A loss-in-weight measuring method and device for weighing powder materials

Abstract

The present invention discloses a loss-in-weight metering method and device for weighing powder materials. First, initialization control is performed to put each device in the production process into an initial state. Then, the metering bin is replenished according to the current material quantity in the metering bin. Then, the instantaneous powder quantity in the metering bin at each time point within a unit time period is weighed and the average value is taken, thereby controlling the feeding speed of the spiral feeding device in real time and adjusting the amount of powder sent to the next production device. The device for weightless metering of powder using the above method includes a material receiving bin, a metering bin, a spiral feeding device and a control system. The material receiving bin is arranged above the metering bin. The metering bin is arranged below the spiral feeding device. The spiral feeding device is connected to the next process equipment. Through the above method and device, it is possible to accurately and stably weigh powders that produce large fluctuations, and adjust the equipment feeding speed in real time according to the weighing situation to ensure the accuracy of the powder use process.

Claims

1. A loss-in-weight method for weighing powder materials, characterized by: include: Step 1: Equipment initialization control; powder enters the material receiving bin (1) through the material pipeline (4); the powder metering device (7) is turned on in an automatic control mode, and the equipment is initialized first, so that the equipment is in the initial state; Step 2: feeding control before metering; after the powder metering device (7) is initialized, the control system checks the weight of the material in the metering bin (2) through the powder metering device (7). If the weight of the material is lower than the middle line of the metering interval of the metering bin (2), feeding is started, the feeding dome valve and the pressure relief valve (15) are opened, and the fluidizing valve is opened intermittently. The powder enters the metering bin (2) through the feeding pipe (5) until the weight of the metering bin (2) is greater than the upper limit of the metering interval of the metering bin (2). This avoids insufficient adjustment time before the next feeding cycle, which causes large fluctuations in the instantaneous material amount. The feeding control period before metering is called the pre-feeding period. If the weight of the material is greater than or equal to the middle line of the metering interval of the metering bin (2) after initialization, the pre-feeding period is skipped. The median line of the material measuring interval in the metering bin (2) during the pre-feeding period The calculation is as follows: ， :Measuring bin (2) material measuring interval median line; :Measuring bin (2) measuring interval lower limit; :Measuring bin (2) upper limit of measuring interval; Step 3: metering start control; when the equipment initialization is completed and the weight of the material in the metering bin (2) meets the requirement of being greater than or equal to the middle line of the material metering interval of the metering bin (2) or the pre-feeding period is over, metering starts, and each device component switches to the device state during metering; the material quantity adjustment PID maintains the manual mode, and the frequency converter of the spiral feeding device (3) starts at the starting frequency. After 5 seconds of starting, the material quantity adjustment PID switches to the automatic mode, and uses the instantaneous material quantity as the feedback value. The frequency setting value of the frequency converter of the spiral feeding device (3) is adjusted from the initial setting value at the time of starting, and the fixed adjustment amount and the minimum value of the absolute value of the deviation between the current setting value and the target setting value are used as the actual adjustment amount to increase or decrease until the set material quantity is reached; the instantaneous material quantity is calculated by calculating the reduction in the weight of the metering bin (2) and is adjusted stably. The metering start control period is called the starting period; Instantaneous material quantity The weight change of the measuring bin (2) is calculated by differential calculation, and the calculation formula is as follows: ， : Instantaneous material quantity; : The weight of the measuring chamber (2) at all times; : The weight of the measuring chamber (2) at all times; : time interval; Initial setting value when material quantity adjustment PID starts According to the maximum value of the instantaneous material quantity when the frequency converter of the spiral feeding device (3) is at the starting frequency and the 5% range of the powder metering device (7), the calculation formula is as follows: ， ， : The initial setting value when the material quantity adjustment PID is started; : The instantaneous material quantity of the spiral feeding device (3) when the inverter is at the starting frequency; : The measuring range of the powder metering device (7); : The upper limit of the measuring range of the powder metering device (7); : The lower limit of the range of the powder metering device (7), usually 0; The fixed adjustment amount of the material quantity adjustment PID set value is determined according to 2% of the design range of the powder metering device (7). The actual adjustment amount is determined according to the minimum value of the fixed adjustment amount and the target deviation amount. The calculation formula is as follows: ， ， : Fixed adjustment