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Lubrication means apply of
lubricating element at right position, right amount and right time. In case of
bearing lubrication is very necessary to minimize the bearing resistance,
frictions and power losses.
Purpose of lubrication:
ØTo reduce the sliding frictions.
ØTo remove heat from contact surfaces.
ØTo prevent corrosions.
ØTo keep contaminants out of surface.
The elements which
are used for lubrication are known as lubricant. There are mainly two types of
Properties of good lubricants:
ØHigher wear resistance
ØHaving unbroken film
ØTransparent and chemically stable
ØRemoves heats from contact surface
ØRemain stable under several operations
Lubricant selections: It depends upon the parameters –
It is used for light and moderate
loads operating at high speed with 30oF – 200oF.
ØPower transmission equipments
Grease is a mixture of
lubricating oil and thickening substances like soap, graphite etc. It is used
at low temperature under heavy loads. It also prevents the dust particles and
It depends upon the factors-
Hardness is expressed in terms of
number. Higher the number indicates higher hardness.
Generally greases are classified
When number = 6, then most hard
When number = 0, then softer.
Softer grease is easy to apply
anywhere and more efficient.
Relation with temperature:
vGrease life becomes half with every 25oF
vGrease life becomes double with every 25oF
The equivalent circuit of a four point – pole dynamo with a simplex winding.
The voltage induced in each path is assumed to both to be same and should be if
the reluctance of each magnetic path is the same, so that the lines of flux cut
by each inductor of each path are the same. However wear of the bearings or
deflection of the armature shaft may cause the armature to be closer to some
poles and farther from others, thus changing the length of the air gap, and
therefore the reluctance of the magnetic circuits of the poles is not
identical. This factors cause the voltage in the materials making up the
magnetic circuit. These factors cause the voltage in each parallel path differ,
and the unequal voltages in turn cause flow of a circulatingcurrent through the windings and brushes ,
undue heating of the armature and waste the power. To reduce the circulating
current, points on the winding which should be at the same potentials are
brought to the same potentials by connecting them with …
A steam boiler is usually a closed vessel made of steel. Its function
is to transfer the heat produced by the combustion of fuel to water and
ultimately to generate steam. Types of boiler: 1. Fire tube or smoke tube boiler 2. Water tube boiler
Figure: Boiler Fire tube boiler:
In fire tube steam boilers, the flames and hot gases, produced by the
combustion of fuel pass through the tubes which are surrounded by water.
Fire tube boilers are generally used for relatively small steam
capacities and low to medium steam pressure. As a guideline fire tube
boilers are completive for steam rates up to 12000kg/h and pressures up
to 18 kg/cm².Fire tube boilers are available for operation with oil, gas
or solid fuel.
Figure: Vrious parts of boiler Example: Cochran boiler, Locomotive boiler, Scotch marine boiler, Velcon boiler, simple vertical boiler.
Progressive die: The dies which performed two or more
operations at different stages every time the ram descends is known as
Progressive die. The principle advantage of Progressive die is in the number of
operations that can be achieved with one handling of the stock strip. The main
disadvantage is that work pieces may become “dished” as they pushed through the
die as they generally have very little support.
Compound die: A compound die differs from a progressive
die in that it performs two or more cutting operations during one stroke of the
press at one station only.
Compound dies are slower in operation than progressive dies but they
have advantages for certain jobs, especially where tolerance are close (1)the cutting operation, by the action of the
knockout plate ,ensures flatness of the blank.2 Large parts can be blanked in a
smaller press if compound dies rather than progressive dies areused. Combination dies:A die
in which a cutting operation is combined with a noncutting operation …