DT Theory

• Elastic State - the state in which a thermoforming polymer is at a temperature that produces a stretchy consistency and in which it can be shaped, but will not retain its form without being held in place. The elastic state is used for instance in line bending, vacuum forming or dome blowing.

• Plastic State - the state in which a thermoforming polymer is at a temperature that produces a consistency that is softer and more malleable than the elastic state. The plastic state is used for instance in injection moulding

• Thermoforming - plastic materials that can be repeatedly softened by heat and formed into shapes which become hard when cooled.

• Thermosetting - plastic materials that can be softened and formed into shapes which become hard when cooled and cannot be softened again.

Thermoforming plastics:

1. Nylon

• Propertles - commonly used as a fibre in clothing and textiles, nylon is also a common engineering thermoplastic (TP) available in rod, tube, sheet and powder. Nylon resists abrasion and has a low friction characteristics and good chemical resistance.

• Uses - Mechanical components, such as gears, bushes, bearings and cams, and in fibre form: rope, fabrics, toothbrushes bristles, and weather proof castings.

2. Low & high density polytherine

• Properties - the most common TP. low density polytherine (LDPE) is less expensive ans commonly known as polytherine. High density polytherine (HDPE) is more expensive and is available in a range of densities. PE's have good resistance to chemicals and some grades float in water

• Uses - injection & blow moulded bottles and containers, waste bins, packaging films (for example heat shrink), electrical insulation, pallets, toys and bullet proof vests

3. Polyethylene terephthalate (PET)

• Properties - PET is a hard, stiff, strong and stable material with a low water absorption. It also had good chemical resistance (with the expectation of alkalis) and gas barrier properties.

• Uses - signs, drinks bottles and bank/ smart cards.

4. Polyvinyl chloride (PVC)

• Properties - good resistance to chemicals and solvents. Good tensile strength, reasonably impact resistant and some grades are flexible. Available in coloured or clear. PVC is also fire resistant

• Uses - rain, water and sewage pipes, toys, clothing and footwear, adhesive tapes, medical goods and packaging.

5. Acrylic (PMMA)

• Properties - Acrylic is hard with reasonable tensile strength and good resistance to UV light and weather. Available in a range of colour. Available in cast and extruded form - both are easily cemented with solvent.

• Uses - bathroom furniture (for example baths), aircraft canopies, headlight tenses, signs & kitchen products.

6. Polystyrene (PS)

Properties – One of the most commonly used plastics. High impact polystyrene is a mixture of polybutadiene and polystyrene, having better impact resistance. Poor resistance to UV.

Uses – Toys, light fittings, computer cases, buttons, car fittings, freezer linings, packaging trays, domestic appliance.

7. Polypropylene (PP)

Properties –High resistance to chemicals and virtually impervious to water. Highly flexible and resistant to stress.

Uses – Chemical containers and tanks, carpets, fuel cans, toys, marine ropes and underwater bearings, dishwasher containers.

8. Acrylonitrile-butadiene-styrene (ABS)

Properties – Durable, weather and chemical resistant. ABS is rigid with rubber-like characteristics, giving it good impact resistance.

Uses – Boat, dinghy hulls, domestic appliance housing, dashboard, casings for power outlets.

9. Melamine Formaldehyde (MF)

Properties – A clear, hard and chemical resistant thermosetting resin, often known simply as melamine.

Uses – Electrical plugs, switches and sockets, gear wheels, adhesives to bond plywood layers.

Thermosetting plastics :

1. Melamine Formaldehyde (MF)

Properties – A clear, hard and chemical resistant thermosetting resin, often known simply as melamine.

Uses – Electrical plugs, switches and sockets, gear wheels, adhesives to bond plywood layers.

2. Urea Formaldehyde (UF)

Properties – High tensile strength and surface hardness. Low water absorption and mould shrinkage.

Uses – Buttons, toilet seats, electrical fittings, adhesive to bond pressed wood products.

3. Phenol Formaldehyde (PF)

Properties – A synthetic polymer with high hardness, good thermal stability and chemical resistance.

Uses – Laboratory worktops, billiard balls, printed circuit boards.

4. Polyester Resin

Properties - Stable, low cost and easy to use. Good mechanical, chemical resistance and electrical properties

Uses - Glass reinforced for boat hulls, car body panels, adhesives, coatings, printed circuit boards

5. Epoxy Resin

Properties - High adhesive strength and well mechanical properties, as well as high electrical insulation and good chemical resistance

Uses - Adhesives, sealants, coatings, moulds/dies for thermoforming plastic parts, printed circuit boards

Soft woods :

1. Scots Pine

Properties - straight grained and prone to knots, pale in colour, strong yet easy to work with, cheap and readily available. ​

​Uses – Low cost furniture, construction work. Simple joinery.

2. ​Parana Pine​

​Properties – Hard and straight-grained, virtually knot-free, fairly strong, comparatively expensive. Pale yellow in colour with darker brown streaks.​

​Uses – Better quality furniture, structural carpentry that is visible such as windows, doors and staircases.

