【正文】 ed in very accurate thicknesses of to inches and can be ground or EDM’ed. Thus, electroless nickel often is used for dimensional buildups under flash chrome and for enlarging threaded cores and inserts or precisely sizing cavities. It also works very well on entire mold bases, A and B plates, ejectorbase housings, pin plates and pillar supports, providing years of lowmaintenance, rustfree operation. Know Your Mold Finishes Before determining what coating to use—if one is needed—the mold finish must be taken into account because, as noted earlier, certain finishes may actually increase the need for a mold coating, and some binations work extremely well together improving lubricity and release properties. There are four standard SPI finishes: diamond, stone, paper and blast. Each gives the molding surface a different appearance, from a glossy, mirrorlike surface (A1 Diamond) to a fairly rough, gritty texture (from blasting with glass beads or aluminum oxide). Each of the four finishes has three grades as well. Diamond The A1 Diamond finish is the most perfect finish available, which means it has the lowest RA value (roughness average). There are no high or low ridges. For example, a paper scratch on steel can rate a 2 to 4 RA finish, whereas an A1 Diamond is lensquality smoothness, generally 1 RA or less. Roughness is almost immeasurable. But a number of plastic materials tend to stick like glue to the flawless, mirrorlike finish, making such perfect smoothness almost detrimental in many molding applications. One good example is molding polystyrene on a polished straightwall core with 1d or less draft. Streak or drag lines can appear on the parts. This can be solved by flashchrome plating the core, which creates a surface with microcracks. Impregnating those cracks with PTFE and then reestablishing the A1 Diamond finish solves the problem in more than 95 percent of cases. In thinwall molding applications such as these, a light beadblast finish is applied—just enough to very slightly interrupt the flawless A2 Diamond surface. The surface is buffed again, leaving just a bit of almost invisible stipple. This finish plus a coating of nickelPTFE will greatly improve part release and enhance mold filling. Phenolics and other thermosets almost demand a perfect polish and work extraordinarily well with a diamond finish. Combine that with a hard, protective coating like chrome or diamondchrome, and you will strengthen the mold’s surface and optimize release. Phenolics and other thermosets almost demand a perfect polish and work extraordinarily well with a diamond finish. Combine that with a hard, protective coating like chrome or diamondchrome, and you will strengthen the mold’s surface and optimize release. Texture and Release There are many textured surfaces today, including faux leather for automobile dashboards, wood grains, geometric patterns and stipple patterns found on pagers, cell phones and puter ponents. A plated mold coating is often essential to obtaining a textured surface with adequate lubricity. Textured surfaces require protection. The peaks of the textured surfaces are the first areas of mold detail to experience wear, making it very important to check the mold periodically with a profilometer to measure grain depth and peak counts. Mold coatings help decrease the frequency of repairs and refurbishment by maintaining the integrity of the textured surface. If a diamond finish presents release problems, a blast finish can be the answer—particularly when molding textured parts using materials such as silicone rubber, flexible PVC, TPES and some soft polypropylenes. These products tend to cling to a polished finish, but breaking up the surface with a light blasting improves release. Add a coating of nickelPTFE and you get even better release. Hard chrome and electroless nickel plating will help protect textured surfaces, as will a nickelcobalt coating. Unlike hard chrome, electreless nickelcobalt plates uniformly, which makes it ideal for very detailed molds with deep ribs and bosses. It bines the corrosion protection and lubricity of electroless nickel with the strength of cobalt. Summary If you’re looking for enhanced performance in your molds, the proper bination of surface treatment and finish can provide additional benefit by extending production times between preventive maintenance. Your coatings vendor can be a valuable resource for educating your personnel on how coatings you use will wear over time, as well as a way to reduce downtime and cut c