Unit 2 An Introduction to Materials and Systems Flashcards
How can fibres be combined?
By Blending or mixing
What does a combination of different fibres do to a fabric?
Gives better properties
What does blending fibres do?
- Blend is when 2 or more different fibres are combined to produce a yarn
- Then woven or knitted to make a blended fabric
Properties of blended fabrics
- Even stronger and remains hard-wearing
- Less absorbent - dries more quickly
- Soft and comfortable
- Resists creasing - easier to iron
- Doesn’t shrink easily
- BUT is highly flammable
What does mixing fibres do?
- Mix is when a fabric is made of 2 or more different types of yarn
- 2 different types of yarn can be knitted or woven together to make a mixed fabric
How can boards be manufactured?
Processed pieces of wood can be combined with glue and compressed into panels
Examples of manufactured boards
- Medium Density Fibreboard (MDF)
- Plywood
- Chipboard
Medium Density Fibreboard (MDF)
- Made from tiny fibres of softwood timber held together by glue
- No natural grain
- Cheap, dense, smooth uniform surface that can take paint and other finishes well
- Porous -> can be damaged by moist
- Often used for shelves and flat-pack furniture
Plywood
- Made of several layers of softwood or hardwood, glued together with their grain at right angles to one another
- Makes it very strong for its weight and thickness, compared with solid wood
- Very popular for building and furniture
Chipboard
- Compressing wood chips, shavings and sawdust together with glue -> usually used with a veneered surface
- Cheap but not very strong
Absorbent so can be easily damaged by moisture - Often used in cheap self-assembly furniture
How do trees get turned into paper or board?
- Cut down and taken to a paper mill
- The bark is stripped off.
- Wood cut into small pieces by a chipper
- Chemical or mechanical pulping to turn them into a mushy brown pulp
- Pulp is washed and bleached to make it white
- Pressed flat between rollers, dried and cut to size
What is pulping and why is it important?
- Converts the wood into individual cellulose fibres (pulp)
- Mechanical pulping grinds down the wood to separate the fibres.
- Chemical pulping involves heating the wood with chemicals -> dissolves other parts of the wood, leaving just the fibres behind
Where can the cellulose fibres used for paper and board come from?
Other plants like grasses. The process is similar to trees but no debarking or chipping is required
What is air-drying?
Involves stacking wood up outside or in sheds and allowing air to circulate it
What is kiln-drying?
Similar to air-drying but done in a heated chamber with fans to circulate the air -> quicker but conditions have to be controlled to avoid the wood drying too fast
How does manufactured timber use cellulose fibres?
MDF - a similar way to paper and board production
Chipboard - Mixture of dried wood chips, shavings and sawdust - often material that has been discarded as waste from another process
Plywood - Wood that has been softened either through soaking in hot water or steaming it. Thin sheets peeled from the softwood, cut to a suitable size and dried. Then it is made as normal plywood is made
What are the 2 linkages?
- Push/Pull Linkages
- Bell Crank
What is a push/pull linkage?
- Use 2 fixed pivots
- Input and output motions of the linkage are in the same direction. The motion of the link arm is in the opposite direction
- Each fixed pivot is in the centre of an arm. Changing the positions of these pivots will change the magnitude of the output force
E.g. toolbox draws can be opened upward
What is a bell crank?
- Changes the direction of a force through 90 degrees
- Magnitude of the output force can be changed by moving the fixed pivot so it’s not an equal distance between the two moving pivots
What are gears?
Toothed wheels that interlock -> transfer motion from one to another
What is a gear train and what is it used for?
- Where two or more gears are linked together
- Used to change the direction of motion or magnitude of the input force
Driver gear
- Turned by hand or motor, turns the driven gear
- Both will turn in opposite directions
Idler
- If you use a third gear, the driver and the driver gears will both turn in the same direction.
- The size of the idler won’t alter the speed of the other two gears
How to describe the relationship between the driver and the driven gears?
Gear ratio = number of teeth on the driven gear / number of teeth on the driver gear
How to calculate output speed?
Output speed = Speed of driver gear (input speed) / gear ratio
