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контрольная работа: 1. Read the text. Gear A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. 2. Give Russian equivalents to the following word combinations. 1. dirt tolerance 2. low speed meshing 3. nonferrous alloys. 3. Match the words with their definitions. 1. torque 2. Gearbox 3. mechanical advantage (MA). 4. Match English and Russian equivalen
2015
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Контрольная работа №10
1. Readthetext.
Gear
A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, magnitude, and direction of a power source. The most common situation is for a gear to mesh with another gear; however a gear can also mesh a non-rotating toothed part, called a rack, thereby producing translation instead of rotation.
The gears in a transmission are analogous to the wheels in a pulley. An advantage of gears is that the teeth of a gear prevent slipping. When two gears of unequal number of teeth are combined a mechanical advantage is produced, with both the rotational speeds and the torques of the two gears differing in a simple relationship.
In transmissions which offer multiple gear ratios, such as bicycles and cars, the term gear refers to a gear ratio rather than an actual physical gear. The term is used to describe similar devices even when gear ratio is continuous rather than discrete or when the device does not actually contain any gears, as in a continuously variable transmission.
Gears are most commonly produced via hobbing, but they are also shaped, broached, cast, and in the case of plastic gears, injection molded. For metal gears the teeth are usually heat treated to make them hard and more wear resistant while leaving the core soft and tough. For large gears that are prone to warp a quench press is used.
Numerous nonferrous alloys, cast irons, powder-metallurgy and even plastics are used in the manufacture of gears. However steels are most commonly used because of their high strength to weight ratio and low cost. Plastic is commonly used where cost or weight is a concern. A properly designed plastic gear can replace steel in many cases because it has many desirable properties, including dirt tolerance, low speed meshing, and the ability to "skip" quite well. Manufacturers have employed plastic gears to make consumer items affordable in items like copy machines, optical storage devices, VCRs, cheap dynamos, consumer audio equipment and printers.
Types of gears:
Spur gears or straight-cut gears are the simplest type of gear. They consist of a cylinder or disk with the teeth projecting radially, and although they are not straight-sided in form, the edge of each tooth is straight and aligned parallel to the axis of rotation. These gears can be meshed together correctly only if they are fitted to parallel axles.
Double helical gears. Each gear in a double helical gear can be thought of as two standard mirror image helical gears stacked. This cancels out the thrust since each half of the gear thrusts in the opposite direction. Double helical gears are more difficult to manufacture due to their more complicated shape.
Hypoid gears resemble spiral bevel gears except the shaft axes do not intersect. The pitch surfaces appear conical but, to compensate for the offset shaft, are in fact hyperboloids of revolution. Hypoid gears are almost always designed to operate with shafts at 90 degrees. Depending on which side the shaft is offset to, relative to the angling of the teeth, contact between hypoid gear teeth may be even smoother and more gradual than with spiral bevel gear teeth.
Crown gears are a particular form of bevel gear whose teeth project at right angles to the plane of the wheel; in their orientation the teeth resemble the points on a crown. A crown gear can only mesh accurately with another bevel gear, although crown gears are sometimes seen meshing with spur gears. A crown gear is also sometimes meshed with an escapement such as found in mechanical clocks.
Worm gears resemble screws. A worm gear is usually meshed with an ordinary looking, disk-shaped gear, which is called the gear, wheel, or worm wheel. Worm-and-gear sets are a simple and compact way to achieve a high torque, low speed gear ratio. A disadvantage is the potential for considerable sliding action, leading to low efficiency.
Non-circular gears are designed for special purposes. While a regular gear is optimized to transmit torque to another engaged member with minimum noise and wear and maximum efficiency, a non-circular gear's main objective might be ratio variations, axle displacement oscillations and more. Common applications include textile machines, potentiometers and continuously variable transmissions.
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2. Give Russian equivalents to the following word combinations.
1. dirt tolerance
2. low speed meshing
3. nonferrous alloys
4. cast irons
5. powder-metallurgy
6. injection molded
7. mechanical advantage
8. rotational speed
9. continuously variable transmission
10. simple machine
11. power source
3. Match the words with their definitions.
1. torque
2. Gearbox
3. mechanical advantage (MA)
4. gear ratio
5. simple machine
6. translation
7. wheel
8. continuously variable transmission
9. wear
10. pulley
a. is the relationship between the numbers of teeth on two gears that are meshed or two sprockets connected with a common roller chain
b. is a mechanical device that changes the direction or magnitude of a force
c. is a circular device that is capable of rotating on an axle through its center, facilitating movement or transportation while supporting a load (mass), or performing labour in machines.
d. is the tendency of a force to rotate an object about an axis
e. provides speed and torque conversions from a rotating power source to another device using gear ratios.
f. is a mechanism composed of a wheel on an axle or shaft that may have a groove between two flanges around its circumference
g. is movement that changes the position of an object, as opposed to rotation.
h. is the erosion of material from a solid surface by the action of another surface.
i. is a transmission that can change steplessly through an infinite number of effective gear ratios between maximum and minimum values.
j. is the factor by which a mechanism multiplies the force or torque applied to it.
