Silk Manufacturing

Iravatha Silk Manufacturing
Iravatha Silk Manufacturing Company is one among a few silk manufacturing and marketing
companies in Karnataka State in India, which produce high quality silk yarn of various grades. It is one
of the company which has recently set up a planning unit with the objective of adopting modern,
technology for improving both its production and marketing operations.
Cocoons form the major raw material input for silk yarn production. These are mainly of two types
namely, Multivoltine and Bivoltine, based on the silkworm race. The multivoltine cocoons bought
from the market usually contain different grades, known in the trade circles as Improved A, Improved
B, Improved C, and Ordinary. As soon as the bought out cocoons arrive at the production facility, they
are stifled and sorted into three types, Good, Double and Bad, based on their quality. The percentage
composition of the multivoltine cocoons and bivoltine cocoons, and the quality composition in a batch
of bought cocoons are given in Table 1. The current market price for the bad cocoons is Rs.10/- per
Table 1: Quality parameters of a batch of cocoons

Types of
Grades of
of arrivals
Quality Composition of batch of
Silk waste
Good Double Bad
Multivoltine Improved-A 10% 95% 1.8% 3.2% 3.2%
Improved-B 50% 90% 2.5% 7.5% 7.5%
Improved-C 20% 85% 4.0% 11.0% 11.0%
Ordinary 20% 75% 8.0% 17.0% 17.0%
Bivoltine 90% 2.5% 7.5% 7.5%

Raw silk is produced from the cocoons using an operation called Reeling. The raw silk so obtained is
re-reeled to overcome defects like short length of fine sizes, broken threads, entanglements and hard
gum spots, etc. In the process of reeling and re-reeling, some amount of wastage is inevitable and this
is known as silk waste. At present, the silk waste is selling at Rs.50/- per Kg. The composition of silk
waste for different grades of cocoons is also shown in Table 1.
The silk reeled from the multivoltine cocoons are called as Multivoltine silk or more commonly as
Filature silk. Bivoltine silk is that which is reeled from the bivoltine cocoons. The silk which is reeled
from the double cocoons is called Dupion silk; however, dupion silk can also be produced using good

Iravatha Silk Manufacturing
cocoons. Usually, the silk produced from reeling and re-reeling procedures can be graded on the basis
of their denier values. Denier is the weight in grams of 9000 meters of a filament of silk yarn. It is
dependent on the strand thickness of the filament from each cocoon and the number of cocoons used to
produce the silk yarn. From the past experience and through detailed market surveys, the company has
come to the conclusion that 13/15, 16/18, 18/20, 20/22, 26/28, 28/32 and 40/45 grades of filature silk
and 20/22, 28/32 grades of bivoltine silk have substantial market potential at present.
The company produces different grades of silk each month. The production of different grades of silk
require different amounts of manual time, machine time, and raw material. The finer the denier, the
higher the Renditta (Renditta is the quantity of cocoons used to produce one Kg of raw silk). The
renditta from different grades of cocoons used to produce different grades of silk are presented in Table
2. After the silk filament is unwound or reeled, the cocoon shells which contain dead pupae in it are left
out. These dead pupae, which are used for producing oil, could be sold as by-products. From the past
experience, it has been found that the weight of dead pupae is around 20% of the weight of the cocoons
consumed. The present market price for the dead pupae is Re.1 per Kg.
Table 2: Renditta from different grades of cocoons

Types of
Grades of Cocoons Grades of Silk
13/15 16/18 18/20 20/22 26/28 28/32 40/45
Multivoltine Improved-A 9.5 9.3 9.1 8.9 8.6 8.6 8.5
Improved-B 10.0 9.8 9.6 9.4 9.2 9.2 9.0
Improved-C * 11.0 10.75 10.25 10.0 10.0 9.5
Ordinary * 14.0 13.0 12.0 11.0 11.0 10.5
Bivoltine * * * 9.0 * 8.6 *

