The Finished Part

Crushed Glass Grit

noreply@blogger.com (Steven Schneider) — Thu, 31 May 2012 14:07:00 +0000

Here is an excerpt of a great rave by 'MasterBlaster' from on contractortalk.com on the benefits of Crushed Glass Grit:

"...Crushed glass is by far the Greenest and safest of all blast media's available today.

Crushed glass has a super small carbon footprint..... because it's made from 100% post consumable products as in "recycled glass".... this is same stuff you put out at curbside for recycling pickup.... and in most cases recycled glass is produced, recycled and packaged within 50 miles of where it's being used....while other products like olivine, garnet and star-blast have to be mined, processed and shipped hundreds and or thousands of miles to get it to market and in those cases use valuable fossil fuels to get it to market... "recycled glass is the GREENEST and CLEANEST product available today and uses very little fossil fuel to produce."

Crushed glass is also considered the waste product of the glass recycling industry.... again when they recycle glass they recycle it for the larger pieces which are separated by color (Which saves energy... because when you start with COLORED GLASS to produse COLORED CLASS it saves a lot more energy and fossil fuel) also the crushed glass we use can't be separated by color so it's the waste product and before we used it for media blasting it use to go direcly to the landfill... (So by use using it for media blasting they found another use for it and YET ANOTHER USE FOR THIS RECYCLED PRODUCT as in media blasting.... AGAIN THE GREENIES LOVE IT AND EAT IT UP.

As far dust goes... recycled glass produces a lot less dust especially if you're doing wet abrasive blasting... and while it's always a good practice to do containment on all you job to prevent your media from getting on the ground.... the one thing to keep in mind is recycled glass 100% inert so what gets on the ground is relatively safe and isn't considered a contaminate like Black Beauty, Soda and or steel shot... it doesn't change color or contaminat the groud, it doesn't kill plants or wildlife and it blends into the ground like granular dirt... not that I'm saying it's ok to leave any waste behind, but yes it blends in well..."

The full post and the related string can be found on contractortalk.com.

Edge Rounding Aluminum Parts

noreply@blogger.com (Steven Schneider) — Thu, 24 May 2012 14:54:00 +0000

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.

Heat Treat Discoloration

noreply@blogger.com (Steven Schneider) — Fri, 11 May 2012 14:15:00 +0000

Stainless steel parts are often heat treated to anneal (harden) the metal and relieve stress in the parts. While most stainless steels are resistant to oxidation at low temperatures, the various metal in the steel formulation (iron, chromium, molybdenum, etc.) can form oxides at higher temperatures. This oxidation causes the discoloration often seen on steel after heat treatments.

The knife blade picture above was heat treated to create a harder, more durable product. The part on the left shows the telltale blue, green and black discoloration due to elevated temperatures. Prior to further processing such as polishing and sharpening, the blade needs to be restored to it's original surface finish and coloration.

The part on the right was abrasive blasted with a Medium Glass Bead at 80 psi to result in a satin-like, smooth surface finish. This part is now ready for the next step in the process.

Tumbling Frustration

noreply@blogger.com (Steven Schneider) — Fri, 27 Apr 2012 13:49:00 +0000

A question about deburring, cleaning and polishing brass, copper and aluminum parts. It's worth reading through the entire question as it provides an excellent description of what may small shops are doing and the frustrations they have.

