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

The use of single screw (four pets) extrude in the manufacturing process for powder coatings This 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 The extruder plays an important role in the production of powder It is one of the main machines in the production line of powder coating, which is the key equipment for the uniform distribution of each component of powder coating With the development of coating industry, the production of some powder coatings with special properties puts forward higher requirements for extrusion equipment These 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 life In 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 conditions This kind of extruder is made by improving the design and manufacture of screw and barrel on the basis of common single screw reciprocating extruder Its 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 model In order to promote the application of this machine in powder production, the following issues related to this machine are discussed The development of single screw reciprocating extruder has been nearly 20 years since it was imported from abroad and used in powder production in 1980s In the past two decades, China's equipment has made great progress in introduction, digestion, development and improvement At 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 mechanism 30, 46, 60, 70, 100 models have been launched to meet the needs of the majority of users The 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 equipment investment and foreign exchange In order to adapt to the continuous development of coating production requirements, foreign equipment and domestic equipment are constantly improving technology The 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 3 Comparison of structure and performance between new single screw (four disc) and common single screw (three disc) reciprocating extruder 3.1 comparison of structure, arrangement and structure of screw and pin see Figure 1 [upload = JPG] / powder / UploadFile / 200492197013431 JPG [/ upload] Figure 1A arrangement of new (four disc) single screw extruder [upload = GIF] / powder / UploadFile / 200492198223890 GIF [/ upload] Figure 1b arrangement of common (three disc) single screw extruder Figure 1 structure comparison between New (four disc) single screw extruder and common (three disc) single screw extruder It can be seen from Figure 1 that the difference between the two lies in: (1) the number of rectangular intermittent thread lobes with different thread number and density is different The number of thread lobes distributed on a full pitch within 3600 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) (2) There are four rows of pins with different row number and density, and the spacing is sparse The common machine has three rows of pins with dense spacing (3) The size of the disc is bigger, the thread is stronger and the pitch is bigger Its four lobes interlace in the axial direction to form a closed thread group, so it has a stronger pushing force (4) The bigger and stronger pin of four disc extruder with different pin diameter can meet the stress requirements of large output extruder (5) The movement track of pin relative to thread is the same, but the track occupation rate is different The ratio of pin occupation of thread space of four lobe machine is higher than that of common machine by 96%, which is 30% higher than that of common machine It can be more effective in-depth mixing and dispersion of materials (6) Under the same screw diameter and screw sleeve length, the shear area of the four disc machine is 54% higher than that of the common machine, in other words, the shear effect of the four disc machine is improved synchronously 3.2 performance comparison: compared with the general machine, the comprehensive performance of the four valve machine is improved in the following two aspects: under the same dispersion effect, the output of the four valve machine can be doubled - four Flap machine has lower material residue and higher cleaning convenience 4 Industrial production comparison of single screw (four disc) extruder and twin screw extruder in order to make a list of the working characteristics of the screw (four disc) extruder from theory to practice and provide basis for the selection of the user's equipment, we choose the customers of both single screw and twin screw extruder to carry out the sampling comparative analysis of the industrial production and find out the difference between them The sampling is as follows (1) Production location: Shanghai Caiyun powder Co., Ltd (2) production date: April 23-24, 2003 (3) extruder and main technical parameters - jd70d single screw (four disc) extruder host power: 45KW length diameter ratio: 11:1 screw diameter: 70mm screw speed: 500r / min - js60f twin screw extruder host power: 45KW length diameter ratio: 16:1 screw diameter: 60mm Screw speed: 500r / min (4) production conditions - power supply voltage: 370v - room temperature: 22 ℃ - cooling water temperature: 29 ℃ - materials used: the same batch of ordinary flat powder - material input: 2.5t (twin screw), 2T (single screw); (5) main process parameters [upload = GIF] / powder / UploadFile / 20049219105310077 GIF [/ upload] (7) result analysis - Under the same water-cooling condition, the temperature of the cylinder and discharge of the twin-screw machine is 15-25 ℃ higher than that of the single screw machine due to the friction heat - similar process parameters, the output of single screw machine is 88kg / h higher than that of double screw machine - for the main motor with the same power and specification, the extra power consumption of twin-screw machine is 7.5kW - for the same material, the effect of twin screw machine is worse than that of single screw machine (8) Sampling and comparison conclusion: a large amount of friction heat produced by twin-screw extruder makes the material temperature rise Water cooling must be used to reduce the temperature so as to avoid material quality change Therefore, the cooling water temperature of large-scale twin-screw extruder should be below 15 ℃, and that of single screw extruder should be below 30 ℃ - the pulverizing performance of single screw extruder is better than that of twin screw extruder - under the same output, the power saving of single screw machine is 1 / 3 that of double screw machine - the discharge temperature of single screw machine is 15 ~ 20 ℃ lower than that of twin screw machine, which can better meet the processing requirements of high-grade powder coating 5 Comparison of production suitability of high performance and special performance powder coating In terms of the requirements for extrusion equipment in the production of high-performance powder coating, the competitive advantages of the two extruders are as follows 5.1 the extrusion process and residence time can be seen from the above: under the premise of similar process parameters and mixing effect, the screw of the twin-screw machine is longer, and the single screw is about 1 / 3 shorter than it, which shows that the processing process and residence time of the single screw machine are shorter, which can effectively prevent the deterioration of materials 5.2 the phenomenon that the material remains in the extrusion process tend to stick and deposit in a certain part of the screw sleeve and barrel is called material residue 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 However, the feeding and kneading of the 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 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 residual tendency of the twin-screw extruder is larger than that of the single screw extruder 5.3 temperature control accuracy is an important guarantee for the production of high-performance powder coating (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 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 ℃ The temperature control system of single screw extruder can better meet the production requirements of thermosensitive coatings such as electronic packaging materials 5.4 the dispersibility of the dispersive extruder refers to the property that the material is sheared, extruded, stirred and dispersed by the processing parts when passing through the extruder to achieve the degree of micro homogenization 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 Twin Screw Extruder mainly relies on dozens of kneading blocks to extrude and shear materials to complete the dispersion work The dispersing mechanism and intensity of the two are different, and the dispersing effect is obviously different stay