amount of material quantity adjustment PID set value; : The actual adjustment amount of the material quantity adjustment PID set value; : Material quantity adjustment PID current setting value; : Material quantity adjustment PID target setting value; Step 4: Detect and automatically control the flow rate of the powder material according to the set material flow rate; the powder material metering device (7) maintains the material quantity adjustment PID in the automatic mode and automatically adjusts according to the set material quantity; when the set material quantity changes, the material quantity adjustment PID set value increases or decreases according to the above-mentioned fixed adjustment amount until the set material quantity is reached and the adjustment is stabilized; at the beginning and end of the period of detecting and automatically controlling the flow rate of the powder material according to the set material flow rate, a point is taken to calculate the relationship between the actual set frequency of the frequency converter and the set material quantity and the weight of the metering bin (2) to obtain a correction coefficient; the period of detecting and automatically controlling the flow rate of the powder material according to the set material flow rate is called the metering period; Under the same weight of the metering bin (2), the higher the set material quantity, the higher the frequency set for the frequency converter. In an ideal state, the set frequency is directly proportional to the set material quantity. During actual use, due to the fluidity of the powder material, the greater the self-weight of the material, the stronger its fluidity. Therefore, under the same set material quantity, the heavier the weight of the material in the metering bin (2), the lower the frequency set for the frequency converter, and the set frequency is inversely proportional to the weight of the metering bin (2). Thus, the following relationship exists among the three: ， : Inverter frequency setting value; : Correction coefficient : Material quantity adjustment PID setting value; : Material weight in measuring bin (2); :constant; During the metering process of the powder metering device (7), the frequency setting value of the inverter at t2 seconds after the feeding is completed is , Material quantity adjustment PID setting value , Material weight in measuring bin (2) , and the inverter frequency setting value at the end of the measurement period , Material quantity adjustment PID setting value , Material weight in measuring bin (2) , the correction coefficient can be obtained ,Right now: ， t2 is the correction coefficient calculated during the measurement period Sampling time: Step Five: Detect and control the material weight in the metering bin (2); according to the above method, the material weight in the metering bin (2) is detected in real time. When the weight of the metering bin (2) is less than the lower limit of the metering range of the metering bin (2), feeding starts until the weight of the metering bin (2) is greater than the upper limit of the metering range of the metering bin (2), at which point the feeding ends; the period during which the material weight in the metering bin (2) is detected and controlled is called the feeding period; Step Six: Automatically perform feedforward control of the material flow during the feeding period and the stable period after feeding in the metering bin (2); after the feeding in the metering bin (2) ends, due to the delay in closing the feeding valve (6) and the time required for the material to stabilize, a stable period of a fixed time t1 is set after the feeding ends, where t1 < t2 - 15s; during the feeding period and the stable period, the frequency PID adjustment function block of the frequency converter switches to the manual mode and directly performs proportional adjustment according to the above correction coefficient K. After the stable period ends, the program automatically enters the metering period and performs control according to Step Four; During the feeding period and the stable period, the calculation formulas for the set value of the frequency of the frequency converter are as follows, and the calculation results of the two formulas are the same: ， Or: ； Step Seven: Metering stop control; when the powder metering device (7) stops, all equipment and control modules return to their initial positions; the period during which metering stop control is performed is called the stop period; Step Eight: When the powder metering device (7) needs to empty the metering bin (2) due to maintenance reasons in Step Seven, a bin emptying command will be issued through local or remote control. Then, when the material weight in the metering bin (2) is less than the lower limit of the metering range of the metering bin (2), feeding will no longer be performed, and control will continue according to the metering period until the weight of the metering bin (2) is 0; the period during which the powder metering device (7) needs to empty the metering bin (2) due to maintenance reasons is called the bin emptying period; Step Nine: In Step Eight, when the powder metering device (7) experiences a major emergency stop failure, immediately execute the stop command unconditionally, all equipment and control modules return to their initial positions, and the equipment is inspected; Major failures include on-site and local or remote emergency stop button activation, screw feeder (3) failure, More than 20s, metering bin (2) material weight display failure, metering bin (2) material weight higher than the upper limit, metering bin (2) material weight lower than the lower limit and not in the clearing period, feeding dome valve closing timeout failure, feeding timeout failure.

