This document summarizes the manufacturing processes for glass and plastic. It describes the key steps for glass manufacturing as batch preparation, heating the materials, refining, conditioning, annealing, and molding. The main plastic manufacturing methods covered are injection molding for thermoplastics and casting for thermosetting materials. The document also outlines the lens surfacing process from blank to finished lens, including marking, blocking, grinding, smoothing, polishing, and cleaning.

1. MANUFACTURING OF
GLASS & PLASTIC
BY:
SASANKA SHEKHOR DUTTA
PRIYOM PARASHAR

2. GLASS MANUFACTURING

3. BRIEF HISTORY OF GLASS:
 History doesn't show when people first began to manufacture glass or even who
discovered how to turn sand into glass.
What we do know is that the oldest pieces of manufactured glass are beads that
date to around 3500 BC.

4. PROCESS:
 Batch Preparation:
Raw materials which includes oxides or salts of metals including silica, sodium, potassium,
calcium and aluminium are carefully checked against specifications, weighted and blended
before transferring to the furnace .
 Heating of Batch Material:
Above ingredients are mixed with CULLET (waste glass from previous melts) which facilitates
the mixing of ingredients. The furnace heated between 1000 – 1500 degree which in turn converts
the mixtures into a viscus stage.

5.  Refining Stage:
It is the purifying stage of the composition. It is done by raising furnace temperature up
to 1600 degrees in order to eliminate all gases present in the composition.
 Conditioning Stage:
The liquid form of glass from the previous processes are allow to cooled to make it more
homogenous for molding. The mixture is constantly stirred during conditioning stage.
 Annealing:
The lens is slowly cooled to room temperature to avoid internal stresses.
 Molding Stage:
After annealing when the correct consistency is reached the glass is cut into small pieces,
reheated and then molded into rough blanks. It is done with the help of rigid frame called
mold or matrix. The blank is then grind and polished to get the desired curvature.

6. PLASTIC MANUFACTURING

7. Introduction
• A plastic material is defined as a “polymeric material” of large molecular
weight which can be shaped by flow.
• At present times if plastics are processed properly and tailored for
appropriate applications, they may offer many advantages compared with the
materials they replace.
• Most plastics are synthetic materials formed by combining various organic
ingredients with inorganic materials such as carbon, hydrogen, oxygen,
nitrogen, Sulphur, chlorine etc.

8. Types
On the basis of physical properties, plastic lenses can be classified as:
i. Thermoplastic materials, which soften when heated and therefore can be
remolded.
ii. Thermosetting materials, which once hardened cannot be softened even at high
temperatures.

9. Thermoplastic Manufacturing:
Injection molding
 Thermoplastic materials have their molecules arranged in long chains.
 They are usually supplied in pellet, granular or sheet form.
 The material softens when heated and can be stretched, pressed or moulded into
complex shapes with no appreciable changes in its chemical structure.
 When cooled, the material hardens and shrinks and has the same configuration as the
mold in which it was heated.

10.  Since no chemical change transpires, the softening and hardening cycle maybe
repeated indefinitely.
 Thermoplastic materials are less dimensionally stable than thermosetting
materials and they can withstand less heat without deformation.
 Examples of thermoplastic materials are polymethyl methacrylates, cellulose
acetate, cellulose nitrate, polycarbonate, polystyrene etc.

11. Thermosetting Manufacturing
 Thermosetting materials are supplied in liquid monomer form and cast into
molds.
 Plasticizers, dyes, binding monomers and catalysts may be added to the basic
chemical compound, after which polymerization occurs.
 The molecules form a three dimensional cross-linked, lattice pattern rather than
the two dimensional structure of thermoplastic materials.
 This process transforms a liquid monomer first into a syrup, then into a gel and
finally into a solid.

12.  The relationship between the time and temperature required in the hardening process is
known as the curing cycle.
 Once hardened the material cannot be softened(even at high temperatures).
 If the thermosetting materials are subjected to high temperatures, the material
decomposes without melting or substantially softening.
 Examples: allyl diglycol carbonate{ Columbia Resin 39 (Pittsburg plate glass)}, melamine
compounds etc.

13. LENS SURFACING (From Blank to Lens)
Spectacle lens manufacturing involving many steps , collectively called as Lens surfacing.
1. Marking
2. Blocking
3. Grinding
4. Smoothing
5. Polishing
6. De –blocking & cleaning.

14. MARKING
 To correctly locate the lens for different stages of surfacing ,certain
markings are essential.
 Optical center position ,cylinder axis, base apex direction in case of prism.
 Done by marking with suitable ink or jugging at blocking stage.

15. Preparing Lens Blank
For all sphero-cylinder lenses axis position must be marked before blocking the
lens.

16. BLOCKING
 The block holds the lens in place through entire surfacing process.
 Alloy or wax is used to hold the lens blank to the surfacing block.

17. GRINDING
Optical surfaces on glass are produced by the process of grinding and polishing.
 Roughing
 First stage is removing the unwanted materials from the lens surface. This is followed
by trueing and smoothing.
 Roughing is performed by machines known as surface generators and the process is
termed as generating.
 The grinding agent is usually a diamond – bonded disc or wheel, termed as lap.

18. SMOOTHING

19. POLISHING
 Presently the polishing tools are lined with pads cut from polyurethane sheets.

20. De –Blocking & Cleaning
 The process of polishing is completed ,the lens is separated from its holder ( De-blocking )
and cleaned properly.
 Lacquer can be used for cleaning.

23. THANK
YOU