Fiber Friction

Fiber Friction

WHAT IS FIBRE:

Fibre is a class of materials that are continuous filaments, having high length to width ratio. Fibres are made of polymers.Polymers are long chained elements.

Friction:

            Force that opposes the relative motion or tendency toward such motion of two surfaces in contact is called friction. It is not a fundamental force, as it is made up of electromagnetic forces between atoms.

According to Amontons basic law of friction

Frictional force is proportional to the normal force between surfaces in contact.

Mathematically it can be represented in such a way

Ff=µN

Where

Ff= Frictional force

N= Normal force pressing two surfaces

And

µ= Coefficient of friction

FIBRE FRICTION:

It is the surface property of the fibre when two solid surfaces slide against each other. When we talk about fiber friction then it is very necessary because it is the the force that holds together the fibre in a spun yarn and the interlacing threads in a fabric.

It is the surface property of the fibers when two solid surfaces slide against each other. For example if we rub silk fabric with itself or any other type of material static charge and heat energy is produced due to fiber friction.

There may be two kinds of fiber frictions

Fiber Fiber friction that is in between two same or different fibers.

Fiber Solid friction that is present in between fiber and solid particle or surface.

Fiber friction is very important in fiber technology, For example

High friction is required..

·         To enable drafting.

·         To provide effective transfer of fiber strength to yarn strength.

Low Friction is required..

·         To pas yarn through guides

·         To Provide good fabric drape

·         To minimize wear of fibers and fabrics

Effects of fibers friction on fibers:

·         Fiber friction can lead to damage of fiber surface

·         It weakens the fibers, even causes breakage of fibers.

Types of friction:

There are two types of frictions

Static Friction:

                        It is the force that must be overcome to begin sliding of two objects or fibers in contact.It is independent of area of contect

Kinetic or Dynamic friction:

                        It is the force that must be overcome to continue sliding. It is independent of sliding speed, however in case of some semi crystalline polymers this behavior is very complex.

One thing keep in mind that kinetic friction is always less than that of static friction.

Capstone’s equation is used to determine the development of tension as a fiber or yarn passes over a cylindrical surface.

The equation is

T1 /T2  =exp (-ө)

Where

T1 = Incoming tension

T2= outgoing tension

Ө= Angle of wrap or contact

By using this equation friction can be determined on a fiber..

The coefficient of friction is a function of the normal load, this simplest equation describe the relationship between friction force F and normal force N

Where F is frictional force

A and n are constants, and depends upon fiber and direction of rubbing and generally falls between ¾  - 0.9.

while N is the normal force

Fiber Fiber friction can be observed by this table

Fibers name	µ of static friction	µ of kinetic friction
Rayon on Rayon	0.35	0.26
Nylon on Nylon	0.47	0.40
Whole on Whole with scale	0.13	0.11
Whole on Whole against scale	0.61	0.38

Friction of Fiber on solids can be seen by this table

Fibers	µ of Fiber (axial)	µ Fiber (normal)	Steel	porcelain
Nylon	0.14-0.6	0.47	0.321	0.43
Rayon	0.19	0.43	0.39	0.43
Cotton	0.29, 0.57	0.22	0.29	0.32
Polyester		0.58
Oxide glass		0.13
Polytetrafluroethylene		0.04

Factors Affecting fiber friction:

·         Fiber weight

·         Force applied

·         Rough surface

·         Surface Area

·          Cross-sectional area

Fiber weight:

            If the weight of the fiber is large, the normal pressing force increases due to which the frictional force on the fiber will also increases.

Rough surface:

            It the surfaces to be moved are more rough, there are more crimps in the fibers then friction between them is also large.

Surface:

            Friction describes the resistance to being dragged or slid along a surface. The structured surface has more friction as compared to the smooth surface due to the scales or any other crimps on the fiber surface.

This can be observed in the figure given below..

coarse wool has more rough scales on the surface than fine wool, which produce the resistance when it rub with other material heat energy and static charge is produced. Polyester fiber, it has smooth surface but it also has the friction. Its Static behavior shows this property.

Cross sectional area:

            Cross sectional shape provide an area of link between two fiber surfaces, which is directly proportional to the fiber friction.

Fibre Friction in different fibres:

WOOL:

Wool have greater friction with respect to other fibres.

Hair is the best example of wool

Friction in flax fibre:

            It has less resistance or friction.

Friction in cotton fibres:

            Cotton has maximum friction due to convolution (natural crimp).

            A point to be noted that the wool fiber has less friction as compared to the cotton .due to high friction less fibrils produced in cotton yarn as compared to the wool yarn its due to natural crimp which has high friction.

DRAWBACKS OF FRICTION:

          Friction causes weakening or breakage of fibers. Some synthetic fibers contains small amount of titania TiO2, it is very abrasive and wear of clean the surfaces of metals. Therefore it can damage the whole machine.

 LUBRICATION:

          Polymers or fibers are lubricated with any suitable lubricant to prevent or minimize the effect of friction. Lubricants also prevents the static charges on the fibers, that effects the electrical circuits of machine.
Characteristics of a lubricant:

            Lubricants should posses following properties

Ø  It should be neutral with no charge carrier or any ion

Ø  It should be of low shear strength to adhere the surface of fiber or polymer strongly

Ø  It should be thermally stable, as in high speed processing large amount of heat is generated, so for a good lubricant it should be stable at that heat.

Hydrodynamic friction is achieved by imposing a continuous layer of lubricants between sliding surfaces in hydrodynamic region.