The key components of cold milling

Milling drum assembly

Point-attack cutting tools are fitted on the mechanically driven milling drum in the shape of a helix. They remove the pavement material while the milling drum rotates, granulating it at the same time. Ejectors on the milling drum facilitate transfer of the milled material to the conveyor system. The milling drum is sprayed with water during the milling operation, cooling the cutting tools.

The milling drum works in a fully enclosed drum housing. For certain applications, the side plates and the scraper blade behind the milling drum can, however, be raised via hydraulic cylinders. The only opening in the drum housing is an outlet for transferring the milled material to the conveyor system.

In all front-loading machines, a gradation control beam presses down on the surface to be milled immediately in front of the milling drum. It prevents large slabs from breaking out of the pavement layer.

Levelling system

Milling the pavement material at precisely the required depth is crucial in the removal of pavement layers in road construction. That is the job of the cold milling machines’ levelling system: It ensures that the specified milling depth is maintained.

The levelling system continuously matches the actual milling depth with the pre-selected target values. The actual milling depth is measured by optical or mechanical sensors scanning a reference surface. A slope sensor combined with a height regulator can be used if the milled surface needs to have a particular cross slope. The Wirtgen levelling system can operate with a large variety of different sensors.

Deviations from the target value are compensated by means of proportional control. The automatic system responds quickly and without overshooting.

Material loading system

A material loading system conveys the milled material from the milling drum to the waiting truck. This system comprises one or two loading conveyors, depending on the machine model.

In small milling machines with working widths of up to 1 m, the conveyor is located at the rear of the machine. It can be adjusted in height and slewed to either side, enabling the machine operator to flexibly adapt to job site conditions and to fill trucks or wheel loader buckets right to the top.

All larger milling machines are front loaders and have a two-stage conveyor system. The first conveyor (primary conveyor) accepts the milled material from the milling chamber. The second conveyor (discharge conveyor) transports it to waiting trucks in a continuous operation. The discharge conveyor can be adjusted in height and slewed to either side. The variable belt speed enables the machine operator to change the discharge parabola, and to fill trucks right to the top.