Common Use Plastic--PA

author: YITECH

2024-10-21

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1. PA performance

PA is also a crystalline plastic (nylon is a ductile angular translucent or milky crystalline resin), as an engineering plastic nylon molecular weight is generally 1.5-30,000, many varieties, used in injection molding commonly used nylon 6, nylon 66, nylon 1010, nylon 610 and so on.

Nylon has toughness, wear resistance and self-lubrication, its main advantages of high organic mechanical strength, good toughness, fatigue resistance, smooth surface, high softening point, heat resistance, low friction coefficient, wear resistance, self-lubrication, shock absorption and noise attenuation, oil resistance, weak acid resistance, alkali resistance and general solvents, good electrical insulation, self-extinguishing, non-toxic, odorless, good weather resistance.

The disadvantage is that the water absorption is large, the dyeing is poor, affecting the dimensional stability and electrical properties, and the fiber reinforcement can reduce the water absorption rate, so that it can work at high temperature and high humidity. Nylon and glass fiber affinity is very good (100℃ can be used for a long time), corrosion resistance, light weight, easy to form. The main shortcomings of PA are: easy water absorption, injection molding technology requirements are stricter, dimensional stability is poor, because of its specific heat, the product is hot.

PA66 is the highest mechanical strength and most widely used variety in the PA series. Its crystallinity is high, so its rigidity, hardness, heat resistance are high. PA1010 is originated in 1958, translucent, small specific gravity, large elasticity and flexibility, lower water absorption than PA66, dimensional stability is reliable.

Nylon nylon 66 has the highest hardness and rigidity, but the worst toughness. The order of nylon toughness is: PA66 < PA66/6 < PA6 < PA610 < PA11 < PA12

The flammability of nylon is ULS44-2, the oxygen index is 24-28, the decomposition temperature of nylon is > 299℃, and spontaneous combustion will occur at 449~499℃. The melt fluidity of nylon is good, so the wall thickness of the product can be as small as 1mm.

2. Process characteristics of PA

2.1 PA is easy to absorb moisture, must be fully dried before processing, water content should be controlled below 0.3%. The raw material is dry well, the product is shiny, otherwise it is rough, PA will not gradually soften with the increase of the heating temperature, but soften in a narrow temperature range near the melting point, the melting point is obvious, and the temperature will flow once it is reached (different from PS, PE, PP and other materials).

The viscosity of PA is much lower than that of other thermoplastics, and its melting temperature range is narrow (only about 5 ° C). PA fluidity is good, easy to fill molding, but also easy to walk. The nozzle is prone to "salivation", and the glue needs to be larger.

The PA melting point is high, the freezing point is high, and the molten material will solidify at any time in the mold due to the temperature falling below the melting point, which prevents the completion of the filling molding. Therefore, high-speed injection must be used (especially for thin-walled or long process parts). Nylon mold should have more adequate exhaust measures.

In the molten state, PA has poor thermal stability and is easy to degrade. The temperature of the barrel should not exceed 300℃, and the heating time of the molten material in the barrel should not exceed 30 minutes. The PA has high requirements on the mold temperature, and the mold temperature can be used to control its crystallinity to obtain the required performance.

The mold temperature of PA is better at 50-90℃, the processing temperature of PA1010 is appropriate at 220-240℃, and the processing temperature of PA66 is 270-290℃. PA products sometimes need to be "annealed" or "humidified" according to quality requirements.

2.2 The humidity of PA12 polyamide 12 or nylon 12 should be ensured below 0.1% before processing. If the material is stored exposed to 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 equilibrium. Melting temperature 240~300C; Do not exceed 310C for ordinary materials, and do not exceed 270C for materials with flame retardant properties.

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

Runner and gate: For materials without additives, the diameter of the runner should be about 30mm due to the low viscosity of the material. For enhanced materials, a large runner diameter of 5~8mm is required. The shape of the runner should all be circular. The injection port should be as short as possible.

A variety of gate forms can be used. Do not use small gates for large plastic parts, in order to avoid excessive pressure or excessive shrinkage of plastic parts. Gate thickness should be equal to the thickness of plastic parts. If a submerged gate is used, a minimum diameter of 0.8mm is recommended. Hot runner molds are effective, but require precise temperature control to prevent material from leaking or solidifying at the nozzle. If the hot runner is used, the gate size should be smaller than the cold runner.

2.3 PA6 polyamide 6 or nylon 6: Because PA6 easily absorbs water, special attention should be paid to drying before processing. If the material is supplied in a waterproof packaging, the container should be kept airtight. 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 it for more than 105C, 8 hours.

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

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

Injection speed: high speed (slightly lower for enhanced materials). Runner and gate: Due to the short setting time of PA6, the location of gate is very important. The aperture of the gate should not be less than 0.5*t (where t is the thickness of the plastic part). If a hot runner is used, the gate size should be smaller than if a conventional runner is used, because the hot runner can help prevent the material from setting prematurely. If a submerged gate is used, the minimum diameter of the gate should be 0.75mm.

2.4 PA66 polyamide 66 or nylon 66 If the material is sealed before processing, then there is no need to dry. 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%, it is also necessary to perform 105C, 12 hours of vacuum drying.

Melting temperature: 260~290C. The product of glass additive is 275~280C. The melting temperature should not be higher than 300C. Mold temperature: 80C recommended. Mold temperature will affect the crystallinity, and 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 is required. Injection pressure: usually 750 to 1250bar, depending on material and product design. Injection speed: High speed (slightly lower for enhanced materials).

Runner and gate: Because the solidification time of PA66 is very short, the location of gate is very important. The aperture of the gate should not be less than 0.5*t (where t is the thickness of the plastic part). If a hot runner is used, the gate size should be smaller than if a conventional runner is used, because the hot runner can help prevent the material from setting prematurely. If a submerged gate is used, the minimum diameter of the gate should be 0.75mm.

3. Typical application range:

3.1 PA12 polyamide 12 or nylon 12 applications: water meters and other commercial equipment, cable sleeves, mechanical cams, sliding mechanisms and bearings.

3.2 PA6 polyamide 6 or nylon 6 application range: It is widely used in structural components due to its good mechanical strength and stiffness. Because of its good wear resistance, it is also used in the manufacture of bearings.

3.3 PA66 polyamide 66 or nylon 66 application range: compared with PA6, PA66 is more widely used in the automotive industry, instrument housing and other products requiring impact resistance and high strength requirements.

Our company provide all kinds of plastic parts including PA/POM/PMMA/etc parts, we also provide custom injection mold service, if you have any needs please do not hesitate to contact us!

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