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The PVC compounding system is a front-end component of the PVC profile production line. It is one of the keys to the long-term stable production of the production line. The degree of automation of the compounding determines the degree of automation of the entire production line. A fully automatic PVC compounding system usually consists of the following subsystems: material collection system, material conveying system, metering and batching system, mixing unit, material storage system, extruder feeding system, dust removal system: central control system, central monitoring system, etc. The composition and principles of each subsystem are introduced below. 1. Material collection system The material collection system is used to collect bulk or bagged raw materials into the storage silo through various methods. Bulk materials can be directly sent to the storage silo through the pneumatic conveying device on the tanker, and bagged materials are collected by the bag opening station. The material at the contact point between the box material and the material at the bag opening station is 1Cr18Ni9Ti stainless steel. The inner surface is polished and has a sealed structure. The bag opening station is divided into two types: automatic bag opening and manual bag opening: The manual bag opening station is composed of a protective door, a vibrating screen, a magnetic frame, an arch breaker, etc. The protective door is divided into two layers: an inner and an outer layer. The outer layer is a stainless steel door. Open it to place the packaging bag. Close it to form a sealed box. The inner layer is equipped with a soft curtain door. It can effectively prevent powder when discharging. Due to the diffusion of dust, the vibrating screen can effectively screen out impurities mixed in the powder, such as sewing thread, shredded paper, large particles, etc. The magnetic frame can initially remove iron impurities in the material. The arch breaking device consists of a cylinder and an arch breaker to promote the smooth flow of the material. The automatic bag opening station consists of a conveyor, bag opener, filter, collector, discharge port, etc. The packaging bag enters the bag opener through the conveyor. The bag opener is equipped with a spiral reamer. Through the rotational motion, the bag and the material are sent to the filter while breaking the bag. The filter separates the material and packaging bag. The material enters the collector. The broken bags enter the discharge port and are discharged. 2. Material transportation system The transportation of materials is the key to realizing the automation of the compounding production line. In the PVC fully automatic compounding system, the conveying system occupies a large proportion: including the transportation of raw materials from the bag opening station to the transition bin above the batching scale. The transportation of finished materials from the mixer to the finished product bin. The transportation of finished materials from the finished bin to the extruder. There are two main forms that are widely used here: screw conveying and pneumatic conveying. Pneumatic conveying can choose dilute phase positive pressure, dilute phase negative pressure, dense phase positive pressure and other methods according to the actual situation on site. The screw conveyor consists of a motor, a reducer and a spiral body. It has a simple structure and reliable operation. However, the cost is higher when the conveying distance is long. The core part of the dense phase pneumatic conveying system is a storage-type pneumatic sending pump (referred to as a warehouse pump). The warehouse pump is composed of a warehouse body, a butterfly valve, an exhaust valve, a feeding port, a gas pipeline, etc. It is the main equipment in the dense phase pneumatic conveying system. When the compressed air enters the air inlet valve of the sender, and then from the air inlet valve to the protruding air nozzle inside the cone, the gas generates a vortex. As the internal pressure of the sender increases, the material being sent flows in a vortex to achieve the purpose of smooth transportation of the material. Lower air pressure can be used to achieve low speed and high concentration transportation. This system has the advantages of low noise, long conveying distance, low energy consumption, large conveying volume and low pipeline wear. And because of its high working pressure (0.15~0.3MPa), it will not form blockages in the pipeline. And because the pipeline increases at regular intervals, Adding a booster device makes the material move forward in the pipeline in the shape of a plug (that is, a segment of air columns and material columns spaced apart from each other). Therefore, there is no possibility of material segregation and stratification. It is especially suitable for the transportation of mixed materials. The use of a booster device can also effectively reduce the forward speed of the material. Dilute phase positive pressure pneumatic conveying equipment generally consists of Roots blower, rotary feeder and Venturi generator. The Roots blower is responsible for providing the low-pressure air required for conveying materials. In order to ensure the stability of the air pressure, the upper part of the Roots blower is specially equipped with an air storage bag of a certain volume. The rotary feeder is a quantitative feeding device that can ensure continuous and uniform feeding. Since the rotary feeder is combined with the Roots blower The venturi generator is used in conjunction with the fan. In order to prevent accidents from air leakage into the silo, the air locking performance of the feeder is better. The shape of the venturi generator is similar to a tee. But its internal air circulation pipeline is designed using the venturi principle. The air flow resistance is small and the air flow diverges less. The biggest advantage of this dilute-phase pneumatic positive pressure conveying is that it does not require a special compressed air source. The investment is small, but the noise is high. The conveying distance is short, and the segregation and stratification of materials are easy to form during the conveying process. The dilute-phase pneumatic negative pressure conveying mainly uses a vortex fan to generate a vacuum to absorb the material, and then separates the material from the gas through a dust filtering device. The advantages and disadvantages of this negative pressure conveying are similar to those of dilute-phase positive pressure conveying. But it is not easy to cause blockage and the investment is smaller. 