Вступ до методичних рекомендацій

Методичні рекомендації

до навчання читання технічної літератури (частина II)

 

з дисципліни англійська мова

 

для студентів 1 - 2 курсу

 

для напряму підготовки 6.050502 Інженерна механіка

Машинобудування

 

галузі знань 0505 Машинобудування та

Матеріалообробкі

 

факультету МАШИНОБУДУВАННЯ

 

Херсон – 2009р.

 

Методичні рекомендації до навчання читання технічної літератури

(частина IІ) студентів з дисципліни іноземна мова (англійська)

Укладач (і): викл.Голованова Н.П,викл. Статкевич О.К. сторінок 116

 

 

Рецензент: доц. Фоменко Н.С.

 

 

Затверджено

на засіданні кафедри іноземних мов

протокол № 7 від 2.03.09

Зав. кафедри доц.Фоменко Н.С.

 

 

Відповідальний за випуск Н.С.Фоменко к.філол.н., доц., завідувач кафедри іноземних мов

 

Вступ до методичних рекомендацій

Методичні рекомендації до практичних занять ІI – IІІ етапу призначені для навчання студентів напряму інженерна механіка та машинобудування читанню текстів з фаху на англійській мові та розумінню їх для вилучення необхідної інформації та проведення бесіди зі спеціальності студента.

МР містять 7 тем: „Різьба”, „ Підшипник”, „Зубчате колесо”, „Зчеплення”, „Токарний верстат”, „Свердлильний верстат”, „Фрезерувальний верстат”. Кожний урок (unit) містить такі розділи: Language, Reading, Comprehension, Oral Practice, Writing. Тексти МР підібрані з сучасної технічної оригінальної літератури на англійській мові та Інтернету, що викликає у студентів інтерес до вивчення професійного текстового матеріалу. Тексти призначені для формування навиків та вмінь різних видів читання: вивчаючого, ознайомлюючого, оглядового та пошукового, що забезпечується розробленою системою методичних вправ. Тексти уроків також використовуються як основа для навчання усному мовленню у обговоренні, переказі, монологічному мовленні із застосуванням денотатних схем текстів, а також у розмовах, іграх. Крім того у розділі “Oral Practice” є проблемні завдання, типу: доведіть, прокоментуйте, поясніть, що носять творчий характер та сприяють розвитку вмінь усного мовлення.

 

Unit 6

Threads

I. Language

Ex. 1. Remember the following words and word combinations:

thread   interconnection   transmit motion external thread internal thread shape depend on (upon) threading   angle major diameter minor diameter pitch diameter depth pitch screw   clockwise   nut counterclockwise   fastening lead advance axially turn   single thread double thread triple thread pipe thread resemble   apex spare parts clutch

різьба, нарізка   взаємодія, з’єднання   передавати рух зовнішня різьба внутрішня різьба профіль залежати від різьбонарізний інструмент кут зовнішній діаметр внутрішній діаметр помірний діаметр глибина відстань, поступ гвинт, пригвинчувати   за годинниковою стрілкою гайка проти годинникової стрілки закріплювання відстань, поступ рух подачі вздовж осі поворот, повертати оборот одно західна різьба двох західна різьба трьох західна різьба трубна різьба скидатися на   вершина запасні частини зчеплення, муфта зчіплювання

резьба, нарезка, нарезать резьбу взаимосвязь, соединение передавать движение наружная резьба внутренняя резьба форма зависеть от резьбонарезной инструмент угол наружный диаметр внутренний диаметр средний диаметр глубина шаг винт, ввинчивать, скреплять винтами по часовой стрелке   гайка против часовой стрелки   крепление шаг (винта, спирали) движение подачи по оси оборот, поворот, повертывать однозаходная резьба двухзаходная резьба трёхзаходная резьба трубная резьба походить, иметь сходство вершина, пик запасные части сцепление, муфта сцепления

 

 

Ex. 2. Read the following international words and guess their meaning.

Transmission, motion, profile, internal, trapezoidal, element, external, distance, metric, application.

 

Ex. 3. Translate these words into English:

Рух, внутрішній, застосування, передача, дистанція, зовнішній.

 

Ex. 4. Put these words according to the alphabet and translate:

Interconnection, depend on, pitch, screw, resemble, internal, counterclockwise, advance, transmit, axially, nut.

 

Ex.5. Find the meaning of the words turn and obtain in the dictionary and translate the sentences:

1. He turned his head when I called him.

2. She turned pale.

3. Left-handed screw should be turned counterclockwise.

4. Whose turn is it to read?

5. Lead of the thread is the distance a screw thread advances axially in one turn.

6. They have obtained interesting results.

7. The results obtained showed that there was a mistake.

8. Having obtained interesting results, they continued the experiments.

 

ІІ. Reading

Ex.6. Read and translate the text A:

 

Text A

Threads

Threads are applied for interconnection of machine parts and for transmitting motion from one part to another. When a thread is cut on the outside of a part it is known as an external or "male thread". A thread is callad an "internal" or "female thread" When cut inside a part. Depending on the shape of the threading tool different profiles of thread are obtained, such as triangular, square, or trapezoidal.

In practice triangular threads are most widely used. The main elements of a thread are: the angle of the thread, the major, minor and pitch diameters, the depth and the pitch.

