Mass Finishing Media, Part 3 – Why Discharging Undersized Media, Maintaining Media Levels Are Crucial
Mass finishing processes are effective because the motion of media against work pieces transforms the surface of the work pieces. The deflashing, descaling, edge rounding, polishing/smoothing, cleaning/oil removal/degreasing, and/or grinding effects change the surface of the media itself along with the work pieces.
As a result, media wears down over time, losing its shape, size, and effectiveness. Known as undersized media, this worn media must be discharged and replaced with fresh media to ensure proper processing and safety.
Whether a process uses ceramic, plastic, or polishing and drying media, Rosler stresses the importance of monitoring media levels and the mix of new and worn media for precise and safe mass finishing results.
Worn Media Reduces Process Effectiveness
Over time, media wears and becomes smaller. This undersized media can throw a process completely out of balance in several ways, including:
- Media lodging in the work pieces which could cause safety issues later in the process.
- Clogging drains within the finishing machine and causing flooding.
- Failing to meet finishing standards.
- Increasing required finishing times.
Timely and effective discharge of the undersized media and replacing it with new media is, therefore, critical for the stability of any mass finishing process.
Discharge can be done continuously by building suitable undersize screens into the actual mass finishing machine or in the vibratory screening unit. To prevent media clogging, undersize screens themselves must also be monitored. If lodging or clogged drains occur over time, undersize screens with larger holes should be installed.
In rotary vibrators with internal separation, the undersized media discharge can sometimes be inefficient. Running the complete media charge through an external vibratory screening machine equipped with special undersize screens every few days provides effective removal of undersized media and helps maintain the optimal media mix.
New Media Offsets Undersized Loss
Removing undersized media must be offset by the addition of new media. Without timely replacement, the media level in the machine will become lower, which may drastically impact the finishing process in several ways.
Decreases in the media-to-work piece ratio will cause nicking and scratching of the work pieces.
A higher portion of smaller media in the machine will prevent the process water from getting drained from the machine resulting in dirty work pieces.
In vibratory machines, the spiral movement of the media/work piece mix will collapse if the media level drops too low resulting in poorer finishing results and longer cycle times.
In all cases, the process will completely collapse within a few days—sometimes within a few hours!
Depending on the machine and media type, new media should be added at regular intervals such as with every work piece batch, once every few hours, or once a day. Your media supplier should be able to help you with frequency based on test batches and careful monitoring.
Equipment updates may also be available to automate media replacement such as the installation of a timer- or weight-controlled media replenishment system to help maintain the right media working mix.