Classification and Selection of Materials and Components

1. Classification and Selection of Materials and Components

2. Hardwoods Oak Mahogany Beech Ash Teak Softwoods Pine Natural Timbers

3. Softwood Pine Hardwood Oak Mahogany Teak Beech Ash Easy to work. Knotty and prone to warping (going out of shape). Hard and Tough. Durable. Finishes well. Heavy. Contain an acid which corrodes steel. Easy to work. Durable. Finishes well. Prone to warping. A hardwood that contains oils which means it is resistant to decay. This is often used to make garden furniture or for wood block flooring. Used for exterior furniture. Tough. Flexible (good elastic properties). Works and finishes well. Hard and tough. Finishes well. Prone to warping. Turns well. Natural Timbers

4. Primary materials These are processed to produce standard stock sizes and sections suitable for manufacturing into products. This range of sizes allows designers to see what is available before they start designing.  This is done during the conversion process. Using standard stock sizes can reduce costs later as the timber will not need machining to specific sizes. Secondary processing These can take the form of: Cutting Planing, Drilling Shaping Using Routers Primary Materials

5. Wood - Shapes and Sections • You may wish to buy your material as ‘square section’. What part of a table could be made from this section? • Moulds are unusual shapes. How do you think a mould could be used? • Dowel rod can be bought in different diameters. What could be made from this type of section?

6. PROPERTIES AND CHARACTERISTICS • The properties and characteristics of timbers can be categorized by their: Colour          Grain          Texture          Figure          Hardness          Elastisticity • The mechanical strength of a wood is dependent upon how compact the cells are. Hardwood cells are more compact than softwood cells. Hardwoods generally have a greater mechanical strength and hardness in comparison to softwoods.

7. Exam Questions • Name two different hardwoods that could be used in the production of a dining room table. 2 marks Acceptable answer Oak and Mahogany  2. Describe one advantage of using veneers rather than using solid timber. 2 marks Acceptable answer Using Veneers means that fewer trees will have to be cut down because the thinner veneers can be used to cover cheaper manufactured boards/go further.

8. MDF Plywood Hardboard Blockboard Chipboard Manufactured Boards

9. Advantages Available in large sheets (2440 x 1220 mm) Good dimensional stability (plywood) Easily decorated (veneers) Easily bent and shaped over formers (laminating) Waste products can be used in the making of manufactured boards Disadvantages Blunt tools quickly Thin sheets flop if not suspended Difficult to join Edges must be concealed Cutting and sanding of some boards can generate hazardous dust particles. ADVANTAGES & DISADVANTAGES OF USING MANUFACTURING BOARDS

10. MDF Plywood Hardboard Blockboard Chipboard A quality board, relatively cheap. This board is composed of fine wood dust and resin pressed into a board. This material can be worked, shaped and machined easily. Paint can be applied to it without the need for an undercoat or primer. Used in the building and furniture trades. This is made from veneers (plies) of timber with each grain layer being at right angles to each other and bonded together by resin and pressure. A number of grades are available, designed to suit a variety of situations.1. Marine plywood that is moisture resistant.2. Weather and boil proof plywood.3. Boil resistant plywood.4. Interior plywood. This is made from wood fibres that have been pulped. The pulp is put under pressure until the fibres bond to produce a tough board that is smooth on one side and rough on the other. It is not as strong as the other boards. This is built up with a core of softwood strips bonded together with adhesive and covered with a sheet of plywood on either side. Used as a building material and for furniture manufacture including fitted kitchens / bedrooms. This is made up of small chips of wood bonded together with resin and formed into sheets by compression. It is not as strong as plywood and block board but it is not expensive. Chipboard is often covered with a plastic laminate or wood veneer and used in furniture Manufactured Boards

11. Exam Question • Explain one reason which makes hardboard unsuitable for outside use. 2 marks Acceptable answer Hardboard is unsuitable for outside use because it is not waterproof. Therefore it will absorb water and eventually rot and break down.

12. THE DIFFERENCE BETWEEN FERROUS AND NON-FERROUS METALS Ferrous • Metals that are composed mainly of ferrite or iron. • Metals that are magnetic. • Metals that corrode easily (turn orange). • An example is Iron. Alloys • Metals that have been formed by mixing two or more metals and sometimes other elements. • Alloys are normally grouped into ferrous and non-ferrous alloys. Non-ferrous • Metals that contain no iron and almost entirely consists of pure metals. • Metals are non-magnetic. • Examples are Aluminium, Copper, Zinc, Tin and Lead

13. Ferrous Alloys- examples are Mild Steel, Stainless Steel, Silver Steel • Steel is an alloy of iron and carbon. Mild steel, stainless steel and silver steel are all ferrous alloys. Only a small amount of carbon (0.3%) in iron will change the mechanical properties significantly. • Other elements such as chromium and vanadium can be introduced to improve resistance to corrosion. A small addition of silver will improve its ability to retain a cutting edge and this materials- silver steel, is often used for cutting tools and kitchen implements.