3. The weighing and batching unit is in the PVC automatic batching system. The weighing and batching system is normally composed of two independent subsystems. A main material weighing and batching system and an auxiliary material weighing and batching system. Each batching system is composed of a loading bin for each material, a corresponding screw conveyor, a batching scale and other parts. The main material scale has a larger rated weighing value and is suitable for weighing main materials with a high proportion. The auxiliary material scale has a smaller rated weighing value and is suitable for weighing materials with a small proportion. This design helps improve the accuracy of ingredients. The loading silo needs to be designed separately according to different materials. It generally includes a dust collector on the top of the silo, and a high and low material level meter is installed on the silo wall. The outlet of the material with good fluidity adopts a tapered natural falling material. When the fluidity is poor, an electric or pneumatic silo wall vibrator can be added to the outer wall of the silo. Airflow boosters can also be installed on the inner wall or a special material coating can be applied to promote the smooth flow of materials. For materials that are particularly easy to bond, the silo can be designed with a flat bottom and forced feeding is implemented. The main form of the main and auxiliary material feeder is a screw conveyor. The spiral blades are designed with variable pitch to ensure uniform feeding. The feeding speed is adjusted through a frequency converter. The discharge port of the screw machine is equipped with a manhole, an inner sealing box, a ventilation port, etc. The material is discharged into the weighing unit through the sealing box. When the signal from the weighing unit reaches a predetermined value, the closing door is driven by the cylinder to intercept the falling material column in the air. This structure allows The amount of material falling into the weighing unit from the air column is reduced, making it easy to control the measurement accuracy. Similarly, the screw machine is also easy to maintain. Open the relevant inspection holes, and the operation status of each part will be clear. The shaft seal is set away from the inlet and outlet of the solid material.* * It simplifies the sealing of the shaft and effectively prevents solid materials from pressing on the seal. It improves the reliability of use. In addition, it only needs to unscrew a few bolts to clean and repair. It is very convenient. Due to different materials, the screw conveyor is equipped with two different feeding types: single and double screw feeding. The double-screw feeding unit consists of two screw machines, a large one and a small one. When the feeding starts, the large and small screw machines work at the same time. When the feeding reaches 90% of the rated value, the large screw machine stops and the small screw machine continues to work. This kind of feeder can not only increase the weighing speed but also improve the weighing accuracy. It is suitable for materials with small proportions. The single-screw feeder is only used for feeding materials with large proportions because the feeding speed is not graded and has slightly poor accuracy. The batching scale consists of a main ingredient scale and an auxiliary ingredient scale. The specific structure is shown in the figure: The key component of the weighing part, the load cell, uses the Z6 stainless steel shear beam bellows sensor produced by HBM Company in Germany. Its comprehensive error is 0.02%. The protection level is as high as IP67. The sensor strain gauge is in the bellows, and the interior is filled with nitrogen protection. It has the characteristics of high accuracy, good reliability, and long service life. The force transmission reset mechanism adopts the company's unique frame point contact mechanism. It is connected to the sensor through its uniquely designed rocking key. It has the characteristics of fast return to zero, no offset error, and stability and reliability. The weighing machine has a sophisticated structure, accurate weighing, fast speed, high corrosion resistance, and long-term stability and reliability. The scale body is an integral fluidity hopper. The integral hopper can ensure that when the discharge port is opened, every particle of the material in the hopper starts to move. It flows according to the flow sequence of the material that enters the silo first and is discharged first. There are no dead corners in the hopper. The discharge is uniform. The discharged material has a stable density. It eliminates uneven distribution, interruption, pulsation and jet flow of materials. The pressure on any horizontal cross-section in the hopper is relatively uniform. The segregation of materials can be kept to a minimum. Limit. It is the best flow mode for the flow of bulk solid materials with predictable properties. It also has strong bridging performance for CaCO3 material adhesion. The outlet of the auxiliary material scale hopper is equipped with a flow-assisted air cushion plate (a closed cavity covered with a porous plate with micropores. After the compressed air is introduced, the powder material is suspended on the air cushion and is always in a fluidized state. It can effectively prevent the powder material from arching.). Its use effect is obviously better than using rubber patches or Teflon coatings. 4. High mixing equipment, cold mixing unit is the first choice equipment suitable for PVC mixing process. Although the domestic high cold mixing unit is mature in technology, it has been serialized in production. It has been widely used in many domestic PVC manufacturers. However, the failure rate is high. Therefore, our company uses products from Taiwan Qiaolong Company in the plan. The high cold mixing unit is composed of a high-speed mixer and a horizontal refrigeration unit. The high-speed mixer is equipped with three mixing blades and a deflector. Under its action, the material undergoes complex movements such as high-speed rotation and flipping, causing the temperature to rise rapidly to meet the material mixing process requirements. Then, it enters the horizontal cooling mixer. Through the heat exchange between the low-speed operation of the stirring blades and the water cooling system, the material is quickly cooled to meet the production process requirements. 