Drafting elements - Guidelines

Basic Concept of Ring Spinning

GMT 05:10 2015 Thursday ,14 May

Sriyadithatextile - Basic Concept of Ring Spinning

Ring Spinning - Drafting
TFA

BASIC CONCEPT OF RING SPINNING

The ring spinning will continue to be the most widely used form of spinning machine in
the near future because it exhibits significant advantages in comparison with the new
spinning processes.

Following are the advantages of ring spinning frame
• It is universaly applicable, i.e.any material can be spun to any required count
• It delivers a material with optimum charactersticss, especially with regard to
structure and strength.
• it is simple and easy to master
• the know-how is well established and accessible for everyone
• Functions of ringframe
      - to draft the roving until the reqired fineness is achieved
      - to impart strength to the fibre, by inserting twist
      - to wind up the twisted strand (yarn) in a form suitable for storage,
        transportaion and further processing.

DRAFTING
• Drafting arrangement is the most important part of the machine. It influences
mainly evenness and strength The following points are therefore very important
   - drafting type
   - design of drafting system
   - drafting settings
   - selection of drafting elements like cots, aprong, traveller etc
   - choice of appropriate draft
   - service and maintenance


• Drafting arrangement influence the economics of the machine - directly by
affecting the end break rate and indirectly by the maximum draft possible.

• If higher drafts can be used with a drafting arrangement, then coarser roving can
be used as a feeding material.This results in higher production rate at the roving
frame and thus reducing the number roving machines required space, personnel
and so on.
• In fact increase in draft affects the yarn quality beyond certain limit. Within the
limit some studies show that increase in draft improves yarn quality. The
following draft limits have been established for practical operation:
   - carded cotton- upto 35
   - carded blends - upto 40
   - combed cotton and blends(medium counts) - upto 40
   - combed cotton and blends(fine counts) - upto 45
   - synthetic fibres - upto 50
• The break draft must be adapted to the total draft in each case since the main
draft should not exceed 25 to 30. It should be noted that higher the break draft,
more critical is the break draft setting
• The front top roller is set slightly forward by a distance of 2 to 4mm relative to the
front bottom roller, while the middle top roller is arranged a short distance of 2mm
behind the middle bottom roller.
• Overhang of the front top roller gives smooth running of the top rollers and
shortens the spinning triangle.This has a correspondigly favourable influence on
the end break rate.
• Rubber cots with hardness less than 60 degrees shore are normally unsuitable
because they can not recover from the deformation caused by the pressure on
the top roller while running.
• Soft rubbercots for toprollers have a greater area of contact, enclose the fibre
strand more completely and therefore provide better guidance for the
fibres.However softer cots wear out significantly faster and tend to form more
laps.
• Normally harder rubbercots are used for back top rollers, because the roving
which enters the backroller is compact, little twisted and it does not require any
additional guidance for better fibre control.

In the front top roller, only few fibres remain in the strand and these exhibit a
tendency to slide apart Additional fibre guidance is therefore
necessary.Therefore rubbercots with hardness levels of the order 80 degrees to
85 degrees shore are mostly used at the back roller and 63 degrees and 65
degrees at the front roller.
• If coarse yarns and synthetic yarns are being spun, harder rubbercots are used
at the front roller because of increased wear and in the case of synthetic yarns to
reduce lapups.
• Three kinds of top roller weighting(loading) are presently in use
   - spring loading
   - pneumatic loading
   - magnetic weighting
• With pneumatic loading system, the total pressure applied to all top rolers is
obtained by simple adjustment of the pressure in the hose using pressure
reducing valve. Moreover the rubbercots will not get deformed if the machine is
stopped for a longer duration, because the pressure on top rollers can be
released to the minimum level.
• The fibre strand in the main drafting field consists of only a few remaining fibres.
There is hardly any friction field and fibre guidance provided by the rollers alone
is inadequate. Special fibre guiding devices are therefore needed to carry out a
satisfactory drafting operation. Double apron drafting arrangements with longer
bottom aprons is the most widely used guding system in all the modern
ringframes.
• In doube apron drafting system two revolving aprons driven by the middle rollers
form a fibre guiding assembly. In order to be able to guide the fibres, the upper
apron must be pressed with controlled force against the lower apron. For this
purpose, a controlled spacing (exit opening), precisely adapted to the fibre
volume is needed between the two aprons at the delivery. This spacing is set by
"spacer" or "distance clips"Long bottom aprons have the advantage in
comparison wiht short ones, that they can be easily replaced in the event of
damage and there is less danger of choking with fluff.
• Spindles and their drive have a great influence on power consumption and noise
level in the machine The running characteristics of a spindle, especially
imbalance and eccentricity relative to the ring flange, also affect yarn quality and
of course the number of end breakage. Almost all yarn parameters are affected
by poorly running spindles. Hence it should be ensured that the centering of the
spindles relative to the rings is as accurate as possible. Since the ring and
spindle form independent units and are able to shift relative to each other in
operation, these two parts must be re-centered from time to time. Previously, this
was done by shifting the spindle relative to the ring, but now it is usually carried
out by adjusting the ring.
• In comparison with Tangential belt drive, the 4-spindle drive has the advantages
of lower noise level and energy consumption, and tapes are easier to replace.
• Lappet guide performs the same sequence of movements as the ringrail, but with
a shorter stroke, this movement of the guide ensures that differences in the
balloon height caused by changes in the ring rail positions do not become too
large. This helps to control the yarn tension variation with in control, so that ends
down rate and yarn charactersitics are under control.
• Spindles used today are relatively long. The spacing between the ring and the
thread guide is correspondingly long, thus giving a high balloon. This has two
negative influence
   - A high balloon results in large bobbin diameter leading to space problems
   - Larger the balloon diameter , higher the air drag on the yarn.This inturn
     causes increased deformation of the balloon curve out of hte plane
     intersecting the spindle axis.This deformation can lead to balloon stability
     there is increase danger of collapse.
Both these disadvantages result in higher yarn tension, thereby higher
endbreaks.In order to avoid this balloon control rings are used. It divides the
balloon into two smaller sub-balloons. Inspite of its large overall height, the
double-balloon created in this way is thoroughly stable even at relatively low yarn
tension.
• Balloon control rings therefore help to run the mahcine with long spindles(longer
lift) and at high spindle speed, but with lower yarn tension. Since the yarn rubs
against the control ring, it may cause roughening of the yarn.
• Most ends down arise from breaks in the spinning triangle, because very high
forces are exerted on a strand consisting of fibres which have not yet been fully
bound together in the spinning triangle.

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