14. Alloys • An alloy is made by combining two or more metallic elements to make a new material with improved properties such as hardness or tensile strength. Non-Ferrous Alloys- examples are Brass, Duralumin and Bronze • Brass is a non-ferrous alloy and has improved resistance t corrosion. It is made from combining two non-ferrous metals, 65% Copper and 35% Zinc. It also casts and machines easily and is therefore ideal as a material for boat and plumbing fittings.

15. Iron and Steel

16. Non-Ferrous Metals

17. SECTIONS - SOLIDS AND TUBES

18. Exam Questions 1. Describe two advantages of making alloys 4 marks Acceptable answer Alloys can have improved mechanical properties such as greater hardness/toughness. The physical properties can be improved such as increasing a material’s resistance to corrosion 2. Stainless steel is hard and tough.  It also has excellent resistance to corrosion.  Give two uses of stainless steel. 2 marks Acceptable answer Cutlery/kitchen sinks/pots and pans.

19. THE DIFFERENCE BETWEEN THERMOPLASTICS AND THERMOSETTING PLASTICS Most plastics are derived from crude oil. The oil is processed in a fractioning tower where it is split into various compounds and materials.

20. Classification of Plastics

21. Properties of Thermoplastics These plastics possess a common property, they soften when heated and are often used in schools to vacuum form shapes. Usually, when heated and formed into a shape – if reheated they return to their original shape.   • Acrylic is a stiff, hard and durable plastic. It is easily scratched. It is a good electrical insulator. It can be polished and finishedwell. This is the most common plastic in a school workshop. It is purchased usually in the form of sheets and comes in a range of colours. It can be translucent (e.g. smoked), transparent or opaque. It is resistant to most acids and weather conditions. It is used for making baths and bathroom furniture, car indicators covers and reflectors.   • Polythene is resistant to chemicals, soft and flexible and a good electrical insulator. Can be moulded into almost any form due to its excellent moulding qualities. Used for the production of bottles, bowls, toys, tube etc... It is available in large sheets and in a wide range of colours. There are two types: High density which is rigid and hard, and low density which is tough and flexible. Machine parts are generally made from high density polystyrene whilst bottles are made from the low density polystyrene. • ABS is a very tough plastic with excellent high impact strength properties. It is relatively lightweight and durable and due to its good resistance to chemicals. It is available in a wide range of colours and is used to make telephones, kitchenware and children's toys due to its high quality of surface finish.

22. Properties of Thermosetting plastics • Many adhesives (glues) are thermosetting plastics. A good example is epoxy resin that hardens when a second chemical is added (a catalyst). It will bond most materials including woods and metals as well as some plastics. It can has excellent strength when used as a bonding agent on fibrous materials such as fibre glass to make canoes and boat hulls.   • Polyurethane. This forms the basis of many paints and varnishes because it is very tough and has water resistant qualities.   • Melamine Formaldehyde. Used in the production of plastic laminates because of its smooth surface and hygienic qualities. It is also used in electrical plugs and sockets because it can be cast and it is an excellent insulator.   • Polyester resins. If resins are combined with a material such as fibre glass the result is a very tough material that can resist impact. This type of material is known as a glass reinforced plastic (GRP) and is used in car body repairs, sailing boats, corrugated sheet because of its lightness, toughness and resistance to water.

23. Other Plastics • Polyvinyl Chloride. Better known as PVC. It is a tough material which can be purchased as a hard material or alternatively a flexible form. It can be welded or bonded with an adhesive. It has a range of uses including water pipes, raincoats, long play records, coating on electrical wires and many more.   • Styrofoam. This is a light-weight dense foam. It is easy to shape with saws, files and abrasive paper and is ideal as a model making material.   • Expanded Polystyrene. An efficient insulator used in cavity walls and as decorative tiles and covering on ceilings. It can also be used for basic model making.   • Nylon. Is used in engineering to make gears and bearings. It’s oily nature means that friction is reduced between moving parts made from nylon.

24. Exam Question • Describe one difference between the structure of thermoplastics and thermosetting plastics.                                                                                                        2 marks Acceptable answer Thermosetting plastics have cross-linked chains which make them stiff whereas thermoplastics have long tangled chains making them more soft and flexible.