Building Material (Part-III) (GENERAL ENGINEERING) (SSC JE)

 Annual rings :

• These are concentric layers of wood known as growth rings or annual rings.

• During growth season, the wood added during the early part is different from the wood added during the late part.

• The early wood is softer, coarser and more porous than the late wood.

• Growth rings are apparent because of this difference between the early wood and the late wood.

When ordinary Portland cement hydrates it emitted heat because Hydration of OPC is exothermic reaction.

Exothermic reaction are reaction or process that releases energy usually in the form of heat or light.

 Glass–

• Glass is an inorganic solid material that is usually transparent or translucent as well as hard, brittle and impervious to the natural elements.

• Cooling molten glass increases the viscosity of glass.

• Rapid cooling results in the formation of fragile glass.

• Annealing results in the formation of transparent glass.

• Glass is a good thermal insulator.

Bitumen paints–

• This type of paint is manufactured by dissolving asphalt or vegetable bitumen in oil or petroleum.

• It is black in colour.

• It used over iron works under water

Cobalt–

• Cobalt is the binding material in cemented carbide.

• Cemented carbide is also called cermets, its constituent tungsten, titanium, tantalum.

• Cemented carbide manufactured by powder metallurgy.

• Its temperature from 900ºC to 1000ºC and cutting speed 150-200 m/min.

• These tool materials much harder are chemically more stable, have better hot hardness, high stiffness, and lower friction and operate at higher cutting speeds than HSS.

Continuous chips– Formed during machining of ductile materials at high speed.

 Favorable conditions for this type of chip to be formed are–

• Ductile material

• High cutting speed

• Large cutting angle

• Low depth of cut

• Proper use of coolant and lubricant

Difference between soft wood and hard wood–

Facing sand–

• A sand used for facing of the mould is called facing sand.

• It is specially prepared sand from silica sand and clay, without the addition of used sand.

• The thickness of layer of facing sand in a mould ranges from 20 to 30 mm and is used directly next to the surface of the pattern.

• Ground-Granulated blast furnace slag have self-cementing property.

• Portland slag cement is produced by inter-grinding cement clinkers, hard-burnt gypsum and granulated blast furnace slag in specified proportion.

Vicat apparatus–

• Vicat apparatus is a penetration device used to testing of hydraulic cement and similar materials to determine their normal or standard consisting.

• It is also used to determine the initial setting time.

• Needle with collar is used for final setting time.

• Plunger is used for standard consistency.