SBS modified asphalt’s pavement performance largely depends on complete swelling and uniform crosslinking reaction between SBS modifier and base asphalt. Traditional manual semi-automatic production lines suffer from unstable temperature control, inconsistent swelling duration, uneven material circulation and manual parameter deviation, resulting in fluctuating penetration, ductility and softening point of finished asphalt. The full-automatic PLC intelligent modified asphalt production line realizes closed-loop automatic control of feeding, heating, shearing, swelling and maturation through central PLC system. This paper introduces the overall intelligent layout of the production line, constant temperature tank structure design, and systematic optimization strategies for swelling and maturation technological parameters to stabilize modified asphalt quality and lower comprehensive energy consumption.

1. Defects of Conventional Semi-Automatic Swelling & Maturation Process

1.1 Temperature fluctuation interference Manual adjustment of heat conduction oil heating leads to large temperature swing in mixing and maturation tanks. Excessively high temperature triggers SBS thermal degradation, while low temperature slows down polymer swelling, leaving undissolved rubber agglomerates.

1.2 Uncontrolled swelling holding time Relying on manual timing to transfer materials, some batches stay insufficiently swollen and others over-swollen, causing inconsistent elastic network formation of SBS.

1.3 Dead zones in tank without circulating stirring Single-point stirring cannot eliminate material static sedimentation at tank bottom; SBS particles sink and agglomerate, resulting in uneven dispersion before shearing.

1.4 Discontinuous data recording No automatic data storage of temperature, flow and holding time, unable to trace production batches for quality inspection of highway engineering.

1.5 Unmatched linkage of shearing and maturation Manual coordination between colloid mill circulation and maturation tank feeding easily causes material backlog or empty tank, reducing continuous production efficiency.

2. Overall Structure & PLC Intelligent Control Framework of Full-Automatic Production Line

The complete line consists of base asphalt feeding unit, automatic modifier dosing system, pre-swelling mixing tank group, high-shear colloid mill circulation unit, constant temperature maturation tank bank, heat conduction oil heating system, PLC central control cabinet, online sampling detection module and finished asphalt storage tank. The whole process adopts PLC + touch screen centralized control, with interlock protection of all equipment links.

2.1 PLC Central Intelligent Control System Core Functions

1) One-click recipe calling: Store multiple sets of parameter formulas for 4%–6% SBS modified asphalt, rubber powder modified asphalt and high-viscosity modified asphalt; switch formulas automatically without manual resetting.

2) Multi-point temperature closed-loop interlock: Temperature sensors installed in mixing tank, colloid mill jacket and maturation tank transmit real-time data to PLC, automatically adjusting heat conduction oil burner power and circulating pump frequency to stabilize temperature within set range.

3) Automatic timing & material transfer interlock: PLC records swelling holding time, automatically starts circulation pump and colloid mill after reaching preset swelling duration; after multi-cycle shearing is completed, materials are automatically pumped into maturation tanks.

4) Alarm linkage protection: High temperature, low liquid level, motor overload and pipeline blockage trigger sound-light alarm, and automatically stop related equipment to avoid safety accidents and material waste.

5) Full-process data recording & export: Automatically store temperature, holding time, flow and equipment operation data for each batch, support USB export to meet engineering quality filing requirements.

2.2 Constant Temperature Tank Group Structural Design for Swelling & Maturation

2.2.1 Double-layer heat conduction oil thermal insulation tank body

Tank wall adopts inner stainless steel asphalt storage layer, middle heat conduction oil circulation jacket and outer multi-layer silicate thermal insulation cotton. Uniform heat conduction oil coil layout eliminates local cold areas at tank bottom and side walls, realizing whole-tank constant temperature field without temperature difference dead zone.

2.2.2 Multi-layer spiral stirring system

Each tank is equipped with vertical variable-frequency double-layer spiral agitator. Low-speed stirring during swelling stage prevents SBS sedimentation; medium-speed circulation during maturation promotes full crosslinking between polymer and asphalt molecules. Agitator frequency interlocks with PLC temperature program to adjust rotation speed automatically according to material viscosity.

2.2.3 Circulation external mixing pipeline auxiliary homogenization

External circulating pump connects the top and bottom of the tank to form external large circulation. Static asphalt at tank bottom is continuously pumped to the upper layer to eliminate material stratification, ensuring consistent swelling degree of all materials in the tank.

2.2.4 Liquid level real-time monitoring module

High and low liquid level transmitters feed back signals to PLC, automatically stop feeding when tank is full and send feeding reminder when liquid level is low, avoiding dry burning of heating coil or material overflow.

3. Constant Temperature Swelling Process Optimization Scheme

Swelling is the pre-treatment before high-shear crushing, which determines the difficulty of SBS dispersion. Optimized PLC automatic segmented swelling process is divided into heating stage, constant temperature holding stage and homogenization circulation stage.

3.1 Temperature parameter matching standard

Base asphalt preheating temperature: 165℃ ~ 172℃; swelling constant temperature set value: 170℃ ~ 178℃; temperature fluctuation controlled within ±2℃ by PLC closed-loop adjustment. Temperature lower than 165℃ increases asphalt viscosity and hinders asphalt infiltration into SBS particles; temperature over 180℃ initiates early thermal aging of SBS.

