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| Stainless Steel Polishing |
Machined stainless steel parts typically have sharp edges, burrs and a matte surface finish. Vibratory tumbling can be used to get a polished finish sometimes even down to just a few Ra surface profile. This is often a multi-step process.
The part on the left is the 'raw' part ready for deburring and polishing. The first step is to deburr and round the edges. This was accomplished using a KM general purpose Ceramic Media. This was a wet process using a solution of Kramco 1010 General Purpose Compound. The result at this point (not pictured) was a matte, tumbled finish with rounded edges.
The second step needed to get the pictured polish (on the right) involved tumbling with a Precision Ceramic Sphere and a solution of Kramco 2020 Burnishing Compound. Generally, a rounder media will produce a smoother finish than an angular media.
This part could be further polished with other tumbling media or hand buffed to a near-mirror finish.
After heat treating and laser cutting stainless steel parts, the edges generally need to be deburred and the surface needs to be cleaned from scale and discoloration prior to polishing. A two-step vibratory tumbling process is normally used to achieve a uniform surface finish.
The part on the far left in the picture shows the burrs and slight discoloration on the edges. The first step was to tumble the parts with a Ceramic Media to get a the uniform, tumbled, matte finish shown on the part in the center of the picture. For this particular part a 2 hour cycle time with a general purpose tumbling compound resulted in the finish seen.
The second step (far right in picture) was also a 2 hour vibratory tumble with a Precision Ceramic polishing (porcelain-type) media and a high lubricity tumbling compound. The surface is improved to a more uniform and brighter finish and the part is ready for a clear coat or further polishing as needed.
Equipment like coffee machines, hot water heaters, boilers and other commercial and industrial equipment that use hot water eventually shows a build-up on the parts. This residue is the deposition of the salts and minerals in the water on the surfaces.
If not removed, this scale can become quite thick and affect the performance of the equipment The heat will not transfer efficiently from one area to another and holes and pipes will start to get blocked. Stripping down the scale, especially on smaller parts and in internal areas can be accomplished quite efficiently with vibratory tumbling.
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| Hard Water Scale Removal |
Tumbling the parts with the proper media and compound can make a huge difference. Common sense would be to use as abrasive a media as possible to strip off the scale. But this is not always to best way.
The part on the left was tumbled with an abrasive Ceramic Media and a general purpose tumbling compound. This is a traditional deburring process and did knock-off some of scale (see oblong area in the middle of the part). The bulk of the residue wasn't touched and if the part was left too long in this type of process, the threads, edges, holes, etc on the part may have been worn down so that the part was out of tolerance.
The part on the right (which looked the same as the one on the left before tumbling), was tumbled with a polishing Ceramic Media. While this was a much less abrasive process, the appropriate compound, Kramco 1030 Mild Acid Cleaner, was used to soften, dissolve and then remove the scale. Because this was a polishing media, the part came out bright and clean with no wear on critical areas of the part.
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| Dirty Cartridge Brass |
Cleaning cartridge brass (see 'dirty' brass above) has traditionally been accomplished using a vibratory or barrel tumbler with a dry media such as Walnut Shell Grit or Corn Cob Grit. Both of these medias will do a good job of cleaning the dirt and oxidation off the brass but typically require a long cycle time (12-24 hours or more).
Alternatives to this long tumbling time are available that will result in clean, bright brass is as short a time frame as 10-15 minutes. These alternatives also require a vibratory or barrel tumbling system but with different media and use a wet (chemical compound solution) process. This post and the next will review the results using different tumbling methods as well as comparisons of different media.
The basic process involves (vibe or barrel) tumbling the brass with a polishing media. A typical ratio is about 3 parts of media to 1 part of brass by volume. The solution would be added to the level of the load in a barrel tumbler. In a vibratory tumbler, the solution could be circulated through the media/parts load or could be added as a small amount (usually about 5% by volume of the load size) in a batch process. The selection of compound (i.e, Kramco 1030 Mild Acid Cleaner) is critical to achieving good results. Obviously, it is important to ensure that the equipment being used is designed for a wet process.
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| Vibratory vs Barrel Tumbler |
This picture shows the results using the exact same media type, parts/media ratio and solution but with different tumbling system types. The parts on the left were vibratory tumbled for 15 minutes with a recirculating solution of Kramco 1030 compound. The brass on the right were barrel tumbled also for 15 minutes with the same solution filled to the level of the load.
