The Modification of Properties For Specific Purposes (AQA GCSE Design & Technology): Revision Note

Additives to prevent moisture transfer in papers and boards

• Additives are added to papers and boards to prevent moisture transfer

• To do this, the following process is followed:

  • Step 1. Wood chips from cut down and chopped up trees are cooked to turn them into a mushy pulp containing fibres

  • Step 2: The raw pulp is mixed with additives including resins and waxes

  • Step 3: The mixture is sprayed onto metal rollers which heats and presses the pulp flat onto their surface

  • Step 4: This thin layer of pulp mixed with additives dries, forming a large sheet of paper with much of the moisture removed

  • Step 5: The finished paper is rolled up into very large rolls ready to be cut into stock forms

  • Step 6: The final paper has greater moisture resistance due to the resin and wax composition

Seasoning to reduce moisture content of timbers

• Timbers are seasoned to reduce their moisture content

• This ensures that the timber is at the right level of moisture content, usually around 8-10% for use indoors

• If the timber is too wet i.e. the moisture content is high, it would dry out whilst in use and cause the material to twist or become misshapen, damaging the product

• The process of seasoning timber is as follows:

  • Step 1. Trees both hardwood and softwood are cut down and moved to a wood mill

    Step 2. At the wood mill, the bark is removed leaving only the trunk

    Step 3: The trees are sawn into large boards/planks which are suitable to be stacked

    Step 4: The timber now stacked, is either air seasoned i.e. left outside to dry out naturally or kiln seasoned baked in an oven for faster and controlled drying

    Step 5: With the moisture content lowered, the timber is sawn into useful sizes and planed given a smooth surface

    Step 6: The final timber has much lower water content, resulting in a stable board which will be less likely to twist and become misshapen due to drying out

Annealing to soften metals to improve malleability

• Metals can go through a process of annealing to change their working properties

• This is the case for mild steel, where a process called annealing can be used to soften the steel to make it easier to shape and form
  

• The process of annealing mild steel is as follows:

  • Step 1. Heat the mild steel part up in a furnace to a high temperature

  • Step 2. Keep the mild steel at that high temperature for a period to time, which will remove any internal stresses in the material

  • Step 3: Remove the part from the heat and allow to cool slowly often still in a furnace which is turned off and allowed to cool down

  • Step 4: The final mild steel part will now be softer and much more malleable, which allows a manufacturer to shape and form it easier

Stabilisers to resist uv degradation in polymers

• Polymers which will be exposed to natural sunlight known as ultra violet light or UV for long periods of time can become damaged by changing colour or weakening/degrading

• Manufacturers can add stabilisers to polymers, to make sure they can resist UV light from the sun

  • This prevents the polymer from degrading

• The process of adding stabilisers to polymers is as follows:

  • Step 1. Crude oil is refined into a polymer through a process called distillation

  • Step 2. The polymer is shaped into pellets/granules, which can be fed into polymer forming machines e.g. injection moulding machine

  • Step 3: The UV stabilisers are mixed into the pellets and heated

• Step 4: The resulted molten mix of stabiliser and pellet is shaped into the product/part through a polymer forming process e.g. Injection moulding or extrusion

• Step 5: The stabiliser has been evenly distributed throughout the material, therefore it is also throughout the product/part

• Step 6: The final polymer product will be resistant to UV light, and no longer degrade or discolour over time due to being exposed to sunlight

Flame retardants to reduce combustion and fire hazards in textiles

• Textiles used for home furnishings such as curtains or sofa coverings will become a fuel for a fire in the home, if they are not treated to prevent them from burning

• This can be very dangerous and would lead to a house fire spreading rapidly

• Flame retardants can be applied to textiles to reduce the risk of them catching fire, and improving the overall safety of the textile based product

• The process for applying flame retardant to a textile is as follows:

  • Step 1. The textile is produced from a natural e.g. cotton or synthetic polyester source into a knitted or woven fabric sheet

  • Step 2. The fabric sheet is sprayed or soaked into the flame-retardant solution which coats all of the fibres

  • Step 3: The fabric is dried and cured to fix the treatment in place

  • Step 4: The textile is cut and shaped to fit the furniture piece e.g. a sofa or chair over

  • Step 5: The final textile product is flame retardant and will help to slow or prevent the product from catching fire

Printed Circuit Boards (PCBs)

• A PCB is the central surface onto which all electronic circuits are mounted, inside electronic products

• A PCB is used to hold and connect all of the individual electronic components in the circuit design created by the designer/manufacturer.

• Photosensitive PCBs are made through the following process

  • Step 1: A copper coated board is covered in a photosensitive layer called photoresist

  • Step 2: A circuit design is placed over the top of this photosensitive layer, masking the design

  • Step 3: The board is exposed to UV light, which causes the photosensitive layer to harden where it is covered by the masking

  • Step 4: The board is next placed into a development solution, which will remove all of the photosensitive layer except that which has hardened

  • Step 5: The board is next placed in an etching solution, which removes the unwanted copper, again leaving the copper coated in the photosensitive layer

  • Step 6: The remaining photo-resistance is removed using chemicals, leaving the circuit on the board only

  • Step 7: All of the holes for electronic components are drilled

  • Step 8: The PCB is now ready for components to be soldered onto the board

Anodising

• Anodising is the process of electro-chemically treating a metal surface to form a rapidly created thin layer of protective oxide

• Anodising can be applied to the surface of various metals, including aluminium, in order to:

  • Make it corrosion resistant which prevents rusting or damage

  • Improve the hardness and durability of the surface

  • Enhance the appearance of the metal often anodising causes a colour change on the surface of the metal

  • Prepare surfaces for paints or other coatings to be applied afterwards

• The process of anodising is as follows

  • Step 1: The metal part is cleaned of all grease

  • Step 2: The metal part is submerged into a bath of acidic electrolyte solution 

  • Step 3: An electric current is passed through the solution

  • Step 4: The oxygen in the solution reacts to the metal part, and causes it to form a rapidly appearing oxide layer to the surface

  • Step 5: The surface will be permanently changed to a new colour

  • Step 6: The surface is now sealed, which improves durability, is scratch resistant, and will ensure no corrosion.