With the increasing demand for environmental protection and the demanding of saving energy and reducing consumption, the PVC plastic products processing industry, especially the PVC plastic pipe manufacturing enterprises, are gradually eliminating the traditional labor-intensive operations in the raw material supply upstream of the extrusion line , Instead of using a fully automated centralized feeding program.
In addition, in the raw material mixing process of the centralized feeding system, in order to ensure the mixing quality and mixing efficiency of PVC, calcium powder and recipe materials, it is generally desirable to add a certain proportion of the granules together for stirring.
As a result, PVC, light calcium, additive formulations, and plastic pellets will be included in the mix, and how to effectively deliver the mix and eventually distribute it to each extrusion line is often addressed The following five questions.
First, an effective solution to the long-distance transmission of powder plugging phenomenon
Material in the long distance of the delivery process, the most likely to cause congestion is the pipe corner, and, the material in the pipeline at high speed movement, the elbow at the greatest friction.In order to extend the life of the elbow, the general use of Special wear-resistant material, because of the wear-resistant material attached to the inner wall of the steel pipe, can further increase the resistance of the material in the pipeline.Universal plastic machine through continuous design and field testing, developed a smaller air consumption with spiral air propulsion Role of the 'booster' not only make the elbow material along the pipe wall to form a swirl, but also in time for the material to obtain secondary acceleration, so that not only reduces the transport of the phenomenon of pipe plugging, and reduce the powder 'Acceptance' in the 'gas separation' burden.
Second, design a suitable feed gas ratio
In a pneumatic conveying system, the design of a suitable 'material to gas ratio μ' (ie powder conveyed per cubic gas): μ = qws / (ρa * qva), where qws is the flow of powder (kg / h) , ρa is the density of the gas (kg / m3), qva is the gas flow (m3 / h). In general, the higher the value of μ, the amount of air consumed is small, the energy consumption per unit is low, However, if μ is too large, the pipeline is easy to block, so in the overall pipeline design and construction, reasonable pipeline size and reasonable curve structure design (to ensure that the pressure drop under the premise of wear ), A reasonable pipeline layout and quality control during the construction process is very important.Lian Plastic Machinery in the first point on the basis of the above advantages, combined with the plastic extrusion industry in recent years a large number of projects implemented and accumulated Valuable practical experience.
Third, through a variety of means to reduce the mixture 'layered'
For the delivery of several powder materials (PVC, light calcium and plastic particles) with large differences in density at the same time, it is the basis for ensuring the quality assurance of PVC plastic pipe production to minimize the "stratification" of the mixture during the transportation process. In general, there are several options:
It is well known that plastic or secondary granulated plastic particles are inevitably in direct contact with the air during the process of adding and transporting and can easily absorb the moisture in the air to become heavy. Starting with the material process, PVC, light calcium and formulation materials are mixed. Removing the mixer's dependence on the plastic particles due to the mixing quality and efficiency can greatly solve the 'stratification' problem of the mixed conveying. First, , How to improve the rapid heating problem of the mixing machine (in the hot mixing process, if more plastic granules are involved, it is easy to frictionally heat up each other), the heat mixer can be designed with active heating Auxiliary devices, and set up a special diversion device to increase the heating rate of mixed materials, shorten the heating time.Secondly, due to its light weight relative to PVC, in the hot mix process, a large number of light calcium in the hot mix paddle Under the action of the high-speed centrifugal force of the leaf, it is extremely easy to separate out and float at the top, causing the mixed quality to not meet the standard. How to solve this problem? By trying molding machine using a special formula, middle and lower blades, let alone try to 'escape' of the upper layer is formed of light calcium 'vortex' to return to the lower layer while stirring continuously, can greatly improve the quality of mixing.
◆ For several kinds of mixed powder with large difference in density, during conveying, try to adopt the form of "dense phase" for conveying, ie, when the two phases of gas and material flow in the pipe, the gas and material will be cut off Because of the pressure difference between the compressed air adjacent to the front and back of the material column, the material is forced to move by the movement of the static pressure difference, so that the greater the concentration of the material to be transported, The smaller the stratification;
◆ In the pumped storage bin, a 'homogenization silo' is set up. Its purpose is to make the mixed material transported by 'long distance' be relatively "stratified" and during the drop of the bunker, several materials Mix again to achieve the purpose of secondary mixing prior to dispensing to the extruder.
Fourth, the correct 'chain conveyor' approach
At the end of pneumatic conveying, what follows is a common chain conveyor: how to distribute the mix in an orderly fashion for the extruder hopper that requires the very end, according to the ' Quantity, but also the plastic particles more content of the final distribution of PVC mixture, we must deal with the following series of questions:
◆ Pipe chain 'off' problem: The mixture is driven by the chain drive sprocket chain, chain and then move the 'scraper' to move the material, because the mixture mixed with a large number of different shapes of plastic particles, Once the transported mixture is accumulated to a certain extent in the sprocket casing, the particulate material enters between the sprocket and the chain, causing the chain to unravel from the sprocket, which is a difficult problem to solve .
In the continuous optimization, Liansu machines designed a transmission box pile material automatically sent back to the main silo patented device can be very limited space, low energy consumption, maintenance-free, and easy to install the device to completely solve Chain out of the chain and the problem of easy to pull loose.
◆ Mixture, due to the high content of light calcium, poor mobility of light calcium easily lead to a series of 'bridging' problem: It is no exaggeration to say that PVC mixture if the content of light calcium to a certain extent, arrived in the mix The tube link to warehouse to the extrusion station allocation, the following links will cause the bridge:
(1) Pipeline operation continued to squeeze the powder out of the hopper, resulting in further deterioration of the fluidity of the powder;
② tube running, even at the same speed conditions, the chain plate feeding instability (because of the uneven feeding tube feeding);
Extruder hopper poor air permeability;
④ Extruded to the mouth of the magnetic frame on the powder secondary barrier;
⑤ extruder feed screw inlet neck 'neck' effect.
For the above, Liansu machine solutions are:
① extruder hopper 'always dissatisfied with the expected' approach to feed, to avoid the extrusion of powder in the extrusion hopper and hopper to ensure high permeability;
② in the chain into the mouth with quantitative feeding methods to ensure that the chain plate feeding uniformity;
③ years of servo motor design experience, the design of high through the 'strong magnetic flux' magnetic frame, which is the patented product of plastic machinery;
④ combined with more than 20 years of extruder design experience, designed for high calcium content of the special screw extruder screw extruder, a large extent, solve the material out of the mouth hopper neck card.
PVC powder central feed system flow diagram
Fifth, the meaning of system integration
PVC powder centralized feeding system and excellent electronic control system is an essential guarantee: Liansu machine system, from the raw material feeding station, to the delivery of raw materials, metering, mixing, secondary feed mixture, chain Of the redistribution of the mixture, each node, are 'net in the end', and finally focus on the central control room centralized monitoring (remote local control), and focus on the status of each actuator display, fault alarm and report archiving capabilities In addition, Liansu machines can follow the customer's needs, the client's close attention to the operation and monitoring screen, WEB pages published in the form, the customer can use any mobile phone mobile terminal can monitor the status of centralized feeding system.
The contents of the above five points are based on the experience of many years of plastic pipe equipment manufacturing by Liansu Machinery Company and the experience gained from the project of many centralized supply systems.