3. Spruce

​Properties – Creamy-white with small hard knots, not very hardwearing. ​

​Uses – Indoor furniture including bedrooms and kitchens.

4. Yellow cedar

​Properties – Very pale in colour, light in weight yet rigid.​

​Uses – Furniture, boat building and veneers.

5. Redwood​

Properties – Relatively strong, knotty, durable when treated with a suitable coating or treatment, low cost.​

​Uses – General woodwork, cupboard, shelves, roofs.

Hardwoods :​

1. Ash

Properties – a light creamy brown colour, open grained.​

​Uses – Sport equipment, wooden ladders, tools.​

2. Beech

Properties – white in colour, close grained, hard and strong, prone to warping.​

​Uses – Furniture, toys, tool handles.

3. Elm

​Properties –Light brown, open grained, tough, resists splitting, durable in water and outdoor settings.​

​Uses – Indoor and outdoor furniture.

4. Mahogany

Properties – Rich, reddish-brown colour, strong and durable, interlocking grain.​

​Uses – Good quality furniture.

5. Oak

​Properties – Light brown colour, strong and tough, open grained, corrodes steel screws and fittings and reacts with certain adhesives.​

​Uses – High quality furniture and interior woodwork.

Manufactured boards :​

1. Block board

Properties – Block board is manufactured with a central core of softwood strips bonded together with adhesives and covered with a sheet of plywood on either side, and then often a finishing veneer.​

2. Chip Board​

​Properties – Chipboard is made up of small chips of wood bonded together with a resin and compressed to form sheets. It is not as strong as plywood and block board, nor does it come in thicker sheets sizes, but it is comparatively cheaper. Chipboard is often used in furniture for use indoors, and it is covered in a plastic coating or veneer for a more aesthetically pleasing timber. ​

3. Hardboard ​

​Properties – Hardboard is made up from pulped wood fibre that are pressurised until the fibres bond together to produce a board that is smooth on one side and rough on the other. It is not as strong as the other boards and it is typically used in non structural situations, such as the back of cupboards.​

4. Medium Density Fibreboard (MDF)​

​Properties – MDF is made up form very fine wood dust and resin pressed into a board. This material can be worked, shaped by machines easily and has considerably more strength than hardboard due to its use of resin as a bonding agent. It is used in many applications, indoors, and it can be easily finished with veneers or paint.

5. ​Plywood​

​Properties – Plywood is made up from veneers of timber with a grain of each layer being at right angles to the layers either side of it. The layers are bonded together by resin and pressure. A number of different types of plywood are available, and these are often referred to as grades. They are manufactured differently and designed for different proposes.

​wood processes:

1. steam bending

​Thin layers of timber (veneers) are placed in a steam chamber. Steam is introduced at one end and travels through the chamber, heating the veneer and absorbing into the timber as it does. ​

As the steam cools, and condenses it turns back into water and it simply drains away.​

​After a period of time immersed in the steam, the veneers are removed and are malleable and flexible. This change in their properties makes it possible to bend them to a different shape. They are positioned around a former and clamped, or held, into place and left to cool. Upon being unclamped and cooled, they will retain their new shape.​

​2. laminating

This is the process that involves no heat. It involves using a number of think laminates of timber and bonding them to each other over a former. Unlike steam bending, there is no need to try and get the sections into a steam chamber, and they retain their shapes by being bonded to other layers of laminates. Whilst the adhesives used in this process cure and set, the layers of laminates need to be held in place​

Adhesive curing times and strengths vary from product to product. PVA adhesive is commonly used to bond timber as it is relatively cheap, non toxic, and easy to work with. PVA is a white liquid which, when dry after application and exposure to air, becomes transparent. ​

There are many trades and names. Typically PVA is left to set for a period of 24 hours before removing the clamps, to ensure that it is fully set. Synthetic powdered resins can also be used. Often these are water resistant and they need to be mixed with water before application and use.

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environmental considerations:

Trees are natural resources. They remove harmful gases from the atmosphere, notably carbon dioxide, replacing it with oxygen. As we harvest trees it is essential that we replant them so that the ecological impact is minimised and the cycle can continue for years to come. ​

Some tropical hardwoods; for example, teak and mahogany, take many hundreds of years to grow, so it is essential that we continue to plant new trees in order to take their place. ​

The Forest Stewardship Council (FSC) is a global organisation set up to certify that timber sources from their members is done so with these basic principles in mind. Timber from an accredited FSC supplier displays their logo.

composites:

Composite – a material that is made from two or more materials which have significantly different physical or chemical properties. When combined they create a single materials which is often lighter and stronger than the original individual materials on their own.

​​Composites are used because they can be engineered to meet the exact requirements of a specific application. By combining individual materials, each becomes enhanced and typically the advantages of the new material means it is more efficient, stronger and lighter.​