Unit 8. Mechanical elements (Part 1)

T ask 1. Discuss the following questions:

1. Imagine the world without mechanical devices. What technological difficulties could we meet?

2. That’s how we make predictions about the future in English. Study this table.

   MAKING PREDICTIONS ABOUT THE FUTURE: think … I (don’t) expect … I’ll … suppose … I’ll probably … imagine … I probably won’t …

3. List as many mechanical parts as you know. Compare your list with that of your partner expressing certainty and uncertainty in English. Study this table.

HOW TO EXPRESS CERTAINTY AND UNCERTAINTY: Yes, certainly. I’m not sure … Definitely. As far as I know … I’m sure. If I’m not mistaken … There is no doubt about it. If I remember right … I think so. I don’t think so …

Task 2. Read the text and translate all unfamiliar words and word combinations.

Machine Elements: Keys and Pins

In mechanical engineering, a key is a machine element used to connect a rotating machine element to a shaft. Through this connection the key prevents relative rotation between the two parts and allows torque to be transmitted through. For a key to function the shaft and rotating machine element must have a keyway, also known as a keyseat, which is a slot or pocket for the key to fit in. The whole system is called a keyed joint. There are three main types of keys: parallel, Woodruff, and tapered keys.

The keyway in a shaft for a parallel key	A sprocket with an internal parallel keyway	Cross-section of a parallel keyed joint

Parallel keys are the most widely used. They have a square or rectangular cross-section. Square keys are used for smaller shafts and rectangular faced keys are used for shaft diameters over 6.5 in (170 mm) or when the wall thickness of the mating hub is of concern. The keyway is a longitudinal slot in both the shaft and mating part.

Fig 1.

Fig 2.

Fig 3.

Fig 4

Woodruff keys are semicircular shaped keys that, when installed, leave a protruding tab. The keyway in the shaft is a semi-circular pocket and the mating part has a longitudinal slot. They are used to improve the concentricity of the shaft and the mating part, which is critical for high speed operations. The main advantage of the Woodruff key is that avoids the milling of a keyway near shaft shoulders, which already have stress concentration. Common applications include machine tools, automotive applications, snowblowers and marine propellers. In figure 1 you can see gear G that is held on shaft S by Woodruff key N.

The final type of key is the tapered key, which is tapered on one side, the side that engages the hub. The keyway in the hub is broached with a taper matching that of the tapered key. Some taper keys have a gib, or tab, for easier removal during disassembly. The problem with taper keys is that they can change the center of rotation of the shaft to be slightly off of the mating part. A pin is a device used for fastening objects or material together. It is usually made of steel, or on occasion copper or brass. Tapered pins (Fig. 2) can be used to transmit very small torques or for positioning. They should be fitted so that the parts are drawn together to prevent their working loose when the pin is driven home. Straight pins, likewise, are used for transmission of light torques or for positioning. Spring pins have come into wide use recently. Two types shown in Fig. 3 deform elastically in the radial direction when driven. They can replace straight and taper pins and combine the advantages of both, i.e., simple tooling, ease of removal, reusability, ability to be driven from either side. Cotter pins (Fig. 4) are used to secure or lock nuts, clevises, etc. Driven into holes in the shaft, the eye prevents complete passage, and the split ends, deformed after insertion, prevent withdrawal.

NOTES:

keyseat or keyway – шпонковий паз / канавка

feather or spline key – шпонка напрямна або призматична

according to – згідно

in most cases – у більшості випадків

dovetailed key – шпонка у вигляді ластівкового хвосту

slot – паз

shaft – вал

in spite of – не зважаючи на

mating part – парна деталь

positioning – розміщення

insertion – вставка, вкладка

Task 3. Answer the following questions:

1. What is the main function of a key?

2. What types of keys can you name?

3. How can keys be distinguished according to various characteristics?

4. What is the difference between cotter and tapered pins?

5. How can pins be divided geometrically?

6. What is the form of the keyway in the shaft if we are talking of a Woodruff key?

7. What are the advantages of spring pins?

8. What is the main disadvantage of tapered pins?

Task 4. Find English equivalents for the following words and word combinations in the text:

шпонка напрямна, обертальний рух, конічна шпонка, крутний момент, шпонка у вигляді ластівкового хвоста, не звертаючи увагу на, вісь, гайка, передача, перевага, застосування, з’єднання, встановити, навантаження, поперечний переріз, скоба, парна деталь.

