Extension cross-slope up to 10%
  • Robustly constructed telescoping system with 3-point suspension
  • Innovative electric heating system
  • ErgoPlus operating concept for easy handling
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Main applications

On construction projects involving wider paving widths, precise adherence to line and level is a decisive factor when the specifications demand the delivery of first-class pavement quality, regardless of the layer thickness. In this respect, the VÖGELE VR 600 screed offers an impressive range of options. The screed has a basic paving width of 3.05 metres that can be hydraulically extended to a width of 6 metres – almost twice the basic width. The screed can further extended with bolt-on extensions to enable a maximum paving width of 8.6 metres. The screed is fitted with vibrators that cover the entire paving width. A quick-fit system enables fast and easy installation of the 0.65 m wide bolt-on extensions. In view of its outstanding overall technical concept, the VR 600 screed is the perfect choice for medium and large-scale road construction projects. When it comes to paving asphalt on multi-lane roads, the new screed also brings substantial advantages over single-lane paving, as it avoids longitudinal joints, the weak points of all asphalt pavements.

Facts
Compaction types

The aim of the screed's compacting systems is to achieve the greatest possible pre-compaction so that different layer thicknesses have less influence on the amount of rolling required for final compaction. VÖGELE employs the compacting systems listed below:

  • T > Tamper: The vertical reciprocating motion of the tamper is initiated by an eccentric drive shaft.
  • V > Vibrators: The vibrations acting on the screed plate are generated by a shaft with an unbalanced mass perpendicular to the direction of motion.
  • P > Pressure bar: The pressure bars are hydraulically pressed onto the material at a frequency of approx. 68 Hz and a maximum pressure of 130 bar.
  • P1 > Version with one pressure bar
  • P2 > Version with two pressure bars
  • Plus > Version with two pressure bars; modified tamper geometry and additional weights in the screed frame

Applications

V and TV screeds can be used for all conventional mixes that are easier to compact. Less final compaction effort is necessary when TP1 and TP2 screeds are used. The two variants differ with regard to the compaction values that can be achieved; whereby all conventional mixes can be processed. The TP2 variant delivers a high level of pre-compaction, particularly in the case of thicker paved layers.

TVP2 screeds can be used for paving with all conventional mixes. This variant is also suitable for paving PCC (Paver Compacted Concrete), as surfaces paved using this method require no final compaction. The TP2 Plus variant offers even higher compaction values and is used in the VÖGELE InLine Pave train for the production of the binder course. Due to the immediately following paver, this layer must already have final compaction values. All compacting systems on VÖGELE screeds - tampers, vibrators and pressure bars - are independently controlled and can be switched on or off as required.

Compaction aggregates of extending screeds

(1) V: Vibrators

(2) TV: Tamper and vibrators

(3) TP1: Tamper and one pressure bar

(4) TP2 (Plus): Tamper and two pressure bars

Compaction aggregates of fixed-width screeds

(1) TV: Tamper and vibrators

(2) TP1: Tamper and one pressure bar

(3) TP2: Tamper and two pressure bars

(4) TVP2 (Plus): Tamper, vibrators and two pressure bars

The interaction of the tamper, the base of the screed (screed plate), bevel iron, side plate ski and pressure bar ensures that the mix is held in place as a package that counteracts material spreading in any direction. The end-result is an almost finally compacted asphalt package.

Tamper bars

The downward vertical stroke of the tamper presses the mix to be paved under the base of the screed. It ensures a regulated feed of material to the screed and achieves the required degree of pre-compaction.

The materials from which the tamper is constructed must fulfil particularly high standards due to the continuous impact loads from its vertical reciprocating motion. A hard surface and a ductile core are among the most important properties of tamper bars. At the beginning of the manufacturing process, profile rods are cut to the required length for the tamper bars with a CNC-controlled saw. Thanks to the chamfered leading edge, the tampers ensure even mix feed and optimal compaction in later use. The service life of these components depends on their hardness. Induction hardening, the process also used for the pressure bars, ensures consistent hardness over the entire length of the bar and achieves a hardening depth of at least 5 mm. The core remains ductile and flexible, while the surface, which is in constant contact with the mix to be compacted, retains its high resistance to wear. The bores for the heating rods are drilled on a CNC deep hole drilling machine developed especially for VÖGELE. In these this bores, the heating rods heat the bars (tamper bars and pressure bars) centrally from the inside over the entire length and guarantee homogeneous heating. In this way, bitumen residues are prevented from adhering during subsequent paving (particularly during the pre-heating phase prior to starting work) and abrasive wear on contact surfaces is reduced.

