Brief Discussion on Domestic Flour Milling Equipment

Discussion on domestic equipment for powder coatings manufacturing Ruan mengfa (Taizhou Kaidi chemical powder equipment Co., Ltd.) Abstract: from the aspects of design, manufacturing, material selection, heat treatment, marketing and after-sales service of powder manufacturing equipment, this paper discusses the current situation of China's powder manufacturing equipment industry, and puts forward good suggestions for industry construction With the development of powder coating industry, the domestic pulverizing equipment in China has developed from imitation and improvement to self-designed and specialized production The design and production of pulverizing equipment have made great progress At present, in addition to the early and a few large-scale pulverizers, they are basically using domestic pulverizing equipment There are nearly 20 professional manufacturers with complete production capacity, and the export volume of equipment is also increasing year by year With the deepening of China's political and economic system reform, the powder industry and its equipment manufacturing industry will achieve greater development Powder coating industry is a new industry For equipment manufacturers, people have put forward more and more, higher and higher requirements for a variety of single machine in-depth research Now, the awareness of environmental protection and product quality has been constantly improved, which has made the era of low demand, high price and high profit no longer exist, leaving us with fierce market competition However, at present, this kind of low price market competition is not conducive to the development of the enterprise itself The author holds the attitude of discussing with peers, and talks about our views on domestic pulverizing equipment in the way of throwing bricks and attracting jade 2 The design of any product can not be separated from the principle The design principle can only be realized if the reasonable structure and parameters are selected However, there are various design principles of the equipment, such as extruder At the beginning, a threaded screw was used to rotate in a smooth cylinder to achieve the purpose of mixing Later, there were damped, reciprocating, twin-screw, three screw and multi screw extruders, which is the result of selecting different structures for different design principles Whether the structure of a certain kind of equipment is superior or not is closely related to its design parameters If the center distance of twin-screw with the same appearance is different, different mixing effects and proportional productivity will be obtained The structural parameters of the extruder include the ratio of length to diameter, rotating speed, zone and its temperature control range, clearance, internal pressure, exhaust, and the residence time of materials in the inner cylinder of the extruder We found that the determination of equipment parameters is an organic whole and interrelated through the investigation and research of various models of various manufacturers For example, the design temperature value is related to the fit clearance, screw speed, heating and cooling method, processing medium type, internal cooling or not, and the position and depth of probe hole; the designed melting section temperature should make the fusible material melt rapidly, at least higher than the softening point; if the design temperature is lower, it means that the melting section of the screw barrel lags behind, which means that the length diameter ratio is smaller; involving temperature On the high side, the temperature of the feeding section will rise, resulting in insufficient feeding and even stop feeding We have done such tests on 58 machine: at the position of 100 ~ 200mm from the feeding port, the temperature value of every 30mm displacement changes to 5 ~ 10 ℃, so it is necessary to first determine the temperature and gradient distribution of the melting section, and then set the position of the measuring point, as well as the shape and arrangement of screw elements When the wear of the machine, that is, the gap increases, the conveying capacity decreases, the internal pressure also decreases, and the mixing effect becomes worse In general, the method of reducing the setting temperature of melting section is used to increase the feeding quantity and internal pressure At this time, the actual length diameter ratio becomes smaller, and the non threaded section in the melting section highlights the crushing effect of solid-state rolling, which not only increases the power consumption, but also accelerates the screw wear, making the whole machine in a bad state Our country's raw materials, technological level and tooling conditions are different from those of foreign countries, which requires us to design equipment according to the actual situation, either for foreign prototypes or for foreign information, and absorb them after digestion For example, ACM mill, the whole unit has three aspects in terms of structure and technology: first, temperature rise, second, sealing and third, wind power transmission In the conventional mechanical design, the temperature rise control is relatively high within 30-40 ℃, while the coating characteristic requires that the temperature rise should not be greater than 20 ℃, otherwise, normal production can not be guaranteed under the indoor temperature of 35-38 ℃ in summer, and we do not advocate that users install air conditioning or refrigeration equipment to transform conflicts In addition to the particularity of dust sealing, the sealing problem is also limited by temperature rise We have studied the grinding head separately It is found that the heat generated in the high-speed operation of the oil seal (fluororubber oil seal with high-speed resistance and small wear resistance) added to prevent leakage is still far greater than that generated in the material crushing Later, we used radial labyrinth and other structures, i.e using D-class precision bearings to make it operate normally Wind power transmission is the key point of grinding process The air volume and pressure should be determined reasonably, and then the fan power should be configured At present, the blower rather than induced draft fan is widely used In the whole process of air supply, the resistance coefficient of the pulse dedusting part is the largest, and it increases rapidly with the increase of the powder content of the filter bag At this time, the blower may be completely stuck without air We have done two kinds of tests, one is to use the conventional fan to draw in air from the cyclone separator and then blow it into the dust remover, the other is to design a new fan separately The former is very effective, but it is troublesome to clean the fan regularly; the latter is more effective, which not only improves the output (at this time, the air volume is the effective air volume, less affected by the external conditions, so the relative air volume is large), but also reduces the power consumption 3 The market demand of equipment manufacturing determines that the manufacturing of pulverizing equipment can not be large