Among the most common sandblasting mistakes is using the wrong abrasive media. A blasting material unsuitable for a particular blasting job can damage the project you’re working on. When it gets worse, you might have to do it all over again.
Sandblasting serves different purposes. The most common? Finishing, cleaning, or prepping surfaces for paint or coatings. Using the correct type of abrasive material will allow you to complete a successful blasting job. Also, choose whether you like dry or wet, siphon blast, or direct pressure.
Here are the things to consider before choosing a sandblasting medium. Let’s get into it.
Blasting for finishing and surface preparation
When blasting for surface preparation, choosing a suitable abrasive material is important. Different types of media have varied characteristics that make different surface profiles.
An abrasive material creates an anchor pattern, determining how well a coating adheres to a prepared surface. The type of anchor pattern you’ll need to apply a coating depends on the surface you’re working with.
Below are the things you need to consider when choosing an abrasive medium:
1. Mohs hardness
A German mineralogist and geologist, Friedrich Mohs, invented a scale that measures the hardness of materials. The Mohs Hardness Scale. This scale is one of the methods used to evaluate abrasives. The softer the mineral, the lower the number on the scale. On the other hand, the mineral is harder when the number is higher.
For example, Talc is 1 while diamond is 10. Minerals that scale higher can etch or scratch those with lower numbers. Below is the Mohs hardness for popular abrasive mediums:
- Crushed glass – 5 to 6
- Aluminum oxide – 9
- Glass beads – 5 to 6
- Silicon carbide – 9 to 9.5
- Garnet – 7.5 to 8.5
- Nickel slag – 7
- Steel shot – 8
- Copper slag – 7
- Steel grit – 8
- Staurolite – 7 to 7.5
- Plastic abrasive – 3 to 4
- Walnut shell – 4 to 5
- Baking soda – 2.5
- Corn cob – 4 to 4.5
Softer abrasive makes a more refined finish. It is also ideal for removing grime, grease, and light coatings. If you don’t wish to leave an anchor pattern on the surface you’re working on, softer abrasives are your best option.
Meanwhile, harder types of abrasive mediums are ideal for steel sandblasting. It helps remove rust, corrosion, and other stubborn stains. Also, use the correct blasting pressure according to the abrasive.
Aside from Mohs hardness, also consider the density of the abrasive material. Blasting abrasives come in a variety of densities. The denser a molecule is, the more tightly the atoms are jammed together. Therefore, a substance with a higher density can contain more kinetic energy.
Also, denser abrasive mediums have more impact over a small region. It means it could penetrate deeper than less dense particles.
Basting abrasives come in four basic shapes: sub-angular, angular, rounded, and sub-rounded.
- Sub-angular abrasives- It features less jagged edges than angular abrasives. Plastic and garnet are among the abrasives that belong in this category.
- Angular abrasives- This abrasive shape has different facets, vertices, and jagged faces. Crushed glass is ideal for removing rust and corrosion among its best examples.
- Rounded abrasives- It is smooth and spherical. This type is ideal for stripping off mill scale or thin coatings. Steel shot and glass beads are among the best examples of this abrasive shape
- Sub-rounded abrasives- Unlike rounded abrasives, this type of blasting abrasive material is not so smooth. Walnut shells and staurolite are among their best examples.
4. Patterns and surface profiles
Abrasive materials create substrate profiles. These profiles depend on their shape once they hit the surface. For example, commercial sandblasting that utilizes rounded abrasives can leave dimpled profiles. Conversely, sub-angular and angular abrasives create deeper, more noticeable anchor patterns.
5. Mesh size
Utilizing the finest abrasive out there is generally ideal. Usually, abrasive mediums are measured in mesh size, grit size, and microns.
6. Total cost
Silicon carbide aluminum oxide is more expensive upfront. But since you can reuse them, you will save money over time.
Overall, the type of abrasive medium you use for sandblasting can affect the outcome of your project. So, consider the factors mentioned earlier, such as the abrasive material’s mesh size, patterns, density, shape, and more.