PA66 processing conditions

PA66 processing conditions

Generic Class

PA66 (Polyamide 66, or Nylon 66, or poly (hexamethylene adipamide))

Applications

Competes with PA6 for most applications. PA66 is heavily used in the automotive industry, appliance housings, and generally where impact resistance and strength are required.

Injection Molding Processing conditions

Drying

Drying is not required if the material is sealed prior to molding; however, if the containers are left open, drying in a hot air oven at 85 C (185 F) is recommended. If the moisture content is > 0.2%, vacuum drying at 105 C (220 F) for 12 hours is recommended. 
Melt Temperature  260 - 290 C (500 - 554 F); 275 - 280 C (527 - 536 F) for glass filled grades; melt temperatures above 300 C (572 F) should be avoided 

Mold Temperature

80 C (176 F) suggested. Mold temperature affects crystallinity level which in turn affects physical properties. In the case of thin walled parts, crystallinity changes with time if mold temperatures of less than 40 C (104 F) are used. In such cases, annealing may be needed to retain dimensional stability. 

Material Injection Pressure

Generally between 75 - 125 MPa, depends on material and product design 

Injection Speed

High (slightly lower for reinforced grades) 

Runners and Gates

The gate location is important because of very fast freeze-off times. Any type of gate may be used; the aperture should not be less than half the thickness of the part. When hot runners are used, the size of the gates can be smaller than when cold runners are used, because premature freeze-off is prevented. When using submarine gates, the minimum diameter of the gate should be 0.75 mm.

Chemical and physical properties

PA66 homopolymer is produced by the polymerization of hexamethylene diamine and adipic acid (a dibasic acid). Among commercially available polyamides, PA66 has one of the highest melting points. It is a semicrystalline-crystalline material. The grades have strength and stiffness which is retained at elevated temperatures. It does absorb moisture after molding, but the retention is not as much as in the case of PA6. Moisture absorption depends on the composition of the material, wall thickness, and environmental conditions. Dimensional stability and properties are all affected by the amount of moisture absorption which must be taken into account for product design.

Various modifiers are added to improve mechanical properties; glass is one of the most commonly used filler. Addition of elastomers such as EPDM or SBR improves impact resistance.

The viscosity is low and therefore, it flows easily (but not as easily as PA6). This allows molding of thin components. The viscosity is very sensitive to temperature. Shrinkage is of the order of 0.01 - 0.02 mm/mm (1 - 2%). Addition of reinforcing glass fibers reduces the shrinkage to 0.2 - 1%. Differential shrinkage in the flow and cross-flow directions is quite high. Mineral fillers yield more isotropic moldings. PA66 is resistant to most solvents but not to strong acids or oxidizing agents.


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