Dry Mix Concrete Plant

This is one of the most common problems on site. When the batching weight departs from the set value beyond the allowable range, generally ±2% for aggregates and ±1% for powder, the concrete mix ratio and quality will be directly affected. On real job sites, this problem usually comes from three things, sensors blocked by materials or damaged, hoppers of batching machines out of shape, and electrical circuits in poor contact. This is not a serious breakdown in most cases, but it must be handled at once. If not fixed in time, this can stop production for 2–4 hours and waste a large amount of raw materials.

Solution: Shut down the machine and clean the residual materials on the sensors, check whether the sensors are loose, and replace them with spare ones temporarily if they are broken. We can correct the slightly deformed hopper temporarily, but we have to stop the machine to repair or replace the seriously deformed one to keep it level. For loose circuits, just plug the interfaces again to make them firm, then recalibrate the batching machine, and we can use it again when the error is within the allowable range.

Uneven mixing leads to insufficient concrete strength, and we can see cement clumps and uneven aggregate distribution in the dry mixture. From our practical experience, this problem is mostly caused by worn mixing blades, unreasonable mixing time setting, or wrong formula logic in the automatic control system.
Solution: Shut down the machine and check the mixing blades. Replace them in time if there are mixing dead corners or obvious efficiency drop. We check and replace the blades every 6 to 8 months as a routine. For forced-action mixers, the mixing time is usually set at 30 to 90 seconds according to the equipment manual to ensure even mixing of dry materials. We also need to check the formula logic in the control system to avoid uneven mixing caused by wrong feeding sequence.

Belt conveyors are the most prone to problems, such as belt deviation, material jamming, or even failure to start. Common reasons include loose belts, materials accumulated on rollers, damaged or stuck idlers, and motor failures. If we hear abnormal noise, see serious belt variation or belt slipping, we must shut down the machine immediately to check to avoid making the fault worse.

Solution: Adjust the roller position and tighten the belt if it departs, getting into the habit of checking belt tension every 3 months. Clean up the materials on rollers if there is accumulation to prevent jamming. If the motor cannot start, check the circuit and power supply to eliminate short circuits. If the motor is overloaded, we have to find out the cause like material jamming or bearing problems before restarting, otherwise the motor will be burned out.

Cement silo blockage is mainly caused by damp and agglomerated cement, especially in rainy construction. The screw conveyor cannot convey cement or the conveying capacity drops significantly. This issue is especially common in rainy regions like Southeast Asia, southern China and coastal areas. The real reasons are poor sealing of the cement silo and damp cement caused by feeding in rainy days.

Solution: Close the feeding port of the cement silo first to stop more damp cement from entering, then use the air cannon to break up the agglomerated cement inside the silo. If the blockage is serious, open the bottom access door to clean it manually. After cleaning, check the sealing parts and replace the damaged gaskets to prevent moisture from entering again. Damp cement must be tested qualified before use, otherwise it will affect the structural quality.
In rainy seasons, turn on the silo top dehumidifier or keep ventilation, and check the silo sealing regularly to reduce the risk of blockage.

Clean the mixer, conveyor and storage bins thoroughly before leaving work every day to prevent material clumping from affecting the next use. Residual dry materials in storage bins and mixers will harden over time, causing equipment blockage and 2 to 4 hours of shutdown.

Check rotating parts such as bearings and gears to ensure sufficient lubrication, and replenish lubricating oil in time to prevent component wear. Insufficient lubrication of bearings will significantly shorten their service life, especially under high load.

In addition, carefully check the control cabinet and electrical system for loose circuits, because electrical problems are one of the most common causes of shutdown on site.

Replace worn parts regularly such as belts, mixing blades and seals. Their service life is affected by usage frequency, material type and working conditions. Under normal working conditions, mixing blades last about 6 to 8 months, and belts last 12 to 15 months, which can be adjusted according to usage intensity. Timely replacement is necessary to avoid affecting equipment performance and causing faults.

Tune the batching machine regularly to ensure measurement accuracy, preferably every 3 to 6 months, and shorten the cycle if used frequently, so as to avoid inaccurate batching from affecting concrete quality. Meanwhile, check the cement silo for cracks or corrosion, especially at the welding parts, and handle problems in time to prevent cement leakage, material waste and potential safety hazards.

In winter, focus on anti-freezing measures, insulate water pipes and equipment to prevent freezing and cracking from affecting water adding operation. Electrical components are more prone to faults in low temperature, so check them in advance to avoid unnecessary shutdown.
In summer, electrical components are easy to overheat and break down. Take cooling measures, install cooling fans next to the control cabinet, and avoid long-time operation under direct sunlight.

Avoid common maintenance mistakes, such as ignoring the cleaning of the dust removal system leading to dust blockage, or overloading the mixer causing accelerated wear.