Tracked Asphalt Paver

Overview

A tracked asphalt paver lays a uniform, pre-compacted mat of hot-mix asphalt across a roadway in a single continuous pass. Dump trucks deliver mix into the Receiving Hopper at the front, the machine meters that material rearward and outward, and a heated screed strikes it off to the target thickness and profile. The crawler configuration, built around the Crawler Tractor Unit, gives the high traction and stable footing needed on soft sub-base and thick lifts, which is why tracked machines dominate highway and airfield work over wheeled pavers.

The machine is organized as a tractor that supplies power and motion, a material chain that moves mix from the hopper to the road, and a floating screed that does the actual forming. Mat quality depends on keeping material flow, machine speed, and screed temperature constant, so most of the control electronics exist to hold those three variables steady while the operator concentrates on line and grade.

Crawler tractor unit

The Crawler Tractor Unit carries the Diesel Engine, a turbocharged four-cylinder diesel rated between 120 and 160 kW and certified to Stage V / Tier 4 Final through a DOC/DPF/SCR Aftertreatment stack of diesel oxidation catalyst, particulate filter, and SCR. The engine drives a tandem of hydrostatic pumps for propulsion and a separate pump for work functions, so the tracks and the material system can be commanded independently.

Each Crawler Track is a steel chain fitted with bolt-on rubber Track Pad segments so the machine can pave over finished surfaces without marking them. The chain runs over a Drive Sprocket, a front Front Idler Wheel, and seven Track Roller units per side, each sealed on a Ball Bearing pair with an Oil Seal to keep asphalt grit out. A grease-charged Grease Track Tensioner holds chain tension. Power reaches the chain through a Track Final Drive, a two-stage planetary reduction driven by a Hydrostatic Track Motor running in Final Drive Gear Oil. The Cooling Package mounts the Radiator, a charge-air cooler, and a Hydraulic Oil Cooler under a single hydraulically driven fan, since hydraulic oil temperature rises quickly under continuous paving load.

Material feed system

Mix dumped into the Receiving Hopper falls onto two independent Slat (Drag) Conveyor chains running along the machine floor. Each drag conveyor uses a heat-treated Conveyor Drag Chain carrying slat bars over a Conveyor Floor Wear Plate of Hardox wear plate, driven by a Conveyor Hydraulic Motor. The conveyors discharge mix into the auger chamber ahead of the screed, where two Spreading Auger assemblies spread it across the full paving width. Each auger is built from bolt-on Auger Flight Segment segments so worn flights can be replaced without removing the shaft, and the outboard end rides on a sealed Auger Outboard Bearing.

A Material Feed Sensor at each auger end measures the depth of material against the screed and modulates conveyor and auger speed so the head of mix stays roughly half the auger diameter. A steady head is what prevents segregation and density variation, so this loop runs continuously. A pair of Material Flow Gate plates set the coarse material split between left and right.

Heated vibrating screed

The Heated Vibrating Screed floats on the asphalt behind the tractor, towed from two pivoting Screed Tow Arm beams. Because it floats, the screed seeks its own level and averages out small variations in the underlying surface, which is the core principle of a free-floating screed. The Main Screed Body body carries a replaceable Screed Plate of boron wear steel; two hydraulic Hydraulic Screed Extension units slide out on Linear Guide Rail rails to widen the mat without stopping.

Compaction comes from two devices. A Tamper Bar Assembly driven by an eccentric shaft pre-compacts the mix just ahead of the plate, and a Screed Vibrator Assembly shakes the plate itself to finish density. Both are hydraulically driven and run on Ball Bearing sets. The plate must be hot before paving starts, so the Main Screed Heating Bank bank packs electric Heating Element rods into the plate, regulated by a Screed Thermostat and fed from an engine-driven Screed Heating Generator; the extensions carry their own Extension Heating Bank elements. A Screed Crown Adjuster using a Ball Screw and Servo Motor sets the transverse crown of the mat.

Grade and slope control

Mat thickness and cross-slope are held automatically by the Grade & Slope Control system rather than by operator feel. A Grade Reference Sensor tracks a reference, a stringline, a curb, or the existing surface, using an ultrasonic Ultrasonic Transducer array, while a Cross-Slope Sensor reads cross-slope from a MEMS Inclinometer (MEMS). The Grade Control Module compares these against the target and drives the Screed Leveling Cylinder units at the screed tow points up or down. Raising or lowering the tow point changes the screed angle of attack, and the floating screed responds by laying a thicker or thinner mat a few metres later. The feedback is deliberately slow so the system does not chase short bumps.

Hydraulics, station, and electrics

The Hydraulic System splits into a closed hydrostatic loop for the tracks, fed by two Variable Displacement Drive Pump units, and an open load-sensing circuit for conveyors, augers, screed functions, and cylinders, fed by the Work Function Pump through a Control Valve Block of Proportional Solenoid Valve solenoid valves. Oil is held in the Hydraulic Reservoir and cleaned by a Hydraulic Filter pair. The Operator Station slides side to side on a Sliding Operator Platform so the operator can sit at the mat edge, with a Control Console and Operator Display Terminal on each side. The 24 V Electrical System runs on CAN bus from the Machine Control ECU, distributes power through the Power Distribution Box box, and charges the batteries from the Alternator.

Materials and variants

Wear governs material choice across the feed path. Hopper liners, conveyor floor plates, and auger flights see abrasive hot mix and use Hardox and abrasion-resistant cast steel; the Screed Plate uses boron wear steel that is bolt-replaceable. Structural frames are S355 steel. Variants are defined mainly by class: highway-class machines in the 19-23 tonne range carry wide screeds for 9 m paving, while smaller city-class tracked pavers trade width and hopper size for tighter manoeuvring. Screed type is the other axis, tamper-and-vibration screeds give higher pre-compaction for thick lifts, while vibration-only screeds suit thin surface courses.