Screw threafds are of both right-hand and left-hand types. In right-hand threads the direction of the thread is from the right to the left. Right-hand thread screws are turned clockwise to be screwed into a nut, while left-handed screws should
be turned counterclockwise to do that. In screw fastenings threads are made of various shapes, but always of the triangular type: such as: single thread, double thread and triple thread. On the type of the latter depends the lead of the
thread which is the distance a screw thread advances axially in in one turn. On a single thread screw the lead and the pitch are the same; on the double thread screw the lead is twice the pitch, while on a triple thread screw the lead is three
times the pitch.

The most widely used systems of triangular threads in machine-building are: metric, inch and pipe threads, Each thread has its own angle and application. A metric thread profile resembles a triangle with an angle of 60° at its apex. Such a thread is widely used for bolts and nuts. An inch thread profile has an angle of 55°. This type of thread may be used when making spare parts for foreign-made machines. An angle of 55° is also used with pipe threads. Pipe threads are applied for gas and water pipes, as well as for clutches connecting such pipes.

 

ІІІ. Language

Ex.7. Match word and word combinations in column A with those in column B:

Column A Column B 1. thread 2. shape 3. depend on 4. screw 5. nut 6. clockwise 7. counterclockwise 8. spare parts 9. fastening 10. pitch 1. гвинт 2. кріплення 3. форма 4. запасні частини 5. поступ 6. гайка 7. різьба 8. залежати від 9. за годинною стрілкою 10. проти годинникової стрілки

Ex.8. Find in the text nouns for these verbs:

To move, to part, to screw, to direct, to faster, to turn, to lead, to apply, to connect.

 

Ex. 9. Fill in the blanks using the following words:

 

a) depending on, b) turn, c) nuts, d) triangular thread, e) clutches, f) spare parts,

g)pipe thread, h) external thread.

 

1. When a thread is cut on the outside of a part it is known as an ………..

2. …… the shape of the thread tool different profiles of thread are obtained.

3. In practice ………. are most widely used.

4. On the type of the thread depends …………… of the thread.

5. The most widely used system of triangular thread in machine-building are: metric, inch and …………..

6. A metric thread profile is widely used for bolts and …………...

7. An inch thread profile may be used when making ……………. For foreign-made machines.

8. Pipe threads are applied for gas and water pipes and for ………….. connecting such pipes.

 

Ex.10. Match the beginning of the sentence in column A with the ending in column B:

 

Column A Column B 1. Threads are applied 2. A thread is called internal 3. The main elements of a thread are 4. In right-hand thread 5. Depending on the shape of the threading tool   a) the direction of the thread is from the right to the left. b) different profiles of thread are obtained, such as: triangular, square or trapezoidal. c) for interconnection of machine parts and for transmitting motion from one part to another. d) when cut inside a part. e) the angle of the thread, the major, minor and pitch diameters the depth and the pitch.

ІV. Comprehension

Ex. 11. Agree or disagree with the following statements:

1. Threads are applied for interconnection of machine parts.

2. A thread is called an “ internal ” or “ female thread” when cut inside a part.

3. In practice square threads are most widely used.

4. Screw threads are of both right-hand and left-hand types.

5. Left-hand thread screws are turned clockwise to be screwed into a nut.

6. Each thread has its own angle and application.

7. A metric thread profile resembles a triangle with an angle of 60 at its apex.

8. An inch thread profile has an angle of 55.

 

Ex. 12. Answer the questions:

1. What are treads used for?

2. What types of threads do you know?

3. What are the main elements of a thread?

4. What types of screw threads do you know?

5. What are the most widely used systems of triangular threads in machine-building?

 

V. Oral Practice

 

Text B

History of standardization

Graphic representation of formulas for the pitches of threads of screw bolts

The first historically important intra-company standardization of screw threads began with Henry Maudslay around 1800, when the modern screw-cutting lathe made interchangeable screws a practical commodity. During the next 40 years, standardization continued to occur on the intra-company and inter-company level. In 1841, Joseph Whitworth created a design that, through its adoption by many British railroad companies, became a national standard for the United Kingdom called British Standard Whitworth. During the 1840s through 1860s, this standard was often used in the United States and Canada as well, in addition to myriad intra- and inter-company standards. In April 1864, William Sellers presented a paper to the Franklin Institute in Philadelphia, proposing a new standard to replace the U.S.'s poorly standardized screw thread practice. Sellers simplified the Whitworth design by adopting a thread profile of 60° and a flattened tip (in contrast to Whitworth's 55° angle and rounded tip). The 60° angle was already in common use in America, but Sellers's system promised to make it and all other details of threadform consistent.

The Sellers thread, easier for ordinary machinists to produce, became an important standard in the U.S. during the late 1860s and early 1870s, when it was chosen as a standard for work done under U.S. government contracts, and it was also adopted as a standard by highly influential railroad industry corporations such as the Baldwin Locomotive Works and the Pennsylvania Railroad. Other corporations adopted it, and it soon became a national standard for the U.S., later becoming generally known as the United States Standard. Over the next 30 years the standard was further defined and extended and evolved into a set of standards including National Coarse (NC), National Fine (NF), and National Pipe Taper (NPT).

For a good summary of screw thread standards

in curre

nt use in 1914, see Colvin FH,

Stanley FA (eds) (1914):

American Machinists' Handbook, 2nd ed.

New York and London: McGraw-Hill, pp. 16-22.

 

During this era, in continental Europe, the British and American threadforms were well known, but also various metric thread standards were evolving, which usually employed 60° profiles. Some of these evolved into national or quasi-national standards. They were mostly unified in 1898 by the International Congress for the standardization of screw threads at Zurich, which defined the new international metric thread standards as having the same profile as the Sellers thread, but with metric sizes. Efforts were made in the early 20th century to convince the governments of the U.S., UK, and Canada to adopt these international thread standards and the metric system in general, but they were defeated with arguments that the capital cost of the necessary retooling would damage corporations and hamper the economy. (The mixed use of dualling inch and metric standards has since cost much, much more, but the bearing of these costs has been more distributed across national and global economies rather than being borne up front by particular governments or corporations, which helps explain the lobbying efforts.)

