A little knowledge about plastics-3 (Introduction to properties of plastic raw materials)

ABS: (acrylonitrile butadiene styrene)

English name: acrylonitrile butadiene styrene

Specific Gravity: 1.05 g/cc

Shaping shrinkage: 0.4-0.7%

Forming temperature: 200-240℃

Drying conditions: 80-90℃ for 2 hours

Material properties

1. Good overall performance, high impact strength, chemical stability and good electrical performance.

2. Good alloy with 372 plexiglass, made of two-color plastic parts, and surface can be chromed and painted.

3. There are shock-resistant, high-temperature-resistant, fire-resistant, reinforced, transparent and other grades

4. The flow is slightly worse than HIPS, better than PMMA, PC, etc., and has good flexibility. Suitable for making general mechanical parts, wear-reducing and wear-resistant parts, transmission parts and telecommunication parts.


1. Amorphous materials with medium fluidity and high moisture absorption must be completely dried. Plastic parts that require a glossy surface should be preheated and dried at a temperature of 80-90 degrees for a long time for 3 hours.

2. It is desirable to use high material temperature and high mold temperature, but if material temperature is too high, it is easy to decompose (decomposition temperature > 270 degrees for high-precision plastic parts, mold temperature should be 50-60 degrees for high gloss. For heat-resistant plastic parts, temperature mold should be 60-80 degrees.

3. If you need to eliminate watermark, you need to improve fluidity of material, accept high temperature of material and high temperature of mold,

4. If heat-resistant or fire-resistant materials are molded, plastic degradation products will remain on mold surface after 3-7 days of production, resulting in mold surface gloss. needs to be cleaned in time, and exhaust position on mold surface needs to be added.

PS plastic (polystyrene)

English name polystyrene

Specific Gravity: 1.05 g/cc

Shaping shrinkage: 0.6-0.8%

Forming temperature: 170-250℃

Drying conditions: ---

Material properties

Excellent electrical insulation (especially high frequency insulation), colorless and transparent, light transmission second only to organic glass, staining, water resistance and good chemical resistance,

Suitable for making insulating transparent parts, decorative parts and chemical instruments, optical instruments and other parts

Production of insulating transparent parts, decorative parts and chemical instruments, optical instruments and other parts.


1. Amorphous material with low moisture absorption does not need to be completely dried and is not easy to decompose, but has a large cocoefficient of thermal expansion and is subject to internal stresses, has good fluidity and can be molded. using a screw or plunger injection machine.

2. It is advisable to use high quality materials

3.Different gate shapes can be used, and gate is connected by arcs of plastic parts to avoid damage to plastic parts when gate is removed.The demoulding slope is large and ejection is uniform.Inserts if any inserts need to be preheated.< /p>

PMMA plastic (plexiglass)

(Polymethyl methacrylate)

English name of polymethyl methacrylate

Specific gravity: 1.18 g/cm3

Shaping shrinkage: 0.5-0.7%

Forming temperature: 160-230℃

Drying conditions: 70-90℃ for 4 hours

Material properties

Excellent transparency, high strength, certain heat and cold resistance, corrosion resistance, good insulation, comprehensive performance, superior to polystyrene, but brittle, easy to melt in organic solvents such as light-transmitting materials. Surface hardness is slightly lower< /p>

Suitable for making transparent insulating parts and parts with general strength.


1. Amorphous materials, with high moisture absorption, should be dry, non-degradable, medium fluidity, prone to poor filling,

2. It is suitable for high pressure injection. Under condition of no defects, adopts high material temperature and high mold temperature to increase fluidity, reduce internal stress, improve transparency and strength. Large, even release. At same time, an outlet is provided from time to time to prevent foaming.

