It can be packed to any required shape — ему можно придать любую нужную форму

sand molds are used only once — воспользоваться земляными излож­ницами можно только один раз

129

д-2776

at times — иногда coated inside — покрытые внутри refractory material — огнеупорный металл (материал) made in two parts — изготовлено из двух частей in most cases finished smooth — в большинстве случаев изготовляется гладкой

14. CUPOLA MELTING

Most of the gray cast iron produced is melted in the cupola fur­nace. The cupola is a vertical cylin-drical type of furnace, consisting of a steel shell lined with firebrick. Usually the charging door is located 15 to 25 ft above the bottom plate. At the lower end of the furnace is a wind box or air box. Air enters the cupola openings called tuyeres. Some cu­polas are equipped with a single row of tuyeres; others have an auxiliary upper row of tuyeres. Opin-ion is divided as to whether a single or a double row is more desirable. A patented cupola known as the “bal­anced blast cupola”, developed by the British Cast Iron Research Asso-ciation, has three rows of tuyeres. A number of furnaces of this type have been installed in this country.

The cupola is a simple and economical melting unit, because the fuel and the metal are in intimate contact with each other. Fuel, metal and flux enter the cupola through the charging door. The ini­tial charge of coke is known as the “bed charge”. The metal is de­posited on the coke. The alter-nate layers of coke and iron are add­ed.

Generally a flux is charged on the coke and the coke bed ignited by means of kindling wood or an oil torch. This bed usually extends from 36 to 60 in. above the top of the lower tuyeres. The make up of the charge and the charging are most important in obtaining uniform results in melting.

15. MACHINE-TOOLS

Machine-tools are a class of metal removing machines such as lathes, millers and drillers. The basis of the cutting process is the move­ment of the cutting tool in relation to the material in a precise orienta­tion and by a precise amount.

Traditional numerical control (NC) is based upon the movement being controlled via a pre-prepared punched paper tape. The develop­ment of microprocessors and compact computers has extended the so­phistication of the control available, so that the term “computer nu­merical control” (CNC) is used. In practice, movements in all three dimensions are controlled.

The actual movement and monitoring of the controlled axes are carried out by motors and position transducers.

On the above basis numerical control machine-tools have been used for many years prior to the development of the microelectronics. The application of microcomputers allows for more sophisticated control. When metal is machined, its cutting properties can vary throughout the workpiece, particularly if it is a forging or casting. Microcomputers can add a further aspect of adaptive control by reacting to the current power consumption, torque, etc. of the driving motors.

Due to the nature of microcomputer systems a distributed process­ing approach can be adopted for the control of the various functions of a machine tool. This also allows a modular approach to the develop­ment of the hardware and software. In addition, greater operator inter­action for unexpected situations is possible due to the work cycle not being restricted to preprogrammed punched paper tape.

Instead of being a substantial part of the cost of a machine tool, the use of microcomputers makes the numerical control cost less and adds relatively little to the cost of the machine tool.

Some control systems are too complex for a single microprocessor. One approach is to use a bit slice microprocessor system whereby the codes of the data bus are broken into slices, each having the same number of bits (e.g. 16 bit into 4 slices of 4 bits). Each of the slices is then proc­essed in a separate processor.

An alternative to bit slice microprocessor for complex systems is to use several microprocessors together.

Microcomputer A acts as a programmable interface between the machine tool and the system. It also handles tape and operator input and output. Microcomputer Вcalculates the axes motions as a func­tion of time and hence the path of the cutter and microcomputerСcontrols the position of the feed axes. The three microcomputers share a common data memory. As more microcomputers are linked to the machine, a greater on-line processing capability is built up. For exam­ple, “worksurface programming” is the technique whereby the desired profile of the workpiece is specified and the size of the blank is entered. The control system works out the pattern of cuts necessary to produce the component. In some cases, this is displayed on the YDU as a check before the operator commits the machine.

The addition of VDUs machine tool control system allows a con­versational approach which guides the operator when inputting the required data. The use of microcomputers has enabled the develop­ment of digital readout systems (with memory). The current posi­tion of all co-ordinates is displayed and in some cases the display can be switched at any time from one system of units to another and vice versa.

Notes:

machine-tool —металлорежущийстанокlathe —токарныйстанокmiller — фрезерныйстанокdriller — сверлильныйстанок

in a precise orientation and by a precise amount — вопределенномположенииивточнозаданныхпределахpunched paper tape — бумажнаяперфолента

computer numerical control (CNC) — числовое программное управле­ние (ЧПУ)

monitoring of the controlled axes — отслеживание (положения) контролируемых (координатных) осей position transducer — датчик положения

when metal is machined, its cutting properties can very throughout the work­piece — когда металл обрабатывается, его режущие свойства могут меняться в пределах одной заготовки (детали) torque — вращающий момент

distributed processing approach — принцип распределения обработки (данных)

modular approach — модульный принцип

bit slice... system — система, секционированная по двоичным разрядам; система с разрядной организацией VDU = Visual Display Unit — устройство визуального отображения, дисплей

before the operator commits the machine — прежде чем оператор начнет станочную обработку conversational approach — режим диалога

digital readout system — система цифрового отображения (информа­ции)

16. CUTTING FLUIDS

Coolants or cutting fluids are applied to reduce the heating of a tool and to prolong its life. Milling cutters are cooled with special cutting fluids. Cutting fluids should be supplied in a continuous stream and immediately that milling has begun.

