In highway municipal, airport runway, park pavement and other infrastructure projects, asphalt mixing station is the core key equipment to ensure the stable production of asphalt mixture. The stability of equipment operation and the quality of mixture directly determine the pavement construction effect and road service life.Asphalt mixing plant is a set of integrated, high-precision industrial equipment, by hundreds of accessories, more than ten sets of functional systems coordinated operation, long-term operation in high temperature, dust, high intensity friction under harsh conditions.Most of the equipment failure, production capacity decline, finished materials are not up to standard, environmental protection exceeds the standard and other problems, not the equipment failure, but the core parts wear, maintenance is not in place, improper selection and adaptation, troubleshooting is not timely caused.
In order to help the majority of equipment operation and maintenance personnel, procurement personnel and engineering practitioners fully master the knowledge of asphalt mixing plant accessories, this article systematically combs the mixing plant equipment principle, core accessories function, production process flow, wearing parts loss law, standardized maintenance scheme, common troubleshooting skills and high-quality accessories purchase points, comprehensively covers the whole scene of equipment operation and maintenance, maintenance and procurement, helps reduce equipment failure rate, reduce downtime loss and control operation and maintenance cost. Ensure the efficient and steady progress of the project.
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Asphalt mixing plant is also often called asphalt mixing plant, hot mix asphalt equipment, intermittent asphalt mixing plant, which is the core industrial complete equipment in the field of road infrastructure. Its core function is to produce hot mix asphalt mixture. The finished products are widely used in various pavement projects such as expressway, municipal road, parking lot, airport runway and park pavement.
According to the fixed proportioning process, the whole set of equipment will accurately proportion crushed stone, gravel, sand and other aggregates of different specifications, asphalt binder, mineral powder filler and various modified additives, heat at high temperature and fully mix, finally forming a hot mix asphalt mixture with stable performance.According to the production mode, the industry mainstream is divided into two categories: intermittent and continuous drum; according to the installation form, it can be divided into fixed asphalt mixing stations and mobile asphalt mixing stations.
A complete set of asphalt mixing plant consists of 12 core system accessories, from raw material feeding, heating and screening, metering and mixing, asphalt supply, dust removal and environmental protection to automatic control. Each system accessory performs its own duties and directly determines the quality of the finished mixture. The following subsystems disassemble all key accessories and functions:
Core accessories: 3 - 6 bin multi-cell cold bin, frequency conversion feeder, belt conveyor, bin wall vibrator, roller, cleaner
Core function: Classify and store sand aggregate of different particle sizes, accurately control the discharge flow of various aggregates by frequency conversion feeder, stably convey the belt to the drying process, and control the ratio of coarse and fine aggregates from the source.Silo vibrator prevents aggregate from moisture and blocking, ensures continuous and stable supply, and is the first pass of proportioning accuracy.
Core accessories: rotary drying drum, drum internal lifting plate, fuel oil/gas/pulverized coal burner, support wheel, sealing wear flange, drum liner
Core function: the heat source core of the whole set of equipment, the burner produces high temperature flue gas, the drum continues to rotate, the internal lifting plate will continuously raise the aggregate to form a curtain, maximize contact with hot air flow, thoroughly dry the aggregate moisture and heat to the process standard temperature.Roller seals eliminate air and heat leakage, reduce heat loss and fuel consumption.
Core accessories: bucket elevator, conveyor chain, hopper, drive motor, bearing block, wear-resistant liner
Core function: to accept the high temperature aggregate at the discharge end of the drying cylinder, vertically convey it to the upper screening main building, all accessories are made of high temperature resistant and wear-resistant materials to avoid wear and leakage of high temperature aggregate, and ensure stable transportation of high temperature aggregate. It is a key transfer component connecting drying and screening.
Core accessories: multi-layer vibrating screen, wear-resistant screen, screen tension device, damping spring, vibration exciter
Core function: only batch mixing plant standard, mixed high temperature aggregate according to particle size classification screening, separation of coarse aggregate, medium aggregate, fine aggregate, to ensure that each specification aggregate particle size in line with the mixture design grading.Screen damage, insufficient tension will directly lead to gradation imbalance, road segregation, pit disease.Continuous drum type equipment simplifies or eliminates the screening structure.
