1、 How Surface Treatments Keep Molds Operating Longer Important tips and information about mold coatings to help you achieve the level of production that you and your customers desire. By Steven . Bales Mold making technology January 2006 Abstract Theres an awful lot to know these days about molding p
2、lastic and how to get the very best performance from the valuable tools you build or run. This guide has been written to provide important tips and information about mold coatings. After reading this, you should have a very good idea of what coatingsfrom the very traditional to the very latestwill h
3、elp you to achieve the level of production you and your customers desire. After all, these tools are an investment and they need to be protected for the life of the products they mold. Key Words mold coatings preventive maintenance (PM) program benefit nickel Cobalt diamond-chrome nickel-PTFE nickel
4、-boron nitride electroless nickel texture The Key Role of Coatings Before introducing you to the wide range of coatings on the market today, its important to note the role coatings can play in an effective preventive maintenance (PM) program. PM is really the key to protecting your tooling, your inv
5、estment. Why? Because it saves time and money. Once you invest in a mold coating to improve tool performance, then a PM program is always a good idea to ensure you get the maximum benefit. These two steps should be a given in any shop. Remember, no coating lasts forever, and producing substandard pa
6、rts from a mold with a worn coating is no way to win customers and stay profitable. PM is probably the most cost-effective strategy you can put in place. The key is to educate your personnel on how mold coatings wear during production. Every coating is different, so its of benefit to have employees
7、learn how to tell when the coating is showing deterioration, especially in high-wear 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 approximate
8、ly 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 recog
9、nize 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 compared to the somewhat tarnished look of the nickel coating. This know
10、ledge 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 recommended tool for measuring the wear level of any coating is an electr
11、onic thickness gauge that uses a combination of magnetism and eddy current to accurately measure surface thickness. When the mold first arrives in your plant, take the time to measure the surface thicknessespecially in high-wear areasusing this specialized tool. As you run production on the mold, oc
12、casionally pause to re-measure 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 requi
13、rements for the tool. A cycle counter installed on the mold will allow your tooling engineer to record wear levels as compared to piece part counts, thereby doubling the effectiveness of your PM program. Part counts are a great way to determine maintenance needs, especially with high-volume molding
14、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 servic
15、e 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 thats running it. Coating Challenges Even today, there are those who question the benefits of using fancysometimes more
16、expensivecoatings to prolong tooling life or enhance performance. To some, the tried and true hard chrome or electroless nickel are all theyll ever need to accomplish those goals. But we all know that todays engineered plastic materials can be pretty rough on injection molds. Challenges to mold main
17、tenance extend beyond glass- and mineral-fillers to include rice hulls, wood fibers, metal powders, flame retardants and other additivesnot to mention the resins themselves. In addition, outgassing and moisture acidity often accompany abrasive wear, taking an even bigger toll on expensive tooling. I
18、n addition, growing complexity 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
19、 Science If you are molding highly intricate parts using glass-filled 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 unifor
20、mly in detailed areas like ribs and bosses. There is a newer solutiona nickel-cobalt alloy coating that can overcome that limitation. Nickel Cobalt Nickel-cobalt can be an economical alternative to hard chrome. Hard chrome requires construction of a conforming anode to coat the mold. The more detail
21、 in the mold, the more time it takes to build the anode and the more expensive the process becomes. This nickel-cobalt 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, 1
22、0 points lower than hard chrome. Is it worth paying extra for hard chromes superior wear protection? You have to consider the material being run in the mold. Whats the percentage of glass? Is corrosion a greater concern than abrasion? Diamond Chrome Hard chrome and a nickel-cobalt alloy coating offe
23、r two very good solutions for abrasion resistance, but for very high-wear conditions, an even newer product called diamond-chrome offers exceptional protection. It has an RC rating greater than 85 and is a chromium-matrix composite coating with a dispersion of nanometer-size, spherical diamond parti
24、cles. Since diamonds are unmatched for hardness, this coating offers protection beyond the norm. Though their Rockwell ratings are comparable, diamond-chrome outperforms titanium nitride (TiN) coating because it wont compromise the dimensional integrity of the plated tool. The difference is that it
25、is applied at only about 130oF while TiN requires application temperatures of 800oF or higher. Diamond-chrome can plate prehardened, heat-treated or nitrided steel and other base materials such as aluminum, beryllium-copper, brass and stainless steel. Recommended uses include cores, cavities, slides
26、, ejector sleeves, and rotating and unscrewing cores. Its anti-galling properties are advantageous on moving cores and slides. Diamond-chrome also is very strippable and has no adverse effect on the base material, saving time and money when maintenance is needed. TiN is strippable as well, but it ca
27、n take up to several days to remove with a peroxide-based solution. Diamond-chrome can be stripped in minutes using reverse electrolysis in a caustic solution. In addition, diamond-chrome can be deposited at any controlled thickness from 20 millionths of an inch to 0.001 in. TiN is generally only ap
28、plied in thin deposits of a few millionths of an inch. Diamond-chrome can coat complex details, while TiN has very limited coverage of complex details. While TiN is very lubricious, with a coefficient of friction (COF) of 0.4 (against steel), diamond-chrome has a COF of 0.15nearly three times more lubricious. Nickel-Boron Nitride When it comes to molders needs for a specialty coating that offers excellent release properties and high resistance to wear, heat, and corrosion, an electroless nickel-phosphorus matrix containing boron nitride particles should be considered.
