Application of single-screw (four-lobe) reciprocating extruder in the production of high-performance coatings

< br / > the useof single screw (four petals) extrude in the manufacturing process for powder coatings < br / > Zou Lijian (Yantai Qitong Chemical Equipment Co., Ltd.) < br / > Abstract: extruder is the main equipment for powder coating productionThis paper discusses the performance and structural characteristics of single screw (four lobe) reciprocating machine, and compares it with common single screw machine and twin screw machine< br / > < br / > 1 preface < br / > extruder plays an extremely important role in the production of powderOne of the main machines in the production line of powder coating is the key equipment for the uniform distribution of each component of powder coatingWith the development of coating industry, the production of some special powder coatings has put forward higher requirements for extrusion equipmentThese requirements include: (1) shortening extrusion process and residence time; (2) little or no material remains in the extrusion process; (3) high temperature control accuracy; (4) good dispersion effect; (5) easy cleaning machine; (6) low energy consumption; (7) high reliability and high lifeIn order to meet the above requirements, the mill manufacturers have developed a single screw (four disc) reciprocating extruder, which is suitable for the above requirements, by studying the advanced technology abroad and combining with the national conditionsThis kind of extruder is made by improving the design and manufacture of screw and barrel on the basis of common single screw reciprocating extruderIts overall performance is superior to that of common single screw extruder; its extrusion performance is obviously superior to that of twin screw extruder; especially in the field of high-grade and high-performance powder production, single screw (four lobe) reciprocating extruder is the first choice and irreplaceable modelIn order to promote the application of this machine in powder production, the following issues related to this machine are discussed< br / > < br / > 2 the development of single screw reciprocating extruder < br / > it has been nearly 20 years since the single screw reciprocating extruder (mainly 46 models) was introduced from abroad and used in powder production in 1980sIn the past two decades, China's equipment has made great progress in introduction, digestion, development and improvementAt the beginning of its development, 46 model was taken as the research object, and necessary improvements were made on the basis of clarifying its working principle and structural mechanism30, 46, 60, 70, 100 models have been launched to meet the needs of the majority of usersThe main pulverizing performance of the domestic machine is similar to that of the imported machine, but the price is only 1 / 8 ~ 1 / 10 of that of the imported machine, which greatly saves the equipment investment and foreign exchangeIn order to adapt to the continuous development of coating production requirements, foreign equipment and domestic equipment are constantly improving technologyThe improvement of single screw reciprocating Extruder mainly focuses on the aspects of increasing production, improving working reliability and dispersion The essential difference between the improved single screw extruder and the former lies in the structure and number of threads and the arrangement of pins, so we call it the single screw (four disc) reciprocating extruder It has the characteristics of high output, strong bearing capacity and strong dispersion This model was launched in 2002, almost at the same time as the same kind of foreign products The model has been granted two patents by the State Intellectual Property Office < br / > < br / > 3 Comparison of structure and performance between new single screw (four disc) and common single screw (three disc) reciprocating extruder < br / > 3.1 structure comparison < br / > arrangement and structure comparison of thread and pin are shown in Figure 1 < br / > Figure 1 shows the difference between the two: < br / > (1) the number of threads is different, the density is different < br / > the number of thread lobes distributed on a full pitch of 3600 for the rectangular intermittent thread lobes of the two is different: the new machine has four lobes and the common machine has three lobes The arrangement of new machines is sparse and that of common machines is dense Therefore, we call the new single screw reciprocating extruder the single screw (four disc) reciprocating extruder (four disc extruder for short) < br / > (2) the number of pin rows and density are different < br / > the four disc machine has four rows of pins with sparse spacing The common machine has three rows of pins with dense spacing < br / > (3) different thread disc sizes and pitches < br / > four disc machines have larger thread disc sizes, stronger threads and larger pitches Its four lobes interlace in the axial direction to form a closed thread group, so it has a stronger pushing force < br / > (4) the pin diameter is different < br / > the pin of four disc extruder is thicker and stronger, which can meet the stress requirements of large output extruder < br / > (5) the movement track of the pin relative to the thread is the same, but the track occupation rate is different < br / > the proportion of the pin occupying the thread space of the four disc machine is higher than that of the ordinary machine by 96%, which is 30% higher than that of the ordinary machine, and can be more effectively stirred and dispersed inside the material < br / > (6) the shear area of the pin is different from that of the thread flap < br / > under the same screw diameter and screw sleeve length, the shear area of the four Flap machine is 54% higher than that of the common machine, in other words, the shear effect of the four Flap