Vibratory Residue Problems
Q. How can we remove the white residue left on parts after vibratory finishing without an expensive, additional cleaning/drying operation after finishing? –R.M.
A. The white residue left on the part after vibratory finishing is the media bonding agent that is designed to break down to expose new cutting elements. We have three suggestions to minimize or possibly eliminate the residue:
1. Use a compound delivery system and the correct soap compound.
A flow-through compound delivery system that precisely mixes the soap and water, and accurately flows the mixture through the machine and to the drain is very important. A batch or re-circulating compound system will not eliminate residue.
The normal vibratory soap/water mixture is 1 to 2 oz of soap per gal of water with flow rates of 1 to 2 gal/cu ft per hr. For example, a 5-cu-ft machine will run 5 oz of soap and 5 gal of water per hr. Increased soap and water flows decrease residue problems.
The correct soap is important to many metals and contaminants. Throw your clothes in a washing machine without soap and see how clean they come out. Soap grabs the contaminants within the vibratory machine and washes them out. Soap pH levels make a big difference on metals. When you process zinc with too-high a pH level it darkens the metal, and if you process it with too-low a pH it can actually dissolve the metal. The correct soap will clean and brighten metals.
2. Use cleaner running media.
Cleaner running media produce less residue. Non-abrasive polished (white porcelain) ceramic, steel and stainless media are very clean-running. Another advantage of these media is that they have very low attrition rates, which minimizes media lodging problems. The non-abrasive media utilize only the weight of the media for deburring and should be tested first to see if that’s enough to deburr your parts.
3. Use the correct part-rinsing procedure.
Correct part rinsing is critical to eliminating residue, and it must be done while the parts are still wet from the vibratory process. If the parts flash dry before rinsing, the residue dries into the valleys of the surface profile, creating a difficult cleaning situation.
In summary, the average vibratory finishing machine application with a flow-through soap compound system, the right soap, correct rinsing procedures and the cleanest running media may eliminate additional cleaning system requirements.
This paper is a peer-reviewed and edited version of a presentation delivered at NASF SUR/FIN 2012 in Las Vegas, Nev., on June 12, 2012.
Here’s a primer on the types of finishes required for equipment used in sanitary applications.
Surface finish types for commercially supplied stainless steel sheet are detailed in various standards. ASTM A480-12 and EN10088-2 are two; BS 1449-2 (1983) is still available, although no longer active. These standards are very similar in that they define eight grades of surface finish for stainless steel. Grade 7 is “buff polished,” while the highest polish—the so-called mirror polish—is designated Grade 8