Скачать 211.31 Kb.
|Методический материал по обучению чтению литературы на английском языке по специальности «Обработка металлов давлением» для студентов 3 курса (6-ой семестр)|
obsolete ['Obsqli:t] –устаревший
reciprocating weight – возвратно-поступательное движение за счет массы
stem from(v) – происходить из
pound(v) [paund] – отбивать, подвергать удару
progress(v) – протекать, происходить
to be amenable [q'mi:nqbl] – поддаваться
intermittent ["intq'mit(q)nt] – прерывистый, пульсирующий
precipitation – осадкообразование, осаждение, оседание
kneading – размешивание, разминание
recessed [ri'sest] – углубленный
Forging is the term for shaping metal by using localized compressive forces. Cold forging is done at room temperatures or near room temperature. Hot forging is done at high temperature, which makes metal easier to shape and less likely to fracture. Warm forging is done at intermediate temperature between room temperature and hot forging temperatures. Forged parts can range in weight from less than one kilogram to 170 metric tons. Forged parts usually require further processing to achieve a finished part.
History: Forging is one of the oldest known metalworking processes. It was done historically by a smith using a hammer and an anvil, and though the use of water power in the production and working of iron date to the 12th century, the hammer and anvil are not obsolete. The smithy has evolved over centuries to the forge shop with engineered processes, production equipment, tooling, raw materials and products to meet the demands of modern industry. In modern times industrial forging is done either with presses or with hammers powered by compressed air, electricity, hydraulics or steam. These hammers are large, having reciprocating weights in thousands of pounds. Smaller power hammers, 500 pounds or less reciprocating weight, and hydraulic presses are common in art smithies as well. Steam hammers are becoming obsolete.
Advantages and disadvantages: Forging results in metal that is stronger than cast or machined metal parts. This stems from the grain flow caused through forging. As the metal is pounded the grains deform to follow the shape of the part, thus the grains are unbroken throughout the part. Some modern parts take advantage of this for a high strength-to-weight ratio.
Many metals are forged cold, but iron and its alloys are almost always forged hot. This is for two reasons: first, if work hardening were allowed to progress, hard materials such as iron and steel would become extremely difficult to work with; secondly, steel can be strengthened by other means than cold working, thus it is more economical to hot forge and then heat treat. Alloys that are amenable to precipitation hardening, such as most alloys of aluminum and titanium, can also be hot forged, then hardened. Other materials must be strengthened by the forging process itself.
Open and closed die operations can be used in forging. In open-die forging dies are either flat or rounded. Large forgings can be formed by successive applications of force on different parts of the material. Hydraulic presses and forging machines are both employed in closed die forging. In closed-die forging the metal is trapped in recessed impressions, which are machined into the top and bottoms dies. As the dies press together, the material is forced to fill the impressions. Flash, or excess metal, is squeezed out between the dies. Closed-die forging can produce parts with more complex shapes than open-die forging. The final shape and the improvement of metallurgical properties are dependent on the skill of the operator. Closer dimensional tolerances can be held with closed die forgings and the operator requires less skills.
Forging is divided into three main methods: hammer, press, and rolled types. Hammer Forging (Flat Die) is a preferred method for individual forgings. The shaping of metal, or other material, occurs by an instantaneous application of pressure to relatively small area. A hammer or a ram, delivering intermittent blows to the section to be forged, applies this pressure. A hammer is dropped from its maximum height, usually raised by steam or air pressure. Hammer forging can produce a wide variety of shapes and sizes. The disadvantage of this process is that finish machining is often required, as close dimensional tolerances cannot be obtained.
Press Forging is similar to kneading, where slow continuous pressure is applied to the area to be forged. The pressure will extend deep into the material and can be completed either cold or hot. Press forging is more economical than hammer forging (except when dealing with low production numbers), and closer tolerances can be obtained. A greater proportion of the work done is transmitted to the workpiece, differing from that of the hammering operation, where much of the work is absorbed by the machine and foundation. This method can also be used to produce larger forgings, as there is no limitation in the size of machine.
In roll forging a bar stock, round or flat, is placed between die rollers, which reduces the cross-section and increases the length.