Notes:

To defeat – завдавати поразки

To damage – руйнувати

To hamper –перешкоджати

To inspect –провіряти

 

Ex.15. Agree or disagree with the following statements:

1. The first historically important intra-company standardization of screw threads began with Robert Boil.

2. Sellers simplified the Whitworth design by adopting a thread profile of 50.

3. The Ukrainian threadforms were well known.

4. Engineers found that ensuring the reliable interchangeability of screw threads was a multi-faceted.

5. Small addition of carbon reduces the melting point.

 

Ex. 16. Answer the following questions:

1. What was the first intra-company standardization of screw threads?

2. What were the Sellers threads?

3. What threadforms were well known?

 

Text C

Joseph Whitworth

Personal information
Name	Sir Joseph Whitworth
Nationality	British
Birth date	December 21, 1803
Birth place	Stockport
Date of death	January 22, 1887
Place of death	Monte Carlo
Spouse	Francis Anker (m. 1825) Mary Louisa Orrell (m. 1871)
Work
Institution memberships	Royal Society Institution of Mechanical Engineers
Significant advance	Whitworth standardised screw threads

Early life

Whitworth was born in Stockport, the son of Charles Whitworth, a teacher (some sources say that he was a Congregational minister), and at a young age developed an interest in machinery.

Career

After leaving school Whitworth became an indentured apprentice to an uncle who was a cotton spinner in Derbyshire. This was for a four year term after which he worked for another four years as a mechanic in a factory in Manchester. He then moved to London where he found employment working for Henry Maudslay, the inventor of the screw-cutting lathe, alongside such people has James Nasmyth (inventor of the steam hammer) and Richard Roberts.

Whitworth developed great skill as a mechanic while working for Maudslay, developing various precision machine tools and also introducing a box casting scheme for the iron frames of machine tools that simultaneously increased their rigidity and reduced their weight.

Whitworth also worked for Holtzapffel & Co (makers of ornamental lathes) and Joseph Clement. While at Clement's workshop he helped with the manufacture of Charles Babbage's calculating machine, the Difference engine. He returned to Openshaw, Manchester, in 1833 to start his own business manufacturing lathes and other machine tools, which became renowned for their high standard of workmanship. In 1850, architect Edward Walters was commissioned to build The Firs for Whitworth. This was a grand mansion at Fallowfield Manchester, which still stands today, functioning as Chancellors Hotel & Conference Centre.

Inventions

Whitworth popularized a method of producing accurate flat surfaces during the 1830s, using engineer's blue and scraping techniques on three trial surfaces. Up until his introduction of the scraping technique, the same three plate method was employed using polishing techniques, giving less accurate results. This led to an explosion of development of precision instruments using these flat surface generation techniques as a basis for further construction of precise shapes.

His next innovation, in 1840, was a measuring technique called "end measurements" that used a precision flat plane and measuring screw, both of his own invention. The system, with a precision of one millionth of an inch, was demonstrated at the Great Exhibition of 1851.

In 1841 Whitworth devised a standard for screw threads with a fixed thread angle of 55° and having a standard pitch for a given diameter. This soon became the first nationally standardized system; its adoption by the railway companies, who until then had all used different screw threads, leading to its widespread acceptance. It later became a British Standard, "British Standard Whitworth", abbreviated to BSW and governed by BS 84:1956.

Whitworth rifle

Whitworth was commissioned by the War Department of the British government to design a replacement for the calibre.577-inch Pattern 1853 Enfield, whose shortcomings had been revealed during the recent Crimean War. The Whitworth rifle had a smaller bore of 0.451 inch (11 mm) which was hexagonal, fired an elongated hexagonal bullet and had a faster rate of twist rifling [one turn in twenty inches] than the Enfield, and its performance during tests in 1859 was superior to the Enfield's in every way. The test was reported in The Times on April 23 as a great success. However, the new bore design was found to be prone to fouling and it was four times as expensive to manufacture than the Enfield, so it was rejected by the British government, only to be adopted by the French Army. An unspecified number of Whitworth rifles found their way to the Confederate states in the American Civil War, where they were called "Whitworth Sharpshooters".

The Enfield rifle was converted to Snider-Enfield Rifle by Jacob Snider, a Dutch-American wine merchant from Philadelphia. By converting existing Enfield rifles this way, the cost of a "new" breech-loading Snider-Enfield rifle was only 12 shillings.

Queen Victoria opened the first meeting of the British Rifle Association at Wimbledon, in 1860 by firing a Whitworth rifle from a fixed mechanical rest. The rifle scored a bull's eye at a range of 400 yards (366 m).

Breech-loading artillery

Whitworth also designed a large Rifled Breech Loading gun with a 2.75 inch (70 mm) bore, a 12 pound 11 ounce (5.75 kg) projectile and a range of about six miles (10 km). The spirally-grooved projectile was patented in 1855. This was also rejected by the British army, who preferred the guns from Armstrong, but was also used in the American Civil War.

While trying to increase the bursting strength of his gun barrels, Whitworth patented a process called "fluid-compressed steel" for casting steel under pressure, and built a new steel works near Manchester. Some of his castings were shown at the Great Exhibition in Paris ca. 1883.

