1
Abstract:
Moisture in atmosphere has a
great impact on the physical and mechanical properties of textile fibers and
yarns. Relative humidity and temperature decide the amount of moisture in the atmosphere.
High speed spinning machines generate high friction and provide additional heat
to the yarn, as a result moisture content of yarn is decreased due to
evaporation of its moisture content by additional heat. Increasing the speeds
in spinning result in decreased yarn quality for other processes because dry
yarn has the worse properties and if it is sold then result in monetary loss.
Conditioning is to provide an
economical device for supplying the necessary moisture to yarn to achieve its
natural moisture content. In this assignment yarn conditioning mechanism,
process parameters of conditioning, applications of yarn conditioning,
advantages and disadvantages of yarn conditioning are discussed and explained.
2
Introduction:
Yarn physical and mechanical
properties are directly affected by its moisture content and due to heat of
high production machines, it evaporates and deteriorate the yarn properties. Moreover
now a high production level is achieved in weaving and knitting machines due to
which yarn quality required to run on these machines should be very good. To
satisfy these demands without changing the raw material, it is possible to use
inherent properties of cotton fibers in short staple spinning. Cotton fiber is
hygroscopic material and has the ability to absorb water in the form of steam.
Hygroscopic property of cotton Fibers is directly related with relative humidity.
The higher the humidity and more will be the moisture absorption. An increase
in relative humidity of atmosphere increase the moisture content of cotton
fiber.
The fiber strength and elasticity
increase with the increase in moisture content. If the water content of the
cotton fiber is increased, the fiber swells and result in an increased fiber to
fiber friction in the twisted yarn structure due to which strength and
elasticity of yarn are increased. So, to increase moisture conditioning
processes are used to increase humidity in yarn surroundings to increase its
moisture content.
3
What is yarn conditioning?
“Yarn conditioning is a process
in which yarn is conditioned for better performance (such as strength, serviceability,
luster, handle etc.) by increasing relative humidity in its surroundings or by
providing moisture in steam or any suitable form.”
4
Why conditioning is required?
Today modern weaving and knitting
machines have high production rates at high speed operations. To run on these
machines, yarn should have best mechanical properties and also its physical
properties should not disturb. Yarn properties especially cotton yarn
properties have direct relation with moisture content of cotton fibers.
Moisture content is directly related with temperature and humidity of
atmosphere. Moisture content of cotton is 8.5% naturally but cotton fibers have
to pass through different spinning operations (opening, cleaning, carding,
drawing, combing, roving formation, ring spinning & winding). In these
processes, it is impossible to maintain 8.5% moisture due to heat produced by
high speed machines which continuously evaporate the moisture from fibers. As a
result a dry yarn or a yarn with low moisture content than natural is formed,
which has worst properties (strength, elasticity, luster, handle etc.) to run
on subsequent weaving and knitting properties.
In addition to subsequent
processes problems, monetary loss for a spinner is increased because the
evaporation of moisture results in weight loss of final yarn package. To
overcome all these problems, the best way is to maintain the natural moisture
content or to provide enough humidity at the end for moisture regain of fibers.
The first condition is impossible to achieve but the second way is applicable
and is used. So conditioning is must for a spinner to optimize monetary losses
and for a weaver and knitter for smooth (low breakage) running of operations.
5
Types of conditioning:
Yarn conditioning at the end of
spinning processes is mostly done by using steam. But another option of
conditioning is available which is mostly used in different spinning processes
to control humidity and temperature is to use humidifiers. Humidifiers are very
less used for yarn conditioning at the end of spinning. So, conditioning has
two types:
- Conditioning by steam
- Conditioning by humidifiers
5.1
Conditioning by steam:
Saturated steam is used to
provide enough humid atmosphere to yarn packages for natural moisture regain of
fibers. Steam could be produced by a separate boiler or by a machine which
provides moisture to yarn packages. Steam conditioning has two methods of
application:
- Conventional conditioning
- Vacuum / Mechanical conditioning
5.1.1
Conventional conditioning:
In this process saturated steam
of 100OC is produced by a boiler and supplied to yarn conditioning
room where yarn packages are placed. Yarn packages are kept in conditioning
room for 24 hours for moisture absorption. Cotton fibers absorb moisture to
8.5% in conditioning room and regain their moisture that was evaporated in
spinning operations. Water jets could also be used instead of steam.
