Polyoxymethylene (POM) is a linear polymer without side chain, high density, high crystallinity, has good mechanical properties, excellent creep resistance and stress relaxation ability, fatigue resistance is very high in thermoplastics, and has outstanding self-lubricating, wear resistance and drug resistance, is a very widely used engineering plastics.
POM hygroscopicity is small, the resin generally does not need to dry before processing. If necessary, can be in 90 ~ 100 ℃, dry 2 ~ 4h. POM melt viscosity is sensitive to the shear rate. Therefore, to improve the melt fluidity, can not be used alone to improve the temperature, but also from improving the injection rate and injection pressure. POM is a heat-sensitive plastic, 240 ℃ will be severely decomposed. At 210℃. Dwell time can not exceed 20min; even at 190 ℃, dwell time is best not to exceed 1h. injection molding, under the premise of ensuring the fluidity of the material, should try to choose a lower molding temperature and a shorter heating time. POM has a relatively obvious melting point, *** poly POM for 165 ℃, homopolymerization POM for 175 ℃. Molding, barrel temperature distribution: 190 ~ 200 ℃ in the front section, 180 ~ 190 ℃ in the middle section, 150 ~ 180 ℃ in the back section, the nozzle temperature of 170 ~ 180 ℃. For thin-walled products, the barrel temperature can be increased appropriately, but not more than 210 ℃. Mold temperature is usually controlled at 80 ~ 100 ℃, for thin-walled products with long flow distance and complex shape, the mold temperature can be increased to 120 ℃. Improve the mold temperature is beneficial to the melt flow work, to avoid defects in products due to the cooling rate is too fast, and can also improve the impact strength of the products, but also improve the molding shrinkage. Injection pressure on the mechanical properties of POM products has a small impact, but the melt fluidity and surface quality of the product has a great impact. The size of the injection pressure, mainly by the shape of the product, wall thickness, mold circulation, gate size and mold temperature. For small gate, thin wall, long flow distance, large area products, injection pressure is higher, 120 ~ 140MPa; and large gate, thick wall, short flow distance, small area products, injection pressure of 40 ~ 80 MPa; general products for about 100MPa. Appropriately increase the injection pressure, favorable to improve the melt fluidity and product surface quality, but the pressure is too high will cause product overflow. Due to the high crystallinity of POM, volume shrinkage, in order to prevent the products appear hollow, dents and other defects, there must be enough holding time to make up for shrinkage. In general, the thicker the product, the longer the holding time. The speed of the injection rate depends on the wall thickness of the product. Thin-walled products should be injected quickly to avoid premature solidification of the melt; thick-walled products should be injected slowly to avoid jetting, affecting the appearance of the product and internal quality. In order to eliminate the residual internal stress in the product and reduce shrinkage, usually need to be heat-treated. Heat treatment is to air or oil as a medium, the temperature of 120 ~ 130 ℃, the length of time by the wall thickness of the product; generally, the wall thickness of each increase of 1mm, annealing time increased by about 10min. Heat treatment effect can be used to determine the polar solvent impregnation method; will be heat-treated products, into the 30% hydrochloric acid solution impregnated for 30min, if there is no crack, indicating that the products in the residual internal stress is small, to achieve the purpose of treatment. POM plastic over a certain temperature or processing temperature for a long time after the heat, will be degraded, release a large number of harmful formaldehyde gas, not only affect the quality of products, corrosion molds, hazardous to human health, in serious cases, it will cause gas expansion in the cylinder and produce explosions and other production accidents. Therefore, in addition to strict control of the operation of the molding process conditions, should also pay attention to the following points: ① strict control of the molding temperature of the POM and the residence time of the material in the cylinder; ② drive before the temperature, the first preheating nozzle, after heating the cylinder; ③ processing POM, if the cylinder memory processing temperature exceeds the POM material, the first PE as a cleaning material will be cleaned up the cylinder, to be reduced to the temperature of the processing of POM Temperature, and then use PE to clean the barrel, before the material can be fed into the molding operation; ④ in the molding process, such as the discovery of a serious pungent formaldehyde flavor, yellowish-brown stripes on the product, indicating that the material has been degraded, at this time should be immediately used to empty the barrel of the injection method, and use PE to clean the barrel, to be normal and then processed; ⑤ some materials or additives (such as PVC, halogenated flame retardants, etc.), to the POM, the material should be used as a cleaning material to clean the barrel. ⑤ Certain materials or additives (such as PVC, halogenated flame retardants, etc.), POM has a role in promoting degradation, must be strictly separated, not allowed to mix with each other. Polyformaldehyde, also known as polyoxymethylene, the English name poly0xymethylene (POM for short). Molecular structure regularity and crystallinity make its physical and mechanical properties are very excellent, there are metal plastic called. POM for milky white opaque crystalline linear thermoplastic resin, with good overall performance and coloring, has a high modulus of elasticity, high rigidity and hardness, than the strength and rigidity close to the metal; tensile strength, bending strength, creep resistance and fatigue resistance, resistance to repeated impacts, de-loaded back to the superiority of the coefficient