Overview of powder coating production equipment

0 The manufacturing
coatings is based on equipment widely used in the plastics and micro-powder industry. As a result, powder coating plants are designed to be completely different from ordinary liquid coatings. The production of powder coatings includes the connection of different sections of work in a reasonable order, including the preparation time for the premixed steps, the preparation time for the main equipment, and the quality control
the
. Often smaller powder coating plants can produce processes that are not continuous, and for powder coatings plants with higher production capacity, individual processes can often be assembled into a continuous production process.
1 Premixed
diagram depicts the design schematic of continuous production of powder coatings in modern plants. The arrangement of equipment for the production of powders can vary depending on the production line capacity and the type of product. Premixing the various parts of powder coating before hot melt mixing is an important process that can never be ignored and plays a decisive role in the performance of powder coating. Especially those additives and coloring pigments that are used in small quantities, if premixed adequately, can not be compensated during the second stage of hot melt extrusion. Hot melt extrusion is a continuous process, and ensuring an equal feeding speed throughout the extrusion process is a prerequisite for ensuring product quality.
If the premix in the first step is not sufficient, the composition of the coating film will be uneven, resulting in poor leveling of the coating surface, poor mechanical performance, uneven color of the coating surface, low gloss, surface defects and so on. Generally speaking, the raw materials of powder coatings are solid, and it is obviously not possible to achieve the best results in the premix phase only if the various ingredients that need to be mixed have the same size. Because the particle size of the resin and pigment is several orders of magnitude, a small amount of additives, such as leveling agents or catalyst additions, are overcome by using mastering techniques.
to prevent the substing from being too crushed, it is important to take appropriate mixing time. The ideal granularity of the premixed base should be at 2? At 4 m m, if the particles are too small, they tend to flow during feeding during the extruse process, and if the particles are too large, additional power is required to allow the premix to flow in the mixer. Mixers are selected on the basis of mixing strength, color change frequency and whether the operating process is continuous or intermittent, as the cleaning time of the replacement variety is critical to the entire production operation. As a result, the variety of formulations produced by powder coating plants can also affect the selection of mixers. For production lines that change color frequently, high-speed premixers or container premixers should be preferred, with the advantage that they are easy to clean and have a short mixing time of only 2-3 min;
addition to the operating process, in order to create a consistent performance coating film or the loss of the mixing equipment itself, special attention should be paid to the structure of the mixer, the mixer needs to be properly constructed. Especially during the operation of the mixer, it may be stopped for sudden reasons or deliberately to check the operation process. In this case, the drive must be able to withstand the most basic requirement of repeated starting at full load.
is the DC motor, which provides 2 to 3 times the additional torque compared to normal start-up. When this drive does not meet the requirements, drive devices with different DC can be used (e.g. sliding rings, liquid couplings and centrifugal clutches or indirect devices transmitted with V-bands).
, the high-speed mixer has several advantages over the slow-moving mixer and becomes a better mixing equipment in powder coating manufacturing.
feature of this machine is that it can be mixed very highly in a very short mixing time, and even a small amount of coloring pigment can be easily premixed and evenly dispersed. Because the rapid mixing effect is conducive to full color display, in order to obtain elegant and beautiful color, can reduce the amount of pigment used, so as to achieve the purpose of saving. Small amounts of liquid can also be evenly dispersed, so there is no need to spend expensive money on liquid additives to make master ingredients. In summary, the benefits of quick cleaning, coupled with several mixing containers to share a mixing head, and a short mixing time eliminate frequent color changes at least during the premix phase.
