Blow room lecture # 2, Functions of the blowroom Cleaning , Blending, blow room cleaning, blow room Blending, blow room opening, blow room process pdf.

 

   Cleaning

   The need for cleaning

 The trash and other impurities contained in cotton received by the spinner must be removed as completely as possible to enable an effective spinning operation to be performed at high speeds.

The exception to the above statement applies to spinners of novelty yarns and those who spin “low end” very coarse yarns.

 

Well-cleaned cotton enables the spinner to.

-       minimize ends down in spinning,

-       reduce the weak places caused by trash in the yarn,

-       spin fine yarns,

-       produce a more uniform yarn and fabric,

-       obtain a clean yarn and fabric,

-       improve downstream processing efficiencies.

   Factors influencing cleaning

•  Normally trash is separated from the cotton by centrifugal force.
•  The material is moved at high speed in a circular motion.
•  The trash tends to sling out from the fiber surface.
•  Grid bars are provided to allow the trash to escape and separate from the fiber that passes over the grid bars.
•  The grid bars are adjustable to vary the angle and open space allowing more, or less trash to be removed.
•  With an increase in the grid bar opening, there is an increase in the amount of good fiber that goes into the waste with the trash.
•  Good fiber in the waste is normally kept to a minimal amount. However, if maximum cleaning is required there will be good fiber in the waste.
•   The figures show the amount of trash, fine waste collected at the filter drum and cotton fiber in the waste. The accumulated waste percentage removed is shown as a function of the grid bar angle settings at two beater rotational speeds.
•   This is the basis of the VarioSet control system developed by Rieter for the UNIclean and UNIflex.

• Trash, filter waste and fiber removed at beater speed 740rpm
• Trash, filter waste and fiber removed at beater speed 550 rpm

•  New tuft surfaces must be created continuously to facilitate cleaning.
•  Larger, heavier particles are relatively easy to remove,
•  Beating devices tend to break large trash particles making them smaller and more difficult to remove. Large trash should be removed at the beginning of the cleaning process. For this reason, cotton removed from the bales should be in small tufts for effective cleaning.
•  Very small trash particles tend to be carried with the cotton in the transport air and it is difficult to obtain separation. Condensers and fiber separators help with the removal of dust sized particles.

 

   Degree of cleaning in the blow room

 The trash content of cotton varies greatly, from 1% to as high as 15%. It is much more difficult to remove trash from well-cleaned cotton than it is from dirty cotton.

 The following table shows how much trash is normally removed from cottons with different trash levels.

 

Original trash content	Quantity of trash removed
< 1.2%	< 40%
1.3 – 2.0%	40 – 50%
2.1 – 4.0 %	50 – 60%
4.1 – 7.0 %	55 – 65%
>= 7.1 %	60 – 75%

 As mentioned above some good fiber is lost with the trash. The appearance of the waste indicates the selectivity of the cleaning machine. The cleaning machines have to be carefully set to avoid excessive loss of good fiber but yet obtain the necessary trash removal action.

An analysis of the waste using the Shirley Analyzer can give an objective measurement of the amount of good fiber in the waste. This can be expressed as a percentage of the waste material or as a percentage of the total material fed. Care has to be taken to avoid confusion when discussing the “good fiber %” of the waste.

   Blending

    The need for blending

 Natural fibers properties vary widely with differences in varieties, countries, regions, climatic conditions, farming methods, harvesting and storage techniques. Even the fibers in one cotton-boll have varying properties.

 The fibers vary in length, fineness, strength, color and maturity. Plus there are impurities of various kinds in the baled cotton. It is the goal of the textile plant to produce yarn and fabric that is as uniform as possible and, additionally, the plant tries to run at consistently high levels of efficiency. Care has to be taken to ensure homogeneous and consistent blending to meet these criteria.

 Another factor affecting the composition of the raw materials is cotton price. Every yarn quality has market value. Consequently, some lower quality fibers are used to try to reduce the spinning costs and enable the spinner to compete. These special “low cost “ materials usually require careful handling and blending to avoid occasional, unexpected processing problems.

    Blending options

 Blending results in the intimate combination of the various fibers to obtain a homogeneous product. The first steps in the blending procedure are, mixing the various components and this starts by feeding fibers from the bales in the laydown.

  Manual feeding

 Where the fiber is manually removed from the bales and placed onto a feeding belt or into feeding hoppers, the role of the operator is extremely important. Normally, several bales are fed to one of several hoppers. The hopper should be fed with thin layers of each bale so that material from every bale is included in the mixing process. Unfortunately, un- supervised operators sometimes feed large portions from only a few bales, which prevents thorough mixing and subsequent blending is compromised. This can result in the blend varying and ultimately causing temporary increases in the spinning ends-down rate and possibly fabric defects such as filling bands, streaks or color shade differences.

One benefit of manual feeding is that the operators perform a visual inspection of the cotton and remove undesirable foreign material.

   Automatic feeding

 With automatic machines many operator problems are solved. Once the bale laydown has been correctly arranged the feeding and mixing can be performed with much more consistency. Care has to be taken to arrange the bales so that quality waves do not occur due to an accumulation of similar bales in one location in the laydown. One particular problem can occur when waste bales are placed at the end of the laydown. The machine feeds some of the waste bale as it comes to the end in one direction and then again feeds waste as it reverses its direction of travel.

 

   Bale blooming

 It is important to remove the bale ties and allow the bales to bloom before the cotton is used. Blooming enables the cotton to relax and absorb moisture that increases the fiber strength and reduces subsequent fiber damage.

 

   Waste blending

 There are several kinds of waste produced in spinning plants. Some waste has to be disposed of whereas; other waste can be used in small proportions and blended with the normal cotton.

•   When the waste is in bale form it can be incorporated into the bale laydown, but must be careful placed in the middle so as to minimize its impact.
•  Loose waste such as sliver, pnuemafil and roving has to pre opened before it can be mixed with the normal cotton. A waste hopper-feeding unit is used to meter the waste into opening/cleaning line. One problem with the use of the waste hopper system is that operators can over feed the waste to reduce their job load. This creates an excessively high surge in the percentage of re-usable waste and this frequently leads to problems in spinning and with yarn quality.
•  It is also bad practice to abruptly change from feeding one type of waste to a different type. For example, if the waste component is changed from combed sliver waste to comber noil, the short fiber content of the cotton in process will change significantly.
• Warning: Card flat strips and grid waste should not be re-used. They create excessive yarn defects and processing stops.

 

   Pneumatic Transportation

    Transport air and exhaust air

 When the fiber passes through a fan there can be fiber damage and excessive nep formation. Additionally, the system should be correctly installed to avoid the following problems:

 

•  A material handling fan must be used to minimize fiber entanglement.
•  Run the fan as slow as practical to reduce the energy consumption,
•  Avoid excessive high vacuum in the cleaning machines otherwise the trash will tend to stay with the fiber or waste will be sucked back into the transport air.
•  The exhaust fan must draw more air than the transport fan delivers. Backpressures in air systems usually create problems.
•  The ideal fan speed must be determined by tests.
•  After every transfer of cotton from one machine to another, air and fiber must be separated. The duct cross- section and filter surface must be sufficient to ensure back pressure does not occur.

    Measuring air speed and under pressure

    To be added later.

    Air-conditions in the blowroom

      To be added later.