Abrasives

Abrasives

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If you still think that the best abrasive for sandblasting is sand, then you are living in the dark ages! There are so many different abrasives available now for so many different applications that you practically have to be an abrasive engineer to pick one.

Some of the choices you may be faced with if you are etching and carving glass include glass beads, beach sand (brown), white crystal silica sand, garnet, aluminum oxide (white, brown, or pink), and silicon carbide (black or green).

These materials will vary in price from less than $4 per hundred pounds to over $200 per hundred pounds. When you consider that in a given blasting job you may be using as much as 50 to 100 pounds or more in an hour, it becomes obvious that you need a little more information before making your purchasing decision.

Features

Glastar carries two different types of abrasive: Aluminum Oxide and Silicone carbide. Each of these has its own uses and blasting qualities. Your decision of which abrasive to use will depend on the cost-effectiveness of each abrasive for the job, and your blasting equipment and technique.

Aluminum Oxide:

  • Good for etching stone, wood and glass. Also for works well for metal finishing
  • A very hard, tough abrasive that cuts glass quickly
  • No free silica
  • Brown is the most common and is the cheapest. White & pink are higher purity and cost, but no increase in cutting speed
  • The major drawback is the generation of static electricity, causing dust to cling to the back of glass being blasted. Makes it hard to see what you are doing if you prefer lighting the glass from behind

Silicon Carbide:

  • Good for glass etching as well as metal finishing
  • Harder than aluminum oxide; cuts glass faster because it constantly breaks off small pieces, exposing new cutting edges
  • No static electricity
  • No free silica
  • Black is the most common. Green is sometimes available, is slightly harder, but costs more
  • Creates "flashlight effect" of small sparks where particles hit the glass, making it easy to see the area being blasted

Recommendations

The cost-effectiveness of an abrasive is a measure of how much glass you can etch per dollar spent on abrasive and labor. The more efficient (faster) an abrasive is, the lower the labor cost to produce an etching. The more times you can recycle an abrasive without losing etching speed, the lower the abrasive cost (If the abrasive loses etching speed with continued reuse, the labor cost necessarily goes up).

The equipment you are using is important because that determines whether or not you can recycle the abrasive. If you have a good blast cabinet or blast room in which to etch, you can use any of the abrasives which can be recycled.

If you are using a leaky, poorly constructed cabinet or blast room, or if you are blasting outside, you will lose a lot of abrasive. You can't use the recyclable abrasives in those situations since they are a lot more expensive per pound than the others.

Cost-Effectiveness of Abrasives
Type of Abrasive Etching Speed # of Cycles Cost per 100 lbs Cost used in 50 cycles (100 lbs qty.) Approx. cost per hour of use
Brown sand Medium slow 2 $5.00 $125.00 $1.25
White crystal silica sand Medium slow 2 $5.00 $125.00 $1.25
Garnet Medium 4-8 $25.00 $150.00 $1.50
Aluminum Oxide Medium fast 60-80 $100.00 $63.00 $0.63
Silicone Carbide Fast 80-100 $150.00 $75.00 $0.75

Cost figures are approximate and may vary with different suppliers. Figures for many cycles vary with the type of blasting done and the technique of the person doing the blasting.

The number of cycles for all materials except carbide depends on how quickly the particles get dull (i.e. how hard the material is). Carbide never gets dull, it just breaks down into finer and finer particles (see "Other Facts" in table #1). As the particles get smaller, more is sucked out of the cabinet by the dust collector. With a stronger vacuum system, you get fewer cycles per pound of grit (although there is less dust to obscure vision).

Based on an estimated average of 2 hours per cycle, 100-pound quantity.

More Information

True Grit

The size of grit you use has a lot to do with the way your finished etchings will look. The size of the grit is specified by number, with the higher numbers denoting smaller particle sizes. A smaller grit size cuts slightly slower but leaves a smoother finish on the glass.

The most common grit sizes for etching windows and architectural size pieces are 100 to 150. For a finer finish on trophies and glassware, 150 to 220 is used. Micro blasting equipment uses 220 to 400 grit. When blasting wood or stone, the most common grits are 30 to 80.

Conclusions

As you can see from the table, the abrasives which cost less per pound to purchase actually cost much more per hour to use since they cannot be effectively recycled. The really significant advantage to carbide or oxide is the fact that they etch glass about twice as fast as the other abrasives.

So, in addition to savings on materials costs, the oxide and carbide provide an almost 50% saving in labor costs as well.

There is so little difference in cost per hour between carbide and oxide, your choice between the two will depend more on whether you are willing to put up with the static electricity of the oxide and how much benefit you feel the flashlight effect of the carbide provides. As far as safety goes, the Material Safety Data Sheets information on both materials classifies them only as "nuisance dust", and not as hazardous materials.

It is obvious from these facts that if you have blasting equipment that captures the grit and allows you to recycle it, you should be using either the carbide or the oxide. If you don't have such equipment, you should seriously consider getting it, because your savings in labor and abrasion could pay for the equipment in a very short time.

Prices:

ABRASIVES
TYPE GRIT SIZE QTY LBS ITEM # PRICE PER LB
Silicon Carbide 80 50 P35000-50 $120.00 $2.40
Silicon Carbide 80 300 P35000-30 $605.00 $2.02
Silicon Carbide 100 50 P35001-50 $125.00 $2.50
Silicon Carbide 100 300 P35001-30 $640.00 $2.13
Silicon Carbide 120 50 P35002-50 $125.00 $2.50
Silicon Carbide 120 300 P35002-30 $640.00 $2.13
Silicon Carbide 150 50 P35003-50 $125.00 $2.50
Silicon Carbide 150 300 P35003-30 $640.00 $2.13
Silicon Carbide 180 25 P35008-25 $75.00 $3.00
Silicon Carbide 180 50 P35008-50 $140.00 $2.80
Silicon Carbide 220 20 P35004-20 $70.00 $3.50
Silicon Carbide 220 50 P35004-50 $130.00 $2.60
Aluminum Oxide 100 50 P35106-50 $76.00 $1.52
Aluminum Oxide 100 300 P35106-30 $420.00 $1.40
Aluminum Oxide 120 50 P35102-50 $76.00 $1.52
Aluminum Oxide 120 300 P35102-33 $420.00 $1.40
Aluminum Oxide 150 50 P35109-50 $74.00 $1.48
Aluminum Oxide 150 300 P35109-33 $420.00 $1.40
Aluminum Oxide 180 25 P35105-25 $45.00 $1.80
Aluminum Oxide 180 50 P35105-50 $74.50 $1.49
Aluminum Oxide 220 20 P35103-20 $45.00 $2.25
Aluminum Oxide 220 50 P35103-50 $74.50 $1.49
Aluminum Oxide 400 10 P35104-10 $92.00 $9.20