Quality Aspects of Rovings
Control of quality at roving stage is very important since speed frame is the final process before the actual yarn production.
 Roving process contributes for about 15-20% of the yarn Irregularity.
 About 80% of the source of yarn faults can be attributed to the bad condition of roving bobbin.
 High roving CV% and periodic variations tend to deteriorate the tensile characteristics of yarn.
 Short-term variations in rovings become medium term yarn variations leading to end breakage.
Roving Strength
Roving strength plays an important role for optimizing the roving TM and the ring frame drafting parameters.
Defects in roving quality is caused by work practices also.
 Sliver piecing at creel
 Roving piecing
 Cleanliness of drafting zone and flyers
 Poor handling of sliver cans
 Mechanical condition of individual spindles.
Roving Quality Parameters
Roving Hank/Count
Decided on the basis of
 Optimum Ring Frame Draft (32-50)
 Total draft at roving frame.
Yarn Count (Ne)
Roving Ne
Sliver Ne
16-20
0.75
0.120
30-40
1.10
0.125
50-60
1.35
0.135
80-90
1.65
0.165
Roving count variation
Between
Bobbins
Hank CV%
(Count)
Within
Bobbins
Between bobbin count CV% is affected by
 Variation in drafting pressure
 Quality of sliver (1m CV %)
This variation will also lead to high yarn count CV% and weft bar in woven fabric.
Within Bobbin CV % - possible causes
 Uneven tension during bobbin built-up
 Sliver splitting and stretching at creel zone.
 Roller lapping
 Defective Spindle
Hight within bobbin CV leads to yarn 10m CV % which results in streaks in knitted fabric.
Unevenness (U%) (Standard U% values)
Yarn (Ne)
Up to
Carded Cotton
15s…………………………….
1630s………………………………….
Combed Cotton
(Standard U% values)
6.5
6.0
5.5
5.0
Above
30s…………………………….
P/v Blends
30-
4.5
3.5-4.5
P/c Blends
50s………………………………….
4.5-5.0
Above
50s…………………………….
Causes :







Quality of cots,
Aprons,
Spacer size,
Draft,
Condenser size,
Break draft,
Top arm pressure
Twisting zone:
 Optimized twist geometry
 Better understanding of frictional behavior of fibers led to improved flyer top.
 Flyer tops made up of nylon or polyurethanes.
High Level of false twist for roving without changes in real twist will leads to
 Less fly generation.
 Less roving hairiness
 Less roller lapping
 Less roving breaks
 Compact package
 High production rate for speed frame
 Improved unwinding behavior of roving at Ring frame.
Quality Related
Process control measures
a) Spindle Speed
High speeds - More tension fluctuation
- Coil bursting at the top of bobbin
Typical special speeds (rpm)
Carded counts
1100
Combed (coarse)
950
Combed (fine)
800
b) Break draft
High break draft -> high roving U% and yarn cv(1m)
Typical range
1.08 – 1.10
c) Creel Tension draft
1.01 for corded counts
0.99 for combed cotton counts
d) Drafting Pressure
Range
18-22 kg
e) Roller gauges
Wider settings increases the amplitude of drafting waves leading to long yarn faults (thick & thin)
f) Roving TM
Low TM leads to long thin faults
g) Condition of can springs
If the can plate does not move properly, sliver stretch occurs in the case of bottom portion of material -> long thin faults.
h) Drafting Elements
Cots/Aprons
 Eccentricity of cots : I 0.002 mm
 Cracks/groove formation to be avoided
Spacer
Spacer influences the following parameters
 Long thin faults
 U%
 Imperfections
Smaller spaces will provide better fiber control
Condenser
Size depends on the sliver & roving hank
Laying:
Wrong laying of coils increases the yarn count CV %
Performance related process control measure
Roving Break
 Tension control of roving in front row of flyer
 Condition of ‘flyer top’
 Pressure arm condition
 Flyer condition & cleaning
 Lapping
 Roving TM & strength
Creel Breaks
 Trumpet size at draw frame
 Height & length of creel
 Condition of can springs
Other Features
Creel
Number of rows of creel rollers increased to 7 from 3 or 4 to accommodate bigger cans from HP draw frames.
Package Size
 Lift has increased from 8 to 16 inches .Diameter has increased from 4 to 6.5 inches.
Inverter Drive
 Power supply variation influencing the roving tension is monitored.
 Good smooth starting
 Variable spindle speed (in accordance to end breakage rate)
Winding of Bobbins
 The roving bobbins carries relatively large quantity of material due to its compactness
 The taper angle depends upon the adherence of the material
 Larger angle-more material
 Smaller angle-better stability
Following are the defects and its prevention methods in roving
Sr.No. Defects
Prevention Measures
1.
Roving tension Roving tension is directly related to machine. The roving tension depends upon delivery rate and the difference between
flyer speed and bobbin. For preventive action we should keep the delivery length and the speed difference constant then the
tension in this case will be ideal.
2.
Improper
handling of
material


Roving material is very sensitive regarding to quality point of view. It is necessary to take care of material. The
material should be handled in such a way that fine dust must not affect the material. It must be avoided touching
because of its sensitivity. Fresh material should be used for next process. This material should not be keep for long
time. If it will be kept for long time then it will create variation. C.V% increases if material is not used .
Supervisor must treat its worker in a proper way so that handling of material should be according to policy of mill.
3.
Improper
piecing in
roving
Supervisor should train his workers in a proper way. If end breakage is disturbed then its treatment should be proper. If
piecing will not be proper then it will affect the next process.
4.
Roving
breakage
This problem is caused due to maintenance problem. Maintenance required machine stoppage but it is against the
production. To enhance the quality of product, the machine maintenance is the chief requirement. For the proper solution
of roving breakage, speed of machine, trained operator and proper management should be must otherwise it create severe
Sr.No. Defects
Prevention Measures
problems in ring section.