According to the PVC production control process environment and process control needs, after research, analysis, to determine the PVC production process microcomputer control system selected IPC-DCS system, PC-DCS system for the upper and lower two-stage structure. Control of the upper computer using two industrial control computers, due to the system to detect more points, and taking into account the system upgrade requirements, the lower computer using a large PLC. monitoring software, including the upper unit configuration control software, communication software, and the lower machine ladder programming software. The system has a high performance-price ratio; the system is open and easy to upgrade; the system has high control accuracy and excellent performance; the system has high measurement accuracy, fast speed and reliable operation, which fully meets the technical requirements of PVC production process.

Upper computer software system design

The upper computer can directly set and modify the control parameters of each mixer, real-time monitoring of the lower computer, displaying the temperature, formula and other data, as well as solenoid valves, motor status; in addition, the temperature and other data must be recorded for historical inquiries, generate reports. And for the various alarm conditions that can be dealt with during the operation of the system, the host computer must automatically detect and pop up the alarm window, which displays in detail the name of the alarm variable, the value of the variable at the time of the alarm, the reason for the alarm, the state of the description of a series of information, and at the same time, in the response of the host computer in the corresponding position of the screen appears on the alarm light indication.

The feeding system is composed of the following functional modules:

Data Acquisition and Transmission Module: Data acquisition is realized by the on-site sensing and measuring elements in the network, and data transmission depends on the network connection between the PLC and the host computer. Acquisition and transmission module to achieve the function of the field equipment collected by the equipment operation information, and then sent to the host computer port, in accordance with certain network communication protocols decoded and sent to the PC, the software will be sent to the data display and secondary processing.

Unit information monitoring module: The module will be sent to the system of various equipment operating status for the screen display, trying to be the most simple and direct way to the field unit information on the monitor real-time monitoring. This part contains real-time analog quantity, system operation status graph, alarm and time screen, record screen, unit information secondary screen.

Alarm and Processing Module: This module handles the abnormal condition information of each unit and the connected equipment of the unit, and the output of the processed information is available in three ways: display output, printer output and analog screen output. The alarm information has secondary processing and traceability functions.

Mixing system control subroutine: mixing system control subroutine to achieve the auxiliary material warehouse after the allocation of material mixing, the system must be configured before mixing the control parameters used.

Storage system control subroutine: storage system control subroutine to achieve the final material storage function, the system real-time detection of the storage bin on the material level is valid to meet the upper material level is invalid, the transition bin on the material level meter is valid, start the corresponding feeding fan, when detected in the transition bin under the material level meter is valid, after a two-minute delay, shut down the fan, open the pulse blowing, to remove the dust.

Weighing meter value reading subroutine: it is mainly used for reading the weighing meter and completing the simple data processing function.

Alarm subroutine: When any of the following situations occurs, it will give an alarm and stop the related equipment: the cover of the hot/cold machine is not closed, the protection switch of each motor is effective, and the material level meter on the storage bin is effective. Give sound and light prompts when any bin is empty or full.

Manual control subroutine: when the system fails, use this program, at this time, the upper and lower computer only play a monitoring function of the system, can not operate the system, the system has a manual, automatic control buttons.

System debugging the lower computer programming using OMRON's professional ladder programming software CX-ProgrammerV3.10, and refer to the OMRON programmable controller C200HX / C200HG / C200HE Programming Manual content. According to the requirements of PVC mixing production process and program flow chart to write the program segments, the program will be written to the PLC, in the CX-Programmer monitoring mode for debugging and modification, until it meets the requirements, when the upper program is written, but also to carry out the upper and lower joint debugging, when there are contradictions and conflicts, should be appropriate to modify the upper or lower program. When there are contradictions and conflicts, the upper or lower computer program should be modified appropriately.

Partial program segment description:

Mixing process segment program implementation

Module for sending information and output from field units to provide control functions. Event Record and Processing Module: This module provides the historical record of the changes of the on-site equipment for the operator in analyzing and judging the operation of the system, and provides the original reference number for the next operation of the system.

User rights management module: According to different users to give different levels of management rights. The upper computer human-computer interface is mainly to display the operation status on the screen, trying to monitor the field unit information on the monitor in real time in the most simple and direct way, this part contains real-time analog quantity, system operation status chart, alarm and time screen.

