Injection molding bottle bottom drum how to solve

Polycarbonate (PC) is a colorless and transparent engineering plastics, with very high impact strength, a wide range of operating temperatures, good creep resistance, electrical insulation and dimensional stability; drawbacks are notch-sensitive, poor resistance to environmental stress cracking, molding products with metal inserts more difficult. Polycarbonate, the English name Polycarbonate, referred to as PC. PC is an amorphous, odorless, non-toxic, highly transparent colorless or yellowish thermoplastic engineering plastics, with excellent physical and mechanical properties, especially impact resistance, tensile strength, bending strength, compression strength; creep is small, dimensional stability; good heat resistance and low temperature resistance, stable mechanical properties over a wide temperature range. Range of stable mechanical properties, dimensional stability, electrical properties and flame retardant, can be used for a long time at -60 ~ 120 ℃; no significant melting point, at 220-230 ℃ is molten; due to the rigidity of the molecular chain, the resin viscosity of the melt is large; water absorption is small, shrinkage is small, high dimensional accuracy, dimensional stability, film permeability is small; is a self-extinguishing material; light stable, but not UV-resistant. Good weather resistance; oil, acid, not resistant to strong alkali, oxidizing acids and amines, ketones, soluble in chlorinated hydrocarbons and aromatic solvents, long-term hydrolysis and cracking in water, the disadvantage is that due to poor fatigue strength, prone to stress cracking, poor solvent resistance, poor abrasion resistance. Physical and chemical properties of PC plastic process characteristics are as follows: ① is an amorphous plastic, Tg 149 ~ 150 ℃; Tf 215 ~ 225 ℃; molding temperature of 250 ~ 310 ℃; the relative average molecular mass of 2 ~ 4 million. ② thermal stability is good, and with the increase in relative molecular mass and improve. ③ Rheological properties close to Newtonian liquids, apparent viscosity is affected by the temperature, less affected by the shear rate, and increases with the increase of relative average molecular mass. There is no obvious melting point, melt viscosity is higher. pc molecular chain has a benzene ring, so, the rigidity of the molecular chain. ④PC has good creep resistance and good dimensional stability; however, the internal stress is not easy to eliminate. ⑤PC is easy to be degraded when it meets water at high temperature, and the moisture content is required to be below 0.02% when molding. ⑥Products are easy to crack. Before molding, PC resin must be fully dried. Drying method can be used boiling bed drying (temperature 120 ~ 130 ℃, time 1 ~ 2h), vacuum drying (temperature 110 ℃, vacuum degree of 96kPa above, time 10 ~ 25h), hot air circulation drying (temperature 120 ~ 130 ℃, time 6h above). In order to prevent the dried resin from re-hygroscopicity, it should be placed in a holding tank at 90℃, and should be taken as it is used, and should not be stored for a long time. Molding hopper must be closed, the hopper should be equipped with a heating device, the temperature is not less than 100 ℃, no insulation device for the hopper, a charging amount of the best less than half an hour's worth of dosage, and to be covered with a tight lid. To determine the drying effect of the rapid test method, is used in the injection molding machine "to the empty injection". If the material from the nozzle slowly out of the uniform transparent, bright and no silver and bubbles in the thin strip, it is qualified. This method is applicable to general plastics, the melt viscosity of PC is much larger than that of PA, PS, PE, etc., and the fluidity is poor. The flow characteristics of the melt is close to Newtonian fluid, melt viscosity by the shear rate is less affected, and very sensitive to changes in temperature, therefore, molding as long as the adjustment of the processing temperature, you can effectively control the performance of the PC viscosity. The choice of molding temperature and the relative average molecular mass of the resin and its distribution, the shape and size of the product, the type of injection molding machine, etc., generally controlled in the range of 250 ~ 310 ℃. Injection molding materials, it is appropriate to use a slightly lower relative average molecular mass of the resin, MFR for 5 to 7g/10min; complex shape or thin-walled products. Molding temperature should be high, 285 ~ 305 ℃; and thick-walled products, molding temperature is slightly lower, 250 ~ 280 ℃. Different injection molding machine, molding temperature is not the same. Screw type is 260～285℃, plunger type is 270～310℃. The barrel temperature is set in a front-high and back-low manner, and the back barrel temperature near the hopper end should be controlled above the softening temperature of PC, i.e., greater than 230°C, in order to reduce material resistance and injection pressure loss. Although increasing the molding temperature is beneficial to melt filling. However, it should not exceed 230 ℃, otherwise, PC will be degraded, so that the color of the product becomes darker, the surface of the silver wire, dark bars, black spots, bubbles and other defects, at the same time, the physical and mechanical properties will be significantly reduced. Nozzle temperature of 260 ~ 310 ℃, two types of injection molding machine nozzle temperature control is different. Mold temperature has a great influence on the mechanical properties of products. With the increase in mold temperature. The temperature difference between the