5 Must-Have Features in a Blasting Glass Beads

Applications

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Glass beads are a non-metallic blasting media, which can be used on various substrates like steel, aluminum and stainless steel. The purpose can be both esthetical as functional:

• Glass bead blasting is effective in removing contaminants like rust, oil, dirt, and light coatings from surfaces, without creating a surface profile on the work piece.
• To esthetically improve the surface and create a matte satin like finish on stainless steel.
• Removing the blue heat marks from welding or bending marks on stainless steel.
• Smoothening the surface of (stainless) steel, making it difficult for dust and contaminants to stick onto. The surface stays cleaner and is easier to clean as well.
• Improving the fatigue life of metal components by peening.
• When using the right equipment and correct glass beads a roughness acceptable for the food grade and medical industry can be achieved.
• Improving resistance against corrosion.

On stainless steel the glass bead blasting can be the final treatment of the object, but it also creates a good basis for powder coating.

Roughness and pressure

With normal grit blasting or sandblasting, the goal is often to clean the substrate and create an anchor profile for the coating to adhere. With glass bead blasting the goal is to lower the roughness and polish the surface.

Glass bead blasting is performed in a blast room or blast cabinet and the glass beads can be reused / recycled. When using  glass beads as the blasting media, the pressure is normally set at a relatively low level, from 2,5 to 5 bars. This way the glass beads gently polish the surface for the best result and the glass beads have a better durability.

The glass beads are normally rather fine in grain size as compared to other blasting media. Typically glass beads 100-200 um (or 0,10 to 0,20 mm) are used, but also even finer glass beads when food grade specifications need to be achieved.

With normal glass bead blasting a roughness of RA = 1,5 um can be achieved at low pressures. When using the Rotin principle in combination with Rotin beads, roughness of RA < 0,8 um are possible.

ROTIN Blasting Principle

With the Rotin blast nozzle, glass bead blasting without stains or bead blasting to very low roughness within the parameters set by the food- and medical industry are possible.  The ROTIN blasting principle is developed by Cees Kalfsvel from Holland after years of experience in glass bead blasting.

How Rotin works

Normal blast nozzles use a straight narrow jet, which have a hotspot of beads impacting within the blasting pattern. There will always be the operators risk of incorrect overlap of his blasting passes, creating ugly stains on the stainless steel work piece.

The rotating insert (ROTIN) is placed before the blast nozzle. This insert widens the rotating jet proportionally, and sprays it at an angle. The hotspot of beads impacting within the blast pattern is eliminated. The surface will be blasted with a wide uniform rotating jet at equal intensity at every angle.

Rotin blasting is done with a finer abrasive at a lower pressure (2,5 – 3 bars) for the best result.

Advantages of Rotin blasting principle

If you are looking for more details, kindly visit Blasting Glass Beads.

Steel Shot

Steel shot is another type of media that can be used. It is made by casting small steel beads according to SAE standard sizes ranging from S-70 (~0.125mm screen size) to S930 (~3mm screen size). There are also multiple hardness ranges, which go from a hardness of 40 Rc up to 62 Rc. The hardness and density of steel shot make it highly durable and in many cases enable it to be re-used for hundreds of cycles! The most common uses for this type of media are cleaning, de-rusting, stripping, and shot peening applications. Metal surfaces can be stress-relieved and hardened to prevent metal fatigue when shot peened using steel shot media.

Steel shot is best used for heavy-duty applications and materials such as steel and cast iron; it is not generally suitable for softer metals or plastics.

Aluminum Oxide

Aluminum Oxide is a tough and abrasive grit media with an angular shape and is often used as a substitute in the sand blasting process. Due to its hardness and angular shape, it is effective at quickly cutting into and etching even the hardest materials. It is often used to prepare surfaces for paint, round sharp edges, and provide a consistent-looking finish. The roughness of the finish will generally correlate to the grit size used. Larger-sized grit will etch the surface more quickly and leave a rougher finish, while finer grits will leave a smoother finish with longer processing times.

Surfaces blasted with aluminum oxide will attain a consistent matte finish with a dull appearance. Aluminum oxide is generally brown in color and can cause some discoloration. Aluminum oxide can be used prior to anodizing to produce uniformly matte anodized parts. It is not suitable for applying finishes to plastic parts.

