Maintaining the right ratio of media to work pieces is essential to achieving precise, repeatable results in mass finishing processes where work pieces and media loosely tumble in the processing bowl.
Ensuring that the work pieces are properly embedded in the media allows the media to perform its designated grinding or polishing function as well as cushioning the work pieces from damage caused by part-on-part impingement.
Building upon our last post on the series about navigating the complex media selection considerations, Rosler’s team of experts now discusses tips for determining the best media-to-work piece ratio.
Basic Rule of Thumb
The standard ratio of media to work pieces is around 3-to-1 by volume – meaning that the mix is 3 parts media to 1 part of work pieces – but the exact ratio varies based on the aggressiveness of finishing required as well as the work piece’s material, shape, size, weight, and delicacy or lack thereof.
For simple, sturdy work pieces, the ratio may be lower than the standard while work pieces that are very delicate; made from soft, heavy metals; or must receive a high-gloss polish require a much higher ratio of 10-to-1 and higher.
Typically, media-to-work piece ratios increase with the more extreme smoothing and finishing, higher material softness, large and heavy work pieces, and those with more complex or fragile construction.
Pinpoint Your Ratio
Determining the exact ratio for your mass finishing process requires digging a bit deeper into your specific media and machine specifications.
- Determine the “usable volume” in cubic feet of the processing bowl. This information is usually supplied by the equipment manufacturer.
- Determine the number or weight of work pieces that fit into 1 cu ft, e.g. for small parts use a 12x12x12” shipping box and transfer parts until the box is full.
- Use the bulk density of the specific media type to calculate the required media quantity by weight. For reference:
- Ceramic media = 95 – 105 lbs/cu ft
- Porcelain and high density media = 115 – 145 lbs/cu ft
- Plastic media = 70 – 85 lbs/cu ft
The usable volume of a processing bowl is 12 cu ft and the desired ratio is 5-to-1. Therefore, 10 cu ft of media and 2 cu ft of work pieces should be filled in the machine.
We’ve determined that 50 work pieces fit into 1 cu ft so you would place 100 work pieces into the machine. If we were dealing with small, bulk goods, we would measure out 2 cu ft instead of counting individual pieces.
Let’s assume we’re using ceramic media which weighs around 100 lbs/cu ft. Because we need 10 cu ft to balance out the work pieces, we will need 1,000 lbs of media. If we were using plastic media, the total would be around 750 lbs; high-density media would require about 1,400 lbs.
Once established, the initial media-to-work piece ratio must be constantly monitored. If the ratio becomes too low, new media must be added.
Equipment updates may be available to help maintain the optimal media levels. For certain applications, timer- or widget-controlled media replenishment systems may be beneficial.
The Rosler Way
From the engineering of a mass finishing machine all the way through process refinement and service, Rosler partners with you to achieve precise and efficient results. Contact us for help with all aspects of your surface finishing process.
The complete Mass Finishing Media Series includes:
- Part 1 – “Don’t Navigate the Complex Selection Process Alone.”
- Part 2 – “Tips for Measuring Media-to-Work Piece Ratio.”
- Part 3 – “Why Discharging Undersized Media, Maintaining Media Levels are Crucial.”
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