Common Problem
Common engineering plastics application knowledge
2020/7/15 8:59:55   270

ABS Acrylonitrile-Butadiene-Styrene copolymer (Acrylonitrile-Butadiene-Styrene)


Typical application range:

Automobiles (dashboards, tool hatches, wheel covers, mirror boxes, etc.), refrigerators, high-strength tools (hair dryers, blenders, food processors, lawn mowers, etc.), telephone casings, typewriter keyboards , Recreational vehicles such as golf carts and jet skis.


Injection mold process conditions:

Drying treatment: ABS material is hygroscopic and requires drying treatment before processing. The recommended drying condition is at least 2 hours at 80~90C. The material temperature should be less than 0.1%. Melting temperature: 210~280C; recommended temperature: 245C. Mold temperature: 25...70C. (Mold temperature will affect the finish of plastic parts, lower temperature will result in lower finish). Injection pressure: 500~1000bar. Injection speed: medium to high speed.


Chemical and physical properties:

ABS is synthesized from three chemical monomers: acrylonitrile, butadiene and styrene. Each monomer has different characteristics: Acrylonitrile has high strength, thermal stability and chemical stability; butadiene has toughness and impact resistance; styrene has easy processing, high smoothness and high strength. From the morphological point of view, ABS is an amorphous material. The polymerization of the three monomers produces a terpolymer with two phases, one is the continuous phase of styrene-acrylonitrile, and the other is the dispersed phase of polybutadiene rubber. The characteristics of ABS mainly depend on the ratio of the three monomers and the molecular structure in the two phases. This allows great flexibility in product design, and hundreds of different quality ABS materials have been produced on the market. These different quality materials provide different characteristics, such as medium to high impact resistance, low to high finish and high temperature distortion characteristics. ABS material has super easy processability, appearance characteristics, low creep and excellent dimensional stability and high impact strength.


PA12 Polyamide 12 or Nylon 12


Typical application range:

Water meters and other commercial equipment, cable sets, mechanical cams, sliding mechanisms and bearings, etc.


Injection mold process conditions:

Drying treatment: Ensure that the humidity is below 0.1% before processing. If the material is stored in the air, it is recommended to dry it 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 characteristics.


Mold temperature: 30-40C for unreinforced materials, 80-90C for thin-walled or large-area components, and 90-100C for reinforced materials. Increasing the temperature will increase the crystallinity of the material. Precise control of mold temperature is very important for PA12.


Injection pressure: up to 1000bar (recommended to use low holding pressure and high melting temperature).


Injection speed: high speed (better for materials with glass additives).


Runner and gate:


For materials without additives, the diameter of the flow channel should be about 30mm due to the low viscosity of the material. For reinforced materials, a large runner diameter of 5-8mm is required. The shape of the runners should all be circular. The injection port should be as short as possible. Various gates can be used. Do not use small gates for large plastic parts. This is to avoid excessive pressure or excessive shrinkage of the plastic parts. The thickness of the gate is preferably equal to the thickness of the plastic part. If using a submerged gate, the smallest diameter recommended is 0.8mm. Hot runner molds are very effective, but require precise temperature control to prevent material from leaking or solidifying at the nozzle. If a hot runner is used, the gate size should be smaller than that of the cold runner.


Chemical and physical properties:


PA12 is a linear, semi-crystalline-crystalline thermoplastic material from butadiene. Its characteristics are similar to PA11, but the crystal structure is different. PA12 is a good electrical insulator and will not affect the insulation performance due to moisture like other polyamides. It has good impact resistance and chemical stability. There are many improved varieties of PA12 in terms of plasticizing properties and strengthening properties. Compared with PA6 and PA66, these materials have a lower melting point and density, and a very high moisture regain. PA12 has no resistance to strong oxidizing acids.


The viscosity of PA12 mainly depends on humidity, temperature and storage time. It is very fluid. The shrinkage rate is between 0.5% and 2%, which mainly depends on the material variety, wall thickness and other process conditions.


PA6 polyamide 6 or nylon 6


Typical application range:

Because of its good mechanical strength and rigidity, it is widely used in structural parts. Due to its good wear resistance, it is also used in the manufacture of bearings.


Injection mold process conditions:

Drying treatment: As PA6 easily absorbs moisture, special attention should be paid to drying before processing. If the material is supplied in waterproof packaging, the container should be kept tightly closed. If the humidity is greater than 0.2%, it is recommended to dry it in hot air above 80C for 16 hours. If the material has been exposed to the air for more than 8 hours, it is recommended to perform vacuum drying at 105C for more than 8 hours.


Melting temperature: 230~280C, 250~280C for reinforced 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 parts, so the recommended mold temperature is 80~90C. For thin-walled, longer plastic parts, it is also recommended to apply higher mold temperature. Increasing the mold temperature can increase the strength and stiffness of the plastic part, but it reduces the toughness. If the wall thickness is greater than 3mm, it is recommended to use a low temperature mold of 20~40C. For glass reinforced materials, the mold temperature should be greater than 80C.


Injection pressure: generally between 750 and 1250 bar (depending on the material and product design).


Injection speed: high speed (slightly reduced for reinforced materials).


