1. Lubrication (Tribology)
Old Ans.
Lubrication: The principal of supporting a sliding load on a friction reducing film is known as lubrication. The substance of the which film is composed as a lubricant and to apply it is to lubricate. These are not new concepts, nor, in their essence, particularly involved ones.
Moden machinery has many times more complicated and the demands placed upon the lubricant have become propotionally more exacitng. Though the basic principle still prevails - the prevention of metal to metla contact by means of an intervening layer of fluid or fluid like material- modern lubrication have become a complex study.
Basically, lubrication is governed by one of two principles: hydrodynamic and boundary lubrications. In the former, a continious full-fluid film seperates the sliding surfaces. In the latter, the oil film is not sufficient to prevent metal to metal contact.
(Practical Lubrication for Industrial Facilities, Heinz P. Bloch, pg. 1, 3)
New Ans. -better-
In any engine, a number of its parts move in order to transmit some kind of energy or perform some work. These movements are accompanied by the liberation of heat due to friction between moving partsi and therefore lessens the effeciency of the machine. This is a great problem that must be overcome by machine designers and builders.
The solution to this problem is lubrication, which involves the application of oil between the sliding surfaces to minimize friction. Proper lubrication can only be attained by selecting the right kind of oil for a definite application. This may be done by considering the size of bearings, pressure, speed of the shaft, clearances, and operating temperature.
...
If the rubbing surfaces are seperated from each other by a thin film of lubricant, the friction encountered is known as boundary or greasy lubrication.
...
When the rubbing surfaces are seperated by a fluid film and the load on the surfaces is wholly carried by the hydrostatic pressure in the film, the friction is known as complete or viscous lubrication.
(Nino E., Industrial Lubrication, p.1)
2. Transverse Cracking (welding)
Old Ans.
Transverse Cracking
Transverse cracks in weld metal formed when predominanr contraction are in directionof the weld axis They can be hot cracks which seperates intergranularly as the result of hot shortness or localized planar shrinkage, or thet can be transgranular separations produced by stresses exceeding the strength of the material. Tranverse cracks lie in a plane normal to the axis of the weld. and are usually open to the surface. They usually extend across the entire face of weld and usually open the surface. They usually extend the across the entire face of weld and sometimes porpagete into the base metal.
Tranverse cracks in base metal occur on surface in or near the HAZ. They are result of the high residual stresses induced by thermal cycling during welding. high hardness excessive restraint and the precense of hydrogen promote theri formation. Such crack propoganete ino the weld or beyond the HAZ into the base metal. as far as needed to relive the residual stresses.
Steve Lampman,ASM International, Weld integrity and performance: a source book adapted from ASM international
Transverse cracks in weld metal formed when predominanr contraction are in directionof the weld axis They can be hot cracks which seperates intergranularly as the result of hot shortness or localized planar shrinkage, or thet can be transgranular separations produced by stresses exceeding the strength of the material. Tranverse cracks lie in a plane normal to the axis of the weld. and are usually open to the surface. They usually extend across the entire face of weld and usually open the surface. They usually extend the across the entire face of weld and sometimes porpagete into the base metal.
Tranverse cracks in base metal occur on surface in or near the HAZ. They are result of the high residual stresses induced by thermal cycling during welding. high hardness excessive restraint and the precense of hydrogen promote theri formation. Such crack propoganete ino the weld or beyond the HAZ into the base metal. as far as needed to relive the residual stresses.
Steve Lampman,ASM International, Weld integrity and performance: a source book adapted from ASM international
New Ans. -better-
Transverse cracks
A less common type of crack known as transverse cracks shows up across the weld, 90 degrees to the length of the bead. Transverse cracks can be caused by too much hydrogen in the weld bead. The second cause is using filler metal with a much higher tensile strength than the base metal. For example, using an E11018 electrode as your filler metal (110,000 psi tensile strength) to weld A36 steel (36,000 psi minumum tensile strength).
(Bridigum T., How to Weld, p. 52)
3. Polyester Glass (Material)
Old Ans.-better-
Polyester glass : It is type of common plastic.Its properties are extremely tough, high dielectric strength, heat resistant, low water absorption, antitracking electrically,self-extinguishing, machinable. Typical uses are insulators and bus braces, switch phase barriers, general electrical insulation, mechanical insulated push rods for switches and breakers, contact blocks, and terminal blocks.
(McGraw-Hill Machining and Metalworking Handbook-3rd Edition-McGraw Hill-Ronald A. Walsh-Chapter 4-P.264)
New Ans.
The woven or matten glass-fiber cloth reinforcement in polyster laminates is commonly described in literature by the two words fiber glass. The polyster-glass cloth laminate so produced is also called fiberglass, one word, and this is a common usage among artists, builders, and craftspersons.Fiberglas is a trade name of the Owens-Corning Fiberglas Corporation of Toledo,
(Andrews O., Living Materials: A Sculptor's Handbook, p.149)
4. Flowability (Manufacturing)
Old Ans.
Flowability
It is that property of the metal powder by virtue if which it flows readily, uniformly and rapidly into the die or mould cavity. It governs the time required to fill a die or mould and the rate of production. The shapes of the particle, size and its distribution, coefficient of inter-particle friction and the absorbed moisture are the factors affecting flowability. Coarse and spherical particle possess good and maximum flowability whereas fine and irregular particles have poor as well as reduced flowability respectively.
New Ans.-better-
Flowability of moulding sand refers to its ability to behave like a fluid so that, when rammed, it will flow to all portions of a mould and pack all-round the pattern and take up the required shape. The sand should respond to different moulding processes. High flowability is required of a moulding sand to get compacted to a uniform density and to obtain good impression of the pattern in the mould. Good flowability is very essential where energy for compaction during ramming is transmitted through the sand mass as in machine moulding. Flowability increases as clay and water contest increase.
(Elenchezhian C., Manufacturing Technology-I, p. 20)
5. Sintering Ability (manufacturing)
Old Ans.-better-
Sintering Ability (17:30)
The characteristic of a metal powder which provides and promotes adhesion between all the particles, on sintering at controlled temperature is known as sintering ability. It should be sufficiently high for the successful production of parts. Irregular and spherical shaped particles possess good pressing and sintering properties.
(Manufacturing Process, Yazar: S. K. Sharma, Savita Sharma, Page: 235)
The characteristic of a metal powder which provides and promotes adhesion between all the particles, on sintering at controlled temperature is known as sintering ability. It should be sufficiently high for the successful production of parts. Irregular and spherical shaped particles possess good pressing and sintering properties.
(Manufacturing Process, Yazar: S. K. Sharma, Savita Sharma, Page: 235)
New Ans.
20.3.10 Ability to be Sintered
It is the property of the metal powders due to which they do not require too narrow a temperature range for the purpose of sintering. Every metal powder has a good sintering ability. A metal powder having good sintering ability possesses good bonding among its particles, and consequently results in better mechanical and physical properties of the product.
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