Cold Planer

Overview

A cold planer, also called a cold milling machine or road milling machine, removes a controlled layer of worn asphalt or concrete from a road so a fresh surface can be laid. The work is "cold" because no heat is applied: a rotating drum studded with carbide cutting tools grinds the pavement at ambient temperature, and the broken material is carried away by conveyor. A half-lane machine of this class mills a 2,000 mm wide cut up to 330 mm deep in one pass while loading the milled material directly into a haul truck driving ahead of it.

The machine is built around a welded Machine Frame that carries a diesel Diesel Engine, the Cutter Drum Unit, a four-post Leg Column, four crawler Crawler Track tracks, the Conveyor System, and the supporting Hydraulic System and Electrical & Grade Control. A Water Spray System keeps dust down and cools the tools.

How it works

The engine drives the cutter drum through a mechanical path: a wet Drum Clutch engages the driveline, a set of Drive Belt poly-V belts transmits torque, and a planetary Drum Drive Gearbox gives the final reduction to roughly 100 rpm. As the machine creeps forward at up to 35 m/min, the drum rotates up-cut against the direction of travel so the tools bite into the pavement and throw the broken material upward and rearward.

Cutting depth is not set at the drum. The whole machine rides on four Leg Column posts, and each post contains a Lift Cylinder that raises or lowers that corner of the frame. Extending or retracting the columns moves the fixed drum closer to or further from the road, so the column stroke is what sets the milling depth. A Leg Position Sensor on each post reports its extension so the control system can hold depth and cross-slope automatically.

Milled material is augered toward the machine centerline by Feed Paddle vanes welded inside the Drum Body, then lifted by the Primary Conveyor and handed to the slewing Discharge Conveyor, which loads it into a truck. The discharge conveyor swings about ±60° and lifts on a Conveyor Lift Cylinder so the operator can load trucks on either side.

Cutter drum and tools

The drum is the consumable heart of the machine. Each of the 168 cutting positions has a Pick Holder welded or bolted to the drum tube, and a Cutting Pick drops into it. The pick is a conical bit with a tungsten-carbide tip; it rotates freely in its holder so it wears evenly and self-sharpens. Picks are the most frequently replaced part on the machine, sometimes several sets per shift in hard or abrasive pavement. Because they are quick-change, a worn pick is knocked out and a new one tapped in without removing the holder, and a damaged Holder Base Block can be replaced on its own.

Undercarriage and travel

Four independent crawler tracks give the machine traction and let it steer tightly on a job site. Each Crawler Track runs a steel Track Chain fitted with bolt-on polyurethane Track Pad shoes that protect finished surfaces. A Track Drive Motor drives each track through its own Hydraulic Motor, so travel speed and turning are set hydraulically rather than by a mechanical transmission. A spring-and-grease Track Tensioner keeps chain tension correct as the pads wear.

Materials and construction

The Main Frame Weldment is fabricated from S355 structural steel, while surfaces exposed to the abrasive milled material use harder grades: the Replaceable Wear Liner panels inside the drum housing are Hardox 450 and are bolted in so they can be swapped when worn. The Piston Rod in each lift cylinder is chrome-plated for corrosion and scoring resistance, and the holder blocks are case-hardened steel. The water tank is molded polyethylene to resist rust from the gritty slurry that the Spray Nozzle array produces.

Grade and slope control

Automatic leveling is what makes the finished cut usable for repaving. A Grade Control Unit reads a Sonic Grade Sensor tracking a reference surface such as a curb, stringline, or the untouched lane, and a Slope Sensor measuring cross-slope. The unit compares the measured depth and slope against the operator's target and commands the lift cylinders through the Valve Block to hold the set grade as the machine moves. The Machine ECU coordinates engine load, drum speed, and travel so the cut stays even when the pavement hardness changes.

Variants and use

Cold planers range from small one-meter machines used for utility patches and lane edges up to large four-track half-lane machines like this one used for full road rehabilitation and airport runways. Narrow drums are fitted for milling around manholes and trenches, while fine-milling drums with close pick spacing leave a smooth texture for thin overlays. The same chassis is commonly offered with the Cutter Drum Unit sized for several widths, since the drum and its housing are designed to be exchanged for different jobs.