batch, only small batch, or even single piece and single set, but the processing accuracy of its components is particularly high It is difficult to guarantee the quality of the parts when they are processed on the conventional equipment Under the influence of large, small and whole system in the planned economy period, China's mechanical processing industry has not yet formed a pattern of socialized production Even though some enterprises have some high-grade processing equipment, it can not be effectively used for many reasons The author discusses the following three problems 3.1 at present, most of the manufacturers use 38CrMoAl as the main material of extruder We know that the extruder (especially the gear and shaft in the reducer transfer case) needs high strength and thick high hard wear-resistant layer, while the strength and wear resistance of 38crmoti or 30CrMnSi materials are not as good as those of 30crmnti or 30CrMnSi, and the latter is lower than the former in terms of price On the contrary, some hard rings of mechanical seals need to be made of nitrided antirust ferrous metal parts The gear ring and striking column of ACM mill bear the high-speed impact of powder during operation, which provides conditions for surface cold work hardening Therefore, we may choose materials sensitive to cold work hardening, so as to reduce heat treatment process and cost In our investigation, we also found that the hardness difference of the same screw mandrel of the domestic extruder is relatively large, generally about 20hb, and some even reach 50hb The cylindricity of the screw mandrel is generally large, and the greater the hardness difference is, the greater the value is, which indicates that the rough tempering is unqualified At the same time, the quenching and tempering of all these super long shafts are treated the same as that of the general quenching and tempering parts The box type electric furnace is used for heating, quenching and tempering, and the temperature is uneven Material selection and heat treatment shall be comprehensively considered according to the use requirements and technical characteristics of the parts If there are substitute materials and their processes, they shall also conform to the relevant national regulations 3.2 due to the different equipment conditions, producers' technical level and managers' abilities of each equipment manufacturer, there is no identical process and tooling, and the key is to ensure the quality For example, the classifier of ACM mill includes rough machining - Welding - finishing, as well as the whole forging rough machining - tempering - finishing and other processes In contrast, the latter is superior, but if the former has a very high level of welders, and there is a tire mold when welding, it can carry out stress relief annealing and balance treatment after welding, so as to ensure the quality The latter is divided into milling pin and wire cutting The surface roughness of WEDM is better than that of milling, and the shape and position tolerance and surface roughness of blade are one of the main factors that affect the particle size distribution of powder, so WEDM is better, but if the blade is milled and polished again, it may be better than WEDM Another example is the process of transfer shaft The first design is the coupling gear Under mutual interference, only 38CrMoAl nitriding parts can be used In fact, the deformation of workpieces after nitriding has been out of tolerance Therefore, the second design component is separated from the body, the gear and shaft are processed separately, and the material selection and technology are determined according to their respective requirements Therefore, the transfer shaft has 38CrMoAl nitriding, 20CrMnTi carburizing and quenching, 42CrMo nitriding and 30CrMnSi or 30crmnti carburizing and quenching, etc We found that the shaft retaining ring groove of the carburized part has fracture phenomenon The reason is that the process arrangement is improper: the retaining ring groove should be cut out after carburizing, and the tail end thread should also be processed after carburizing, otherwise the groove and thread will produce volume during carburizing Expansion and quenching produce great stress, which makes the ring groove fracture In addition, nitriding parts also have stress concentration phenomenon, but the degree is much lighter After nitriding, sharp edges are particularly vulnerable, and slag will fall off if there is a slight impact Therefore, the threaded parts and small-size splines of nitriding parts should be isolated from non nitriding As for the grinding cover, almost all manufacturers use castings, and the machining accuracy is guaranteed by the lathe workers, so its quality is not easy to be stable, and there are many human factors We used to use shallow drawing parts, and the die was welded into a grinding cover with internal cooling, which not only ensured the final accuracy, but also improved the structural design Whether there is tooling in the welding of guide vane and return ring, whether the quality of artificial arc welding is good or not, how to control the welding deformation, whether there is stress relief annealing before finishing and so on, all affect the precision of these workpieces, and it is these workpieces that determine the performance of the grinding In a word, a good design must be guaranteed by a reliable process and tooling, and a good process and tooling can only be used for a good design, otherwise it will only promote waste 3.3 due to the high technical content of the pulverizing equipment, many manufacturing links must be carried out in the assembly, otherwise the cost will be greatly increased At the same time, because of the high precision and difficulty of some parts, it is necessary to adopt the combined processing method, so the assembly is not only in the final process, but also in the processing of components or parts In the design of the extruder, in order to improve the performance of the equipment, the overlapping degree of the screw must be increased, which reduces the center distance of the gear In order to ensure the strength of the gear, it is necessary to use high-grade materials and increase the tooth width coefficient In the transfer case parts of the extruder, almost the best materials purchased in China (limited by batches) are used at present, so the tooth width coefficient is mostly higher than that of the push Recommend value In order to ensure the bearing capacity of the gear, measures such as trimming and matching must be taken, which increases the technical content of the assembly In the screw design, in order to improve the overall accuracy of the screw, it is the best to design the screw as a whole, which increases the difficulty in the processing, and also increases the difficulty in the assembly, because the joint part of the screw and the mixer, and the existence of its phase deviation, must be ensured through the matching research in the assembly In a word, the machining accuracy of parts is required to be high, but in fact, the qualification rate of key primary machining of each manufacturer is relatively low, so it is necessary to pass the