Notes:

Flat surface – плоска поверхня To scrap – здавати на брухт

Explosion- вибух Techniques - техніка

Rifle – гвинтівк

VII. Oral Practice.

Supplementary reading

Screw thread

A screw thread is a helical or tapered structure used to convert between rotational and linear movement or force.

A screw thread may be thought of as an inclined plane wrapped around a cylinder or cone. The tightening of a fastener's screw thread is comparable to driving a wedge into a gap until it sticks fast through friction and slight plastic deformation.

In most applications, the thread pitch of a screw is chosen so that friction is sufficient to prevent linear motion being converted to rotary, that is so the screw does not slip even when linear force is applied so long as no external rotational force is present. This characteristic is essential to the vast majority of its uses.

Internal and external threads illustrated using a common nut and bolt. The screw and nut pair can be used to convert torque into linear force. As the screw (or bolt) is rotated, the screw moves along its axis through the fixed nut, or the non-rotating nut moves along the lead-screw.

 

Screw thread, used to convert torque into the linear force in the flood gate. The operator rotates the two long vertical bolts (via bevel gear).

Screw threads have several applications:

• Fastening
• Fasteners such as wood screws, machine screws, nuts and bolts.
• Connecting threaded pipes and hoses to each other and to caps and fixtures.
• Gear reduction via worm drives
• Moving objects linearly by converting rotary motion to linear motion, as in a screw jack.
• Measuring by correlating linear motion to rotary motion (and simultaneously amplifying it), as in a micrometer.
• Both moving objects linearly and simultaneously measuring the movement, combining the two aforementioned functions, as in a leadscrew.

In all of these applications, the screw thread has two main functions:

• It converts rotary motion into linear motion.
• It prevents linear motion without the corresponding rotation.

Standard threads

Standards for machine screw threads have evolved since the early nineteenth century to facilitate compatibility between different manufacturers and users. Many of these standards also specified corresponding bolt head and nut sizes, to facilitate compatibility between spanners and other driving tools.

Nearly all threads are oriented so that a bolt or nut, seen from above, is tightened (the item turned moves away from the viewer) by turning it in a clockwise direction, and loosened (the item moves towards the viewer) by turning anticlockwise. This is known as a right-handed thread, since the natural screwing motion for a right-handed person is clockwise, and is the default because most people are right-handed. Threads oriented in the opposite direction are known as left-handed. There are also self-tapping screw threads where no nut is required.

Left-handed threads are used:

• Where the rotation of a shaft would cause a conventional right-handed nut to loosen rather than to tighten due to fretting induced precession, e.g. on a left-hand bicycle pedal.
• In combination with right-handed threads in turnbuckles.
• In some gas supply connections to prevent dangerous misconnections, for example in gas welding the flammable gas supply uses left-handed threads.
• In some instances, for example early ballpoint pens, to provide a "secret" method of disassembly.
• In some applications of a leadscrew, for example the cross slide of a lathe, where it is desirable for the cross slide to move away from the operator when the leadscrew is turned clockwise.

Unless stated otherwise, all standards below specify right-handed threads.

ISO standard threads

The most common threads in use are the ISO metric screw threads (M) and BSP threads also called G threads for pipes.

These were standardized by the International Organization for Standardization in 1947. Before that, there were separate metric thread standards used in France, Germany, and Japan, and the Swiss had a set of threads for watches.

 

 

Generating screw threads

 

Page 23 of Colvin FH, Stanley FA (eds) (1914): American Machinists' Handbook, 2nd ed. New York and London: McGraw-Hill. Summarizes screw thread rolling practice as of 1914.

There are various methods for generating screw threads. The method chosen for any one application is chosen based on constraints—time; money; degree of precision needed (or not needed); what equipment is already available; what equipment purchases could be justified based on resulting unit price of the threaded part (which depends on how many parts are planned); etc.

In general, certain thread-generating processes tend to fall along certain portions of the spectrum from toolroom-made parts to mass-produced parts, although there can be considerable overlap. For example, thread lapping following thread grinding would fall only on the extreme toolroom end of the spectrum, while thread rolling is a large and diverse area of practice that is used for everything from microlathe leadscrews (somewhat pricey and very precise) to the cheapest deck screws (very affordable and with precision to spare).

The various methods are summarized below.

Thread cutting

The excess material is cut away, with taps and dies for most smaller diameters, or with single-point thread-cutting on a lathe for larger ones (or smaller ones needing very high concentricity).

Thread rolling

The material is extruded into a male thread through mechanical pressure as the screw blank is rolled between a matched pair of flat dies. (See Cold forming.) Thread rolling is more common for high-volume production, and produces threads of diameters typically smaller than one inch. Also, materials with good deformation characteristics are better used with rolling; these materials include softer (more ductile) metals and exclude brittle materials, such as cast iron. A rolled thread can often be easily recognized because the thread has a larger diameter than the blank rod from which it has been made. (However, necks and shoulders can be cut or rolled to different diameters, so this in itself is not a forensic give-away.) Also, the end of the screw usually looks a bit different from the end of a cut-thread screw. Rolled male threads tend to be slightly stronger than cut male threads. Thread rolling is a very economical way of producing large quantities with good dimensional accuracy. The cost of thread rolling depends on the quantity; the more parts made, the cheaper the unit cost.

Thread forming

This is the female-thread analogue of the male-thread-rolling process described above. The material is extruded into a thread through mechanical pressure by a tap that is similar to a cutting tap except that it has no flutes. Instead of cutting, the tap squeezes the material out of its way. Formed female threads tend to be slightly stronger than cut female threads.

