glass bead blasting

Glass Bead Blasting: Abrasive Shape, Hardness and Recycle Rate

Of all media blasting abrasives, glass bead blasting is arguably the most popular and the easiest on equipment. This is in part because glass beads are very versatile. They are a medium-hard abrasive and come in a range of sizes, shapes and hardness levels. It’s these characteristics of glass beads that make them desirable and impact their recycle rate.

ProTip: Do your homework and research how hard an abrasive is before you use it. Buying medium hardness abrasive is like a medium steak, you don’t want to end up with what the cook thinks is “medium,” you want what you consider “medium.” Luckily, glass bead blasting typically ensures you’re using a medium-hardness abrasive.

Measuring Abrasive Hardness

Most blasting abrasives are listed for hardness using the Mohs Scale for Mineral Hardness but occasionally abrasive hardness is measured using the Rockwell C Scale, HRC or Vickers Scale. Almost all blasting abrasives for abrasive blasting cabinets use the Mohs Scale of Mineral Hardness, so at Media Blast® we go by that scale.

The Mohs Scale for Mineral Hardness measures anything from Talc, the softest mineral on the scale, to Diamond, the hardest mineral on the scale. Soda abrasive falls closer to Talc, and Silicon Carbide falls on the harder end of the scale near Diamond.

Glass beads rate about 5.5 hardness on the Mohs Scale, putting them at the very middle of the road. Most projects can withstand glass bead blasting because they are neither too hard nor too soft. There are also different types of glass bead blasting that use beads that vary in degree of hardness. E-Beads are tempered glass beads and last much longer than any standard bead, but the trade for longer-lasting abrasive is a slower cleaning speed.

ProTip: Think of Glass beads like Goldilocks and the Three Bears – Glass beads are “just right” in most scenarios.

Glass Bead Blasting: The Ideal Abrasive Shape

The shape of the blasting grain is another important factor that is rarely discussed. While glass beads rate about 5.5 hardness on the Mohs Scale, the bead shape puts them at a distinct advantage over other abrasive types.

Slags and Garnet have a slightly harder Mohs Scale rating than glass beads, but they have a much weaker grain shape. Round beads bounce off the surface being blasted, but Slags and Garnet are imperfect shaped grains that look similar to coarse salt or flakes of rust. Yes, Slags and Garnet have a bigger impact on the part being processed than Glass beads. Unfortunately, they also sustain more damage during the blasting process than Glass beads. This means they have a lower recycle rate, they cannot be used as many times before the abrasive has to be replaced. Did we mention that glass beads can make a part larger?

ProTip: Imagine the difference in blasting with glass snowflakes compared to round glass beads. The snowflakes would break apart much more quickly than the beads, resulting in more abrasive byproduct and a shorter recycle rate but the same hardness.

Recycle Rates by Abrasive Type

The hardest abrasives can be brittle as well as very sharp. The right application for each abrasive type is important, but a general rule is to use hard abrasive against soft material like glass, wood, and plastics and use hard abrasive against soft material. Glass beads are used to clean steel, aluminum, cast iron and texture wood.

Real World Example: Abrasive blasting isn’t so different from sandpaper. Pink or red sandpaper is often made with Garnet and suggested for use with softer wood parts. Brown sandpaper usually contains aluminum oxide and is used for general sanding and grinding softer steel parts. Black sandpaper is usually silicon carbide, very sharp and very hard but that does not mean long-lasting. (Fun Fact: Some Slags are also black; this is not a coincidence.)

It’s important to know what you are using as an abrasive so you can choose the right abrasive for your application. Here’s a recycle rate cheat sheet:

High Recycle Rates:

  • Ceramic Beads
  • Carbon Steel Cut Wire
  • Stainless Steel Shot
  • Steel Grit

Medium Recycle Rates:

  • Aluminum Oxide
  • Glass Beads
  • Plastic Type I, II, III, and IV
  • Silicon Carbide

Low Recycle Rates:

  • Walnut
  • Garnet
  • All Slags, Tin, Copper and Coal
  • Crushed Glass
  • Silica Sand
  • Soda

To Sum It Up

The shape of the abrasive being used is equally as important as its hardness rating. A round circle is one of the strongest shapes you can use, which is part of the reason glass bead blasting is so prevalent. If you want an even harder shear, use a ceramic bead.

Slags show a harder Mohs scale reading but do not recycle at the same rate as glass because of the less-resilient shape of Slag abrasive. Using slag and other abrasives that have a low recycle rate can quickly plug any blasting cabinet that doesn’t use a separator reclaimer on the dust collector. This is why Slags and Garnet are great for one-time use in portable pots but not advised for abrasive blasting cabinets.

If you aren’t sure what abrasive is right for your application, give us a call. If you’re not sure what size bead you need for your glass bead blasting application, reference our glass bead conversion chart.