Where the
world gathers for metal finishing
Q&As since 1989


-----

Need Surface Finish polishing or coating for a small Plastic Worm Gear Injection Mold

We are looking for a method to either Polish or Surface Coat a Nickel Mold Component used to make Acetyl Worm Gears. The Outside Diameter of the Worm Gear is 5.24 mm with a Root Diameter of 2.99 mm. This means a through hole of less than 3.0 mm for a working diameter. The overall Length is 10 mm. The finished molded parts are unscrewed from the Insert and over time this causes wear that shown up as radial rings on the finished parts. The Polish or coating method will be used to reduce or eliminate the rings that cause defects in the molded parts.

Martin Cook
Injection Molding of Gears - Springfield, Tennessee, USA
July 23, 2008

The most important things to consider when choosing a protective coating are the superficial loads which will determine physical damage (deformation, scratches, etc.) and chemical attack. Both, heat treated, fully hardened Electroless Nickel (64/66 Rc, 0.001"/0.002" thick) or Titanium Nitride (78/80 Rc, 0.00003"/0.00005") have good chemical resistance for most plastic resins and may solve your problem after a professional polish. Titanium nitride works better when the substrate is hard enough to resist deformation, then it takes care of superficial wear with its exceptional hardness and lubricity. When the base material is softer and made of nickel or a nickel alloy, EN is a better choice because it adheres better and its thickness helps stop deep scratches and smearing.

Guillermo Marrufo
Monterrey, NL, Mexico
July 26, 2008