The best mass finishing equipment is useless without the proper media. That’s why the experienced engineers at Rosler Metal Finishing pair their quality equipment with the right type and amount of media to achieve consistent results.
Understanding how your machine, the work pieces it is finishing, and the selected media will interact is key to delivering an optimal finish each cycle. Doing so requires understanding why media levels are important, determining and tracking levels, and evaluating media consumption to avoid issues.
How do Media Levels Effect Processing?
Without a proper media level, a machine won’t work properly. Levels that are too high and too low can cause issues that result in poor processing results and unnecessary workpiece and machine damage.
Running a machine with low media levels can result in part-on-part impingement or workpieces getting stuck in the middle of the bowl.
Low media levels can be a result of an issue known as “media carry out” during separation cycles. This means that media is not being effectively separated or screened from the parts and exits with the parts. Proper separation screens and media sizing helps eliminate the carry out. The video below is an example of proper screen seperation:
Running a machine with low media levels then causes multiple issues such as: part-on-part impingement, workpieces getting stuck in the middle of the bowl, and increased processing times all to solve a media carry out issue.
When media levels are too high, motion of the mix and its effect on workpieces is reduced. This motion is necessary to create friction vital to the finishing process. Reducing the amount of media will allow for more movement and interaction of the media on parts.
Media level as well as the makeup of the mix also effect the pressure of the media on the part. Gaps between media and the part are a lost opportunity for finishing.
Smaller media alone at times will not have enough pressure to deliver results in a desirable time. Bigger media alone could shadow areas, cause impingement, and/or cause parts to find one another, leading them to stick together (water tension).
In a work mix, bigger media provides pressure to drive smaller media to critical features along the work piece. The result is media mix harmony.
Consider the analogy of a glass and various sizes of rocks and sediment. Filling the glass with only rocks leaves gaps of air. If you pour in pea rocks, they will fill larger spaces, but still leave some spaces for air. Adding sand will filter into the available spaces that remain, completely filling the glass.
Comparing the media to this analogy, the best make-up is 50 percent large, original-sized pieces like the rocks, 25 percent step down like the pea gravel, and 25 percent a second step down similar to the sand.
How are Media Levels Determined and Tracked?
When a process is first developed an ideal workpiece load will be determined. The full load – workpieces and media combined – should fill the process bowl as follows:
- Rotary vibratory bowls with separation screens should be 70 percent full to the top allowing media and parts to pass under the separation screen without touching the underside of the screen.
- Rotary vibratory bowls without screens should be 70 to 80 percent full to the top.
- Trough vibratory bowls should be 80 to 90 percent full to the top.
The easiest way to track media levels is by placing a mark on the inside of the bowl. For vibratory bowls, media levels should typically be 3-4 inches below the separation deck.
New media added to reach the predetermined fill line is referred to as top fill. Referring to the glass analogy, this media provides pressure while smaller media provides coverage. A balance of both affects is necessary for optimized finishing.
As media (ceramic and/or plastic) wears, the level in a machine can drop significantly over time. It is important to monitor levels regularly because mass finishing processes work by covering the workpiece with media as it moves over the edges to create the deburring, radiusing, and other affects. If there is not enough media coverage, the finishing abilities of the process will suffer.
Too little media can cause lackluster deburring, radiusing, etc.; longer processing times; and, difficulty unloading machines with separation screens.
The Rosler Way
Rosler Metal Finishing is committed to building specialized machines and pairing the equipment with the most effective media for your needs to help you find a better way. Contact us today to discuss your unique challenges.
Look for part 2 of our Optimal Media Mix series discussing factors of media consumption in a few weeks.