Question: I primarily machine small parts out of 6061 aluminum, a small amount out of C360 brass and a handful out of C145 copper. I currently use a small vibratory tumbler to finish my parts. I use a small (about .25" square base) green plastic triangle to do the deburr and initial cleaning cycle. The problem with this, is it takes two to three days to run to get satisfactory results. I have tried running dry, but it takes even longer to achieve the results I want. I usually add a small cup of water to add some lubrication. But I have to take the tumbler bowl off and rinse it out and wash off the media every 6-8 hours because I get a thick black foam that fills the bowl and turns the media into a solid mass that just moves around the bowl. After this step, I clean out the tumbler and add a relatively fine red corn cob media to do a polish. But that also takes two to three days of tumbling to achieve a decent finish. I never add rouge or other polishing compound because I have no idea what to use. I just use the pre-treated corn cob media and replace it every 3 or 4 months. I am hoping to add a new machine to my shop and expect to produce several hundred parts a week that need polishing (I do not need to polish to a mirror shine, I merely need to deburr after the machining operations and provide a nice level of shine). Obviously, I would like to find a better way to accomplish this over what I have been doing. My parts are typically small - 1.2" diameter x 0.12" thick discs, 0.75" diameter x 0.25" thick slugs, 0.8" x 0.375" x 2" bars. Many of the parts have threaded holes and small slots (1/16" wide). I spend a lot of time hand cleaning the corncob out of the slots with a small pick. I have tried to do research to find a better solution, but it is one of those ask a dozen people, get 2 dozen answers types of questions. Some people tell me I need flow through on my first step. Some recommend ceramic some plastic and some steel shot. Corn cob and walnut shell seem to be recommended for finishing - some say pre-treated and others say to add rouge. I am at a loss now as to which direction to proceed so I figured it was time to seek more professional advise. Would you be able to help me find the best solution to my problem? I do not have a large space to set up multiple large tumblers, I need a compact solution with at most, two tumblers.

Response: I will try to address your questions and offer a simple and reasonable recommendation.

Plastic Media, Ceramic Media and other types of deburring media like this require a wet process using an appropriate tumbling compound (i.e., soap/lubricant). Assuming the proper shape and size of media is being used, the cycle times on the types of metal you noted (aluminum, brass and copper) should not be more than a couple of hours. The cycle times could be longer if you have very heavy burrs or need to get a highly rounded edge. The foam is probably a result of not using enough water and no compound. This is common with Plastic Media with no flow-through system for the solution.
Given the surface finish requirement of a 'nice shine' and parts descriptions, I would recommend using a 3/8" x 3/8" KSV Synthetic Cone Media and a solution of Kramco 1030 Mild Acid Cleaner. This media is a light, deburring media that will result in a smooth, pre-plate finish. The Kramco 1030 will leave the metals you are using with a bright finish. This media choice may require a slightly longer cycle time than a more aggressive media (i.e., Ceramic Media) but the surface finish will be much better. In addition, a flow-system is recommended for the best results.
The polishing media you are using - treated corn cob grit - may be treated with a rouge or something similar. Cycle times with dry tumbling like this are often long, 24 hours or more, but can produce excellent, near-mirror finishes. Of course, if the parts have holes or slots that are similar in size to the grit, it is common for the media to get stuck. Using the recommendation in #2 above may eliminate the need for a second polishing step (depending on the specific finish desired).
An alternative polishing step could be with a polishing Ceramic Media or Precision Ceramic Media instead of the dry process. While this may not result in the near-mirror finish achievable with a Corn Cob Grit, the finish can be a smooth, polishing, bright surface. A solution of Kramco 2030 Neutral Burnishing Compound would be used in this step.

Wood Parts Tumbling

noreply@blogger.com (Steven Schneider) — Thu, 12 Apr 2012 15:18:00 +0000

Hand sanding wood parts can be a tedious and labor intensive process. The ability to smooth the surface, remove cutting marks and round edges on a large quantity of parts can same time and money.

The part pictured above needed to be sanded down prior to the application of a stain and coating. The part on the right shows the sharp edges and some flashing after the initial cutting of the part. A two step barrel tumbling process was used to achieve the end result on the left.

Step 1 involved using a Hardwood Peg Media and relatively coarse White Aluminum Oxide Grit. This produced the edge rounding and major 'sanding' of the part.

Step 2 used a similar Peg Media along with a much finer grade of White Aluminum Oxide Grit to result in a smoother, sanded finish. If necessary, subsequent steps with even finer grades of Grit or a quick hand sanding to the final required surface finish can be used. Barrel tumbling the parts in this dry process can eliminate most if not all of the hand sanding often done.

Powder Coat Stripping

noreply@blogger.com (Steven Schneider) — Tue, 27 Mar 2012 19:29:00 +0000

Powder coating is used in applications where a tougher finish is required than a traditional liquid paint. The free-flowing, dry powder is typically applied electrostatically and then heat cured to form the bond. Powder coatings are very difficult to remove from the sub-surface as they are often thicker and more aggressively bonded to the surface than more traditional coatings.