In the final step this phase, all bars are straightened in a straightening jig. The maximum permissible flatness deviation is 0.5 mm.

Screed plates

The wear-resistant steel used in the manufacturing of screed plates combines properties such as ductility and fracture strength. In view of the sliding friction that takes place between the screed plate and the paving mix, these particular properties play a decisive role in maximising the service life of these components.

During the manufacturing process, the raw material for the screed plates is first laser-cut to the required dimensions. A chamfer that assures good material feed behind the tamper bar is milled off the later underside of the front screed plate in the direction of travel. To prevent cold welding between the back of the tamper and the leading edge of the screed plate (in the forward direction of travel), this area is also correspondingly machined. This optimisation ensures precise tamper bar guidance and also significantly increases the service life of both components. Following stress-relieved straightening to ensure evenness, the threaded bolts are welded onto the upper surface by a CNC-controlled stud welding machine. On average, 25 threaded bolts with maximum tensile and shear strength are welded to each screed plate.

A laser cuts out the required shape from Hardox steel.

The required screed plate chamfer is cut by special milling tools.

The final step of the manufacturing process is the stress-relieved straightening of the screed plates.

Pressure bars

In operation, the pressure bars powered by single or double pulsed-flow hydraulics (TP1 or TP2 variants) are subjected to similar loads as the tamper bars.

All high compaction screeds from VÖGELE are equipped with pressure bars. They are located immediately behind the screed plates and perform the final phase of compaction by the screed. The positioning of the pressure bars at the end of the screed has the advantage that the compaction effect can be regulated independent of the material feed and pre-compaction. If the profile of the pressure bars is already too heavily worn, the compaction results will be well below the values stipulated by the client. The manufacturing processes for pressure bars and tamper bars are very similar, except that there are two different types of pressure bars:

Pressure bar 1, immediately behind the screed plate, has a uniformly bevelled profile. The rearmost third of pressure bar 2, which follows, is flattened. TP1 screeds have only type 2 pressure bars.

A CNC-controlled saw cuts the profile rods to the required length.

Profile and plane-parallel milling of the blanks.

The CNC deep hole boring machine drills a 20-mm bore for the heating rods.

Electrical heating systems

VÖGELE leads the field when it comes to electric screed heating. As early as 1952 VÖGELE was the first road paver manufacturer to use this highly efficient, eco-friendly design and, to the present day, continues to shape the development of screed heating with numerous innovations. All compacting systems are heated across the full screed width to maximise compaction performance and assure the delivery of a faultless and uniformly sealed surface texture. This effectively prevents the adhesion of mix and provides the ideal operating temperature for the floating behaviour of the screed. Tamper and pressure bars are heated evenly from the inside by integrated heating rods. Screed plates are fitted with a heating rod as a standard feature that distributes heat across the entire plate surface. As a further option, the bevel irons and the side plate skis can also be fitted with heating elements.

Heating rods

Screed heating

On all VÖGELE road pavers, powerful and robust three-phase A.C. generators supply the screed heating with the energy it needs. Smart generator management ensures that they work with optimal efficiency. It ensures that sufficient generator power is available for the current paving width, independent of the engine speed. Power reserves are available in full for paving.

