41) Why is cast iron drilled dry ?
The cutting fluid is not necessary during cast iron drilling because the graphite in the casting reduces the friction and chips breaks easily .The mixture of cutting fluid and cutting chips may clog the drill in the hole may cause poor work finish.
42) What is immersion brazing ?
It is the process for brazing the articles in mass production.
43) What is the difference between White cast iron and Grey cast iron ?
- White cast iron : It contains 2.5 to 3% carbon in combined form. This is very hard and brittle and difficult to be machined. It is used for lower quality castings where hard coating is required.
- Grey cast iron : It contains 3.25 to 3.75% carbon in free state or graphite. It has better machinability .It is generally used to make machine beds and frames ,brackets, cylinders pipes etc.
44) What is High carbon steel ?
It contains 0.715 % carbon. HCS is harder ,stronger, less ductile and can be hardened and tempered. It is mainly used for making chisels, files, dies, drills ,taps etc.
45) What are the different alloying elements and their effects on the properties of the steel ?
- Cobalt: It gives excellent magnetic property and improves the cutting quality of the steel.
- Chromium: It gives greater hardness and resists corrosion and forging.
- Molybdenum: It gives greater hardness and resistance to drawing and forging.
- Nickel: It lifts the tensile strength, improves wearing property and protects from corrosion.
- Tungsten: It gives fine grain structure, greater hardness and cutting toughness.
- Vanadium: It gives cutting toughness resistance to wear and tear and greater hardness.
46) What is the difference between Metal and Alloy ?
- Metal: Metal is a substance which is manufactured after purifying the iron ores with limited properties. All metals are found in solid form except mercury.
- Alloy: It is the combination of two or more metals and has special properties depending upon the quality of alloying elements. Commonly found in solid form.
47) What is Soldering ?
It is a process of joining two or more metal pieces by using solder.
48) What do you mean by Mild steel ?
It contains 0.05 to 0.25% of carbon. M.S is ductile, malleable and easy for forging, welding. Mainly used to make sheets ,rods ,wires ,flats, round angles channels and other structural works.
49) What is the material of gears ?
The material of gears should be selected according to the capacity and nature of work. Gears are generally made of cast iron, bronze, tool steel, chromium steel , alloy steel etc.
50) Explain briefly the rates of contraction of different metals and alloys ?
Generally following rates of contraction are considered, Steel2%,Cast iron1%,Aluminium 1.8%,Brass 1.4%