1. High mechanical strength, good toughness, high tensile and compressive strength. Specific tensile strength is higher than that of metal, and specific compressive strength is comparable to that of metal, but its rigidity is not as good as that of metal. Tensile strength is close to yield strength, more than twice as high as ABS. Ability to absorb shock, stress and vibration is strong, impact strength is much higher than that of general plastics, and is better than acetal resin.
2. Outstanding fatigue resistance, parts can maintain original mechanical strength after repeated inflections. Common escalator handrails, new bicycle plastic rims and other occasions where periodic fatigue is extremely obvious, PA is often used.
3. High softening point and heat resistance (such as nylon 46, etc., high crystalline nylon has a high heat distortion temperature and can be used for a long time at 150 degrees. After PA66 is reinforced with glass fiber, its heat distortion temperature can reach 250 degrees or more).
4. Surface is smooth, friction coefficient is small, and it is wear-resistant. It is self-lubricating when used as a movable mechanical component and has low noise. When friction is not too high, it can be used without lubricant; if it is really necessary to use lubricant to reduce friction or help heat dissipation, water, oil, grease can be selected. As a result, it has a long service life as a transmission component.
5. Corrosion resistance, very resistant to alkalis and most salt solutions, also resistant to weak acids, engine oils, gasoline, aromatic compounds and general solvents, inert to aromatic compounds, but not resistant to strong acids and oxidants. It can resist erosion of gasoline, oil, fat, alcohol, weak base, etc. and has good anti-aging ability. It can be used as packaging material for lubricating oil and fuel.
6. It is self-extinguishing, non-toxic, odorless, good weather resistance, inert to biological erosion, has good antibacterial and antifungal capabilities.
7. It has excellent electrical properties. Good electrical insulation. Nylon has a high volume resistance and high breakdown voltage. It can be used as a power frequency insulating material in a dry environment, and it has good electrical insulation even in a high-humidity environment.
8. Parts are light in weight, easy to dye and easy to shape. Because of its low melt viscosity, it can flow quickly. It is easy to fill mold, freezing point is high after mold is filled, shape can be set quickly, so molding cycle is short and production efficiency is high.　

 

1. Easy to absorb water. Water absorption is large, and saturated water can reach more than 3%. To a certain extent, dimensional stability and electrical performance are affected, especially thickening of thin-walled parts has a greater impact; water absorption will also greatly reduce mechanical strength of plastic. When selecting materials, consideration should be given to influence of use environment and accuracy of coordination with other components.
Fiber reinforcement can reduce water absorption rate of resin, so that it can work under high temperature and high humidity. Nylon has a very good affinity with glass fiber. It is often used to make combs, toothbrushes, clothes hooks, fan bones, net bag ropes, fruit outer packaging bags and so on. Non-toxic, but not long-term contact with acid and alkali. It is worth noting that after adding glass fiber, tensile strength of nylon can be increased by about 2 times, temperature resistance can be improved accordingly.　
2. Poor light resistance. In a long-term high temperature environment, it will oxidize with oxygen in air, and color will turn brown at the beginning, then surface will be broken and cracked.
3. Injection molding technology requirements are strict: presence of trace moisture will cause great damage to molding quality; dimensional stability of product is difficult to control due to thermal expansion; existence of sharp corners in product will cause stress concentration and reduce mechanical strength; if wall thickness is not uniform, it will cause distortion and deformation of part; equipment requires high precision during post-processing of part.　
4. It will swell by absorbing water and alcohol. It is not resistant to strong acids and oxidants, and cannot be used as acid-resistant materials.

PMMA is commonly known as plexiglass, acrylic and so on. Chemical name is polymethyl methacrylate. Due to shortcomings of PMMA surface hardness, easy scratching, low impact resistance, poor molding fluidity, etc., modification of PMMA has appeared one after another. Such as copolymerization of methyl methacrylate with styrene and butadiene, blending of PMMA and PC, etc. 372 plexiglass is obtained by copolymerization of methyl methacrylate and styrene. If a small amount of nitrile rubber (about 50%) is added to 372 plexiglass, it can become 373 plexiglass.
Flow of PMMA is worse than that of PS and ABS, and melt viscosity is more sensitive to temperature changes. During molding process, melt viscosity is mainly changed from injection temperature. PMMA is an amorphous polymer with a melting temperature greater than 160℃ and a decomposition temperature of 270℃.

PMMA has a certain degree of water absorption, with a water absorption rate of 0.3-0.4%, and injection molding must be at a temperature below 0.1%, usually 0.04%. Presence of water causes bubbles, gas lines, and reduced transparency in melt, so it must be dried. Drying temperature is 80-90℃, time is more than 3 hours.
Recycled materials can be used 100% in some cases. Actual amount depends on quality requirements, usually over 30%. Recycled materials should avoid pollution, otherwise it will affect transparency and properties of finished product.

PMMA has no special requirements for injection molding machines. Because of its high melt viscosity, a deeper screw groove and a larger diameter nozzle hole are required. If strength of product is higher, a screw with a larger length to diameter ratio should be used for low-temperature plasticization. In addition, PMMA must be stored in a dry hopper.

Mold temperature can be 60℃-80℃. Diameter of main runner should match inner taper. The best angle is 5 to 7. If you want to inject 4mm or more products, angle should be 7, and diameter of runner should reach 8 to 10mm. Overall length of gate should not exceed 50mm.
For products with a wall thickness of less than 4mm, diameter of runner should be 6-8mm.
For products with wall thickness greater than 4mm, diameter of runner should be 8-12mm.
Diagonal, fan-shaped and tabular gate depth should be 0.7 to 0.9t (t is thickness of product wall), diameter of needle gate should be 0.8 to 2mm; low viscosity should choose a smaller size.
Common vent holes are 0.05 to 0.07mm deep and 6mm wide
Demolding slope is between 30'-1 and 35'-130 in cavity portion.

It can be measured by air injection method: ranging from 210℃ to 270℃, depending on information provided by supplier.

Fast injection can be used, but to avoid high internal stress, it is advisable to use multi-stage injection, such as slow-fast-slow, etc. When injecting thick parts, use slow speed.

If temperature is 260℃, residence time cannot exceed 10 minutes at most, and if temperature is 270℃, residence time cannot exceed 8 minutes.