It is clear that both tumbling processes did an excellent job of cleaning the brass and that the results are very similar. Based on this test, it seems that either a barrel tumbling system or a vibratory tumbling system can be used to clean cartridge brass. The decision comes down to the type of equipment available and the desired in-house handling process.
The next post will compare different types of media all in a barrel tumbling process.
The selection of tumbling media for a particular application depends not only on the type of material/metal being tumbled but also on the finish required for the next step(s) in the processing of the part. While less aggressive medias such as Plastic Media or Synthetic Media are typically used with softer metals like aluminum, the results above show a comparison of a Plastic Media versus a more aggressive Ceramic Media.
The picture shows the machined part on the far left followed by a part tumbled with a general purpose Plastic Triangle (middle) with a different part tumbled with a Ceramic Triangle on the far right. Both tumbled parts were vibratory tumbled for 1 hour with the same Kramco 1030 mild acid compound.
The machined part shows heavy burrs and machining marks on the surface. Both media types removed the machine marks and the burrs on the edges. The differences show up when looking more closely at the 'roughness' of the surface finish and the amount of edge rounding after the 1 hour cycle time.
The Plastic Media tumbled part shows slight edge rounding and a matte but uniform surface finish. This is a good finish for anodizing the aluminum part to a matte, smooth finish. The Ceramic Media tumbled part has noticeably more edge rounding and a more tumbled, 'rough-looking' surface finish. This finish is better for accepting paint or powder coating.
Similar to aluminum, lighter weight magnesium metal parts are often machined to create the required shapes and features (see picture above). The machining process leaves burrs, sharp edges and (most noticeably) machining lines and swirls. These imperfections in the surface need to be removed prior to further processing of the part.
As similar to aluminum and other reactive metals, magnesium is subject to oxidation. When vibratory tumbling the part, using the proper chemistry is important. This part was deburred and made smooth using a Ceramic Angle Cut Cylinder tumbling media and a solution of Kramco 1030 Mild Acid Compound (see 2nd picture above).
Ceramic media was used to keep the cycle time to a minimum with maximum surface finishing. The Angle Cut Cylinders removed the machining marks all the way into the interior corners of the machined areas as well as provided an even deburr and edge rounding across the entire part. The slightly acidic pH of the Kramco 1030 prevented the part from oxidizing during the tumbling process and resulted in a clean, white-metal finish.
Question: I have a small vibratory tumbler (designed for gun casings). I would like to use it to clean and polish small parts from motorcycles as I restore them. This would include nuts, bolts and washers (steel, stainless steel, brass) and some aluminum parts. I assume a variety of media would be needed -- can you please let me know which media I should get?
Response: Small motorcycle parts can be cleaned using either a wet or dry process. Vibratory tumbling the parts with Corn Cob Grit in a dry process will remove the soils (oil, grease, etc.) and leave the parts clean. Depending on how dirty the parts are and what type of surface finish is required, a dry tumbling process can be up to 6 hours or even longer.
A wet process using a Ceramic Media such as a 3/16" x 3/8" KM (general purpose bond) Angle Cut Cylinder with a general purpose compound such as Kramco 1010 will degrease the parts, remove light rust (if any) and leave the parts clean. This process is typically a maximum of 1-2 hours. It is important to make sure that the vibratory tumbler being used is able to handle the weight of Ceramic Media.
Achieving a near-mirror finish on many metals using only mass finishing such as vibratory tumbling or barrel tumbling can be a challenging process. The combination of tumbling media, equipment and compound will determine the results. And these results will vary depending on the type of metal being polished.
This stainless steel part has a very flat geometry with minor scratches and imperfections. Generally, the heavier and rounder the tumbling media, the better the surface finish. Additionally, a tumbling process that produces a smooth, even tumbling action will produce the best results.
The part was barrel tumbled to give a nice rolling action of the media against the part. A Stainless Steel Round Ball (Sphere) in combination with a highly lubricating, tumbling compound ( Kramco 910) kept the process clean and resulted in a near-mirror finish on this stainless steel part. The total tumbling time get from the before (top picture) to the after (bottom picture) was 1 hour.
There are a number of strategies that can be used to increase the abrasiveness of both barrel and vibratory tumbling operations. These can be used when a boost to more aggressive surface finishing. deburring or edge rounding is needed.
- Increase the rpm (barrel tumbler) or the amplitude (vibratory tumbler).
- Use a denser/heavier media (i.e., switch from Synthetic Media to Ceramic Media).
- Switch to a more aggressive bond/formulation of tumbling media.
- Reduce the amount of water and/or compound in the process.
