1.2 - Performance Characteristics Of Materials

Question 1

What are paper and boards?

Answer 1

Compliant materials, meaning that they are suitable for scoring, cutting and folding to produce items such as packaging.

Question 2

What is the original source of paper?

Answer 2

Wood pulp, which is grey in colour.

Question 3

What happens to wood pulp during paper manufacture?

Answer 3

During manufacture, bleaches are added to transform the grey pulp into whiter paper.

Question 4

What is the benefit of using wood pulp to manufacture paper?

Answer 4

The natural source makes paper and boards suitable for recycling or if left in landfill, they will naturally biodegrade.

Question 5

Name different types of paper

Answer 5

1) Layout paper
2) Cartridge paper
3) Tracing paper
4) Bleed-proof paper
5) Treated paper
6) Watercolour paper
7) Corrugated card
8) Bleached card
9) Mount board
10) Duplex card
11) Foil backed card
12) Laminated card
13) Metal effect card
14) Moulded paper pulp

Question 6

What stock forms are available for paper?

Answer 6

Standard sizes:
* A0 (largest) to A8 (smallest).
* Each ‘A’ size is half the size of the previous one.

Commercial printers may work with ‘paper-untrimmed sizes’ (raw format A - RA and supplementary raw format A - SRA) which are slightly larger than the standard A sizes.

The larger sizes allow for any bleed from the printing process, and the papers are trimmed to size after they have been printed.

Question 7

How is paper thickness measured?

Give some examples.

Answer 7

Paper thickness is measured in grams per square metre (gsm).

• Photocopying = 80gsm
• Mount board = 1,000gsm

-> The lower the gsm, the more lightweight the paper, and the easier it is to bend, cut and score.

Question 8

What is polymer-based sheet and film used for?

Answer 8

Produced in sheet form of varying thicknesses for purposes from model making to packaging.

Question 9

How sustainable is polymer-based sheet and film?

Answer 9

Sustainability (each differ):
* E.g., cellulose acetate = comes from a natural source -> will biodegrade

*E.g., fluted polypropylene (PP) = can be recycled.

It is more difficult to recycle foam board due to the foam core and outer sheets of card -> more likely to be reused than recycled.

Question 10

Describe wood fibres / how they grow

Answer 10

The wood fibres grow along the length of the tree or branch (grain) and these fibres consist of hollow cells (tracheids) supported by lignin resin.

Question 11

Explain why the direction of grain is significant in wood.

Answer 11

Timber:
* Strong = direction of the grain (along the grain)
* Weaker across the grain.

Means when using a jack plane to smooth:
* Cut well = moved with the grain.
* Chipping == used across the grain.

Table top:
*Long planks running in the direction of the grain.

• If lengthways (with the grain running across board) = easy to split.

Question 12

Explain what happens to wood prior to use

Answer 12

• Wood is converted (sawn into useable pieces)
• Seasoned (removing the excess moisture: 80-90%)

There are 2 main forms of seasoning:
* Air seasoning
* Kiln seasoning

Question 13

What are the 2 main forms of seasoning?

Answer 13

• Air seasoning
• Kiln seasoning

Question 14

What is air seasoning?

Answer 14

A traditional, inexpensive method with involves stacking the wood under a shelter, protected from the rain.

Air circulates between the planks to slowly remove the excess moisture.

Question 15

What is air seasoned wood used for? Why?

Answer 15

• Outdoor wooden products

Why?
It is seasoned to the same moisture content as its surroundings -> therefore the wood will be less prone to defects.

Question 16

What is kiln seasoning?

Answer 16

A more expensive (to air seasoning), but controlled method which is very quick and can take just a few weeks.

Planks are stacked onto trolleys and placed in the kiln where both temperature and humidity are controlled.

Initially, the kiln atmosphere is very steamy but this is gradually changed to become hotter and drier.

Question 17

What is kiln seasoned wood used for? Why?

Answer 17

• Indoor products such as furniture

Why?
It has been seasoned to meet indoor conditions and will have lower moisture content than air-dried wood.

Question 18

Why is wood seasoned?

Answer 18

If an unseasoned plank is placed in a heated room, it will twist, warp, cup or bow when drying out and cracks or gaps may appear.

Question 19

What advantages does seasoning wood give?

Answer 19

1) Greater immunity from decay and increased resistance to rot.

2) Increased strength and stability

3) Helps preservatives to penetrate

4) Makes wood less corrosive to metals

Question 20

What abbreviations are used for air-dried and kiln-dried seasoned wood?

Answer 20

A-D and K-D

Question 21

What happens to wood when humidity changes?

Answer 21

As it is a natural material:
It expands and shrinks with changes in humidity (the amount of water present in the atmosphere).

Question 22

What should be done to reduce the time taken to season wood to the correct moisture content?

Answer 22

Trees should be felled in the winter when they grow less, have less sap and therefore contain the least moisture.

Question 23

When does the largest shrinkage occur in wood?

Answer 23

After the tree is cut down and while it is being seasoned.

Question 24

Why must care be taken when seasoning wood?

Answer 24

Wood shrinks by different amounts in different directions, with almost no shrinkage in the direction of the wood’s grain (lengthwise).

Some shrinkage happens radially (perpendicular to the growth rings), with a greater amount occurring tangentially (along curvature of growth rings).

The ends of the wood tend to lose moisture content more quickly than the core, and sometimes cracks can appear on the plank ends.

CARE MUST BE TAKEN WHEN SEASONINING THE WOOD so that the whole plank will shrink uniformly.

Question 25

What happens once wood has been seasoned? Why?

Answer 25

Usually:
Any end cracks will close as the plank is now in equilibrium throughout.

Question 26

What additional reasons can seasoned wood be susceptible to shrinkage?

Answer 26

Seasonal changes in the ambient humidity.

(Less of a concern in modern homes where temperatures are fairly constant due to heating etc.)