2 molten extrusion
powder coatings consists of several steps and is done in separate equipment. In its step production, the substation and curing agent (not necessarily there) are melted and mixed at the molecular level, the pigment mass is broken into primitive particles and, together with the additive, is evenly dispersed in the molten substation/curing agent mixture, while the surface of the pigment particle is moistened by the molten base material. In principle, there are 3 types of machines that can be used for hot melt extruse. Although it is also available with a double-roll grinder like the Z-blade kneading machine and heating, the main equipment is the extruder.
are often used in the production of powder coating machinery and equipment: single screw extruder, twin screw extruder, planetary screw extruder. All 3 extruders can be operated without pressure and have some openings on the walls of their screws for filling. Through the characteristics of the change characterization system of screw design, the pinch block of transmission, neutral and reverse transmission is applied in the twin screw extruder, the transfer, semi-transmission or various pinch structures (changing the number of pinch blocks, the gap between pinch blocks and pins on the wall) are used in the co-pinching machine, or the continuous rotation process is used in the planetary screw extruder to affect the mixing and pinching operation.
depending on the type of product being extruded, there are two ways to heat the screw and the screw. A system consists of water, which circulates on the inside of the screw and whose temperature is controlled by a separate instrument. The other is a joint system of electric heating and cooling water that directly controls the temperature in the sleeve. In the recently produced extruder, one or more pinch pins are replaced with the thermocouples with the same shape as the pinch pins to control the internal processing temperature more precisely.
, energy is needed to break down the polygroups formed by subdivision pigments and fillers when extruding. However, energy formed by high shock pressure can cause local overheating and cure powder coatings to form gel particles. To avoid these effects, replace high shock energy with "weakened" forces, providing moderate energy that can be safely treated even for fast extrusion or low-temperature curing powder coatings. This so-called "micromix" effect provides uniformity at certain molecular levels, which is important for powder coating uniform curing and thin coating applications.
the insemination layer formed in the barrel wall will greatly reduce the heat transmission efficiency, but the self-cleaning and precise control gap tolerances of the new generation of extruders can effectively reduce the formation of the insular layer. In addition, the thickness of the sleeve sleeve and screw cooling center is kept to a minimum, reducing the resistance to heat transmission. It is important to control the reactivity of the thermoo-solid powder coating during extrusion. Therefore, it is necessary to ensure short stay, narrow allocation of dwell time and high self-cleaning efficiency. Manufacturers of twin screw extruders have made a number of modifications to the design to meet the requirements of modern thermosoend powder coatings to improve the mixing effect of this machine.
General extruder manufacturers give their own extruders economic and technical advantages: (1) for single screw extruders: good temperature control and high speed;
3 Fine
is finely crushed after the hot melt is extruded. Powder coating manufacturers use different types of shredders to keep the coating's granularity to the desired range, all of which are manufactured using the grinding principle. In this case, the decrease in particle size is caused by a collision or collision between solid particles or sheets of wood and the surface of the grinder. Contemporary crushing systems are supplied in packages, including granular graders and dust removers. Since the 1960s, grinder manufacturers have focused on developing complete sets of equipment that can be shredded and graded together to simplify plant design. In 1962, "Mikro ACM" appeared on the market as the first air grading mill, and it is suitable for all industrial products to reduce particle size requirements, including, of course, powder coatings. The most eye-catching is the simple and clear component arrangement of the A C M, which combines impact crushing with complete dynamic grading to provide the perfect solution for fine and ultra-fine grinding standards and medium standards of products.
A C M its operating principle is as follows: by pneumatic action to add the product to the grinding, relying on the material particles and rotating grinding surface or fixed bushing collision can reduce particle size. When the grading wheel impact speed reaches 140 m/s, the particle size can reach d 97 x 10 μ m. The air used for cooling, transmission and grading enters the grinder through a downstream blower and then passes through the blades of the ring to take away the metered material. A typical feature of "M i k r oACM" is its complete dynamics rating.
/product mixture is evenly dispersed by the blades into the rotating grader. Due to the opposite effect of 2 and the different mass of the material particles, they are divided into coarse particles and fine particles in the grader. High-mass particles are thrown by centrifugal forces, and substandard particles are returned to the milling area. The fine powder is taken away by the air and passed through the grader to the exit. Figure 2 shows a diagram of the "M i k r o A C M" grinding. The cut point can be changed by adjusting the speed of the grader, even during shredding operations. "M i k r o A C M" can be designed differently. Many important features have been optimized during decades of development and improvement.
feature of the A C M grader is that the drive shafts of the grader and grinding disc are coaxial. The compact rotor consists of the following sections: grader, shredding disc, bearing and V-belt pulley. Drive bearings have a reliable sealing system that prevents product penetration while also avoiding lubricant leakage, even during prolonged operation.
