INJECTION MOLDING: Hot-Runner Valve Gating Without Knit Lines

New nozzles promise better part appearance and strength.

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A common cause of cosmetic flaws, especially with metallic pigments, is the melt flow path inside many valve-gate systems. The melt flows around the valve pin, forming a knit line that is propagated into the part. The solution, according to Paul Boettger, president of Technoject Machinery Corp., Bolton, Ont., is an unrestricted melt channel, so that the flow does not divide around the needle before reaching the gate. That’s the secret of the new Free-Flow nozzles from Heitec Heisskanaltechnik in Germany, represented here by Technoject. Besides appearance parts like covers and enclosures and optical lenses, these nozzles are recommended for larger automotive and appliance parts, where they offer both improved appearance and mechanical strength, due to reduced stresses. The design is also said to enable fast color changes.