Traditional materials

Transcription

1 Raw materials Traditional process Industrial process Natural resources Traditional materials Processed materials Recycled materials Recycled furniture Natural resources (recursos naturales): are materials provided by the Earth that humans can use to make more complex (human-made) products. For example land, forests, mineral deposits, water, etc. Raw materials (materias primas): they are obtained from nature, such as wool, wood, cork, clay, iron ore Traditional materials (materiales artesanales): they are objects produced directly with natural materials. Processed materials (materiales transformados): materials are not used as they are found in nature; rather they are subjected to modifications by means of some kind of process of transformation. Recycled materials (materiales reciclados): materials that once used, through transformation processes can be reused in the production of new objects.

2 The materials we use to produce objects can be classified into five major groups from a technical point of view: Wood: Metal: Plastic: Stone and ceramic materials (materiales pétreos y cerámicos): Textile materials (materiales textiles): This is a natural material that comes from trees. Its main derivatives are paper and cardboard. This comes from minerals extracted from mines which are then transformed for subsequent application. This is a synthetic material obtained primarily from petroleum and coal. There are also natural in origin, the first consist primarily of stone and sand and second mainly of clay. Some of these are obtained directly from raw materials like cotton, wool, linen, silk, etc., but the great majority of textiles are artificial and synthetic such as rayon, polyester, polyamide, etc. Material properties are a set of characteristics which define each material and distinguish it from others. Material properties can be classified into three groups: 1. Technological properties: define the behaviour of materials as they are being worked. 2. Physical properties: define the behaviour of materials when they are subjected to the action of different agents such as heat, electrical current, gravity, etc. 3. Chemical properties (propiedades químicas): define the behaviour of materials as they are subjected to atmospheric or chemical agents. 1. Technological properties: 1.1. Malleability (maleabilidad): some materials can be easily flattened into sheets when pressure is applied to them. One example of this is aluminium foil, but metals and plastics are also generally malleable Fusibility (fusibilidad): this property allows some materials to go from a solid to a liquid state when they are subjected to certain temperatures; this means they can be poured into moulds. Bronze, brass and iron are very fusible materials Ductility (ductilidad): this is the quality that some materials exhibit which allows them to be stretched to form threads. Metals like gold, silver, copper, lead, aluminium and some plastic materials are ductile Weldability (soldabilidad): this is the quality that some materials exhibit which allows them to be welded. Steels and plastics have a high degree of weldability.

3 2. Physical properties: 2.1. Density (densidad): is calculated like this: density = mass (kg) / volum (m 3 ). Materials can have low density or high-density Mechanical properties: Hardness (dureza): indicates the resistance to being scratched or penetrated. Hard materials can scratch softer materials. The opposite of hard is soft (blando). Toughness (tenacidad): allows materials to be hit or struck without breaking. Materials that do not resist impact well are called fragile materials. Elasticity (elasticidad): allows some materials to recover their original shape after having been deformed. Materials that do not recover from deformation are called plastic materials. Mechanical resistance. Stress (resistencia mecánica. Esfuerzos): allows materials to withstand forces without deforming excessively or breaking. Structural elements are subjected to the action of external forces which tend to deform or move them. These elements are subject to certain types of stress: a) Tensile (tracción): the forces acting on the structural element tend to pull or stretch it. b) Shear (Corte o cizalladura): the forces acting on the structural element tend to cut it. c) Compressive (compresión): the forces acting on the structural element tend to compress it. d) Flexural (flexión): the forces acting on the structural element tend to bend it. e) Torsion (torsión): the forces acting on the structural element tend to twist it. Tensile Shear Compressive Flexural Torsion 2.3. Thermal and electrical properties: Thermal conductivity (conductividad térmica): this is a material s capacity to transmit heat. Metals are good conductors of heat. Materials like wood, plastic and ceramic materials that heat cannot easily pass through are called thermal insulators (aislantes térmicos). Thermal expansion (expansión térmica): this is the property that some materials exhibit of expanding their volume when heated. It is quite common in metals. Melting point (punto de fusión): this is the temperature at which a material goes from a solid to a liquid state. The melting point for water is 0.

4 Electrical conductivity (conductividad eléctrica): this is the capacity of some materials to allow an electrical current to pass through them. Metals are good conductors of electricity. A material that is not a good electrical conductor, like wood, is called an electrical insulator (aislante eléctrico). 3. Chemical properties: Oxidation: when a material is combined with oxigen, transforming it to oxide, it undergoes an oxidation reaction. Metal materials in general create a surface layer of oxide when exposed to oxygen. Corrosion: if oxidation takes place in the presence of water, the material corrodes. Corrosion is more dangerous than oxidation because the oxide layer does not accumulate on the surface of the material, but detaches from it.

