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c In pairs, discuss why the properties of Kevlar® are especially important for each
application described in the text.

a ►2.4 Read a conversation about the properties of materials used in a specific type of tool
and answer the following questions.
1 Where does the conversation take place?
2 What tool is being discussed?
3 Which materials can be used for its different parts?

Toby: That's certainly a scary-looking collection of tools.
Esther: Yes, some of them do look quite menacing, don’t they?
Toby: Is that titanium? The drill handle?
Esther: Urn ... yes.
Toby: I'm an engineer, that’s why I, urn ...
Esther: Oh, I see. Yes, titanium's great. It’s expensive, obviously, but very light. That’s the big
advantage. Ideally, you want it to be lightweight, to give you better control.
Toby: Nn.
Esther: These are the most impressive things, though, the burs on the end. The latest ones can
rotate at over half a million revs per minute.
Toby: Nn.
Esther: They’re coated with tungsten carbide, which I think is one of the hardest materials in
existence, isn’t it? Along with diamond. That’s also used.
Toby: Nn.
Esther: The key requirement is abrasion resistance, of course. Obviously, they need to be very
durable. And you don’t want them snapping, either. The last thing you want is a brittle material.
Apparently, that was the trouble they had in the past, making the bur tough enough so it didn't
break. I think part of the problem was heat, as well. Drilling into a tooth at high speed, you
obviously get a lot of heat build-up. You need a good degree of thermal stability.
Toby: Nn.
Esther: See what I mean? You can actually smell burning. And that’s after a few seconds.
Imagine the heat build-up after several minutes.
Toby: Nn.

b Complete the following extracts from the conversation using the properties in Exercise
8c. Listen again and check your answers.
1 The handle mustn’t be heavy. Ideally, you want it to be .
2 Resisting friction is essential. The key requirement is .
3 The bur has to be built to last. Obviously, they need to be very .
4 Heat builds up in the bur. You need a good degree of .

c Match the words and phrases (1-5) from Exercise 10b to the synonyms (a-e).
1 ideally a it's clear that
2 obviously b for the best results
3 the last thing you want c the most important factor
4 the key requirement d a lot of / a high level of
5 a good degree of e the worst situation

a You work for a manufacturer of hand tools and have been asked to investigate using
alternative materials in your products. In pairs, read the notes and discuss the main
properties required of the materials used to make the tools.

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