Always Having Issues Processing PA66? This Article Explains These Common Faults And Their Causes!

Always Having Issues Processing PA66? This Article Explains These Common Faults and Their Causes!

As a "powerhouse" among engineering plastics, PA66 is widely used in automotive, electronics, machinery, and other fields due to its advantages of high strength, wear resistance, and oil resistance. However, many practitioners frequently encounter obstacles during processing, resulting in either flawed part appearance or failure to meet dimensional accuracy, seriously impacting production efficiency and product quality. In fact, most of these problems are related to PA66's characteristics such as hygroscopicity and crystallinity. Today, let's review the most common faults in processing to help you pinpoint the root causes.

I. Surface "Silver Streaks" and Bubbles, Compromising Both Appearance and Performance
This is the most frequently occurring problem in PA66 processing. Fine, silvery-white filamentous streaks often appear on the surface of parts, sometimes accompanied by tiny raised bubbles, especially noticeable near gates and at sudden changes in wall thickness. The core reason is actually quite simple. PA66 is extremely hygroscopic. If drying before processing is insufficient, the moisture in the raw material turns into steam under the high temperature (250-270°C) in the barrel. This steam, mixed into the melt during injection molding, forms silver streaks and bubbles. Additionally, contamination of the raw material with dust or oil, or an excessively high proportion of recycled material, can also trigger such issues.

II. Poor Gloss and Flow Marks, Making Parts Look "Cheap"
Often, processed PA66 parts have a dull, matte surface with obvious streaky marks along the melt flow direction, particularly common in large, flat parts. There are three main causes. First, the mold temperature is too low. PA66 molding typically requires a mold temperature of 80-120°C. If the temperature is insufficient, the melt cools too quickly and cannot fully conform to the mold surface. Second, the melt temperature is too low, resulting in poor fluidity, or the injection speed or pressure is insufficient, preventing the melt from spreading uniformly in the mold. Third, oil stains or scratches on the mold surface, or impurities in the raw material, can all affect part gloss.

III. Pronounced Weld Lines, Breaking Easily with a Light Bend
A distinct line often appears at locations with multiple gates or holes, which is the weld line. It not only affects appearance but, more critically, significantly reduces strength in the weld line area, making it prone to breakage during assembly or use. This is because the PA66 melt cools rapidly. When divided melt streams converge inside the mold, their temperature has already dropped substantially, preventing polymer chains from fully intertwining. If the mold temperature or melt temperature is too low, or the injection speed is too slow, the weld line problem becomes more severe.

IV. Part Warpage and Deformation, Failing to Meet Dimensional Standards
Thin-walled, elongated, or asymmetrically structured PA66 parts are prone to bending or twisting after cooling, with significant dimensional variation, potentially differing even within the same batch. This is related to PA66's crystallization characteristics. Crystallization causes relatively large volumetric shrinkage. If different areas of the part cool at uneven rates, leading to different crystallinity, internal stresses become imbalanced, resulting in warpage and deformation. Furthermore, improper gate location, uneven cooling system distribution, or unreasonably set injection pressure and holding time can also lead to loss of dimensional accuracy control.

V. Brittle Parts Lacking Toughness, Easily Damaged in Use
Normal PA66 parts have good toughness. However, if they fracture under slight external force after processing, with a smooth fracture surface, it indicates a severe loss of toughness. This is likely due to excessive drying of the raw material or excessively high processing temperatures, causing PA66 molecular chain degradation and compromised mechanical properties. It could also be caused by excessively low mold temperature, leading to uneven part crystallization. An excessively high proportion of recycled material or the mixing of degraded material into the raw material can also make parts brittle and prone to breakage.

VI. Frequent "Jams" During Processing, Greatly Affecting Production Efficiency
Apart from issues with the parts themselves, faults like melt fracture, sticking in the mold, or poor feeding can occur during processing. For example, a rough surface or wavy pattern when the melt extrudes from the nozzle is caused by excessive shear stress due to low melt temperature or too high injection speed. Parts sticking to the mold and failing to eject are often due to excessively high mold temperature, insufficient draft angle, or excessively long injection pressure/holding time. Raw material clumping and clogging at the feed throat is caused by moisture-absorbed material clumping when heated or improper temperature settings in the feed zone.

In fact, most PA66 processing problems have traceable causes. The core is controlling the two key aspects: "drying" and "temperature". It is essential to thoroughly dry the raw material at 100-120°C for 4-6 hours before processing, ensuring moisture content is reduced below 0.2%. Then, optimize mold design based on part structure and precisely control process parameters like melt temperature and mold temperature. Most faults can be effectively avoided this way.
What other challenging problems have you encountered in PA66 processing? Feel free to share in the comments.