Sand Blasting Aluminum: The Complete Guide in 2022
Updated: December 02, 2023
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When we talk about the surface finish for aluminum parts, including CNC machining, extrude or mold casting. Anodizing is the most common type, this finish can help to remove the surface defect and offer great appearance, such as iphone and ipad case. Sand blasting the pre-process for anodizing, this steps can offer proper roughness and metallic texture.
In this post, we will explain the sand blasting process for aluminum part, including the cause, main type and some useful tips for beginners.
1. Why do aluminum parts need sand blasting?
Manufacturing processes often leave products with imperfections emanating from the production cycle. For example, cast products may have undefined edges and machined products may need to deburring. Sand blasting helps to remove the manufacturing process imperfections on a component. It also helps to clean surfaces for next processing.
Aluminum anodization is a process commonly used to protect aluminum. It is an electrochemical process where the top surface is converted into an Aluminum oxide layer. Aluminum has a naturally occurring Aluminum oxide layer but this natural layer is too thin to offer an acceptable degree of protection.
In anodizing, the workpiece is placed in an acidic, electrolytic bath. An electrical charge is introduced into the bath and this process causes an Aluminum oxide layer to form on the surface. This oxide layer formed by anodizing is durable and has good corrosion and wear resistance. Before the anodizing process, the Aluminum must first be thoroughly cleaned. This is accomplished by sandblasting.
It is important to note that the term sand blasting is sometimes loosely used to encompass several types of abrasive blasting media, not just sand. For example, one can talk about sand blasting with walnut shells.
2. Wet Blasting vs Dry Blasting Aluminum
Blasting is a process where blasting media is fed into a chamber that is connected to a pressurized air supply. The pressurized mixture of air and blast media travels through a blast hose and is then fired out through a blast gun directed onto the surface. On impact, the particles dimple the surface causing the removal of coatings previously applied.
3. Wet Blasting Advantages and Disadvantages
Wet blasting is similar to dry blasting except that for wet blasting, a liquid is used in the blasting process instead of air. When dry blasting, heat is generated by friction when the abrasive material hits the surface being prepared. This heat can result in a lower-quality finish, especially for delicate materials. Wet blasting solves the heat problem because water acts as a coolant. Wet blasting is also safer than dry blasting because it does not produce dust.
The disadvantage of wet blasting is that you must apply the protective coat quicker than you would for a dry-blasted aluminum profile. Applying the coat quicker ensures that the applied coat adheres to the surface well, before the formation of the natural oxide layer.
Other drawbacks of a wet blast system are its higher initial costs. There are also application restrictions and potential issues with containing the spent blast media.
4. Dry Blasting Advantages
Dry blasting is more affordable because it doesn’t require additional equipment or the containment and removal of water and wet waste.
Dry blasting is more versatile. It can be done in a larger variety of locations and requires less preparation and equipment.
Reference Post: How Much Does Sand Blasting Cost for Metal Part?
5. Useful tips for sand blasting aluminum
5.1 Choosing the Right Blast Media
While there are many blasting methods to choose from, it is important to know their effect on the end result of the product. The media most often used for blasting Aluminum include walnut shells, bead blasting, glass grit, and Sodium Bicarbonate.
Steel abrasives such as steel shot and steel grit are not appropriate for blasting Aluminum. Steel is harder than Aluminum as such it impregnates the Aluminum surface. This means that small particles of the steel embed themselves on the surface of the Aluminum and this leads to corrosion over time.
Glass beads and Sodium Bicarbonate are suitable media choices if the goal is only to clean or remove paint from the Aluminum surface. These methods are suitable because they are gentle on the surface profile and leave a smooth surface. Rougher surfaces are obtained by using harder abrasive media such as crushed glass. Rough finishes are best suited for workpieces that will need to be painted or coated. The rough surface aids the adhesion of the coating applications onto the workpiece.
Aluminum oxide is also an available option for blasting Aluminum. Its advantages are that the abrasive material can be recycled.
5.2 Sand blasting Pressure for Aluminum Surface
The blasting process must be started at the lowest possible pressure. The pressure must then be gradually increased to a suitable working point. This ensures that the workpiece will not be damaged by excessive pressure.
Pressure between 3-4 bar (50 – 60 PSI) is a safe starting place. The optimum pressure will depend on the size of your actual setup. Nozzle size varies. The smaller the blast nozzle size the more pressure your workpiece will experience for a given pressure. Thus, starting at a low pressure removes the risk of firing excessively at the workpiece.
5.3 Test a Small Section of the Surface First
Aluminum profiles are sometimes thin and flimsy. It is advisable to test out a control surface first in order to optimize the process parameters. The test section will give an indication of process parameters as well as the end result of the process. For thinner Aluminum sections, testing a small section will also prevent any unwanted damage such as denting or warping.
For achieving the desired result, the following factors can be changed; air pressure, the abrasive particle size of blasting media, blasting distance as well as blasting angle. One can test all the above on a small section in order to optimize and then complete the workpiece to produce the desired result.
The most common Aluminum items that undergo blasting are vehicle wheel rims, engine blocks, and boat hulls. Blasting is also used in the medical industry for clinical applications
Good quality results when sand blasting Aluminum materials comes down to whether or not suitable blasting media was chosen. The size and quantity of the part to be sandblasted also dictate which equipment should be used. Abrasive blasting cabinets are great for small jobs that can actually fit into the cabinet like wheel rims. For larger jobs, you will need to use a blast pot sandblaster.
More abrasive blasting media must be chosen if an industrial coating will be applied. Gentler media are a great choice for removing paint only or cleaning only with no follow-up processes afterward.