Plastics: Properties, Classification, and Manufacturing Techniques
1. Plastics: Origin and Transformation
Plastics play a prominent role in the development of various sectors. They are materials made of polymers, which consist of long chains of carbon atoms. Depending on its source, plastic can be:
- Natural Plastics: Obtained directly from plant or animal materials.
- Synthetic or Artificial Plastics: Prepared from compounds derived from petroleum, natural gas, or coal.
The industrial processing of these raw materials into plastics is called polymerization. During manufacturing, additives known as loads are incorporated, along with other substances like plasticizers and pigments.
Properties of Plastics
The properties of plastics depend on their nature and composition:
- Physical Properties: Hardness, elasticity, stiffness, toughness, and flexibility are specific properties of certain plastics.
- Ecological Properties: Most plastics are not biodegradable and are often eliminated through incineration. However, biodegradable plastics also exist. Plastic materials can undergo recycling processes, including:
- Chemical Recycling: Recovering the original constituents to obtain new materials.
- Mechanical Recycling: Crushing materials into granules to produce new plastic or blends for composite materials.
2. Classification of Plastics
- Thermoplastics: Mostly derived from petroleum, thermoplastics are made up of weakly bonded chains. They soften when heated and can be molded.
- Thermoset Plastics: Also derived from petroleum, thermosets consist of tightly linked chains. They become rigid when heated.
- Elastomers: Obtained by vulcanization, elastomers are composed of folded unit chains.
3. Conformation Techniques
- Extrusion: Thermoplastic pellets are fed into an extruder, heated, and forced through a mold by a screw. The material cools and solidifies, then collected.
- Calendering: Thermoplastic material is passed between rotating cylinders to create sheets and plates.
- Vacuum Forming: Heated thermoplastic sheets are molded by suction, conforming to the mold’s shape.
- Blow Molding: A tube-shaped material is placed in a mold and inflated with compressed air to take the desired shape.
- Injection Molding: Molten thermoplastic is injected into a mold, cooled, and then removed.
- Compression Molding: Thermosetting powder is placed in a mold, compressed, heated, and cooled to form the piece.
4. Handling Techniques
Cutting
- Cutter: Cuts plates of varying thickness and hardness.
- Scissors: Cut soft and flexible sheets.
- Steel Tip: Cuts sheets up to 1mm thick.
- Coping Saw: Cuts soft plastics up to 1mm thick.
- Jigsaw: Cuts large sheets.
- Press or Die: Cuts sheets up to 5mm thick.
- Hot Metal Wire: Cuts soft thermoplastic sheets.
- Drill: Creates holes using rotating drill bits.
- File and Rasp: Remove excess material; file for hard materials, rasp for soft.
Joining
Disassembly Joints
- Screw and Nut: Bolt through pieces, secured with a nut.
- Screw Joint: Screw threads into one of the pieces.
- Threaded Joint: Two threaded parts are joined together.
Fixed Joints
- Adhesives: Substances used to permanently bond surfaces.
- Welding: Joining thermoplastics using heat and pressure.