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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.
An interesting thread about deflashing and surface finishing 3D printed parts has been started on the ShopTalk Forum. As this 3D manufacturing process becomes more popular and mainstream, surface finishing using both barrel tumbling and vibratory tumbling will continue to be an issue. Please provide any comments and experience you have either on The Finished Part Blog here or on the Forum.
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 Casings |
In the last post we discussed the differences in performance between vibratory tumbling and barrel tumbling to clean brass cartridge casings. A wet process using a polishing media is a much quicker method to clean brass than dry processes using Walnut Shell Grit or Corn Cob Grit. The test results indicated very similar results in both types of wet tumbling systems.
This post will focus on three different media options for cleaning the dirt and oxidation off the brass. In all three cases, the same solution of Kramco 1030 Mild Acid Cleaner was used and all tests were conducted in a barrel tumbler with a tumble time of 15 minutes.
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| Carbon Steel vs Stainless Steel |
The first test compared the differences between Carbon Steel Tumbling Media and Stainless Steel Tumbling Media. It is pretty clear from the picture above that the Stainless Steel was much more effective at cleaning the brass. While this difference would not be expected initially, the reason may have something to do with the characteristic of the Carbon Steel Media to oxidize and possibly the transfer of iron to the brass casings. This reason will be more clear after reviewing the results of the second test.
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| Polishing Ceramic vs Stainless Steel |
Once the Stainless Steel Media was declared the winner in the first test, the next step was to compare this heavy, burninshing media with a less dense (and less expensive) media. The above pictures compares the results of a K-Polish Precision Ceramic Media to the same Stainless Steel Media used in the first test. The K-Polish Precision Ceramic Media is a high-alumina, porcelain-type media used commonly in many different tumble polishing applications. Both of these media types are extremely long lasting with the capability for 1,000+ operating hours.
As the results for the Stainless Steel Media and the Precision Ceramic Media are very similar, the decision on which media to use will hinge on the type of equipment being used (many vibratory systems can't handle the weight of steel media), the available budget and the overall desired process.
In conclusion, these tests would seem to indicate that excellent results can be obtained in very short cycle times using either a Stainless Steel Tumbling Media or a K-Polish Precision Ceramic Tumbling Media in either a barrel tumbler or vibratory tumbler.
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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 far left in the picture shows a laser-cut, stainless steel part with sharp edges and heavy burrs. The goal is to clean up the edges and leave a smooth, polished surface finish. The part will need to be deburred and then polished. This will be a two-step process as an abrasive process like deburring will typically leave a smooth but matte surface finish.
In this situation, the part was first vibratory tumbled with a moderately aggressive Ceramic Media to remove the burrs and discoloration. This process took a couple of hours to result in the smooth, rounded edges and tumbled, matte surface finish shown in the middle part.
The second step used a polishing Precision Ceramic Media to improve the surface finish and brighten the part. The part on the far right have a smooth, polished look after about 2 hours in the tumbler with the polishing media. Overall, a good result without any hand deburring and polishing or manual labor.
Selecting the proper media can be as much an art as a science. A clear understanding of all the finishing requirements is necessary. Considering the needed edge rounding, surface finishing, cycle time, metal type and many other factors are critical.
Notice the very heavy flashing on this aluminum part (far left in picture) left over from the machining process. This 'raw' part also had some machining marks on the surface that needed to be removed. The easy solution to finishing this part is to throw it in a vibratory tumbler with some Ceramic Media (see part on right) to remove the flashing and surface marks. Alternatively, Plastic Media will take a little longer to deflash the part but will result in a smoother surface finish and less edge rounding (see middle part).
For this project, the objective was to get a smooth surface finish with slightly rounded edges in order prepare the part for a painting process. Ceramic Media was the best selection in this case due to the shorter cycle time, increased edge rounding and 'rougher' surface finish.
Ceramic Media is the most commonly used tumbling media for deburring and surface finishing on steel. This is due to the fact that Ceramic Media is heavier and more aggressive than most other tumbling media and that steel is harder than many other metals (i.e., aluminum, copper, brass, etc.).
The 17-4 stainless steel part on the right in this picture has sharp edges and machining lines that need to be removed. In as little as 1 hour, a general purpose Ceramic Cone in a vibratory tumbler resulted in a uniform, matte surface finish and slightly rounded edges.
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.
Aluminum is a relatively soft metal and care needs to be taken when tumbling to ensure that the finish is uniform. It is easy to 'over work' some areas of a part if the proper media shape, size and type if used. Often light cutting media such as the Plastic or Synthetic Media is used to build a margin of error and prevent too much edge rounding or a rough surface finish.
Sometimes, parts need to have a heavily rounded edge. Ceramic Media is much denser and more aggressive media than Plastic or Synthetic and is used on aluminum in these scenarios. The picture above shows the raw, cut aluminum part (left in picture) with the rough edges and the smooth surface finish.
After vibratory tumbling with an aggressive Ceramic Media, the edges are rounded and the part has a matte, tumbled surface finish. This result was accomplished in less than 1 hour. These results can be achieved with steel parts but the cycle times are typically longer.
Deburring stainless steel parts is a well established process that can be accomplished in a variety of different ways. Vibratory tumbling with a ceramic media is a common method. Cycle times are typically 1-2 hours or less. The challenging aspect (read: art) begins when the parts don't want to behave nicely.
