First of all, there are two main methods of creating a CD copy. First of them is replication, also known as disc manufacturing, while the second is duplication, aka disc burning.
In this post I’d like to tell you something more about disc replication.
According to Wikipedia, compact disc manufacturing is the process, by which commercial compact discs (CDs) are replicated in mass quantities using a master version created from a source recording.
Probably you are now wondering how it’s done, so lte me tell you:
CD moulding machines are specifically designed high temperature polycarbonate injection moulders. They have a throughput up to 1000 discs per hour, per moulding line.
Clear polycarbonate pellets are first dried at around 130 degrees Celsius for nominally three hours (dependent on which optical grade resin is used). Ten, they are fed via vacuum transport into the one end of the injection moulder’s barrel (called the feed throat) and are transported to the injection chamber via a large screw inside the barrel.
The barrel, wrapped with heater bands ranging in temperature from circa 210 to 320 degrees Celsius melts the polycarbonate. When the mould is closed the screw moves forward to inject molten plastic into the mould cavity. When the mould is full, cool water running through mould halves, outside the cavity, cools the plastic so it solidifies somewhat.
The entire process from the mould closing, injection and opening again takes approximately 3 to 5 seconds.
The moulded “disc” (often called informally ‘green’ disc, i.e. unprocessed) is removed from the mould by vacuum high-speed robots with vacuum suction caps and moved onto the infeed conveyor or cooling station of the finishing line before metallisation.
At this point the discs are clear and contains all the digital information. But because there is no reflective layer, they cannot be played. Yet 
Discs then pass, one at a time, into the metaliser. It’s a small chamber operating at approximately 10E-3 Torr vacuum.
This process is called ’sputtering’. The metaliser contains a metal “target” made of an alloy of mostly aluminium and some small amounts of other metals.
There is a system of a load-lock (like an airlock) so that the process chamber can maintain high vacuum as the discs are exchanged. When the disc is rotated into the processing position by the swivel arm in the vacuum chamber, a small dose of argon gas is injected into the process chamber and electrical current is applied to the target. This results in a plasma ignition and the aluminium target evaporates onto the disc (Speaking scientificly it should be called an anode – cathode reaction).
The metal coats the information side of the disc (upper surface) and covers the pits.
This metal layer is the reflective surface that can be seen on the reverse of a CD.
This thin layer of metal is unstable and will oxidise if it is not protected by a lacquer.
That’s the reason why after metalisation the discs pass onto a spin-coater, where UV curable lacquer is dispensed on to the metal layer and spun rapidly to coat the entire disc in a very thin layer (circa 70 nm).
After the lacquer is applied it passes under a high intensity UV lamp which cures the lacquer. The lacquer also provides a surface for the screen printing or offset printing ink to adhere to.
CD technology allows to store up to 800 megabytes of audio, video, and data in various formats which are defined in the Rainbow Books.
A CDÂ can usually be manufactured with strict manufacturing tolerances for only a few US cents.
If you want to learn more about the prices, visit this CD replication site.
Thank you for reading. Next time I’d like to tell you about cd/dvd duplication.
