How to Find Out Sewing Time with Machine RPM

Introduction: 
Calculation of sewing time is an important task for industrial engineers. Because it will be effective to get actual time to be taken by a sewing operator to sew a specific length of seam. From this we can get an operator production efficiency easily. If you read article with concentrately then I think you easily calculate sewing time. 

Sewing by an operator

Estimation of Sewing Time Using Machine RPM: 
Machine RPM means Revolution Per Minute of that machine. By machine RPM we can get time to sew a specific length of seam with specific Stitch per Inch (SPI). Before calculating garments sewing time by using machine RPM, an industrial engineer should confirm about the below points: 

• Stitch per inch (SPI) of the garments,
• Seam length in inch of the garments,
• Sewing machine RPM (Revolution per minute).

Now by using the below formula, an industrial engineer can easily calculate the required garments sewing time from machine RPM. 

Machine cycle time or sewing time (in second), 

   Stitch per inch (SPI) x Seam length in inch x 60
= ……………………………………………………………
                 Sewing Machine RPM 

If we see an example then concept will be clear, 
Example: 
If a plain stitch sewing machine RPM is 1400. How much time needed to sew a 40 inch length seam, where stitch per inch (SPI) is 8? 

Solution: 

Here, 

Sewing machine RPM= 1400,
Seam length in inch= 50”,
Stitch per inch (SPI) = 8. 

We know that, 

Machine cycle time or sewing time (in second), 

   Stitch per inch (SPI) x Seam length in inch x 60
= ………………………………………………………
                  Sewing Machine RPM 

   8 x 50 x 60
= …………………
       1400 

   24000
= …………
   1400 

= 17.14 sec 

So. Sewing time of that machine is 17.14 sec. 

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Important Measurement Point for Determining Fiber Quality

In yarn manufacturing, its very important to know or determine fiber qualities. Because the lion share cost of yarn manufacturing goes to raw materials. So attaining a quality garments its very argent to dignify raw material’s qualities. Thats why we have some specific measurement points by which we can specify actual yarn quality. Some of them are given below with small description.

Cotton fiber bell

1. Uniformity Ratio: 

                                Mean fiber length            100 
Uniformity ratio = …………..……………. × ………
                             Upper half mean length         1 

Mean length is the average length of all fibres approximately ¼’’ and longer,and upper half mean length is the estimate of the lengths of fibres in the upper half portion as measured by the fibrograph. 

Rating of cotton fibres with respect to uniformity ratio 

Uniformity Ratio	Rating
Above 80	Uniform
76-80	Average Uniform
71-75	Slight irregular
70 and below	Irregular

Coefficient of Variation (CV): 
CV is relative measure of the length variation.The larger the value, the greater the variation in fibre lengths, and, conversely the smaller the value, the more uniform are the fobre lengths. 

Rating of cotton samples with regard to fibre length variation 

CV%	Rating
Below 27	Low variability
27-34	Average variability
35 and above	High variability

Fibre Fineness rating in micrograms/inch: 

Fibre Fineness	Rating
Very fine	Below 3.0
Fine	3.0 to 3.9
Average	4.0 to 4.9
Course	5.0 to 5.9
Very course	6 and above

Maturity ratings: 

Rating	Maturity Ratio
Very mature	Above 84%
Mature	77 to 84%
Average	68 to 76%
Immature	60 to 67%
Very Immature	Below 60%

Fibre strength rating in 1000lbs. per square inch: 

Rating	Strength rating in 1000 lbs.
Superior	93 and above
Very superior	87 to 92
strong	81 to 86
Average	75 to 80
Fair	70 to 74
Weak	Below 70

Effect of short fibre in yarn: 

For good spinning 14% short fibre is accepted as allowable
Short  fibre%	8%	13%	15%
Break Factor	1904	1723	1620
Elongation	8.3	7.8	7.2
Break per 100	32	52	54.8
Spindle hourse

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