Cost of Sizing

Cost of Sizing

The cost of sizing ( excluding cost of sizing chemicals) is generally expressed as cost per unit length. Hence contribution of sizing cost can be calculated as:

cost of sizing= cost per unit length x tape length

cost of sizing chemcials is expressed as cost per unit length of size mixture. The cost per piece of fabric can be calculated as:

Cost of sizing chemicals per piece length= cost/kg x (warp weight per piece length x size add on %)

Basic stitches- Animation

Basic Stitches Animations

This site talks about how sewing machine works. It is replete with animations. It starts by saying that it was inefficient to mechanically copy the process of hand sewing. This site has animations for the following stitches:

1. Basic chain stitch
2. Twisted chain stitch
3. Lock stitch
4. Oscillating hook lockstitch
5. Rotating hook lockstitch
6. Double locking chainstitch

A very nice site to visit !

Should I mention that on the same parent site there is this amazing guitar tutorial !!

Efficiency of Sizing

Efficiency of Sizing Department

The major causes of loss of machine efficiency are:

1. Creeling, which includes removing the exhausted beams, mounting new beams, denting, leasing etc.
2. Replacement of weaver's beam on consumption

Efficiency in sizing

Let yarn count= 34
Set length on warper's beam= 18000 m
length of yarn on weavers beam= 1500m
Total number of ends= 4000
Full running speed= 50 m/min
No of lappers per 3000 ends per 1000 m = 3
Time to cut a lapper = 90 sec
Time to doff a beam and put new lease rods = 600 seconds
time to change a set = 6300 sec
Time loss/1000 m due to miscellaneous causes= 60 sec

Calculations

Sizing time of one beam with no stops : R = (1500x60)/50 = 1800 seconds
Lappers per beam of 1500 m per 4000 ends = 6
time lost in cuttin glappers per beam = 540 seconds
Number of weavers beam per set= 12
time lost per beam in a set change = 6300/12=525 seconds
time loss in beam doffing and leasing per beam = 600 seconds
Miscellaneous losses per beam of 1500 m = 90 sec
total time to size one beam = 3555 seconds
Machine efficiency = (1800 x 100)/3555 = 50.6%

Sizing Control points, sizing defects

Control of Yarn Stretch

During sizing, the yarns are under tension, this results in a slight permanent stretch in the yarn. It leads to a decrease in extensibility or elongation at break of the sized yarn, which leads to more breakage at the loom shed.

The various zones of stretch control on modern sizing machines are:

1. Creel zone: start- last warper beam, end-Dry nip
2. Wet Zone; Start- dry nip, end- first drying cylinder
3. Drying Zone: start- first drying cylinder, end- last drying cylinder
5. Splitting Zone: start-last drying cylinder, end- drag roll
6. Winding Zone: start- drag roll, end- loom beam

Control of Stretch in Creel Zone

The creel stretch on the existing type of sizing machines has to be controlled manually. The yarn tension in the creel zone increases gradually with reduction in diameter of the warper's beam. To counter this, the tightening of the beam is required to be adjusted suitably as the sizing progresses.

Control of Stretch in the Wet Zone

The control of stretch in this zone can be done with the help of 'positive dry nip'.

On multicylinder sizing machines, stretch can be controlled by synchronising the PIV gear during the cylinders with that driving he finishing squeeze roller in the wet zone.

Control of Moisture in sized yarns

A moisture control of 8-10% should be maintained in the sized cotton yarns. With excessive drying, the size film becomes brittle and harsh.
Very high moisture content is also undesirable because it makes the size films soft and the yarn sticky.

Quality of Sized Beams

A satisfactory weaver's beam should unwind well on the loom. These are some of the important package faults:

1. Density of sized beams: A loosly packed weaver's beam does not work well. The density is mainly influenced by two factors:
a. effectiveness of the friction clutch or the DC drive
b. effectiveness of the bream pressing motion.

2. Broken ends, missing ends, crossed ends, sticky ends

The major sources of all these faults are
a. lappers
b. invisible breaks during sizing

A lapper is an accumulaiton of layers of yarn on the warper's beam.

Those end breaks during sizing that do not form lappers are called invisible breaks.

Both lappers and invisible breaks result in missing and broken ends in the sized beams.

Crossed Ends- these are formed during weaving whenever the leading end is not available in the appropriate place on the beam,and, therefore, the weaver has to knot the trailing end to an end that is far away. This happens because in some cases the leading end of an invisible break migrates to a distant place.

Sticky ends - These are caused when broken ends from the warper's beam migrate to the yarn of another warper's beam.
In order to control these faults, it is necessary to control the incidence of lappers and invisible breaks.

Factors affecting lappers:
- End breakage rate at warping
- Efficiency of warp stop motion at warping
- condition of beam flanges (warper's)

Factors affecting invisible breaks
- High stretch at sizing
- weak places in the yarn

Defective selvedges

There are two types of defective selvedges that cause more difficulty in unwinding during weaving than the ends of the beam of thebeam. These are:
1. Sunken selvedges
2. Bulging selvedges

These defects can be controlled by
a. correctly setting the expandable comb at the headstock
b. Using the correct size of beam pressing roller so that it reaches both the beam flanges.
c. Ensuring that beam flanges are true.

Formation of ridges on the Beam

Ridges on the beam are formed when the ends that are taken in one dent of the comb do not spread out. To minimise the falut the eccentric dancing rollers at the headstock should be adjusted properly.