This process is more often employed in soft, ductile metals (such as aluminum) than in hard, brittle metals (such as cast iron).

Thread casting

The threads take the shape of whatever mold or die that the (liquid or gas) material is poured into. When the material freezes into a solid, it retains the shape. Material is either heated to a liquid (or rarely a gas), or mixed with a liquid that will either dry or cure (such as plaster or cement). Alternately, the material may be forced into a mould as a powder and compressed into a solid, as with graphite.

Cast threads in metal parts may be finished by machining, or may be left in the as-cast state. (The same can be said of cast gear teeth.) Whether or not to bother with the additional expense of a machining operation depends on the application. For parts where the extra precision and surface finish is not strictly necessary (although it might be nice), the machining is forgone in order to achieve a lower cost. With sand cast parts this means a rather rough finish; but with molded plastic or die-cast metal, the threads can be very nice indeed straight from the mold or die.

Thread grinding

Thread grinding is done on cylindrical grinders using specially dressed wheels matching the shape of the threads. Although expensive, threads produced by grinding are highly accurate and have a very fine surface finish with applications such as ball screw mechanisms used for precise movement of machine components.

Technically, thread grinding is a subset of thread cutting, as grinding is a true metalcutting process. Each grain of abrasive functions as a microscopic single-point cutting edge (although of high negative rake angle), and shears a tiny chip that is analogous to what would conventionally be called a "cut" chip (turning, milling, drilling, tapping, etc.). However, among people who work in the machining fields, the term cutting is understood to refer to the macroscopic cutting operations, and grinding is mentally categorized as a "separate" process. This is why the terms are usually used in contradistinction in shop-floor practice, even though technically grinding is a subset of cutting.

Thread lapping

Rarely, thread grinding will be followed by thread lapping in order to achieve the highest precision and surface finish achievable. This is an ultra-deluxe toolroom practice, rarely employed except for the leadscrews or ballscrews of high-end machine tools

 

Unit 7

Gears

I. Language

Ex.1. Remember the following words and word combinations:

 

gear   toothed wheel angular velocity ratio   driving shaft driven shaft rate   intersecting shaft non-coplanar curved helical gear     bevel gear eccentric gear   herringbone gear   screw gear   spur gear   worm gear plane incline converge revolution   strength speed width treat grind (ground, ground) accurate smooth   running cone   resemble   frequently body forward motion   connect external gearing   internal gearing   rack-and-pinion gearing   serve lathe right angle

зубчате колесо, приладнувати зубчате колесо коефіцієнт кутової швидкості ведучий вал відомий вал швидкість, рівень   перетинаючий вал некопланарний вигнутий, зігнутий вінтовe колесо (гелікоїдальне косозубе колесо) конічна передача ексцентрична зубчата передача шевронне зубчате колесо гвинтове зубчате колесо   циліндричне прямозубе колесо черв’ячне колесо площина нахиляти сходитися кругове обертання, оборот сила, міць швидкість ширина обробляти шліфувати точний рівний, гладенький, плавний робота конус   скидатися на   часто тіло, кістяк рух уперед   з’єднувати зовнішнє пристосування внутрішнє пристосування передача шестерної і зубчатою рейкою служити токарний верстат прямій кут

шестерня, зубчатое колесо, сцепляться зубчатое колесо коэффициент угловой скорости ведущий вал ведомый вал величина, скорость, степень пересекающий вал некопланарный кривой винтовое колесо (геликоидальное косозубое колесо) коническая передача эксцентрическая зубчатая передача шевронное зубчатое колесо винтовое зубчатое колесо цилиндрическое прямозубое колесо червячное колесо плоскость наклонять сходиться круговое вращение, оборот сила, прочность скорость ширина обрабатывать шлифовать, протирать точный ровный, плавный, гладкий работа, эксплуатация конус, деталь конической формы походить, иметь сходство часто тело, корпус поступательное движение соединять внешнее зацепление   внутреннее зацепление   передача шестерней и зубчатой рейкой служить токарный станок прямой угол

 

 

ІІ. Reading

 

Text A

Gears.

A gear is a toothed wheel used to transmit rotary motion from one shaft to another. If power is transmitted between the two shafts, the angular velocity ratio of these two shafts is constant and the driving shaft and the driven shaft rotate an a uniform rate. Shafts may be parallel, intersecting and non-coplanar. Gears may be classified according to their shape and according to the position which the teeth occupy respectively to the axis of rotation. The teeth cut on the face of a gear may be curved,
straight or helical.

The main types of gears are: bevel gears, eccentric gears, helical or spiral gears, herringbone gears, screw gears, spur gears and worm gears.

Bevel gearing is used to transmit power bettween two shafts, whhich lie in a common plane and whose axes intersect each other. The axes may be inclined to each other an any angle, although 90° is the most common one. The teeth of bevel gears may be either straight or spiral,

Helical or spiral gears operate on parallel shafts at high speeds, providing maximun strength of gear teeth for a given width of face. Such gears are heat-treated and then ground to accurate shape and size necessary for smooth and quiet running
at high speeds.

Herringbone gears similary to helical gears also operate on parallel shafts. Herringbone gears have helical teeth radiating from the centre of the face towards the sides of the gear body.

Screw gearing is used for converting some rotary motion into a forward motion, and for connecting shafts which are not intersecting. Spur gears are gears having straight or helical teeth cut on a cylindrical surface at an angle to the shaft axis.

