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Ductility is the ability of a material to undergo permanent deformation under tensile force, so it can be drawn into wires. Malleability is a similar property but refers to forming thin sheets by hammering or rolling. Brittle materials fracture without noticeable deformation, and elasticity is recovery after unloading.
Pig iron is produced by reducing iron ore with coke and limestone in a blast furnace. The product contains a high percentage of carbon and is later refined into cast iron or steel. Bessemer, open-hearth and electric arc furnaces are steelmaking units.
Non-ferrous metals do not contain iron as the principal constituent; aluminium is a typical example. Cast iron, mild steel and stainless steel are ferrous materials because iron is their base element.
Hardness is the resistance offered by a surface to indentation, scratching or abrasion. Toughness is energy absorption before fracture, stiffness is resistance to elastic deformation, and creep is time-dependent deformation under sustained load.
Grey cast iron contains carbon in the form of graphite flakes, which give it good vibration damping and machinability. White cast iron has carbon combined as cementite and is hard and brittle. Malleable cast iron is made by heat-treating white cast iron, while nodular cast iron contains spheroidal graphite.
Mild steel, also called low-carbon steel, contains about 0.05% to 0.30% carbon, which makes it ductile and weldable. Medium-carbon steels contain roughly 0.30–0.60% carbon, high-carbon steels about 0.60–1.00%, and cast irons generally above 2% carbon.
Annealing consists of heating steel to a suitable temperature above the critical range, holding it, and cooling slowly in the furnace. Slow cooling softens the steel, relieves internal stresses and improves machinability. Normalising cools in air, quenching uses a rapid cooling medium, and tempering is a reheating treatment after hardening.
Bronze is basically a copper–tin alloy, although small amounts of other elements may be added for specific properties. Brass, by contrast, is mainly a copper–zinc alloy. Copper–nickel and copper–aluminium alloys are known by their own specific names.
Failure under repeated or alternating stresses is called fatigue, so the relevant design property is fatigue strength or fatigue limit. Creep resistance concerns slow deformation at high temperature, impact toughness concerns sudden loading, and surface hardness concerns indentation and wear.
Thermosetting plastics undergo irreversible cross-linking during curing, so they char rather than soften when reheated; Bakelite is a common phenolic thermosetting plastic. Polyethylene, PVC and polystyrene are thermoplastics that soften on heating and can be reshaped repeatedly.
Malleability is the property that allows a metal to be deformed in compression into thin sheets by hammering or rolling without cracking. Ductility involves tensile drawing into wire, elasticity is shape recovery, and toughness is energy absorption before fracture.
Toughness is the ability of a material to absorb energy during impact or shock loading without fracturing. Hardness resists indentation, stiffness resists elastic deflection, and creep resistance limits slow deformation at high temperature.
Chromium is the essential alloying element in stainless steel because it forms a thin, adherent passive oxide film on the surface that protects the metal from corrosion. Nickel improves toughness and some forms of corrosion resistance, but chromium is the element that makes steel stainless.
Quenching produces a hard but brittle martensitic structure with high internal stresses. Tempering reheats the steel to a temperature below the critical range to relieve those stresses and restore useful toughness while retaining adequate hardness.
Duralumin is an aluminium-copper alloy, typically containing about 3.5 to 4.5 percent copper with small additions of magnesium and manganese. Copper is its principal alloying element and gives the alloy the strength needed for aircraft structures after suitable heat treatment.
Silicon is a powerful graphitising element in cast iron. It promotes the precipitation of carbon as graphite rather than cementite, which softens the iron and improves machinability, so silicon content is controlled carefully in grey cast iron.
Carburising is a case-hardening treatment in which low-carbon steel is heated in contact with a carbon-rich medium so that carbon diffuses into the surface. Subsequent quenching hardens the high-carbon case while the low-carbon core remains tough.
Tin-base Babbit metal is a low-friction bearing alloy containing mainly tin with antimony and copper. Its soft matrix with hard intermetallic particles gives good conformability and embeddability in plain bearings.
