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General Engineering Plastics Guide

2018-08-20

General engineering plastics: polycarbonate PC, polyoxymethylene POM, polyamide PA, thermoplastic polyester PBT/PET, modified polyphenylene ether MPPO.


What is the basic physical property of each material?


1. Polyamide: (common name: nylon, PA, PA6, PA66, PA610, PA1010, etc.).


PA6: Polycaprolactam. PA66: polyhexamethylenediamine adipate.

Advantages:

Low specific gravity (only 1/7 of metal), "soft and soft" can be processed into various products instead of metal.

Heat resistance, oil, grinding, self-lubricating (low friction coefficient);

High tensile strength, excellent impact toughness, electrical insulation;

Gas barrier properties, better blocking oxygen.


Disadvantages:

The shrinkage rate is relatively large and the dimensional stability is poor.

High water absorption, easy to absorb moisture, increase in size, (hydrolysis).

Easy to oxidize and yellow (pyrolysis).


Comparative analysis:

Impact resistance, solubility resistance, water absorption (disadvantages): PA6>PA66

Wear resistance, heat resistance (heat distortion temperature), melting point: PA66>PA6. Therefore, the market price PA66 is higher than PA6.

Toughness: PA66


Typical application:

Pump impeller, fan blades, valve seat, bushings, bearings, various instrument panels, automotive electrical instruments, hot and cold air conditioning valves and other components. About 3.6 to 4 kilograms of nylon products are consumed per car. Polyamide has the largest consumption ratio in the automotive industry, by electrical and electronic.


2. Polycarbonate (PC):


Advantages:

Optical grade transparency is high, and can be arbitrarily colored.

The impact strength is extremely high and can not be destroyed by hammering.

Aging resistance (2 years).

Fire resistance, decomposition produces CO2 flame retardant, self-extinguishing.

Heat resistance, electrical insulation is good.

Low shrinkage, high dimensional stability, low warpage.

Has the same strength as non-ferrous metals, but also has both ductility and toughness. Can withstand the explosion of TV screens.


Disadvantages:

It is prone to internal stress cracking.

Poor wear resistance.

Sensitive to the gap.

Poor solvent resistance (alkali), high temperature easy to hydrolyze.

Poor fatigue resistance.

Surface hardness is low.

Poor compatibility with other resins.

Friction coefficient is large, no self-lubricating.


Comparative analysis:

Creep resistance: PC> (PA and POM series products)

The market price is moderate.


Typical application:

Safety lampshades, signal lights, transparent protective panels for stadiums and stadiums, lighting glass, high-rise building glass, car mirrors, windshield panels, aircraft cabin glass, motorcycle driving helmets. The most used markets are computers, office equipment, automobiles, alternative glass and sheets, and CD and DVD discs are among the most promising markets.


3. Polyoxymethylene (POM):


Advantages:

Wear resistance is excellent. Similar to the hardness, strength and rigidity of metals.

The impact strength is high.

Electrical insulation is better.

Low water absorption, good dimensional stability. (no need to dry)

The limit PV value is large and the self-lubricating property is good.

Stiffness and elasticity are good. Good fatigue resistance.


Disadvantages:

Poor weather resistance, easy to powder, crack.

Density is large (1.42).

It is very sensitive to the gap.

Poor solvent resistance (acid).

Molding shrinkage rate is large.

High temperature thermal stability is poor, decomposition of odor formaldehyde.


Comparative analysis:

Impact strength: (PC and ABS series products)> POM

Wear resistance: POM>PA66>PA6>ABS>HPVC>PS>PC

The market price POM is moderate.


Typical application:

Electrical and electronic, machinery, instrumentation, daily light industry, automotive, building materials, agriculture and other fields. Applications in many new fields, medical technology, sports equipment.


4. Polybutylene terephthalate (PBT) and polyethylene terephthalate (PET)


PBT:


Advantages:

Fast crystallization, rapid prototyping, short processing cycle. (PBT has a low glass transition temperature and can be crystallized quickly when the mold temperature is 50 °C).

Wear resistance, weather resistance is good.

Electrical insulation is better.

Impact toughness is good.


Disadvantages:

It is very sensitive to the gap.

PBT must be dried at 110~120 °C for about 3 hours before injection molding. The molding processing temperature is 250-270 °C, and the mold temperature is controlled at 50-75 °C.

PBT is easy to decompose in case of water (use caution in high temperature and high humidity environments).


Comparative analysis:

Tg: PET (75 ° C) > PBT (40 ° C)

Wear amount: POM>PBT

Melting point: PET>PBT

Heat resistance: PET>PBT

Wear resistance: PET

PET has a high crystallization temperature, a slow crystallization rate, a high mold temperature in the injection molding machine, and a long molding cycle limits PET applications. The market price PBT is moderate.


Typical application:

In the electronics, electrical and automotive industries. Due to the high insulation and temperature resistance of PBT, it can be used as a flyback transformer for TV sets, car distribution boards and ignition coils, office equipment housings and bases, various automotive exterior parts, air conditioner fans, electronic stove bases, office Equipment shell.


5. Polyphenylene ether PPO/PPE:


PPO:

Advantages:

Low shrinkage, dimensional stability.

Wide temperature range (-127~121 °C). Self-extinguishing and self-extinguishing properties of nylon are a meaning, but PPO's self-extinguishing properties are better.

Density 1.06 "the lowest engineering plastics".

Wear resistance, water resistance, steam resistance. Good acid and alkali resistance.

Tensile strength, impact strength, creep resistance.

Outstanding electrical insulation dielectric properties "the first of engineering plastics.


Disadvantages:

Melt flow is poor.

Poor resistance to organic solvents.

Poor light resistance.


Comparative analysis:

Density: POM>PBT>PC>PA>PPO.


Typical application:

Instead of stainless steel, surgical medical instruments are manufactured. In the electromechanical industry, gears, blower blades, pipes, valves, screws and other fasteners and connectors can be made. They are also used to make parts in the electronics and electrical industries, such as coil bobbins and printed circuit boards.


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