Compact Discs
We all use CDs/DVDs to store our data which we can reuse whenever required.
Compact Discs were made available worldwide in late 1982. These CDs have diameter of 120 millimetres which can hold
digital data upto 700 MB in size.
Lets see how Compact Discs are made.
Compact Discs are made from original glass discs. These glass discs are very thin and are placed in the machine
which brushes and cleans the surface of the glass disc. Cleaning of disc is done using ionized water and a brush.
One thing might have happened that during cleaning, water must have accumulated on the disc. This water is then
removed by placing the disc onto another machine which moves the disc rapidly. Once water is removed, then disc is
moved into surface analyzer machine. This machine consists of laser beam which inspects the cleanliness of the surface.
At this stage, two chemicals are applied on the discs, primer and photo resistant coder. This process needs to be
done at the temperature of 21 degrees centigrade for about 3 minutes.
Once this process gets complete, the disc needs to be delicately removed from the surface analyzer machine. Then
disc is applied on photo resistant machine for 30 minutes approximately. After this, ionized water is again applied on
the disc along with the chemical solution which edges the data on the glass. This process helps in engraving information
on the disc. This information is the same information which is stored in the compact disc and consumes few bytes of
compact disc's size.
Then the disc is placed in metal coating machine in which thin coating of Nickel and Vanadium. This process creates
a master unit, an important material from which compact discs will be made. This material of glass is then put into a
chemical solution for about 70 minutes. After 70 minutes, CD like structure is coated on its surface. It is called
as dye. This dye is then sent for a finishing from which fine compact disc will get fabricated from this mater unit.
Machine does stamping on the master unit thus resulting in very thin and fine compact disc like structure. Then
the coating is removed from the surface of this fine unit which had protected the engraved data which was engraved
in earlier process. Discs are made from plastics called as Polycarbonate. This unit is then sent to a moulding machine
where special solution of liquid polycarbonate is injected onto the disc.
After moulding the disc, the disc is then removed from the moulding machine and is sent for metal coating. This
metal coating will enable compact disc reader to read the data stored in it. At the time of metal coating, thin layer
of Aluminium is coated on to the disc. As all process is automated, compact disc production company can make
of about 100 thousands compact discs on an average per day.
Once metal coating is done, disc needs to be protected as it plays an important role while reading the compact
disc. For this, coat of varnish is applied. Once the coat is varnish is applied, discs are then moved into
pressing machine where labels are applied. This label applying process is very fast as the system prints 70 discs
in 60 seconds.
Once label printing onto the disc gets completed, these discs are then moved for packaging and are then ready to get
dispatched.
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