Core accessories: thermal insulation bin, level gauge, pneumatic discharge gate, sealing gasket
Core function: Storing screened high temperature aggregate by grade, heat preservation structure of bin body locks aggregate temperature to prevent cooling and caking; material level sensor real-time monitoring of material balance in bin, discharge gate accurately controls discharge amount, and provides material reserve for subsequent accurate weighing.
Core accessories: aggregate weighing hopper, asphalt weighing tank, mineral powder weighing hopper, weighing sensor (weighing module), pneumatic valve, cylinder, sealing baffle
Core function: a complete set of mixing plant precision core components, through high-precision weighing sensors, in strict accordance with the road formula weighing aggregate, asphalt, mineral powder consumption.Weighing error exceeding the standard will cause too high or insufficient asphalt content, resulting in quality problems such as road surface flooding and looseness. It is necessary to calibrate the sensor regularly every day.
Core accessories: double horizontal shaft forced mixing cylinder, mixing arm, wear-resistant mixing blade, alloy lining plate, discharge door, reducer, transmission shaft, shaft end seal
Core function: the core unit of mixture molding, aggregates, hot asphalt, mineral powder all enter the mixing tank, mixing blades high speed stirring mixing, single batch standard mixing time of 45 - 60 seconds, until all the aggregate surface evenly coated asphalt, forming a homogeneous mixture.Mixing blades and lining plates belong to ultra-high loss parts, which will be mixed unevenly and exposed aggregates after wear.
Core accessories: thermal insulation asphalt storage tank, thermal oil heating furnace, asphalt delivery pump, high temperature resistant valve, thermal insulation pipeline, thermocouple temperature probe, sealing gasket
Core function: Store solid asphalt and heat it continuously to 150 - 170 ℃ liquid state, and transport it to mixing tank quantitatively through insulation pipeline and metering pump.Full temperature control system real-time monitoring, avoid asphalt temperature too high aging smoke, temperature too low insufficient fluidity can not evenly coat aggregate, pump body seals, pipeline gasket easy to heat aging leakage.
Core accessories: mineral powder storage bin, screw conveyor auger, mineral powder weighing hopper, discharge valve
Core function: Limestone ore powder storage, recovery dust fine powder, screw auger quantitative transport to the metering system.Mineral powder can fill the voids of aggregate, improve the compactness, cohesion and pavement stability of mixture, and is the key auxiliary material to optimize pavement strength.
Core accessories: primary cyclone dust collector, bag dust collector, high temperature dust filter bag, bag cage, pulse injection valve, dust discharge fan, induced draft fan, dust pipe wear elbow
Core functions: processing dust generated in the whole process of drying, screening and mixing, capturing ultrafine particles, recycling available mineral powder for secondary use, and controlling exhaust dust emissions to meet environmental emission standards.Blocked and damaged filter bags will cause excessive dust in the factory area, poor ventilation of the main engine, and reduced production capacity.
Core accessories: insulation finished goods bin, discharge gate, conveyor chute, wear-resistant liner
Core function: temporary storage of mixed high temperature asphalt mixture, silo insulation structure to delay the mixture cooling, prevent the separation of aggregates and asphalt, unloading and loading as required, adapt to multiple vehicles continuous discharge construction.
Core accessories: PLC control cabinet, temperature sensor, pressure transmitter, level switch, variable frequency driver, operating software, signal line
Core functions: mixing plant brain, centralized monitoring of the whole process temperature, weight, conveying speed, mixing cycle, support for storage of dozens of sets of pavement formula, automatic one-button production, automatic recording of production data, convenient quality traceability, various sensor failures will cause equipment false alarm, out of control ratio.