1. What is forging? 2. What types of forging do you know? 3. What are the advantages and disadvantages of forging? 4. How is hammer forging done? 5. In what way does hammer forging differ from press forging? 6. What types of presses are employed in closed die forging? 7. Can you compare parts produced by open and closed die operations?
assembly – узел, механизм
anvil – шабот, наковальня
air clutch – пневматическая муфта
bottom dead centre – нижняя мёртвая точка
drive shaft – ведущий вал, приводной вал
exert a force – оказывать давление
gravity drop hammer/ power drop hammer – штамповочный молот
single acting hammer – штамповочный молот простого действия
fasten – прикреплять к чему-либо
incorporate – включать в себя
impart a stroke – сообщать ход
impose – налагать, спускать
derive from – происходить от
low profile forging – простая поковка
piston rod – шток
rated size – номинальный размер
stroke – ход
trimming – обрезка
squeeze – сдавливать
weighted rams – падающие части
The type of machinery to be used depends on the shape, size, material, and the number of pieces to be made. Heavy forgings are produced in different types of presses and lighter ones by hammers.
Conventional drop forging hammers incorporate a weighted ram that, when it moves vertically in a downward stroke, exerts a striking force against a stationary component of the anvil near the base of the hammer. Forging dies being fastened to the weighted ram and the anvil assembly, and a workpiece being placed between them, the striking force is imposed on the workpiece, causing it to deform plastically with each successive blow, thus providing a forged configuration.
Power drop hammers are equipped at the top with a cylinder, a piston and a piston rod that is attached to the ram and that is powered by steam or compressed air. The piston is used to raise the ram and movable die to the desired height and to add force to the force of gravity on the downstroke. These hammers range in rated size from 500 to 35,000 lb. In general, they are used to produce medium-size to large open-die and close3d-die forgings. Gravity drop hammers derive their downward force entirely from the force of gravity, mechanical means raising the ram for the succeeding stroke or blow. Gravity drop hammers typically have a falling weight, or rated size, of 400 to 10,000 lb. and are used in the production of smaller and lighter open-die or closed-die forgings.
Conventional presses incorporate a ram that moves in a vertical direction to exert a squeezing action on the work metal. Such presses develop far less noise and vibration than hammers. Depending on their actuation, forging presses are classified as mechanical or hydraulic. Maximum capacities, exceeding those of the largest steam hammers, are developed by hydraulic presses. In general, presses can produce all of the types of forgings produced by hammers.
Mechanical presses are driven by a motor and controlled by an air clutch; they have a full eccentric type of drive shaft that imparts a constant stroke to a vertically operating ram. Because of the short stroke, mechanical presses are best suited for low-profile forgings. Presses are rated on the maximum force they will exert at 3/8 or ¼ in. from the bottom dead centre. Capacities typically range from about 300 to 8000 tons. In smaller sizes (50 to 250 tons) they are widely used for trimming forgings produced on other types of equipment. As for hydraulic presses they produce high tolerance forgings. Capacities of hydraulic presses are known to range from 300 to 50000 tons.
1. What exerts a striking force against a stationary component of the anvil near the base of the hammer? 2. What is the piston used for? 3. What hammers are used in the production of smaller and lighter open-die or closed-die forgings? 4. What are the advantages of forging presses as compared with power drop hammers?
IV. Find the following phrases in the text:
С каждым последующим ударом; нужная (необходимая) высота; вообще; в зависимости от; лучше всего подходят; широко используются; что касается; мощность гидравлического пресса.
1. Conventional drop forging hammers…….a weighted ram that, when it moves vertically in a downward stroke…….a striking force against a stationary component.
2. When forging dies are……to the weighted ram and the anvil assembly, the striking force is…….on the workpiece.
3. Gravity drop hammers…….their downward force entirely from the force of gravity.
4. The ram moves in a vertical direction and…….a squeezing action on the work metal.
5. Mechanical presses are drive by a motor and have a full eccentric type of shaft that…….a constant stroke to a vertically operating ram.
VI. Translate the following sentences paying a special attention to the word “force”.
1. In pneumatic hammers the rams fall not only under their own weight but are also forced to fall by the action of compressed air above the piston.
2. The force of the blow is controlled by a handle which adjusts the opening of the valve through a system of levers.
3. During the upward stroke the piston of the working cylinder compresses the air in the upper part of the cylinder and forces it through the upper channel into the working cylinder.
