Understanding Plastics: Types, Properties, and Processing
Understanding Plastics: Materials, Properties, and Processes
Plastics are materials that can be molded. There are several types, known for their acceptable resistance, ease of work, and moldability. They are often produced synthetically from other products like petroleum and gas. Based on their thermal behavior, they are classified as either thermoplastic or thermoset.
Thermoplastics vs. Thermosets
- Thermoplastics: These can be molded with heat, and when cooled, they can be reheated and reshaped multiple times.
- Thermosets: These plastics are heated and can only be molded once.
Obtaining and Identifying Plastic Properties
The raw materials for plastics are often natural products such as cellulose, carbon, petroleum, and gas. Plastic manufacturing involves a rough process. Identifying plastic properties can be done through simple tests:
- Softer plastics can be identified by scratching them with a pointed instrument.
- The density of plastics can be determined by observing whether they sink or float in water.
- Burning a small piece of plastic and observing the flame can reveal certain properties.
Plastic Molding Techniques
- Injection Molding: Plastic granules are introduced into a hopper and moved through a heated tube where they melt. The molten plastic is then injected into a mold.
- Bandage Molding: Thermoset plastic is applied in a press, using a powdered material. The press is closed, and the material acquires the shape of the mold.
- Clearing (Vacuum Forming): A sheet of thermoplastic material is placed over a mold and heated until pliable. Vacuum pressure is then applied to form the plastic to the mold’s shape.
- Extrusion: This is used for manufacturing tubes, pipes, and electrical conduits.
- Blow Molding: This is used for making hollow objects like toys or bottles. Material in the form of cylinders is introduced into a mold. Compressed air is injected, inflating the material to conform to the mold walls.
- Calendering: Plastic mass is passed through rollers to create a flat shape.
Plastic Machining Techniques
- Marking: Plastics commonly used in schools are often protected by a layer of transparent plastic.
- Cutting and Breaking: For thin sheets, a groove can be made with a scriber, and then the two parts can be separated.
- Sawing: For thicker pieces, a serrated saw is used, similar to cutting wood or metal.
- Drilling: Even thin sheets can be drilled using a drill with appropriate bits.
Plastic Joining Techniques
- Adhesion: Special glues are used for joining plastic pieces.
- Cohesion: Solvents are used to merge two pieces of plastic.
- Mechanical Fasteners: Rivets, screws, and different types of threads can be used.
Treatment of Plastic Waste
Household waste is classified into organic matter, paper, cardboard, glass, plastic, and metals. Proper sorting is essential for effective recycling.
Stone Materials and Agglomerates
Stone materials include sand, gravel, and slabs, forming a hard, solid mass. Agglomerates are materials that set when mixed with water.
- Mortar: A mixture of water, sand, and cement.
- Concrete: Comprises gravel, sand, and water, and becomes highly resistant to compression when hardened.
Ceramic Materials
Ceramic materials are formed by mixing clay, which results from the disintegration of rocks and exhibits plasticity. Other ceramic materials include:
- Tiles: Thin ceramic pieces coated with a layer of enamel.
- Sandstone: A compact and waterproof mass, ideal for flooring.
- Refractories: Materials able to withstand high temperatures.
Tools for Stone Materials
- Tools for moving materials, such as preparing mortar for construction.
- Tools for raising walls or placing tiles.
- Tools for partial or total demolition work, such as drilling a wall for conduits.
- Tools for checking the extent and level of tiled walls.