3.2 Automatic dosing & preliminary mixing control

PLC controls screw conveyor to quantitatively deliver SBS modifier and stabilizer according to formula proportion. After feeding is completed, the agitator runs at medium speed for 5–10 min to realize primary mixing of asphalt and rubber particles before entering constant temperature swelling.

3.3 Swelling holding time intelligent control

Conventional 5% SBS formula: constant temperature swelling holding time 25–35 min; high doping 6% SBS: extend to 40–50 min. PLC starts timing automatically after temperature reaches standard value; timing cannot be ended in advance to prevent incomplete swelling. During holding period, low-speed stirring + external circulation runs continuously to avoid SBS agglomeration and sedimentation.

3.4 Interlock transfer to shearing procedure

When swelling timing is finished, PLC automatically starts the delivery pump to send materials to the colloid mill circulation loop, and simultaneously adjusts the heating power of the mixing tank to prepare for the next batch of feeding, realizing uninterrupted continuous production.

4. Constant Temperature Maturation Crosslinking Process Optimization Strategy

After high-shear crushing, SBS micro-particles are evenly distributed in asphalt. Constant temperature maturation promotes full swelling and crosslinking between polymer and asphalt to form stable three-dimensional elastic network, which is the key procedure to determine finished asphalt road performance.

4.1 Maturation constant temperature setting optimization

Optimal maturation temperature range: 172℃ ~ 180℃. Too low temperature slows molecular movement and crosslinking reaction; temperature above 185℃ causes chain scission of SBS polymer, sharply reducing ductility and low-temperature crack resistance. PLC monitors maturation tank temperature in real time and adjusts heat conduction oil flow to maintain stable temperature field.

4.2 Segmented stirring speed control

Early maturation stage (0–30 min): Medium speed circulation stirring to accelerate uniform mixing of micro SBS particles; Late maturation stage (30–60 min): Low-speed soft stirring to avoid shear damage to formed elastic network; All speed switching actions are automatically executed by PLC timing program without manual operation.

4.3 Maturation holding time grading matching

1) Conventional highway SBS modified asphalt: constant temperature maturation 40–60 min; 2) High-grade bridge deck, ultra-thin wearing course modified asphalt: extend maturation to 70–90 min for sufficient crosslinking; 3) Rubber powder modified asphalt: long-term maturation 120–180 min to complete chemical interaction between rubber powder and asphalt.

4.4 Online quality linkage detection

Online sampling valve at maturation tank outlet collects samples regularly; detection data of penetration and softening point are fed back to PLC. If indexes are unqualified, the system automatically extends maturation holding time and starts auxiliary circulation stirring until performance meets standard before outputting finished asphalt.

4.5 Finished material automatic transfer storage

After maturation is completed, PLC automatically opens the delivery valve to pump qualified modified asphalt into thermal insulation finished product tank, and keeps the finished tank at 160℃ ~ 170℃ for heat preservation standby, avoiding secondary cooling and re-heating energy loss.

5. Common Process Defects & PLC Intelligent Optimization Countermeasures

5.1 Residual SBS rubber particles in finished asphalt: Swelling holding time insufficient, temperature fluctuation large; adjust PLC timing program to extend swelling duration, optimize temperature closed-loop PID parameters to reduce temperature difference.

5.2 Modified asphalt ductility fails to reach standard: Maturation temperature too high or holding time too short; lower maturation set temperature, prolong automatic crosslinking timing.

5.3 Large performance difference between front and rear batches: Manual unstable feeding and stirring speed; enable automatic dosing and PLC variable-frequency stirring linkage program to standardize full-process parameters.

5.4 Excessive fuel consumption of heating system: Long-term high-power heating without segmented control; PLC sets segmented heating power curve, reduce power after reaching constant temperature to save energy.

5.5 Material sedimentation at tank bottom after long-time static maturation: No automatic external circulation; activate PLC timing circulation program to start circulating pump every 10 minutes for homogenization.

6. Production Line Intelligent Operation Acceptance Standard

1. Temperature control precision: Swelling and maturation tank temperature fluctuation ≤±2℃ under continuous 24h operation; 2. Timing control error: Automatic swelling/maturation timing error ≤±1min; 3. Batch quality consistency: Penetration, softening point deviation of continuous 5 batches ≤±2.5%; 4. Interlock response speed: Over-temperature, overload alarm and equipment shutdown action completed within 3s; 5. Data storage function: Automatically store production data for more than 1 year, complete batch traceability.

Conclusion

The full-automatic PLC intelligent modified asphalt production line realizes unmanned closed-loop control of the whole production flow through multi-point temperature sensing, timing interlock and frequency conversion linkage. The double-layer constant temperature thermal insulation tank with internal and external circulating stirring eliminates temperature dead zone and material stratification. By optimizing segmented constant temperature, automatic timing and graded stirring parameters of swelling and maturation procedures, the production line ensures full infiltration of SBS in swelling stage and sufficient polymer crosslinking in maturation stage. This intelligent process optimization effectively stabilizes the high and low temperature performance of modified asphalt, reduces manual operation errors and fuel energy consumption, and meets the large-scale standardized production demands of high-grade pavement engineering.