When it comes to surface finishing for aluminum products and parts made through CNC machining or die casting, anodizing is widely used. This process helps not only improve the overall appearance but also get rid of surface defects. Sandblasting is carried out as a pre-treatment for anodizing.
What is Aluminum Sandblasting?
This is a procedure done to get rid of defects on an aluminum part by applying solid abrasives. Some of the common abrasives used include glass beads and sand. This helps roughen or smoothen aluminum surfaces, improve surface features, and even remove paint.
Advantages of Aluminum Sandblasting
Various manufacturing processes such as CNC machining and die casting can result in imperfections or defects on the surface. For instance, it is possible to find aluminum products that require deburring or have sharp edges. Through sandblasting, you can get rid of such imperfections. Moreover, it prepares surfaces for the next surface finishing process.
The following are some benefits of sandblasting aluminum:
- Smooth surfaces without fractions
- Uses minimal equipment
- It is a time-saving process
- Results in clean surfaces that are free from grease and dirt
- Creates aesthetically pleasing aluminum surfaces with matte or shiny finish
The following are some of the reasons it is necessary to carry out sandblasting on aluminum parts:
- Cleaning off rust
- Getting rid of paints or primers
- Cleanup after damage
- Pre-treatment process for powder coating
- Smoothing rough surfaces
Limitations of Aluminum Sandblasting
These are some of the limitations that are associated with aluminum sandblasting:
- Although it requires minimal equipment, most of it can be quite expensive such as blast pots and containers.
- Need for adequate space that can be unavailable or expensive considering ventilation requirements.
Types of Aluminum Sandblasting Media
Crushed Glass
This is made up of recycled glass. It is widely used in removing aluminum coats. You can identify it by its sharp profile. When crushed glass is used in sandblasting, the result is a clearer finish as compared to using slags or sand.
The good thing about crushed glass is that it works with water and it is fast. Moreover, it is non-toxic as it does not produce harmful airborne waste.
Plastic
When it comes to sandblasting aluminum, plastic abrasives have a range of uses, thanks to their ready availability in a variety of properties. The main compounds used include polystyrene and polycarbonate. These plastic abrasives are used in mold and paint removal, especially from delicate parts.
Plastic abrasives do not leave anchor patterns because plastic is light and soft. Moreover, it is less hazardous when you compare it with chemical stripping.
Silica Sand
For many years, silica sand was the most popular sandblasting media because of its ready availability and low cost. However, its use is limited because of the toxic fumes it produces. Studies show that it can cause respiratory problems. In addition, moisture in silica can result in rusting of the sandblasting equipment.
Aluminum Oxide
Being a hard abrasive and affordable, it is widely used in sandblasting. It has applications in etching and paint removal. It helps smoothen out edges in the deburring process. The good thing about this media is that it is available in a variety of sizes and can be used multiple times.
Walnut Shells
Walnut shells are also used as sandblasting media for cleaning and polishing applications. They are preferred because they are less rigid as compared to metals and plastics. They have found applications in cleaning motors, antique surfaces, polishing jewelry, and getting rid of mold.
Although they do not result in anchor patterns, they are non-recyclable and slow the sandblasting process.
Staurolite
Ideally, this is silica that contains iron. It is a natural compound sourced from metamorphic rocks. It is quite effective in getting rid of thin coatings of rust and paint. When you compare it with most abrasives, it produces minimal dust. In addition, its sub-angular shape helps to minimize surface profiling.
Corn Cobs
These are natural abrasives produced by grinding corn cobs. They are suitable for sandblasting delicate aluminum parts. The abrasive material gets rid of grease, coatings, and dirt whilst protecting the aluminum surface. It can also be used for polishing and deburring aluminum parts.
Corn cobs are non-toxic, but result in a slow sandblasting process. Also, they are not recyclable.
Soda
This sandblasting media is non-damaging. It is used to remove paint and clean surfaces. In some cases, it is used to get rid of rust from surfaces. The good thing about soda abrasive is that it does not cause deformation on parts. However, it cannot be recycled or used multiple times.
Garnet
Another naturally occurring compound that contains silicate. The fact that it has excellent adhesion properties, it has applications in both dry and wet sandblasting. It is useful in the removal of paint, powder coats, and rust.
Being a fast method with low consumption, it is an all-purpose abrasive media. Moreover, it produces minimal dust and has a higher stripping rate compared to other sandblasting media. It can be used multiple times, although not more than four cycles.
Glass Beads
Glass beads have a spherical shape and when used in sandblasting, they result in bright and smooth surfaces. They are widely used in polishing aluminum turbine blades and propellers. In addition, they can be used in general removal of automotive paint and industrial cleaning applications.
What Media is Best for Aluminum?
Although there are several sandblasting media to choose from, you need to understand the effect they have on the product. The most common media used for sandblasting aluminum include soda, walnut shells, glass beads, and crushed glass.
Aluminum oxide has excellent angular structure and toughness, making the adhesion of a new coat easier. This makes it suitable for liquid painting and powder coating applications.
If you want to achieve a polished appearance, you should opt for glass beads. These abrasives leave an aluminum surface crisp and clean. In addition, they can be reused.
If you want to only remove paint or clean the aluminum part, you should opt for Sodium Bicarbonate (soda). This media is ideal because it results in a smoother surface and it is gentle on aluminum.
However, if you want to achieve a rougher surface, you should use crushed glass. You should note that rougher finishes are perfect for workpieces that need coating or painting.
You should avoid using steel abrasives. This is because steel is harder as compared to aluminum. Therefore, it can impregnate aluminum surfaces making them susceptible to corrosion.
What Need to Consider When Selecting Blast Media for Aluminum?
When choosing sandblasting media for aluminum, you should consider the following properties:
Shape
Coarse particles are more abrasive as compared to round ones. Angle sharpness has an impact on depth profile. This means sharp abrasives penetrate aluminum deeper. The common shapes of abrasive media used in aluminum sandblasting include round, angular, sub-rounded, and sub-angular.
Size
A mesh is used to determine the size of abrasive media. For instance, a mesh size of 20 suits large particles, whereas a mesh size of 280 implies small particles. It is advisable to use small abrasive particles as they create smaller impact craters as compared to their larger counterparts.
Density
The density of an abrasive media determines its behavior when it comes into contact with an aluminum surface. Ideally, dense media has a high mass-to-volume ratio. Moreover, dense particles exert high kinetic energy, unlike dense ones that can collapse when they absorb energy. Even then, these particles can be used in paint removal applications and general cleaning.
Hardness
Hard media penetrates the aluminum surface easily, whereas soft media has a minimal anchor pattern. Thus, soft media is suitable for cleaning applications that involve the removal of paint, grease, and dirt.
Can You Sandblast Aluminum?
Yes, it is possible to sandblast aluminum. It is advisable to start the sandblasting process at low pressure and then increase it gradually to the desirable working point. In this way, you ensure that aluminum parts are not damaged due to excessive pressure. The suitable pressure depends on the actual setup and nozzle size.
Experts at Sunrise Metal recommend that you start by testing small sections of the part first. This is because some aluminum parts can be flimsy and thin. By running a test, it is possible to optimize the process by selecting the right parameters. In addition, it helps prevent unnecessary damage such as warping and denting.
Conclusion
Various aluminum parts undergo sandblasting. Therefore, many industries benefit from this surface-finishing process. Some of the industries that benefit include automotive, transport, aviation, and medical.
Remember to achieve the best results possible, you need to choose the right blasting media. Also, the quantity and size of the aluminum part determines the equipment to be used.