Media Selection Guide For mass finishing
The selection of the proper media for a specific application is critical for optimum deburring and surface finishing results. As a result, we need a proper media selection guide to improve mass finishing process. Because of the diversified requirement of numerous applications and workpieces and the wide variety of types, sizes, and shapes of media available.
In many cases, the optimum selection is made on the trial-and-error basis. The most common media in mass finishing including ceramic media, plastic media, steel media, corn cob media, and walnut shell media.
Media Selection guide for various tumbling media
Workpiece material, size and geometry, burr sizes and locations, and finishing requirement also very important factors to determine the type of media to use.
Ceramic Tumbling Media
Ceramic tumbling media is a preformed ceramic-bonded media which produced by mixing of porcelain, Kaolin Clay, river clay or other vitreous materials with varying percentage of, or with no abrasives. The wet material is formed into different shapes by extrusion and cutting process. Then it sintered into the solid state.
The ceramic media with 80# abrasive is the most aggressive cutting and fastest material for deburring, edge rounding, and scale removal.
The extra fast cut, fast cut, medium cut, moderate cut, and slow-to-no cut grades are typical ceramic media. The ceramic media can be made with abrasive 10-40% on weight while the binder is at 60-90%. The binder acts as a surface burnish and this works against rapid cutting.
The abrasive grain size can be large grain size 80# to fine cutting grain 240#. By using large grain abrasive, rapid cutting is provided, but that also cause a rough surface. Cutting media generate a dull, matt surface finishing. The fine cutting ceramic media offer slight deburring and cutting power on metal and rubber surface for deburring and deoxidation.
Ceramic media is suggested for deburring of hard metal like stainless steel, Iron material parts. For degreasing and cleaning, ceramic media used together with cleaning compound can effectively clean metal surface in short processing time. Besides, ceramic media can also remove casting scale of rubber o-ring washer in short processing time.
Plastic Tumbling Media:
The plastic media is softer and lower density than preformed ceramic media.
The plastic media is formed by bonding abrasives (typically 40-70% by weight) into polyester resins, usually by casting. After casting, plastic media is treated with a heated temperature for 12 hours to promote chemical reaction of polyester. The heating process makes stronger bonding between polyester and abrasives and it makes plastic media longer life. After the heating process, plastic media is typically pre-tumbled to remove flash.
During finishing, the polyester matrix is eroded and leaves the abrasive to perform the work.
The plastic media provides a crushing effect and sometimes has a shorter life. It is well suitable for finishing softer metals and fragile parts. Aluminium parts and copper parts are the softer metal parts are softer metal parts which can we use plastic media of different grade to deburr.
Another application of plastic media is the treatment of metal parts before electroplating. For example for zink/zamak3 electro pre-plating treatment, it achieves a smooth finish as low as 2 microinches.
Besides, plastic media offer no surface hardening of workpieces and have lower noise during tumbling.
Porcelain Tumbling Media:
Porcelain with no included abrasive is long wearing, and can develop extremely good surface finishes and produces very little wear. Because it is non-abrasive it brightens the surface of most metals.
In brass shell reloading application, porcelain ball can brighten and clean surface with help of polishing chemicals. Porcelain ball is also widely used for plastic 3D printing parts post-treatment.
Stainless Steel Media:
The stainless steel tumbling media is primarily used for ball burnishing to achieve maximum lustre for decorative purpose, for light deburring applications, and for heavy-duty cleaning. It is the media most used in ball burnishing process in short processing time with good cost saving. Frequent application of stainless steel media burnishing and polishing including stainless steel water jet cut parts, aluminium die casting parts, the stainless steel plasma cutting parts, laser cutting parts.
In ball burnishing process, a matte surface with numerous hills and valleys or ridges and grooves is treated with steel tumbling media. The steel tumbling media with burnishing process peens down these imperfections and produces smooth and brilliant surfaces. The action in vibratory equipment provides interior action as well as exterior so burnished finishes can be obtained on inside dimensional areas as well as on outside surfaces.
The advantage of stainless steel tumbling media includes uniformity of shape and size, the elimination of possible media fracturing in use, and almost no wearing. The high bulk density of steel media results in rapid peening and deburring and supports the workpieces. The preformed steel media for burnishing is case-hardened, polished and accurate in dimension.
Steel media is not abrasive in nature, therefore it does not scratch or cut parts surface of workpieces
Because of the heavy density of mass steel media (specific gravity 7.9g/cm3), it delivers a very fast finish in deburring, degreasing and de-flashing operation. Cycle time generally is 15-30 minutes. It has an average lifetime of 10 years.
Walnut Shell Media and Corn Cob media:
Grounded walnut shell tumbling media is always related to dry polishing or dry-processing. It offers a good lustre on workpieces after cleaning and smoothing. The typical application of walnut shell is in Jewellery Industry. The jewellery accessories polished with mixed of polishing paste and walnut shell. The paste or wax is transferred into the metal surface with the walnut shell as intermediate. This process improves the surface reflectivity of precious metal like silver and gold after plastic smoothing. The dry polishing process usually performances in dry polishing centrifugal disc finishing machine (gyrate polishing machine) or small centrifugal barrel finishing machine.
Grounded corn cob tumbling media is selected for drying process in the vibratory dryer. Not only offers surface cleaning and drying after wet mass finishing process, corn cob media also rubs on the metal surface and offer slight polishing.