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pfonline.com/experts Mass Finishing for Maximum Part Brightness Q. We have small, flat, stainless stamped parts with have slight die marks that need the highest shine possible. What mass finishing machine and process can help us? A. Maximum part brightness achieved with mass finishing is the centrifugal barrel machine running dry media impregnated with a polishing compound. This process will remove slight die marks and keep flat parts from sticking together. The dry media most commonly used is a ground corn cob, available in fine, medium and coarse grits. The polishing/brightening compound additives vary with the manufacturers producing it. The centrifugal barrel, centrifugal disc or spindle machines produce the high compressive impact energy required to obtain polish or deburring with dry media. The centrifugal barrel, running at least 120 rpm, at 20–60 minute process times, will do the finishing required. A few process tips for dry finishing in centrifugal barrel machines: • A pre-dry process of the parts may be required to remove the stamping oils so the light flat parts will not stick together. • A post-wash or dry untreated cob process will be required to clean the oily residue left from the finishing process. • The dry cob process generates heat, so an alternate batch of cob media will be required under constant production. While one batch is processing, the other batch of media is cooling. • The barrels of the centrifugal barrel machines should be filled to 60–75 percent full by volume. • New polishing cob can run for 12–48 hours and longer in production before replenishing. Replace just 25–50 percent of the cob at a time. • New polishing cob media requires 3–4 cycles for break in. The initial few processes create an excessive oily haze on the surface of the finished part. • Heavier parts require divided compartments to elimi- nate part-to-part damage. Dry media do not protect the parts like a wet media. Heavy parts will accelerate through the dry mass and ding into each other. The centrifugal barrel with cob polishing media is an excellent choice for brightening your stainless stamped parts. A separate deburring process for small stamped parts can also be accomplished by adding cutting abrasives like silicon carbide into the cob. Steel Mold Cleaning Q. What process can we use to clean steel molds used for bottle making without damaging them? A. Blasting is the most common and effective process for mold cleaning. The blast media most commonly used for mold clean are: • Dry ice; cleans molds on the machine, eliminating mold change. • Plastic media; very soft, angular, quick cleaning at low pressures. • Sodium bicarbonate; blasted wet or dry, good for oily parts, one pass. • Fine glass or ceramic beads; standard product for auto- mated systems. The machines used for mold air blast cleaning are manual hand cabinets and automated systems. The standard automated air blast machine in the glass bottle mold cleaning industry is a 9-gun body, rotary head, automated turn table blast system. Parts are loaded onto the turntable; the machine is turned on; and the parts rotate under the rotary head blast guns for a predeter- mined time cycle. This automated process can clean 9–15 molds within 15 minutes. Robotic or Dedicated Deburring Machine Q. We have a stainless part that needs deburring. Our deburring machine choice is a robot or a dedicated specialty automated deburring machine. Which would you recommend we purchase? A. If production rates can be met by both systems and the pricing is relatively the same, I recommend the robot. We have sold the dedicated machines for years. Once the product is changed or discontinued, the dedicated machine becomes a boat anchor. If the burr is larger than average, the dedicated machine may not work and sending the part through the machine twice is not practical. However, dedicated machines produce large production rates and can be faster than robots. On the other hand, an industrial robot is multi- purpose, which is with declining product life cycles, improved quality requirements, deburring time cycle flexibility and reduced production rates. Consider the average robot service life of 15 years. The dedicated machine may also last 15 years, but will the job last 15 years? Most U.S. manufacturers look for a one-year machine payback. If a robot is paid for in one year, there are 14 more years that it can be used for other projects. Flexibility is key. Manufacturing in the U.S. is moving toward specialty industries, more complex parts and less production. Robots work well in these environments. 50 NOVEMBER 2015 — pfonline.com p f o n l i n e . c o m / e x p e r t s MECHANICAL FINISHING C L I N I C PAT WENINO / M.C. Finishing massfnishing@pfonline.com