Sliver feed to the scanning rollers
It is essential that sliver funnel and the
scanning rolls of the auto leveler are very carefully set. An incorrect setting
can cause cutting of the fibers, sliver tags and highly compressed sliver
fringes that are not subsequently drafted.
· The funnel should be correctly located and
be 0.5 -1mm from the scanning rolls.
· The
funnel must be centered relative to the scanning roll groove.
· The tongue and groove onents must not make contact with each other.
· The
sensing scanning roll must not touch the funnel.
The clearances between
the scanning rolls should be checked at ¼ turn positions to be sure that they
are correctly aligned.Clearances should be checked above and below the tongue
as well as between the tongue and inside of the grooved roll Sharp edges of the
scanning rolls can cause cutting of fibers.
This shows up as an
increase in short fiber content after drawing. Additionally synthetic fibers
can be fused. The sharp edges should be polished away by using fine “Scotch
Bright” or similar polishing material. The pressure on the scanning roll should
be carefully adjusted to suit the processing speed and the material being
drawn. If there is scanning roll vibration the pressure should be increased
incrementally. For bulky coarse synthetic fibers it is sometimes necessary to
increase the pressure For polyester the pressure is usually light.
Check that the scanning
roll assembly screws do not touch the table. This is a problem if a change is
made to smaller scanning rolls and using the same length screws. Clean the
funnel. There should be no contamination, burrs or rough places.
Funnel and scanning rolls
Scanning rollers to drafting system
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Sliver tension
The sliver tension must be carefully adjusted to
avoid sliver stretching but to be sufficient to cause the slivers to spread
after the high compression of the scanning rolls. High tension will cause
irregular stretch that cannot be corrected by the auto leveler. With combed
cotton the piecings can be disturbed and the autoleveler will not function
correctly. Reduce the tension until the slivers are slightly loose and then
increase the tension one step. The sliver should not drag on the table.
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Sliver spreading
When the slivers leave the scanning rolls the
material is very compacted and has to spread to a “side by side” condition
prior to entering the drafting system. Slivers must not roll and cross each
other.
The sliver guide bars L1, L2, L3, and L4 must be
set so that the slivers are:
• in the
center, uniformly next to each other, without gaps between the slivers, no
slivers crossing,
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without rolling and twisting.
In
addition to the sliver tension, the relative heights of the sliver guide bars
influence the spreading action. The convex shape of the guide bars helps in the
spreading action. Initially set the bar heights with L1 in the high position, L4
below the back roll of the drafting system, L3 and L4 as shown in the
diagram. If the spreading is excessive and the slivers are moved apart then
lower L3 or raise L2 The sliver path must be as that shown in the diagram,
otherwise the correct leveling and drafting functions will be disturbed.
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Drafting
Sliver path through the Drafting System
The
drafting system is basically 3 over 3 with an additional “Deflection” roll (7)
on the delivery roll to direct the sliver toward the coiler.
The top
rolls are numbered (1, 2, 3) and corresponding bottom rolls are, - back roll
(4), middle roll (5) and delivery roll (6).
There is a pressure bar (8) located between the
top rolls 2 and 3 to help control the fibers in the main draft zone.The
fundamental settings of the drafting system are the roll distances and the
draft distribution. Each greatly influences the quality of the delivered
sliver.
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Critical factors affecting the drafting
action
• Roll settings, draft distribution, roll
pressure, speed, top roll cot condition
removal of dust, fly and
clearer waste.
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Roll setting
Drafting
roll distances have to be set as close as practicable:
To control the short and floating fibers, Not so
close as to break the longest fibers, nor Not so close as create high drafting
forces and over control.
The roll setting has to be optimized according to:
• Staple
length, ( 2.5% on HVI or AFIS and 1.0% on the Peyer AL-101) fiber orientation,
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sliver weight
fiber
crimp, bulk and cohesion. The number of fiber hooks are decreased and the degree
of fiber orientation is increased each drawing process. Therefore, it is
necessary to set the roll spacing with this in mind.
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Setting tip
From the
practical setting perspective, the main draft rolls should be set first,
followed by the setting of the break draft zone. Any change of the distance
between rolls (5) and (6) automatically changes the distances between rolls (4)
and (5). Consequently, a change of setting of the main draft zone must be
followed by an adjustment of the break draft rolls.
The converse is not so. A change of the distance
of the break draft zone does not change the positions of rolls (5) and (6).The
main draft zone roll – setting (H V D)
• The main draft rolls have an actual minimum
setting of 35.5 mm, which is used for all fibers with staple length shorter
than 27 mm.
