PA 66 molding

PA 66
Generic Class
PA 66 (Polyamide 66, or Nylon 66, or poly (hexamethylene adipamide))

Applications
Competes with PA 6 for most applications. PA 66 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.

Resin Injection Pressure
Generally between 750 - 1,250 bar (~11,000 - 18,000 psi), 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
PA 66 homopolymer is produced by the polymerization of hexamethylene diamine and adipic acid (a dibasic acid). Among commercially available polyamides, PA 66 has one of the highest melting points. It is a semicrystalline-crystalline material. The resins 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 PA 6. 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 PA 6). 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. PA 66 is resistant to most solvents but not to strong acids or oxidizing agents.

Major Manufacturers
BASF (Ultramid A), DuPont (Minlon - mineral reinforced grades; Zytel), Monsanto (Vydyne), DSM (Akulon).

PA6 molding

PA 6
Generic Class
PA 6 (Polyamide 6, or Nylon 6, or Polycaprolactam)

Applications
Used in many structural applications because of its good mechanical strength and rigidity. It is used in bearings because of its good wear resistance.

Injection Molding processing conditions
　

　

Drying
Since PA 6 absorbs moisture readily, care should be taken to ensure its dryness prior to molding. If the material is supplied in watertight packaging, the containers should be kept closed. If the moisture content is >0.2%, drying in a hot air oven at 80 C (176 F) for 16 hours is recommended. If the material has been exposed to air for more than 8 hours, vacuum drying at 105 C (221 F) for more than 8 hours is recommended.

Melt Temperature
230 - 280 C (446 - 536 F); 250 - 300 C (482 - 572 F) for reinforced grades

Mold Temperature
80 - 90 C (176 - 194 F). Mold temperature significantly influences the crystallinity level which in turn affects the mechanical properties. For structural parts, a high degree of crystallization is required and mold temperatures of 80 - 90 C (176 - 194 F) are recommended. High mold temperatures are also recommended for thin-wall parts with long flow lengths. Increasing the mold temperature increases the strength and hardness, but the toughness is decreased. When the wall thickness is greater than 3 mm, a cold mold is recommended (20 - 40 C / 68 - 104 F), which leads to a higher and more uniform degree of crystallinity. Glass reinforced resins are always processed at mold temperatures greater than 80 C (176 F).

Resin Injection Pressure
Generally between 750 - 1,250 bar (~11,000 - 18,000 psi) (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
The molecular structure of polyamides consist of amide (CONH) groups joined by linear aliphatic sections (based on methylene groups). The toughness, rigidity, crystallinity, and thermal resistance of polyamide resins are due to the strong interchain attraction caused by the polarity of the amide groups. The CONH groups also cause a lot of moisture absorption.

Nylon 6 is produced by polymerization of caprolactam. The chemical and physical properties are similar to that of PA 66. However, its melting point is lower than PA 66 and it has a wider processing temperature range. Its impact strength and solvent resistance are better than PA 66, but its moisture absorption is higher. Many properties are affected by moisture absorption, which must be taken into account when designing with this resin. Various modifiers are added to improve mechanical properties; glass is one of the most commonly used fillers. Addition of elastomers such as EPDM or SBR improves impact resistance.

For unfilled grades, shrinkage is of the order of .01 - .015 mm/mm (1 - 1.5%). Addition of glass fibers reduce the shrinkage to as low as 0.3% in the flow direction (but could be as high as 1% in the cross-flow direction). The post-molding shrinkage is affected mainly by the crystallinity level and moisture absorption. The actual shrinkage is a function of part design, wall thickness, and processing conditions.

Major Manufacturers
BASF (Ultramid B), DuPont (Zytel), DSM (Akulon)