Modified asphalt equipment (mixers, heaters, dosing systems) is prone to operational issues during long-term high-temperature, high-viscosity operation—poor mixing uniformity, temperature fluctuations, and additive blockages are the most frequent, accounting for over 60% of equipment downtime. These issues not only reduce modified asphalt quality (e.g., uneven additive dispersion leading to poor pavement performance) but also increase maintenance costs and delay construction schedules. This article systematically analyzes the root causes of each issue and provides step-by-step troubleshooting solutions, helping operators resolve problems efficiently.

1. Poor Mixing Uniformity: Causes and Troubleshooting

Poor mixing uniformity manifests as additive agglomeration (e.g., SBS lumps), uneven viscosity distribution, or inconsistent performance indicators (e.g., dynamic stability variation > 20%). The core causes lie in inadequate mixing intensity, mismatched additive characteristics, or improper parameter settings.

1.1 Root Causes

Cause Category
Specific Reasons

Insufficient Mixing Intensity
- High-shear mixer blades are worn (edge dullness reduces shear rate < 3,000 s⁻¹).

- Agitator speed is too low (e.g., paddle mixer < 50 rpm for rubber powder).

- Mixer capacity is overloaded (batch volume exceeds rated capacity by > 10%).

Additive Mismatch
- Additive particle size is too large (e.g., SBS granules > 3 mm, hard to break).

- Additive moisture content is high (> 0.5%, causing agglomeration during heating).

Parameter Setting Errors
- Mixing time is too short (e.g., SBS mixing < 15 minutes, insufficient dispersion).

- Mixing temperature is too low (e.g., < 160°C for APP, failing to melt pellets).

1.2 Step-by-Step Troubleshooting

Check Mixing Intensity:

Inspect high-shear mixer blades: If blade edges are worn (thickness reduced by > 20%) or chipped, replace them with alloy blades (e.g., WC-Co coated blades, wear-resistant).

Verify agitator speed: Use a tachometer to measure speed—adjust to rated values (e.g., 60–80 rpm for rubber powder mixers, 1,500–2,000 rpm for colloid mills).

Reduce batch volume: If overloaded (mixer fills > 80% of tank volume), decrease each batch by 10–15% to ensure sufficient mixing space.

Address Additive Issues:

Screen additive particle size: Use a sieve (1–2 mm mesh) to remove oversized particles; for SBS, grind granules to < 1 mm before feeding.

Dry high-moisture additives: Use a hot-air dryer (60–80°C) to reduce moisture content to < 0.5% (test with a moisture meter) before dosing.

Optimize Mixing Parameters:

Extend mixing time: For SBS, increase time from 15 to 25–30 minutes; for rubber powder, add 5–10 minutes after pre-soaking.

Raise mixing temperature: Increase by 5–10°C (e.g., from 160°C to 165–170°C for APP) to ensure full additive melting—monitor with a PT100 sensor to avoid overheating (> 190°C, causing asphalt aging).

Verify Uniformity:

After adjustments, take 3–5 samples from different parts of the mixer (top, middle, bottom) and test additive dispersion (use a microscope to check particle size: SBS should be 1–5 μm). If variation is < 10%, the issue is resolved.

2. Temperature Fluctuations: Causes and Troubleshooting

Temperature fluctuations (deviations > ±5°C from the set value, e.g., 170°C → 160°C → 180°C) disrupt additive melting and asphalt viscosity, leading to poor mixing or material degradation. Key causes involve heating system failures, heat loss, or control system errors.

2.1 Root Causes

Heating System Malfunctions: Thermal oil pump failure (low flow rate < 50 L/min), electric heating tube burnout (partial heating loss), or direct fire burner flame instability (fuel pressure fluctuations).

Excessive Heat Loss: Mixer jacket insulation is damaged (e.g., ceramic fiber insulation cracks), or discharge port is not sealed (hot asphalt contacts cold air).

Control System Errors: PID controller parameters are misconfigured (e.g., proportional gain too low, causing slow temperature response), or temperature sensor (PT100) is faulty (readings deviate > ±2°C).

2.2 Step-by-Step Troubleshooting

Inspect Heating System:

Thermal oil heating: Check pump flow rate with a flowmeter—if low, clean the pump filter (remove asphalt deposits) or replace worn pump impellers. For electric heating, use a multimeter to test heating tubes: if resistance is infinite, replace the tube.