5.1.1.1 Advantages:
- It
is very efficient in twist setting of yarn that will reduce snarling effect in
subsequent processes.
- Simple process and don’t need any special
monitoring or operating skills.
5.1.1.2 Disadvantages:
- It
is a time consuming process.
- Top
layers of yarn package got a high moisture and inner layers gain a very low
moisture or may remain dry that produce variations in subsequent processes.
- A
large space (conditioning room) is required.
- It
prevents optimum flow of goods.
- Due
to large space yarn packages have tendency to re-adjust moisture content to
ambient conditions.
- The
steam used for conditioning could have moisture droplets in it.
5.1.2
Mechanical conditioning:
Xorella introduced CONTEXXOR
process of yarn conditioning. In this method a capsule shaped space is used by
machine and steam is produced within the machine and no separate boiler is
required. Low temperature (40-60OC) saturated steam is produced in which 100%
moisture is converted to gaseous state.
In process, yarn packages enter
in capsule and vacuum is created in it to eliminate air pockets in between yarn
structure. Then 100% gaseous steam is supplied and due to vacuum moisture is
evenly distributed from outer layer to inner layer of the package in 40-45
minutes.
5.1.2.1 Advantages:
- Due
to vacuum even distribution of moisture is ensured.
- Less
space required to machine as compare to a room in conventional.
- 100%
dry moisture ensures that no droplets are deposited to package.
- Process
is short and time efficient. Only 40-45 minutes are required.
- Low
energy consumption.
- Low
installation and maintenance cost.
5.1.2.2 Disadvantages:
- Operating and monitoring skills are required.
5.2
Conditioning by humidifiers:
Humidifiers are the devices used
to add moisture to any area where humid atmosphere is required. Humidifiers are
only used for conventional conditioning and add moisture to the room where
packages are placed for 24 hours.
Different types of humidifiers
are available:
- Spray type air washers
- Pan evaporative humidifiers
- Electrically operated humidifiers
- Air operated humidifiers
5.2.1
Spray type air washers:
Air washers consist of a row of
spray nozzles inside a chamber or casing. A tank at the bottom of the chamber
provides collection of water as it falls through the air and comes into contact
with the wet surface of the chamber baffles. The principal functions of the air
washers are to cool the air passed through the spray chamber and to control
humidity.
5.2.2
Pan evaporative humidifiers:
The evaporative type humidifier
is fully automatic, the water level being controlled by means of a float
control. In operation, when the relative humidity drops below the
humidity-control setting, the humidifier fan blows air over the surface of the
heated water in the tank. The air picks up moisture. The air is blown to the
space to be humidified. When the humidity control is satisfied, the humidifier
fan stops.
5.2.3
Electrically operated humidifiers:
Dry-steam electrically operated
humidifiers operate by means of a solenoid valve, which is energized by a
humidistat. When the relative humidity drops slightly below the desired level
set by the humidistat a solenoid valve actuated by the humidistat, admits steam
from the separating chamber to the re-evaporating chamber. The fan (which is
energized when the solenoid valve opens) assists in dispersing the steam into
the area to be humidified.
5.2.4
Air operated humidifiers:
These utilize a pneumatic
hygrostat as a humidity controller and an air operator to open or close the
steam valve. A decrease in relative humidity increases the air pressure under a
spring loaded diaphragm to open the steam valve wider. An increase in relative
humidity reduces the pressure under the diaphragm and allows the valve to
restrict the steam flow.
