How to prepare surfaces with aluminum oxide is a question our clients have asked us several times. For that reason, we decided to create a guide that could help anyone else out there who is having the same question.
Before doing anything it should be established that aluminum oxide is the right media for the surface you need to prepare. Also, you need to make sure that the equipment you are going to use is ideal for aluminum oxide.
With these 2 answers down, it is time to get to details.
So, as you can see, is not just a matter to get the media and start blasting. There is more involved. So, let’s get started with this guide.
What is aluminum oxide and what is used for?
We call aluminum oxide a very hard and angular media that provides an extra coarse blast. Since is extremely hard and sharp, is used widely for deep cleaning, grinding, deburring, and polishing of hard-constructed metals.
Aluminum oxide does not contain any free silica (which makes it safer to use than sand) and since the grit size is more consistent and cuts much faster than sand, it leaves a smoother surface, and the blasting takes less time.
Due to its sharpness, it doesn’t break as frequently as other media, which increases its usable life and the dust cloud is lower, making it more environmental-friendly.
It is very commonly used because is low-cost, can be recycled many times, and comes in a variety of sizes. Surface preparation and blast finishing experts use it frequently.
To summarize, some of the features of aluminum oxide are:
- Sharp, an angular shape
- Almost no iron content
- Recyclable for multiple turns
- Chemically inert
- High-melting point
- Medium to high bulk density
- Micro, macro, and custom grit sizes and blends are available
- Hardness is around 9 on the Mohs scale
Surfaces and applications where aluminum oxide can be used
Aluminum oxide can be used as a media for sandblasting on a variety of materials such as ferrous metal, steel, stainless steel, stone, marble, granite, glass, ceramic, many metal alloys, and other hard surfaces.
This media can be used for a wide range of applications from cleaning valves, engine heads, pistons, and to lettering in monument inscriptions. This media can be also used for matte finishing, as well as for cleaning and preparing parts for metalizing, plating, and welding.
If we want to point out its main uses, we can include the following:
- Abrasive blasting
- Polishing
- Lapping
- Anti-skid surfaces
- Cleaning of investment castings
- Anchor profile for best adhesion of coatings
- Surface preparation for thermal spray coatings
- Stone and granite monument lettering removal
- Matte surface finishing
- Glass etching or frosting
Benefits of using aluminum oxide when blasting
One of the main benefits of this media is that almost does not contain iron. This is important because is not prone to rust. If the media does not contain rust it is also not contaminating the surface, causing it to rust again.
The aluminum oxide does not rust even with water, which makes this media perfect for wet blasting or some blasting operation with vapor. The blasting operation can be done outdoors, under humidity conditions, and still, it won’t damage the abrasive media.
Also, due to its hardness, above the average, when being blasted does not produce much dust, easing the operation and keeping it safe for the operators. In the same line, this hardness that belongs to aluminum oxide makes it recyclable, way more than other also recyclable media abrasives.
A final but very important benefit of aluminum oxide is its cost. Since it is cheaper than, for example, steel shots, is widely used by professionals on surfaces that can be blasted with it.
Prepare surfaces with aluminum oxide: what cannot be blasted with it
Aluminum oxide is one of the hardest media out there, so it is not ideal for thin gauge metals. If you try to use aluminum oxide to blast a delicate surface you might end up causing damage, no matter what nozzle you choose to work with.
Automotive parts should not be blasted with aluminum oxide as a preparation for painting because it could cause damage. Many parts belonging to the aerospace industry should not be blasted with aluminum oxide. In a few words, any surface that can be considered delicate should not be blasted with aluminum oxide.
Step 1: Prepare the area and the surface to be blasted
It might sound redundant since sandblasting is a preparation process for surfaces, but actually, you need to prepare the surface to be sandblasted.
Preparing the area
In this first step, you need to prepare the area, this is, the location where you plan to sandblast the surfaces. You will have to define whether you would be sandblasting in a warehouse or in a blasting room.
If you have a blast room, which is ideal, you can cover the ground with paper or plastic in order to contain all the media that goes out of the nozzle. Some blasting rooms have special features to contain the media blasted. Take advantage of any of them, because the recycling of the abrasive media is key to lower costs.
Preparing the surface
Once the area is ready, you need to prepare the surfaces to be blasted. In order to do that you need to clean it up with a potent degreaser. If the surface contains a lot of oxides it might be a good idea to use a rust converter or rust neutralizer. There are plenty of products to that end, available even online.
Cleaning up the surface with a rust neutralizer can improve your sandblasting operation because it would remove or lose the hardest chunks, so you could spend less time and media when actually blasting.
If the surface is an iron-based metal containing both cold roll or hot roll steels it is essential that you degrease it and neutralize the corrosion before the blasting.