Lower computer software system design

Since the weighing accuracy of the main material scale and auxiliary material scale is required to be high, the Proportional Integral Differential (PID) control algorithm is used in the control system. A PLC-based control system is designed in this system, which is a time-discrete control system for continuous control of multiple control loops. The system adopts frequency converter to control the rotational speed of the screw feeder motor and incremental PID control algorithm.The whole production process of PVC blending is mainly divided into feeding section, batching section, mixing section and storage section. According to the system process characteristics, the

The lower computer program includes the following parts:

System initialization subroutine: initialize the system, read the control parameters of PVC production process, firstly, carry out the state detection of the silo, detect that the silo is not empty, then carry out the checking of the current value of the main material scale and the auxiliary material scale, and carry out the dosage process under the condition that the scale value is relative to zero, the end of the dosage will be carried out in the mixing process, and the final discharge of the material into the storage silo. The material is discharged into the storage bin. Main material loading system control subroutine: the loading system control subroutine mainly completes the function of loading the main material warehouse, the system detects the position switch of the lower material position of the main material warehouse in real time, when it is valid, the system gives the indication of lack of material, and automatically opens the loading fan, and sends the main material to the main material warehouse from the dumping station of the main material by using the aerodynamic force until the system detects that the position of loading is valid, then it will turn off the loading fan and the dust-removing fan in sequence, and open the pulse blowing for 5 minutes to clean up the material, and then it will be blown away. Pulse blowing for 5 minutes to clean up the dust caused by feeding. Auxiliary material feeding system control subroutine: the auxiliary material system control subroutine mainly completes the function of feeding the auxiliary material warehouse, when the system detects that the material level meter switch of any auxiliary material warehouse is valid, the system will give the indication of lack of material, notify to throw auxiliary material, turn on the feeding blower, turn off the door of the auxiliary material after throwing, cut off the corresponding position switch, turn off the feeding blower and the dust removing blower according to the order, turn on the pulse spraying for 5 minutes, and clean up the dust caused by the feeding. The mixing system of PVC usually consists of the following parts

PVC mixing system usually consists of the following sub-systems: material collection system, material handling system, measuring and dosing system, mixing unit, material storage system, extruder feeding system, dust removal system: centralized control system, centralized monitoring system, etc., the following on the composition of the sub-systems and the principle of the respective introduction:

1, the material collection system is used to bulk or bagged raw materials through a variety of ways to collect to the storage silo, bulk materials can be sent directly through the tank car comes with pneumatic conveying device to the storage silo, bagged materials using the open bag station to collect. Bag opening station box material and material contact materials are 1Cr18Ni9Ti stainless steel, polished inner surface, for the sealing structure, bag opening station is divided into automatic bag opening and manual bag opening two kinds. Artificial bag opening station by the protective door, vibrating screen, magnetic frame, broken arch, etc., protective door is divided into two layers, the outer layer of stainless steel door, open the bag can be put, closed that is a sealed box, the inner layer is equipped with a soft curtain door, the discharge of materials can be effectively prevented from the diffusion of dust, the vibrating screen can be effectively screened out of the impurities mixed in the powder, such as sewing thread, shredded paper, large particles of material, etc., magnetic frame can be initially removed from the material of iron impurities, broken arch device consists of a cylinder and broken arch device, the arch is made of a cylinder and a broken arch. The arching device consists of cylinder and arch breaker to facilitate the smooth flow of materials. The automatic bag opening station consists of conveyor, bag opener, filter, collector, discharge port, etc. The bag enters into the bag opener through the conveyor, and the bag opener is equipped with spiral reamer, which sends the bag and the material together to the filter through the rotating movement while breaking the bag, and the filter separates the material and the bag, and the material enters into the collector, and the broken bag enters into the discharge port and is discharged.

