2,5 STEEL
The most important metal in industry is iron and its alloy — steel. Steel is an alloy of iron and carbon. It is strong and stiff, but corrodes easily through rusting, although stainless and other special steels resist corrosion. The amount of carbon in a steel influences its properties considerably. Steels of low carbon content (mild steels) are quite ductile and are used in the manufacture of sheet iron, wire, and pipes. Medium-carbon steels containing from 0.2 to 0.4 per cent carbon are tougher and stronger and are used as structural steels. Both mild and medium-carbon steels are suitable for forging and welding. High-carbon steels contain from 0.4 to 1.5 per cent carbon, are hard and brittle and are used in cutting tools, surgical instruments, razor blades and springs. Tool steel, also called silver steel, contains about 1 per cent carbon and is strengthened and toughened by quenching and tempering.
The inclusion of other elements affects the properties of the steel. Manganese gives extra strength and toughness. Steel containing 4 per cent silicon is used for transformer cores or electromagnets because it has large grains acting like small magnets. The addition of chromium gives extra strength and corrosion resistance, so we can get rust-proof steels. Heating in the presence of carbon or nitrogen-rich materials is used to form a hard surface on steel (case-hardening). High-speed steels, which are extremely important in machine-tools, contain chromium and tungsten plus smaller amounts of vanadium, molybdenum and other metals.
3,6 METHODS OF STEEL HEAT TREATMENT
Quenching is a heat treatment when metal at a high temperature is rapidly cooled by immersion in water or oil. Quenching makes steel harder and more brittle, with small grains structure.
Tempering is a heat treatment applied to steel and certain alloys. Hardened steel after quenching from a high temperature is too hard and brittle for many applications and is also brittle. Tempering, that is re-heating to an intermediate temperature and cooling slowly, reduces this hardness and brittleness. Tempering temperatures depend on the composition of the steel but are frequently between 100 and 650 °C. Higher temperatures usually give a softer, tougher product. The colour of the oxide film produced on the surface of the heated metal often serves as the indicator of its temperature.
Annealing is a heat treatment in which a material at high temperature is cooled slowly. After cooling the metal again becomes malleable and ductile (capable of being bent many times without cracking).
All these methods of steel heat treatment are used to obtain steels with certain mechanical properties for certain needs.
4,7 MECHANICAL SYSTEMS
Some kinematic concepts that apply to all mechanical systems are discussed in this paper. A mechanical system is defined as anything that is composed of matter. The first step in an analysis of a mechanical system should be a precise and definitive description of the system under, consideration. Since the modern theories of the constitution of matter will not be considered, the particles that compose a mechanical system are regarded as mathematical abstractions; they are more properly called "material points". The simultaneous positions of all the material points of a mechanical system are called the "configuration" of the system. For example, the displacement vector field of a deformable body defines a configuration of the body. To define the configuration of a mechanical system, we require a coordinate system that is attached to some rigid system, known as a "reference frame". In the theory of kinematics the reference frame is arbitrary.
A general problem of static is to determine the equilibrium configurations of mechanical systems under prescribed types of loadings and to ascertain which among them are stable. An important general problem of dynamics is to express the configuration of a given mechanical system as a function of time.
A mechanical system is said to experience a displacement if any of its material points are displaced. In other words, any change of the configuration of a mechanical system is a displacement.
Usually the material points of a mechanical system cannot be displaced independently. Geometrical restrictions on the displacements of the material points of a system are called "constraints". For example, the constraints in a rigid body are such that any two particles of the body remain at a constant distance from each other. The constraints in an incompressible fluid are such that the volume of any part of the fluid remains constant. The constraints of an ideal cantilever beam are such that the displacement vector vanishes at the clamped end.
9,8 DEFINITION OF FORCE
The subject of mechanics is concerned with relationships between forces and motions which result from the application of forces. Later chapters in this book will consider the study of motion as such. The present chapter will be concerned only with forces and the analysis of combinations of forces. It is well known to anyone who has experimented with bodies subjected- to several forces that the effect of several forces cannot be obtained by simply adding numerically the magnitudes of the forces, since the directions in which the forces are applied are also significant.
