【正文】 ting is showing deterioration, especially in highwear areas such as gates and runners. For example, wear in and around gate areas plated with hard chrome is the first sign that your mold needs servicing. How can you tell there is wear? The chrome coating is approximately 20 RC points harder than the base steel, so exposed steel will wear much faster than the coated surfaces surrounding it, causing a slight or pronounced edge or “step” on the surface. Conversely, nickel will wear almost evenly, causing a kind of feathering effect, making it more difficult to recognize wear. A more identifiable difference will be the color because when nickel coating wears, it produces a shadow or halo effect on the steel. No step or edge will be evident. The steel also will have a more silver appearance pared to the somewhat tarnished look of the nickel coating. This knowledge makes pulling a mold for maintenance before the coating wears through an ultra important aspect of a PM program. To miss important wear signals means more costly repairs and additional polishing expense. Measuring Wear A remended tool for measuring the wear level of any coating is an electronic thickness gauge that uses a bination of magism and eddy current to accurately measure surface thickness. When the mold first arrives in your plant, take the time to measure the surface thickness—especially in highwear areas—using this specialized tool. As you run production on the mold, occasionally pause to remeasure those areas. When you have determined that the finish is wearing to a critical level, pull the mold and send it out for maintenance. Part Counts Be sure to record the measurements taken with the thickness gauge and use the notes to create a history of maintenance requirements for the tool. A cycle counter installed on the mold will allow your tooling engineer to record wear levels as pared to piece part counts, thereby doubling the effectiveness of your PM program. Part counts are a great way to determine maintenance needs, especially with highvolume molding projects. From the very first time you run the mold, keep an accurate piece count until it is ready for its first maintenance work. Use that count as a gauge for when the next maintenance is due. Because you know approximately when the mold will be ready to be refurbished, you can arrange the service in advance with your coating vendor. This not only gives him ample time to schedule your mold maintenance, but it also allows you to optimize the use of the mold and the machine that’s running it. Coating Challenges Even today, there are those who question the benefits of using fancy—sometimes more expensive—coatings to prolong tooling life or enhance performance. To some, the tried and true hard chrome or electroless nickel are all they’ll ever need to acplish those goals. But we all know that today’s engineered plastic materials can be pretty rough on injection molds. Challenges to mold maintenance extend beyond glass and mineralfillers to include rice hulls, wood fibers, metal powders, flame retardants and other additives—not to mention the resins themselves. In addition, outgassing and moisture acidity often acpany abrasive wear, taking an even bigger toll on expensive tooling. In addition, growing plexity in mold design involves tinier, more intricate flow passages and more frequent use of moving cores and slides. All of these circumstances have prompted the development of a wider variety of mold coatings that can keep molds operating longer between repairs. New Coating Science If you are molding highly intricate parts using glassfilled materials, you might think using hard chrome will be sufficient because it is a classic, reliable way to protect your mold from both corrosion and abrasion. However, hard chrome, for all its benefits, does not tend to plate uniformly in detailed areas like ribs and bosses. There is a newer solution—a nickelcobalt alloy coating that can overe that limitation. Nickel Cobalt Nickelcobalt can be an economical alternative to hard chrome. Hard chrome requires construction of a conforming anode to coat the mold. The more detail in the mold, the more time it takes to build the anode and the more expensive the process bees. This nickelcobalt alloy coating requires no anode, and because of its electroless properties, it plates much more uniformly. The cobalt gives it good abrasion resistance, but its hardness is 62 RC, 10 points lower than hard chrome. Is it worth paying extra for hard chrome’s superior wear protection? You