Discussion on the centralized feeding system of PV

Talking about the solution of centralized feeding system for PVC powder and high light calcium filler

with the increasing requirements for environmental protection and the stringent requirements for energy conservation and consumption reduction, in the PVC plastic products processing industry, especially the PVC plastic pipe production enterprises, in the raw material supply upstream of the extrusion production line, the traditional labor-intensive operation is gradually being eliminated and the fully automatic centralized feeding scheme is being adopted

in the actual production process of PVC pipes, generally speaking, in addition to PVC resin powder, a certain proportion of calcium carbonate should be added to the material formula, especially for drainage pipes, the content of calcium powder will be relatively high. In order to ensure the service life of the extrusion screw, the manufacturer will try to choose light calcium with very light density to reduce the wear of calcium powder on the screw

in addition, in the raw material mixing process in the centralized feeding system, in order to ensure the mixing quality and mixing efficiency of PVC, calcium powder and formula materials, it is generally hoped to add a certain proportion of granular materials for mixing

in this way, the mixture will include PVC, light calcium, auxiliary formula and plastic particles. How to effectively transport this mixture and finally smoothly distribute it to each extrusion line usually needs to solve the following five problems

first, it can effectively solve the pipe blockage phenomenon of long-distance transportation of powder.

in the process of long-distance transportation of materials, the most likely place to cause blockage is the turning of the pipeline, and when the materials move at high speed in the transportation pipeline, the friction at the elbow is the largest. In order to prolong the service life of elbows, special wear-resistant materials are generally used, because wear-resistant materials are attached to the inner wall of steel pipes, which can further increase the resistance of materials in the pipeline and jointly build the Silk Road Economic Belt. After continuous design and field testing, the Liansu machine has developed a "booster" with small air consumption and spiral air propulsion. It not only makes the materials passing through the elbow form swirling flow along the inner wall of the pipe, but also makes the materials obtain secondary acceleration in time. In this way, it not only reduces the pipe blockage phenomenon in the transportation process, but also reduces the burden of "material gas separation" in the powder "receiving bin"

second, design the appropriate material gas ratio

in the pneumatic conveying system, the appropriate "material gas ratio" μ” (i.e. powder conveyed per cubic meter of gas) design: μ= qws/（ ρ A*qva), where QWs is the flow rate of powder (kg/h), ρ A is the density of gas (kg/m3), qva is the flow of gas (m3/h). Generally speaking, μ The higher the design value is, the smaller the air consumption is, the lower the unit energy consumption is, and the conveying capacity of powder is also increased. However, if μ If the pipeline is too large, it is easy to block. Therefore, in the overall pipeline design and construction, reasonable pipeline diameter, reasonable bend structure design (to ensure the minimization of pressure drop under the premise of wear resistance), reasonable pipeline layout and quality monitoring in the construction process are very important. Based on the advantages of the first point above, combined with the implementation of many projects in the plastic extrusion industry in recent years, Liansu machine has accumulated valuable practical experience

III. reduce the "delamination" of the mixture through various means

for the simultaneous transportation of several powder materials with large density differences (PVC, light calcium and plastic particles), how to minimize the "delamination" of the mixture in the transportation process is the basis of ensuring the production quality of PVC plastic pipes. Generally speaking, there are the following schemes:

◆ as we all know, plastic particles that break plastic or secondary granulation inevitably come into direct contact with the air in the process of adding and conveying, and it is easy to absorb moisture in the air and become "heavy". If we start with the mixing process at the front end of the conveying, just mix PVC, light calcium and formula materials, and remove the dependence of the mixer on plastic particles because of the mixing quality and efficiency, we can greatly solve the "stratification" problem of mixing and conveying: first, for the absence of the intervention of plastic particles, How to improve the rapid temperature rise of the mixer (in the process of hot mixing, if there are more plastic particles involved, it is easy to friction with each other for temperature rise), an auxiliary device with active heating can be designed in the cylinder block of the hot mixer, and a special guide device can be set to improve the temperature rise speed of the mixed materials and shorten the temperature rise time. Secondly, due to its light weight relative to PVC, in the process of hot mixing, a large amount of light calcium is extremely easy to separate out alone and float on the top under the high-speed centrifugal force of the hot mixing blade, resulting in the mixing quality not up to standard. How to solve this problem? Through continuous attempts, the Liansu machine adopts special upper, middle and lower blades to try to make the upper light calcium that "escaped" alone form a "vortex" and constantly return to the lower layer for mixing, which can greatly improve the quality of mixing