Direct fire heating: Check fuel pressure (should be 0.3–0.5 MPa for diesel burners)—adjust the pressure regulator or clean the fuel nozzle (clogged by impurities).

Reduce Heat Loss:

Repair insulation: Replace damaged mixer jacket insulation (use high-temperature ceramic fiber, thickness ≥ 50 mm) and seal joints with high-temperature silicone.

Seal discharge port: Install a heat-resistant rubber gasket (耐温> 200°C) at the discharge valve to prevent cold air ingress.

Calibrate Control System:

Reconfigure PID parameters: Increase proportional gain (e.g., from 5 to 8) to speed up response, or reset to factory defaults (consult equipment manual).

Calibrate temperature sensor: Compare the sensor reading with a standard thermometer (accuracy ±0.5°C)—if deviation > ±2°C, replace the sensor or adjust the controller offset.

Monitor Stability:

After adjustments, record temperature every 5 minutes for 1 hour—if fluctuations are < ±2°C, the system is stable. For long-term operation, install a temperature data logger to track trends.

3. Additive Blockages: Causes and Troubleshooting

Additive blockages occur in dosing systems (hoppers, screws, or feed ports) or mixer inlets, stopping additive supply and causing asphalt quality defects (e.g., insufficient additive content). Common causes include additive moisture, poor flowability, or system design flaws.

3.1 Root Causes

Additive Properties: Powdered additives (e.g., APP powder) absorb moisture and cake (hard lumps > 10 mm), or granular additives (e.g., SBS) stick together due to high temperature (> 40°C in the hopper).

Dosing System Issues: Screw feeder is worn (clearance > 2 mm, causing powder leakage and blockage), or hopper lacks anti-bridging devices (additive accumulates at the outlet).

Mixer Inlet Blockage: Additive is not preheated (cold additive sticks to hot mixer inlet walls) or inlet diameter is too small (mismatched with additive particle size).

3.2 Step-by-Step Troubleshooting

Resolve Additive Caking:

Dry caked powder: Break lumps with a mechanical crusher (for APP powder) and re-dry to moisture < 0.5%. For granular additives, cool the hopper (install a small fan) to keep temperature < 30°C.

Improve flowability: Add a flow aid (e.g., talc powder, 1–2% of additive weight) to powdered additives, or use a vibratory hopper to prevent bridging.

Maintain Dosing System:

Repair screw feeder: Replace worn screw blades (clearance ≤ 1 mm) or install a rubber scraper to clean powder residues. For anti-bridging, add a rotating agitator (speed 10–15 rpm) in the hopper.

Clear blockages: Use a high-pressure air gun (0.4–0.6 MPa) to blow out hopper or screw blockages—avoid using hard tools (e.g., hammers) to prevent system damage.

Optimize Mixer Inlet:

Preheat additives: Install a small electric heater (50–60°C) at the inlet to prevent cold additive sticking.

Enlarge inlet diameter: For additives with particle size > 5 mm (e.g., coarse rubber powder), increase inlet diameter from 50 mm to 80–100 mm to avoid clogging.

Prevent Recurrence:

Install a blockage sensor (e.g., photoelectric sensor) at the feed port—if blocked, the sensor triggers an alarm and pauses the system.

Clean the dosing system daily after operation (use compressed air to blow residues) to avoid long-term accumulation.

4. Preventive Maintenance Tips to Reduce Common Issues

Regular Inspection Schedule:

Daily: Check mixer blades for wear, heating system pressure/flow, and additive hopper for bridging.

Weekly: Calibrate temperature sensors, lubricate agitator bearings (use high-temperature grease, ≥ 200°C), and clean thermal oil filters.

Monthly: Replace worn parts (e.g., heating tubes, screw blades) and inspect insulation for damage.

Operational Standardization:

Follow additive pre-processing requirements (screening, drying) to avoid mismatched materials.

Set mixing parameters per additive type (e.g., 170–180°C, 25–30 minutes for SBS) and avoid overloading.

Training for Operators:

Train operators to recognize early signs (e.g., abnormal mixer noise = blade wear; temperature spikes = heating system failure) and perform basic troubleshooting.

By systematically troubleshooting each issue and implementing preventive maintenance, operators can reduce modified asphalt equipment downtime by 40–50%, ensure consistent product quality, and extend equipment service life by 2–3 years.