Silk Manufacturing Process

Sakunthala Athukorala

Ag/07/012

Silk Manufacturing Process

Silk is a natural protein fiber produced by certain caterpillars in order to

encase themselves in the form of cocoons. Silk has set the standard in

luxury fabrics for several millennia. The origins of silk date back to Ancient China.

Legend has it that a Chinese princess was sipping tea in her garden when a cocoon

fell into her cup, and the hot tea loosened the long strand of silk. Ancient literature,

however, attributes the popularization of silk to the Chinese Empress Si-Ling, to

around 2600 B.C. Called the Goddess of the Silkworm; Si-Ling apparently raised

silkworms and designed a loom for making silk fabrics. The making of silk is

different from that of other natural fibers. There are many steps involved in silk

manufacturing.

Cultivation of Cocoons ( Sericulture)

Filature Operations

Manufacturing of Silk Yarns

Finishing of Silk Fabrics

Manufacturing Process for Silk Yarns

Silk is a fine translucent fiber produced from the silkworm. The manufacturing

process of silk starts with the rearing of cocoons. There are many varieties of the

silkworm from which the silk fiber can be obtained. However, it is found that the

fiber obtained from the larva of Bombyxmori is of commercial value. The process of

obtaining silk fiber from Bombyxmori requires careful nourishment of the cocoons

which is put through the spinning process.

Cultivation of Cocoons:

The process of cultivating the silkworm for the production of raw silk is called as

sericulture. Silk fiber is a continuous filament fiber consisting of the fibroin, which is

connected together with the silk gum, sericin. This natural protein or fibroin is

secreted from two salivary glands.

There are four stages in the life cycle of the moth which are as follows:

1. The egg, which develops into a larva, or caterpillar – the silkworm

2. The silkworm, which spins its cocoon for protection, to permit development

into the pupa

3. The pupa emerges from the cocoon as the moth.

4. Female moth lays eggs, so continuing the life cycle.

They may be hatched three times a year. The female moth lays around 350 to 400

eggs and the moths die soon after. As they are subject to hereditary infection, the

eggs from infected moths are destroyed which results into production of fine silk.

Larvae of about 3mm are hatched from the eggs. For about 20 to 30 days, they are

carefully nurtured and are fed five times a day on chopped mulberry leaves. Ideal

temperature 23c-27c, humidity is 65%-80%.The silk moth lays eggs,

The flowing pathway is used to the production of silk fiber:

Sexing

Silk of moth caterpillars has been used for textile manufacture.

When sexing pupae are used by identification of male and female pupae by

looking at the back.

Have to do sexing on 8th day after pupation. Then cut the cocoon do not

separate cut top, and then place the cocoons in a box like drawer.

Cover the box with tissue paper and two boxes separate male and female.

Mating

The silk-moths cannot fly because their bodies are too heavy in relation

to their wings. Male’s silk-moths die soon after mating while one single female

silk-moth lies from 300 to 500 tiny eggs before she dies. The eggs hatch into the

silkworms in spring time and the complete cycle takes approximately about two

months.

In 11thday, just after emergence mating with male and female by both are

coupling.

Mating for about one day every 30 minutes ejaculate sperms.

Silk-worms Moths MatingDecoupling

After 1 ½ hours. Because need three ejaculations.

Egg laying Silk moths lay eggs on specially prepared paper by using paper card method.

Laying eggs

Chemical treatment of eggs

I) Formaldehyde treatment (2%)-When immersing eggs are disinfected.

II) Acid treatment (1.1 5g Hcl)-eggs are immersed for 5 minuets

III) Washing in running water

IV) Air drying-keeping under the fan

Incubation

I) 1st day to 7thkeep the eggs rapped in a tissue paper.

II) 8th day-black boxing, eggs are rapped with black paper or put in to black box

to prevent irregular hatching.

Hatching

11th day morning all the eggs are gray in color with dark spot.

Expose eggs to light and then eggs are hatched around an hour.

Silkworm are white but this stage black in ant stage

.Which hatch into an ant called as larva about 1/8 inches (3mm) in length.

This can be done at breeding station or rearing station.

Brushing

Keep the eggs cards are rearing trays and removal of warms from egg

shells/cards.

Then giving 1stfeed (1cm strips of lender mulberry leaves).warms are very

attractive to mulberry leaves because it contain citral.

Warm rearing station

I) feeding

II) Cleaning

III) Increasing space

Feeding the larva

The larva at this stage has voracious appetite and requires careful nourishment.

They are fed 5 times a day on chopped mulberry leaves.

After four changes of skin or molting the worm reaches full growth of about 3

½ inches (9cm) long.

At this stage the interest in the food ceases and is ready to spin its cocoon.

The silkworm begins to secrete a protein like substance through a small

opening under the caterpillar’s jaws which is called as the spinneret.

The silk solidifies when it comes in contact with the air.

On 3rd day, 20000 warms need 0.8 square meters.

Stop feeding for about day 20 hours need molting.

4th day do not feed even feed even feed they do not eat. End of the 3rdmoulting

management and maintain low RH.

5th day-2nd instars-spacing gradually increase.

7th day -molting management

8th day-3rdinstar,increasespace,feeding mature leaves and cleaning

11th day -molting

12th day-4th instars

16th day-molting

17th day-27th day-5thinstar, branch feeding. This called flour rearing or table

rearing.

Early silkworms mature silkworm’s larvae

Pupation-On 27th day they leave the leaves and look for a corner to build a

cocoon. Within twenty – four hours and in three days the cocoon is complete to a

size and shape of a peanut shell.

The filament is in the form of a double strand of fibroin, which is held together by

a gummy substance called sericin, or silk gum.

As this cutting through damages the cocoon, the filament cannot be unwound in

one long thread. The life cycle is terminated at this point by a process known as

stoving, or stifling.

If left undisturbed, the pupae inside the cocoon develop into a moth within two

weeks. To emerge, the moth breaks open the cocoon by secreting an alkaline

liquid that dissolves the filament.

Processing & grading

The silk yarn production begins with selecting for their quality.

The cocoons will be sorted into normal and abnormal cocoons.

The fresh cocoons normal are reelable to produce raw silk but the abnormal

cocoons are unreelable.

The abnormal cocoons are double cocoons, perforated cocoons, internally and

externally soiled cocoons, thin-end cocoons, thin-middle cocoons, malformed

cocoons, etc.

After the first selection of cocoons,

They have to be dried.

The first goal of cocoon drying is the protection of cocoon quality, to preserve

conditions for reeling cocoons and prevent damage that might be caused by

long periods of storage.

Drying kills the pupa and evaporates moisture that would otherwise ruin

cocoons.

Dried cocoon storage conditions are designed to keep the raw material for long

periods without any damage from moulds and pests.

Cocoon storage should preferably be built with double walls. Cloth or

polyethylene bags are recommended as containers for dried cocoon storage.

In most modern factories which aim at producing high-grade raw silk, the

cocoons are graded on visual inspection or by mechanical tests are actually

mixed as in the required proportions. This is called cocoon mixing or blending

and is done to ensure speed and uniformity of reeling as well as to obtain the

desired effect in raw silk.

The reelable cocoons have then to undergo the reeling processing, after which

they are either processed further to raw silk or to thrown silk. The unreelable

silk is processed further to spun silk.

The technological process of silk reeling.

Technological process for silk reeling.

The End