◆ for the mixed transportation of several powder materials with large density differences, try to adopt the form of "dense phase" in the transportation process, that is, when the "gas and material" two phases flow in the pipeline, the gas and material are separated and transported, so that the mixed materials fill the pipeline in a columnar interval. Due to the pressure difference between the adjacent compressed air in front of and behind the material column, the materials are forced to move by the movement of the static pressure difference. In this way, the greater the conveying concentration of materials, the smaller the stratification between them

◆ set up a "homogenizing silo" in the receiving silo of pneumatic conveying, which is used to force several materials to mix again in the falling process of the silo under the condition of relative "stratification" of the mixed materials transported through "long distance", so as to achieve the purpose of secondary mixing before being distributed to the extruder

fourth, the correct "pipe chain conveying" method

at the end of pneumatic conveying, followed by the common pipe chain conveying: how to distribute the mixture orderly to the extruder hopper at the end of demand according to the distribution principle of "take what you need servo motor drive ball screw to apply experimental force", for the final distribution of PVC mixture with high light calcium filling and high plastic particle content, We must deal with the following series of problems:

◆ the problem of "chain disconnection" of the pipe chain: the mixture is driven by the transmission sprocket of the pipe chain, and then the chain drives the "scraper" to move the material, because the mixture is mixed with a large number of plastic particles of different shapes. Once the transported mixture forms a certain degree of accumulation in the sprocket transmission box, the granular material will enter between the sprocket and the chain, so, It is difficult to solve the problem that the chain inevitably breaks away from the sprocket

in continuous optimization, Liansu machine has designed a patented device that automatically sends the accumulated materials of the transmission box back to the main material bin. It can completely solve the problems of chain falling and easy marathon in a very limited space, with extremely low energy consumption, maintenance free and simple installation

◆ in the mixture, due to the high content of light calcium, the poor fluidity of light calcium is easy to cause a series of "bridging" problems: it is no exaggeration to say that green environmental protection has become the trend. If the content of light calcium in PVC mixture is high to a certain extent, the following links will cause bridging in the distribution from the mixture to the pipe link receiving bin to the extruder table:

① the pipe chain operation continues to squeeze the powder in the extrusion hopper, Further deterioration of powder fluidity

② during the operation of the pipe chain, even at the same speed, the feeding amount of the chain plate is unstable (because the feeding at the feeding port of the pipe chain is uneven)

③ poor permeability of extruder hopper

④ the secondary barrier of the magnetic frame at the extrusion feeding port to the powder

⑤ the "neck effect" of the feed screw inlet of the extruder

in view of the above, the solution of the United plastic machine is:

① the feeding method of "always insufficient material" in the hopper of the extruder, so as to avoid the extrusion of powder in the extrusion hopper and ensure the high permeability of the hopper

② adopt the quantitative feeding method at the feeding port of the pipe chain to ensure the uniform feeding of the pipe chain plate

③ combined with many years of design experience of servo motor, a "strong magnetic flux" magnetic frame with high trafficability is designed, which is also a patented product of Liansu machine

④ combined with more than 20 years of experience in extruder design, a special extruder screw feeder for high calcium content is designed to solve the problem of jam at the neck of the extrusion hopper to a great extent

pvc powder central feeding system flow diagram

v. the significance of system integration

pvc powder centralized feeding system and excellent electric control system are essential guarantees: the Liansu machine system, from the feeding station of raw materials to the transportation, metering, mixing and mixing of raw materials, the secondary transportation of mixtures, and the redistribution of mixtures in pipe chains, is "one to the end" at every node, Finally, the curing of the test specimens in the curing pool. The curing of the test specimens requires that each curing pool only cures the cement test specimens of the same type. It can be centrally monitored in the central control room (or remotely controlled locally), and centralizes the status display, fault alarm and report filing functions of each actuator. Moreover, Liansu machine can release the operation and monitoring pictures that customers pay close attention to in the form of web pages according to the needs of customers. Customers can monitor the status of the centralized feeding system with the help of any mobile terminal

the above five points are the practical experience summarized by Liansu machinery company based on years of experience in manufacturing plastic pipe equipment and combined with the project experience of many centralized feeding systems, which we will share with you