2, material conveying is the key to automation of blending production line, in the PVC automatic blending system in the conveying system occupies a large proportion: including raw materials from the bag opening station to the dosage scale above the excessive silo conveying, finished product from the mixer to the finished product silo conveying, finished product from the finished product silo to the extruder conveying. Here there are two main forms of application: screw conveyor and pneumatic conveying, and pneumatic conveying can be selected according to the actual site of the dilute-phase positive pressure, dilute-phase negative pressure, dense-phase positive pressure and so on several ways. Screw conveyor consists of motor, reducer, screw body, simple structure, reliable work, but the cost is higher when the conveying distance is longer. Dense-phase pneumatic conveying system is the core part of a storage type pneumatic sending pump (referred to as warehouse pump), warehouse pump by the warehouse body, butterfly valve, exhaust valve, feeding port, gas piping, etc., for the main equipment in the dense-phase pneumatic conveying system, when the compressed air into the sender of the intake valve, and then from the intake valve to the cone inside the protruding nozzle, so that the gas generates vortex, along with the increase in the pressure inside the sender, the material to be sent With the increase of pressure inside the sender, the material to be sent into a vortex-like flow, in order to achieve the purpose of smooth conveying of materials, can be utilized to achieve low-speed, high-concentration conveying with low air pressure. The system has the advantages of low noise, long conveying distance, low energy consumption, low wear and tear of pipeline with large conveying capacity, etc. Moreover, because of its high working pressure (0,15~0,3MPa), it will not be blocked in the pipeline, and because of the addition of a set of boosting device in the pipeline at certain intervals to make the material in the pipeline in the form of a peg (i.e., a segment of mutually spaced columns of air and material columns) forward movement, so it is impossible to Material separation and stratification phenomenon, especially suitable for the transportation of mixed materials, the use of boosting devices can also effectively reduce the forward speed of the material. Dilute-phase positive pressure pneumatic conveying equipment generally consists of Roz fan, rotary feeder, venturi generator, Roz fan is responsible for providing low-pressure air needed to transport materials, in order to ensure the stability of the air pressure, Roz fan on the upper part of the specially equipped with a certain volume of the air storage package, rotary feeder is a quantitative feeding device to ensure that continuous and uniform feeding, due to the rotary feeder is used in conjunction with the Roz fan to prevent As the rotary feeder is used with the Roz fan, in order to prevent the air leakage to the silo accident, the air locking performance of the feeder should be good, the appearance of the venturi generator is similar to a tee, but its internal air flow piping for the use of the Venturi principle of design, the air flow resistance is small, the air flow dispersion is less, the dilute phase pneumatic positive pressure conveyor is a quantitative feeding device to ensure continuous and uniform feeding.

The advantages of the dilute phase pneumatic positive pressure conveying is that it doesn't need special compressed air source, smaller, but the noise is higher, the conveying distance is shorter, and it is easy to form the material's separation and stratification in the conveying process. Dilute-phase pneumatic negative-pressure conveying mainly utilizes the vortex fan to produce a vacuum to absorb the material, and then separates the material from the gas through the dust-cutting and filtering device. The advantages and disadvantages of the negative pressure conveying are similar to the dilute phase positive pressure conveying, but it is not easy to cause clogging is also small.

3, weighing and batching unit in the PVC automatic blending system, weighing and batching system normally consists of two sets of independent subsystems, a set of main material weighing and batching system and a set of auxiliary material weighing and batching system, each batching system consists of the material feeding bin, the corresponding screw conveyor, batching scales and other parts of the composition. The main material scale has a larger rated value, which is suitable for the main material with high weighing ratio, while the auxiliary material scale has a smaller rated value, which is suitable for the material with less weighing ratio, and this design can help to improve the dosage accuracy. Feeding silo needs to be designed according to different materials, generally including the top of the silo dust remover, the silo wall is set with a high and low level meter, good fluidity of the material outlet using a conical natural fall, poor fluidity can be added in the silo wall electric or pneumatic silo wall vibration, but also can be installed in the inner wall of the air flow cushion or coated with a special material coating to promote smooth flow of the material, the material especially easy to adhere to the silo can be designed as a flat bottom, the implementation of forced feeding. For materials that are particularly easy to stick, the silo can be designed as a flat bottom to implement forced feeding. The main and auxiliary material feeder is mainly in the form of screw conveyor feeding, the screw blade is designed for variable pitch to ensure uniform feeding, and the feeding speed is adjusted by frequency converter. Screw machine outlet with access holes, internal sealing box, breathable mouth, etc., the material is discharged into the weighing unit through the sealing box, when the weighing unit sends a signal to reach a predetermined value, the shutdown door is driven by a cylinder to intercept the falling air material column, this structure makes the air material column falls into the weighing unit to reduce the material, easy to control the measurement of precision, likewise, the screw machine is also easy to maintain, open the relevant access holes, the operation of the various parts of the Similarly, the spiral machine is also easy to maintain, open the relevant access holes, the operation of each part is very clear, the shaft seal is set far away from the inlet and outlet of solid materials, greatly simplifying the sealing of the shaft, but also effectively prevent the solid materials from pressing on the seal to improve the reliability of the use of the machine, and, in addition, it is only necessary to unscrew a few bolts to clean up and overhaul, which is very convenient.

