Development and application of melt gear pump for

Development and application of melt gear pump for polymer processing

nowadays, polymer melt gear pump has been widely used in chemical fiber, film, profile, pipe, plate, cable, composite extrusion, granulation and other production lines. The processable materials cover most of the polymer materials, such as PE, PC, PP, PVC, hips, PS, pet, PUR, fluoropolymer, polyurethane, polyester, thermoplastic elastomer, rubber and thermal adhesive

polymer melt gear pump is a hydrostatic positive displacement pump with positive displacement transmission characteristics. It operates according to the principle of closed volume transmission. The conveying medium (polymer melt) is conveyed from the low pressure side to the high pressure side through a plurality of almost closed chambers formed by the gap between the teeth of the gear. Through the action of these teeth, the low-pressure side and high-pressure side are separated from each other at the top of the teeth, so as to play a sealing role. Through the rotary meshing of a pair of gears, the slots at the feeding end are loosened freely, the volume is increased and the material is filled. At the discharge end, the cogging volume is reduced again through the meshing of the teeth, so as to extrude the material

performance of melt gear pump

as an auxiliary device of extruder, melt gear pump mainly has the following advantages

(1) realize stable extrusion, improve the dimensional accuracy of extruded products and reduce the scrap rate

in the process of extrusion, it is difficult to avoid such phenomena as uneven feeding amount of materials, fluctuation of barrel and head temperature, pulsation of screw speed and so on. In the precision extrusion production line, the use of melt gear pump can eliminate the feeding error of the feeding system and further improve the stability of the system

(2) increase production, reduce energy consumption, realize low-temperature extrusion, and extend the service life of the machine

because the polymer melt gear pump is installed on the extruder, the pressure building function of the extruder is transferred to the gear pump. The extruder can work under low pressure and low temperature, with greatly reduced leakage flow and increased output

(3) it has linear extrusion characteristics, which is convenient for the coordination of upstream and downstream equipment

due to the small leakage flow of the gear pump, the conveying capacity of the pump is basically linear with the rotation speed. After the rotation speed of the gear pump changes, the flow can be accurately known. Therefore, the synchronous working speed of the upstream and downstream equipment and the gear pump can be determined, and the pressure, temperature and other information collected at the inlet and outlet of the gear pump can be used to realize the whole process monitoring and feedback control of the whole extrusion process

(4) reduce production costs and improve the competitiveness of enterprises

because the gear pump used in the extrusion system can reduce the scrap rate and energy consumption, it can save the production cost of enterprises. For example, in rubber production, the application experience of gear pump in the mixing and extrusion process shows that the service life of extruder screw can be nearly doubled by using gear pump. The payback period for installing gear pumps on rubber processing equipment is generally 1 year, and the payback period for large-scale systems is usually shorter. While reducing costs, product quality has also been improved, thereby improving the competitiveness of enterprises

uses and characteristics of different types of melt gear pumps

melt gear pumps for plastic extrusion

plastic melt gear pumps are mainly used to process thermoplastic polymer melts with relatively low viscosity. They are widely used at home and abroad and can be used in the extrusion molding of most plastic products. Especially in the field of precision extrusion molding such as biaxial tensile film, non-woven fabric, coating, wire and cable, multilayer composite film, chemical fiber, etc., plastic melt gear pump has been widely used. At present, the principle, performance, structural characteristics and application technology of plastic melt gear pump have been studied to a certain extent at home and abroad

after years of systematic research on melt gear pump, the rubber and Plastic Machinery Research Institute of Beijing University of chemical technology has successfully completed the series development and development of plastic melt gear pump. Now it can design and manufacture plastic melt gear pump products, such as 28/28 (center distance/tooth width), 56/56, 70/70, 90/90, etc. the maximum inlet and outlet pressure difference can reach 30MPa, which can meet the requirements of various output, and has been applied in practice and achieved good results. Figure 1 shows the pcp28/28 plastic melt gear pump developed by Beijing University of chemical technology

Figure 1 pcp28/28 plastic melt gear pump

plastic melt gear pump mainly adopts the sliding bearing structure of self-lubricating polymer melt, which is the most significant structural feature of plastic melt gear pump and the most important structural form of melt gear pump. A complete gear pump device includes motor, reducer, coupling, control part and pump body. The pump body is composed of the main pump body, front and rear side covers, gear shafts, sliding bearings and sealing bearings

there is a temperature control jacket inside the pump body, which is used to accurately control the temperature inside the gear pump. There are inlet and outlet flanges on both sides, and the inlet diameter is larger than the outlet, which is particularly important for the suction conditions of high viscosity and low pressure, which can improve the pump efficiency and operation stability

gear is the key part of gear pump. Gears are divided into straight teeth, helical teeth and herringbone teeth according to the tooth direction. Compared with spur gears, helical gears have an increased degree of coincidence in gear meshing, which can continuously and smoothly squeeze materials during meshing and reduce pressure fluctuations. At the same time, due to its self-cleaning effect during rotation, it can keep the tooth root clean and avoid the deposition and decomposition of materials, but it will produce axial force during operation, affect the service life of bearings, and also aggravate the shear of melt in the backlash between teeth, so the bevel angle should not be too large. The spur gear produces balanced bearing load when it works, and the processing cost is low. Its main disadvantage is that the pressure fluctuates greatly. Herringbone gear can not only realize relatively stable extrusion, but also balance the axial force. It has the advantages of helical gear and spur gear, but herringbone gear is easy to make materials stay at the root of the tooth, and the processing cost is high

