Roughness and the right blasting media: advice and knowledge
You probably visit our site because you are interested in Straaltechniek as a (potential) partner for your projects. Or because you have doubts about the blasting media. “Which blasting media do I really need?”, “How do I know which media to use?”. “How does the roughness relate to the speed of the blasting?”. Hopefully you will find the answer to your question below. But don’t hesitate to ask us, because every application is different!
The first purpose of your blasting media and installation
You almost always use blasting to clean. It can be rust or mill scale, or to remove unnecessary remnants from 3d printed products. Castings are also often post-blasted.
The second purpose of blasting: the right roughness
You have already thought about creating the right roughness. Roughness is often necessary for a protective layer for your product. Wet paint, powder coating or perhaps metallization. If you are going to do shoot peening, you should have another goal, which is to increase fatigue resistance. Click here to learn more about this. But do you already know what roughness you need?
Which roughness and which blasting media?
Below you will get a feel for what is involved in achieving the right roughness values.
The figure above clearly shows what is involved in selecting the correct abrasive. Here you can see schematically what a so-called anchor profile is. It ensures that the paint adheres. In the case of the figure above, the primer layer thickness must in any case be greater than the roughness.
This will give you a quick idea of how to determine the desired roughness. Note: these are all rules of thumb. Let us personally advise you and also by your supplier of the paint or coating.
Akzo Nobel shows in its epoxy spec sheet which anchor profile is desired. Click here for an example. It can be seen here that the roughness in this case is 75 microns at a typical (dry) layer thickness of 200 µm.
Blasting media size = 10 x the required roughness.
This rule of thumb is by no means sacred, but it gives a feeling and understanding of what approximately happens when blasting.
It would be ideal to have some type of blast media selection program. Unfortunately this does not exist. Fortunately, there is literature in this area, which is again very valuable, for understanding how the process works. Below you can see indicative measurement results for different types of abrasives and the resulting roughness.
There are 5 things of enormous importance for the end result of your blasting process: the blasting media, the blasting installation, the blasting process, the product to be blasted and clear specifications of, among other things, the roughness to be achieved.
Whichever abrasive you choose, the following matters are important.
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