Meaning
Flat contact surfaces on the mould halves provide the seal that prevents plastic from escaping the cavity. This area, known as the parting line land, is the only part of the mould face that touches when the tool is closed. By limiting the contact to a small strip around the cavity, the moulder focuses the clamping force where it is most needed.
This prevents the tool from deforming and ensures the parts are free of flash.
Pressure Concentration
Reducing the total contact area increases the actual pressure on the sealing surface. The parting line land usually extends only a few millimetres from the edge of the cavity.
Venting Integration
Small grooves machined into the surface allow air to escape while the plastic fills the mould. These vents are placed at the outer edge of the parting line land to ensure the air is not trapped. The depth of these vents is small enough to stop the resin but large enough to let the air pass.
Surface Wear
Repeated opening and closing of the tool eventually wears down the contact surfaces. A hardened parting line land resists this wear and maintains its dimensions over many cycles. Regular maintenance and cleaning prevent debris from being crushed into the land and damaging the seal.
Worn surfaces allow plastic to enter the vent channels and block the air flow. Proper lubrication of the guide pins prevents the misalignment that leads to uneven land wear.
