Meaning
Machined clearance behind a sealing surface prevents excessive wear and damage to the mould. This shut-off land relief limits the contact area to the minimum required for a clean part. By removing material just behind the parting line, the designer ensures that any misalignment does not crush the entire face.
It also provides a path for gases to escape away from the cavity.
Area Reduction
Cutting away the steel behind the seal focuses the clamping force on the critical shut-off edge. This shut-off land relief prevents the mould from flashing by ensuring the pressure is high enough to stop the plastic.
Tool Protection
Preventing the contact of large flat surfaces reduces the risk of the mould halves becoming stuck due to vacuum. The shut-off land relief ensures that only the intended areas touch when the tool closes. This protects the delicate details of the cavity from being damaged by uneven clamping.
Gas Venting
Escaping air moves from the cavity vents into the larger space created by the clearance. This shut-off land relief acts as a secondary channel that leads the gases out to the atmosphere. It prevents the buildup of pressure that could lead to burn marks on the moulded parts.
Machining this relief into both halves of the tool provides the best results for high-speed production. Regular cleaning of the relief area prevents the accumulation of wax and gas residues.
