Abrasive Blasting Media - Glass Bead

Glass Bead is a unique blasting media. Being a solid, round sphere made of soda-lime glass, this media will produce a very smooth uniform finish on a variety of surfaces. Glass Bead is used for cleaning and light stripping but mostly for surface finish preparation without etching or changing part tolerances.

Glass Bead has a similar hardness to sand but is silica-free media and can be re-used many times. Coarse sizes will clean at a slower rate but can produce a more intense peened effect (higher surface RMS). Finer sizes will result in more impacts per pound during blasting producing a lower surface RMS and even more uniform surface finish. The round shape of Glass Bead results in a smooth, clean, bright, satin-like surface finish on metals such as aluminum, steel, brass, bronze and copper.

Unlike most blasting operations, Glass Bead is generally blasted at a 90 degree angle to the surface (instead of 45 degrees). While this may 'consume' the media faster, the peening intensity and performance is increased at this angle. The hardness of the surface being blasted and blasting distance from the surface will also determine the media life.

When the Tumbling Barrel IS the part...

Question: The part is the barrel itself. It is a 12" diameter pipe that has an inner coating of ~2mm that needs to be removed. The material to be removed has a Shore D hardness rating of 80. The pipe can be sealed at each end and rotated if a liquid would be required. What type of tumbling media and procedure should be used to remove that ~2mm inner coating?

Response: This can be achieved by filling the pipe with tumbling media almost half way. The media recommendation is a 1" x 1" or 1-1/2" x 1-1/2" KXF Cylindrical Wedge Ceramic Media. This is an extra fast cutting bond that can abrade hard metals. The process can be sped up by adding some 60 Mesh Silicon Carbide Grit to the load (about 1/4 to 1/2 lb per gallon of water). The water level should just cover the media load. A 12" diameter pipe should be rotated 30-45 RPM. The running time may take anywhere from 8 hrs to an overnight run.

{Summarized from a post on the ShopTalk Forum.}

Abrasive Blasting Media - Aluminum Oxide

Aluminum Oxide Grit is probably one of the most versatile and widely used blasting media. Virgin Aluminum Oxide is refined from bauxite mineral ore. The blasting grit is about 95% pure with a hardenss of about 8.5 on the MOHS scale (diamond is rated a 10).

Due to the angular shape of Aluminum Oxide it exhibits excellent stripping and etching properties. This media is used to remove heavy oxidation, multiple layers of coatings and to produce at etched surface. Available grit sizes range from a very aggressive 12 mesh to a super fine 320 mesh. Finer sizes are available but are only used in specialty applications such as micro-blasting.

The hardness and aggressive nature of blasting with Aluminum Oxide makes it ideal for blasting hard surfaces such as steel or where surface etching and micro-finishing (often prior to coating or painting) is required.

Aluminum Oxide is a relatively expensive media but breaks down slowly. This combination would rate the overall operating cost as affordable. Aluminum Oxide is ideal for use in a blasting cabinet (versus a portable system) or a blast room where the maximum amount of media can be recovered and re-used.

White Aluminum Oxide is a more refined version (>99% purity) that has specialty applications such as dental, medical or electronic parts where purity surface contamination is of concern.

Abrasive Blasting Media - Introduction

There are many different types of abrasive blasting media available. Each of these media will produce a different finish on the surface being blasted. The finishes can range from ultra-rough to nearly polished to no affect at all. There are many variables that determine the surface finish achieved including blasting pressure, angle and distance of the blasting, hardness of the grit media, blasting time, etc.

Knowing the basic differences in abrasive blasting media is required to determine the optimal process for different applications. In addition to the media type, grit or mesh size is another factor to consider. The final choice of media depends on the nature of the work required and on the blasting equipment that is employed.

The series of posts to follow this one will deal with abrasive media selection only and outline some of the advantages of the different types of blasting media and some guidelines for choosing the best media for your application

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 millimiters, 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.