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Loader loading → multi-bin cold bin → belt conveyor (optional pre-impurity screen) → drying drum + burner (flue gas discharged into dust removal system) → hot aggregate bucket elevator → multi-layer vibrating screen classification → thermal insulation hot bin storage → pneumatic gate unloading to aggregate weighing system
Two auxiliary lines are simultaneously matched:
Asphalt auxiliary line: thermal insulation asphalt tank → thermal oil heating system → asphalt conveying pump → asphalt weighing tank
Mineral powder auxiliary line: mineral powder bin → screw conveyor → mineral powder weighing hopper
After all raw materials are weighed, they are simultaneously sent into the double-horizontal shaft mixing tank for forced mixing for 45 - 60 seconds → finished product insulation bin temporary storage → automatic unloading and loading to the construction site
Parallel supporting dust removal process: drying cylinder exhaust gas → primary cyclone dust removal → bag filter → clean air discharge, collected dust is re-mixed into the mineral powder system for recycling
The whole PLC control cabinet controls the temperature, weight and operation sequence of all processes.
Cold bin batching conveying → integrated drying mixing drum (asphalt, mineral powder directly injected into the drum synchronous mixing) → finished material elevator → insulation bin → loading
No independent hot bin, vibration screening equipment, short process, continuous and stable production capacity.
Asphalt mixing plant long-term operation at high temperature above 140 ℃, sand continuous friction impact, asphalt corrosion conditions, a large number of accessories continue to withstand wear, high temperature oxidation, material impact, known as wearing parts.
Drying drum system wearing parts
comprises a roller lifting plate, a cylinder inner lining plate, a discharging lifting sheet, a supporting wheel and a roller sealing flange.
Wear reasons: high temperature aggregate continuous rolling to form strong friction, long-term high temperature thermal deformation, smoke corrosion; lifting plate deformation can not form a complete curtain, drying efficiency greatly reduced.
Wear-resistant materials: high chromium alloy, Alloy-K wear-resistant steel, tungsten carbide spray parts, service life of 12 - 60 months.
Mixing cylinder core wear parts
Stirring blade, stirring arm, blade wear head, cylinder lining wear plate, shaft end seal sleeve
Reasons for wear: continuous friction of sand and gravel at high speed stirring, sharp impact of aggregates, asphalt bonding intensifies material grinding, which is the fastest part of the whole equipment.
Wear-resistant material: 12%-26% high chromium cast iron, tungsten carbide welding head, hardness HRC 55 - 62; industry recommendations to prepare 2 - 3 sets of spare parts.
Conveying and lifting equipment wearing parts
Belt conveyor belt, conveyor chain, chain wheel, hopper, chute wear liner, roller roller
Wear reasons: sand continuous friction, material falling impact, chain long-term high temperature tensile deformation.
Service life reference: conveyor chain 12 - 18 months, sprocket wear faster than chain.
Vibration screening system wearing parts
Wear screen, screen tension strip, shock absorbing spring
Wear reasons: high temperature aggregate continuous impact, friction, screen long-term high-frequency vibration broken wire, holes, direct damage to aggregate grading.
Bag dust removal system wear parts
High temperature dust filter bag, bag cage, pulse solenoid valve, discharge fan, dust elbow liner
Causes of wear: erosion and wear of ultrafine dust, aging of high-temperature flue gas, repeated impact of pulsed air flow; blockage of filter bags will cause abnormal negative pressure in the host and reduce production capacity.
Special materials: Nomex aramid, PPS high temperature resistant filter, PTFE coated filter bag, can withstand high temperature above 180 ℃ for a long time.
asphalt pipeline system wear parts
Asphalt pump mechanical seal, high temperature valve, sealing gasket, heat transfer oil pipeline sealing ring
Wear reasons: high temperature liquid asphalt corrosion, impurity erosion, seal long-term high temperature aging leakage.
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Standard parts maintenance can extend the service life of wear-resistant parts by 30%-200%, reduce fuel and spare parts procurement costs, reduce unplanned downtime, maintenance work is divided into daily inspection, weekly inspection, monthly inspection, seasonal overhaul four-level standard, all maintenance operations must implement equipment power off locking safety specifications.
