Plastic Injection Moulding Specialists. Est 1948.

Plastic injection moulding machines control variables in the moudling process by allowing the setter to define parameter ranges and then raising an alarm if parameters are broken. The following variables are critical to maintain:

Temperatures

Machine Barrel / Nozzle – The barrel has regional heater ‘bands’ allowing plastic to be progressively heated as it approaches the mould, reducing the chance of burning or ‘cooking’ material. Material is required to be just above its melting point as it reaches the nozzle at the end of the barrel.

Strokes, Speeds & Times

Mould Opening, Closing / Ejection / Screw Rotation, Retraction / Back Pressure – Control over the time and speed and at which parts of the machine move during the cycle can be set to precise tolerances. These values are optimised during mould trials so that production occours with moulds running at their most efficient cycles. The optimum settings for each mould can be recorded in the NC computers ROM for recall when the tool is run again.

Pressures

Injection / Follow Up / Nozzle Contact / Ejection – The pressure at which the molten plastic is injected into the mould, and the subsequent follow up pressure required to pack the plastic into the mould differ from tool to tool. The pressure required will be dictated by the amount of resistance that the mould tool puts on the flowing plastic. Design features such as hinges and narrow wall thicknesses restrict flow of plastic and so call for higher injection pressures.

The pressure at which the nozzle is applied to the back of the mould can be adjusted to prevent any material leakage as can the force with which the ejector pins push the moulding from the cavity.

Lock Adjustment

Fine adjustments can be made to the pressure holding the two halves of the mould together during the injection process. The mould must not be pushed apart at this stage as this will cause ‘flashing’ where the moulding will be useless and overblown. The pressure of the plastic can actually force the mould tool apart with extreme flashing damaging the tool. Most often when plastic flows across the mould face into mechanical parts of the tool.