Q: What is the relation between CV% and U%? Also, write the difference between both.
C.V. % = 1.25 X U%
The irregularity U% is proportional to the intensity of the mass variations around the mean value.
The U% is independent of the evaluating time or tested material length with a homogeneously distributed mass variation.
The larger deviations from the mean value are much more intensively taken into consideration in the calculation of the coefficient of variation C.V. %.
C.V. % has received more recognition in modern statistics than the irregularity value U%.
The coefficient of variation C.V.% can be determined extremely accurately by electronic means, whereas the calculation of the irregularity U% is based on an approximation method.
Q: While testing ring yarn in the Uster evenness tester the peak observed was around 9 cm in regularity trace. What will be the probable cause of the peak, explain.
The probability of faults is due to damaged front roller cots or rollers in the R/F drafting zone. Explanation:
The front roller diameter is 27 mm so the circumference of the front roller is (3.14 * 2.7 = 8.6 cm i.e. approximately 9 cm). so the cause of the fault is due to the front roller or cots in the R/F drafting zone.
Q: Calculate the limit irregularity for a 20 Tex cotton yarn spun from 150 mTex fibres. If the actual measured CV% is 23.2%, what is the Index of Irregularity?
The average no. of fiber in yarn cross section = (20 * 1000) / 150 = 134
For cotton limit irregularity CVlim = 106 / √134 = 9.15%
Index of irregularity = CVact / CVlim = 23.2 / 9.5 = 2.54%
Q: Two roving each with a CV of 8% are fed into a spinning zone. If the spinning unit adds a CV of 18%, what will be CV of the output yarn?
CV% yarn w/o addition of CV in R/F is = CV% / √n = 8 / √2 = 5.7%
CV % of output yarn = √(5.7+18) = 18.88%
Q: On a draw frame Polyester and Cotton slivers are blended on a 6-ends-up system with a draft of 6 to get a 20 ktex sliver with approximately 67:33 P/C blend by weight. Input cotton sliver of 1.2 denier cotton fibre has a CV of 4% and the polyester sliver of 1.5 denier have a CV of 3%. Drafting introduces an additional CV of 2%. Calculate the Index of Irregularity, neglecting the variability of fibres.
Sliver Linear density = 20 kTex = 20,000 Tex
Polyester = 20000 x 0.67 = 13400 tex
Cotton = 20000 x 0.33 = 6600 tex
No. of cotton fibres in the sliver cross section = (6600 * 9)/1.2 = 49500 = N1
No. of polyester fibres in the sliver cross section = (13400 * 9)/1.5 = 80400 = N2
Total no. of fibres = 49500 + 80400 = 129900 = NT
CVlim = 100 / √ NT = 100 / √129900 = 0.28
CVdoub = √(NcVc2 + NpVp2 ) / (Nc + Np)
Nc & Np are no. of cotton and polyester sliver ends
CVdoub = √(2 * 42 + 4 * 32 ) / (2+4) = 1.37%
Actual CV% of input sliver
CVactual = √(CVd2 + CVdraft2 ) = √(1.372 + 22 ) = 2.427
Index of Irregularity = CVact / CVlim = 2.427 / 0.28 = 8.66
Q: The U% of a single yarn is 17.3%. The expected CV% of a 3 ply yarn made from these single yarn will be,
CV of single yarn is = 1.25 * U%
= 1.25 * 17.3 = 21.625 %
CV% of 3 ply yarn = CV of single yarn / √n where n = no. of doublings
= 21.625 / √3 = 12.5%
Q: Calculate the CV% of the combed sliver which is fed in the finisher draw frame. CV% of the Draw frame sliver is 1.85% and No. of doubling is 6.
The formula is
CV% of doubling = CV% of single / √n where n = no. of doublings
1.8 = CV% of single / √6
CV% of singles = 4.41%
i.e. CV% of comber sliver is 4.41%.
Q: Two roving having 7.8 CV% are fed into the ring frame making yarns and ring frame adds CV% 4.8 then what will be the final yarn CV%. Three of the same yarn doubled in the doubling machine means what will be CV% of the doubled yarn?
CV of ring yarn (exclude of CV% added in R/F) = CV% of roving / √n
= 7.8 / √2 = 5.52
CV% of ring yarn with added
CV% in Ring frame = √ (5.522 + 4.82 ) = 7.32
CV% doubled yarn having 3 single of above yarn = 7.32 / √3 = 4.23
Q: A draw frame is fed with 8 cotton slivers of 0.25 Nm with a mean CV of sliver is 2.5%. What is the extent of the irregularity which is produced by the drafting elements of the draw frame? The CV of the output sliver is also 2.5%.
CV of doubling = 2.5 / √N = 2.5/√8 = 0.88
CVoutput = (CVdoub2 + CVadd2 ) 1/2 or CVadd = (CVo/p 2 - CVdou 2 ) 1/2
= (2.52 – 0.882 ) 1/2 = 2.34%
Q: Mention the online yarn monitoring system used in rotor spinning and what kind of information we may obtain from ‘corolab-7’?
Schlafhorst has incorporated a yarn monitoring system on the rotor spinning machines using an optoelectronic sensor ‘Corolab7’ - It measures yarn diameter online and can provide details about the evenness, imperfections, detection of faults etc. Uster poly guard is an online yarn supervisory attachment for the automatic rotor spinning machines - Based on the capacitive measuring principle. - Gives detailed information for all the rotor heads.
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