machine is improved synchronously < br / > < br / > < br / > < br / > industrial production comparison between single screw (four disc) extruder and twin screw extruder The sampling is as follows < br / > Diameter: 60mm screw speed: 500r / min < br / > (4) production conditions < br / > - power supply voltage: 370v < br / > - room temperature: 22 ℃ < br / > - cooling water temperature: 29 ℃ < br / > - materials used: common flat powder of the same batch < br / > - materials input: 2.5t (twin screw), 2T (single screw); < br / > (5) main process parameters < br / > [upload = GIF] / powder / UploadFile / 20049219105310077 GIF [/ upload < br / >] < br/ >(7) Results analysis < br / > - under the same water-cooling condition, the temperature of cylinder and discharge of twin-screw machine is 15 ~ 25 ℃ higher than that of single screw machine due to the friction heat during operation < br / > < br / > < br / > < br / > (8) sampling comparison conclusion < br / > - a large amount of friction heat produced by twin-screw extruder in the extrusion process makes the material temperature rise, so it is necessary to use water cooling to reduce the temperature to avoid material quality change Therefore, the cooling water temperature of large capacity twin-screw extruder should be below 15 ℃, and that of single screw extruder should be below 30 ℃ < br / > < br / > < br / > < br / > < br / > in terms of the requirements of extrusion equipment for the production of high-performance powder coating, the competitive advantages of the two extruders are as follows < br / > < br / > Under the action of high temperature, the residual material will change qualitatively, which will pollute the material after falling off The residual tendency of material is directly related to the screw and barrel structure of extruder For single screw extruders and twin screw extruders, the deposition tendency of the outer circle of the screw and the inner wall of the barrel is approximately the same, and the deposition tendency increases when the gap between the screw and the barrel increases For both of them, the deposition tendency of the thread part is not much different - the material on the surface of the opposite thread is cleaned by the thread in the two-screw machine, and the material on the side and bottom surface of the thread is cleaned by the pin for the single thread < br / > however, the feeding and kneading of single screw extruder is completed by a screw pin system; each screw disc is composed of two left-handed and two right-handed surfaces as long as the screw rotating materials are always in motion, it is not easy to produce adhesion Feeding and kneading of twin screw extruder are two different parts The feeding part is composed of thread group, which has the function of anti deposition material The other kneading part is composed of kneading blocks with the tendency of depositing materials Each kneading block has two ends perpendicular to the axis The materials adhered on the end cannot be eliminated by the rotation of the screw, but can only be cut by the corresponding kneading block of the other screw Therefore, a certain amount of material must be deposited on the end face The amount of deposition is related to the manufacturing accuracy, wear degree and design requirements of kneading block In addition, when the shape of kneading block is not well co strangled (large meshing clearance), the material is easy to deposit locally < br / > if the deposition tendency is considered from the contact area between the processing element and the material, the deposition tendency of the twin-screw machine is far greater than that of the single screw machine Compared with the single twin screw extruder with similar output, the contact area of the twin screw extruder is 2.5 times of that of the single screw extruder It can be seen that the material residue tendency of the twin screw extruder is larger than that of the single screw extruder < br / > < br / > 5.3 temperature control accuracy < br / > temperature control accuracy is an important guarantee for the production of high-performance powder coatings (temperature sensitivity, impurity content, curing time) The characteristics of the friction heat of the twin-screw machine make it difficult to control the temperature regulating system, which is mainly manifested as: large inertia, low precision, high requirements for operating conditions, especially for the extruder with high speed and large output In the production process, the temperature control is often to find a balance point of the maximum allowable temperature among the factors of material formula, output and cooling water temperature, which is difficult to adjust the temperature In production, some uncertain factors such as short-time power failure, instantaneous unsmooth cutting, fluctuation of water system and power supply voltage may cause sudden change of material temperature, resulting in sudden shutdown and overload Restarting is often time-consuming and laborious < br / > the single screw extruder has the characteristics of low friction heat The temperature of the barrel can be controlled at ± 1 ℃ with the intelligent temperature controller adjusted by PID By adjusting the cooling water volume, the temperature of the barrel can be lowered to below 110 ℃ even when the cooling water temperature is 30 ℃ < br / > the temperature control system of single screw extruder can better meet the production requirements of thermosensitive coatings such as electronic packaging materials < br / > The extruder with good dispersity can obtain higher micro homogenization in a shorter treatment process The single screw extruder mainly relies on several rows of dozens of pins deep into the material and the relative movement of the material and the thread flap to stir and shear it to complete the dispersion work The Twin-Screw Extruder mainly relies on dozens of