4. Match English and Russian equivalents.
1. moment of force
2. transmission
3. gear ratio
4. simple machine
5. to mesh
6. translation
7. warp
8. heattreatment
9. gear
10. direction
11. magnitude
12. quench
13. continuouslyvariabletransmission
14. pulley
a. зацепляться; сцепляться
b. простейшие механизмы
c. деформация
d. коробка переключения передач
e. крутящий момент
f. термическая обработка металлов и сплавов
g. передаточное отношение
h. поступательное движение в
i. направление
j. передаточный механизм, шестерня
k. вариатор
l. блокhttp://www.sibznanie.ru/admin/work/edit/0/sort/work_id/dir/desc
m. величина, размеры
n. закаливать
5. Match the synonyms.
1. efficiency
2. resemble
3. particular
4. device
5. cancels
6. property
7. prevent
8. continuous
9. discrete
a. special
b. mechanism
c. effectiveness
d. compare
e. avert, obviate
f. cross out
g. quality
h. separate
i. persistent
6. Put the words given to complete the sentences. Translate them.
Transmission; quenched; wheel; continuous; prone; warps; meshing; prevent.
1. The steel was … with water. 2. Old wood seldom … in the wetting. 3. Nothing shall … us from reaching our aim! 4. One could hear … weeping from the adjacent room. 5. Man is … to error. 6. There's something wrong with this machine; the wheels aren't …properly with each other. 7. The most common use of … is in motor vehicles, where it adapts the output of the internal combustion engine to the drive wheels. 8. A … is a circular device that is capable of rotating on an axle through its center.
7. Complete the sentences using the information from the text. Translate them.
1. A gear is … having cut teeth, which mesh with another toothed part in order to transmit torque.
2. The most common situation is for a gear to mesh with another gear; however a gear can also mesh … .
3. For … the teeth are usually heat treated to make them hard and more wear resistant while leaving the core soft and tough.
4. … are the simplest type of gear, which consist of a cylinder or disk with the teeth projecting radially.
5. … are commonly used in textile machines, potentiometers and continuously variable transmissions.
6. … are almost always designed to operate with shafts at 90 degrees.
8. Decide whether the following statements are true [T] or false [F] in relation to the information in the text. If you feel a statement is false, change it to make it true. Translate them.
1. Two or more gears working in tandem are called a pulley and can produce a mechanical advantage through a gear ratio.
2. While using geared devices it is impossible to change the speed, magnitude, and direction of a power source.
3. In the manufacture of gears plastics are most commonly used because of their high strength to weight ratio and low cost.
4. Manufacturers have employed plastic gears to make consumer items affordable in items like copy machines, optical storage devices, VCRs, cheap dynamos, consumer audio equipment and printers.
5. Crown gears are a particular form of bevel gear that resembles screws.
6. Each gear in a double helical gear can be thought of as three standard mirror image helical gears stacked.
9. Put the sentence in all possible forms of Continuous, Simple, Perfect Tenses both Active and Passive.
10. Translate into Russian.
Worm gears resemble screws. Worm-and-gear sets are a simple and compact way to achieve a high torque, low speed gear ratio. For example, helical gears are normally limited to gear ratios of less than 10:1 while worm-and-gear sets vary from 10:1 to 500:1. A disadvantage is the potential for considerable sliding action, leading to low efficiency.
Worm gears can be considered a species of helical gear, but its helix angle is usually somewhat large (close to 90 degrees) and its body is usually fairly long in the axial direction; and it is these attributes which give it its screw like qualities. The distinction between a worm and a helical gear is made when at least one tooth persists for a full rotation around the helix. If this occurs, it is a 'worm'; if not, it is a 'helical gear'. A worm may have as few as one tooth. If that tooth persists for several turns around the helix, the worm will appear, superficially, to have more than one tooth, but what one in fact sees is the same tooth reappearing at intervals along the length of the worm. The usual screw nomenclature applies: a one-toothed worm; a worm with more than one tooth is called multiple thread. The helix angle of a worm is not usually specified. Instead, the lead angle, which is equal to 90 degrees minus the helix angle, is given.
In a worm-and-gear set, the worm can always drive the gear. However, if the gear attempts to drive the worm, it may or may not succeed. Particularly if the lead angle is small, the gear's teeth may simply lock against the worm's teeth, because the force component circumferential to the worm is not sufficient to overcome friction. Worm-and-gear sets that do lock are called self locking, which can be used to advantage, as for instance when it is desired to set the position of a mechanism by turning the worm and then have the mechanism hold that position. An example is the machine head found on some types of stringed instruments.
Worm gears can be right or left-handed following the long established practice for screw threads.
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11. Translate into English.
Зубча́тое колесо́ (шестерня́) — основная деталь зубчатой передачи в виде диска с зубьями на цилиндрической или конической поверхности, входящими в зацепление с зубьями другого зубчатого колеса. В машиностроении принято малое ведущее зубчатое колесо независимо от числа зубьев называть шестернёй, а большое ведомое — колесом.
Однако часто все зубчатые колёса называют шестерня́ми.
Зубчатые колёса обычно используются па́рами с разным числом зубьев с целью преобразования вращающего момента и числа оборотов вала на выходе. Колесо, к которому вращающий момент подводится извне, называется ведущим, а колесо, с которого момент снимается — ведомым. Если диаметр ведущего колеса меньше, то вращающий момент ведомого колеса увеличивается за счёт пропорционального уменьшения скорости вращения, и наоборот.
В соответствии с передаточным отношением, увеличение крутящего момента будет вызывать пропорциональное уменьшение угловой скорости вращения ведомой шестерни, а их произведение — механическая мощность — останется неизменным. Данное соотношение справедливо для идеального случая, не учитывающего потери на трение и другие эффекты, характерные для реальных устройств.
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12. Make a short summary about gears, base on the following plan:
1. What is gear.
2. Types of gears.
3. Appliance of gears.
