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НОТ WORKING OF STEEL
An important feature of hot working is that it provides the improvement of mechanical properties of metals. Hot-working (hot-rolling or hot-forging) eliminates porosity, directionality, and segregation that are usually present in metals. Hot-worked products have better ductility and toughness than the unworked casting. During the forging of a bar, the grains of the metal become greatly elongated in the direction of flow. As a result, the toughness of the metal is greatly improved in this direction and weakened in directions transverse to the flow. Good forging makes the flow lines in the finished part oriented so as to lie in the direction of maximum stress when the part is placed in service. The ability of a metal to resist thinning and fracture during cold-working operations plays an important role in alloy selection. In operations that involve stretching, the best alloys are those which grow stronger with strain (are strain hardening) – for example, the copper-zinc alloy, brass, used for cartridges and the aluminum-magnesium alloys in beverage cans, which exhibit greater strain hardening. Fracture of the workpiece during forming can result from inner flaws in the metal. These flaws often consist of nonmetallic inclusions such as oxides or sulfides that are trapped in the metal during refining. Such inclusions can be avoided by proper manufacturing procedures. The ability of different metals to undergo strain varies. The change of the shape after one forming operation is often limited by the tensile ductility of the metal. Metals such as copper and aluminum are more ductile in such operations than other metals.
2. Прочитайте текст снова и письменно ответьте на вопросы:
1. What process improves the mechanical properties of metals?
2. What new properties do hot-worked products have?
3. How are the flow lines in the forged metal oriented and how does it affect the strength of the forged part?
4. What are the best strain-hardening alloys?
5. Where can we use strain-hardening alloys?
ВАРИАНТ 5
1. Прочитайте и письменно переведите на русский язык текст:
Drilling Machines
Drilling machines are very old machine tools employed for drilling holes of different sizes in metal or any other solid material. In addition to drilling holes, such operations as tapping, reaming, lapping, countersinking and counterboring may be performed on the drilling machines.
Drilling machines of different design are classified in various classes, the main of them are the following: upright or vertical spindle drilling machines; multiple-spindle drilling machines; radial spindle machines.
In all three types, the drill spindle rotates in a sleeve which does not rotate but is free to move axially to provide the not necessary feed for the drill.
In vertical spindle drilling machine the spindle is in a vertical position. The upright drilling machine has an upright column resting on a heavy base. The column equipped with a gearbox has a feed mechanism.
The feed mechanism represents a feed shaft with the necessary gearing by which the drill is cut into the work at a proper speed. The shaft and the gearing provide a mechanical feed and any adjustment of both the drilling head mounted on the top of the column and the table for drilling operations.
All adjustment for different classes of work is made by moving the table which is accomplished by turning the crank. The machine is also equipped with a ratchet lever for hand feeding the drill.
2. Прочитайте текст снова и письменно ответьте на вопросы:
1. What operations may be performed on drilling machines?
2. How are drilling machines classified?
3. Where does the drilling machine spindle rotate?
4. How is the spindle sleeve moved and what is provided by such a movement?
5. What structural feature gives the upright drilling machine its name?