Spinning Techniques

Engr. Shan Imtiaz

Definition

• Spinning is the process used

to convert the materials into

fibers.

Spinning Methods

• The method of spinning selected to manufacture certain

fibers is dependent primarily on the chemical

composition of the fiber. Some fibers can be

manufactured by more than one method.

• The three most commonly used methods for spinning

are

1. Melt spinning

2. Dry spinning and

3. Wet spinning

Gel spinning is a comparatively new technology

used more for high performance fibers.

Steps

Three main steps used in spinning

techniques

1.Conversion of a polymer into a liquid or

spinning solution, also called a dope.

2.Extruding the solution through a spinneret

i.e. pumping the dope

3.Solidification of the liquid into filaments

(solid)

Spinnerets

• To produce the manmade fibres the polymer in solution or molten form

is passed through a spinneret (a bathroom shower like screen with

very small holes). The spinneret converts the solution in very thin

streams which are then solidified to form fibres.

• The shape and size of the fiber can be easily changed by changing the

shape and size of the spinneret.

• Rate of holes per spinneret may be

100000 numbers per square inch and

space of holes in the spinneret could

be varied.

Melt Spinning

• Melt Spinning is used to manufacture thermoplastic

fibers such as nylon and polyester.

• The melt spinning process is the simplest and least

expensive spinning method.

Melt Spinning

Melt Spinning

• Polymer is heated and it melts to form a liquid spinning

solution. Chips of polymers are fed to a hopper which is

heated.

• There is a grid (sieve) at the base which permits only

molten liquid to pass through.

• Extrusion is done through spinneret vertically.

• Solidification is done by cooling, for which cool air

currents are used.

• For polymers which cannot be converted

into molten stage, two options exists

• Dry Spinning

• Wet Spinning

Dry Spinning • Dry spinning used to manufacture fibers that can easily

be dissolved in a solvent and then recovered without a

change in the polymer properties.

• Acetate, acrylic, modacrylic, and spandex fibers are

manufactured using the dry spinning method.

• In this case, a volatile solvent (acetone) is used to

dissolve the polymer and form a solution. Extrusion is

also in a vertical position. Solidification by evaporation

occurs when filaments come in contact with warm air

currents.

Dry Spinning

• The following steps are required for

using the dry spinning process:

1. Dissolving the fiber-forming substance in

a solvent

2. Filtering the fluid

3. Extruding the fluid through the spinneret

4. Solidifying the fiber by evaporating the

solvent using warm air (solvent is

recovered and reused)

5. Stretching or drawing the partially

solidified fiber

Wet Spinning

• This is the oldest method of man made yarn manufacturing.

• Rayon, spandex, and some acrylic fibers are produced using the

wet spinning method.

• A non-volatile solvent is used to convert the raw material (polymer)

into a solution.

• The solution is extruded directly in a horizontal position into the

precipitating liquid, this process for making fibers is called wet

spinning.

• The spinneret is submerged in a chemical

bath that causes the fibre to precipitate,

and then solidify, as it emerges.

• Solidification occurs through coagulation.

Comparison

MELT DRY WET

Disadvantages Separate drawing step

(unless spin draw)

Slow speed (200-400

yds/min)

Slow(70-150

yds/min)

Solvent recovery Solvent and

chemical

recovery

Flammable solvent

hazards

Washing to

remove

impurities

Advantages High speed

(275 to 1500 yds/min)

(4000 yds/min spin

draw)

Yarn does not require

purification

Large tows can

be handled

No solvents

No purification

problems

Gel spinning

• It is also known as dry-wet spinning because

the filaments first pass through air and then are

cooled further in a liquid bath.

• Gelled resins are spun into fibers. In the

gelstate, the fibers are partially bonded together,

resulting in increased orientation, and hence

higher strength, than that which results from the

other spinning processes.

• Examples are polyethylene and aramid fibers.

Spinning Techniques (Schematic Diagram)

Secondary processes

• After spinning, the fibers may be further

treated to improve properties, especially

stiffness and strength.

• Secondary processes include cooling,

annealing, drying, and, most important,

drawing.

Drawing

• Drawing is stretching the solid fiber. This

increases orientation and further induces

crystallization or reforming of crystals in

the oriented state.