Basic 7 · Career Technology · Resistant Materials

How Resistant Materials Are Produced

In this topic you will explain how timber, plastics, manufactured boards, ceramics and glass are produced, and relate each production process to the properties and uses of the material.

By the end of these notes you should be able to:

Describe how timber is produced from trees
Describe how plastics are produced from crude oil
Describe how manufactured boards, ceramics and glass are made

What you already know

Types of resistant materials

Copy everything that has a blue line on its left into your notebook. The other parts are for reading.

Lesson 1

Strand: Materials for Production
Sub-strand: Resistant Materials
Indicator: B7.2.2.1.3 – Explain how each of the resistant materials is manufactured/produced

Introduction

A tall odum tree in the forest and a crude-oil well off the coast of Takoradi seem very different, but both are sources of materials we use every day: timber and plastics.

1. Producing Timber

From tree to timber

Stage	What happens
1. felling	the mature tree is cut down with a chainsaw or axe
2. logging	branches are removed and the trunk is cut into logs
3. transporting	logs are carried to the sawmill
4. conversion	logs are sawn into planks and boards
5. seasoning	timber is dried to reduce its moisture content
6. storage	planks are stacked with spacers to allow air to flow

Logs being cut into planks at a sawmill

Figure 1: Sawmill Draw the stages from tree to plank.

2. Why Timber Is Seasoned

Freshly cut (green) timber contains a lot of water. If it is used before drying, it shrinks, twists, splits and may rot. Seasoning removes much of this water. In air seasoning, planks are stacked outdoors under a roof for months. In kiln seasoning, they are dried in a heated chamber for a few days, which is faster but more expensive. Seasoned timber is stronger, lighter and easier to work.

3. Producing Plastics

From crude oil to plastic products

Stage	What happens
1. drilling	crude oil is pumped from underground
2. refining	oil is heated and separated into parts (fractions) such as petrol and naphtha
3. cracking	large molecules are broken into small ones, such as ethene
4. polymerisation	small molecules (monomers) are joined into long chains (polymers)
5. forming	plastic granules are melted and shaped by moulding or extrusion

4. Shaping Plastics

Plastic granules are melted and shaped in several ways. In injection moulding, melted plastic is forced into a mould to make items such as chairs and bottle caps. In blow moulding, air is blown into soft plastic inside a mould to make bottles. In extrusion, plastic is pushed through a shaped hole to make pipes and sachet film.

5. Responsible Use and Disposal

Timber and plastics both affect the environment. Illegal logging destroys forests, so trees should be replanted and only mature trees felled. Plastic waste lasts for centuries, so plastics should be reused and recycled rather than dumped or burned. Offcuts of timber can be reused for small products or as firewood.

New words

felling: Cutting down a tree.
seasoning: Drying timber to reduce its moisture.
polymer: A long chain of joined small molecules.
injection moulding: Forcing melted plastic into a mould.

Summary

Timber is produced by felling, logging, conversion and seasoning.
Seasoning prevents shrinking, twisting and rot.
Plastics come from crude oil by refining, cracking, polymerisation and moulding.

Class activity: Production Sequence

Inspect the grain of a timber offcut and the surface of a plastic container offcut.
Arrange printed cards for timber and plastic production in order.
Explain one local use and one responsible disposal or reuse practice for each.

You need: Local timber offcut, Clean plastic-container offcut, Printed wood-and-plastic production sequence

Exercises

Answer in your exercise book first, then check your answers.

1. Cutting down a tree is called…
- A. felling
- B. seasoning
- C. moulding
- D. refining
Show answer
Answer: fellingFirst stage.
2. Kiln seasoning is…
- A. faster than air seasoning
- B. slower than air seasoning
- C. done underwater
- D. done before felling
Show answer
Answer: faster than air seasoningUses heat.
3. Plastics are made mainly from crude oil.
- A. True
- B. False
Show answer
Answer: TruePetrochemicals.
4. Joining small molecules into long chains is called ______.
Show answer
Answer: polymerisationMakes polymers.
5. State the stages of producing timber.
Show answer
Answer: Felling, logging, transporting, conversion, seasoning, storage.In order.
6. Explain why green timber should not be used for furniture.
Show answer
Answer: It contains much water, so it will shrink, twist, split or rot as it dries.Moisture problems.