Task 5. Match the terms (1-6) with their definitions (a-f).

	Term		Definition
1	transmission		the act of applying to a particular purpose or use
2	rotation		something that is attached or joined
3	applications		any force or system of forces that causes or tends to cause rotation
4	fastening		the spinning motion of a body, such as a planet, about an internal axis
5	torques		a system of shafts, gears, torque converters, etc., that transmits power of the engine to the driving wheels of a motor vehicle
6	shaft		a revolving rod that transmits motion or power: usually used of axial rotation

Task 6. Fill in the gaps using the words and word combinations below. Use each word or word combination only once.

washer, nut, engineering, prevent, diameter, sunk keys, threaded, fastener, width, lengthwise, rods, tapered pins

A tapered pin is a 1)_______ used in mechanical 2)_______. They are steel 3)______ with one end having a slightly larger 4)_______ than the other. Some 5)______ have a male screw thread on the small end that holds the pin in place with a 6)________ and a nut. Other pins are 7)_______ on both ends, on the thick end to pull the pin out with the same 8)_______ that holds the pin in place.

The minimum stock length of keys is 4 times the key 9)_______, and maximum stock length of keys is 16 times the key width. The increments of increase of length are 2 times the width.

10)_______ are adapted particularly to the case of fitting adjacent parts with neither end of the key accessible. Feather keys 11)_______ parts from turning on a shaft while allowing them to move in a 12)_______ direction.

Task 7. Match words from column A with the words from column B and translate them into Ukrainian:

	A		B
1.	mechanical	a	rotation
2.	feather	b	cross-section
3.	radial	c	engineering
4.	mating	d	slot
5.	center of	e	keys
6.	longitudinal	f	power
7.	rectangular	g	part
8.	transmits	h	direction

Task 8. Put these words into the right word order, make sentences and translate them into Ukrainian :

1. assembled /is to transmit / The main function of a key / on it / torque between / a shaft and a machine part .

2. such keys /In some constructions /spine keys / keys allow / the shaft and the hub, / are called / an axial motion between /feather or.

3. into cylindrical pins, / pins can be divided / and conical or /called straight pins,/ Geometrically / taper pins.

4. can be used to/ transmit / Tapered pins/ or for positioning / very small torques.

Task 9. Translate the following sentences into English:

1. Шпонко­ве з'єднання застосовують у механічних пе­редачах, коли потрібно, щоб разом з валом оберталась розмі­щена на ньому деталь.

2. Шпонка з'єднує вал з іншою деталлю завдяки тому, що вона одночасно заходить в паз на валу і в такий самий паз в отворі насадженої на вал деталі.

3. Пази у з'єднуваних деталях називають шпонковими канавками.

4. Наочне зображення шпонкового з'єднання показано на рисунку 221.

5. Найбільш поширеними шпонковим з’єднанням є призматичні шпонки з заокруглени­ми торцями.

6. Штифт — деталь циліндричної або конічної форми для нерухомого з'єднання деталей.

7. За формою штифти бувають конічні і циліндричні.

Task 10. Imagine that you work as a reporter for the newspaper in your university. Write about the main functions of keys and pins. Write your report using 120-150 words. The following opening phrases may help you:

As a matter of fact … On the whole … Fortunately …

So …anyway … Luckily … By the way …

In any case ... Unfortunately … On the other hand…

Actually … You know … You see …