4 Powder collection and dust removal
usually using a side filter or preferring to use a cyclone separator with a side filter to collect fine powder for the air graded outlet. Several typical designs for the last part of the powder production process are shown in Figure 3. Figure 3 (a) represents a cyclone-free fine powder pre-separator, which is the most economical design from an investment and maintenance point of view, but has little practical use value.
, the airflow fine powder pre-separator with cyclone separator is shown in Figure 3 (b). Cyclone separator has become the basic component of modern powder coating crushing process. Compared with the filter can be obvious cleaning, low cost, even if the frequent color change system, can be calmly coped with. However, with the increase of cyclone separator size, its collection efficiency decreases.
is relatively inefficient for Cyclone separators with a capacity greater than 1,000 k g/h. The dust collection device for powder coatings depends on the output of the plant and the type and color of the powder coating. Tail dust filters can also improve the reliability of crushing and grading operations and improve pollution control with little repair work.
5 Multi-Cyclone Powder Recovery System
Due to various reasons of electrostectrectrectrative spraying of powder coatings, there will always be some powders that are not fully utilized, and a multi-cyclone powder recovery system has been developed to solve this problem. Its function is to collect the powder dropped during the spraying process, separate it into available powder and non-usable waste powder, and send it to the corresponding device.
multi-cyclone powder recovery system is divided into inhalation segment, separation segment, filtration segment and discharge segment 4 parts. The suction segment consists of a freely adjustable air plate, a regulatory system and a air port, which act as a separation from the spray chamber by inhaling powder dust floating in the air or unused powder into the separation system. The operating time adjusts the system according to the specific situation, adjusts the air intake of the air intake by changing the air intake size, improves the environment, collects the dust and powder. The
separation segment consists of a cyclone separator, a filter sieve and an air in and out of the air port, and its function is to make the available powder into the original powder tank mixed with the raw powder and re-enter the spray cycle, while the other part of the powder with small particles is charged because it is difficult to capture electrons in the spray electric field, so it is basically impossible to be applied to the workpiece, called waste powder.
the powder/gas mixture from the separation segment into the filter segment. The filter section consists of a filter chamber, a waste powder collection tank and a cleaning gas system, and the filter chamber consists of a set of filter elements and their accessories, the main function of which is to filter the mixture coming from the front.
exhaust section consists of a fan, a dud and a filter. The fan is used for exhausting the air and is the driving force of the air flow throughout the system. The wind channel determines the wind, the filter is the last protection, so that the air flow into the atmosphere as clean as possible, multi-cyclone powder recovery system advantages are: structural multi-stage and set separation, to ensure that the mixture after entry to get a rapid and complete separation.
6 Conclusion
domestic production equipment enterprises have done a lot of work in the localization of powder-making equipment, providing a guarantee for powder production. After years of development, powder equipment enterprises have gradually matured, and in product research and development investment, Bonding mixed equipment, three-dimensional thin coating production line, the use of P S R11 explosion-proof technology grinding units have been put on the market, at the same time domestic powdering equipment is also exported to overseas.
But the powdering equipment industry has the following problems:
(1) equipment varieties are single, many varieties are derived from imitation, independent research and development of equipment products are too few, the vast majority of manufacturers are from mixing, extruding to crushing, screening all equipment production. Germany is the main producer of powder equipment, these enterprises only do one kind of equipment, no company can provide the entire production line, so Germany's equipment specialization, fine degree is very high;
(2) design investment is small, research and development is not enough,
(3) scientific research units and institutions of higher learning technology investment is too little, research strength has not been put in this regard;
(4) enterprise development is difficult, management is not sound, especially capital investment, technology and market development is more inadequate;
(5) price competition is being more intense, not only make the powder coating industry threshold lower, but also make enterprise profits greatly weakened, enterprises are unable to carry out technological innovation. To that end, we should be fully aware of these problems and address them step by step.