2. Roving

2.3Builder Mechanism-Part I

Builder Motion :

Builder motion is used to wind the roving in a parallel wound package with conical ends as shown in Figure 1. The package is formed layer by layer. The lift of each layer is shortened by a small length which decides the taper angle .The animation A1 demonstrates the basics of formation of the roving package.

Figure 1. Roving package

The rovings are wound in coils around the bare bobbin to start with. The winding of coils starts from the bottom position determind by the position of the bobbin rail. As the bobbin rail moves up the coils are wound upwards forming the first layer of rovings on the bare bobbin. After reaching the top position of the lift for the first layer, the bobbin rail reverses the direction of movement and starts to move downwards. Now the coils are placed downwards and second layer of roving are wound on the first layer of rovings. This time the bobbin rail does not go all the way to the starting point of the first layer. Instead, it returns and start to move upwards from a level just above the starting level of the first layer, the difference in these levels is called as shift (S). The third layer of roving is wound over the second layer of rovings upwards. Again the bobbin rail does move all the way up to the starting level of the second layer but returns from a level just lower by S and starts forming the fourth layer. The distance S decide the taper angle. Higher is S, smaller will be .

The roving can be wound onto the bobbin using either Flyer lead method or Bobbin lead method.

Flyer Lead

Flyer surface speed is faster Flyer winds the roving on the bobbins surface

Bobbins Lead

Bobbins surface speed is faster Bobbins winds the roving onto itself

Advantages of Bobbins Lead

In case of roving break, the direction of roving on the bobbins provides stable outer layer The drive to the spindle is shortest hence it starts faster than the bobbins. This leads to more roving breaks in flyer lead while staring.

Figure 2 : Spindle speed and Bobbin speed for different Winding methods

In both the cases, the spindle speed remains constant through out the winding process, since changing the spindle speed will change the twist density in the roving. The bobbin speed is changed according to the requirement. Figure 2 shows the manner in which the bobbin speed has to be changed in case of bobbin lead and flyer lead methods.

In both the cases, the roving delivery speed is constant decided by the surface speed of the front pair of drafting rollers. But, as the bobbin builds up the diameter and the circumference of the bobbin increases. If the bobbin rotates at a fixed speed, then the roving will get stretched more and more in case of bobbin lead method since the bobbin is leading and winding the roving on to itself as the winding proceeds; the roving will get slackened more and more in case of flyer lead method as in this case the flyer is leading and winding the roving onto the bobbin. The difference between the peripherals speeds of the flyer and the bobbins needs to be kept constant for proper winding.

Hence, in case of bobbin lead method the bobbin speed has to be gradually decreased and in the case of flyer lead the bobbin speed has to be gradually increased in order to keep the roving tension constant while winding the rovings on the bobbin.

For cotton system, because of the advantages of bobbin lead method and the difficulties associated with flyer lead method, the bobbin lead method is always used.

Flyer Lead

Flyer surface speed is faster Flyer winds the roving on the bobbins surface

Bobbins Lead

Bobbins surface speed is faster Bobbins winds the roving onto itself

REQUIREMENTS FOR BOBBIN BUILDING :

Based on the above discussions, in order to have proper winding of the rovings on the bobbins, the following requirements should be met:

The rotational rate of the bobbin should be reduced for layer formation

Shorten the lift after each layer to form tapered ends on the bobbin

Reverse the direction of movement of the bobbin rail after each layer formation

The speed of the movement of the bobbin rail should be reduced after formation of every layer, as it will take more time to lay one coil as the bobbin builds up.

Drive system in Roviing Frame :

Figure 3 : Typical drive system in a roving frame

The main shaft received the drive from the motor and rotates at a constant speed. It provides the constant drive to the differential gear assembly, top cone, drafting system and the spindle as shown inFigure 3. The bobbin rails gets it motion directly from the bottom cone drum. The bobbins get their drive from the output of the differential drive which combines the fixed speed from the main shaft and the variable speed from the bottom cone drum. The operating principles of cone drums and the differential drive are explained below.

Cone drive transmission:

The reduction in the rotational rate of the bobbin and the reduction in the speed of movement of bobbin rail are obtained with a cone drive mechanism. In this mechanism, shown in Figure 4 there are two cone drums out of which the top cone drum receive a constant rate of rotation from the motor. Depending up on the position of the drive belt between them, the speed of the bottom cone drum changes. Hence, at any given position of the belt the sum of diameter of the top cone drum (d1) and diameter of the bottom cone drum (d2) should be a constant.

Cone Profile

Variation in bobbins rotation rate occurs in small steps owing to shifting of the cone belt after each lift stroke

Where K is the delivery rate, D is the diameter of the bare bobbin, dris the diameter of the roving, and ntis the numbe of roving wound.

The bobbins winding speed reduces in a hyperbolic fashion as the bobbins building up. If the shifting of belt is constant for each lift stoke then the cone profile should be

(i) Convex for top (driving cone)

(ii) Concave for bottom (driven cone)

Figure : 4 Cone belts shifting mechanism

Top cone drum rotates at fixed speed of U1rpm. Speed of bottom cone drum depents upon D1and D2which depend on L.

Moving belt in direction X increases U2

Moving belt in direction Y increases U2

Figure 5 : Differential gearbox mechanism

Figure 5represents speed of flyer and wind-on speed with differential gear box. Over the cone pulleys belts are shifted, due to which differential speed is obtained from differential gear box as U output = U1 U2rpm.

