1. Basic knowledge of six common plastics

1.PE

Polyethylene plastic, PE is relatively soft and has a waxy texture to touch. Compared to same plastic, it is lighter in weight and has some transparency. When burning, flame is blue. It is often used to make plastic film, plastic vest bags, plastic food bags, baby bottles, buckets, kettles, etc.

2.PP

PP plastic, non-toxic and tasteless, can be soaked in boiling water at 100 °C without deformation or damage. Ordinary acid and alkali organic solvents have little effect on it, and can be decomposed by high temperature and oxidation. Polypropylene is widely used in production of clothing, blankets and other fiber products, medical equipment, automobiles, bicycles, parts, pipelines, chemical containers, etc., and is also used in food and drug packaging.

3. PS

Polystyrene plastic, colorless and transparent, polystyrene plastic is widely used in optical instruments, chemical industry and daily necessities for making tea trays, sugar bowls, soap dishes, cigarette boxes, student rulers, combs, etc. Because of its certain air permeability in production of film products, it can also be used as a good food packaging material.

4. PVC

PVC plastic, bright color, often smells of a special smell. Soft PVC can be made into a better quality agricultural film, which is often used to make raincoats, tablecloths, curtains, ticket clips, bags, etc. It is also widely used in production of plastic shoes and artificial leather. PVC is commonly used for outer sheath of power cables. From rigid PVC it ​​is possible to obtain transparent, translucent and mother-of-pearl products of various colors. Soap dishes, combs, washboards, stationery boxes, various pipes, etc. are often made from it. Polyvinyl chloride cannot be used for food packaging.

5. ABS

This is a plastic polymerized with acrylonitrile, butadiene and styrene. It is attractive in color, heat resistant, durable and can be plated with metallic films such as chromium and nickel on outer surface. used in mechanical engineering, electrical engineering, textiles, automobiles, aircraft, manufacturing industries such as ships and chemicals.

6.PA

Nylon, non-toxic, wear-resistant, corrosion-resistant, used for wear-resistant parts, transmission structural parts, household electrical appliance parts, automobile manufacturing parts, screw rods to prevent mechanical parts, chemical equipment parts,chemical equipment. In civilian use, it can be mixed or simply spun into various medical and knitwear, in industry, nylon is widely used for manufacture of cords, technical fabrics, cables, conveyor belts, tents, fishing nets, etc.

Secondly, what types of plastic can be used for transparent plastic products?

1. ABS:

Chemical name: acrylonitrile-butadiene-styrene copolymer

Text name: acrylonitrile butadiene styrene

Specific gravity: 1.05 g/cm3 Mold shrinkage: 0.4-0.7%

Shaping temperature: 200-240℃ Drying conditions: 80-90℃ for 2 hours

Features:

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

2.Good alloy with 372 plexiglass, made of two-tone plastic parts, chrome and paintable.

3. There are grades with high impact resistance, high temperature resistance, flame retardant, reinforced, transparent and other grades.

4. The flow is slightly worse than HIPS, better than PMMA, PC, etc., and has good flexibility.

Application: It is suitable for making general mechanical parts, wear-reducing and wear-resistant parts, transmission parts and telecommunication parts.

ABS engineering plastics are generally opaque, light ivory in color, non-toxic, tasteless, and have characteristics such as toughness, hardness, and rigidity. They burn slowly, flame is yellow, black smoke appears. After burning, plastic softens and burns. , emits a special smell of cinnamon, but does not drip melt.

ABS engineering plastics have excellent comprehensive properties such as excellent toughness, good dimensional stability, electrical properties, wear resistance, chemical resistance, coloring ability, good molding and machining. ABS resin is resistant to water, inorganic salts, alkalis and acids, insoluble in most alcohols and hydrocarbon solvents, but readily soluble in aldehydes, ketones, esters and some chlorinated hydrocarbons.

Disadvantages of engineering ABS plastics: low heat distortion temperature, flammability, poor weather resistance.

2. PET plastic

Open Classification: Industrial PlasticsPolyethylene terephthalate plastics mainly include polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).

PET has good optical properties and weather resistance, and amorphous PET has good optical transparency. In addition, PET has excellent abrasion resistance, dimensional stability, and electrical insulation. PET bottles are widely used due to their high strength, good transparency, non-toxicity, impermeability,light weight and high production efficiency. The molecular chain structure of PBT is similar to that of PET, and most of properties are same, except that main chain of molecule has changed from two methylene groups to four, so molecule is more flexible and processing performance is higher. better.

Main applications of polyethylene terephthalate:

Film and sheet materials: all kinds of food, drugs, non-toxic and sterile packaging materials; textiles, precision instruments, high quality packaging materials for electrical components; audio cassettes, video cassettes, film tapes, computer diskettes, metal coatings and photosensitive materials Substrates such as films, electronic and mechanical fields such as electrical insulating materials, capacitor films, flexible printed circuit boards and membrane switches.

Packaging bottle applications: Its application has evolved from original carbonated drink to modern beer bottle, edible oil bottle, condiment bottle, medicine bottle, cosmetic bottle, etc.

Electronic appliances: production of connectors, coils, integrated circuits, capacitors, transformers, TV accessories, tuners, switches, timer cases, automatic fuses, motor and relay brackets, etc.

Auto parts: such as switchboard covers, ignition coils, various valves, exhaust system parts, distributor caps, instrument caps, small engine caps, etc., can also use excellent paintability, gloss and hardness of PET surface to produce outdoor details. for cars.

