· DRAFTING
· Drafting arrangement is the most important
part of the machine. It influences mainly evenness and strength
The following points are therefore very important
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.
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.
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.
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 back roller 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.
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.