(1) Diesel engine
(5) Generator
(2) Control panel
(4) Junction box
(6) Tamper bar with heating rod
(7) Screed plates with two heating rods
(3) Switch and fuse box
Telescoping system for extending screeds

3-point suspension

The 3-point suspension for VÖGELE extending screeds comprises the following components: the telescoping tube, the hydraulic cylinders in conjunction with the guide tube, and the torque restraint system. The ErgoPlus console controls two hydraulic cylinders that precisely set the width of the extending screed. The generously dimensioned telescoping tube keeps the extension units securely in position. At full screed extension the three concentric tubes that make up the telescoping tube remain supported by at least one half. Due to the large bearing span, this reliably counteracts the vertical uplift forces. The smooth movement of the telescoping tubes, without jamming or tilting, is an important prerequisite for faultless project execution – particularly when frequently changing paving widths are required. The slide tapes inside the tubes guarantee freedom from play and ensure jerk-free movement when being extended and retracted. VÖGELE achieves width variability while retaining high stability by using an additional guide tube. This tube, which is connected to the extending unit via a linear sliding bearing, enables precise, parallel adjustment of the width of the screed up to even the largest paving widths. The screed's extension units are subjected to enormous material pressure in the horizontal plane, which results in a torque force.

This torque force is counteracted by bracing, the torque restraint system, that stops the extension unit twisting or turning around the telescoping tube.

(1) Torque restraint system
(2) Guide tube mount
(3) Mounting point for the telescoping tube
Telescoping tubes

The telescoping tubes provide the extending screeds with the necessary stability (system stiffness) and ensure maximum precision (freedom of the system from play) during extension and retraction. While the stiffness is determined above all by the large tube diameter, the extremely precise concentric fit of the inner and outer tubes is crucial factor in ensuring freedom from play. Due to the precision engineering required in the production of the telescoping tubes, they are manufactured in an elaborate process with several phases. After the machining processes, the elements are passed on to a series of honing and grinding processes to guarantee an absolute minimum amount of play in the concentric fit. On the honing machine, the inner surfaces of the telescoping tubes are finely honed to achieve a high-precision surface finish with a maximum roughness depth of 0.005 millimetres.

In comparison, the diameter of a human hair is approximately 0.1 mm.

To achieve a hard and corrosion-resistant surface, the outer surfaces are first polished, painstakingly cleaned and then electroless nickel plating according to the Kanigen® process. The telescoping tubes from VÖGELE are manufactured exclusively as sets in a single process. This safeguards their characteristic properties of stability and precision and guarantees the consistently high paving quality clients expect.

Guide strips and sliding blocks

Guide strips and sliding blocks are parts of the VÖGELE torque restraint system. The guide strip is attached to the screed body of the extension units by screws. A special locking compound is applied to the roughened underside of the screws. This counteracts the loosening of the screws due to the continuous vibration of the screed. The sliding blocks are mounted on the outer extension units of the extending screed. One sliding block is located above, and the other below the guide bar.

The bottom sliding block is securely bolted down attached, while the other is mounted in such a way that it can be adjusted without any problems in the event of wear via an eccentric mounting This configuration ensures safe and secure guidance of the extension units and high stiffness of the overall screed system.

The sliding blocks sit tightly on the guide strip.

The guide strips and sliding blocks of the torque restraint system.

Maintenance

All elements of the screeds, and especially those that are directly involved in the compaction process (tamper bars, screed plates and pressure bars), are subject to varying degrees of material-dependent wear. There are many different reasons for this. Although wear can be delayed to a certain extent, it can nevertheless not be avoided. Fouling, incorrect assembly or poorly-fitting parts from third-party providers affect not only productivity and/or pavement quality, but can also increase wear on other components.

Among the most common reasons for unusually short component service life are:

  • Incrustations and accumulations of old mix (due to inadequate cleaning or, for example, the use of tamper bars without heating rods)
  • Insufficient pre-heating of the paving screed
  • Paving with abrasive materials (e.g. polymer asphalt)
  • Incorrect or sub-optimal screed settings
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What exactly is wear?

Wear is caused by the pressure between two elements in contact (e.g. between the mix being paved and the screed plate) when the elements move relative to one another. In such cases, friction detaches small particles from the surfaces of both elements.

How can wear be avoided or prevented?

Fouling increases wear: abrasive materials grind material away at all points of contact and drastically shorten the service life of components. Regular maintenance and cleaning is essential for maximising the service life of components.

Increasing service life means:
  • Ensuring that a thorough daily cleaning regime is in place and observed (before and after paving).
  • Ensuring that regular checks of all wearing parts are conducted at appropriate intervals to avoid and prevent wear and damage to other components.
  • Ensuring that regular maintenance and checks on the screed settings are carried out.
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Contributing factors

A general distinction can be made between external and internal factors.

