Injection plastic parts are becoming more and more widely used, and identifying plastics and selecting raw materials is the basis for processing injection parts. This article describes the names, common names, advantages and disadvantages of typical plastics for injection, typical modification methods and applications.
aBS (styrene-butadiene-propylene)
The raw material is ivory, its density is greater than 1, so it will slowly sink to the bottom. The position of the aBS product will be whitish immediately when subjected to external force or tortuosity; it can be burned when tested by the combustion method, the flame is yellow, and the black smoke of the silk floats in the air with the flame.
advantage
a. The parts are hard and tough, and have high impact resistance at low temperatures.
b. Low water absorption is a good insulation material.
c. The parts are shiny, dimensionally stable, have high mold surface replication ability, are not easy to wear on the surface, and have good electrical properties and fluidity.
d. High mechanical strength, strong impact ability, as well as low temperature; good notch sensitivity, good creep resistance, low friction coefficient, little change due to temperature and humidity.
Disadvantage
a. It is not resistant to organic solvents, it will be swollen and will be dissolved by polar solvents; it will be oxidatively decomposed due to poor weather resistance.
b. The viscosity of the solution is large.
c. Chroma is relatively sensitive to temperature.
Modified material
a. aBS+PC or SaN, increase the heat distortion temperature;
b. aBS+PVC to improve fire performance.
use
Housings for electrical appliances, daily necessities, high-end toys, furniture, sports equipment, etc.
GPPS (polystyrene)
The material itself is smooth and transparent, slow in water, the parts are fragile, the internal flame is yellow when burning, the outer flame is black, it will drip, and the fire will have obvious odor after extinguishing.
advantage
a. Good optical performance, light transmittance of 88%-92%, and refractive index of 1.59-1.60.
b. Good electrical performance, volume resistance is 1018 ohms.
c. Low specific heat, low melt viscosity, strong plasticizing ability, fast heating and molding, short molding cycle, long difference between molding temperature and decomposition temperature, low crystallinity and good dimensional stability.
d. Good fluidity and heat stability, low shrinkage and radiation resistance.
e. The plastic itself is smooth and transparent, with good coloration and convenient use.
Disadvantage
a. Brittleness, impact strength is 83.3-98 Pa, poor wear resistance results in high packaging, storage and transportation requirements.
b. Low heat resistance, the highest temperature is 60-80 degrees, rigid material, large thermal expansion coefficient, and poor thermal load.
c. The molding process requires high requirements, the aging of the parts is obvious, and the sensitivity to heat is large.
d. Poor acid resistance.
e. Fragile, flammable, high static and easy to vacuum.
use
It can be used as a molding machine cleaning agent without side effects; it can also be used to make toys, stationery, daily necessities and containers.
HIPS (modified polystyrene, not broken)
HIPS is a modified product of GPPS added with rubber material. Its purpose is to improve the impact strength of the material. The material is colorless and transparent, and can be colored according to requirements.
advantage
a. It has good fluidity and good impact strength.
b. Easy to process coloring.
Disadvantage
a. The content of rubber material in HIPS is 15%, which affects the fluidity to some extent. Therefore, the injection pressure and molding temperature should be slightly higher than GPPS, and the opening of the mold gate should be as reasonable as possible.
b. The material is cooled slowly. In addition to having sufficient holding time and speed, the mold should have good heat exchange capacity to reduce local shrinkage and deformation after ejection.
c. In actual production, most of HIPS and GPPS are used in combination. The characteristics are: good gloss, fresh color, good hand feeling, good rigidity, modified HIPS account for 20%-70% of the total, PS accounted for 80%-30%.
d. Due to the incorporation of rubber molecules, the internal force elasticity of the plastic causes the edges of the product to become white. The solution is to increase the mold temperature at the position where the whit is located, provided that a reliable clamping force is required.
use
Used in the production of toys, daily necessities, radio casings and TV casings.
PC (bulletproof rubber)
The raw material is transparent, easy to color, the heat distortion temperature is 135-143 degrees, the product can burn, the flame is yellow, no foaming, it will flow, and will be extinguished slowly when the external fire source is detached.
advantage
a. Mechanical properties are better than any plastic material, heat resistance and weather resistance are very good.
b. High molding precision, good dimensional stability, good optical performance, and light transmittance of 75%-89%.
c. The product is resistant to dilute acid.
