Products Finishing

OCT 2013

Products Finishing magazine is the No. 1 industrial finishing publication in the world. We keep our readers informed about the latest news and trends in plating, painting, powder coating, anodizing, electrocoating, parts cleaning, and pretreatment.

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Page 95 of 115

CLINIC MASS FINISHING High-Energy Mass Finishing Q. We produce two parts that cannot be deburred in our bowl vibratory machine. One is a small (0.35 × 0.25 × 0.20inch) machined 304 stainless part with large burrs, and the other is a 0.375-inch diameter × 0.02-inch stamped stainless flat washer. We have tried all types of media and time cycles. Is there another finishing system that would deburr these parts? —B.K. A. Small parts with large burrs and flat parts that stick together can be difficult to deburr or process in vibratory machines. There are a number of high-energy mass finishing systems that are 10 to 20 times the energy of vibratory machines. The centrifugal barrel (CB) is a good choice for your application because it's capable of driving smaller media with significant energy to deburr large burrs in tight areas of smaller, lighter parts. As a batch processing machine, it enables glass beads to be added to the media to eliminate the surface tension that keeps small, light, flat, wet parts from sticking together. The CB machine looks and operates similar to a ferris wheel on steroids. The energy is produced by a variable speed (1 to 240 rpm) rotating turret, with two to four hexagon-shaped barrels mounted within the turret, counter rotating at a 1-to-1 ratio. The media and parts are contained within the fully enclosed barrels producing a compressive-sliding-grinding action. The centrifugal barrel produces amongst the highest energy of all the mass-finishing systems, with up to 20 times the energy of vibratory systems. Other advantages of using a CB include the ability to divide barrels to separate large parts, short time cycles and the ability to process wet or dry. Disadvantages include the fact that part loading/unloading is a bit cumbersome, taking 10-15 minutes of operator attendance, but it will successfully run a lot of hardto-process parts. The CB also is only capable of batch processing, and it cannot be automated. Pre-Plate Finishing Q. We chrome plate a small aluminum fitting. We first use a vibratory process on the part to produce a competitive, refined, pre-plate finish. This often creates small part dings PAT WENINO / M.C. Finishing and surface orange peel that only show up after plating. The vibratory polyester plastic media produces a matte finish that you can't see through. What causes the surface damage, and how can we test for part damage on the hard-to-see-through matte finish prior to plating to avoid an expensive strip and re-plate process? —J.P. A. The first thing that's concerning is that you're using a media harder that your part. This is one of the main causes of small dings and surface orange peel. Below is a list of possible reasons for part damage within a vibratory system: 1. Media hardness (media harder than the part). 2. Media size (small media produces a tighter mass that protects part). 3. Part-on-part damage (too many parts within the mass). 4. Compound/water flow (soap and water cushions the mass). 5. Machine setting (running too aggressively). Testing for part damage hidden by the vibratory polyester's media matte surface prior to plating can be inspected or determined by: 1. Rubbing the part surface with a pencil eraser to remove the matte (created by the polyester media), exposing the underlying surface for visual inspection of part damage. 2. Adding a secondary vibratory burnishing (surface brightening) operation to expose or amplify part damage. Centrifugal barrel action. 94 OCTOBER 2013 — To determine if part-on-part damage is the cause of your dings, put only one part in the machine. If there is no damage, this could be the problem, however, this is

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