in polymer melt gear pumps, most of them use "d" type sliding bearings, because the sliding bearings have simple structure, convenient installation, low working noise, good impact resistance, and the polymer itself is a good lubricant, which can form a good dynamic lubricating film and can bear quite high loads on the gear shaft

melt gear pump for rubber extrusion

rubber melt gear pump is mainly used in rubber extrusion molding. Similar to the plastic melt gear pump, the working characteristics of the rubber melt gear pump are further improved from the level of manufacturing technology and overall strength. It has strong adaptability to different types of rubber, head resistance and operating process conditions. Therefore, it has a very wide range of applications, especially in precision extrusion molding, rubber filtration process and calendering feeding, It has become a new hot spot in the field of international rubber and thermoplastic elastomer processing, and has attracted extensive attention from insiders. Relevant research shows that the rubber gear pump extruder can be applied to the filtration, preheating, plasticization and molding of rubber, extruding and feeding to the calender, matching with the hot feed extruder, cold feed extruder and cold feed exhaust extruder, and carrying out the composite extrusion, transportation, traction belt, flat products, rubber tubes, rubber strips, inner tubes The device accuracy of the extrusion tension testing machine of wires and cables stops rechecking the molding, the coating of rubber rollers and the filling of high-capacity molds. At present, the gear pump has not been used in the rubber industry for a long time. According to froester company, it combines the gear pump with the conventional GS extruder, QSM (PIN) extruder and exhaust extruder to make the rubber products produced by this company reach the highest international level in precision and quality

Figure 2 xcp150/100 rubber melt gear pump

in order to meet the domestic demand for rubber melt gear pump, Beijing University of chemical technology, in cooperation with Beijing Aerospace Manufacturing Engineering Research Institute and Hangzhou Chaoyang Rubber Co., Ltd., has begun to develop two types of rubber melt gear pump extrusion units, xcp150/100 and xcp120/90. Figure 2 shows the appearance effect of xcp150/100 rubber melt gear pump. Its main features are:

1 The unit has ideal working characteristics, ensuring that the extrusion volume is in linear relationship with the speed of the gear pump, which can realize accurate control of output and improve the dimensional accuracy of products. Using the pressure collected at the inlet and outlet of the gear pump, and the elongation at break of ordinary polymer materials is mostly between% ～ 100%, temperature and other information, the upstream and downstream equipment can work synchronously with the gear pump to realize the whole process monitoring and feedback control of the extrusion process

2. The unique temperature control method can realize accurate temperature closed-loop control, strictly control the temperature of the rubber within the set temperature range, prevent the rubber from scorching, and realize low-temperature extrusion

3. The special structure can effectively prevent rubber leakage and realize self-cleaning

4. Through the unloading groove on the end cover in contact with the gear, the adverse effect of "trapped oil" on the gear pump is eliminated, the service life of the gear pump is improved, and the stability of rubber conveying is increased. Temperature accuracy: ± 0.5 ℃ Temperature resolution: 0.1 ℃ Deformation range: 0 (1) mm Deformation accuracy: 0.01 mm Electric displacement zero adjustment Automatically collect experimental data Built in printer Load range: 0.75n (5) 0n Experimental span: 60 ⑴ 20 ㎜ continuously adjustable

5. The gear pump adopts a pair of modified helical gears to mesh, and the gear is integrated with the shaft. The gear shaft adopts high wear-resistant materials, and the tooth surface is quenched with high frequency. The surface hardness reaches HRC, and the accuracy grade is 6hk

6. The feeding port and discharge port of the gear pump adopt a unique design, so that the materials are fed into the gear pump smoothly, and it is not easy to produce retention and cavitation. The radial force on the gear shaft is reduced, and the service life of the bearing is improved

integration of extruder and gear pump

traditional gear pump - extruder unit requires separate drive (motor, reducer) and separate control because of the extruder and gear, which makes the whole unit occupy a larger area and cost higher. After the extruder is equipped with a gear pump, the power consumption or torque required by the extruder gear pump unit system is much lower than that of the traditional cold feed extruder. Therefore, the extruder equipped with standard driving power should also have a large torque margin for use. The screw of the integrated gear pump extruder makes use of these torque margins to realize the integration of the gear pump and the extruder. In this way, unnecessary independent driving mechanism can be removed

its specific structure is: install a four thread screw section at the rear of the feeding section of the standard double thread extruder screw. The geometric structure of the screw of the four thread extruder is uniformly transformed into the geometric structure of the actual gear pump. The gear pump itself contains 4 planetary gears, which can rotate around its own bearings. These planetary gears mesh with hollow gears (barrels). The material is sent to the gear pump through 4 conveying threads. Under certain pressure, part of the material is pressed into the teeth of the planetary gear and part of the material is pressed into the teeth of the outer hollow gear. Each rotating planetary gear carries the material tributary and sends the torque transmitted by the screw into the high-pressure chamber. At the same time, it plays the role of separating the low-pressure side and the high-pressure side with the toothed barrel. This structure enables the main material flow to be divided into two branches at each entry point, that is, a total of eight branches, which has a certain mixing effect on the materials. At the same time, the co extrusion of multiple gears greatly reduces the extrusion fluctuation and increases the extrusion temperature. Figure 3 is the structural diagram of the all-in-one gear pump extruder

figure