The clamp section is the part of the blowmoulding machine in which the actual blowmoulding of the parisons is done. It is automatically controlled and repeats the same sequence over and over again with split second timing accuracy.
The clamps are fitted with precisely machined mould halves, which resemble the reverse of the part to be made. The moulds are mounted to the clamping plates, called ‘platens’.
The clamp section’s main job is to transport the mould between the parison pickup point under the extruder head and the parison blowing point under the blowing station. It also opens and closes the moulds at specific times during the machine cycle.
Remember that the parisons are continuously extruding. A parison of appropriate length must be quickly captured in the closing mould, severed by a cutting device, when whisked out of the way of the parison which continues to extrude in preparation for the next cycle.
The clamp section then positions the mould under the blowing station, and the blow pins are inserted into the parison which is now hanging in the mould. Compressed air is turned on and the hot plastic expands to fill the mould cavity there by taking its final shape.
Enough blowing time is applied to allow the parison to cool and cure against the walls of the cold mould. When the blowing is completed, the compressed air is relaxed, the mould is opened, and the blow pin is withdrawn. A newly blown hollow article falls away to a conveyer that will remove it from inside the machine. The clamp section is now ready to begin another cycle.
The blowmoulding machine shown here in full front view is a two sided shuttle machine. Each set of the platens contains a set of mould halves. They are alternately transported to capture the continuously extruded parisons. There is a blowing station on each side of the machine.
This one high output extruder is all that is required to process enough plastic into the three parisons being captured and blown in six mould cavities. This machine is typical of most continuous extrusion blow moulders; two-sided, multi-parison, high output extruder, and multiple mould cavities.
Two-Sided, Multi-Parison, High Output Extruder and Multiple Mould Cavities.
This one high output extruder is all that is required to process enough plastic into the three parisons being captured and blown in six mould cavities. This machine is typical of most continuous extrusion blow moulders; two-sided, multi-parison, high output extruder, and multiple mould cavities.
Inherent in continuous extrusion blowmoulding is some excess unblown plastic. This excess is called ‘flash’ and is the top and bottom of the parison which sealed outside of the mould.
Flash
Normally, the flash is automatically removed inside the machine by equipment attached to the mould or the blow pins, or by a secondary trimming unit. Sometimes it is removed after the part leaves the machine by a secondary deflashing machine or by a manual operation.
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