Parting Line Steel Preload Calculation for Multi Cavity Injection Moulds
Calculate multi cavity parting line preload by balancing machine clamp force against internal hydraulic separation force to maintain positive shut-off land sealing stress.
Land Relief Depth
Meaning
Recessed area on a mould parting line reduces the total surface contact between the two halves of the tool. Land relief depth ensures that the clamping force is concentrated on a narrow area surrounding the cavities. This configuration prevents the tool from deforming under the high pressures of the injection press.
Surface Area
Contact between the tool plates is restricted to a land that typically extends three to ten millimeters from the cavity edge. Land relief depth is the distance that the rest of the plate is ground down to create a clearance. By reducing the contact area, the moulder can achieve a better seal at the parting line with lower tonnages.
Venting Efficiency
Air and gases trapped in the cavity must have a path to escape during the high-speed injection phase. Land relief depth provides a wide channel for these gases to move into after they pass through the shallow vents at the cavity edge. This prevents gas burns on the parts and reduces the buildup of deposits on the tool surface.
Tool Longevity
Maintenance requirements and tool life are improved by preventing the crushing of the parting line. Land relief depth protects the precision-machined edges of the cavity from the full force of the clamp. Without this relief, the entire surface of the plate would eventually become uneven, leading to flash and part quality issues.
A depth of 0.5 to 1.0 millimeter is usually sufficient to ensure that the plates do not touch outside of the land area. This practice is a standard requirement in high-volume production where tools must run millions of cycles without losing their seal.