material temperature and mold temperature becomes smaller, the shear stress is reduced, the melt can be slowly cooled in the mold cavity, the molecular chain can be relaxed, the degree of orientation is reduced, thus reducing the internal stress of the product, but the impact strength of the product, the elongation of the product decreased significantly, at the same time, there will be a product demolding difficulties. Easy to deform when demolding, and prolong the molding cycle, reducing productivity; and lower mold temperature, but will make the products of the internal stress increases. Therefore, the mold temperature must be controlled. Usually, the mold temperature of PC is 80 to 120 ℃. Ordinary products are controlled at 80 ~ 100 ℃, while for complex shapes, thin-walled and demanding products, it is controlled at 100 ~ 120 ℃, not allowed to exceed its heat distortion temperature. Molding PC thick-walled products, mold temperature control is particularly important. For example, in the molding of simply supported beam impact test sample (thickness of 10mm), if the mold does not control the temperature, the molding of the sample of the internal shrinkage of a lot of holes, is also very large. At this time, if the mold is not equipped with a heating device, a simple method can be used to heat the main flow channel of the mold. The simple method is in a wire tied to a cotton ball, dipped in industrial alcohol, heating the main stream, so that, although it can not eliminate shrinkage, but the number of shrinkage is greatly reduced. The degree is greatly reduced. Of course. This is not a law of the law, is a kind of hygienic method, do not recommend the use of. Because of this, it is easy to make the mold main stream deformation and oxidation. Although the injection pressure on the melt strength and fluidity of injection molding has less impact, but due to the high viscosity of the PC melt, poor fluidity, therefore, the injection pressure can not be too low, generally controlled at 80 ~ 120MPa, the use of plunger-type injection molding machine, the injection pressure should be 100 ~ 150MPa; and for the thin-walled, long-flow distance, the shape of the complexity of the product, the gate size of the smaller products, in order to enable the melt to smooth, timely filling of the mold. Injection pressure should be increased to 120-150MPa. The general principle of PC injection molding process control is: high material temperature, low pressure. Holding pressure size and holding time directly affects the quality of the product. Holding pressure is too small, the shrinkage effect is small, the products will be formed inside the bubble due to shrinkage, the surface of the product will also appear dents; Holding pressure is too large. If the holding pressure is too high, it is easy to produce large internal stress around the gate. Holding pressure time is long, high dimensional accuracy, low shrinkage, good surface quality, but increased internal stress in the product, prolonging the molding cycle. Holding pressure of 80 ~ 100MPa. As previously mentioned methods - heating the main flow channel with fire to extend the solidification time of the melt in the gate to increase the effect of shrinkage. pc injection molding, back pressure can be increased. Injection rate has little effect on the performance of the product. But from the molding point of view, the injection rate should not be too slow, otherwise the melt into the cavity is easy to condense and lead to insufficient mold filling, even if full, the surface of the product package is prone to ripples, material flow marks and other defects; injection rate should not be too fast to prevent wrapping into the air and melt rupture phenomenon. Production, generally using medium or slow speed, it is best to use multi-stage injection molding. Injection, the speed is not set as slow → fast → slow, which can greatly improve product quality. Screw speed should not be too high, generally 30 ~ 60 r / min. inserts need to be preheated to 200 ℃, at least 120 ℃, generally 110 ~ 130 ℃. The number of times of regeneration of recycled material is not more than 3 times, the amount of about 20%. pc is transparent plastic, molding is generally not recommended to use mold release agent, so as not to affect the transparency of the products. For products that have difficulties in mold release, stearic acid or silicone oil can be used as a mold release agent, but the dosage should be strictly controlled.PC products should try to avoid the use of metal inserts. If you do need to use metal inserts, the metal inserts must be preheated to about 200 ℃, and then placed in the mold cavity for injection molding, so as to avoid the coefficient of expansion of the disparity between the difference between the contraction of the cooling occurs when the inconsistency of the greater internal stress, so that the product cracking. Reduce the internal stress of the method, in addition to the products in the shape of the design to avoid gaps, sharp corners, thick and thin disparities and the use of the correct molding process parameters, it is best to products for heat treatment, heat treatment temperature control in 125 ~ 135 ℃ (resin Tg below 10 ~ 20 ℃), processing time of 2h or so, the thicker the products the longer the processing time. General wall thickness of less than 5mm products, time for 8h; greater than 20mm products, time for 24h. the size of the internal stress of the product can be polarized light test method and solvent impregnation method. Polarized light test method for a variety of transparent products, it is the use of PC transparency, the products are placed