Fibre-reinforced plastics combine strong, stiff fibres with a lightweight polymer matrix, giving a high strength-to-weight ratio and good corrosion resistance. These properties make them suitable for boat hulls, sporting goods, and aerospace panels.
Sulphur forms iron sulphide films at grain boundaries, and these low-melting films cause hot shortness when steel is rolled or forged at high temperature. Manganese is therefore added to combine with sulphur and form harmless manganese sulphide inclusions.
In the initial linear region the metal obeys Hooke's law, and the slope of the stress-strain line is Young's modulus, also called the modulus of elasticity. This property indicates the stiffness or rigidity of the material, that is, its resistance to elastic deformation under load. Hardness, elongation and impact strength are separate properties measured by other tests.
A small addition of magnesium, or sometimes cerium, to molten cast iron makes the graphite solidify as nodules rather than flakes. This nodular graphite interrupts the metal matrix far less than flakes do, so SG iron has higher strength and ductility than ordinary grey cast iron. Silicon promotes graphite formation but does not produce the spheroidal shape.
Tungsten carbide is a cemented carbide made by bonding hard tungsten carbide particles with cobalt, and it retains high hardness even when the tool tip becomes red hot. This hot hardness allows much higher cutting speeds than plain high-carbon steel tools, which soften on heating. Grey cast iron and aluminium bronze do not have the combination of hardness and hot strength needed for cutting-tool tips.
At the eutectoid point, austenite of about 0.8% carbon decomposes on slow cooling into pearlite, which is a lamellar mixture of ferrite and cementite. The alternating soft ferrite and hard cementite lamellae give pearlite its characteristic property balance. Martensite, by contrast, requires rapid quenching rather than slow cooling.
The title block records the drawing number, title, scale, date and other identification data. Standard practice places it at the bottom right corner so that the folded sheet shows the title panel on the outside. Any other position would interfere with the drawing space or with standard folding.
In the ISO A-series, each size is obtained by halving the longer side of the previous size, so A0 is 841 mm × 1189 mm and A1 is 594 mm × 841 mm. Halving the 841 mm side of A1 gives the A2 sheet as 420 mm × 594 mm. This size is widely used for machine drawing sheets in the Higher Secondary practical work.
First-angle projection assumes that the object is placed between the observer and the plane of projection, so the plane is behind the object. The view is therefore projected through the object onto the plane. This is why in first-angle layout the top view appears below the front view and the left side view appears on the right.
A scale of 1:20 means one unit on the drawing represents twenty units of the real object. The actual length is therefore 35 mm × 20 = 700 mm, that is 0.7 m. Reducing scales with a representative fraction smaller than one are used when the object is too large to be drawn full size.
BIS line conventions reserve continuous thick lines for visible outlines and short dashed lines of medium thickness for edges that are hidden from the viewing direction. Long chain thin lines mark centre lines and pitch circles, while wavy lines are used for break lines. Keeping these conventions distinct prevents ambiguity in reading the drawing.
In the aligned system the figures are written above an unbroken dimension line and are oriented along it, so they can be read from the bottom or from the right-hand edge of the sheet. The unidirectional system instead keeps all figures horizontal and is read from the bottom only. Mixing the two systems on one drawing is not permitted.
By convention the crest of the thread is drawn with a continuous thick line and the root with a continuous thin line, both parallel to the axis of the screw. For an internal thread the convention is reversed in terms of diameters but the root is still a thin line. Hatching in a sectional view is carried only up to the crest line.
An offset section uses a cutting plane bent at right angles to pass through holes, ribs or other features lying on different planes, and all of them are then shown in one section. A half section removes only one quarter of the object and is used for symmetrical parts. Revolved and removed sections describe where the sectional shape is drawn, not a stepped cutting plane.