5. Material storage equipment Material storage equipment mainly refers to various silos used for the storage of raw materials and finished materials. The effective volume of the PVC raw material storage silo is designed to be 150m3. The materials in contact with the materials are all 1Cr18Ni9Ti stainless steel. The inner surface is polished and the outer surface is pickled and passivated. It is composed of a silo body, a dust collector on the top of the silo, a steel ladder, a guardrail, a decompression cap, a gate door and other components. The material feeding and discharging can be automatically controlled through the set high and low material level gauges. It also has the characteristics of beautiful appearance, solid structure, windproof and other features. In order to ensure the qualified product rate of pipe forming, it should be considered that the volume of the finished product silo should have a certain margin. Generally, it should not be less than 12 hours. In addition, the finished product silo is designed to adopt a homogenized structure to ensure that the materials do not segregate and stratify. 6. The dust removal system varies according to the use occasions. The dust collector models vary. It is recommended that the filter material of the dust collector be imported coating material. The pore size of the filter element is less than 0.5 microns. It is the most advanced filter material in the world. If you choose a sintered filter element filter, the service life can be extended to more than ten years without replacement. 7. Electrical system The electrical control system connects the entire set of equipment together. It is the guarantee for the long-term stable operation of the compounding line. The electrical control system designed by our company includes on-site operation cabinets and central control systems. It can realize the following functions. Automatic detection function: ●Automatically detect the operation of all motors during the production process, ●Automatically detect the in-position status of various types of switches and valves during the production process, ●Automatically detect the weight information of each packaging scale and ingredients during the production process, ●Automatically detect the display, record, and cumulative production volume during the production process. Control functions (the entire system realizes three-level control): ●Hard-hand operation of individual on-site switch buttons, ●Manual operation in the control room, ●PLC automatic control and keyboard and mouse control on the PC screen. Once the computer fails, it is necessary to ensure that the PLC is used to maintain production for a period of time until the computer fault is eliminated. Automatic alarm and interlock function ● Abnormal motor status alarm ● Abnormal valve position alarm ● Upper and lower limit alarms for process parameters, such as material level, weight, pressure, etc. ● Gating and interlock control of various valve positions ● Hierarchical alarm self-diagnosis function for important equipment such as high-cold mixer interlock control ● Detection of each equipment fault, indication, alarm management function ● Full Chinese visual display Machine interface ● Process flow chart. Display of the overall screen and sub-screens ● Control parameter trend graph ● Operation guidance ● Automatic production control curve ● Automatic collection and saving of data. And classification management. Automatic statistical processing of data ● Historical data management. Can print shift reports, daily reports, monthly reports and annual reports. As well as bar charts for senior leaders to consult. ●Automatic printing ●Safety. Confidential group management. Weighted operation ●Open structure. Expandable. Remote networking. The central control system is developed using configuration software. Full Chinese interface. Suitable for China's national conditions. 8. Auxiliary equipment Auxiliary equipment includes operating platform, screening machine, rotor diverter, switching valve, pipeline and other operating platforms. The operating platform adopts carbon steel assembly structure. It is easy to disassemble and facilitate transportation. The pipelines include compressed air pipelines for warehouse pumps and material transportation pipelines, as well as compressed air pipelines for control and dust removal air induction pipelines. The first two are made of stainless steel seamless pipes. The connections between pipelines and equipment use quick connectors to facilitate equipment maintenance. The control air line uses imported ABS plastic hoses, which are high in strength and not easy to break. The dust removal pipelines use steel wire hoses, which are beautiful and durable. The working principle of the screening machine: Materials enter from the feed port. Qualified materials are separated from unqualified materials through the screen. They are discharged from the two discharge ports respectively to achieve material screening. The rotor diverter is a single-channel pipeline reversing valve. It is used to switch the transport direction in the pneumatic conveying pipeline. It can switch the materials transported in one pipeline to another pipeline. It can also switch the materials transported in two pipelines to the same pipeline for transportation. The switching valve is a one-way pipeline reversing valve. It is used to switch the direction of material transportation. That is, the material transported in one pipeline is switched to another pipeline. The material transported in two pipelines can also be switched to the same pipeline one after another. The valve is a necessary equipment for the air flow feeding system and the plastic mixing line. The signal of the opening and closing of the feeding pipeline is transmitted to the control system by the travel switch. It is easy to observe and control. 9. Extruder feeding system The extruder feeding system can be composed of a vacuum feeder or a spring feeder. The vacuum feeder is composed of a hopper, a suction gun, a vortex fan, a pulse filter, a butterfly valve and a storage bin. Its rated feeding capacity is the largest. * * At 1500kg/h. The spring feeder is actually a rodless screw conveyor. It can achieve a certain degree of bending and is suitable for feeding the extruder. In summary, the UPVC automatic compounding system needs to determine specific plans based on different site conditions and different investment amounts.