Flat parts or stubborn burrs or scale or oxidation can all create problems when trying to deburr and surface finish a part. The part pictured above (left) is a hardened stainless steel, laser-cut, flat part. Sharp edges, burrs, heat scale and oxidation were all present on this part. Testing in a vibratory tumbler and in a barrel tumbler with a general purpose ceramic media did not provide the necessary deburring and edge rounding. The geometry of the part also lead to the parts sticking or sandwiching together in the tumbler.
In order to get the clean surface finish and proper deburring and edge rounding (right), the part was barrel tumbled with a fast cutting, dense KDF Ceramic Media. To prevent the parts from sticking together, an additional fine media was needed to break the surface tension between the parts and allow them to tumble freely in the barrel. The cycle time for this part was 4 hours.
When painting large quantities of parts - especially on a production line - it is common to use plugs and masking materials to prevent paint from being coating on unwanted areas. These materials are often made of flexible materials such as silicone, urethane and rubber in order to make it easier to plug the holes or slots or whatever area needs to be protected. Often, these plugs are discarded after a few uses as the coating builds up on the surface.
Removing the paint off the plugs allows for a longer lifetime of the plugs and significant cost reductions. Many companies will simply roll the plugs on a hard surface to remove the paint or knock them with hammer or similar. Since the plugs are typically flexible, it is difficult (but not impossible) to use a mass finishing process such as vibratory tumbling to get the uneven forces (i.e., rolling on a surface) necessary to knock the coating off. In addition, vibratory tumbling is often done wet so the plugs would need to be dried prior to re-use. Of course, this type of process eliminates the hand cleaning one part at a time.
Abrasive blasting is another process that can be used to strip the paint. On hard rubber plugs and similar, this process works very well especially in a tumble blast system. On more flexible parts, the results vary widely as the media can simply 'bounce' off the surface. The success pictured above was a simple blast cleaning with Walnut Shell Grit to completely strip the paint.
The type and thickness of the coating and the flexibility of the part are important factors when trying to determine whether blasting or tumbling will properly remove the coating. Testing of the parts is typically needed to determine the viability of cleaning re-using the plugs.
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.
Question: I am interested in starting a metal polishing
business mainly for car parts. I am wondering if your wet tumblers would be
best and what type of media would be best for polishing aluminium, rough cast intake manifolds? I have polished some by hand using sand papers, air grinders with various deburring bits and abrasive wheels, polishing wheels and compounds. This is very time consuming, dirty and tiring work. I am looking at an easier way! I am also interested in smoothing and peening other cast or forged metal parts for increased strength and durability!
Response: There are a number of different ways to clean and polish auto
parts. Depending on the final finish required and the size, shape and geometry
of the part, the final surface finish can range from a smooth, bright finish
all the way to a near mirror finish.
If parts simply need to be cleaned prior to painting or coating,
blasting with Glass Bead will result in a smooth, satin-like or matte surface finish. If additional polishing is needed, vibratory (or barrel) tumbling with
a Polishing Precision Ceramic or
Stainless Steel Media can produce much smoother, brighter finishes. The key with both processes is to select the proper media shape and size based on the part
and areas of the part that need to be finished. The size of tumbling equipment is based on the size and quantity of parts that need to be finished.
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.
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| 6061-T6 Aluminum |
Machined aluminum part that needs to be deburred prior to the next production step. The critical areas include the tab (right side of picture) and the swirling machine marks in the center of the part. The overall size of the part is less than two inches so a small media is needed to get into all the inside corners and holes on the part.
The most successful media was a 1/4" ceramic triangle media (see picture below) in a vibratory tumbling process. This media was able to remove the burrs and tabs on the edges as well as leave a uniform, matte finish on the flat surfaces.
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| Deburred aluminum part |
Choosing to proper tumbling media for a specific part can be challenging enough. When you are producing a variety of parts, the decision can be overwhelming. The following steps will provide a guideline for moving through this process as effectively as possible:
- Identify the results you need to accomplish - deburring, polishing, surface profile.
- Calculate the desired cycle time and the volume of parts you need finish per unit time.
- Determine the type of equipment you need (i.e., barrel vs. vibratory tumbling; wet vs. dry, etc.).
- Review the part size and geometry for all the parts that need to be finished.
- Select the proper media and compound to achieve the desired results with these parts.
- Confirm the process and media selections with testing.
And just to make the decision more difficult, there are many surface finishing options such as abrasive blasting, high energy tumbling, shot blasting and others that may result in as good a process or even better.
Machined Aluminum
Anodizing is an electrochemical process where a very thin portion of the surface of the metal is converted into a protecting coating such as aluminum oxide in the case of aluminum metal. Since this is quite different from a painted or powder coated surface any 'features' in the surface will be translated to the anodized finish. Anodizing will not fill in the gaps and micro-profile on the surface of the metal. Machining marks (seen above) will be still visible after anodizing.
Pre-anodized, Tumbled Finish
To remove the machine marks and create a smooth surface for anodizing, vibratory tumbling with a Plastic Tumbling Media was used on this part. The features of this part required a media that will leave a smooth finish across the large, flat surface area as well as all the way into the corners. A Plastic Cone proved to be the ideal solution.
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