Mist cooling is a recent development at the plants. For this pur­pose, the machine is equipped with a mixer filled with soluble oil. The mist prolongs tool life and enables the cutting speed to be in­creased.

17. MILLING MACHINE MAINTENANCE

The machine should always be free from dirt, dust, chips. Clean the machine while it stands idle. Dirt and oil are washed off with cotton waste dipped in kerosene. Then wipe off the machine with dry waste. Before off-days the whole machine should be coated with oil to prevent corrosion. After the machine has been cleaned, all used waste should be stowed in a special box.

18. FINISHING SURFACES’S OPERATIONS. FORM TURNING OPERATIONS

A smooth very clean (mirror) finish on some surfaces is obtained by polishing.

Work may be polished much quicker and easier if a simple device called a polishing clamp is employed. It is advisable to coat the surface to be polished with a layer of machine oil or to mix the grain abrasive with this oil. This will produce a brighter finish.

For best results in polishing, apply only a slight force on the clamp and run the lathe at a high speed.

Machine building often requires parts of a shape differing from the cylindrical and tapered surfaces. Hand-les of various shapes, ball-type (spherical) rods, and many other parts have formed surfaces.

A form turning operation may be done with forming tools. Form­ing tools or cutters have a cutting edge of irregular or curvilinear shape which corresponds to the shape of the surface to be machined. They are classified into three types:

1. forged, or shank-type forming tools;

2. dovetail or straight forming tools;

3. circular forming tools.

The first type tools are seldom used, the second type tools provide a better surface finish on the surface being turned; the third type tools is a disc.

Notes:

smooth — гладкий

finishing — чистовая обработка

polishing — полирование, полировка

polishing clamp — полировочный жимок

to coat — покрывать

grain abrasive — зернистый абразив

layer — слой

slight — легкий

force — усилие

clamp — зажим formed — фасонный handle — ручка, рукоятка rod — прут, стержень, брус cutter — резец

cutting edge — главная режущая кромка

shape — форма; профиль

shank-type forming tool — фасонный резец

curvilinear — криволинейный фасонный резец

dovetail or straight forming tool — призматический резьбовой резец

circular forming tool — дисковый резец

19. MEASURING TOOLS

Machined workpieces are measured by accurate mea-suring tools, such as precision vernier calipers, micrometer calipers, inside microm­eters and limit gauges.

In performing accurate work a precision vernier caliper is required. The micrometer caliper, or simply micrometer, is used for more accu­rate measure-ments of external dimensions of work, such as diameters, thickness and lengths. Internal dimensions may be mea-sured with an accuracy of 0.01 mm using inside micrometers.

The best measuring tools for checking threads are standard and limit thread gauges.

Notes:

vernier caliper — штангенциркуль с нониусом micrometer caliper — микрометр inside micrometer — микро-метрический нутромер limit gauge — предельный калибр thread gauge — резьбовой калибр

20. PROCESS CONTROL

The control of processes in general is a wider extension of the princi­ples used in numerical control of machine tools. Instead of monitoring and controlUng solely movement, other parameters, such as temperature, time, gas flow, etc., are monitored and controlled. The possibilities are endless, provided suitable transducers exist for the parameters to be con­trolled. In this case, the more complex the process the more suitable it is for microcomputer control.

Efficient operation of furnaces is an example where energy savings can be substantial when the process is properly controlled. A micro­processor-based system can monitor signals from thermocouples, air flow meters, fuel flow meters and gas analysers, and on the basis of heat loss calculation and furnace efficiency optimise the fuel/air ration.

In an application such as this, it is also possible to collect informa­tion of the furnace performance over time. An analysis of this informa­tion provides a valuable guide to damage and wear and to establishing the time for appropriate corrective maintenance.

Another heat dependent process is injection moulding. A micro­processor can monitor melt temperature, die temperature, pressure, cooling time, etc. to control the cycle in accordance with the specifica­tion of the material being used.

In practice, despite theoretical laws, many industrial process pa­rameters are chosen and varied according to industry branch accumu­lated data and operator judgement. This can lead to erratic production and quality problems. With microcomputer control systems, this data can be stored and drawn upon from computer memory leading to great­er uniformity of output.

The calculation of optimum tool life from theoretical laws, from example, is not practical because of the variations in the properties of the actual workpiece. Optimum tool life more realistically should be based upon actual experience. It is feasible nowadays to monitor and analyse data to recalculate continuously optimum tool life.

Continuous monitoring of vibration in machinery allows the vibra­tion pattern to be analysed. Any abnormal wear or breakdown of bear­ings will show up as a dramatic change in the pattern of vibration.

Notes:

provided — при условии что, в случае если

provides a valuable guide to damage and wear and to establishing the time for appropriate corrective maintenance — дает ценные сведения о повреждениях, износе и о времени необходимого профилакти­ческого ремонта

to erratic production and quality problems — к неустойчивости произ­водства и снижению качества продукции