General Maintenance Basics Guidelines
Establish standardized maintenance accounts, record parts wear thickness, operating temperature, pressure difference, maintenance and replacement records, and predict wear cycle through data;
All high temperature running parts must use the original equipment high temperature resistant grease, the reducer regularly replace the special gear oil;
Keep the equipment clean, and clean up aggregate agglomeration, asphalt aggregate and dust accumulation in time. Aggregate accumulation will aggravate the wear of accessories and cause unbalanced operation of equipment;
Core wearing parts are stocked in advance, and high wear-resistant upgraded materials are preferred to replace ordinary carbon steel parts;
Pre-job training for operators, and immediately stop the machine for inspection if abnormal noise, vibration, or abnormal mixture are found.
Special maintenance rules for accessories of each system
Maintenance of drying drum and burner
Daily: Check whether there is cracking in the cylinder body, material accumulation at the inlet is blocked, observe whether the combustion flame is stable, and whether there is abnormal noise and abnormal vibration;
Weekly/monthly: after shutdown and cooling, open the access port, detect whether the lifting plate is bent and worn, measure the thickness of the steel plate of the cylinder body; regularly correct the position of the supporting wheel, and add bearing grease;
Annual overhaul: professional personnel adjust the air-fuel ratio of the burner, clean the carbon deposit of the nozzle, replace the aging seal; the material lifting plate is worn more than 30% and replaced immediately, so as to avoid the decrease of drying efficiency and increase fuel consumption.
Maintenance of double horizontal shaft mixing cylinder
Before daily operation: listen to the operation noise of mixing cylinder. If abnormal noise and vibration are too large, check blade wear and bearing overheating (temperature> 70 ℃ is fault warning); observe the coating state of mixture during discharging, and bare aggregate represents severe blade wear;
Monthly: disassemble and measure the residual thickness of blades and lining plates, replace them in sets if the wear thickness exceeds 10mm; fill high temperature grease into the bearings of stirring shaft every 500 hours, and check whether there is asphalt leakage in the shaft end seal;
Maintenance points: replace the blades in a complete set to avoid uneven stress and unilateral rapid wear caused by mixing the old and new.
Maintenance of conveyor and bucket elevator
Daily: check belt deviation, tear, material leakage, clean up the transfer of accumulated material;
Weekly: check the chain, sprocket wear, adjust the belt, chain tension, roller stuck timely cleaning lubrication;
Replace chain elongation and sprocket tooth surface wear immediately to prevent chain breakage and shutdown.
Vibrating screen maintenance
Daily visual inspection screen for holes, loose;
Calibrate the tension of screen every week (standard tension 18 - 22 N/mm ²), clean the sticky material on the screen surface to prevent plugging;
Replace the screen as soon as possible if there are broken wires or holes to avoid disorder of aggregate grading.
Maintenance of bag dust removal system
Daily monitoring dust inlet and outlet pressure difference, normal pressure difference 3 - 4 inches of water column, pressure difference suddenly rose on behalf of filter bag blockage; check whether there is dust leakage chimney;
Check pulse injection valve and compressed air pressure (standard 80 - 100 psi) every week, clean pipe ash;
Regularly replace damaged filter bags, do a good job of warehouse insulation, prevent flue gas condensation paste bag; dust recovery screw conveyor regular lubrication, avoid blocking materials.
Maintenance of asphalt supply system
Normalized inspection pipeline, pump body for asphalt leakage, monitor the temperature of heat transfer oil;
Rinse the storage tank and pipeline before long-term shutdown to prevent asphalt precipitation and agglomeration; replace the aged sealing gasket and pump body oil seal regularly to eliminate the hidden danger of high temperature asphalt leakage and fire.
Calibrate weighing sensor, temperature probe and level meter every month; clean dust on sensor surface and check loose circuit joints; control cabinet shall be dust-proof and moisture-proof, and dust inside shall be cleaned regularly to avoid signal disorder.