Here, external factors are those defined by the material to be placed, the tonnage per hour or specific on-site requirements.

Internal factors are generally incorrect settings on the screed or the consequences of inadequate cleaning.

Contributing factors (external):
  • Paving with highly abrasive material
  • Paving with polymer-modified materials
  • Paving surface courses (as a rule, these are a source of significantly more wear than, e.g., thicker binder courses)
  • ‘Hot-on-cold’ paving with heavy wear in the overlap area
  • Paving on construction sites with significantly varying variations in the paving thicknesses across the entire working width (e.g. when compensating for unevenness)
Contributing factors (internal):
  • If tamper speeds are too low, this causes a cause an excessively large screed planing angle, which results in heavy wear on the rear edges of the screed plates.
  • If tamper speeds are too high (in relation to the material and paving speed), this leads to a negative planing angle across the entire screed.
  • Incorrect adjustment of the screed extensions (unequal heights).
  • Incorrect adjustment of the metering gate and the spring steel bar. This will cause a spontaneous build-up of material inside the screed.
  • Heavily contaminated or too tightly attached pressure bars that cannot ‘swing’ freely.
  • Working with heavily worn screed wearing parts.
Planing angle (aka angle of attack)

The planing angle of the screed plays an essential role when paving the asphalt mix. This angle is set by the tow point (aka pull point) on the paver's screed levelling arm. Apart from its response to the adjustment of the height of the screed tow point, the positioning of the screed is also influenced by changes in the advance speed of the paver and the various properties of the mix to be compacted. The paving thickness should be checked after the start of paving to determine the ideal position of the towing shackle mount and, in turn, the resulting screed planing angle. The angle can be positive or negative (refer to the graphics). A slightly positive planing angle is of advantage for the paving quality and quantity. A further benefit is the minimisation of application-related wear.

The greater the paving thickness (layer thickness), the larger the screed planing angle should be. The more material in front of the screed, the greater the uplift of the screed, which, in turn, also influences the screed planing angle.

If the positive screed planing angle is too large, it will cause increased wear on the screed plates and irregularities on the paved surface. A negative screed planing angle, caused when the tamper speed is too high or when the stroke of the tamper bars is too long, produces small, regularly occurring irregularities. When correctly set, with a slightly positive screed planing angle, the entire underside of the screed plate is used to smooth the surface of the pavement.

All screed plates of an extending screed should be set to the same screed planing angle to ensure that different paving widths do not degrade the floating behaviour of the screed. For this purpose, the leading edge of the screed plate of the screed extensions should be set approximately 0.5-1 mm higher than the rear edge when setting up the screed.

Tampers

The tamper is the decisive compacting system when the key concern is the minimisation of wear on components such as the screed plate or pressure bars. This means that if the tamper is heavily worn, wear on the screed plate and pressure bars is already on the way. If increased wear is found in the central section of the tamper, the cause is generally a deformed (twisted) bar. The bar should be checked to ensure it is straight and replaced if necessary. In the event of an incorrect setting for the height of the extension units, or when the screed is incompletely extended, increased wear can occur on the part of the tamper bar behind the basic screed. The ‘freely moving’ section of the tamper bar wears more slowly, as here the material has not yet been compacted by the basic screed and is ‘softer’ than the material already compacted behind the basic screed.

Unusually high wear occurs on the outer edges of the tamper bars if overlapping ‘hot-on-cold’ paving is frequently undertaken. In such cases, the tamper bars compact already compacted pavement over a length of approx. 3-4 cm.

Model of a tamper bar during the compaction process

A sharply pointed tamper bar

The effect of tamper wear on the floating behaviour of the screed

The shape of the tamper affects the floating behaviour of the screed. If the tamper is sharply pointed, the entire screed system loses its pre-compaction effect and the rear edge drops. As a result of this, the screed develops a much too large planing angle. This causes the screed to react strongly during paving, produces an uneven pavement surface and significantly increase wear on all other components.

In the case of sharply pointed tamper bars, all bars on the screed should be removed and replaced as a set.