5 Properties of wood: The characteristics of the wood depend on the type of tree and how it is treated later. In general, most different types of wood have common properties: Abundant and renewable (abundante y renovable): if a forest is harvested, it can be replanted and in a few years it will be able to provide wood again. Density: depends on the type of wood. Most types of wood float in water but there are others which sink in water. Thermal and electrical conductivity: Hardness: wood is a poor conductor of heat and electricity. This makes it a good thermal and electrical insulator. this is the quality of resistance to other objects such as nails, screws, tools, etc. Flexibility: this is the quality that some wood has of being easy to bend in the direction parallel to the fibres. Cleavability (fendibilidad): it is easier to cut the wood in the direction of the grain, or fibres. Hygroscopicity (higroscopicidad): the capacity of wood to absorb or expel moisture (humedad). When wood absorbs moisture, it expands; when it expels moisture, it contracts. The process of obtaining wood: 1. Felling (tala): this is the act of cutting the trunk (tronco) of the tree so that it falls to the ground. 2. Transport (transporte): trunks are taken to the sawmill (serrería). 3. Sawing (aserrado): the bark (corteza) is removed and the wood is cut. 4. Drying (secado): the drying process eliminates moisture from the wood. Felling Transport Sawing Drying

6 Classification of natural wood: Natural wood is generally classified into two main groups: Soft woods: they are generally light and easy to work with. For example, pine (pino) and black poplar (chopo). Hard woods: they are denser and harder to work with. For example, oak (roble) and beech (haya). PINE OAK BLACK POPLAR BEECH Artificial boards (tableros artificiales): Artificial or prefabricated boards are made from wood which is pressed and glued together using natural wood sheets (láminas), shavings (virutas) or fibres (fibras). This artificial or prefabricated wood has the following characteristics: It is available in a wide variety of sizes and finishes. It is significantly less expensive than natural wood. It is not affected by parasites. The most common prefabricated boards are: Plywood (contrachapado): this is made by placing sheets of wood one on top of another with the direction of the grain (veta) in each sheet perpendicular to the one below it and then gluing them together. Most furniture used in schools is made of plywood. Chipboard (aglomerado): this is made with shavings or leftover (restos) wood that is treated with special glue and pressed between rollers. Most furniture is made with chipboard. Pressboard or fibreboard (prensado o de fibras): this is made with wood fibre and synthetic resin which are compressed under high pressure. This is used very frequently on the back of pieces of furniture.

7 Types of metals Industrial classification: metals are classified based on whether they contain a high percentage of iron (hierro) or not. Ferrous metals (metales ferrosos): contain a high percentage of iron. For example, steel (acero). Non-ferrous metals (metales no ferrosos): not contain a high percentage of iron. For example, aluminium, copper (cobre), bronze. Other classifications: Aluminium Copper Bronze A noble metal: is a metal that is resistant to corrosion and oxidation. The most familiar of these are gold and silver. Gold Silver A heavy metal (metal pesado): is a metal with a high density. For example mercury (mercurio) and lead (plomo). Heavy metals are highly toxic to humans. Mercury Lead An alloy (aleación): is a metal made by fusing two or more pure metals, or fusing metals with non-metal materials. For example bronze is made of copper and tin (estaño).

8 Polymers Polymers are materials made of very large molecules, which are in turn made up of groups of smaller molecules called monomers. Depending on their origin, polymers can be: Natural: some are obtained using plant-based materials (materias vegetales) such as latex, cotton or cellulose. Others are extracted from products of animal origin, such as silk (seda). Latex Cotton Cellulose Silk Synthetic: these are mineral-based, and are derived primarily from petroleum and natural gas. Most polymers belong to this group, and are referred to as plastics. Types of plastics Based on their behaviour when heated, plastics can be divided into two groups: Thermoplastic (termoplástico): when heated to a certain temperature, these can be moulded. One of the advantages of this type of plastic is that even after cooling, it can be reheated to repeat the process as many times as desired. Therefore it can be recycled. There are many types of thermoplastics such as: PVC: doors, windows, pipes (tubos)... PET: water bottles, soft drink bottles... PS (Polystyrene): egg cartons, food containers, thermal insulation, toys, yoghurt pots... PVC PET PS Thermostable (termoestable): these can only be heated and moulded one time. Once they have cooled, they will burn if heated again. Therefore it can t be recycled. Types of thermostable: PF: handles for pots and pans (mangos de ollas y sartenes), electrical accessories... UP (Polyester resins): roofing sheets (techos), swimming pools... UF: electrical accessories. PF UP UF Referencia: Tecnología, programación y robótica 1º ESO Editorial Teide.