VII. Read and translate the text without a dictionary.
Counterblow hammers develop striking by the movement of two rams that approach simultaneously from opposite directions and meet at a midway point. The rams are capable of striking from 100 to 200 blows per minute; they develop combined velocities equivalent to about 1.5 times the normal hammer velocities. Capacities of six large power drop and counterblow hammers, ranging in rated size from 25,000 lb. to 125,000 mkg, are related to the production of blocker-type forgings in titanium alloys and low-alloy steel.
drop hammer – штамповочный молот
power hammer – механический молот
link-rod – шатун
chamber ['tSeimbq] – камера, отсек, полость, резервуар
vessel – камера высокого (низкого) давления
tup – баба молота, кувалда молота
flexible pipes – гибкие трубы
charge(v) – (зд.) заполнять
rigidly – жёстко, строго, неподвижно
crank – кривошип
Forging hammers apply force by the impact of a large ram. This may be a drop hammer, or weight falling under them force of gravity, or it may be a power hammer, driven by steam or compressed air. Two types of power hammers are: the smith forging hammer and the drop hammer. The largest hammers can provide a total force as high as 40,000 tons.
For increasing general efficiency and reducing the cost of forgings worked on a double action air hammer, an electro-hydraulic hammer has been developed for many years. There are several series of electro-hydraulic hammers which can be found at the forging equipment market.
However as compared with an air hammer a hydraulic drive system is easier out of order and it is usually quite difficult to find out the problems quickly and correctly due to its complicated structure. It means that the reliability of an electro-hydraulic hammer is not as well as an air hammer and people who have even more knowledge and experiences should be employed to keep the hammer working normally.
A crank hammer is a kind of a new type forging machine, its principle and construction being totally different from other hammers, and its efficiency and reliability can be expected to be higher than those of electro-hydraulic hammers.
From the electric motor to the link-rod the structure of crank hammers is quite similar to a mechanical press. When the link-rod is connected with the piston, the chamber inside the tup is separated by the piston into upper and lower spaces; compressed air is filled into the lower space and the upper space contains liquid. By flexible pipes the lower space is directly linked to the compression air container while the upper space is joined to the low pressure vessel through the valve.
When the crank rotates the tup and the piston rise together rigidly because the valve is closed and the oil confined inside the upper space cannot be squeezed. After the crank passes through its top dead-centre and then arrives at a definite position, one should hold down the handle. The valve opens and the tup is simultaneously accelerated downward by its weight and the expanding energy of the air inside the lower space until strike occurs. The oil of the upper space is charged into the low pressure vessel.
As soon as strike happens the handle is required to be held up again. Although the tup now stays at the anvil the piston will keep moving towards its bottom dead-centre. The air inside the lower space is compressed to the initial pressure and the oil flows back to the upper space from the vessel automatically.
1. What determines the choice of forging equipment? 2. What types of hammers do you know? 3. What caused the development of electro-hydraulic hammers? 4. What are their disadvantages as compared with air hammers? 5. Can you give technical characteristics of a crank hammer? 6. What’s the principle of its work?
leakage – утечка
blanking – вырубка
maintenance work – эксплуатация, техническое обслуживание
drawing – вытяжка
assemble – собирать, монтировать
tooling – оборудование, оснащение, механическая обработка
feeding – подача
handling – разгрузка, управление, обработка
fuel pump – топливный насос
housing – корпус
accomplish – выполнять, завершать
in-roads – вторжение
have in common – иметь общее
rubber molding – штамповка резины
single acting mechanical press – механический пресс простого действия
fluid – жидкость
sheet metal working – обработка тонколистового металла
frame – рама
bed – станина
guide – направляющая
slide – ползун, скользить
lubrication – смазка
power pack – узел привода
«Обработка металлов давлением»/ Авторы – составители: И. М. Курлова, О. И. Макушина. – Магнитогорск: гапоу чо «Политехнический колледж»,...
Определите по суффиксам, к каким частям речи относятся следующие слова, переведите
Методическая разработка составлена в соответствии фгос по специальности среднего профессионального образования 22. 02. 05 «Обработка...
Учебно-методическое и материально-техническое обеспечение курса «международная полиция на английском языке»
Учебно-методическое и материально-техническое обеспечение курса «военно-морской флот на английском языке»
Учебно-методическое пособие по обучению профессионально-ориентированному чтению студентов специальности «Автоматика, телемеханика...
Методические указания к выполнению практических работ обучающимися по дисциплине оп. 05
Рекомендовано к изданию научно-методическим советом Псковского государственного политехнического института
Кафедра иностранных языков Поволжского кооперативного института (филиала) Российского университета кооперации