Removing powder coating from a surface can be a challenging process. In addition to the thickness of the coating, the bond between the powder and the metal often requires more energy to break than the force needed to etch or potentially damage the sub-surface.

This powder coated punched hole wire mesh was stripped (right side) using an abrasive blasting process with 60 mesh Aluminum Oxide Grit. A larger grit size was also tested (which did strip the coating more quickly) but the metal surface became too heavily etched. Less aggressive media such as Glass Bead and Plastic Abrasive Media were unable to efficiently remove the coating.

Polishing Machined Aluminum

noreply@blogger.com (Steven Schneider) — Tue, 13 Mar 2012 13:14:00 +0000

Taking machined aluminum parts and polishing to a smooth, uniform surface finish is often a multi-step process. Each step is designed to accomplish a different task. The part above has burrs, sharp edges and clear machine marks. Vibratory tumbling is the preferred process.

Step 1 - The edges are softened and the machine marks are removed using a Plastic Cone tumbling media. This media is selected due to it's lower density (vs. Ceramic Media) and lesser aggressiveness. The resulting surface finish is smooth and uniform. This part could be anodized to a matte finish, powder coated or painted with excellent results.

Step 2 - In order to brighten the part and prepare for anodizing to a higher luster, the part was tumbled with Polishing Precision Cearmic Spheres. While the finish is bright and smooth, the proper shape must be chosen to ensure that a uniform surface finish is achieved based on the geometry of the part.

Deburring Stainless Steel

noreply@blogger.com (Steven Schneider) — Wed, 15 Feb 2012 18:52:00 +0000

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.

Silica and OSHA

noreply@blogger.com (Steven Schneider) — Thu, 26 Jan 2012 13:33:00 +0000

The Occupational Safety and Health Administration (OSHA) is in final preparations for a hazard communication related to a Occupational Exposure to Crystalline Silica. This rule will basically set standards for exposure to silica dust during blasting (and other operations) in confined work spaces. Inhalation of silica is generally considered to increase the risk of silicosis.

According the OSHA, in 2005 "silicosis was identified on 161 death certificates as an underlying or contributing cause of death. Exposure to crystalline silica has also been associated with an increased risk of developing tuberculosis and other nonmalignant respiratory diseases, as well as renal and autoimmune diseases." The need for the exposure standard is the standardize monitoring, training for use with silica and compliance.

Of course, in an abrasive blasting environment the best way to avoid the hazards of silicosis is to use media that do not contain crystalline silica such as Crushed Glass Grit.

Surface Finishing Aluminum

noreply@blogger.com (Steven Schneider) — Thu, 19 Jan 2012 19:26:00 +0000

Aluminum parts that are stamped, molded. extruded, saw-cut, etc. all need to be deburred. These parts also typically need a specified surface finish. While dense, aggressive media like Ceramic Media will deburr the parts, the matte, tumbled finish and heavy edge rounding is often unneeded.

Softer metals like aluminum tumbled with lighter medias like Plastic or Synthetic Media can result in lightly deburred edges and a smooth surface finish. The part above (before part on right, deburred part on left) was vibratory tumbled with a Plastic Triangle media for only 1 hour. The smooth, matte finish is ready for accepting a coating or anodizing.

Blasting Patterns

noreply@blogger.com (Steven Schneider) — Wed, 11 Jan 2012 14:32:00 +0000

There are many different methods and patterns for blasting flat surface areas. Many of these process (including the Overlap Method pictured above) can result in over-blasting of a large percentage of the surface. This can lead to increased amounts of media used and an inconsistent surface finish (especially with softer surfaces such as log homes).

One alternative is the use a '50% Gap Method' (see picture below). Basically this process involves blasting horizontal strips of the surface leaving about a 50% gap in between each strip. You can then go back over the gap areas resulting in more surface area blasted per unit time and less overlap.

Thank you to Pirate Brand for this blasting tip.

Cleaning Paint Plugs

noreply@blogger.com (Steven Schneider) — Wed, 04 Jan 2012 15:16:00 +0000

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.

Blast Nozzle Size

noreply@blogger.com (Steven Schneider) — Thu, 29 Dec 2011 13:28:00 +0000

Question: Do you have a chart which shows the minimum pressure blaster nozzle size required for each of the mesh sizes of blast media?

