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.
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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 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.
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.
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.
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.
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.
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.
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.
We often speak in broad strokes about deburring and micro-precision sandblasting. Today, let’s look at the nitty-gritty. (Get it? Grit refers to abrasive and to details! Ok, we’ll stop.)
Micro-precision sandblasting, or ‘MicroBlasting’ for short, provides a safe, consistent and precise method for burr removal on small, delicate parts with intricate geometries. Why? In simplest terms, micro-precision sandblasters work on a micro-scale, sending tiny abrasive particles through tiny nozzles at high velocities. The resulting abrasive stream has a laser-beam focus that is easy to aim at tiny targets.
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Let’s investigate and put some deburring examples under the lens.
Most cutting methods tend to push material along the gear surface, resulting in the formation of Poisson burrs. Feather burrs also form, but Poisson burrs are ductile and cannot be knocked off like feather burrs. Instead, Poisson burrs have to be worn down at their roots using an aggressive abrasive. Aluminum oxide is one of our most aggressive abrasives available. Its particle has a sharp, blocky shape and registers at 9 on the Mohs scale.
No control is lost while using aggressive media. The nozzle of a MicroBlasting system provides pinpoint focus to the abrasive stream, regardless of the sharpness or hardness of the particles. An operator can still specifically target and remove a burr without impact to part integrity.
A smooth surface finish reduces friction and prolongs the lifespan of a gear. Glass bead applies a nice, satin finish.
Biocompatibility is a critical feature of spinal implants. Sodium bicarbonate is a great abrasive for deburring spinal implants because its particles are sharp enough to cut through PEEK burrs but not sharp enough to continue cutting past the burr into the underlying surface. Low pressure, a small rectangular nozzle, and a rich abrasive stream work together to gently and cleanly strip pesky burrs off the implant’s surface to improve its biocompatibility.
Picks and knives are often used on PEEK implants, but a micro-abrasive stream is easier to control and reaches smoothly into micro features where fingers and larger rudimentary tools struggle to fit.
*Sodium bicarbonate is water soluble. Running parts through a simple cleaning process after deburring removes all abrasive residue.
The flash, or burrs, that appear on electronics packages form at the seams of their molds. A bit of this material leaks out of these seams during production. This leaked material is quite thin and quite brittle. Soft abrasive, like a blunt-edged plastic media, breaks off the leaked flash without eroding the encapsulation from the electronics package.
See what we mean in this quick video:
Machining stainless steel tends to produce fine burrs with brittle roots. Brittle material responds well to MicroBlasting efficiently. When a micro-abrasive stream is focused specifically at the root of a brittle burr, it quickly breaks the burr-free from the base material.
Aluminum oxide works best for this application because its particles transfer energy from the air stream to this substrate successfully. After a pass on the outside of the valve with the 0.030″ Hi/Performance nozzle, a right angle nozzle can be used to reach deep inside of the main bore. Blasting towards the outside of the valve assembly hits all the burrs at every angle.
*Aluminum oxide leaves a matte surface finish. Polishing or finishing removes this finish quickly.
Aluminum generally requires a more aggressive abrasive than the applications above because it is a ductile material. But machining causes a small amount of the part’s material to smear and heat up at the edge, creating a rollover burr. The rollover burr, thanks to the heat, becomes brittle, which makes it easier to remove at the root.
Aluminum oxide has sharp, block-shaped particles that easily cut through metals, hard surfaces, and brittle parts. Aluminum oxide works fast on metals, especially on large parts. If the part’s surface needs to be restored after deburring, switch out abrasives and run a pass with glass bead. Glass bead should gently tap a nice satin finish on the part surface.
Small rollover burrs form on the top of this curved part-surface during machining. Surface finish is critical on a titanium component and a connector used in aerospace engines. Glass bead is best for this application because it is too soft to impact the surface finish on the area surrounding the burr. The spherical dimensions of its particles transfer energy from the air stream to the part surface, whereupon impact, it breaks off burrs. A glass bead is not sharp enough to cut into the material beyond the base of the burr. Rather, it leaves a satin finish in place of the burr and on the surface surrounding the burr site.
Watch the burrs glide off the part surface:
Let our experts help find the right solution for your part. We know no two applications are the same. Our Technical Specialists manage sample-part testing and processing from start-to-finish. They actively collaborate with our Sales and Engineering Teams while remaining completely accessible to you throughout the process.
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