Thursday, 25 September 2008

FAQ in Cotton spinning-10

Q: what is the object of aprons.
Answer: The object of aprons is to contol the floating fibres to the possible extent and help to produce regular and stronger yarns with greater drafts.

Q. What is the importance of gap between the two aprons.
Answer: The aprons are not be too far apart or too close. Wider gap fails to control the floating fibre movement. If the gap is less, the pressure between the aprons more. The front-roller-gripped fibres suffer undue strain and the result is the formation of the defect known as 'crackers'

Q. What are the top roller cots or coverings. What is their importance.
Ans: the top rollers of draw frames, speed frames and ring frames, are made of metals. These are usually covered with a convenient cushioning material called as cots.

Q. What is the importance of the top roller cots.
Ans: These are needed to avoid the fibres getting crushed or damages, and also to give a proper grip on the fibres when they are being drafted.

Q. What are the requirements of a good cot.
Ans: A good cot is expected to have unifrom quality and performance, capable of being buffed to precise limits. It should have anti-lap up, oil-resistant, antistatic, trouble-free and temperature properties. It must possess good resilience in order to provide the required degree of cushion and must not contribute to end breaks.  It should withstand channeling action and any tendency for flute marding when top rollers are left standing under weight or pressure.

Q. What is the hardness of the cot. what is its importance.
Ans: A shore hardness of 60 deg to 90 deg is preferred. A harder surface would give rise to greater roller slip. A softer surface will lead to more roller lapping.

Q. Why top roll surfaces are grooved.
Ans: The object of grooving is to minimise the lap-up tendency, besides reduction of fly accumulation on top cleaners. The grooving also prevents surface distortions.

Q. What is the object of roller weighting.
Ans: In any pair or rollers, the bottom roller is positively driven while top roller is driven with the grip of the bottom roller. Normally the top rollers themselves fail to exert sufficient pressure and have to be assisted by some suitable external devices. Such devices are known as "roller-weighting devices"

Q. What is roller setting ? What is its importance ?
Ans: The distance between the centres of two pairs of rollers is called roller setting. If the pairs of rollers are set too wide apart, there will be plucking of the fibres instead of even attenuation, and the material that comes forward is full of thick and thin portions. On the other hand, if they are set too close, drafting becomes difficult and many of the long fibres get gripped by both the pairs momentarily. The fibres get either damaged or broken.

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