Lesson 2

Strand: Materials for Production
Sub-strand: Resistant Materials
Indicator: B7.2.2.1.3 – Explain how each of the resistant materials is manufactured/produced

Introduction

Some resistant materials are made by gluing wood waste together, others by baking clay, and others by melting sand. Each process gives the material its special properties.

1. Manufactured Boards

Types of manufactured board

Board	How it is made	Properties and uses
plywood	thin sheets (veneers) glued with grains at right angles	strong in all directions; ceilings, furniture
chipboard	wood chips mixed with glue and pressed	cheap, heavy; kitchen cabinets, shelves
MDF (medium-density fibreboard)	fine wood fibres glued and pressed	smooth surface; furniture, display boards
blockboard	wooden strips sandwiched between veneers	strong and stiff; doors, tables

2. Producing Ceramics

Making ceramic ware

Stage	What happens
1. winning the clay	digging clay from the ground
2. preparing	removing stones and roots, soaking and kneading (wedging)
3. shaping	pinching, coiling, throwing on a wheel or pressing in moulds
4. drying	allowing the work to dry slowly in the shade
5. firing	heating in a kiln or bonfire to make it hard
6. glazing	coating with a glassy layer and firing again (optional)

Clay bricks stacked in or beside a kiln

Figure 2: Clay bricks Draw the stages of making a clay pot.

3. Producing Glass

Glass is made by heating a mixture of silica sand, soda ash (sodium carbonate) and limestone in a furnace to about 1,500 °C until it melts into a thick liquid. Recycled broken glass (cullet) is often added because it melts at a lower temperature, saving energy. The molten glass is then shaped by blowing, pressing into moulds or floating on molten tin to make flat window sheets. Finally it is annealed, meaning it is cooled slowly so it does not crack.

4. Relating Process to Properties

The way a material is made explains its properties. Plywood is strong because its layers are crossed. Ceramics are hard because firing fuses the clay particles together. Glass is transparent because it cools without forming crystals. Knowing this helps designers choose the right material for a product.

5. Safety with Ceramics and Glass

Safety: Never pick up broken glass with bare hands. Sweep it into a dustpan and wrap it in thick paper before throwing it away.

Kilns and furnaces reach very high temperatures, so only trained adults should operate them. In the school workshop, broken ceramics and glass should be handled with gloves, and learners should inspect them without touching sharp edges.

New words

veneer: A thin sheet of wood.
wedging: Kneading clay to remove air bubbles.
kiln: An oven for firing ceramics.
annealing: Cooling glass slowly to prevent cracking.

Summary

Manufactured boards are made by gluing veneers, chips or fibres together.
Ceramics are made by preparing, shaping, drying, firing and glazing clay.
Glass is made by melting sand, soda ash and limestone, then shaping and annealing it.

Class activity: Material Comparison

Compare the layers of a manufactured board offcut with solid timber.
Inspect a clay pot shard and a glass jar without handling broken glass.
Explain the main production steps and match each material to a suitable product.

You need: Man-made board offcut, Clay pot shard, Glass jar

Exercises

Answer in your exercise book first, then check your answers.

1. An oven for firing clay is a…
- A. kiln
- B. loom
- C. furnace for steel only
- D. sawmill
Show answer
Answer: kilnFires ceramics.
2. Plywood is strong because its veneers are…
- A. glued with grains at right angles
- B. all in one direction
- C. unglued
- D. made of plastic
Show answer
Answer: glued with grains at right anglesCrossed layers.
3. Glass is cooled slowly to stop it cracking.
- A. True
- B. False
Show answer
Answer: TrueAnnealing.
4. Kneading clay to remove air bubbles is called ______.
Show answer
Answer: wedgingClay preparation.
5. State the main raw materials for making glass.
Show answer
Answer: Silica sand, soda ash and limestone (and recycled glass).Three main materials.
6. Explain why air bubbles must be removed from clay before firing.
Show answer
Answer: Air expands when heated and can make the pot crack or explode in the kiln.Expansion of air.

Homework

Draw a flowchart showing how one resistant material is produced.