Textile Mills
—They are classified into following types
—Cotton
mills
—Woolen
mills
—Dying
and finishing plants
—Knitting
mills
—Rayon
and synthetic fiber mills
Motors Used In Textile Industries
Normally totally closed fan cooled motors
are used in textile mills. Drip proof motors are used in wet locations.
— Loom Motors
Loom motors are used for picking up of
cotton in short time and are designed to have a high torque. These motors
should have a starting torque of 230% of rated torque and pull out torque of
270% of the rated value. Recommended number of poles for such motors are 6 to
8. for light fabrics such as cotton, rayon or silk kw requirement of loom may
vary from 0.37 to 1.50 and for heavy fabrics from 2.2 to 3.7.
—Card motors
They are similar to loom motors but
possess still higher torque i.e. starting torque of order of 350% and 275% 0f running torque and a pull out torque of
375% and 300% of running torque for 8-pole and 6-pole motors respectively. The
card drum is a heavy mass and possess a high moment of inertia. The motor
therefore undergoes a prolonged starting time and a starting currant of 2.5
times the rated current for nearly 2 minutes.
—Spinning Motors
These motors are required to make threads
i.e. Final drawing, twisting and winding of cotton. They must possess smooth
acceleration to avoid breakage of threads. They are recommended to have a
starting torque of 150-200% of running torque and pull out torque of 200-275%
of running torque. Usually smooth acceleration is required because faster
acceleration may cause more breakage and small acceleration may cause knots in
yarn as a result of insufficient tension.
—In paper mills, pulp making and paper
making are the two main processes that take place. The drive required for
larger grinders involved in making pulp is provided by large motors 3000-4000
kw in size.
— Paper formation involves formation of
sheets, removal of water from them and pressing followed by reeling. Both A.C.
and D.C. drives are used for paper making machines. In D.C. drives speed of
paper machine is controlled by changing the armature the armature voltage of
separately excited D.C. motor.
Sugar Mills
— Sugar mills are driven by variable speed
induction motors. Eddy current drives are generally used. When the juice is
extracted remaining matter is known as bygasse. Variable speed motors are used to drive conveyors. The juice is then evaporated
through boiling stages to get sugar crystals.
— Bygasse is used to produce steam in the boilers.
The generation of electricity using bygasse bring down the cost of production of
sugar.
Speed Control In Sugar Mills
—For separating crystals from syrup
centrifugal pumps are used. These centrifuges are run by variable speed
induction motor having two distinctly set of stator windings.
— The motor is connected for regenerative
braking to return energy to supply. This is done by connecting the motors from
high pole to low pole operation.
— The motors used have an insulation which
can withstand the humidity of surroundings.
Cement Mills
Port land cement is a mixture of oxides
of calcium 60-66%, silicon 20-24%, aluminum 4-6%, and iron 2-3% in various
composition. Raw materials used are lime stone, marble, chalk e.t.c.
During manufacture, grinding and proptioning the raw materials which are sent to
rotary kilns and brought out white heat. The resulting clinker and retarder
like gypsum are pulversied
together to form finished port land cement.
Two methods are used for preparation of
cement i.e. Dry and Wet process.
Motors Used In Cement Mills
— Squirrel cage motors are used because of
their low cost and ruggedness and where constant speed is required. Slip ring
motors are used where high starting torque is required and low starting current
is in use for crushers and hammer mills.
— Adjustable speed D.C. motors are used
for greater speed range and close speed control in kilns. All these motors are
dust proof and place where moisture from precipitation Is present totally
enclosed motors are used.
Motors For Mining Industry
—Pumps
Centrifugal pumps are used for removing
water from any depth ground level. Pumps used are driven by squirrel cage motor
which possess low starting torque.
— Ventilating
Fans
They are used for proper working in mines
and are made of synchronous or induction motor.
—
Drilling Motors
These are generally induction motors with
flame proof enclosures. Sometimes high frequency (150 to 200 Hz) motors are
used to drive drills. These drills have reduced size and high power.
—Coal Cutting
Coal cutting is done by coal cutters fitted
with squirrel cage rotor provided with flame proof enclosures. In case of D.C.
supplies compound motors with interpoles are employed. Coal cutting in a big
block of coal facilitate introduction of explosives to break up big blocks of
coal.
— Conveyors
Conveyors are driven by squirrel cage
motors which are totally closed with flame proof materials.
No comments:
Post a Comment