Plastic Media

While there are multiple types of plastic blasting media, the most common and widely used is called Urea. It is made of angular-shaped grains of recycled plastic materials. Being plastic, it is much more gentle than most other abrasives, highly re-usable, and lightweight. This makes it ideal for use on delicate parts or materials without causing damage. Blasting equipment can accelerate the lightweight plastic particles to high velocities, making it effective at quickly stripping light coatings. Plastic blast media is also helpful for de-flashing and deburring operations for molded parts.

While plastic media such as Urea is excellent for cleaning and stripping applications, it is not a good option for achieving cosmetic finishes since the media does not dimple the surface like other types of media.

From the wide selection of available media to the applied pressure and technique, many variables can influence the appearance of your bead blast finished parts. Suppose you are looking to achieve a particular finish. In that case, it is essential to provide specifications to control some of these variables to guide the intended result. When striving for consistent results across production runs or multiple batches, specifications are critical.

When ordering bead blasted parts through Xometry's Instant Quoting Engine, if no further instructions are provided, we will defer to using glass bead media and sufficient pressure to remove tool marks and smooth the surface without damaging the part. The sections below go over tips and best practices you can incorporate to achieve greater control of the process and more predictable and consistent bead blast finishes.

Media Specification

The type of media or abrasive used will significantly influence the look and feel of your finish. For instance, fine glass beads will produce a consistent, satin-like finish, whereas aluminum oxide will yield a uniform but duller appearance. It may take some experimentation to determine what media works best for your project, but you will want to include that information in your order or part drawings notes section once you do. In addition to the type of media, be sure to specify its shape if there are multiple options to choose from.

Abrasive Grade / Grit Size

Another variable that plays a role in how your finish comes out is the particle size of your chosen media. Suppliers often refer to the abrasion grade or grit. The grit is very similar to what you would find when shopping for sandpaper at your local hardware store. The lower the grit, the larger and more coarse the particles are. On the other hand, higher grits will be of finer particles. Mesh size is often referred to as well. The easiest way to understand mesh size is if you were to observe a 1"x1" screen made up of equally sized holes. With a mesh size of 20, there would be 20 holes in the screen, and particles smaller than those holes will pass through, while larger ones will be blocked. With a mesh size of 200, there would be 200 holes in the same 1"x1" area, and thus would be much smaller and only allow finer particles to pass through.

Media size is typically broken down into coarse, medium, fine, and very fine grades. Calling out a grade will simplify your notes and prevent being overly specific, which can limit a manufacturer's options.

Avoid Tight Surface Roughness Callouts

By the nature of the blasting process, the part's surface roughness will be directly impacted. It can be challenging for shops to maintain tight surface roughness requirements while also applying a media blasted finish. When these requirements mix, it is often the case that a shop will want to pause the project and get clarification on what the expectations are.

We recommend limiting surface roughness to no lower than 32 µin Ra when you need a smooth bead blasted part. We do not recommend blasting surfaces that must be lower than 32 µin Ra and instead call out for masking on just those surfaces. Take note that masking requirements can significantly increase labor time and thus cost.

Provide a Boundary Sample

A boundary sample can be invaluable for manufacturers when producing a finish that meets expectations. If your project has strict finishing criteria or detailed notes, a boundary sample can help resolve concerns and provide clarity. Manufacturers can use their knowledge and expertise to produce an output that matches provided examples, reducing the need for detailed notes. If a physical sample is not available, the next best thing would be high-resolution photos taken at various angles. Xometry's engineers and case managers can help you make such arrangements with our manufacturers after placing your order.

Masking Callouts for Critical Features

Lastly, we recommend including masking notes if your part has any critical features or surfaces that should be guarded against abrasion. Examples of these features are sealing surfaces and o-ring grooves. Although most shops already do this per shop practice, we recommend adding masking requirements for threaded features, especially for small or fine pitch threads.

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Example drawing notes for bead blasted finishes:

• "Bead blast all surfaces using fine grade glass bead media."
• "Media blast with #70-100 glass bead at 50-60psi."
• "Mask indicated surfaces and tapped holes prior to media blasting. Media blast un-masked surfaces with medium grade aluminum oxide."