Solving Material Residue Issues in Aging Wirtgen Milling Machines

[MikePhua]

The Wirtgen Legacy and Its Milling Evolution
Wirtgen GmbH, founded in Germany in 1961, has long been a global leader in road milling and surface rehabilitation equipment. Their cold milling machines revolutionized asphalt removal by introducing precision depth control, integrated conveyors, and modular cutter drums. Models like the Wirtgen 1000, 1200F, and 1900DC were widely adopted in North America and Europe throughout the 1990s and early 2000s, prized for their reliability and adaptability across urban and highway projects.
Despite their durability, aging Wirtgen units often exhibit performance degradation, particularly in material collection and discharge. One recurring issue is the presence of residual milled material—often forming windrows on either side of the cut—despite proper machine alignment and conservative operating speeds.
Terminology Annotation
- Windrow: A linear accumulation of milled material left behind during cutting, typically along the edges of the milling path.
- Moldboard: A curved steel plate behind the cutter drum that helps direct milled material toward the conveyor.
- End gate: The vertical side panel of the milling drum housing, often equipped with skids or skis to control depth and material containment.
- Material collector: A component mounted near the center of the drum to gather loose particles and direct them toward the conveyor.
- Floating mode: A hydraulic setting where the rear of the machine is allowed to move vertically with minimal resistance, relying on its own weight for contact pressure.
Common Causes of Residual Material
Operators of older Wirtgen models have reported consistent material left behind on both sides of the cut, even when milling at slow speeds and reducing pace near the end of each pass. The center of the cut remains clean, but the sides accumulate debris, suggesting a failure in lateral containment and moldboard efficiency.
Key contributing factors include:

• Worn moldboard edges that no longer seal against the pavement
  
• Degraded cutter housing allowing side leakage
  
• Missing or worn material collectors at the drum center
  
• Improper end gate alignment or missing control plates
  
• Excessive machine tilt or rear-end misalignment during operation
  

One technician noted that when the rear of the machine is cocked to one side, even slightly, the cutter housing loses its seal, allowing material to escape laterally. Welding reinforcement plates along the moldboard and door edges restored containment in his case.
Teeth Positioning and Drum Configuration
There’s speculation that tooth angle or positioning may contribute to material loss. While angled teeth can affect cutting efficiency and vibration, they rarely cause windrow formation directly. Instead, the absence of center-mounted material collectors or improper drum configuration is more likely to blame.
Recommendations:

• Inspect drum for missing or worn collector plates
  
• Verify tooth spacing and ensure uniform wear across the drum
  
• Replace any broken or misaligned teeth to maintain cutting balance
  
• Consult OEM schematics to confirm correct drum assembly for the model
  

In Guatemala, an operator found that replacing the center collectors on a 1200F dramatically reduced side windrows, even without changing tooth layout.
Conveyor Speed and Milling Depth
Another overlooked variable is conveyor speed relative to milling depth. When cutting deep sections, the volume of material increases exponentially. If the conveyor is not running at full speed, it may fail to evacuate all material, causing overflow and side discharge.
Checklist:

• Always run conveyor at 100% speed during deep milling
  
• Monitor conveyor belt tension and motor performance
  
• Avoid sudden speed changes mid-pass
  
• Use auxiliary conveyors if available for high-volume cuts
  

In Sweden, a crew operating a 1900DC found that increasing conveyor speed by just 10% eliminated residual buildup during a 6 cm deep milling pass.
Custom Modifications and Retrofit Solutions
For machines with extensive wear, factory parts may no longer suffice. Customizing the moldboard with a solid steel or carbide plate across the bottom edge can improve material control. Additionally, aftermarket end gate extensions or ski-mounted control plates can help contain side discharge.
Fabrication tips:

• Use 3/8" hardened steel for moldboard reinforcement
  
• Weld plates flush with the bottom edge to maintain ground contact
  
• Add bolt-on extensions to end gates for easy replacement
  
• Monitor down pressure settings to avoid excessive wear on new components
  

A retired operator in Nevada retrofitted his 1000 model with a full-width carbide moldboard and reported a 90% reduction in windrow formation.
Conclusion
Material left behind during milling is a multifaceted issue, especially in aging Wirtgen machines. While moldboard wear, conveyor speed, and drum configuration are primary culprits, machine alignment and custom retrofits also play a role. By combining OEM diagnostics with field-tested modifications, operators can restore clean cuts and extend the service life of their equipment. In road rehabilitation, precision isn’t just about depth—it’s about leaving nothing behind.