A Input, output and efficiency

10.1 An engineer is talking to a colleague about the design of a fuel tank for a water pump.

average	constant	consumption	duration
capacity	consume	cumulative	rate

 

10.2 The graph below shows water consumption in a washing process at a manufacturing plant. Write figures to complete the comments. Look at A opposite to help you.

1. Water consumption fluctuated between …. and …… litres per second.

2. Averaged out over the period shown, consumption was roughly …… litres per second.

3. 3 Consumption peaked at a rate of …. litres per second.

4. If the process ran to capacity, it could use water at a rate of ……. litres per second.

5. When consumption peaked, the process had spare capacity of ……. litres per second.

10.3 Choose the correct words from the brackets to complete the explanations from a guided tour of a manufacturing plant. Look at A and B opposite to help you.

1. A lot of heat is generated in this part of the process. And all of that (input / output) is recycled - it provides a (demand / supply) of heat for the next stage of the process. So it's quite an (efficient / inefficient) system.

2. Sometimes, there’s (insufficient / surplus) heat, and it can’t all be recycled. At other times there isn’t quite enough recycled heat to keep up with (peak / off-peak) demand for heat energy further along the process.

3. Some material is lost in the washing process, but the mass of water absorbed is greater than the mass of material lost. So there’s a net (loss / gain) in total mass

 

Material types

A Metals and non-metals

Engineering materials can be divided into:

■ metals - examples of metallic materials are iron (Fe) and copper (Cu)

■ non-metals - examples of non-metallic materials are carbon (C) and silicon (Si).

As iron is such a widely used material, metals can be divided into:

■ ferrous metals - those that contain iron

■ non-ferrous metals - those that do not contain iron.

 

B Elements, compounds and mixtures

With regard to the chemical composition of materials - the chemicals they contain, and how those chemicals are combined - three main categories can be used:

- Elements are pure materials in their most basic form. They cannot be broken down into different constituents (‘ingredients’). Examples of elements widely used in engineering materials are iron, carbon and aluminium (Al).

- Compounds consist of two or more elements that are chemically bound - that is, combined by a chemical reaction. An everyday example is water, which is a compound of hydrogen (H) and oxygen (O).

- Mixtures consist of two or more elements or compounds which are mixed together, but which are not chemically bound. In engineering, common examples are alloys - that is, metals which have other metals and/or non-metals mixed with them. A common example is steel, which is an iron-carbon alloy, and can include other alloying metals - metals which are added to alloys, in small quantities relative to the main metal. Examples of widely used alloying metals are chromium (Cr), manganese (Mn) and tungsten (W).

C Composite materials

The article below is from an engineering journal.

Materials under the microscope: composites

When you think of examples of hi-tech materials, composite materials come to mind - such as carbon-fibre, used in aerospace and Formula 1 cars. But although we think of composites as hi-tech and highly expensive, that’s not always true. The earliest examples of composite materials were bricks made from mud and straw. Or, to use the correct composite terms, from straw reinforcement - the structural network that reinforces the material inside, and a mud matrix-the material surrounding the reinforcement.

These terms explain what a composite material is: a matrix with a reinforcing material inside it. A modern, everyday example is fibreglass - correctly called glass- reinforced plastic (GRP) - which has a plastic matrix reinforced with glass fibres.

 

11.1 Complete the sentences using the words in the box.

metal

non-metal

metallic

non-metallic

ferrous

non-ferrous

 

1. Carbon (C) is a ………....……….

2. Copper (Cu) is a ……...……….… metal.

3. Aluminium (Al) is a common ………...….…….

4. Steel (Fe + C) is a widely used ………...….… metal.

5. Although it is used in steel, carbon is ……...…….…….

6. Aluminium is relatively lightweight for a ……………....… material.

 

11.2 Decide whether the sentences below are true or false, and correct the false sentences. Look at B opposite to help you.

1. The elements that make up a compound are chemically bound.

2. Alloys are chemical compounds that are frequently used in engineering.

3. Alloys can contain both metallic and non-metallic constituents.

4. In an alloy, an alloying metal is the biggest constituent, by percentage.

5. Steel is a metallic element.

 

11.3 Complete the extract about concrete and steel, using suitable forms of the word reinforce from C opposite. Sometimes there is more than one possible answer.

(1).....concrete is one of the most widely used construction materials, and one we take for granted. However, using steel bars to (2)..... concrete structures located outdoors is only possible thanks to a fortunate coincidence: concrete and steel have practically the same coefficient of thermal expansion - in other words, as atmospheric temperature varies, the concrete and the steel (3)..... expand and contract at the same rate, allowing uniform movement. Using a (4)........ material with a different coefficient of expansion would not be feasible. For example, (5) aluminium-...... concrete would quickly disintegrate.