5.2.5
Advantages of humidifiers:
Ø Simply
add moisture to the conventional conditioning room and automatically operated.
Ø Spray
type air washers don’t need fuel to convert water to steam.
5.2.6 Disadvantages of humidifiers:
- Steam
or moisturized air provided by humidifiers could have water droplets in it.
- Tendency
of moisture absorption of cotton is good for steam but not absorb much moisture
from moisturized or humid air.
- Due
to low moisture absorption from humid air these are very less used for
conditioning but used to control humidity in back processes of spinning.
6
Pros and cons of yarn conditioning:
Everything in this world has both
positive and negative aspects. Similarly yarn conditioning has some advantages
and disadvantages, described below:
6.1
Pros:
Yarn conditioning improves yarn
performance such as strength, serviceability, luster, handle, etc. of yarn. It
also effects performance of subsequent processes such as weaving and knitting.
6.1.1 Weaving:
- Yarn breakage frequency at weaving is reduced.
- Fly is reduced.
- Due to conditioning yarn take-up of sizing material is increased.
- Aesthetic properties of fabric such as feel and comfort are improved.
6.1.2 Knitting:
- Wax sets well and don’t melt from waxed yarn used in knitting.
- Efficiency of knitting machines is increased by 20%
- Needle breaks are reduced at knitting machines.
- Moisture content is uniformly distributed due to which variations in resultant fabric are reduced.
- Stitch formation is more regular because of reduced breaks.
- Chances of size change in final fabric are reduced.
- Electrostatic charges are eliminated due to moisture regain.
- Fly is reduced.
6.1.4 Dyeing:
- No stripes in dyed fabric.
- Better dye ability.
6.2 Cons:
- Uneven moisture absorption in conventional method produce variations in yarn properties.
- If moisture environment is not controlled to optimum values then yarn properties are deteriorated. More moisture than standard cause cotton fibers to swell and produce mass variations.
- If moisture in conditioning goes too high, it may deteriorate the paper cones.
- Uncontrolled conditioning cause deposition of water droplets on packages.
7 Conditioning process for various yarns:
- 100% Polyester yarn: Yarn is loaded in the form of cones wound on plastic cones, in to a beam dyeing machine. Steam is pushed in and temperature is raised to 100°C at gradual increase of 3°C per minute. Steam is given for 15 minutes at 100°C followed by 15 minutes cooling completes 1 cycle. Cycle is repeated 4 times.
- 100% Nylon: Yarn is loaded in the form of cones wound on plastic cones, in to a beam dyeing machine. Steam is introduced and temperature is raised to 100°C at increase of 3°C per minute. Steam is given for 15 minutes at 100°C followed by 15 minutes cooling to a temperature of 50°C completes 1 cycle. Cycle is repeated for 4 times.
- Silk yarn: Yarn is loaded in the form of cones wound on plastic cones, in to a beam dyeing machine. Steam enters and temperature is raised to 70°C at gradual increase of 3°C per minute. Steaming for 15 minutes at 70°C followed by 15 minutes cooling to a temperature of 30°C complete 1 cycle. Cycle is repeated for 4 times.
- Cotton/Lycra (40's Lycra) or Viscose/Lycra (60's): These are conditioned at parameters same as silk yarn.
8 Conclusion:
After all above explanation, it
is concluded that optimum yarn conditioning should be done for smooth and
efficient running of yarn in weaving and knitting. Yarn conditioning is a great
technique to improve physical properties of yarn and mechanical performance of
yarn especially cotton yarn. Disadvantages are also present but using optimum
parameters eliminate the negative aspects. Different types and methods are
available and used according to requirement and budget by an industry.
Mechanical method by Xorella is widely used and is much efficient as compare to
others.
9 References:
- Research paper titled “Effects of yarn conditioning in short staple spinning” by Fracis & Taylor.
- Research paper titled “Yarn conditioning: An overview” by N. Muthukumar & Dr. P. Kandavadivu
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