Common Plastic Processing Methods

1. (injection molding)

The method of plastic injection mostly applied to plastic processing is to import thermalplastic or thermosetting plastic into heating cartridge of injection machines until ii is completely melted to be injected into sealed cavity of molds with pressure produced by plungers or screws out of thermal energy or friction heat.. After consolidation, the finished products are taken out of molds. The processing technique develops and leads to other processing methods out of changes in materials, mechanical designs, and quality requirements, such as plug-in forming of metal products through top intrusion, plastic injection forming of multicolor mixed color products, bubble forming products, gas-assisted injection molding, coinjection or RIM of special products made of special materials, among others.

2. (extrusion)

To put thermalplastic materials into an extrusion machine, extrude it with screws after heating and pressurizing, section shapes of products vary as per die heads—rods, tubes, plates,, alien shapes, etc. Others like blown film extrusion, extrusion of hollow forming, calendaring, extrusion painting, and kneading cut grandules belong to the first half application of extruders. The current popular trend of coextrusion produces more multifunction products.

3. (compression molding)

A method of thermosetting molding by way of preheating thermosetting resin, put in open mold cavity, add heating and pressurizing after closed mode until the material hardens. Phenolic resin, melamine resin and urea-formal denyde resin etc are often formed in this way. The products made cover hole electrical appliance housing, parts, gears, furniture and dinning sets etc.

4. (blow molding)

To extrude thermoplastic plastics with die head of the extruder to be thin tubes called as a parison before closing the mode, and complete forming by blowing. The method is used more and more widely in automotive industry with materials from traditional PE, PP, PVC, and PET to ingineering plastics of high performance. The advantage is easy to make large products in one molding, while the weakness is nuneasy to control the meat thinkness of the products.

5. (rotational molding)

First pour into rotational molds powder or liquid material of normal temperature, make resin uniformly spread in mold wall surface, and hollow finished products will be available after cooling. The method is most suitable for making large products, but the meat thickness of which uneasy to be controlled.

6. (blown film estursion)

Two film making methods in general:

(a)T-die method): A way of flat die extrusion, products made of this way come with better uniformality than that made of ring-die method. As the tensile force of take-up direction is stronger, making portrait comes with much more strength than that of landscape, many turns to make film by way of biaxial stretching.

(b) Ring-die method: A way of blown film estursion that make film by blowing hot melt glue to be pipe model that becomes film after cooling. Polyolefin materials are made into gabbage bags, shrink film, or food packing wrap, in this way. Modern quality packing film is made by way of co-extrusion.

7. (thermoforming)

To heat and soften thermalplastic material to form by compression molding with vacuum, air, or intermeshed metal. The strength is correlated with thickness of the plastic sheet. The products made should be trimmed, and the edge material is to be recycled.

8. (extrusion coating & lamination)

The method is to melt and extrude thermalplastic plastic, to form flow (curtain) coater after passing T mold head before spreading on contanious moving plate-shape or film shape substrate. Generally used on daily necessities and food packing.

9. (transfer molding)

A way used to thermosetting forming: to preheat and soften plastic material in heating chamber (transfer room), and then force melting material to pass through the runner and gate to enter mold cavity to have hardening reaction. This way fits products with metal insert, as the precision of formed product is higher than that made by compression molding, but mold design is more complicate beesides products coming with lower mechanical strength.

10. (casting)

This method is to inject liquid resin coming with hardener into open molds, let irt to flow to the mold surface and have it dry under atmospheric pressure and complete its polymerization; or to butter liquid resin on mobilizing belts; or to have the precipitation in chemical solution to acquire plastic film.

11. (calender coating)

To apply the heat on the surface of roller to butter melting plastic on cloth, leather or paper. PVC leather cloth is a common product out of this method.

12. (powder coating)

To put powder on the substrate being buttered, heat to melt and spread, method of which available in three ways:

(a) Flam spray: to spray plastic powder with propane or acetone flame and let it adhere to acceptor surface.

(b) Electrostatic coating: Using static to adhere plastic powder onto acceptor surface before heat melting it.

(c) Flow dip coating: To float plastic powder on fluid beds and merge heated metal object into it to form a layer of protection membrane. Common plastic powder cover PE, PP, PVC, Nylon,and Epoxy, etc.

13. (foaming)

Forming materials are those containing bubbles of which apparent specific gravity is lower than substantial density. Classifications as per forming methods are availavle in atmosphere pressure heating, pressurized foaming, extrusion foaming, injection foaming, two-liquid mixing method, and two-stage foaming method. Common mold heads used in forming are T mold and ring mold, and the latter is often used in polystyrene forming board, though, when thickness is larger than 5mm, T mode head is needed for forming. Common materials cover PE, PP, PVC, CPE, ABS, and PE,

14. (pultrusion)

This processing method is to reinforce glass fiber through heated mold head for pultrusion of hardened and reinforced resin before molding

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