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PA

  • Author:Michelle
  • Source:Www.xy-global.com
  • Release on :2018-06-29
1.The performance of the PA

ThePAIt is also a crystalline plastic (Nylon is a tough horny translucent or milky white crystalline resin). As a engineering plastic, the molecular weight of nylon is generally 1.5-30000, and there are many varieties. It is commonly used in injection molding processing of nylon 6, nylon 66, nylon 1010, Nylon 610 and so on.

ThenylonToughness, wear resistance and self-lubrication, its advantages are mainly organic mechanical strength, toughness, fatigue resistance, smooth surface, high softening point, heat resistance, low coefficient of friction, wear resistance, self lubrication, shock absorption and Silence resistance, oil resistance, weak acid resistance, alkali resistance and general solvent, good electrical insulation, self-extinguishing, non-toxic, odorless, good weather resistance.

Disadvantages are high water absorption, poor dyeability, affecting dimensional stability and electrical properties, fiber reinforcement can reduce the water absorption rate, making it work under high temperature and high humidity. The affinity between nylon and glass fiber is very good (long-term use at 100°C), corrosion resistance, light weight and easy molding. The main disadvantages of PA are: easy to absorb water, injection molding technology requirements are strict, and the dimensional stability is poor. Because of its large specific heat, the product is hot.

PA66 is the highest mechanical strength and widest variety in the PA series. Its crystallinity is high, so its rigidity, hardness, and heat resistance are high. PA1010 is the first of its kind in China in 1958. It is semi-transparent, has a small specific gravity, is flexible and flexible, has lower water absorption than PA66, and has reliable dimensional stability.

Nylon 66 has the highest hardness and rigidity, but its toughness is the worst. The order of toughness of various nylons is: PA66

Nylon has a flammability rating of ULS44-2, an oxygen index of 24-28, a nylon decomposition temperature of >299°C, and spontaneous combustion at 449-499°C. Nylon melt flow is good, so the product wall thickness can be as small as 1mm.



2. Process characteristics of PA

(1) PA is easy to absorb moisture, must be fully dried before processing, the water content should be controlled below 0.3%. The raw material is dried well, the product has a high gloss, otherwise it is rough, and the PA does not soften as the heating temperature rises. Instead, the PA softens in a narrow temperature range near the melting point. The melting point is very obvious. Once the temperature is reached, the PA will Flow occurs (unlike PS, PE, PP, etc.).

PA's viscosity is much lower than other thermoplastics, and its melting temperature range is narrow (only about 5 °C). PA has good fluidity, is easy to mold, and is easy to wear.

The PA has a high melting point and a high freezing point, and the molten material will solidify at any time in the mold due to the temperature dropping below the melting point, impeding the completion of the filling molding. Therefore, high-speed injections must be used (especially for thin-walled or long-flow process parts). Nylon molds must have adequate exhaust.

PA in the molten state, the thermal stability is poor, easy to degrade. The barrel temperature should not exceed 300°C, and the heating time of the melt in the barrel should not exceed 30 minutes. The PA requires a higher mold temperature. The mold temperature can be used to control the crystallinity to obtain the desired performance.

The material temperature of the PA material is preferably 50-90°C, the processing temperature of PA1010 is 220-240°C, and the processing temperature of PA66 is 270-290°C. PA products sometimes need to be "annealed" or "conditioned" according to quality requirements.

(2) PA12 polyamide 12 or nylon 12 should be guaranteed to have a humidity below 0.1% before processing. If the material is stored in air, it is recommended to dry in 85C hot air for 4 to 5 hours. If the material is stored in a closed container, it can be used directly after 3 hours of temperature balance. The melting temperature is 240~300C; for ordinary materials, do not exceed 310C, and for materials with flame retardant properties, do not exceed 270C.

Mold temperature: 30 to 40C for unreinforced materials, 80 to 90C for thin-walled or large-area elements, and 90 to 100C for reinforced materials. Increasing the temperature will increase the crystallinity of the material. Accurate control of mold temperature is important for PA12. Injection pressure: up to 1000 bar (low packing pressure and high melting temperature are recommended). Injection speed: high speed (better for materials with glass additives).

