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What is the composition of following alloys ? What are their special characteristics and what for these are used ?

(i) Permalloy, (ii) Invar, (iii) Elinvar, (iv) Platinite, (v) Dumet wire. Ans. (i) Permalloy has 78.5% nickel. It has a high permeability and low hysteresis loss. (i) Invar contains 36% nickel and has an exceedingly low coefficient of linear expansion. Since its expansion is proportional to the temperature within limits of atmospheric temperature change, it is used for secondary standards of length. (ii) Elinvar contains 32% nickel with small percentage of Cr, W, Mn, Si and C. In addit

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What are the important characteristics of various tool steels and what is the criterion for their selection.

Since plain carbon steels are cheapest and easiest to fabricate; first attempt should be to select the material from this category. The next choice should be for oil-or air-hardening steels which have better wear resistance than plain carbon steel but toughness is not good. These offer maximum safety in hardening and minimum dimensional change after heat treatment. These are preferred for dies with adjacent thin and thick sections, sharp corners, or numerous holes. These are, however, not suited

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What is the difference between sheet and strip?

(a) What is the difference between sheet and strip? (b) What are the characteristics of cold rolled sheets ? (c) What do you understand, by (i) orange-peel effect, (ii) stretcher strains or Luders' lines ? (d) Define (i) temper rolling, and (ii) aging in steel.   (a) The difference between sheet and strip is based on width and is arbitrary. (b) Cold working produces a better surface finish, improves the mechanical properties, and permits the rolling of thinner gauge mat

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Write a brief note about weldability of various types of cast irons.

Grey cast iron can be welded with oxyacetylene gas or with electric arc with special precautions (preheating in case of gas welding and post heating in arc welding) to avoid cracking in welding area. Welding of gray iron is usually restricted for repair work. Braze welding with bronze or nickel copper, is however, used for fabrication also. Malleable irons are not considered weldable. It is repaired by brazing, preferably silver brazing. Ductile cast iron needs special considerations i

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What do you understand by vacuum casting and when it is used ?

Ans. It has been observed that hydrogen (even as low as 5 ppm) causes internal flakes in large steel sections, and by pouring the liquid steel in vacuum chamber, it is possible to reduce hydrogen content to 1 ppm. Such vacuum castings are used extensively for large forgings such as electrical rotors. Sometimes to reduce oxygen content to 0.001%, carbon deoxidation is carried out by removal of oxygen as carbon monoxide. This treatment substantially decreases the number of non-metallic inclus

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What are the differences between hot-rolled steels (HRS) and cold rolled steels (CRS)?

Hot-rolled steels contain an oxide scale over their surface. It is formed during the heating process. Accordingly dimensional tolerances are not tight. In cold-rolled steels, the scale is removed before cold rolling process and thus the surface finish is very good in this case. Thus its dimensions are held within closer tolerances. Low-carbon cold rolled steels are easier to machine.

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Describe the following alloy steels : (a) Case-hardening steels (b) Nitriding steels

Describe the following alloy steels : (a) Case-hardening steels (b) Nitriding steels (c) High-tensile steels (d) Wear-resisting steels (e) Corrosion-resisting steels (f ) Heat-resisting steels.    (a) Case hardening steels-These usually contain less than 0.15% carbon. As carbon content is low, the core does not respond to hardening. By adding about 3% nickel and 0.45% manganese, these do not require further refining after carburising. Such a steel can be water-quenched and is used for

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What do you understand by killed steel?

(a) What do you understand by killed steel? (b) What is 'piping' in steel and how it can be minimised ?   (a) Steels in which no gas evolution occurs on solidification are called killed steels. (b) When the steel cools in the mould, shrinkage of the steel on solidifying causes 'piping usually in the upper portion of the ingot. This can be minimised by using a large-end-up mould with a refractory 'hot top' which supplies molten steel to the main body of the ingot while solidificati

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Distinguish between plain carbon steel and alloy steel

(a) Distinguish between plain carbon steel and alloy steel. (b) How the mechanical properties of an untreated plain carbon steel are influenced by increase in the carbon content ?   (a) Plain carbon steel is one which owes its distinctive properties chiefly to the carbon it contains. An alloy steel is one which owes its distinctive properties chiefly to some element or elements other than carbon, or jointly to such other elements and carbon. The other elements are deliberatel

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What do you understand by steel?

(a) What do you understand by steel? (b) What is the difference between hypo-eutectoid and hyper-eutectoid steels ? (c) How the plain carbon steels are classified depending upon carbon content ?   (a) Steel is a malleable alloy of iron and carbon, usually containing substantial quantities of manganese. b) Hypo-eutectoid steels are those which contain less than approximately 0.9% carbon whereas hyper-eutectoid steels contain more than 0.9% carbon. (c) The plain carbon steels a

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Give the ages of carbon in (i) low carbon steels, (ii) medium carbon steels...

(a) Give the ages of carbon in (i) low carbon steels, (ii) medium carbon steels, (iii) high carbon steels. (b) Give the %age of the alloying elements in (i) low alloy steels and (ii) high alloy steels. (c) All cast irons contain at least six elements. Name these elements. (d) When will you recommend carburising of steel ? Give salient features of the process. (e) Give the composition and use of (i) Bronze, (ii) Duralumin.   (a) Carbon in low carbon steel : < 0.25%, me

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Sketch and discuss the defects in a lattice structure of a crystalline material.

Defects in a lattice structure of a crystalline material are : (i) Point Defect. It occurs when an imperfection is restricted to the neighbourhood of a lattice point. Fig. 1.16 illustrates the three different types of point defects. In Fig. 1.16 (a) one lattice atom is missing, creating a vacancy. Since an atom vibrates about its lattice position, the tendency of the atom to jump out of its regular position creating a vacancy increases rapidly with temperature. It is possible to i

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Correction To Mass On Multiple Spring Supports

Mechanics Corner A Journal of Applied Mechanics and Mathematics by DrD, #48-B                                                                               Correction To                                                           Mass On Multiple Spring Supports   Correction The previous post, #48 titled Mass on Multiple Spring Supports had several typographical errors. Strangely, they are all in the brief introductory example regarding the loads on the four legs

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