Maintenance Cycle Execution Checklist
Daily maintenance: appearance inspection, accumulated material cleaning, temperature and pressure data recording, combustion condition inspection;
Weekly maintenance: wear parts appearance inspection, transmission parts lubrication, screen tension adjustment, dust injection system testing;
Monthly maintenance: wear parts thickness measurement, bearing condition detection, equipment alignment calibration, valve cylinder maintenance;
Seasonal shutdown overhaul: complete inspection of drum, replacement of worn parts, replacement of gear oil, deep adjustment of burner, inventory of spare parts.
Practical tips for extending the service life of accessories
When the wear threshold is reached, replace the wearing parts in advance to avoid scratching the main engine cylinder body and stirring cylinder shell after the accessories are completely damaged;
High productivity, high hardness stone working conditions, upgrade high chromium, tungsten carbide wear parts, service life increased by 2 - 3 times;
After the production, the asphalt caking inside the equipment shall be cleaned up in time, and the accumulated material will greatly aggravate the friction loss;
Operators feed back mixture appearance, abnormal noise of equipment and abnormal temperature in real time, so as to handle faults early.
Cold aggregate batching system failure
Fault 1: intermittent blanking, unstable flow
Cause: aggregate blocking bin, feeder calibration deviation, belt tension is insufficient slip;
Maintenance: open bin wall vibrator to dredge aggregate, calibrate feeder flow again, adjust belt tension, clean stuck idler.
Drying drum system failure
Fault 1: low mixture discharge temperature, fuel consumption surge
Cause: material lifting plate wear missing, drum seal air leakage into the cold air, aggregate moisture content exceeds the standard, abnormal burner operating conditions;
Maintenance: shut down and replace deformed lifting plate, replace aging sealing flange, detect moisture content of raw materials, adjust drying time synchronously, adjust burner. Combustion machine system failure
Fault 1: ignition failure, frequent flame extinction
Causes: nozzle clogging, ignition electrode carbon deposition, flame sensor failure, fuel filter clogging;
Maintenance: disassemble and clean nozzle, polish electrode carbon deposit, replace damaged sensor, replace fuel filter element.
Fault 2: incomplete combustion, black smoke
Causes: imbalance of air-fuel ratio, excessive fuel impurities;
Maintenance: Professional personnel readjust air volume and oil pressure and replace qualified fuel.
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Shaker system failure
Fault: aggregate classification disorder, coarse and fine material mixture into the hot bin
Cause: screen breakage, screen tension is insufficient, screen surface blocking;
Maintenance: replace damaged screen, calibrate tension, clean up sticky material on screen surface.
Failure of mixing system of mixing tank
Fault 1: uneven asphalt coating, mixture white segregation
Cause: mixing blade, liner serious wear, single mixing time is insufficient, measurement system error;
Overhaul: measure wear part thickness, replace set, modify mixing cycle of control system, calibrate load cell.
Measurement and weighing system failure
Fault: asphalt content fluctuates, mixture quality is unstable
Causes: drift of the load cell, incomplete discharge of stuck materials at the hopper gate, poor line contact;
Maintenance: Regularly calibrate the weighing module, clean up the accumulated materials on the inner wall of the hopper, and tighten the sensor terminals.
Fault 1: asphalt pumping is not smooth, discharge is more and less
Cause: pipeline temperature is too low asphalt viscosity, pump seal damage, valve blockage;
Maintenance: Increase the temperature of heat transfer oil, replace pump body seals, and disassemble flushing pipeline valves.
Bag dust removal system fault
Fault 1: chimney visible dust emission, environmental protection exceeds standard
Cause: dust filter bag damage, bag cage rust, warehouse air leakage;
Maintenance: fluorescent powder leak detection positioning damaged filter bag, replacement of the whole set, sealing air duct leakage point.
Automatic control system failure
Fault: automatic shutdown of equipment, sensor value jump, frequent alarm
Cause: dust covering sensor, loose circuit, unstable voltage, PLC module aging;
Maintenance: clean all kinds of temperature and pressure sensors, tighten wiring terminals, stabilize power supply voltage, replace faulty electrical components.
The procurement of asphalt mixing plant accessories cannot only compare the unit price. The material, processing precision, adaptability and supplier strength of the accessories directly determine the comprehensive use cost and equipment stability. When purchasing, comprehensive screening shall be carried out from six dimensions to avoid the downtime and secondary damage risks caused by low-cost and inferior accessories.