2. The loss-in-weight method for weighing powder materials according to claim 1, characterized in that: The initial state described in Step One includes that all valves execute the closing command, all electrical equipment executes the stop command, and the material quantity adjustment PID switches to the manual mode; 10 s after the initial state command is issued, check whether all valves are in the closed state, whether all electrical equipment is in the stop state, and whether the measuring point state of the material weight in the metering bin (2) is normal. Otherwise, the initialization fails, and startup is prohibited when it fails; the period 10 s after the initial state command is issued is called the initialization period.

3. The loss-in-weight method for weighing powder materials according to claim 1, characterized in that: The equipment status during the metering period in step 3 includes the following: the exhaust valve (13) is open, the feeding dome valve, the pressure relief valve (15), and the fluidizing valve are closed, the spiral feeding device (3) and the dispersing device (9) are started, and the material quantity adjustment PID remains in manual mode.

4. A loss-in-weight metering device using the loss-in-weight metering method for weighing powder materials according to any one of claims 1 to 3, characterized in that: The invention comprises a material receiving bin (1), a metering bin (2), a spiral feeding device (3) and a control system; the material receiving bin (1) is arranged above the metering bin (2); the top of the material receiving bin (1) is connected to a material pipeline (4), and the bottom is provided with a feeding pipeline (5) connected to the metering bin (2); the feeding pipeline (5) is provided with a feeding valve (6); the metering bin (2) is provided with a powder metering device (7); the spiral feeding device (3) is arranged at the bottom of the metering bin (2) and is connected to the next process equipment.

5. The loss-in-weight metering device for a loss-in-weight metering method for weighing powder materials according to claim 4, characterized in that: A dredging pipe (10) is provided at the lower portion of the material receiving bin (1); the dredging pipe (10) is connected to an air source; a dredging air hole is provided at the portion of the dredging pipe (10) located inside the material receiving bin (1); and a dredging air valve (11) is provided on the dredging pipe (10).

6. The loss-in-weight metering device for a loss-in-weight metering method for weighing powder materials according to claim 4, characterized in that: A discharging barrel (8) is provided at the bottom of the metering bin (2); a dispersing device (9) is provided on the discharging barrel (8); the dispersing device (9) comprises a dispersing stirring rod extending into the discharging barrel (8) and a dispersing motor driving the dispersing stirring rod; the dispersing motor is arranged outside the discharging barrel (8).

7. The loss-in-weight metering device for a loss-in-weight metering method for weighing powder materials according to claim 4, characterized in that: The metering bin (2) is further provided with an exhaust pipe (12); the material receiving bin is further provided with a pressure relief pipe (14); the pressure relief pipe (14) is connected to the exhaust pipe (12); the exhaust pipe (12) is provided with an exhaust valve (13); and the pressure relief pipe (14) is provided with a pressure relief valve (15).

8. The loss-in-weight metering device for a loss-in-weight metering method for weighing powder materials according to claim 4, characterized in that: The control system includes a local control system and a remote control system; the local control system is a control cabinet based on PLC; the remote control system is connected to all production equipment on the production line through a network; the local control system and the remote control system are both equipped with manual control mode and automatic control mode.

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