The weighing screw machine utilizes the changes in the output voltage corresponding to the load changes of the three weighing sensors installed at the bottom of the hopper. The total weight of the powder in the hopper is obtained by adding the three output voltages through an adder. The measured weight is repeatedly compared with the set target value to achieve the purpose of precise quantitative batching. The control program is written in a statement list and mainly achieves the control actions such as weighing calculation, reverse blowing solenoid valve, rotation speed control of the double-screw Feeder, opening/closing control of the top feeding valve, opening/closing control of the bottom discharge valve, opening/closing of the return air valve, and opening/closing of the bag-blowing valve in accordance with the process flow. The screw feeding program is divided into coarse feeding, additive feeding and fine feeding program control, which is controlled based on the difference between the immediate weight in the hopper and the target value. At the beginning of feeding, use coarse feed and feed at a fast speed. When the material in the hopper reaches a certain weight, add the feed and reduce the feeding speed. When the weight of the material in the hopper is not much different from the target weight, fine feeding is adopted to allow the material to enter the hopper slowly, so as to achieve the purpose of precise feeding.

The weighing screw machine adopts the net weight method and double-screw variable frequency feeding. The feeding speed is controlled by the double screw through variable frequency to achieve the requirement of precise quantitative batching. The quantitative measurement is completed by the combination of the hopper scale and the weighing instrument, and the entire batching process is completed by bagging, tying the mouth, bag clamping, nitrogen bag blowing, return air, bag shaking, bag unloading and conveying links.

The process flow consists of four parts: starting the dust removal system, manual bagging, automatic metering and filling. The specific working process is as follows: Press the start button of the dust removal machine, the dust removal fan starts, and at the same time, the nitrogen back-blowing valve of the dust removal machine starts and stops alternately at the set time intervals. The blowing sound of the back-blowing valve can be heard on site. If no sound of the back-blowing valve is heard, the operation of the dust collector should be stopped immediately to ensure the safety of production operation. The packers manually bag the bags, press the switch, and the bag clamps the packaging bags tightly. The discharge valve at the bottom of the hopper scale is closed, and the Electronic scale shows a weight of zero. Turn the automatic/manual metering button to the automatic position, reset the metering emergency stop switch (the button is not pressed), the weighing instrument starts, the feeding valve at the top of the hopper opens, and the screw feeder begins to add materials. After the measurement is completed, close the top feeding valve. The system checks whether the packaging bags are in place. Once the detection is in place, the bag-blowing relay and the bag-blowing time relay open simultaneously, automatically opening the bottom discharge valve. At the same time, start the return air system and the shaking bag system to assist in filling the bags. After the bag filling is completed, the discharge valve will be closed after a delay for a period of time. The bag clamping device and the automatic unhooking device will automatically open, and the conveyor chain plate machine will be started to send away the PTA material bag. Meanwhile, start the next packaging process.