Types of Spinning (Man-Made Fibers)

The polymer being spun must be converted into a fluid state. If the polymer is a thermoplastic then it is just melted, if not then it may be dissolved in a solvent or chemically treated to form soluble or thermoplastic derivatives. The fluid polymer is then forced through the spinneret, where the polymer cools to a rubbery state, and then a solidified state.
There are four types of spinning: wet, dry, melt, and gel spinning.

Wet Spinning

Wet Spinning (Rayon)

In this method the common man made fibres spun are viscose rayon, alginate, acrylic fibres etc. the fibre forming polymer solution first de aerated and then pumped under pressure through metering pump unit, them through the filter and finally through the spinneret. The spinnerets are immersed in a spin bath containing coagulating fluid at a reasonable temperature, as the polymer solution emerges from the spinneret and travel through the bath it becomes coagulated by the chemicals of the spin bath.
Dia of holes, rate of solution feeding and rate of holes per spinneret may be 100000 numbers per squa4e inch diameter and space of holes in the spinneret could be varied.

Typical Wet Spun Fibers:

• Viscose
• Acrilan
• Creslan

Disadvantages:

• Slow(70-150 yds/min)
• Washing to remove impurities
• Solvent and chemical recovery

Advantages:

• Large tows can be handled

Dry Spinning:

One of the three spinning methods for spinning man made fibre is dry spinning method. Fibres produced by this techniques are acetate rayon, acrylic fibres etc. In this technique fibre forming materials are dissolved in volatile solvent. Each spinning unit consists of a pump and spinneret at the top pf a tall shaft about 9 to 15 feet high. There is an air outlet at the top of the tall shift and air in let at the bottom. The fibre spinning solution is forced under pressure from the storage tank to the spinning pump and then through the spinneret.
The number of holes, dia of holes and shape of holes varies according to requirements of a spinneret. The fineness of the filament is determined partly by the diameter of the holes but primarily by the relation between the rate at which solution is forced through the spinneret and rate at which the yarn is wind up. When the fibre spinning solution emerging from spinneret meet the worm air, volatile solvent evaporates leaving the filaments, hence coagulation takes place and becomes dried before leaving the chamber.

Typical Dry Spun Fibers:

• Acetate (acetone solvent)
• Triacetate (methylene chloride)
• Spandex(some) (dimethyl formamide)

Disadvantages:

• Flammable solvent hazards
• Solvent recovery
• Slow(?) (200-400 yds/min)

Advantages:

• Yarn does not require purification

Melt Spinning:

In this technique, the common man made fibres spun are Nylon, polypropylene etc. the fibre forming polymer chips are fed through a hopper into a spinning vessel. In spinning vessel, melts by the heated grid and passes through the grid mesh and collected on the pool. The n the melt is metered by a pump through a filter and finallyu through the spinneret.
The melt solidifies immediately it issues from the jets and so form filaments passes through a cooling chamber in which cold air current swept across the filaments. The spinning speed is approximately 1200 meters per minute.
Melt spinning has two big advantages over dry spinning. It avoids the need for a solvent recovery plant and loss of solvent during recover. The high fibre spinning speeds that are possible here.

Typical Melt Spun Fibers:

• Nylons
• Polyester
• Polypropylene

Disadvantages:

• Seperate drawing step (unless spin draw)

Advantages:

• High speed (275 to 1500 yds/min)(4000 yds/min spin draw)
• No solvents
• No purification problems