- Add an abrasive such as Aluminum Oxide Grit or similar (best with a barrel tumbler).
- Adjust the load level for a more aggressive tumbling action.
Identifying the critical issues with your part will determine which strategy(ies) are best to employ. Of course, all these strategies work just as well in reverse to decrease the abrasiveness.
There are two types of finishes needed for firearms. Most (military and hunting) require a matte or dull finish to minimize reflection and give good 'grip' properties. Firearms used for show pieces or when reflection is not an issue will often need a higher polish or near-mirror finish on certain areas of the gun.
The part above is an as-produced finish. The surface is relatively smooth but dull. To process large quantities of these parts, a single-step process can be used to significantly improve the finish. The same part below was barrel tumbled for 18 hours (overnight) in Stainless Steel Ballcones and a solution of Kramco 910 Burnishing Compound to produce much brighter, mirror-like finish.
Previous posts about the basics of silverware burnishing ( Part 1 and Part 2) described the process through which silverware and flatware are restored in a barrel tumbling process. The basic outline described the flowing of the metal to 'fill' the scratches and the removal of the oxidation on the surface. Below is a picture showing an extreme example of what can be accomplished.
Silverware Burnishing Test Results
- Far left - Before sample with heavy oxidation, scratches and some pitting on the surface
- 2nd from left - Tumbled in Steel Media and a polishing compound. Sometimes testing is required to determine if the combination of media and compound will discolor the surface even though the process removed the scratches and pitting.
- 3rd from left- Tumbled in steel media with an alternative compound. While it is difficult to tell, both the 2nd and 3rd pieces are similarly polished The proper compound (for this application) clearly resulted in a brighter, polished finish.
- Far right - Tumbled with the same compound as the 3rd part but with a Precision Ceramic polishing media. The surface is clean and bright but not quite as good as the Steel Media. This process would be best if the tumbling equipment being used is not designed for heavy media.
 Here is another good example of the polished finish that can be obtained on acrylic plastic using a barrel tumbling process only. The part on the left had been cut and machined to the general shape and size. The machining marks and square edges can be seen rather clearly - along with the dull surface finish. A two-step dry barrel tumbling process was used to achieve the polished results on the right. Both steps used a Hardwood Media. The first step using Shynolyte Pre-Polishing Cream provided the edge rounding and a smooth (but matte) surface finish. The second step using Microlyte Polishing Cream brought out the bright shine and gloss of the plastic. Each step was about 24 hours and the results certainly speak for themselves.
Many small-run, decorative pewter manufacturers either hand polish or have smaller equipment for polishing cast pewter parts. While we have detailed pewter polishing in a previous post using steel tumbling media, small vibe tumblers generally are not able to handle the weight of steel media.       Before (first) - Polished (second)
These lead-free pewter parts showed rough and dull surface finishes. While the objective was not to completely remove the flashing and produce a mirror-like surface finish, these parts did need to be cleaned and polished. A two step process was used in a small (4 gallon capacity) vibratory bowl. The first step used a general purpose Ceramic Media and a mild acid compound to remove oxidation on the surface and soften/remove the flashing. This resulted in a smooth, matte finish. Instead of using steel tumbling media in the second, polishing step, a Precision Ceramic polishing media was able to bring up a nice shine on the parts in a relatively short cycle time of 2 hours. A neutral pH compound was used to keep the parts clean and bright.
Copper is a soft metal that is easily oxidized and stained (note previous post re: green color of Statue of Liberty). Stamped copper parts need to be deburred and cleaned prior to further use in most manufacturing processes.  This picture shows a portion of a copper component of an electronics part. The stamping and cleaning process (part on the left) shows light burrs and clearly visible water spots and staining. In order to get a clean part for proper electrical contact, the part on the right was vibratory tumbled. The customer wanted a short cycle time and was not interested in a polished or bright surface finish. A Ceramic Angle Cut Triangle was used in order to deburr the outside edges as well as the ID of the holes and other features. The media and parts were tumbled in a compound solution of the Kramco 1030 Mild Acid Cleaner to remove the oxidation and water spots. The end result was a clean, smooth surface finish that met the customer's requirements. The total cycle time in the tumbler was only 15 minutes.
