Milling & Micro Milling Mike Bussard General Superintendent, P.R.

Milling & Micro Milling Mike Bussard General Superintendent, P.R. Systems, inc.

The Heart Of Cold Milling Machines A cold milling machine's most important tool is the milling drum. Rotating point-attack cutting bits are inserted in toolholders that are fastened onto the drum body. The texture of the milled surface is determined by the bit spacing, which is the distance between one cutting bit to the next.

The Milling Drum: Standard Drum Standard milling drums with a tool spacing of 5/8”. Ideally suited for the removal of individual layers or complete pavement structures. This drum is used 99% of the time Micro Drum Micro fine milling drums with tool spacing's of up to 1/4”. Ideally suited to remove a very thin layer of the surface to restore the pavement s evenness for thin lift overlays. Skid Resistance

Surface Comparison Standard Milled Surface Micro Milled Surface

Standard Drum Pattern 5/8” Bit spacing Can be used for complete removal up to 14” Most common practice in todays mill & fill

Traditional Mill Process

What is Micro Milling? Roughly 3 times the cutting bits of a standard drum Best if used from 0”-2” milling depths Used when surface texture matters the most

Micro Mill Process

Ridge To Valley Depth (RVD) Traditional Drum RVD 5/16” or 8mm deep Micro Drum RVD 3/32”- 1/8” or 3 – 4mm deep

Micro Milling Results Up Close Micro Milled Surface RAP From Micro Milling

Micro Mill Advantages Shallow grooves and small vertical edges allows you to open to traffic Can grind entire job complete before paving Creates a smaller RAP size Bump Repairs Research shows better adhesion for asphalt When applied correctly micro milling can put IRI values in bonus Range

Determining Factors For Surface Texture/Surface Pattern Bit Spacing (From 1/4” to 5/8”) Wrap Configuration Forward Speed RPM Diameter of Drum, (Typically set by manufacturer) Drum Maintenance (Very Important)

Cutter Drum Maintenance Keep from hitting structures!! Do not use to remove boulders (3” or Larger) Don’t Replace used holders with new holders

Maintaining Cutter Drums New Toolholder vs Used Toolholder

Micro Mill With Multi Plex Sensing Multiplex systems are used to measure sustained, stretched-out unevenness and combine multiple sensors on one or both machine sides (e. g. cable, ultrasonic, cylinder sensor). Using the average value of the connected sensors, the current milling depth is calculated with high precision. Longitudinal waves can thus be highly compensated for. The system is especially suited towards fine milling work. With the Multiplex levelling system, sensor signals are calculated to arrive at an average differential value. This enables unevenness to be smoothed out considerably.

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