Figure 6 : Principle of winding on roving bobbin

Winding Speed profile

Let us take the following parameters and calculate the winding speed for different bobbin diameters and plot it.

Bare bobbin dia=50mmSpindle speed=1000 rpm

Roving =1.2 mmTPI =1.68

Delivery = 15 m.min

Figure 7 : Effect of bobbin diameter on winding speed

Figure 7represents relationship between winding speed and bobbin diameter. As the diameter of the package increases, winding speed is decreases to maintain the same same winding rate.

2.4Builder Mechanism-Part II

BOBBIN DRIVE

The continuously reducing rotational rate from the bottom cone drum is combined with the constant speed of main shaft using a differential mechanism. The output of the differential gear mechanism is provided to the bobbins which are housed in the bobbin rail which is moving up and down. Since the bobbin rail is moving up and down, there is a need for a flexible drive. One example of such drive known as knee swinging joint is shown inFigure 1.

Figure 1 : Swinging knee joint at the bobbin drive shaft

The swinging knee joint method causes additional revolutions that are either added or subtracted from the basic package rotation, depending on the direction of the lift stroke. This leads to tension variation. On the bobbin rail, bevel / helical gears fixed on the longitudinal shaft drive the bevel / helical gears of the bobbin support.

The other method is to use chain and sprocket with suitable mechanism to adjust the varying tension in the chain because of the movement of the bobbin rail.

Cone drum types and belt shifting:

The cone drums can be of two types. In first type which is conventional one, a pair of convex and concave cone drums are used and in second type a pair of cone drums having straight surface is used. In the first type, the belt is moved a constant length every time to get the required speed profile for the bobbin. In the second case, the belt is shifted through different lengths through out the bobbin build up.

Figure 2 : Shifting the belt with hyperbolic and straight sided cones

Hyperbolic cones are difficult to design (Figure 2). During the winding operation the belt is moved on surface of varying inclination. To-day the cones are made straight sided. The belt is shifted through varying magnitude. The initial steps being relatively large and later ones smaller. Instead of hyperbolic profile on the cones (left side), an eccentric is used in the belt shifting mechanism.

Shifting of the Belt:

Shifting of belt is under the control of ratchet wheel, which is permitted to rotate by half tooth for each lift stroke

This half tooth movement is transferred to the cone drum belt through gear train, changes gear and wire rope.

The bobbin diameter increases depending on the roving hank the change wheel Tension change wheel is provided in the gear train to accommodate the changes in the roving hank.

Shifting and Shorting of cone belt :

Metal brackets (3/7) and rods (5/6) induce all changes for the bobbin building mechanism.

Figure 3 : The reversing gears of the lifter motion

The mechanism is fixed to the bobbin rail and raised and lowered as a unit.

Striking of a stationary pin by rods (5/6) makes the micro switch to emit a pulse, which permits the ratchet wheel to rotate by tooth (Figure 3).

Correction Rail:

Useful when the required bobbin speeds are not attained by changing the change wheel only. Normal position of this rail is parallel to belt guide. If this rail inclination is more steep, the extension of the wire rope is not completely transferred to the belt guide. Shifting of the belt taken place through smaller steps than those corresponding directly to paging out of the rope in the builder motion. Reverse effect if the rail inclination is made less steep

Figure 4 : Reversing mechanism for bobbin rail movement

FromFigure 4, reversal of the rail movement originates from the reversing gear (1/2/3).

An electrically operated valve pressurizes the left and right chambers of the double acting cylinders alternatively.

So that, the left hand clutch (1) and right hand clutch (2) are operated successively so that the pinion (3) is meshed either with gear wheel 1 (or) gear wheel 2.

The shaft 10, on which gear wheels 1 & 2 are mounted, always rotates in the same direction. Accordingly, operation of clutch (1) or (2) causes left or right hand rotation of the pinion 3 and shaft 4. The bobbin rail is correspondingly raised or lowered via the bevel gear 5, pinion 6, sprocket 7 and lifting chain 8.

Cone drum change wheel: If the diameter of the tube is altered. The starting speed of the bobbin must be adapted correspondingly. Since the ratchet wheel has not been operated at this stage, the adaptation cannot be performed by way of the builder motion.

Ratchet change wheel determines the amount by which the belt is shifted upon each operation of the ratchet and therefore must be adapted precisely to increase in the bobbin diameter.

LIFTER MOTION

Bobbin are raised and lowered to place the coils placed next to each other.

Lifter motion work with levers or with racks.

To compensate for the increase in bobbin diameter the lift speed is reduced after each lift stroke.

Drive to the bobbin rail is provided from driven cone drum, but not through the differential gear mechanism.

Figure 5 : Lifter motion with levers

Figure 6 : Lifter motion with racks

Lifter motion is used to wind the roving on the package layer by layer i.e placing new coils near to neighboring layers by moving bobbin package up and down, so that winding point is continuously varied.

The required raising and lowering can be carried out by means of several racks secured to the rail (Figure 6).

However several manufactures mount the bobbin rail on a lever and move the rail by an up and down movement of that lever (Figure 5).

As diameter increases, lift speed must be reduced by a small amount after each completed layer (Figure 6)