Plastic POM (polyoxymethylene) racing steel

English name olioxymethylene (polyformaldehyde)

Specific gravity: 1.41–1.43 g/cm3

Shaping shrinkage: 1.2-3.0%

Forming temperature: 170-200℃

Drying conditions: 80-90℃ for 2 hours

Material properties

Good overall performance, high strength, high rigidity, good wear resistance, low water absorption, good dimensional stability but poor thermal stability, easy to ignite in atmosphere

Suitable for making anti-friction and wear-resistant parts, transmission parts, chemical, instrument and other parts


1. Crystallization material, narrow melting range, fast melting and solidification, crystallization occurs when material temperature is slightly lower than melting point. Average mobility. Hygroscopicity is low, without drying treatment.

2. Low coefficient of friction, good elasticity, easy to apply on surface of plastic parts

3. It is very easy to decompose, and decomposition temperature is 240 degrees. Decomposition produces irritating and corrosive gases. That's whythe mold steel must be made from corrosion resistant materials.

PP plastic (polypropylene)

English name polypropylene

Specific gravity: 0.9–0.91 g/cm3

Shaping shrinkage: 1.0-2.5%

Forming temperature: 160-220℃

Drying conditions: ---

Material properties

The low density, strength, stiffness, hardness and heat resistance are better than HDPE, and it can be used at about 100 degrees. becomes brittle at low temperatures and is not heat stable

Suitable for making general mechanical parts, corrosion resistant parts and insulation parts


1. Crystalline material, low hygroscopicity, prone to breakdown when melted, and easily decomposed by long-term contact with hot metal.

2. The fluidity is good, but shrinkage range and amount of shrinkage are large, which can lead to shrinkage, dents and deformation.

3. The cooling rate is fast, filling system and cooling system must dissipate heat slowly and pay attention to molding temperature control. The direction of low temperature of material is obvious. This is especially evident at low temperature and high pressure. When mold temperature is lower than 50 degrees, plastic parts are not smooth. , prone to poor welding, leaving marks, 90

4. The thickness of plastic wall should be same, avoid lack of glue, sharp corners, in order to avoid stress concentration.

PE plastic (polyethylene)

English name for polyethylene

Specific Gravity: 0.94-0.96 g/cu.m. centimeter

Shaping shrinkage: 1.5-3.6%

Forming temperature: 140-220°C

Drying conditions: ---

Material properties

Excellent corrosion resistance, electrical insulation (especially high frequency insulation), amenable to chlorination, irradiation and modification, can be reinforced with glass fiber. LDPE has a high melting point, rigidity, hardness and strength, and low water absorption. , has good electrical properties and radiation resistance; high pressure polyethylene has good softness, elongation, toughness and permeability; Ultra high molecular weight polyethylene has high impact strength, fatigue resistance and wear resistance.

LDPE is suitable for manufacture of corrosion-resistant and insulating parts;

High density polyethylene suitable for making films, etc.

Ultra-high molecular weight polyethylene is suitable for shock-absorbing, wear-resistant and transmission parts.


1. Crystalline material, low moisture absorption, no need to completely dry, excellent fluidity, fluidity is pressure sensitive, high pressure injection is suitable for molding, material temperature is uniforma, filling speed is high, pressure is sufficient. It is not recommended to use a straight sprue to prevent uneven shrinkage and increased internal stress. Pay attention to location of sprue to prevent shrinkage and warping.

2. The shrinkage range and shrinkage value are large, directionality is obvious, and it is easy to deform and deform. The cooling rate should be low, and mold should be equipped with a cold cavity and cooling system.

3. The heating time should not be too long, otherwise it will decompose and burn.

4. If soft plastic parts have shallow lateral grooves, they can be forced out of mold.

5. Melt cracking may occur, so it should not be in contact with organic solvents to prevent cracking.

PVC polyvinyl chloride

English name oly (vinyl chloride)

Specific gravity: 1.38 g/cm3

Shaping shrinkage: 0.6-1.5%

Forming temperature: 160-190°С

Drying conditions: ---

Material properties

Excellent mechanical properties, electrical properties, high resistance to acids and alkalis, good chemical stability,

Suitable for making thin plates, wire and cable insulation layers, seals, etc.


