Toughened Glass

Introduction

Toughened glass acquires a degree of strength for excess of the strength of normal glass sheet or plate glass, which if broken shatters into small and comparatively harmless pieces. It is claimed that the resistance to mechanical stock of toughened plate glass is 4 to 5 times more than that of ordinary plate glass. A toughened glass has better resistance to the vibration, mechanical shock and abrasion.

Toughend Glass has to pass the following important tests:

i. Transfer strength test on sheets on simply supplied (Modules of rupture and electricity)
ii. Impact test: By following weight on sheets supported on two wooden battens
iii. Impact by falling weight on sheet evenly bedded (on putty)
iv. Impact by falling weight on edge of sheet
v. Repeated twisting tests
vi. Sand blast abrasion
vii. Thermal tests

Because of the strength and other specific physical properties mentioned above, it finds applications in the following fields:

Market Potential

With increased transportation facilities the demand of the product is increasing at a steady pace specially in the automobile industry, railways, ships building both for production and replacement.

Basis and Presumptions

The project is based on single shift of 8 hours with 300 working days.

Implementation Schedule

Technical Aspects

Process of Manufacture

The glass plate is heated to a temperature above its softening point and then subjected to rapid cooling. The glass is suddenly chilled and in this process contracts towards the core. It stretches until it has solidified and is no longer able to contract further at this stage the core is still soft. It contracts against restrained exercise by the solidified upper layer of the glass. This compression is responsible for the strength of the glass sheet, which is limited to about 20,000 lb/sq.inch. Thus it is highly stressed and the resultant force is able to nullify the external impact.

The intensity of the stresses depends on the rate of cooling, co-efficient of expansion, thermal conductivity of the glass, its specific heat, elasticity, and certain other physical properties.

Toughening Process

The raw plate glass sheet which is free from waviness, distortion etc., is cut to required size and shape and then all the edges are ground and polished as per end use of the product. This is called edge grinding and polishing and is very important for toughening because it will lead to breakages during process. No glass sheet can be toughened without edge grinding and polishing.

Washing and Drying

After the edge grinding and polishing the glass sheets are washed manually or by machine and then dried. The glass sheets are fed into the furnace (Electrically operated). The sheets are kept in the furnace above its softening point, which varies according to the composition of glass. After attaining required temperature the glass sheets are removed out of the furnace and placed in the air blowing quenching boxes for 20 to 25 seconds. After quenching glass sheet is toughened. For bend glass toughening, the glass sheets passes through a set of dies (as per shape) after furnace and then to the quenching boxes.

Testing

After toughening all the sheet glasses are passed through the polariscope inspection.

Quality Control and Standards

IS 2553:1971
IS 6180:1971
IS 6640:1972

Financial Aspects
A Fixed Capital

(ii) Plant and Machinery

B. Working Capital (Per Month)
( i ) Staff and Labour (per month)

(ii) Raw Materials (per month)
(75% Production in the year)

C. Total Capital Investment

Machinery Utilization

75% utilisation of machinery and manpower has been taken into consideration.

Financial Analysis

2) Turnover

For calculation purposes, it is assumed that the unit shall manufacture flat toughened glass of size 5 to 6 mm. the average sale prices of which is taken at Rs.70 per sq.ft. total 3,84,000 sq.ft. (per year), after allowing rejection of 24,000 sq.ft., the saleable quantity will be 3,60,000 sq.ft., @ Rs.60/- per sq.ft.

(6) Break-even Point

Additional Information

a. Capacity utilisation has been assumed at 75% in the 1st year.

b. The raw materials and sales prices have been taken at the prevailing market and sales prices have been considered ex-factory

Addresses of Machinery Suppliers

1. M/s. Associated Erectors (Calcutta)
14 A, S.N. Banerjee Road,
Kolkata-700 013.

2. M/s. Andrew Yule and Co. Ltd.
Yule House, B. Civil Row,
Kolkata-700 001.

3. M/s. Punam Machine and Tools
10, Ganesh Chandra Avenue,
Kolkata - 700 013.

4. M/s. Eastern Engineering Works
7, Fancy Lane, II Floor,
4 A, Courz in House Street,
Kolkata - 700 001.

5. M/s. Supertuf Industries
3/93, DB Gupta Road,
Paharganj, New Delhi.

Raw Material Suppliers

1. M/s. Shree Vallabha Glass Works
Vallabha Vildyanagar,
Via Anand, Dist. Kaira,
(Gujarat)

2. M/s. Hindusthan Pilkington
Glass Works Ltd.
Assansol, (West Bengal)

3. M/s. Triveni Sheet Glass Works Ltd.
Bhurpur, Allahabad (UP).

4. M/s. Indo Asahi Glass Works Ltd.
Hazaribag, (Bihar)

5. M/s. Haryana Sheet Glass Works Ltd.
20th Mill Stone,
P. S. Rai, Sonepat,
(Haryana)

6. M/s. Saraikela Glass Works Ltd.
Kandra, Singhbum, (Bihar)

Contact for more information:

Information Manager
TIMEIS Project
E-mail: timeis@ficci.com