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Technical description of metering system in mixing plant

Author: admin Release time: June 15, 2017 Number of visits:

The metering system of mixing plant includes aggregate metering and powder metering (cement metering 1 and admixture metering 2), liquid admixture metering 3 and water metering 4. Metering system is one of the key parts of mixing equipment. Generally, mass measurement is adopted, and volume measurement is also adopted (but it should be converted into quality setting or indication). At present, volume measurement is not used for other materials except water and additives.

According to the specific way of force transmission, it can be divided into lever scale, lever electronic scale and electronic scale. At present, the technical performance of the electronic scale has become mature. It has been widely used because of its small size, fast response, high sensitivity, easy to match with the microprocessor, realizing the functions of rough weighing, precise weighing, more buckles and less compensation. Only when the electronic weighing device is used, the necessary protective measures should be taken in the aspects of shockproof, moisture-proof, dustproof and anti-interference.

The weighing system consists of weighing bucket, weighing sensor (diagram), junction box, shielded cable and industrial weighing terminal.

1. Aggregate Measurement

There are also two measurement methods for Aggregate Measurement: cumulative measurement and independent measurement. The aggregate metering device is composed of bucket body, sensor and belt conveyor. The bucket body is connected with the belt conveyor. When all the aggregate is measured, the belt conveyor will start to run and send all the aggregate to the lifting device (lifting bucket and inclined belt conveyor).

The separate metering device of aggregate is composed of measuring bucket body, bucket door, sensor, cylinder, etc. Before the start of measurement, the hopper door is closed, and the two hopper doors of the aggregate bin are opened at the beginning of measurement. When the weight of aggregate reaches a certain set value, one of the hopper doors of the aggregate bin is closed for accurate measurement of aggregate. When the aggregate weight reaches the set weighing value, all the hopper doors will be closed to complete the weighing process. When the metering bucket air cylinder receives the opening signal, the piston rod acts, the bucket door opens and the unloading begins. After weighing empty (the signal measured by the sensor is zero), the action of piston rod is delayed and the door is closed.

2. Powder measurement

Powder weighing is composed of metering hopper, bracket, sensor, pneumatic butterfly valve (as shown in the figure), red rubber tube, pneumatic ball vibrator (as shown in the figure), feeding port, exhaust pipe, etc. The measurement of cement and admixtures is generally required to be carried out in airtight containers due to the heavy dust, serious pollution and easy water absorption of cement and admixtures. In order to make the metering system independent, the connection between the metering bucket and other parts must adopt soft connection to ensure the accuracy of measurement. At the beginning of measurement, the screw conveyor receives the signal and starts to transport powder to the metering hopper, and part of the air and dust in the metering bucket arrive at the dust collection device through the exhaust pipe. When the weight of powder reaches the preset weight value, the screw conveyor stops conveying powder and completes the measurement. When the pneumatic butterfly valve gets the unloading instruction, the pneumatic butterfly valve acts to open the door for unloading. At the same time, the pneumatic ball vibrator began to vibrate to accelerate the unloading speed. After weighing empty, the pneumatic butterfly valve acts in delay, closes the discharge port and stops vibration.

3. Water measurement

Water metering is composed of water inlet pipe 1, sensor 2, liquid additive discharge pipe 3, metering bucket 4, pneumatic discharge butterfly valve 5, red rubber hose 6, etc., as shown in the figure below. At the beginning of water metering, the water pump gets the signal and starts to pump the water in the pool to the metering bucket. When the weight of water reaches the preset weight value, the pump stops working and completes the measurement. When the pneumatic discharge butterfly valve gets the discharge command, the pneumatic discharge butterfly valve acts and opens the door to discharge water. After weighing empty, the pneumatic discharge butterfly valve acts in delay to close the discharge port.

In the process of concrete preparation, the correct realization of the designed water cement ratio is the key to ensure the quality of concrete. In order to accurately control the amount of concrete added, high-precision water measuring equipment is not enough, because the water contained in the sand and gravel will enter the mixer together with the sand and stone. If the water cement ratio cannot be accurately considered in the design. Only by measuring the moisture content of sand and stone in advance and deducting it from the prepared water, can the accuracy of concrete mix proportion be ensured. If the sand and stone moisture content tester is used, the water content of sand and gravel can be continuously measured, thus realizing the automatic correction of water consumption and sand consumption.

4. Measurement of liquid admixture

The additive metering is composed of sensor 1, liquid additive feed pipe 2, metering bucket 3, pneumatic discharge butterfly valve 4, liquid additive discharge pipe 5, etc., as shown in the figure. Due to the strong corrosivity of additives, the metering bucket is usually made of stainless steel. When the admixture metering starts, the admixture pump gets the signal and starts to start, and the admixture in the additive box is pumped to the metering bucket. When the weight of water reaches the preset weight value, the additive pump stops working and completes the measurement. When the pneumatic discharge butterfly valve gets the unloading instruction (after the water weighing is completed), the pneumatic discharge butterfly valve acts and opens the door to discharge the additive to the water metering bucket. After weighing empty, the pneumatic discharge butterfly valve acts in delay to close the discharge port.