In simple language, a force is a directed push or a pull on an object. We shall restrict our attention in this chapter to forces acting on particles, as previously defined. Occasionally finite sized objects will be considered as particles, but in general we shall restrict our attention to masses which occupy a very small region of space. The forces which we are considering and which we have defined as a push or a pull may result from a direct action by virtue of the contact of the particle in question with another particle or object. Forces may also result from the remote action of one mass on another, such as the attraction of the earth on the mass particle (gravity) or from the actions of electromagnetic forces.
Forces are vector quantities. A vector quantity has both magnitude and direction. In order to specify completely what a force vector is, we must give its numerical magnitude, e. g. the number of pounds, kilograms, or tons that measure the force, and we must also specify, relative to some convenient frame of reference, the direction in which the force is acting, such as 4.2 pounds east or northeast or vertically upward, etc. Since we shall consider the problem of combining the effect of several such forces, the rules of combination of vector quantities must be investigated next.
Для специальности 230106 «Техническое обслуживание средств вычислительной техники и компьютерных сетей»
The computers are used in chemical plants, power stations, road-traffic control, etc.
The basic digital computer consists of four main sections: the store, arithmetic unit, control and input / output devices.
The store contains a numerical quantities and data which are to be processed. It also has a programme or list of instructions which are to be performed.
The arithmetic unit normally performs the operation of addition, subtraction, multiplication and division and certain other special operations.
The input and output devices are to supply information and to obtain it from the computer. These devices play a significant part in making the capacity of a computer effective.
The basic unit of information with which digital computers operate is the bit. For many purposes, however, it is better not to be specific about how the information is coded into bits.
A byte is 8 bits and corresponds to a storage unit4 necessary to contain the binary code.
Labels help you keep track of the information on your disks, but you may also need to protect the disks themselves. Some floppy disks are protected, letting you examine information on them without letting you change anything. These are called write-protected disks.
Floppy disks can be write-protected in one of two ways. Some have a small piece of tape, called a tab, covering a notch on the right side of the disk. You can copy information onto a write-protected disk by first removing the write-protect tab; however, you should consider why the disk was protected – before you change its contents. After you have copied or changed a write-protected disk it’s always a good idea to replace the write-protect tab.
If a disk does not have a write-protect notch, it is permanently write-protected. Many application programs, including this version of MS-DOS, come on write-protected disks that protect the files from being destroyed accidentally.
These smaller disks, sometimes called microfloppies, have rigid plastic covers with metal shields that guard the disk from dirt and fingerprints. When you place the disk into the disk drive, the computer automatically moves this shield aside to read the disk.
Note that 3.5-inch disks have a write-protect notch. This notch can be covered with a built-in tab. As with 5.25-inch floppy disks, if the write-protection notch is covered by the tab, no data can be written to the disk.
Be sure to label your 3.5-inch disks and store them in a safe place. As with 5.25-inch floppy disks, extreme temperatures, magnetism, dust, and fingerprints can all harm your data on a disk.
Note MS-DOS works virtually the same way with both 3.5-inch and 5.25-inch floppy disks. So in this documentation, the term floppy disk is used to mean either of these two types of disks.
In addition to floppy disks, some computers use a hard disk, which can store much more information than a floppy disk. Computers also take less time to find information stored on a hard disk than on a floppy disk. A hard disk is usually built into the computer. A hard disk is usually built into the computer.
When you store application programs, including MS-DOS, on your hard disk, you should keep a backup copy of the programs on a floppy disk in case the information on the hard disk is accidentally damaged or destroyed.
Before you can use your new disks for storing information, you must format them. You do this with the format command, a special program that structures a disk so that MS-DOS can find information on it. The format command also checks the disk for defective spots.
You can format both floppy and hard disks. But remember that if a disk is not blank, formatting it destroys any data already on the disk.
8,9 WHAT IS A COMPUTER
The term computer is used to describe a device made up of a combination of electronic and electromechanical (part electronic and part mechanical) components. Computer has no intelligence by itself and is referred to as hardware. A computer system is a combination of five elements:
● Hardware
● Software
● People
● Procedures
● Data/information
When one computer system is set up to communicate with another computer system, connectivity becomes the sixth system element. In other words, the manner in which the various individual systems are connected – for example, by phone lines, microwave transmission, or satellite – is an element of the total computer system.
