Nylon is a synthetic fiber first developed in the world, and it is also the largest production variety of engineering plastics at present.
In recent years, with the development of nylon polymerization, modification and processing molding technology, nylon materials in the manufacturing industry in an increasingly wide range of applications, nylon products abound in daily life.
However, how much do you know about this material? Next, let’s go into the rich world of nylon, feel the charm of polymer materials manufacturing.
- Introduction of nylon materials
Polyamide fibers, commonly known as nylon (Nylon), are named Polyamide (abbreviated as PA) in English, with a density of 1.15g/cm^3. They refer to thermoplastic resins that have repeating amide groups—[NHCO]—on their main chain. This includes aliphatic PA, aliphatic-aromatic PA, and aromatic PA.
Among them, aliphatic PA varieties are numerous, have large production volumes, and are widely used. Their naming is determined by the specific number of carbon atoms in the synthetic monomer, with numbers indicating the carbon atom counts between the acid and amine groups.
A single number signifies that the material is composed of a homopolymer, like PA6, PA11, PA12, etc. Two numbers indicate that the material consists of copolymers, such as PA46, PA66, PA610, PA612, PA1010, etc.
Nylon possesses excellent toughness, self-lubrication, wear resistance, chemical resistance, gas permeability, oil resistance, non-toxicity, and ease of coloring, making it extensively utilized in the industry.
Its impact strength is higher than ABS and POM but lower than PC. However, it has a low heat deformation temperature, high moisture absorption, and poor dimensional stability.
Among nylon materials, PA66 has the strongest structure, while PA6 offers the best processing properties.
- Process characteristics of nylon
Rheological properties
Most of nylon is crystalline resin, when the temperature exceeds its melting point, its melt viscosity is small, melt fluidity is very good, should prevent the occurrence of overflow.
At the same time, due to the rapid condensation of the melt, the material should be prevented from blocking the nozzle, runner, gate and other products caused by the phenomenon of insufficiency.
Mould overflow value of 0.03, and the melt viscosity of temperature and shear changes are more sensitive, but more sensitive to temperature, reduce the melt viscosity from the barrel temperature to start.
Water absorption
Nylon’s water absorption is large, wet nylon in the molding process, the performance of a sharp drop in viscosity and mixed with bubbles appear on the surface of the product silver, the mechanical strength of the resulting products decreased, so the material must be dry before processing.
Crystallization
In addition to transparent nylon, nylon is mostly crystalline polymer, high crystallinity, products tensile strength, abrasion resistance, hardness, lubricity and other properties have been improved, the coefficient of thermal expansion and water absorption tends to decline, but the transparency and impact resistance is not good.
At the same time, the mold temperature in the injection molding process will also have an impact on the crystallinity, mold temperature is high crystallinity, low mold temperature crystallinity is low.
Shrinkage
Similar to other crystalline plastics, nylon resin has a large shrinkage problem, the general shrinkage of nylon with the crystallization of the relationship between the largest, when the crystallinity of the product products will increase the shrinkage of the product, in the molding process to reduce the mold temperature or increase the injection pressure will reduce the shrinkage.
But the product internal stress increases easy to deform. For example, non-glass fiber reinforced PA6 and PA66 shrinkage in 1.5-2%, after adding glass fiber can make the shrinkage rate reduced to 0.3% to 0.8%.
3.Nylon injection molding conditions
Nylon, as a high-performance engineering plastic with good abrasion resistance and thermal stability, is widely used in automotive, electronics, instrumentation and other fields. In the production of nylon products, injection molding is an important processing method.
Controlling the key process parameters of nylon injection molding can better develop a suitable production process.
- Injection Molding Temperature
Because nylon is a crystalline polymer with a distinct melting point, the injection molding temperature will vary for different categories of nylon materials, usually between 240℃~280℃ region. Too low an injection temperature will lead to poor material fluidity, resulting in unfilled, short flow, poor fusion and other problems; too high an injection temperature is prone to cause decomposition, bubbles, sticky material and other problems, affecting the molding quality.
- Mold temperature
The mold temperature of nylon is usually between 70℃~90℃, too high temperature will make the mold easy to deform, while too low temperature will lead to finished product surface roughness, dimensional instability and other problems. The injection molding machine usually adopts hot runner or temperature control system to keep the mold temperature stable when processing nylon.
- Injection Pressure
The injection pressure required for nylon molding is generally in the range of 60MPa ~ 120MPa, the specific value needs to be based on the size of the product, wall thickness, the specifications of the injection molding machine and other factors.
If the injection pressure is insufficient, the injection molded parts are prone to bubbles, short flow, unfilled and other problems, affecting product quality; if the injection pressure is too large, it is easy to cause mold deformation, increase the energy consumption of the injection molding machine and other issues.
- Injection speed
The injection speed of nylon needs to be adjusted according to the characteristics of the material, the wall thickness of the product, mold structure and other factors.
Too fast injection speed will produce instantaneous high pressure in the filling process, which is easy to produce bubbles, shrinkage and other defects; too slow injection speed will lead to incomplete filling, unfilled, hot dead, affecting the quality of finished products.
- Application Scenarios
The application scenarios of nylon injection molding are very wide, mainly in the following aspects:
Automobile: Nylon plastic molding is widely used in automobile manufacturing, such as engine cover, doors, exterior decorative parts and so on. Nylon injection molded parts are lightweight, high strength, wear-resistant and so on, which are very suitable for automobile manufacturing.
Home appliance: home appliance manufacturing is also an important application area of nylon injection molding, such as vacuum cleaners, refrigerator parts, TV brackets, etc.. Nylon injection molded parts have the advantages of high temperature resistance, not easy to aging, etc., which can meet the high requirements for materials in the manufacture of home appliances.
Medical devices: nylon injection molding is also widely used in the manufacture of medical devices, such as medical syringes, catheters, surgical tools and so on. Nylon injection molded parts have anti-bacteria, easy to clean and other characteristics, to meet the high demand for materials in the manufacture of medical devices.
Other fields: nylon injection molding is also widely used in other fields, such as industrial manufacturing, aerospace and so on. Nylon injection molded parts have excellent physical properties and can meet various industrial manufacturing needs.
To sum up, nylon injection molding is very important in the fields of automotive, home appliances and medical devices, and it also plays an important role in various industrial manufacturing.
With the continuous progress of technology and material upgrading, it is believed that nylon injection molding will have a wider application prospect.
