Category Archives: Crushed Glass Media

Picking Grit Size For Sandblasting

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How do you pick a grit size?

A quick and simple answer is to pick a maximum grain size that is about equal to the thickness of the coating being removed.  So if what you are trying to remove is 1.6 mm thick (.063 inch), you would choose a 12 grit.  A bit finer size is often used as well, because you get better coverage as the finer particles fil into grooves, cracks, voids in the surface that the larger particles will not fit into.

A more detailed answer involves selecting a grit size based on the surface profile you are attempting to achieve on your substrate.  A quick guide can be found here.

Keep in mind that the more rounded a particle is, the more contact area it has with your substrate, and this can speed up cleaning rates.  Glass bead is a good example of a cleaning abrasive, whereas the more angular and blocky aluminum oxide particle is useful for actual surface preparation.  (Where you want the abrasive to leave a surface profile for a future coating).

 

 

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What Is A Grit Size – Quick & Dirty Answer

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When it comes to choosing a grit size, it helps to have a mental image to guide you.  The following explanation is a “quick and dirty,” non technical, simple and easy explanation.

First, know that our ANSI grit sizes will match sandpaper grits in a hardware store.  So a 60 grit sandpaper will have particles very similar to our 60 grit loose abrasive – regardless if it is a silicon carbide or aluminum oxide.  If you prefer to view a physical representation, go to a hardware store and take a close look at the particles on a variety of sandpapers.  You will see for example, that a 600 grit sandpaper has very fine particles imbedded in it, whereas an 8 sandpaper has coarse, larger particles.

Second, imagine you held a small 1″ x 1″ square piece of mesh (screen material) in the palm of your hand.  An 8 grit will pass through a screen with 8 holes in that 1″ square mesh.  A finer 240 grit will pass through a screen with 240 smaller holes in the same 1″ square mesh.   In other words, the finer the particle size, the smaller the holes must be on that 1″ square piece of mesh for particles to pass through, and that means there will be lots more holes in the mesh.

Bottom line:  An 8 grit is much coarser than a 360 grit.  Low number = coarser grain size.  As grit size increases in grit number, it decreases in physical size, becoming finer and finer until we are dealing with polishing powders.

We sell sandblasting grits and powders online in a variety of different abrasive medias.

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Sandblasting Profiles: What abrasive should I use?

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Anchor patterns are extremely difficult to approximate due to the many variables at play.  Use this information with Caution!  This is only an approximation.

The type of metal use in this example was hot rolled steel with tightly adhering mil scale.  The type and hardness of your substrate, how thick the scale is, the degree of cleaning you are attempting to achieve, experience and skill of the person performing the sandblasting, etc will all factor into your end result.

In this example, the pressure blasting was done using a 90-100 psi nozzle pressure.  The depth of the anchor profiles listed below are approximations only, and are on average.

1 Mil Profile:

1.5 Mil Profile:

2 Mil Profile:

2.5 Mil Profile:

3 Mil Profile

 

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What Is Friability?

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What Is Friablity?  Short Answer:  How easily/quicky a media shatters on impact and breaks down.  Think of Friability as durability.  This is different from Hardness Rating.  Sandblasting medias may have the same Hardness rating, but completely different Friability Ratings.   One will break down fast, the other will remain intact and can be recycled multiple times.

Brown Fused Aluminum Oxides have a LOW friability, so it will break down slowly, and coarser sizes can be recycled multiple times.

White Fused Aluminum Oxides have a HIGH friabilty, but the SAME HARDNESS rating of Brown Fused Aluminum Oxides.  Even though it is just as hard as Brown Fused AO, it will shatter on impact and break down quickly, without doing as much damage/impact to the substrate.  This is one reason why it is often used for delicate glass etching, and why it makes a nice final polish for rock tumbling.  Its high hardness rating however, makes it appropriate for anti skid flooring applications, traction, etc.

Sinterblast, or Sintered Aluminum Oxide has a MEDIUM friability.  Think of it as the middle ground between Brown Fused and White Fused.  It can be recycled in coarse sizes, but will not have the long life (durability) of a Brown Fused Aluminum Oxide.  It is often preferred by Powdercoating companies due to its lower cost.  If you are just taking off mil scale prior to coating, this is a great media to try out.  It is a lower purity aluminum oxide, and cheaper in cost to manufacture due to the sintering process being less expensive than the fusing process.  THE MEDIUM FRIABILITY OF THIS TYPE OF ALUMINUM OXIDE IS WHY YOU BLAST AT A 60 PSI, AND NOT THE USUAL 80-90 PSI OF BROWN FUSED ALUMINUM OXIDE.  ANYTHING HIGHER AND YOU WILL NOT ACHIEVE GOOD RESULTS BECAUSE THE MEDIA WILL SHATTER UPON ITSELF IN THE AIR STREAM BEFORE GETTING TO YOUR SUBSTRATE.

When choosing an abrasive to use, make sure you take into consideration its friability, not just hardness rating.  Our product descriptions of our sandblasting abrasives include both hardness ratings and friability ratings.

 

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Using Crushed Glass To Clean Precast Concrete

Crushed Bottle Glass Abrasive For Concrete

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Armani Restoration Job SiteCrushed Bottle Glass Abrasive is used to clean and restore the exterior of this 27 story concrete building.  Using a proprietary wet and dry blasting system, the contractor dramatically changed the surface color of the building, as you can see in the photo.  The concrete surface of this building was not smooth – it did have a texture to it, so a medium grade was chosen.  The end result is a much brighter surface color to the concrete, without damaging the exterior.

Crushed glass sandblasting abrasive is the perfect choice for either light cleaning of precast concrete, or by using coarser grades, exposing the aggregate in the concrete.  A medium/fine grade was used for this job, as the customer did not want to damage the surface of the concrete.

Crushed bottle glass abrasive is a 100% recycled product, and is shipped from a variety of locations.  It contains no free silica, no heavy metals, is inert, and it blasts fast and clean.  Many times people will just leave it on the ground rather than clean it up (unless you are blasting off something toxic like lead paint or have local laws requiring cleanup).  This makes it great for blasting log homes and automobiles as it minimizes cleanup in areas where it can be left on the ground as a soil amendment.  Because this type of abrasive is shipped from all multiple points of origin, we will always try to find the closest location to your end job site when quoting.  NOTE:  If left on concrete it will be very slippery!

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