Material properties

Toby: That’s certainly a scary-looking collection of tools.

Ester: Yes, some of them do look quite menacing, don’t they?

Toby: Is that titanium? The drill handle?

Ester: Um… yes.

Toby: I’m an engineer, that’s why I, am…

Ester: Oh, I see. Yes, titanium’s great. It’s expensive, obviously, but very light. That’s the advantage. Ideally, you want it to be lightweight, to give better control.

Toby: Nn…

Ester: 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.

Ester: They are 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.

Ester: The 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 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.

Ester: See what I mean? You can actually smell burning. And that’s after a few seconds. Imagine the heat build-up after several minutes.

Unit 13 NUMBERS

Conversation 1

“When you are going away on holiday?”

“On the ________” (15)

“And when do you get back?”

“On the __________ I’ll give you a ring when we get home.” (24)

Conversation 2

And now the business news. The unemployment rate has risen slightly this month. The national unemployment rate is now __________ and in our area, an estimated __________ people are out of work. (4.2%, 15,000)

Conversation 3

“Can I pay by visa?”

“Yes, that’s fine. Erm – what’s your card number, please?”

“It’s __________ (4929 … 7983 … 0621 … 8849)

“Let me read that back. _____ … _____ … _____ … _____”.

“That’s right”.

Unit 14 NUMERALS

When I was a kid I was top of the class in maths. I was really good at mental arithmetic and doing sums. Things were easy back then, It was all addition and subtraction, multiplication and division. I knew my times tables like the back of my hand. Then, things got difficult when I was about 14. We had to learn stuff like algebra and geometry and lots of other stuff I can’t remember the names of. Suddenly. I wasn’t so good at maths any more. I think there were a few reasons for this. One was my maths teacher, another was because I sat at the back of the class, and another was I talked a lot. I still like maths and know I would be good at it again if I studied. I did statistics when I was at university and loved that.

Unit 15 GEOMETRIC FIGURES

Дата добавления: 2015-10-21