Software is the term used to describe the instructions that tell the hardware how to perform a task. Without software instructions, the hardware doesn’t know what to do. People, however, are the most important component of the computer system: they create the computer software instructions and respond to the procedures that those instructions present.
The basic job of the computer is the processing of information. Computers accept information in the form of instruction called a program and characters called data to perform mathematical and logical operations, and then give the results. The data is raw material while information is organized, processed, refined and useful for decision making. Computer is used to convert data into information. Computer is also used to store information in the digital form.
Для специальности 190604 «Техническое обслуживание и ремонт автомобильного транспорта»
Automobiles are trackless, self-propelled vehicles for land transportation of people or goods, or for moving materials. There are three main types of automobiles. These are passenger cars, buses and lorries (trucks). The automobile consists of the following components: a) the engine; b) the framework; c) the mechanism that transmits the power-engine to the wheels; d) the body.
Passenger cars are, as a rule, propelled by an internal combustion engine. They are distinguished by the horse-power of the engine, the number of cylinders on the engine and the type of the body, the type of transmission, wheelbase, weight and overall length.
There are engines of various designs. They differ in the number of cylinders, their position, their operating cycle, valve mechanism, ignition and cooling system.
Most automobile engines have six or eight cylinders, although some four-, twelve-, and sixteen-cylinder engines are used. The activities that take place in the engine cylinder can be divided into four stages which are called strokes. The four strokes are: intake, compression, power and exhaust. “Stroke” refers to the piston movement. The upper limit of piston movement is called top dead centre, TDC. The lower limit of piston movement is called bottom dead centre, BDC. A stroke constitutes piston movement from TDC to BDC or from BDC to TDC. In other words, the piston completes a stroke each time it changers the direction of motion.
2,5 ENGINE OPERATION
An automobile, powered by petrol engine, begins to operate when the driver turns a flywheel connected to the engine crankshaft. As the crankshaft revolves, a mixture of fuel and air is drawn from a carburetor into the engine cylinders. The ignition system provides the electric sparks that ignite this mixture. The resultant explosions of the mixture turn the crankshaft, and the engine starts moving. By regulating the flow of the fuel and air with a throttle, the driver controls the rotational speed of the crankshaft.
Cooling, electrical ignition and lubrication systems are of great importance for the good performance of a car. The lights, radio and heater add to the flexibility, comfort, and convenience of the car. The indicating devices keep the driver fuel, and battery charging rate.
Brakes are of drum and disk types. The steering system consists of a manually operated steering wheel which is connected by a steering column to the steering gear from which linkages rum to the front wheels. It is difficult to turn the steering wheel, and special hydraulic power mechanisms are used to lessen this effort. Suitable springings are used against shocks. These are leaf springs, coil springs, torsion bars and air suspensions.
3,6 WHOSE FUEL IS IN U.S. CARS?
While President Bush has been campaigning to reduce U.S. dependence on oil imported from the volatile Middle East, imports from the Persian Gulf have been rising steadily. The share of U. S. imports from Persian Gulf countries - Bahrain, Iran, Iraq, Kuwait, Qatar, Saudi Arabia, and the United Arab Emirates - rose to 23,6% in the first quarter of this year, from 20,5% in the first quarter of 2000 and 21% in 2001, according to Energy Dept. data (chart). This year's level is the highest of any first quarter since 1992.
Iraq is the biggest factor. The U.S. imported 2,5 million barrels of Iraqi crude a day in the first quarter of 2002, up from 1,5 million in 2000's first quarter and 1.1 million in the 2001 period. Since then, Iraq's share of U.S. imports has fallen because of its self-imposed embargo in April and U.N. pricing rules that have discouraged purchases of Iraqi oil.
One reason the U.S. is importing more Gulf oil may be that Europe is taking less - because it's getting more of its oil from Russia, says John Kingston, global director for oil at Plats, a unit of The McGraw-Hill Companies.
Unfortunately, that's not all. There is also GM's 20% stake in Italy's troubled Fiat Auto. It came with an ill-timed commitment - a put option - to buy the rest from the parent company as early as 2004 (box). If Fiat's woes worsen, GM may be compelled to make an offer before its value deteriorates much more. Says Deutsehe Bank analyst Rod Laehe: "That's money they don't need to spend right now."