of friction is small, abrasion resistance, good dimensional stability, good surface luster, have a higher Viscoelasticity, excellent electrical insulation, and not affected by temperature;, good insulation resistance and not affected by humidity; excellent chemical resistance: in addition to strong acids, phenols and organic halides, stable to other chemicals, oil resistance; mechanical properties are less affected by temperature, with a high heat distortion temperature. Disadvantages are poor flame retardant, fire Xu Xu burning, oxygen index is small, even if the addition of flame retardant can not get satisfactory requirements, in addition to weathering is not ideal, outdoor applications to add stabilizers. Physical and chemical properties of high specific gravity non-isotropic shrinkage molding more difficult polyacetal (POM) hard, resistant to latent change and strong. Has a low coefficient of friction. They also remain stable when used at high temperatures and provide superior stability in hot water environments. They are virtually unaffected by strong bases, but will be attacked by strong mineral acids.40% glass fiber reinforced polyacetal (POM) has a flexural modulus of 1.6 psi x 10E6 (11024 MPa) and a heat deflection temperature of 330 degrees F (166 degrees C) are all polyformaldehyde is highly crystalline, and has better mechanical strength, rigidity, and heat deflection temperatures than ***Polyformaldehyde ***Polyformaldehyde has a low melting point. Thermal stability, chemical resistance, flow characteristics, processability are better than uniform polyformaldehyde, newly developed products for ultra-high flow (rapid prototyping), impact resistance and reduce mold deposition grades, but also inorganic filler, enhanced grades. POM water absorption is greater than 0.2%, should be pre-dried before molding, POM melting temperature and decomposition temperature is similar to the poor molding, can be injection molding, extrusion, blow molding, rotomolding, welding, bonding, film coating, printing, plating, machining, injection molding is the most important processing methods, molding shrinkage is large, the mold temperature is appropriate to be higher or annealing, or add reinforcing materials (such as alkali-free glass fiber). POM high strength, light weight, commonly used to replace copper, zinc, tin, lead and other non-ferrous metals, widely used in industrial machinery, automobiles, electronics and electrical appliances, daily necessities, pipes and fittings, precision instruments and building materials and other sectors. Typical InjectionMolding Conditions
General injection molding conditions?English
Inch SI Metric
Metric Temperature Rear zone 350 - 390°F177 - 190°F 390°F177 - 199°C Center zone Middle zone 360 - 400°F182 - 204°C Front zone Front zone 370 - 410°F188 - 210°C Melt Melt temperature 360 - 425°F182 - 218°C Mold Mold temperature 175 - 225°F79 - 107°. CPressures Injection Injection 10,000 - 15,000psi69 - 103MPa Hold Hold Pressure 5,000 - 12,000psi34 - 83MPa Back Back Pressure 50 - 100psi0.34 - 0.69MPaSpeeds Speed Fill Fill Speed1 - 2in/sec25 - 51mm/sec Screw 51mm/sec Screw Screw Speed60 - 90rpm60 - 90rpmDrying Drying Conditions Time & Temperature
Time & Temperature2 Hrs @ 250°F2 Hrs @ 121°C Dew Point Dew Point -25°F-32°C Moisture Content
Moisture Content0.15%0.15%Permanent Antistatic CompositesTypical Injection
Molding Conditions
General Injection Molding ConditionsEnglish
English?SI Metric
Metric Temperature Rear zone Rear zone 310 - 350°F154 - 177°C Center zone Middle zone 330 - 370°F166 - 188°C Front zone Front zone 350 - 390°F177 - 199°C Melt Melt temperature 350 - 400°F177 - 204°C Mold Mold Temperature180 - 250°F82 - 121°CPressures Injection Injection 10,000 - 15,000psi69 - 103MPa Hold Hold Pressure 5,000 - 10,000psi34 - 69MPa Back Back Pressure 50 - 100psi0.34 - 0.69MPaSpeeds Speed Fill Fill Speed1 - 2in/sec25 - 51mm/sec Screw Screw RPM60 - 90rpm60 - 90rpmDrying Drying Conditions Time & Temperature
Time & Temperature2 Hrs @ 250°F2 Hrs @ 121°C Dew Point Dew Point- 25°F-32°C Moisture 25°F-32°C Moisture Content
Moisture Content 0.15% 0.15% EMI Masking Composites?Typical Injection
Molding Conditions
General Injection Molding Conditions?English
English?SI Metric
Metric Temperature Rear zone Back zone 370 - 410°F188 - 210°C Center zone Middle zone 360 - 400°F182 - 204°C Front zone Front zone 350 - 390°F177 - 199°C Melt temperature 360 - 425 °F182 - 218°C Mold Mold Temperature180 - 225°F82 - 107°CPressures Injection Injection 10,000 - 15,000psi69 - 103MPa Hold Hold Pressure 5,000 - 10,000psi34 - 69MPa Back Back Pressure 50 - 100psi0.34 - 0.69MPaSpeeds 0.69MPaSpeeds Speed Fill Speed1 - 2in/sec25 - 51mm/sec Screw Screw Speed30 - 60rpm30 - 60rpmDrying Conditions Time & Temperature
Time & Temperature2 Hrs @ 250°F2 Hrs @ 121°C Dew Point Dew Point 121°C Dew Point Dew Point -20°F-29°C Moisture Content
Moisture Content 0.15%0.15%? Applications POM is widely used in the manufacture of a variety of sliding, rotating machinery parts, do a variety of gears, levers, pulleys, sprockets, especially suitable for bearings, hot water valves, precision metering valves, conveyor chain rings and rollers, flow meters, automotive interior and exterior handles, cranks and other window rotating machinery, oil pump bearing housing and impeller gas switch valve, electronic switch parts, tight solid, terminal mirror cover, electric fan parts, Heating plate, instrument knob; audio-video tape bearings; a variety of pipelines and agricultural sprinkler systems and valves, sprinkler heads, faucets, bath tub parts; switch keyboard, buttons, audio-visual tape reel; temperature control timer; power tools, garden finishing tools parts; in addition to surfboards, sailing boats and a variety of sled parts, watches, micro-gear, sports equipment, the frame of the auxiliary and the backpack with a variety of ring buckle, fasteners, Lighters, zippers, grommets; cardiac pacemakers in medical equipment; artificial heart valves, vertebrae, prostheses and so on
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