1. Amorphous material, low moisture absorption, poor fluidity. To improve flow and prevent formation of air bubbles, plastic can be pre-dried. The sprue system of mold should be thick and short, cross section of sprue should be large, and there should be no dead corner. The mold should be cooled, surface is chrome plated.

2. Very easy to decompose. It decomposes more easily on contact with steel and copper at 200 degrees. When decomposed, it does not corrode and irritate

3. When using nozzle of a screw injection molding machine, hole diameter should be large to avoid material stagnation in blind corners. It is better not to have inserts. If there are inserts, then they should be preheated.

PA plastic (nylon) (polyamine)

English name oliamide

Specific Gravity A6-1.14g/cc PA66-1.15g/cc PA1010-1.05g/cc

Shaping shrinkage A6-0.8-2.5% PA66-1.5-2.2%

Forming temperature: 220-300℃

Drying conditions: 100-110℃ for 12 hours

Material properties

Durable, wear-resistant, oil-resistant, water-resistant, antibacterial, but with high water absorption capacity. Nylon 6 has good elasticity, high toughness and great water absorption; nylon 66 has better performance than nylon 6, high strength and good wear resistance; Nylon 610 and Nylon 66 are similar but have lower water absorption and lower stiffness; 1010 nylon is translucent and has less water absorption

Suitable for making general mechanical parts, anti-friction and wearresistant parts, transmission parts, chemical, electrical, instrumentation and other parts


1. Crystallized material with higher melting point and narrow melting point range, poor thermal stability, when material temperature is over 300 degrees and residence time is over 30 minutes, it will decompose. Easily absorbs moisture and requires drying. The water content must not exceed 0.3%.

2. Good fluidity, easy to overflow. Self-locking nozzles should be used and should be heated.

3. The molding shrinkage range and shrinkage rate are large, directionality is obvious, and shrinkage cavity and deformation tend to occur.

4. The mold temperature is selected according to wall thickness of plastic part in range of 20-90 degrees. The injection pressure is selected according to type of injection molding machine, material temperature, plastic shape and size. mold part and system. The molding cycle is selected according to wall thickness of plastic part. Of course. When resin viscosity is low, injection and cooling time should be considered

5. The shape and size of mold gate system, increasing size of runner and gate can reduce shrinkage.

PC plastic (polycarbonate)

English name polycarbonate

Specific gravity: 1.18–1.20 g/cm3

Shaping shrinkage: 0.5-0.8%

Forming temperature: 230-320℃

Drying conditions: 110-120℃ for 8 hours

Material properties

High impact strength, good dimensional stability, colorless and transparent, good colorability, electrical insulation, corrosion resistance, wear resistance, but poor self-lubrication, stress cracking tendency, high temperature and easy hydrolysis, and other woods

Suitable for making small tool parts, insulating transparent parts and high impact parts


1. Amorphous material, good thermal stability, wide molding temperature range, poor fluidity. Low moisture absorption, but sensitive to water, requires drying. The casting shrinkage rate is small, and melt cracking and stress concentration are possible, so casting conditions must be strictly controlled, and plastic parts must be annealed.

2. For plastic parts with high melting point and high viscosity, which exceed 200 g, it is recommended to use a heated extension nozzle.

3. The cooling rate is fast, mold gate system should be thick and short. It is advisable to install a cold well, gate element must be large, and mold must be heated

4. If temperature of material is too low, it will lead to a shortage of material and plastic parts will be dull. If temperature of material is too high, it will easily overflow and plastic parts will bubble. When temperature fThe shape is low, shrinkage rate, elongation rate and toughness are high, but bending resistance, compression resistance and tensile strength are low. When temperature of mold exceeds 120 degrees, cooling of plastic part is slow, it is easily deformed and sticks to mold.