Spur gearing is used to transmit power between two shafts, the axes of which are parallel. Spur gearing may be divided into three types: external gearing, internal gearing and rack-and-pinion gearing. Rack-and-pinion gearing serves for converting rotary motion into forward motion and is widely used in lathes. It con-
sists of a rack-and-pinion.

A worm gear is a gear having the teeth cut at an angle to the axis of rotation of the gear body and radially in the gear face. A worm gear is driven by a worm which resemble a large screw. Worm gearing is applied for transmitting power between non-intersecting shafts which are at right angles to each other.

 

ІІІ. Language

Ex.9. Match word and word combinations in column A with those in column B:

A 1. frequency 2. spur gear 3. bevel gear 4. curved 5. driving shaft 6. incline 7. driven shaft 8. gear 9. intersecting shaft 10. worm gear

B a. шестерня b. ведучий вал c. відомий вал d. перетинаючий вал e. вигнутий f. конічна передача g. циліндричне прямозубе колесо h. черв’ячне колесо i. нахиляти j. часто

 

Ex.10. Match words and their definitions:

1. A gear is 2. Spur gear is 3. Herringbone gear have 4. A worm gear is 5. Screw gearing is 6. Bevel gearing is 7. Helical or spiral gears

a) a toothed wheel used to transmit rotary motion from one shaft to another. b) used to transmit power between two shafts. c) operate on parallel shafts at high speeds. d) helical teeth radiating from the centre of the face towards the sides of the gear body. e) used for converting some rotary motion into a forward motion, and for connecting shafts which are not intersecting. f) used to transmit power between two shafts, the axes of which are parallel. g) A gear having the teeth cut at an angle to the axis of rotation of the gear body and radially in the gear face.

 

Ex. 11. Point out the words with –ing. Are they Participle or Gerund? Translate the sentences:

1. Testing will begin in ten minutes.

2. Testing these devices we sometimes find defects in them.

3. Connecting shafts is done automatically.

4. Connecting shafts engineers used new automatic devices.

5. Increasing the pressure we increase the force of friction.

6. Ice melting begins at 0 C.

7. Spur gears are gears having straight or helical teeth.

8. Screw gearing is used for converting some rotary motion into a forward motion.

 

Ex.12. Find the right ending of the sentences and translate these sentences:

1. If a power is transmitted between two shafts: … ………….

a) they may be inclined to each other at any angle.

b) The angular velocity ratio of these two shafts is constant.

c) The driving shaft and the driven shaft rotates at a uniform rate.

2. Bevel gearing is used ………………………..

a) to provide maximum strength of gear teeth.

b) to transmit a varying angular velocity either continuously or for a portion of revolution.

c) to transmit power between two shafts, which lie in a comment plane and whose axes intersect each other.

3. Helical or spiral gears are ………………………..

a) used for converting some rotary motion into a forward motion.

b) heat –treated and the ground to accurate shape and size.

c) gears having strait or helical teeth.

4. Spur gearing is used ………………………………………………...

a) to transmit power between two shafts the axes of which are parallel.

b) for converting rotary motion into forward motion.

c) to transmit power between two shafts interacting each other.

5. Worm gearing is applied ………………….

a) for transmitting power between non-interacting shafts which are parallel.

b) for transmitting power between non-interacting shafts at right angles to each other.

c) for connecting shafts which are not intersecting.

6. Eccentric gears are used

a) to transmit power between two shafts interesting each other.

b) to transmit power between two shafts which lie in a common plane.

c) to transmit a varying angular velocity either continuously or for a portion of revolution.

 

 

Ex. 13. Fill in the blanks using the following words:

a) forward motion; b) bevel gear; c) gear herringbone; d) screw gear; e) toothed wheel,d) curved, e) intersecting, f) friction gear, g)worm gear, h) rack-and-pinion gearing, i) resembles.

1. A gear is a ……….. used to transmit rotary motion from one shaft to another.

2. Shaft may be parallel, …………… and non-coplanar.

3. The main types of gears are: ………………...

4. Similarly to helical gears …………….. also operate on parallel shafts.

5. Screw gearing is used for converting some rotary motion into ………..

6. Spur gears are gears having straight or ……….. teeth cut on a cylindrical surface at angle to the shaft axis.

7. …………….. serves for converting rotary motion into forward motion and is widely used in lathes.

8. A worm gear is driven by a worm which …………… a large screw.

 

 

IV. Comprehension

Ex.14. Agree or disagree with the following statements:

1. A gear is a toothed wheel used to transmit rotary motion from one shaft to another.

2. Gears may be classified only according to their shape.

3. Bevel gearing is used for converting some rotary motion into a forward motion.

4. The main types of gears are bevel gears, eccentric gears, helical or spiral gears, herringbone gears, screw gears, spur gears and warm gears.

5. Spur gearing is used to transmit power between two shafts.

6. Helical or spiral gears operate on parallel shafts at high speed.

7. Screw gearing is applied for transmitting power between non-intersecting shafts which are at right angles to each other.

 

Ex.15. Answer the following questions:

1. What is a gear and what is it used for?

2. What types of shafts do you know?

3. What do types of shaft depend on?

4. According to what features may gears be classified?

5. What kinds of teeth cut on the gear face do you know?

6. What main types of gears can you enumerate?

 

V. Oral Practice

Fixed-gear bicycle

A fixed-gear bicycle An 18 tooth cog that attaches to the rear

hub of fixed-gear bike

 

A fixed-gear bicycle or fixed wheel bicycle, is a bicycle without the ability to coast. The sprocket is screwed directly on to the hub and there is no freewheel mechanism. A reverse-thread lockring is usually fitted to prevent the sprocket from unscrewing. Whenever the rear wheel is turning, the pedals turn in the same direction. By resisting the rotation of the pedals, a rider can slow the bike to a stop, without the aid of a brake. A fixed gear bicycle can even be ridden in reverse.

