Custom Part Finishes:All About Bead Blasting

Blasting is a finishing process that manages the surface of a wide variety of objects. Bead blasting is one type of shot blasting. This process releases, at high pressure, fine glass beads to clean or finish a surface.

In this process, a bead blaster shoots bead-shaped media from a high-pressured tool towards the material’s surface. A bead blast finish aims to leave a smooth, shiny, and cleaner surface. You find manufacturers using bead blasting for materials like metals, plastic, glass, and rubber to create an excellent surface finish.

The Principle Behind Bead Blast Finish: How Does It Work?

Bead blasting involves throwing bead-shaped or sphere media against a substratum. Aluminum, stainless steel, or any other material that needs a surface finishing via blasting is suitable for use.

Often, a significant amount of abrasive blasting is performed using unevenly cut or rough media and leaves a gritty surface finish. Bead blasting utilizes round spherical media that gives a smooth, uniform finish after being impinged against the surface of a component.

In addition, steel shot blasting in this process permits flexible conditioning of the available substrate. Manufacturers use the bead blasting technique when there is a need for smooth and even finishes. Some people also prefer this technique for parts intended to possess a satin finish that is not sharp.

The bead blast finish allows manufacturers to obtain a quality surface finish that is unrefined but dependable. The fine glass beads are most effective on aluminum parts that require a satin finish. The coarse glass beads give a regular rough finish as they cover any defects in the substrate surface.

Several other materials will make any substrate it collides with even darker, giving it a greyer finish. Materials such as silicon carbide, garnet, or aluminum oxide possess ideal grits. Meanwhile, glass bead blasting permits the substrate to retain its elementary color, giving a polished surface finish.

Equipment And Materials Used For A Bead Blast Finish

The key to a successful bead blasting process is efficient tooling that serves the right purposes. Let’s look at the different tools required to get the best results.

Media Blasting Cabinet
These are sometimes called with the specific name of the media, in this case, bead blasting cabinet. As the name suggests, bead blasting cabinet is piece of equipment used to enclose the process to guarantee cleanliness and safety.

To make sure you are getting the best possible cabinet for your shop, take a look at the following considerations when making your choice:

1. Strong and durable materials used in the construction of the cabinet.
2. Sturdy and well joint legs. Legs are usually welded, so you want to take a look to the integrity of the welding. This is especially important since the legs are the structures supporting all the weight of the cabinet plus the weight of the bead blasted parts and the media used for bead blasting them. Wobbling legs could be problematic and even dangerous.
3. The sealing should be hermetic to ensure no dust or any debris will come out and create a dangerous and unhealthy working environment.
4. Good visibility but better protection. While a big window allows for a great view to guarantee a high-quality process, this window needs to be strong enough to ensure you or your operator are protected while generating a bead blasted surface finish. Of course, the material of the window will wear down with the time due to the impact of the glass beads and the debris, so it is important to verify the cabinet comes with replacement windows and that the window is quick and easy to replace.
5. Good hand protection. Normally, media blasting cabinets come with strong and durable gloves directly attached to the cabinet wall where the view window is located. Apart from being strong enough to protect your hands or the hands of any operator, these gloves should provide enough touch sensitivity and comfort to manipulate the part and the bead blasting gun properly.
6. Speaking of the bead blasting gun, it is obvious that having a high-quality gun is vital. Without it, there would be no bead blasting at all. However, this is a more personal choice since it depends on the skills of the operators. In general, foot pedal blasting guns are preferred for generating bead blasted finish on big parts since they take longer and using the trigger type can be exhausting in those cases.

Bead Blasting Media

The media itself is an essential bead blasting material. Machinists generally use two types of beads for a bead blast surface finish. They are glass beads and steel beads.

Glass Bead

Glass beads are one of the most commonly used media types for the bead blasting process. They are usually made from a type of lead-free, soda-lime glass which is environmentally friendly as it does not contain free silica and is chemically inert. When used appropriately, glass bead media is quite durable and can often be re-used up to 30 times. This type of media will not colorize the surface on impact and thus help maintain the material's base color.

While versatile for many applications, glass bead may not be as suitable for extremely tough materials and is ineffective at etching the surface for paint preparation. This type of media is ideal for surface cleaning, semi-polishing, or peening applications.

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.