Disadvantage
a. High water absorption rate, pre-drying during molding, and dry materials should not be exposed to air for a long time.
b. The processing requirements of the product are high, the machine must have a good clamping force, and it is better to use a special screw, and the fluidity of the material is poor.
c. The material is sensitive to stress, and the precision of the mold is high. When designing the product, the proportion of the wall thickness of the product should be considered.
use
Mostly used in the production of electric toy shells, electrical enclosures, safety helmets, bulletproof glass and electrical components.
PP (100 fold plastic)
advantage
a. Good fluidity and good molding performance.
b. The surface of the parts is bright, and the dyeing effect and traumatic marks are better than polyethylene.
c. The most heat resistant plastic in general purpose plastics.
d. High molecular weight, easy to crystallize, high tensile yield strength.
e. Good electrical performance, low density, stress crack resistance.
Disadvantage
a. The shrinkage rate is large and the part size is not easy to control.
b. A slightly larger inner wall of the part is prone to vacuum.
c. High requirements for mold venting.
d. Printing, pasting, plating and other processing difficulties.
e. Poor fire resistance and poor weather resistance.
f. Insufficient rigidity and low notch strength.
Mechanical index
a. Heat resistant temperature 135-150 degrees.
b. 80 degrees organic acid resistance.
c. PP+10% talcum powder, heat stabilizer, easy to flow, high gloss, used for small appliances, auto parts.
d. PP+20%-40% talcum powder, heat stabilizer, easy to flow, stable size, used in engineering parts.
e. PP+40% talcum powder, detergent, easy to flow, short cycle, used in washing machines, dry cleaning machines.
f. PP+30%-40% chemically coupled glass fiber, heat stabilizer, high stiffness, high strength, low shrinkage for engineering and automotive parts.
g. PP+ flame retardant, UV resistant, easy to flow, weather resistant, mostly used for indoor and outdoor furniture.
use
Packaging plastic bags, drawing, rope, toys, daily necessities, bottles, plastic blue plastic frame, washing machine.
PMMa (Plexiglas, Acrylic)
Plexiglass is difficult to catch fire, but it can burn slowly. It can spontaneously ignite after fire. The flame is blue, the top is white, the plastic melts, foams, and emits strong floral and fruity smell and rotten vegetable smell.
advantage
a. Non-crystalline plastic, which has the best transparency in plastics, and can pass the ultraviolet light of 270nm, which is similar to the light transmittance of optical glass.
b. It can resist non-oxidizing acid, inorganic salt liquid and excellent weather resistance.
c. Good electrical performance and relatively stable size.
Disadvantage
a. Brittleness, although the surface strength is high, it is scarred after being rubbed by a hard object.
b. The notched impact strength is low, the processing is not easy, and the water absorption rate is large.
c. It is sensitive to heat. When the material is dry for too long, it is easy to change color and is light yellow.
use
Transparent plastic sheets, decorations, sunglasses, stationery, lampshades, camera lenses, artificial jewelry, etc.
Pa (nylon)
advantage
a. High mechanical strength, good toughness, high tensile and compressive strength, tensile strength close to yield strength, strong impact energy and vibration absorption.
b. Excellent fatigue resistance, and can maintain the original mechanical strength after repeated bending.
c. Smooth surface, low friction coefficient, wear resistance and lubricity.
d. Corrosion resistant, very resistant to alkali and mostly acid.
e. Non-toxic, inert to bio-erosion, good antibacterial and anti-mildew ability.
f. The heat resistance temperature range is -40-100 degrees, and it can withstand 120-150 degrees in a short time.
Disadvantage
a. Easy to absorb water, unstable in size, not resistant to strong acids and oxidants, can not be used as acid-resistant materials.
b. Poor rotation resistance, thermal oxidation with oxygen in the air at a long-term high temperature begins to brown, and then crack.
c. The injection molding process is strict, the moisture is harmful to the molding, and the thermal expansion size is difficult to control. The inconsistent wall thickness will cause distortion of the workpiece and high requirements for post-processing equipment.
use
Production of wire drawing, bristles, fishing wire, packaging film, gears, power tool housings, electrical accessories, power tools, etc.
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