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Tuesday, December 24, 2019
CARDING PROCESS PARAMETERS,
CARDING PROCESS PARAMETERS:
The selection of correct process parameters is a very important and critical task in any process. The right selection always gets reflected in the form of a better quality of yarn in the carding process. The production cost also reduces with the correct process parameters.
The some common and the most important process parameters are given below:
• Specifications of cylinder wires clothing.
• Specification of flat tops wire clothing.
• Specifications of licker-in wires clothing.
• Specifications of doffer wires clothing.
• Draft between feed roller and doffer.
• Cylinder, flat tops, doffer and licker-in wire’s life.
SPECIFICATIONS OF CYLINDER WIRE’S CLOTHING:
The specifications of cylinder wires play an effective and decisive role in carding performance. The specifications are selected more precisely according to the quality of raw material to be processed, cylinder speed and rate of production of the carding machine. The characteristics to be considered in the selection of wires of the cylinder are given below:
• Front angle of wire.
• Tooth profile.
• Tooth pitch.
• Rib thickness (width).
• Wire population.
• Tooth point.
• Tooth depth.
Front angle of wire:
The front angle of the cylinder wire is selected according to the working speed of the cylinder and fibre to fibre cohesion force acting in the material to be processed. The degree of the front angle is inversely proportional to the working speed of the cylinder. Higher cylinder speed requires a lower front angle of wire for a given fibre. A higher production rate requires a higher cylinder speed. Thus higher production needs higher space in the wires.
The higher speed of the cylinder creates a higher centrifugal force. This force tries to eject the fibre from the cylinder, along with the trash. This centrifugal force affects the wire’s front angle. A cylinder having a low front angle of wire and working at very low speed gives poor quality in the processing of material of high frictional force. This poor quality is found due to fewer fibres transfer from cylinder to doffer. In this way, recycling of fibres takes place, which results in the form of more neps and entangled fibres.
The new profile with a less free blade avoids loading of the cylinder with fibre and trash. This helps in keeping the fibres at the tip of the tooth. The movement of the fibres towards the tip of the tooth coupled with centrifugal action demands an acute front angle to hold the fibre in place during carding.
Since the fine fibres or long-staple fibres has very low stiffness so that such kind of fibres need more control during carding process. This control is achieved by choosing the correct tooth pitch. This tooth pitch provides the correct ratio of the number of teeth to the fibre length. Short fibres and fibres having less stiffness require less tooth pitch.
The rib width decides the number of points across the carding machine. The rib width is selected on the basis of fibre characteristics and the rate of production of the machine. The finer fibres need finer rib width. The finer rib width is selected for the higher rate of production.
The product of the rib thickness and tooth pitch is called the population of a wire. Generally, a higher production rate needs a higher population of wires.
The sharp tooth points penetrate the fibre tuft more easily and help to increase the carding action. The cut-to-point wires are sharp and they have no land at all.
The effective working depth of a cylinder wire tooth for cotton is approximately 0.2mm and for synthetic materials approximately 0.4mm. The man-made fibres require more space in their cylinder wire than cotton. More tooth depth allows the fibre to be recycled, resulting in damaged fibres and neps. If tooth depth is insufficient, fibre control is lost. This results in an even greater nep generation.
SPECIFICATIONS OF DOFFER’S WIRE’S CLOTHING:
The specifications of doffer’s wire are given below:
• The main function of doffer in the carding machine is fibres stripping from the cylinder. This stripping action is also called carding action.
• The front angle of the doffer wire greatly affects the fibre releasing from the cylinder. An optimum angle of 60° is used to achieve better stripping of fibres
• The wire population in doffer is kept below 400 ppsi to achieve a better quality of yarn.
• The doffer wire height is kept 5 mm. in carding machine having a small doffer. This wire height improves the transfer of fibre from cylinder to doffer.
• The fibre friction and high doffer speed greatly reduce the fibre holding capacity of doffer. Therefore wires with striations are used to achieve better results in the carding process.
SPECIFICATION OF LICKER-IN WIRE’S CLOTHING:
• The fibre to fibre opening is achieved by the licker-in. The cotton tufts are open fully with the help of licker-in. A licker-in wire angle of 85° is generally used for the processing of synthetic fibres as well as medium and long-staple cotton.
• A wire angle of 80°gives better performance in the processing of coarse and dirty cotton fibre.
• The hardness and strength of wire and sharpness of wire points have a very big impact on the performance of a carding machine. The wires of licker-in never grind.
• The thinner blades efficiently reach deeply into the fibre tuft. The wire’s life is also increased.
• The higher number of wire rows per inch in licker-in gives better results. Today licker-in has up to 12 wire rows per inch. It gives better performance than licker-in having 8 wire rows per inch.
• If the wire pitch is not insufficient, the wire pitch is compensated by increasing licker-in speed, higher licker-in speed causes fibre rupture. The licker-in speed varies according to the rate of production and types of fibres to be processed.
SPECIFICATIONS OF FLAT TOP WIRES:
The specifications of flat tops to be used commonly in the carding process are given below:
• The use of flat-top having more than one population gives improved carding performance.
• The combination of 80/450 is used in the flat top generally. This combination gives better performance in the processing of both materials (cotton and synthetic fibres). The rigidity of the fillet is used according to the material to be processed. Different fillet rigidity is used in cotton and synthetic fibre.
• The number of wire points on stationary flats is a very important factor in carding production. Normally, the number of wire points varies between 300 to 400. 600 number of wire points are used in high production rate carding machines.
• If flat tops used in the processing of cotton are used for synthetic fibres processing, more heat is generated due to load on the cylinder. Hence high static charges develop and the chances of cylinder loading are increased.
• Semi-rigid flat tops give better performance in the processing of synthetic fibres.
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