Screed plates

If the screed plate is heavily worn with wedge-shaped wear at the rear, this indicates that the screed planing angle has been continually too large and, in consequence, the pre-compaction under the screed has been too low.

The cause of this is generally found to be a permanently too low setting of the tamper speed. There is often heavy wear on the leading edge of the screed plate caused by an excessively high clamping force exerted by the metering gate that is transferred through the tamper to the leading edge of the screed plate. If shadowing occurs in the pavement surface, in the majority of cases partial erosion of the screed plate is the cause. Such erosion is due to heavy, partial wear (e. g. during compensation for unevenness) in combination with strong thermal impact.

In the case of screed plates with through stud bolts (non-original VÖGELE screed plates), partial erosion occurs almost always around the bolts on the underside of the screed plate. This erosion is due to the different wear behaviour of the bolt and screed plate materials.

Heavy erosion on non-original screed plates with through bolts.

Left: heavily worn screed plate with wedge.-shaped wear
Right: screed plate, as new

Examples of wear
TAMPER BAR
  • Condition: The tamper bar is heavily worn. The profile necessary for pre-compaction is completely worn away.
  • Cause and effect: The cause is too low tamper speed, which leads to low pre-compaction and dropping of the rear edge of the screed. In turn, this causes exceptionally high wear on the rear edge of the screed plate. If the incorrect setting is used for an extended period, the screed plate may be completely worn away at the rear edge and look almost like new at the front.
  • Solution: moderately increase the until the screed adopts a balanced screed planing angle again.
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SCREED PLATE
  • Condition: The rear edge of the screed plate shows extremely heavy wear.
  • Cause and effect: The cause of this uneven wear is that too much mix was used in front of the screed, and the higher resistance caused a larger screed planing angle. In such cases of massive wear, the fastening bolts of the screed plate can become detached and its connection to the screed frame is no longer assured.
  • Solution: During paving, always make sure you use the paddle sensors at the end of the scraper belt tunnel and the auger sensors to ensure a correct supply of mix in front of the screed.
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PRESSURE BARS
  • Condition: The pressure bars show an extremely flattened profile and can no longer compact the mix as required.
  • Cause and effect: Over time, pressure bars lose their profile due to continual friction with the paving material. The pressure bars are no longer in direct constant contact with the mix and the necessary high compaction can no longer be achieved.
  • Solution: In this case, a complete replacement of the pressure bars is unavoidable. The pressure bar spacing should be regularly checked and adjusted. Thorough cleaning will significantly slow the wearing process.
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TORQUE RESTRAINT SYSTEM
  • Condition: The bottom face of the top sliding block is worn and is not in contact with the guide bar.
  • Cause and effect: Friction during extension and retraction of the screed and the pressure between the sliding block and the guide strip cause wearing of the brass components. As a result, the counter-pressure developed by the material can longer be fully countered.
  • Solution: The top sliding block can be re-adjusted by means of a threaded cam. In case of excessive wear, the sliding block can be rotated by 180°.
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TELESCOPING TUBES – SCRATCHES
  • Condition: The surface of the tube shows scratches and indentations.
  • Cause and effect: The telescoping tubes can be damaged during everyday operations by shovels or the soles of boots. Mechanical scratches and indentations on the surface of the tube damage the Teflon slide tape when retracting and extending the telescoping tubes and reduce the precision of screed guidance.
  • Solution: To ensure a long service life and maintain precision guidance, the telescoping tubes should smeared daily with genuine WIRTGEN GROUP high-performance silicone grease and contact with sharp objects should be avoided.
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TELESOPING TUBES – ADHERING RESIDUES
  • Condition: The guide system is inadequately coated with grease and becomes prone to the adherence of asphalt residues.
  • Cause and effect: Asphalt may come into contact with the guide tubes when retracting and extending the extension units with a high head of mix. If the telescoping tubes are not adequately coated with silicone grease, the asphalt will adhere to the bare metal. If constant width changes are then made, lasting damage is caused to the guide tape and increases play in the concentric tubes.
  • Solution: Regular lubrication of the telescoping tubes and internal guide tubes with a coat of silicone grease.
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