Priority check accessories material and wear resistance
The working conditions of accessories of different systems vary greatly, so they must match the corresponding high temperature resistance and wear resistance materials. When purchasing, the supplier is required to provide the material test report and hardness test sheet:
Stirring blade, lining plate: 12%-26% high chromium cast iron, hardness HRC55 above, heavy wear conditions selected tungsten carbide surfacing;
Drying material lifting plate: Alloy-K wear-resistant alloy steel, high temperature thermal deformation resistance, impact resistance;
Dust filter bag: Nomex/PPS high temperature filter material is selected for long-term 180 ℃ working condition, PTFE coated anti-sticking filter bag is selected for high viscosity asphalt working condition;
Seals and gaskets: high temperature and oil resistant compound rubber, suitable for asphalt and heat transfer oil corrosion environment;
Screen: high tensile wear-resistant alloy steel wire, tensile strength standards, not easy to break wire.
Strictly match models to ensure size accuracy of accessories
Provide the complete brand, complete machine model, and original parts number of the mixing station before purchase to avoid size deviations of common parts;
For key special-shaped parts such as stirring arm, lifting plate and weighing hopper, ask for processing drawings and size tolerance table; key size tolerance of high-quality parts shall be controlled within ± 0.5mm;
Metering, combustion machine, PLC and other precision components, priority original standard parts, do not use non-standard modified parts.
OEM original parts and high-quality sub-factory wear parts selection scheme
Original OEM parts applicable scenarios: burner, load cell, PLC control system, precision valves, heat transfer oil heating equipment and other core precision parts, original parts matching degree 100%, supporting warranty, the lowest failure rate;
High-end sub-factory wear-resistant parts applicable scenarios: mixing blades, lifting plates, screens, chains, filter bags and other pure wear parts; regular sub-factory can upgrade wear-resistant materials, service life far exceeds the original standard parts, procurement cost is lower, supply cycle is short;
The best procurement strategy: precision core parts choose original, high-frequency wear parts choose professional wear parts manufacturers with material testing qualifications.
Supplier Qualification and Service Capability Screening Criteria
Qualified accessory suppliers must meet the following conditions:
1Deep ploughing asphalt mixing equipment accessories industry for more than 5 years, with a large number of cooperation cases of the same type of mixing station; With ISO9001 production qualification, export models supporting CE certification;
Material test sheet, hardness test report, wear service life measured data can be provided;
A large number of spare parts in stock, emergency supply cycle is short, equipped with professional technicians to provide installation guidance;
Perfect after-sales warranty policy, spare parts with material defects can be replaced free of charge.
Comprehensive accounting of life cycle costs, not simple price comparison
Low-priced inferior accessories seem to have low procurement costs, but there are multiple hidden losses:
Short wear life, double replacement frequency, and continuous increase in manual replacement costs;
The rapid wear of accessories will scratch the mixing cylinder and drying cylinder, resulting in major maintenance of the host;
Parts failure sudden shutdown, site shutdown losses far exceed parts price difference;
As the core production equipment of road infrastructure, asphalt mixing plant relies on dozens of accessory systems such as cold material supply, drying and heating, screening and metering, forced mixing, asphalt supply, dust removal and environmental protection, automatic control, etc. to work together.All kinds of wear-resistant accessories are in high temperature, sand friction and asphalt corrosion for a long time, which is the core short board for stable operation of equipment.
In order to ensure the stable quality of asphalt mixture, reduce the consumption of fuel oil and spare parts and reduce the shutdown loss, three core tasks need to be done well: first, distinguish the function and loss law of each system accessory, establish the graded maintenance inspection system, and regularly detect the wear degree of wearing parts; second, be familiar with the causes and troubleshooting schemes of various high-incidence faults, so as to achieve rapid maintenance and reduce the shutdown time; Third, procurement accessories to material wear resistance, size adaptation, supplier comprehensive strength as the core, calculate the full life cycle cost, reject low-cost inferior accessories.