Mechanical equipment: production of gears, cams, pump casings, pulleys, motor casings and watch parts, and can also be used as microwave oven trays, various ceilings, outdoor billboards and models, etc.

3. Polystyrene plastic

(polystyrene)

English name: polystyreneSpecific gravity: 1.05g/cm3 Mold shrinkage: 0.6-0.8% Molding temperature: 170-250℃

The material has excellent electrical insulation performance (especially high-frequency insulation), colorless and transparent, light transmission second only to organic glass, coloring, water resistance and good chemical resistance. The strength is average, but quality is on top. brittle and easy to manufacture Brittle stress cracking, not resistant to benzene, gasoline and other organic solvents. Suitable for making insulating transparent parts, decorative parts and chemical instruments, optical instruments and other parts.

3. Defect Definition

1. Miscellaneous point (including impurities): has shape of a point, and its largest diameter is equal to its size when measured

2. Burr: linear bulge at edge or join line of a plastic part (usually due to poor molding)

3. Silver wire: Molding gas discolors surface of plastic part (usually white). Most of these gases

This is moisture in resin, and some resins absorb moisture easily, so a drying process must be added before production

4. Bubbles: an isolated area inside plastic forms a round protrusion on surface

5. Deformation: deformation of plastic parts caused by internal stress differences or poor cooling during production

6. Top white: whitening and deformation of finished product when it is ejected from mold usually occurs at other end of ejection point (mold surface)

7. Lack of material: Due to damage to mold or other reasons, a situation of unsaturated lack of material occurs in finished product.

8. Printing error: Printed characters have white spots caused by dirt or other causes during printing.

9. Missing seal. Missing streaks or missing corners of printed content, print defects with more than 0.3mm of font misalignment are also considered non-printing.

10. Color Difference: refers to a comparison between actual color of a part and an approved sample color or a color number that exceeds allowable value.

11. The samecolour point: point where color is close to part color, otherwise they are points of different color.

12. Flow Diagram: due to shaping, a strip of hot melt flow was left on gate.

13. Weld line: Linear marks formed on surface of a part as a result of convergence of two or more jets of molten plastic.

14. Assembly gap: in addition to gap specified in project, gap caused by assembly of two components.

15. Minor scratches. No deep scratches or marks on surface (usually caused by hand handling).

16. Severe scratches. Hard or sharp objects leave deep linear scratches on surface of parts (usually caused by manual operation).

17. Indent Shrinkage: The surface of part is indented or undersized (usually due to poor casting).

18. Color separations. In production of plastics, streaks or dots of colored marks appear in flow zone (usually caused by addition of recycled materials).

19. Invisible: means that defect with a diameter of <0.03 mm is invisible, except for transparent area of ​​the LENS (according to detection distance, providedmaterial of each product).

20. Contusion: The surface or edge of product is hit by a hard object.

Four. Standards for control of plastic products

Common defects:

1. Underfill: (SHOT SHORT) is a phenomenon in which molten plastic does not completely pass through all corners of mold space (cavity).

2. Burr: CONTAMINATION occurs when melted plastic flows into parting surface or into gap of side bar type joint, mold clamping force is sufficient, but occurs at junction of runner and cross runner Excess resin of FLUSH film.

3. Shrinkage: A depression in surface of molded products caused by volumetric shrinkage, typically seen in thick parts, ribs or raised backs, and uneven gating thicknesses. Part.

4. Bubbles. The phenomenon of cavities left by water and volatile gas in molten plastic entering molded article during molding process is called bubbles.

5. Cracking (CRACKING) and cracking (CRAXING): Severe and obvious cracks on surface of molded products are cracks (CRACKING). The surface of molded products has hair-like cracks, and sharp corners of products. This phenomenon is often called cracking.

6. Definition of whitening: When molded article is demoulded due to force of ejector pin or resistance of notch position of molded article (UNCUT), portion with white marks is removed. called whitening (BLUSHING). Peeling is not a crack, but is a sign of cracks (cracks). It should be seen in parts made of ABS, HIPS and other plastics. Whitening is caused by significant residual stresses within molded article, and attention should be paid to appearance of cracks.

7. Deformation (DEFORMATION)-curvature, twisting: Deformation can be divided into two phenomena: deformation and twisting. Parallel lateral deformation is called deformation (REVERSE), diagonal deformation is called deformation. distortion (TORSION).

8. Weld line (weld line): A thin line formed by fusion of two or more molten materials.

9. Flow mark (flow mark): traces of flow of molten material, stripes along center of sprue.

10: The jet flow sign is when molten plastic is injected from sprue into mold cavity and solidifies into a bond, wriggling on surface of molded product. product.

11. Silver stripe (silver stripe): There are silvery white stripes on or near surface of molded article along material flow direction.

12.Usually so-called burnt (burnt): including discoloration of surface of molded product due to overheating of material and blackening of sharp-angled part of molded product. product or front end of hub and rib Combustion is caused by air entering mold space, which cannot be quickly released when molten material enters, and is compressed to heat up significantly, and then material is burned. fire prevention measure is that air is easily collected in a place where air is easily collected. Install a vent or use gap between ejector pin and pin to quickly release residual air. In addition, material temperature can be lowered, injection speed and injection pressure can be reduced, or gate size can be increased.

13. Black streaks (black streaks). Refers to phenomenon of black streaks appearing on molded products. The main reason for this is thermal decomposition of molding material. Usually found in materials with poor thermal stability...

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