Silicon Carbide Blasting

Choosing the proper grit size of media to get the desired finish is often a little bit of trial and error. Different medias at different pressures on different metals with different processes will result in different surface finishes.

These 304 stainless steel washers needed to be etched with Silicon Carbide Grit to achieve a lightly etched finish (Aluminum Oxide Grit was not allowed for this particular situation). Since the exact finish was not specified, a range of grit sizes were tested. Starting at the top and going clockwise, the discs were blasted with 36 Mesh, 60 Mesh, 100 Mesh and 220 Mesh Silicon Carbide Grit at the same blasting pressure.

While a little difficult to see the detail, it is clear that as the grit size gets finer, the finish get much smoother. This is typical of all types of blasting media. Larger grit will result in a heavier etch than finer grit. It's just a question of what grit size gives the desired results for a specific application.

Scratch Resistant Coatings

Improving the life of a coating such as polyurethane, acrylic or epoxy can be achieved with the addition of a small amount of a abrasive such as Aluminum Oxide, White Aluminum Oxide or Silicon Carbide. These materials are significantly harder than the coating material and will increase the scratch resistance of the coating with minimal impact on the other properties of whatever coating you are using.

The specific type of abrasive will depend on a variety of job specific requirements including color, clarity and thickness. The size of the abrasive used is generally a very fine grade such as a 600 or 800 mesh but larger grit (~240 mesh) can be used in thicker coating. The addition rate is also very dependent on the coating you are using specifically related the solids content. Rates of 3 - 5% (about 1/2 pound per gallon) are common.

Rock Tumbling

Rock tumbling and stone polishing is a popular hobby. The most important ingredient to achieving a great finish is time. Polishing is typically a 4-step process involving progressively finer and finer abrasives. Each step is done with a clean barrel, fresh water and a virgin abrasive. The Creetown Gem Rock Museum (in the UK) has a good outline for polishing stones.

The first three steps require a coarse grit (80 mesh) followed by a medium abrasive (220 mesh) and finally a fine grit (400 mesh). Aluminum Oxide or Silicon Carbide are the preferred media due to their durability and hardness.

The fourth step demands a very fine, hard media that will maintain it's 'cutting' ability for the entire cycle time. Cerium or tin oxide are the abrasives of choice as they will maintain their sharp edges as they break down over time. Sawdust can be added to this step to ease the impact and eliminate chipping of the stones.

Hobby size barrel tumblers will generally have capacities of just a few pounds of stones. Tumbling times for each step is about 1 week. Larger, industrial-grade tumblers such as the MT Series Barrel Tumblers will allow for more weight to be tumbled at one time. This often leads to reduced cycle times and higher production rates. Regardless of the equipment, patience is the key to beautifully polished rocks and stones.

Titanium Stents

Finishing medical parts requires very stringent testing and results to ensure that the parts are deburred properly. Titanium stents are inserted into arteries to keep them open. A properly deburred edge and smooth surface finish is absolutely necessary to ensure that the medical part works exactly as expected.

Titanium is a hard metal and is often deburred in a vibratory tumbler with Ceramic Media. The size and shape will depend on the geometry of the part and size of the openings. Adding a medium size grit such as Aluminum Oxide will increase the abrasiveness of the tumbling process and provide a smooth, rounded edge. If embedding of the grit is of concern, using a Ceramic Media that is aluminum oxide free (i.e., KDF Bond) with an addition of Silicon Carbide will also produce excellent results.

Silicon Carbide

Silicon Carbide is manufactured from a high heat reaction of silica sand and carbon. While silicon carbide and silica share similar chemistry, Silicon Carbide used in abrasive blasting contains less than 1% free silica. Free silica or silicon dioxide is the compound that should be avoided (due to risk of silicosis) and not inhaled as a fine particulate. Details about Silicon Carbide can be found on a previous post.

Blasting Stone with Sand

Question: I am thinking of purchasing a small business doing stone engraving. My only concern is blasting with the silica sand which is what is being used right now. We plan to use a blasting room and filtered breathing system but I don't know how safe I can be using silica sand. I am curious about alternatives like silicon carbide and aluminum oxide and could use any tips and advice on how I can do this kind of work safely.

Response: Blasting with silica sand is definitely NOT recommended - even with a breathing apparatus. Both Aluminum Oxide and Silicon Carbide are more aggressive blasting media than sand and will provide quicker results and a better surface finish on stone. Both of these media can be used with standard abrasive blasting systems without modification. Of course, always minimize breathing any kind of dust when blasting.