• For fibers of staple length 27 mm or longer,
the rolls are Normally set at 8 ….10 mm over the 2.5% length value. Break draft
zone - roll setting (V V D)
• The
break draft roll setting is dependent upon the condition of the supplied
sliver. The maximum and average staple lengths, the degree of fiber
orientation, the fiber hooks, the drafting resistance, and the draft
distribution all have an influence on how close the rolls can be set. A simple
test for the break draft resistance is to use a1 or 2 mm feeler gauge and push
it between the first and second rolls into the slivers. The fibers should yield
but with resistance. The rolls are too close if the slivers do not allow the
feeler to be pressed through. Closest roll setting is 36 mm Common roll
settings range from 10…15 mm over the 2.5% staple length.
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Draft distribution
• The
total draft is established by the total mass of the input material and the mass
of the output sliver.
The calculation is:
Total draft (V) = Input
mass ÷ Delivered mass
The total draft is performed in two stages. The
first step is the “Break Draft” (V V), which prepares the slivers for the “Main
Draft” (V H) Break draft zone - Draft (V V ) The function of the break draft in
the draw frame is to pre tension the slivers and remove the sliver crimp so that
the fibers presented to the main draft zone are controlled. The normal range is
1.16 to 1.41, but with polyester for sewing thread and crimped acrylic the break
draft can be up to 1.70. The break draft in the first drawing passage is
usually higher than that of the second passage because the card sliver has a lower
level of fiber orientation. The evenness tester diagram and spectrogram should
be used as a guide in setting the draft.
The following observations can be made:
Breaker
drawing requires higher break draft than subsequent drawing processes.
Warning:
Roll settings that are too close will result in over control, which can be seen
as “spikes” in the evenness diagram. These spikes cause thick and thin places
in the yarn. Finisher drawing requires more open settings and a lower break
draft. Man made fibers require higher break drafts than cotton.Finer fibers,
cotton or man made, require higher break draft than coarser fibers. When the
total draft has to be relatively high (7 to 10) thebreak draft has to be
increased to keep the main draft in the desirable range. When processing short
fibers the break draft should be low.
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Main draft zone – Draft (HV)
The main draft is established by the total
draft and the break draft .The total draft is set by the overall processing
system and usually has to be accepted. However, for high quality products, it
is recommended to limit the draw frame draft to less than eight (8), which means
the main draft will be between 3.5 and 5.5.
• The
best main draft settings are dependent upon the materials being processed, and
the following points generally apply:
Comber noil HV –
3.8,
short carded cotton HV
– 4.75,
carded cotton HV –
5.2,
combed cotton HV –
6.1,
Egyptian combed cotton HV – 7.1,
cotton /MMF Blends HV – 6.2,
viscose HV – 6.3,
acrylic (crimped) HV –
5.2,
polyester (crimped) HV – 6.0,
polyester (sewing thread)
HV – 3.7,
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Roll pressure
The top rolls are pressure - loaded
against the bottom rolls to grip the fibers between the rolls and to increase
the fiber bundle pressure in the drafting zone. The pressure should not be
excessive, but has to be sufficient to maintain a consistent drafting action.
The following points should be noted:
Rolls 1, 2, and 3 are pre set to 320 N,
Deflection roll 7 is preset to 200 N,
For conditions of high drafting forces, such as,
low draft ranges, heavy sliver weights or fibers that have a strong drafting
resistance the top roll pressure has to be increased to:
Top rolls 1 and 2 to 440 N,Top roll 3 to 320
N,Deflection roll 7 remains at 200N.
When the top roll pressure is increased the
effective nip zone is extended reducing the distances between the nip points.
To compensate for this, it may be necessary to increase the draft roll settings
by 1 or 2 mm. Increasing the roll pressure increases the temperature or the
rolls, Lifetime of top rolls is reduced, Top roll deformation will occur if roll
pressure is left on when the machine stops With the pneumatic top roll loading
system, the pressure is automatically released. This prevents the formation of
flat spots on the cots.
Pressure on Drafting System:
Speeds of
the draw frame have been progressively increased. In most cases the maximum
speed of the draw frame is limited by:
• The running condition, which is fiber
dependent, or
• The sliver quality that can deteriorate as the
speed exceeds optimal levels.
• Normally, the draw frames are run at speeds
below the maximum rate because the cost of drawing is a relatively small
component of the overall spinning costs.
Effects
of excessive speed
•
Increased top roll laps,
• Roll temperatures exceed the tolerance of some
man made fibers,
• Increased machine stops and reduced
efficiency,
• Deterioration in sliver quality,
• Reduced lifetime of the cots,
• Overheating of the bearings,
• Guide to maximum draw frame speeds.
The
following chart is taken from the sales documentation and represents the
delivery speed expectancies of current draw frames. It should be emphasized
that speeds approaching the maximum speeds can only be attained when all
conditions are optimal.
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