All machines used in accomplishing the different processes in the textile industry requires electric motors as their drives. Special environmental, operating and drive conditions demand specially designed motors for the textile industry.
Cotton to Slivers
There, they are opened and the impurities are picked up and removed in the blow room. After further opening and cleaning, cotton is transformed into laps and fed to the carding section.
Here it is opened completely and is converted into slivers. The slivers are gathered in cans and then processed on a drawing machine, which makes them uniform by, straightening the fibre.
The slivers are then changed into lap form before feeding them for combing, which parallels the fibre and upgrades it.
The sliver at this stage is in a fragile condition and is also bulky. After reducing the diameter in two or three stages, it is processed on speed frame, which makes it suitable for final spinning.
Before the yarn is actually woven, it is ‘warped’, i.e., made into a uniform layer. Weaving consists of joining two sets of threads, one which extends throughout the length of the fabric and the other whose threads go across. This process is done in a loom.
This consists of a number of processes like bleaching. Dyeing, printing, calendaring, stamping and packing. The impurities like oil and grease are removed and the fabric is made white during bleaching.
Dyeing involves giving a color or shade to the cloth. Printing produces designs and patterns in multicolor.
Motors Used for Different Textile Processes
All machines used in accomplishing the different processes described above require electric motors as their drives. So that different types of textile machinery (i.e. loom, card, ring frame) need a different kind of motor.
1 Loom Motors
In order to accomplish the ‘pick up’ progress in a short time, the starting torque of the loom motor should be high. The loom being essentially a reciprocating mechanism causes both torque and current pulsations.
Also, loom motors are subjected to frequent starts and stops. These result in higher temperature rise and is taken care of by having good thermal dissipation capacity of the motor.
Loom motors are either totally enclose or totally enclosed fan cooled three phase high torque squirrel cage induction motors, Presence of a lot of fluff in the atmosphere requires a smooth surface finish of the housing and end shields so that the fluff does not get collected on the surface of the motor.
The insulation of the motor must be able to withstand high moisture content.
The ratings of the motors used for driving looms for light fabrics such as cotton, silk, rayon, nylon, etc. are 0.37, 0.55, 0.75, 1.1 and 1.5 kW, while those of the motors used for making heavy fabrics (wool and canvas) are 2.2 and 3.7 kW. They are usually of 6 or 8 poles.
2 Card Motors
The general requirement of card motors is almost similar to that of loom motors except that the former are required to have a very high starting torque and must be able to withstand a prolonged starting period.
Both the above requirements for the card motor are due to the very high inertia of the carding drum. Once the drum is started, the operation is continuous and interrupting, unlike that of a loom, where frequent starts and stops are involved.
The commonly used drives for card motors are again totally enclosed and totally enclosed fan cooled three phase high torque squirrel cage induction motors.
The usual ratings of motors for cards of light fabrics are 1.1 and 1.5 kW and those for cards of heavy fabrics are 2.2, 3, 3.7 and 5.5 kW. Here again, the preferred synchronous speeds are 750 and 1000 rpm.
3 Spinning Motors
For good quality spinning, it is essential that the starting torque of spinning motors should be moderate and the acceleration should be smooth.
If the starting torque were low, the tension of the yarn would be insufficient and hence the yarn would get entangled and break. If the starting torque were high, the acceleration would be high and the yarn would snap.
In general, three types of drives are used for spinning frame operation: single speed motor, two-speed motor and two motor drive.
Normally, a 4 pole or 6 poles squirrel cage induction motor is used as a single speed drive.
In order to maximize production with minimum breakage, two-speed motors (4/6 or 6/8 poles) are used. Although those motors would be larger in size and costlier, the increased production may compensate for the additional initial outlay.
In the case of two motor drive, two separate motors are used to drive the common pulley of the ring frame. Although this drive is costlier and requires more space, it has the following advantages:
1 Any desired speed differential can be got by adjusting the speed ratios.
2 The tension of the yarn can be adjusted independently.
3 Production can be continued even when one of the motors fails.
Totally enclosed fan cooled motors ranging from 5-30 kW are used as spinning motors.
From what has been discussed above, it is clear that some form of controlled-torque starting of textile machinery drives is imperative.
Proper starting will minimize yarn breakage, improve the quality of the product and increase the life of the machine. Less downtime obtained will also increase production.
The most common electrical method of controlled-torque starting involves the use of standard squirrel cage motors and different methods of applying reduced voltage to the motors during a selected starting period.
One of the most effective methods of controlling the stator voltage of motors used in the textile industry is that of using series reactors. This method gives stepless, closed transition increase to approximately full speed.
Since the motor terminal voltage is a function of the current drawn from the line, during acceleration the motor voltage will increase as the line current decreases, resulting in greater accelerating energy at the higher speeds and no significant pull on the yarn being processed.
Reactors with fixed tapings may be used to get a variety of starting torques. Variable iron-core inductors offer almost infinite choices of starting torques.
Since the normal starting time is limited to a few seconds, the effect of poor power factor during starting on the overall plant power factor is not appreciable.
Although primary resistor starting has all the advantages of reactor starting, it has not proved practicable, for textile plants because of the possible fire hazards when the resistors get overheated during frequent starting.
With the ever-increasing use of solid state devices, nowadays, regulators are being used to provide control of starting torque.