11.4 Read the text below and find two elements, two compounds, an alloy and a composite. Look at A, B and C opposite to help you.

Generally, the steel used in reinforced concrete will have previously been exposed to water and to the oxygen in the air. As a result, it will usually be partly corroded, being covered with a layer of iron oxide (rust). However, once the steel is inside the hardened concrete, it will be protected from air and water, which prevents further rusting. Additionally, the cement in concrete does not react aggressively with the iron in steel

 

Over to you

Think of some of the materials used to make products or structures you know about. Say whether the materials are elements, compounds, mixtures, alloys or composites. If they are composites, what materials are used (a) as the matrix, and (b) as reinforcement?

 

Steel

A Carbon steels

This extract from an article in an engineering journal is about different types of steel.

Steel is the most widely used engineering material. Technically, though, this well-known alloy of iron and carbon is not as simple as one might think. Steel comes in a huge range of different grades, each with different characteristics. For the inexperienced, it can be difficult, to know where to begin.

A good place to start is with the two main types of steel. The first, carbon steels, consist of iron and carbon, and contain no significant quantities of other metals. Carbon steels can be divided into three main grades:

- Mild steel - the most widely used grade - is a low carbon steel which contains up to approximately 0.3% carbon.

- Medium carbon steel contains between approximately 0.3% and 0.6% carbon.

- High carbon steel contains between approximately 0.6% and 1.4% carbon.

Notes:

The chemical symbol for iron = Fe, and carbon = C.

B Alloy steels

 

The article goes on to look at alloy steels.

The second main category of steel is alloy steels, which consist of iron, carbon and one or more alloying metals. Specific grades of alloy steel include:

- low alloy steels, which contain 90% or more iron, and up to approximately 10% of alloying metals such as chromium, nickel, manganese, molybdenum and vanadium

- high strength low alloy steels (HSLA), which contain smaller quantities of the above metals (typically less than 2%)

- stainless steels, which contain chromium as well as other metals - such as nickel - and which do not rust.

- tool steels, which are extremely hard, and are used in cutting tools. They contain tungsten and/or cobalt. A widely used grade of tool steel is high-speed steel, which is used in cutting tools that operate at high temperatures, such as drill bits.

 

Notes:

The terms carbon steel and alloy steel can cause confusion, as carbon steels are also alloys, and alloy steels also contain carbon. The chemical symbol for chromium = Cr, cobalt = Co, nickel = Ni, manganese = Mn, molybdenum = Mo, tungsten = W, and vanadium = V.

C Corrosion

One weakness of mild steel is that it corrodes - its surface progressively deteriorates due to a chemical reaction. This reaction takes place between the iron in the steel and the oxygen (O₂) in the air, to form iron oxide. When iron corrodes, we say that it rusts. In some metals, such as aluminium (Al), the presence of corrosion is not a problem, as the layer of oxide around the metal remains hard, which prevents it from oxidizing any further. However, when mild steel goes rusty, the rust on the surface comes off continuously, and a new rusty layer forms, progressively ‘eating into’ the metal.

 

12.1 Decide whether the sentences below are true or false, and correct the false sentences. Look at A and B opposite to help you.

1. Steel is an alloy of iron and carbon.

2. Mild steel is a high carbon steel.

3. Alloy steels contain carbon.

4. Chromium and nickel are used as alloying metals in steel.

5. Low alloy steels contain more chromium than iron.

6. Stainless steel is an alloy steel.

7. Tungsten is added to steel to make it softer.

8. High-speed steel is suitable for making cutting tools that get very hot.

 

12.2 Use the words to complete the sentences below. There is more than one possible answer. Look at C opposite to help you.

1. When steel is exposed to air and water, it….

2. A brown/red material on the surface of steel is called …….

3. The strength of steel is reduced if it is ….

 

12.3 Complete the article about a special type of steel, using words from A, B and C opposite

. Weathering steel

The perennial problem with mild (1)….. is that it when exposed to air and water. Generally, the only solution is either to apply a protective coating, or to use another (3) ….. of steel that is resistant to the (4) ….... process - the most well-known being (5)….. steel, which contains significant quantities of (6) …... and, often, nickel.

There is, however, an alternative solution. So-called weathering steel is a special alloy suitable for outdoor use. But rather than being completely protected from corrosion, the surface of the steel is allowed to go (7) ….... Once a layer of (8) …... has formed on the surface, it stabilizes and forms a hard protective layer. This layer differs from ordinary (9) …. oxide, as it does not continue to eat into the metal. While not everyone may like the 'rusty look', weathering steel has been widely used in architectural applications and outdoor sculptures.

Over to you

Think about some items you're familiar with are made of steel, but which are not protected (for example, by paint). How serious is the potential problem of corrosion? How is it prevented or limited - for example, by using a specific grade of steel?

 

Non-ferrous metals