Response: A reasonable guideline for proper media flow would be to use a nozzle bore size that is 7-10 times the average particle size of the abrasive blasting media you are using.

Note: See Mesh and Micron post to get a rough formula to convert from one identification to the other.

Cleaning Motorcycle Parts

noreply@blogger.com (Steven Schneider) — Wed, 21 Dec 2011 13:56:00 +0000

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.

Aging Wood with Blasting

noreply@blogger.com (Steven Schneider) — Wed, 14 Dec 2011 13:00:00 +0000

This picture shows a great example of how wood can be artificially aged using abrasive blasting. Ratherberacin (thank you!) posted pictures of his to 'weather' the wood surfaces on a sauna project . The piece of wood in this picture was abrasive blasted with Fine Crushed Glass Grit to remove the soft grain and leave the tighter, harder grain. After staining the wood will have an aged, weathered look like it had been out in the elements for years.

Here is a link on contractortalk.com. Just scroll down the page a bit to get to ratherberacin's post.

Auto Blasting with Glass Grit

noreply@blogger.com (Steven Schneider) — Wed, 07 Dec 2011 13:00:00 +0000

Coatingsguy (thank you!) posted a couple of great before and after pictures of an auto restoration blasting project. The van in the picture above was stripped and ready for priming after blasting with Fine Crushed Glass Grit. Per his comments (link below), the van required 5-1/2 bags of media and 4 hours.

Here is a link on contractortalk.com. Thanks again for sharing.

Auto Parts Polishing

noreply@blogger.com (Steven Schneider) — Tue, 29 Nov 2011 13:19:00 +0000

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.

Mirror Surface Finishing

noreply@blogger.com (Steven Schneider) — Mon, 14 Nov 2011 20:55:00 +0000

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.

Heavy Slag on Steel

noreply@blogger.com (Steven Schneider) — Fri, 28 Oct 2011 14:58:00 +0000

When laser cut (or saw cut), steel parts can develop heavy slag on the edges (see picture above). The slag is developed as the metal is melted during the laser cutting action and then re-forms on the edges on the 'bottom' of the part. The excess metal can be removed by hand grinding; however, if the parts are small or there are many parts to be cleaned, hand finishing is not efficient.

The finished part above was barrel tumbled part-on-part to remove the slag and excess metal on the edges. A small addition of 36 Mesh Aluminum Oxide Grit increased the abrasiveness of the tumbling action allowing the process to go from the before to the after in only 30 minutes. While the surface finish is rough after the tumbling process, the parts can be painted or sent through additional steps using other tumbling media to smooth out the finish and possibly polish the part.

Increasing Tumbling Abrasiveness

noreply@blogger.com (Steven Schneider) — Wed, 12 Oct 2011 14:51:00 +0000

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.

Polishing Firearm Parts

noreply@blogger.com (Steven Schneider) — Wed, 05 Oct 2011 17:18:00 +0000

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.

Precision Aluminum Deburring

noreply@blogger.com (Steven Schneider) — Wed, 28 Sep 2011 18:39:00 +0000

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.

Deburred aluminum part

Choosing Tumbling Media

noreply@blogger.com (Steven Schneider) — Thu, 22 Sep 2011 15:06:00 +0000

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.

Glass Bead vs Aluminum Oxide

noreply@blogger.com (Steven Schneider) — Wed, 14 Sep 2011 15:30:00 +0000

Aluminum Oxide vs Glass Bead Blasting

Different blast media will create different finishes on different types of metal. The aluminum part pictured was etched and corroded and need to be cleaned to a uniform surface finish. The section on the left was blasted with 120 Mesh Aluminum Oxide Grit to create a relatively smooth, matte, uniform finish. The section on the right was blasted with Medium Glass Bead to result in a bright, satin-like finish. A simple change of media can result in a dramatic change in finish.

Glass Bead Blasting on Steel

noreply@blogger.com (Steven Schneider) — Wed, 07 Sep 2011 14:22:00 +0000

Before

A quick before and after result of Fine Glass Bead blasting on steel parts. Before blasting part shows scratches, machine marks and 'pock' marks on the surface. Blasting with Fine Glass Bead resulted in a smooth, uniform finish ready for polishing, coating or other types of surface finishes.

After Glass Bead Blasting