As mentioned above, we can divide feeding systems into two categories. We can consider the flow process through the injection moulding machine via cold channels as the ‘normal’ feeding system, but this is actually called a cold runner system. So what is the definition of a hot runner system? Obviously, hot runner systems have channels where plastic flows are being heated.
The cold runner system is an unheated channel and has the function to create a passage of molten plastic into a cavity after it is dispensed from a nozzle. The channels of cold runner systems are larger because it needs to transfer a greater flow of plastic with each cycle. A big advantage of a cold runner system is the ability to handle many different polymers and it's rather easy to switch between colors.
The hot runner system is made out of two heated plates. Both these plates are heated internally and externally. The hot runner system is ideal if the flow needs more control and management. Some materials are sensitive to heat, in that case we can use the externally heated moulds only. The materials are kept in a molten condition throughout the process until this material flows into the mould cavity. There are many other methods available for the hot runner system such as heating pipes and heating rods.