Runners and gates: For materials without additives, the flow path diameter should be around 30mm due to the lower viscosity of the material. For reinforced materials, large flow channel diameters of 5 to 8 mm are required. The shape of the runners should all be circular. Injection ports should be as short as possible.

Many forms of gates can be used. Do not use small gates for large plastic parts. This is to avoid excessive pressure or excessive shrinkage of plastic parts. The thickness of the gate is preferably equal to the thickness of the plastic part. If submersible gates are used, a minimum diameter of 0.8mm is recommended. Hot runner molds are effective but require precise temperature control to prevent material leakage or solidification at the nozzle. If hot runners are used, the gate size should be smaller than the cold runners.(3) PA6 Polyamide 6 or Nylon 6: Since PA6 easily absorbs moisture, special attention should be paid to the drying before processing. If the material is supplied in a waterproof material package, the container should be kept closed. If the humidity is greater than 0.2%, it is recommended to dry in hot air above 80C for 16 hours. If the material has been exposed to air for more than 8 hours, it is recommended to vacuum dry at 105C for more than 8 hours.

Melting temperature: 230~280C, 250~280C for enhanced varieties. Mold temperature: 80~90C. The mold temperature affects the crystallinity very significantly, and the crystallinity affects the mechanical properties of the plastic parts. Crystallinity is important for structural parts, so it is recommended that the mold temperature be 80 to 90C.

For thin-walled, longer-lasting plastic parts, it is also recommended to apply higher mold temperatures. Increasing the mold temperature can increase the strength and stiffness of the plastic parts, but it reduces the toughness. If the wall thickness is more than 3mm, it is recommended to use a low temperature mold of 20~40C. For glass reinforced material mold temperature should be greater than 80C. Injection pressure: generally between 750 and 1250 bar (depending on material and product design).

Injection speed: high speed (slightly reduced for reinforced material). Runners and Gates: Since the settling time of the PA6 is very short, the position of the gate is very important. The gate aperture should not be less than 0.5*t (where t is the thickness of the plastic part). If hot runners are used, the gate size should be smaller than with conventional runners because the hot runner can help prevent premature solidification of the material. If using a submerged gate, the minimum diameter of the gate should be 0.75mm.

(4) PA66 Polyamide 66 or Nylon 66 If the material is sealed before processing, there is no need to dry it. However, if the storage container is opened, it is recommended to dry it in hot air at 85C. If the humidity is greater than 0.2%, vacuum drying at 105C for 12 hours is also required.

Melting temperature: 260~290C. The product for glass additives is 275~280C. The melting temperature should be avoided above 300C. Mold temperature: Recommended 80C. The mold temperature will affect the crystallinity, and the crystallinity will affect the physical properties of the product.

For thin-walled plastic parts, if the mold temperature is lower than 40C, the crystallinity of the plastic parts will change with time, and in order to maintain the geometric stability of the plastic parts, annealing treatment is needed. Injection pressure: Usually 750 to 1250 bar, depending on material and product design. Injection speed: high speed (slightly lower for reinforced materials).

Runners and Gates: Due to the short solidification time of the PA66, the position of the gate is very important. The gate aperture should not be less than 0.5*t (where t is the thickness of the plastic part). If hot runners are used, the gate size should be smaller than with conventional runners because the hot runner can help prevent premature solidification of the material. If using a submerged gate, the minimum diameter of the gate should be 0.75mm.

3. Typical application range

(1) PA12 Polyamide 12 or Nylon 12 Applications: Water meters and other commercial equipment, cable jackets, mechanical cams, sliding mechanisms, and bearings.

(2) PA6 Polyamide 6 or Nylon 6 Applications: Due to its good mechanical strength and stiffness, it is widely used in structural components. Because of its good wear resistance, it is also used to make bearings.

(3) PA66 Polyamide 66 or Nylon 66 Application: Compared with PA6, PA66 is more widely used in the automotive industry, instrument housings and other products that require impact resistance and high strength.


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