Most fixed gear bicycles only have one gear ratio. Some have a sprocket on each side of the rear hub, giving the choice of using one of two different gear ratios. Such a hub may have a fixed gear on each side (double-fixed) or a fixed gear on one side and a freewheel gear on the other (fixed-free). To change gear, it is necessary to remove, reverse and refit the rear wheel. Typically, the number of teeth on the sprockets will differ by one or two, for example 19 teeth on one side and 17 on the other, making the latter gear some 11 or 12% higher than the former (for the same chainring).

In the past Sturmey Archer made a fixed multi speed hub gear, the model ASC, allowing the rider to change gear while riding. Its successor company, SunRace Sturmey-Archer, plans to produce a modern equivalent, the S3X, in the near future.

Fixed gear bikes are alternatively known as fixie bikes, or simply fixies.

Uses

A fixed/freewheel rear hub A fixed- gear folding bike.

 

The track bicycle is a form of fixed-gear bicycle used for track cycling in a velodrome. But since a "fixed-gear bicycle" is just a bicycle without a freewheel, a fixed-gear bicycle can be any type of bicycle.

Traditionally, road racing and club cyclists would use a fixed wheel bicycle for training during the winter months, generally using a relatively low gear ratio, believed to help develop a good pedalling style. In the UK until the 1950s it was common for riders to use a fixed wheel for time trials. The fixed wheel was also commonly used, and continues to be used in the end of season hill climb races in the autumn. A typical clubmen's fixed wheel machine would have been a "road-path" or "road/track" cycle. In the era when most riders only had one cycle, the same bike when stripped down and fitted with racing wheels was used for road time trials and track racing, and when fitted with mudguards (fenders) and a bag it was used for club runs, touring and winter training. However by the 1960s multi-gear derailleurs had become the norm and riding fixed wheel on the road declined over the next few decades. Recent years have seen renewed interest and increased popularity of fixed wheel cycling in the UK.

In urban North America recently fixed gear bicycles have acheived tremendous popularity, with the rise of discernible regional aesthetic preferences for finish and design details of the bicycles. The rise in popularity of fixed-gear bicycles in the mid-2000s, complete with adaptations such as spoke cards, is attributed to bicycle messengers. Some messengers disparagingly refer to persons sporting these affectations as 'fakengers,' 'posengers' or 'hipsters'. Riders of fixed-gear bicycles are sometimes referred to as "Clan Members" in both a pejorative and affectionate sense.

Dedicated fixed-gear road bicycles are being produced in greater numbers by established bicycle manufacturers. They are generally low in price, and characterized by a more forgiving, slacker road geometry, as opposed to the steeper, more aggressive geometry of track bicycles. These too are made in increasing numbers at budget, or entry-level price and quality-points.

Fixed-gear bicycles are also used in cycle ball and artistic cycling.

A fixed-gear bicycle is particularly well suited for track stands, a manoeuver in which the bicycle can be held stationary, balanced upright with the rider's feet on the pedals.

A subset of fixed gear track bike riding is emerging from urban youth, often associated with hipsters, with roots in modern skateboarding and Freestyle BMX. Track bike tricks are largely unexplored and like the sport's precursors, have an overwhelming appreciation for style and originality. "Fixies" are also used for increased performance.

Notes:

To coast – пливти вздовж узбережжя

Hub – ступила колеса

Reverse – протилежність, зворотній хід

Trials – випробування

Pejorative-зневажливий

Affectionate - люблячий, ніжний

Ex.20. Agree or disagree with the following statements:

1. A fixed wheel bicycle is a bicycle without the ability to coast.

2. There are many freewheel mechanisms in the fixed-gear bicycle.

3. The rear wheel is turned, the pedals turn in the other direction.

4. Most fixed gear bicycles have only one gear ratio.

5. To change gear, it is necessary to remove, reverse and refit the rear wheel.

 

Ex. 21. Answer the following questions:

1. What is a track bicycle?

2. What would club cyclists use for training during the winter months?

3. Why have fixed gear bicycles recently achieved tremendous popularity in the North America?

4. What are the main characteristics of fixed gear bicycles?

 

VII. Oral Practice.

Reading and comprehension

Supplementary Reading

Mechanical advantage

Intermeshing gears in motion

The interlocking of the teeth in a pair of meshing gears means that their circumferences necessarily move at the same rate of linear motion (eg., metres per second, or feet per minute). Since rotational speed (eg. measured in revolutions per second, revolutions per minute, or radians per second) is proportional to a wheel's circumferential speed divided by its radius, we see that the larger the radius of a gear, the slower will be its rotational speed, when meshed with a gear of given size and speed. The same conclusion can also be reached by a different analytical process: counting teeth. Since the teeth of two meshing gears are locked in a one to one correspondence, when all of the teeth of the smaller gear have passed the point where the gears meet -- ie., when the smaller gear has made one revolution -- not all of the teeth of the larger gear will have passed that point -- the larger gear will have made less than one revolution. The smaller gear makes more revolutions in a given period of time; it turns faster. The speed ratio is simply the reciprocal ratio of the numbers of teeth on the two gears.

(Speed A * Number of teeth A) = (Speed B * Number of teeth B)

This ratio is known as the gear ratio.

