What is Neps in Textile?
Neps are small entanglement of textile fibres in the form of tiny ball that cannot be unraveled, formed during carding or ginning. Presence of neps, on the surface of the fabric, causes undyed or unprinted spots after dyeing or printing. Neps some time contain immature fibers which are usually weaker than normal fibers.
Neps in yarns result in spottiness of dyed or printed fabrics, which lowers the market value of the end product. Neps, consequently, not only need to be removed during yarn production processes, thereby adding to the waste, but also should be prevented from forming by these processes.
Neps usually migrate to the yarn surface during the spinning process and result in poor yarn and fabric appearance; they prevent the uniform appearance of dyed or printed cloth, instead giving spotty looking fabrics of lower market value.
Classification of Neps:
For cotton fiber; there are five types of Neps. These are –
- Process Neps: Commonly produced by faulty carding or up to spinning yarn.
- Mixed Neps: Fibres tangle around a foreign materials. For instance – Grit.
- Immature Neps: Generally form by processing immature fiber.
- Homogeneous Dead Neps: A tangle of nearly all dead fibers.
- Fuzz Neps: A fault of short fuzz fibers.
Again we can classify neps according to structure and size into three groups:
- Biological neps
- Seed coat neps
- Mechanical neps
According to size neps are:
- Small neps
- Medium sized neps
- Large neps
Nep Count:
Nep count is the number of neps per 100 square inches of card web forming (a standard hank of sliver of 0.12 NE on a 40 inch wide card).
How to Measure the Count of Neps?
There are three ways of nep counting,
1. First a web is collected from the card placed on a 10 inch × 10 inch black board. Then the neps are counted and the number of neps found is corrected from any difference in hank or card width.
Mathematically, Nep Count, n = m × 100 [m = number of neps per inch square card web]
2. Use a template which has 34 holes, each hole is 1 in2 in area. Count the number of holes that has neps and estimate the neps per 100 in2 by using the following table.
3. Take 1 gram or 10 grains of cotton web card and count the actual number of neps per gram (or grain) over a black velvet.
Nep Formation:
Neps are usually formed during the mechanical opening and cleaning processes, including ginning in the case of cotton fibres. Along with remnants of dirt, husk and trash particles in the opened mass, neps should be removed by the card. However, depending on fiber properties and carding conditions (i.e., machine settings and operating speeds), neps can be formed during carding, thereby reducing the amount that is removed. In worsted and woolen systems, the number of mechanical opening and cleaning points is much lower than in short-staple processing, which, in appropriate carding conditions, can increase the nep propensity.
Nep Removal Efficiency:
The neps removal efficiency depends on the neps fed to the card. If we feed more neps, then the neps removal efficiency shall be high. What is more important is the neps level in the outgoing material.
The neps in laps and sliver are checked using a suitable instrument. The neps removal efficiency is determined by the difference in neps level between the lap and sliver, expressed as a percent of neps in lap. Poor efficiency of neps removal results in poor appearance of yarn. However, we should know that when the level of neps in the fed material is low, we get poor neps removal efficiency. Therefore, the level of neps in out going sliver is more important than the neps removal efficiency.
The nep removal efficiency can be calculated based on the following formula:
…………………………… ….. ………….neps in comber lap – neps in combed sliver
Neps removal efficiency % (εneps) = ——————————————————————– x 100
…………………………………. . ……………………….neps in comber lap
Nep removal efficiency may vary from 45%- 80% depending upon level of noil %
Card sliver neps: 25-300 nep/g.
Combed sliver neps: 7-80 nep/g.
Example: The nep levels in comber lap and combed sliver are 40 neps/g and 12 neps/g, respectively. Calculate nep removal efficiency. If it is decided to do go for double combing, what will be the nep level in combed sliver after second passage of combing?
Solution: The nep removal efficiency is
………..40 -12
εnep = ————— x 100 = 70%
………….40
Nep level after second passage through combing is
……..12 – x
70 = ————— x 100
……….12
………………..70 x 12
=> x = 12 – ————————- = 12 – 8.4 = 3.6 nep/g (Ans)
…………………100
How to Reduce Neps in Carding?
To reduce neps, following actions may be taken.
- Ensure that the cylinder speed is high, appropriate to the type of card.
- Select proper wire points and ensure that they are sharp and in level.
- Ensure that the fl at and cylinder settings are as close as practicable.
- Keep all surfaces like back plate, front plate, cylinder undercasing, etc., which come in contact with fibers smooth. The smoothness can be achieved by periodic polishing with ‘00’ emery paper, and then applying a paste of French chalk and turpentine, allowing it to dry and the rubbing again with clean, non-oily hard waste.
- Make hank finer and increase the doffer speed to maintain production rate.
- Ensure proper gauge between cylinder and doffer.
- Prevent cylinder loading by ensuring uniform and light feeding.