Screw conveyor due to different materials, set up a single and double screw feeding two different feeding types, double screw feeding unit consists of a large, small two screw machine, the beginning of the feeding by the large, small screw machine work at the same time, when the feeding reaches 90% of the rated value, the large screw machine stops, the small screw machine continues to work, this feeder can improve both the speed and accuracy of the weighing, suitable for the distribution of relatively small materials. This kind of feeder can improve both the weighing speed and weighing precision, and is suitable for the distribution of small materials.

Single screw feeder is only used for feeding materials with large proportion because the feeding speed is not graded and the precision is a little bit poor.

Batching scale is composed of main material weigher and auxiliary material weigher. Weighing part of the key parts of the load cell used in Germany HBM's Z6 type stainless steel shear beam bellows sensor, its comprehensive error of two ten thousandths of a degree of protection up to IP67, the sensor strain gauges in the bellows, and filled with nitrogen protection, with high precision, good reliability, long service life and so on, the force transfer reset mechanism using the company's box-type point of contact mechanism, through the design of the shaking key connected to the sensor, with a high precision, good reliability, long service life and so on. The shaking key is connected with the sensor, which has the characteristics of fast return to zero, no partial load error, stable and reliable. The weighing machine has delicate structure, accurate weighing, fast speed, high anti-corrosion ability, long-term stability and reliability.

Weighing body for the overall mobility hopper, the overall type hopper to ensure that when the discharge port is opened, every piece of material in the hopper began to move, according to the first into the storage bin of material first unloaded out of the flow of the order of flow, hopper without dead ends, discharge uniformity, unloading of the material heap density is stable, eliminating the uneven distribution of materials, broken, pulsating and spraying, etc., hopper any one horizontal cross-section of a relatively uniform pressure, the material segregation can be kept to a minimum, and the material can be used in a variety of ways. Material segregation can be kept to a minimum, for the predicted nature of the flow of bulk solid material flow pattern, and for CaCO3 material adhesion, bridging performance is relatively strong, auxiliary scales hopper outlet is equipped with a flow-assisting air cushion plate (for a closed cavity covered with a microporous pore plate, compressed air passes through, so that the powder material is suspended in the cushion of air, always in the state of fluidization, which effectively prevents the powder material arching), and its The use of rubber patches or Teflon coating.

4, high cold mixing unit is suitable for PVC mixing process equipment, domestic high cold mixing unit, although the technology has matured production has also been serialized, and many PVC manufacturers in the country to get a large number of applications, but the failure rate is high, so the company in the program to use the Taiwan Qiaolong company's products, high cold mixing unit is composed of a high-speed mixer and a combination of a horizontal cooling mixer, high-speed mixing machine is equipped with High-speed mixer is equipped with 3 stirring blades and deflector plate, etc., under the action of which the materials make complex movements such as high-speed rotation and turning, so that the temperature rises rapidly to meet the requirements of the material mixing process, and then enter the horizontal cooling mixer, through the stirring blades of the low-speed operation of the water-cooled system of heat exchange, so that the material is quickly cooled to meet the requirements of the production process.

5, material storage equipment mainly refers to the storage of raw materials and finished materials for the storage of various silos, PVC raw material storage silo effective volume is designed for 150m3, and material contact with the material at the material are 1Cr18Ni9Ti stainless steel, polished inner surface, the outer surface of the pickling and passivation treatment by the silo, silo dust machine, steel ladder, guardrail, depressurization cap, gate and other components, through the setting of the high and low level meters can be Automatic control of feeding, discharging, and has a beautiful appearance, solid structure, windproof and other characteristics, in order to ensure that the pipe molding rate of qualified products, should be considered the volume of the finished bin has a certain amount of affluence, generally not less than 12 hours, in addition, the design of the finished silo adopts the structure of the homogenization, to ensure that the material does not segregate the stratification.