The torque ratio can be determined by considering the force that a tooth of one gear exerts on a tooth of the other gear. Consider two teeth in contact at a point on the line joining the shaft axes of the two gears. In general, the force will have both a radial and a circumferential component. The radial component can be ignored: it merely causes a sideways push on the shaft and does not contribute to turning. The circumferential component causes turning. The torque is equal to the circumferential component of the force times radius. Thus we see that the larger gear experiences greater torque; the smaller gear less. The torque ratio is equal to the ratio of the radii. This is exactly the inverse of the case with the velocity ratio. Higher torque implies lower velocity and vice versa. The fact that the torque ratio is the inverse of the velocity ratio could also be inferred from the law of conservation of energy. Here we have been neglecting the effect of friction on the torque ratio. The velocity ratio is truly given by the tooth or size ratio, but friction will cause the torque ratio to be actually somewhat less than the inverse of the velocity ratio.

In the above discussion we have made mention of the gear "radius". Since a gear is not a proper circle but a roughened circle, it does not have a radius. However, in a pair of meshing gears, each may be considered to have an effective radius, called the pitch radius, the pitch radii being such that smooth wheels of those radii would produce the same velocity ratio that the gears actually produce. The pitch radius can be considered sort of an "average" radius of the gear, somewhere between the outside radius of the gear and the radius at the base of the teeth.

The issue of pitch radius brings up the fact that the point on a gear tooth where it makes contact with a tooth on the mating gear varies during the time the pair of teeth are engaged; also the direction of force may vary. As a result, the velocity ratio (and torque ratio) is not, actually, in general, constant, if one considers the situation in detail, over the course of the period of engagement of a single pair of teeth. The velocity and torque ratios given at the beginning of this section are valid only "in bulk" -- as long-term averages; the values at some particular position of the teeth may be different.

It is in fact possible to choose tooth shapes that will result in the velocity ratio also being absolutely constant -- in the short term as well as the long term. In good quality gears this is usually done, since velocity ratio fluctuations cause undue vibration, and put additional stress on the teeth, which can cause tooth breakage under heavy loads at high speed. Constant velocity ratio may also be desirable for precision in instrumentation gearing, clocks and watches. The involute tooth shape is one that results in a constant velocity ratio, and is the most commonly used of such shapes today.

Gear types

External vs. internal gears

 

Unlike most gears, an internal gear (shown here) does not cause direction reversal.

An external gear is one with the teeth formed on the outer surface of a cylinder or cone. Conversely, an internal gear is one with the teeth formed on the inner surface of a cylinder or cone. For bevel gears, an internal gear is one with the pitch angle exceeding 90 degrees.

Spur gears

Spur gears are the simplest and most common type of gear. Their general form is a cylinder or disk. The teeth project radially, and with these " straight-cut gears ", the leading edges of the teeth are aligned parallel to the axis of rotation. These gears can only mesh correctly if they are fitted to parallel axles.

Helical gears

Helical gears from a Meccano construction set.

Helical gears offer a refinement over spur gears. The leading edges of the teeth are not parallel to the axis of rotation, but are set at an angle. Since the gear is curved, this angling causes the tooth shape to be a segment of a helix. The angled teeth engage more gradually than do spur gear teeth. This causes helical gears to run more smoothly and quietly than spur gears. Helical gears also offer the possibility of using non-parallel shafts. A pair of helical gears can be meshed in two ways: with shafts oriented at either the sum or the difference of the helix angles of the gears. These configurations are referred to as parallel or crossed, respectively. The parallel configuration is the more mechanically sound. In it, the helices of a pair of meshing teeth meet at a common tangent, and the contact between the tooth surfaces will, generally, be a curve extending some distance across their face widths. In the crossed configuration, the helices do not meet tangentially, and only point contact is achieved between tooth surfaces. Because of the small area of contact, crossed helical gears can only be used with light loads.

Quite commonly, helical gears come in pairs where the helix angle of one is the negative of the helix angle of the other; such a pair might also be referred to as having a right-handed helix and a left-handed helix of equal angles. If such a pair is meshed in the 'parallel' mode, the two equal but opposite angles add to zero: the angle between shafts is zero -- that is, the shafts are parallel. If the pair is meshed in the 'crossed' mode, the angle between shafts will be twice the absolute value of either helix angle.

Note that 'parallel' helical gears need not have parallel shafts -- this only occurs if their helix angles are equal but opposite. The 'parallel' in 'parallel helical gears' must refer, if anything, to the (quasi) parallelism of the teeth, not to the shaft orientation.

As mentioned at the start of this section, helical gears operate more smoothly than do spur gears. With parallel helical gears, each pair of teeth first make contact at a single point at one side of the gear wheel; a moving curve of contact then grows gradually across the tooth face. It may span the entire width of the tooth for a time. Finally, it recedes until the teeth break contact at a single point on the opposite side of the wheel. Thus force is taken up and released gradually. With spur gears, the situation is quite different. When a pair of teeth meet, they immediately make line contact across their entire width. This causes impact stress and noise. Spur gears make a characteristic whine at high speeds and can not take as much torque as helical gears because their teeth are receiving impact blows. Whereas spur gears are used for low speed applications and those situations where noise control is not a problem, the use of helical gears is indicated when the application involves high speeds, large power transmission, or where noise abatement is important. The speed is considered to be high when the pitch line velocity (that is, the circumferential velocity) exceeds 5000 ft/minA disadvantage of helical gears is a resultant thrust along the axis of the gear, which needs to be accommodated by appropriate thrust bearings, and a greater degree of sliding friction between the meshing teeth, often addressed with specific additives in the lubricant.

Double helical gears