Meaning
Metal and polymer surfaces that appear flat under macroscopic inspection exhibit microscopic roughness composed of tiny peaks and valleys. At the interface, micro asperity contact occurs where these peaks meet, determining the true area of contact and the friction between the polymer melt and the mould steel. This interaction influences the demoulding process and affects how well the surface finish of the cavity is replicated on the plastic part.
Surface Friction
High ejection forces often result from the interlocking of these microscopic surface features during cooling. When micro asperity contact is high, the polymer replicates the surface roughness of the mould, increasing the force required to push the part out. This resistance can lead to part deformation.
Mould Release
Mould design uses polishing or texturing to modify this interface and reduce ejection difficulties. By controlling the micro asperity contact through appropriate surface treatments or release agents, moulders can reduce the adhesion force during ejection. This reduction protects the part from ejector pin marks.
Defect Control
Demoulding failures and surface scratching often occur when the microscopic contact area is too large. If the micro asperity contact is not optimized, the part can stick to the cavity or sustain cosmetic damage during the ejection cycle. This friction must be minimized to maintain a fast cycle time.