Aluminum is a relatively soft metal that is easily nicked, scratched and damaged by handling - both during the part manufacturing process and after. Restoring aluminum to a uniform and smooth surface finish can be accomplished with mass finishing.  The aluminum part on the left clearly shows the scratches and damage due to heavy handling. The part on the right is the result of a simple mass finishing process to create a uniform, matte surface finish. The part (aluminum cylinders) were vibratory tumbled in a wet process with a general purpose (KM) Ceramic Media and cleaning/lubricating compound for 2 hours. Ceramic Media is typically used with harder metals such as steel; however, in this case, there was no need to further polish the part. If a higher polish is required, a lighter cutting Plastic or Synthetic Media can be used in a (potentially) longer cycle time. This step would be followed with a polishing step.
The purpose of silverware burnishing is to both physically and chemically clean and smooth the fine surface 'grains' of the metal. This is accomplished through the use of a barrel tumbler and the appropriate tumbling media and compound. Stainless steel burnishing balls (media) are used to force the metal to 'flow' and fill the scratches on the surface. As the entire load is rotated in the barrel, the media lifts up the back side of the the barrel and cascades towards the front. As the parts are carried with the media in the sliding area, the weight of the burnishing balls impact with the surface of the silverware. This contact forces the metal to fill the low spots and even out the high spots. In combination with the physical polishing, the water and burnishing compound help to remove the tarnish (silver sulfide) and keep the process lubricated. Using the proper compound (and changing the solution regularly) will limit damage to the silverware in process and keep re-deposition to a minimum. The combination of chemical cleaning and microscopic, physical manipulation leads to a bright and polished surface finish.
Pewter is a soft, malleable metal consisting primarily of tin. Decorative plates, jewelry, figurines and even keys (see picture below) can be made with pewter. Since pewter is so soft, it is difficult to maintain a polished finish on the surface. It is common to treat the pewter design with a black coating that is then polished away from the high spots to produce an exaggerated 3-dimensional effect.  Key Art Co.The black oxide coated parts are vibratory tumbled with Precision Ceramic Spheres and a mild acid cleaner such as Kramco 1030 to 'clean' the high spots. The spheres provide an excellent bright and clean finish without removing the oxide from the interior relief areas of the part. Cycle times can be as short as 10-15 minutes depending on the desired results. If a matte finish is more desirable, a cutting/abrasive version of the Precision Ceramic Spheres can be used. To remove more of the oxide, a triangle media is ideal.
Removing the flash off various types of molded parts (see last post) can be done in a wet or try process. Vibratory tumbling with a Plastic or Ceramic media in a wet process can be a quick and easy method to achieve the desired results. After the deflashing step, the parts will generally need to be rinsed and dried. A traditional dry tumbling process involves the use of Hardwood media that have been treated with an appropriate cream compound. The selection of this compound depends on the needed aggressiveness and required surface finish. The challenge with these compounds isthat sometimes the cream can transfer from the media and become deposited in holes, slots or corners of the part. This then requires cleaning prior to further processing of the part. An alternative to using creams is a similar previously described process for dry tumbling of wood parts. Depending on the type of part and the amount of flashing that needs to be removed, simply tumbling the parts with Hardwood media and an abrasive grit such as White Aluminum Oxide will provide excellent results with only a light dust on the parts. Because the abrasive material is not 'attached' to the media, a barrel tumbler is typically a much better process than vibratory tumbling.
 Heavy flashing on edges
This molded fiberglass part has heavy flashing on the edges that needs to be removed more efficiently than a hand sanding or scraping operation. In addition, a dry process is preferred (in this situation) so the customer does not need to take the extra step of drying the part prior to further processing.  No flashing after vibratory tumbling
A dry tumbling process using Hardwood Peg Media and Dry Abrasive Cream successfully removed the flashing and produced a smooth, rounded edge. In this type of process, the compound is 'coated' to the Pegs and tumbles against the part to abrade away the flashing. If necessary (but not required in this situation), different dry tumbling compounds can be used to polish the part or even produce a high gloss finish.
Manufacturers of ammunition have been working overtime to try to meet the recent surge in demand. Due to lack of supply, many shooters have been doing more and more re-loading. The traditional process of dry vibratory tumbling with Walnut Shell Grit or Corn Cob Grit continues to be the primary method for cleaning the cartridge brass. While this process works well for newer brass, heavily oxidized brass can be more 'stubborn' using this process. Using the same dry vibratory tumbler (assuming it is water-tight) with a Precision Ceramic Media can clean even severely oxidized and soiled brass. In addition, the cycle time can be as little as 15 minutes versus the 12-24 hours for dry tumbling. The key is to use the proper shape and size media for the brass you need to tumble in combination with a cleaning compound such as Kramco 1030. To see a great before and after example, click to this Finished Part post.
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