Runner and gate: Since the solidification time of PA6 is very short, the location 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 you use a hot runner, the gate size should be smaller than using a conventional runner, 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.


  

Chemical and physical properties:

The chemical and physical properties of PA6 are very similar to PA66, however, its melting point is lower and the process temperature range is very wide. Its impact resistance and solubility resistance are better than that of PA66, but it is also more hygroscopic. Because many quality characteristics of plastic parts are affected by hygroscopicity, it is necessary to fully consider this when designing products using PA6. In order to improve the mechanical properties of PA6, various modifiers are often added. Glass is the most common additive. Sometimes synthetic rubber, such as EPDM and SBR, is added to improve impact resistance. For products without additives, the shrinkage of PA6 is between 1% and 1.5%. Adding glass fiber additives can reduce the shrinkage to 0.3% (but it is slightly higher in the direction perpendicular to the process). The shrinkage of molding assembly is mainly affected by the crystallinity and moisture absorption of the material. The actual shrinkage rate is also a function of plastic part design, wall thickness and other process parameters


PA66 Polyamide 66, or Nylon 66, orpoly (hexamethylene adipamide


Typical application range:

Compared with PA6, PA66 is more widely used in the automotive industry, instrument housings and other products that require impact resistance and high strength requirements.


Injection mold process conditions:

Drying treatment: If the material is sealed before processing, then there is no need to dry it. However, if the storage container is opened, it is recommended to dry it in 85C hot air. If the humidity is greater than 0.2%, vacuum drying at 105°C for 12 hours is required.


Melting temperature: 260~290C. The glass additive product is 275~280C. The melting temperature should be avoided higher than 300C.


Mold temperature: 80C is recommended. The mold temperature will affect the crystallinity, and the crystallinity will affect the physical properties of the product. for


For thin-walled plastic parts, if a mold temperature lower than 40C is used, the crystallinity of the plastic parts will change over time. In order to maintain


The geometric stability of plastic parts requires annealing treatment.


Injection pressure: usually 750~1250bar, depending on material and product design.


Injection speed: high speed (slightly lower for reinforced materials).


Runner and gate: Since the solidification time of PA66 is very short, the location 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 you use a hot runner, the gate size should be smaller than using a conventional runner, 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.


Chemical and physical properties:

PA66 has a higher melting point in polyamide materials. It is a semi-crystalline-crystalline material. PA66 can maintain strong strength and rigidity at higher temperatures. PA66 is still hygroscopic after molding, the degree of which mainly depends on the composition of the material, wall thickness and environmental conditions. In product design, the influence of moisture absorption on geometric stability must be considered. In order to improve the mechanical properties of PA66, various modifiers are often added. Glass is the most common additive. Sometimes synthetic rubber, such as EPDM and SBR, is added to improve impact resistance. PA66 has low viscosity, so it has good fluidity (but not as good as PA6). This property can be used to process very thin components. Its viscosity is very sensitive to temperature changes. The shrinkage rate of PA66 is between 1%~2%, adding glass fiber additives can reduce the shrinkage rate to 0.2%~1%. The shrinkage rate differs greatly in the process direction and the direction perpendicular to the process direction. PA66 has solubility resistance to many solvents, but weak resistance to acids and other chlorinating agents.


PBT Polybutylene Terephthalates


Typical application range:

Household appliances (food processing blades, vacuum cleaner components, electric fans, hair dryer housings, coffee utensils, etc.), electrical components (switches, motor housings, fuse boxes, computer keyboard keys, etc.), automotive industry (radiator grilles) , Body panels, wheel covers, door and window parts, etc.).


Injection mold process conditions:

Drying treatment: This material is easily hydrolyzed at high temperatures, so the drying treatment before processing is very important. The recommended drying condition in the air is 120C for 6~8 hours, or 150C for 2~4 hours. The humidity must be less than 0.03%. If you use a moisture-absorbing dryer to dry, the recommended condition is 150C, 2.5 hours ?

Melting temperature: 225~275C, recommended temperature: 250C.

Mold temperature: 40~60C for unreinforced materials. The cooling channel of the mold should be well designed to reduce the bending of the plastic part. The heat loss must be fast and even. It is recommended that the diameter of the mold cooling channel is 12mm.


Injection pressure: medium (up to 1500bar).


Injection speed: The fastest possible injection speed should be used (because PBT solidifies quickly).


Runner and gate: It is recommended to use a circular runner to increase the pressure transmission (empirical formula: runner diameter = plastic part thickness + 1.5mm). Various types of gates can be used. Hot runners can also be used, but care must be taken to prevent material leakage and degradation. The gate diameter should be between 0.8~1.0*t, where t is the thickness of the plastic part. If it is a submerged gate, the recommended minimum diameter is 0.75mm.


Chemical and physical properties:


PBT is one of the toughest engineering thermoplastic materials. It is a semi-crystalline material with very good chemical stability, mechanical strength, electrical insulation properties and thermal stability. These materials have good stability under a wide range of environmental conditions. PBT has weak moisture absorption properties.


The tensile strength of unreinforced PBT is 50MPa, and the tensile strength of glass additive PBT is 170MPa. Too much glass additives will cause the material to become brittle.