Note: Cell value indicates : Kgs. Of cocoons/kg of raw silk and * indicates not produced by the company
The finer the denier, the less is the reeling and re-reeling productivity as more care should be taken by
both the reeler and the re-reeler. The number of working basins (reeling facilities) in Iravatha is 80 for
reeling and 15 for re-reeling. There are 70 reelers and 10 re-reelers working in the company on a
regular basis. The labour absenteeism is assumed to be 10% and is to be constant throughout the
planning period. The reeling productivity for different grades of silk from various grades of cocoons
are given in Table 3 and the re-reeling productivity for different grades of silk is presented in Table 4.
Apart from the regular employees, the company can hire at the most 20 reelers and 4 re-reelers. At
present, the management has fixed the daily wage at Rs.38/-. The number of working days per month is

Iravatha Silk Manufacturing
25 and the company works one shift of 8 hours per day. The variable cost of production related to
power, fuel and other incidental charges is Rs.20 per Kg of silk produced.
Table 3: Reeling Productivity for different grades of silk

Types of
Grades of
Grades of Silk
13/15 16/18 18/20 20/22 26/28 28/32 40/45
Multivoltine Improved-A 600 700 750 825 950 1000 1100
Improved-B 550 650 700 750 900 950 1000
Improved-C * 525 550 600 800 800 900
Ordinary * 450 500 550 800 800 850
Bivoltine * * * 700 * * *

Note: Cell value indicates : in grams/day/basin and * indicates not produced by the company
Reeling productivity for dupion silk 900 gm per basin per day
Table 4: Re-reeling productivity for different grades of silk (same for multivoltine and bivoltine;
dupion silk is not re-reeled)

Grades of Silk
13/15 16/18 18/20 20/22 26/28 28/32 40/45
3.6 4.2 4.2 5.0 6.0 6.0 6.0

Note: Cell value indicates : in kg/day/basin
The purchase department of the unit has planned the maximum quantity of each type of cocoons to be
purchased in each month based on the budget allocation for that month so as to utilize the capacity
available. As a result of this exercise, the maximum quantity of cocoons that could be purchased for the
following month is fixed at 35000 Kgs for multivoltine and 12000 Kgs for bivoltine cocoons.
The planning unit of the company has estimated the average purchase price of cocoons, the selling
prices for each type of silk the company produces and demand for each type of silk for the next month
(Tables 5 and 6) using sound forecasting techniques. This has been done with the purpose of
determining the best product mix of different grades of silk to be produced.
Table 5: Estimated average selling price of different grades of silk

Grades of Silk
13/15 16/18 18/20 20/22 26/28 28/32 40/45
Filature 897.50 821.50 839.70 863.00 790.50 849.20 485.00
Bivoltine 857.00 840.30

Note: Cell value indicates : in in Rs/Kg and — indicates not produced by the company
Dupion silk sells at Rs. 506 per kg.

Iravatha Silk Manufacturing
Table 6: Estimated Average Purchase price of different types of cocoons and estimated
demand (all deniers combined) for different types of silk

A) Type of Cocoon Price (Rs./Kg)
Raw material
B) Type of Silk Demand (Kg/month)
Raw material
Filature Silk
Bivoltine Silk

Usually, the planning unit successfully determines the quantities of cocoons to be purchased, consumed
and held, as well as the ideal quantities of silk to be produced, sold and held in inventory so as to get the
maximum net contribution. But, an important task ignored by the unit (due to time constraints) is to
take into consideration of different denier (grades) of filature and bivoltine silk to be produced so as to
make an uniform utilization of raw material – cocoon, men and machine hours – which yields the best
net contribution.
The objective is to develop a product mix plan which results in the maximum net contribution to the
company. Also, the company has come to know that there is a good market potential for some specific
grades of silk. The details of these grades and their estimated demand are given in Table 7. The
company would like to know whether it is worth producing these grades of silk with the prevailing
market conditions and perceived prices. They also need to know whether they can start producing these
specific grades of silk from the next month onwards.
Formulate the above decision problem as a Linear Programming Model and analyze the implications of
these decisions using the Linear Programming model.
Table 7: Estimated demand for different grades of silk in the market

Type Grade Estimated Demand (in Kg)
Filature Silk 18/20 20
20/22 40
40/45 25
Bivoltine 20/22 50