Stone Engraving

Question: I am thinking of purchasing a small business doing stone engraving. My only concern is blasting with the silica sand which is what is being used right now. We plan to use a blasting room and filtered breathing system but I don't know how safe I can be using silica sand. I am curious about alternatives like silicon carbide and aluminum oxide and could use any tips and advice on how I can do this kind of work safely.

Response: Blasting with silica sand is definitely NOT recommended - even with a breathing apparatus. Both Aluminum Oxide and Silicon Carbide are more aggressive blasting media than sand and will provide quicker results and a better surface finish on stone. Both of these media media can be used with standard abrasive blasting systems without modification. Of course, always minimize breathing any kind of dust when blasting.

Laser Cut Steel Parts

When steel parts are laser cut, heavy slag can develop on the part. These burrs are typically much thicker and heavier than a normal burr or sharp edge and can sometimes be a large a 1/8" thick. Removing this excess metal requires an extremely aggressive operation. For this piece, part-on-part barrel tumbling was required to knock off the extraneous material.


To keep the cycle time to a minimum (less than 8 hours in this case), a hard abrasive grit, Silicon Carbide, was added to increase the deburring properties as well 'even out' the surface finish. After tumbling the part showed no burrs or slag on the edges and had a uniform, matte finish.

After this ultra-aggressive deburring step, the parts can then be tumbled (barrel or vibratory) to improve the surface finish for further processing.

Abrasive Blasting Media - Silicon Carbide

Silicon Carbide is the hardest of the abrasive blasting media. On the Mohs hardness scale, Silicon Carbide has a hardness of 9.5 (diamond is a 10). While this mineral does occur naturally, it is rare and most is manufactured synthetically using an Acheson furnace.

Silicon Carbide is sometimes referred to as 'black sand' but contains no silica. The hardness of this media makes it ideal for etching on surfaces such as glass and stone. Larger grit sizes can result in extremely heavy, rough and deeply etched surfaces while the smaller grit sizes can produce a very fine and 'frosted' etched surface. Silicon Carbide has a very high/fast working speed and is typically used in a blasting cabinet.

Relative to some other abrasive blasting media, Silicon Carbide does break down more quickly. Because of the higher cost of the media and the high fracture rate of the particles, this media is generally used for specialty applications or in areas where Aluminum Oxide (as a more general purpose abrasive media) is not aggressive enough.

Tumbling with Abrasive Grit

Tumbling parts to achieve a deburred, deflashed or rounded edge is a common process. Both vibratory and barrel tumblers are used for this purpose. Choosing the proper media type is critical to achieving the desired finish.

Most applications require the use a preformed tumbling media. These media contain abrasives that are released into the tumbling process to remove the burr, etc. The (relatively) large mass of the media assists in this process by acting as a sanding block of sorts on the edge and surface of the part. After this abrasive process, parts can be tumbling in other media (including grits) to achieve a smoother or polished surface finish.

Tumbling parts simply with an abrasive grit such as Aluminum Oxide, Silicon Carbide or Walnut Shell does not typically achieve the deburring, deflashing or edge rounding required. While the grit may be very sharp, hard and abrasive, there is very little force acting against the edge of the part. The surface finish will probably be affected (roughening, smoothing or even polishing) but the edges will be left mostly untouched.

There are some exceptions to this 'rule' (see this post) but generally preformed tumbling media is superior to grit media for deburring, deflashing and edge rounding.

Beijing Olympics

Wow! An impressive show by the Chinese with these 2008 Olympics. Many of the controls the government put in place to control pollution (stopping construction, closing factories, significantly reduced traffic) seemed to work - although a couple days of well 'placed' rain also helped.

A couple of random thoughts now that we are beyond these Olympic games:

• China spent A LOT of money on these games. While impressive, most of this $$$ came from western countries buying less expensive Chinese goods (one individual purchase at a time) leading, of course, to China's continuing economic growth. Is this really best for our local and global economies?


• Construction and factories were shut down across China to reduce horrible pollution for two weeks. Now that the Chinese have seen what a blue sky looks like again, I wonder if there will be any continuation of this environmental policy. If the Chinese return to the pre-games norm, I suspect that pricing and supply pressures on many materials (Aluminum Oxide, Silicon Carbide and Steel among many others) will be back in full force along with the pollution it generates.

London 2012 has a very tough act to follow. I hope that the world has learned important lessons about balancing the environment, global trade policies and individual consumption to springboard our (collective) path towards a better future.