Silicon Carbide Blasting

Choosing the proper grit size of media to get the desired finish is often a little bit of trial and error. Different medias at different pressures on different metals with different processes will result in different surface finishes.

These 304 stainless steel washers needed to be etched with Silicon Carbide Grit to achieve a lightly etched finish (Aluminum Oxide Grit was not allowed for this particular situation). Since the exact finish was not specified, a range of grit sizes were tested. Starting at the top and going clockwise, the discs were blasted with 36 Mesh, 60 Mesh, 100 Mesh and 220 Mesh Silicon Carbide Grit at the same blasting pressure.

While a little difficult to see the detail, it is clear that as the grit size gets finer, the finish get much smoother. This is typical of all types of blasting media. Larger grit will result in a heavier etch than finer grit. It's just a question of what grit size gives the desired results for a specific application.

Etching Stainless Steel

Stainless steel can be polished to mirror surface finishes. Sometimes, the surface needs to be etched in order accept a coating or prepare the part for a process that requires a little 'grab'. While tumbling in a vibratory system or a barrel tumbler will create a matte finish, the surface is generally not rough enough for many coatings. Also, when the parts are small, it can be difficult to separate the media from the parts in a tumbler.

Stainless Steel Etching

When an etch is required and the parts are small, a tumble blasting process is often an ideal solution. The stainless steel parts above (before and after) are less than 1/2" in any dimension. These parts were tumble blasted with 60 mesh Aluminum Oxide Grit for only 20 minutes. Depending on the size of the blasting basket, batch sizes as large as 3 cubic feet can be processed at one time.

Anchor Profile

The anchor pattern or etch profile on a surface created during abrasive blasting is critical to the subsequent application of a coating such as paint. The anchor pattern is basically the peaks and valleys on the surface of the metal (or any surface) on a microscopic scale. Often coatings manufacturers will specify the profile for optimal adhesion of the coating being used.

The profile is expressed in millimeters, microns or mils. Anchor patterns generally range from 3 mils and lower and is measured by the depth of the 'valley'.

1 mil = 0.001"

39 mils = 1 millimeter

25 microns = 1 mil

The proper profile will be allow the paint to adhere but completely cover the surface.

If too much etching occurs, the 'peaks' will have a tendency to stick above the coating and lead to coating failure over time. If the profile is too small the surface between the material and coating is minimized causing improper bonding.

The media type and grit size, blasting pressure, distance from the surface, angle of blasting and surface hardness will all impact the final anchor profile.