Crushed Glass Grit

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

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

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

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.

1.  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.
2.  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.
3. 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).
4. 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

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.