In an isometric projection every true length is shortened along the axes by the isometric scale factor 0.816, so the drawn length is 60 mm × 0.816 = 48.96 mm, approximately 49.0 mm. In an isometric drawing, by contrast, full true lengths are measured along the axes and the drawing is larger than the projection. Candidates often confuse these two practices.
In the hole-basis system the hole deviation is fixed as H, so the type of fit depends on the shaft letter. Shafts g and h always give clearance fits, shaft k gives a transition fit that may be either clearance or interference, and shaft p gives an interference fit. Hence H7/k6 is the transition fit among the choices given.
A conic section is classified by the angle that the cutting plane makes with the axis of the cone. When the plane is parallel to exactly one generator, the resulting curve has eccentricity equal to one and is a parabola. An ellipse requires the plane to cut all generators, while a hyperbola requires the plane to be parallel to the axis or steeper than a generator.
A cycloid is generated by a point on the circumference of a circle that rolls without slipping along a straight line. The rolling circle is called the generating circle, and the straight line is the base line. This definition distinguishes it from involute and helix curves.
Axes and lines of symmetry are shown by a chain thin line made of long and short dashes. Visible outlines use continuous thick lines, while hidden edges use dashed thin lines. Continuous thin lines are reserved for dimension lines and projection lines.
In first-angle projection the object lies between the observer and the plane of projection. The top view is therefore projected onto the plane below the object and is placed below the front view on the sheet. This is the reverse of third-angle placement.
Cut surfaces in a sectional view are shown by evenly spaced thin section lines. These hatching lines are conventionally drawn at 45 degrees to the principal outlines of the part. The angle may be varied only to suit adjacent parts or special features.
When the lateral surface of a right circular cone is developed, it forms a sector of a circle. The radius of that sector equals the slant height of the cone, because every generator from apex to base is a slant height. The arc length of the sector equals the circumference of the cone base.
A 45-degree miter line is drawn at the intersection of horizontal and vertical projection paths. It transfers depths from the top view to the side view while preserving alignment with the front view. Set squares and T-squares help draw the line, but the construction itself is the miter line.
The fillet weld symbol is a right-angled triangle placed on the reference line of a welding symbol. The vertical leg of the triangle is drawn on the left side of the symbol. A V symbol denotes a single-V butt weld, while a circle indicates an all-around weld.
In isometric projection, a circle in a principal plane becomes an ellipse. The major axis of this ellipse is approximately 1.22 times the true diameter, so for 40 mm it is 1.22 times 40, which equals 48.8 mm. The minor axis would be about 0.71 times 40, which equals 28.4 mm.
A section plane parallel to the base cuts the pyramid in a square that is similar to the base. At 20 mm above the base, the distance from the apex is 30 mm out of the 50 mm axis, so the linear scale is 30/50, which equals 0.6. The section side is therefore 40 times 0.6, which equals 24 mm.
Continuous thin lines are used for dimension lines, extension lines, leader lines and hatching. Visible outlines require continuous thick lines, hidden outlines require dashed lines, and centre lines require chain thin lines.
A diagonal scale is based on the principle of similar triangles, and it subdivides the smallest division into ten equal parts. It is therefore used to read three consecutive units, such as metres, decimetres and centimetres, together with fractions of the smallest unit.
A half sectional view is used for a symmetrical object: one quarter of the object is imagined to be removed so that one half of the view shows the section and the other half shows the exterior. This gives both internal and external details in a single view.
A section plane parallel to the base of a cone produces a circle. The radius decreases linearly from 30 mm at the base to 0 at the 70 mm apex, so at 30 mm above the base the radius is 30 × (70 − 30)/70 = 17.14 mm; the diameter is therefore about 34.3 mm.
Stress is defined as internal resisting force per unit area, so its SI unit is the pascal, equal to one newton per square metre (N/m^2). The other units describe moment, distributed load and density respectively.
Hooke's law states that within the elastic limit the stress produced is directly proportional to the strain. The constant of proportionality is the modulus of elasticity of the material.