in the polarized light between the lenses, from the mirror on the surface of the products to observe the colored light band area, to determine the size of the product to the size of the colored band area to determine the size of the product internal stress, if the observed color packet band area is large, indicating that the products of the internal stress is large; solvent impregnation method is a means of detection commonly used in factories, the method is the PC products immersed in Some solvents (such as benzene, carbon tetrachloride, cyclohexane, ethanol, methanol, etc.), to the product cracking and destruction of the time required to determine the size of the stress, the longer the stress is smaller. If the impregnation 5 ~ 15s on the crack, indicating that the internal stress is very large; if the impregnation 1 ~ 2min does not appear cracks, indicating that the internal stress is very small, this product in the use of the process will not generally crack. Injection molding process drying treatment: PC materials have hygroscopicity, drying before processing is very important. Recommended drying conditions for 100C to 200C, 3 ~ 4 hours. The humidity before processing must be less than 0.02%. Melting temperature: 260~340 C. Mold temperature: 70~120 C. Injection pressure: Use high injection pressure as much as possible. Injection speed: Use low speed injection for smaller gates and high speed injection for other types of gates. Applications PC can be injection molded, extruded, molded, blow molded, thermoformed, printed, bonded, coated, and machined. The most important processing method is injection molding. Must be pre-dried before molding, the moisture content should be less than 0.02%, trace moisture processing at high temperatures will make the products produce a whitish color, silver filaments and bubbles, PC at room temperature has a considerable forced high elastic deformation capacity. The impact toughness is high, so it can be cold pressed, cold drawn, cold rolled and other cold molding process. Extrusion with PC molecular weight should be greater than 30,000, to use gradual compression type screw, L/D ratio 1:18~24, compression ratio 1:2.5, can be used for extrusion blow molding, injection - blowing, injection - pulling - blowing method of molding high-quality, high-transparent bottles. a wide range of PC alloys, to improve the PC melt viscosity (processability) and the products are prone to stress cracking and other defects, PC and different polymers to form alloys or **** blends that Improve material properties. Specifically PC / ABS alloy, PC / ASA alloy, PC / PBT alloy, PC / PET alloy, PC / PET / elastomer **** blend, PC / MBS **** blend, PC / PTFE alloy, PC / PA alloy, etc., Lee has two material performance advantages, and reduce costs, such as the PC / ABS alloy, PC mainly contributes to high heat resistance, better toughness and impact strength, high strength, flame retardant, ABS can improve moldability, apparent quality, reduce density.PC's three major applications are the glass assembly industry, the automotive industry and the electronics, electrical appliances industry, followed by industrial machinery parts, CD-ROMs, packaging, computers, and other office equipment, medical and health care, film, leisure and protective equipment.PC can be used as glass for windows and doors, PC laminates are widely used in banks, embassies, detention centers and public offices. PC can be used as door and window glass, PC laminates are widely used for protective windows in banks, embassies, detention centers and public **** places, for aircraft hatch covers, lighting equipment, industrial security panels and bullet-proof glass. PC boards can be used for various signs, such as gasoline pump dials, automobile dashboards, warehouse and open-air commercial signs, point sliding indicators, PC resins are used in automobile camera systems, dashboard systems, and interior decorative systems, used as headlamp covers, automobile front and rear gear panels with reinforcing ribbing, mirror frames, door frame covers, operating lever guards, and door frame covers. PC resin is used in automotive lighting systems, instrument panel systems and interior decorative systems, as headlight covers, automotive front and rear gear panels with reinforcement, reflector frames, door frame covers, operating rod covers, flow stops, PC is used in junction boxes, sockets, plugs and bushings, spacers, TV converters, communication cable connections under telephone line brackets, switch boxes, telephone switchboards, distribution panel components, relay housings, PC can be used as low load parts for household appliance motors, vacuum cleaners, shampoos, coffee makers, toasters, handles on power tools, all kinds of gears, worm gears, bushings, and other parts of the automotive industry. Gears, worm gears, bushings, guide gauges, shelves inside the refrigerator. pc is the ideal material for optical disk storage media. pc bottles (containers) are transparent, lightweight, good impact resistance, resistant to certain high temperatures and corrosive solution washing, as recyclable bottles (containers). pc and pc alloys can be made into computer racks, housings and auxiliary machines, printer parts. Modified PC is resistant to high-energy radiation sterilization, resistance to boiling and baking disinfection, can be used for blood specimen collection apparatus, blood oxygenator, surgical instruments, kidney dialyzer, etc. PC can be made into helmets and helmets, protective masks, sunglasses and sports eye protection. pc film is widely used in printing charts, pharmaceutical packaging, membrane commutator.