Once the surface is degreased and prepared, rinse it and give it some time to dry before the sandblasting operation.
Step 2: Choose the right blasting, media, and recovery system equipment
Once you have both area and surface ready to go, it is time for you to take a look at your equipment. So, in this step you are going to define your blasting equipment, the media to use (which in our example is aluminum oxide), and the recovery system you plan to use.
The blasting equipment
There is a wide range of blasting equipment available, to satisfy any need. Some of them make possible continuous operation for hours and hours, while others are more limited in their scope.
In order to match you with the right blasting equipment according to your needs, some of the questions that any of our consultants are going to ask you are:
- Is sandblasting a constant operation in your plant or do you just do it eventually?
- What materials are you going to blast?
- How big are the surfaces you need to blast?
- Are the surfaces to be blasted in outdoors?
- What are the weather conditions where you are going to blast?
- What finishing do you require for the surfaces?
The ideal sandblasting operation occurs in a blasting room. It is convenient to use blasting cabinets with media reclaiming belts, an air cleaner system, and cartridge-type air filtration for particle entrapment. This is to ensure the safety and health of the operators.
Most of the blasting equipment allows the operator to choose the nozzle. It is exactly the nozzle that determines the volume of air required for the blasting operation. The bigger the nozzle, the higher the air volume required.
The compressor also plays a role here, because the speed the operator can achieve in the blasting operation depends on both the capacity of the compressor and the nozzle size. Make sure that you will use both the right compressor and the right nozzle for your job.
The media to choose: Aluminum oxide
In our example, we are using aluminum oxide as the chosen media. This abrasive is ideal because does not transfer or contaminate steel. As we mentioned before, it has some other benefits, which are the reason why we recommend it.
Now, depending on the surface you are going to blast, this selection might change. So, check on this article a short definition of each one of the abrasive media mainly used nowadays, so you can take an informed decision. Of course, you can count on us to guide you in your selection.
The recovery system
The media blasted can be recovered by means of a vacuum nozzle. If two operators are in the area at the same time, one of them can blast the media, while the other is recovering. In case only one operator is there, he himself can recover the media now and then, to be able to continue the job.
Many blast cabinets have a recovery section where is put the media collected from the ground. If is a wet blasting operation, in this part of the cabinet the media will dry, before joining the rest of the abrasive in the media container.
Since aluminum oxide does not rust, the media getting wet is not a problem, but in the case of many other abrasives, drying it before putting it together is essential to avoid contaminating the surface to be blasted.
Step 3: Test in a small area
Even if you are an expert at sandblasting, it is a good idea to start by testing in a small area of the surface to be treated. The reason behind the need for this test is to calculate the blasting time, abrasive media, and repositioning or recovery time that the full operation might take.
The time calculation
The first thing to calculate is how much time will the whole operation take. So, count how much time you need to blast a small area of the surface. With that number in mind, determine what percentage represents the proportion of the small area you just blasted and what is the size of the total surface. With these figures, you will do a simple rule of three.
As an example, let’s say that you spent 10 minutes blasting the small area you chose for the test. You know that the total size of the surface is 300 square feet. You calculated that the tested area represents 5% of the total surface, which equals 15 square feet. Now, you multiply 10 (minutes) by 300 (feet) which totals 3,000. Now, divide that by 15 (feet) and you will have as a result 200, which is the number of minutes you will need to complete the job. That equals 3 hours and 20 minutes.
The media calculation
One of the good things about abrasive media is that they are not perishable goods. You can have as much as you want in your warehouse or plant, for a long time, and is going to be good.
So, depending on the blasting operations that you usually have, it is convenient to have enough abrasive media to blast for a long time without the need to recover. Again, you will need to calculate that in the test.
Once you finish blasting in the test, take a look at your media cabinet. How much media was consumed? A 5%? A 10%? Following the example, with the surface, you can also do a rule of three to know when you will need to stop to recover media from the ground.
Of course, this calculation is not needed if another operator is recovering media as soon as is blasted.
The rest of the calculations
Depending on the facilities you are using for sandblasting the media recovery might vary. For that reason is equally important to calculate how much time could take.
For instance, if two operators are involved in the blasting process, one of them is going to blast while the other is going to recover. The media recovery time there is close to none. But it is only one operator doing the job, he will need to stop now and then, depending on how much media he has available, to recover what he just blasted. This can take valuable daytime.
Another detail that can improve drastically the sandblasting operation is having a nozzle with a trigger system. That way the operator can start and stop right whenever he needs to. If the nozzle in use has not a trigger system, the operator might need to walk all the way down to start and stop the blasting operation, which can consume precious time.
Step 4: Blast the surface in an efficient way
Even though it might look like a chaotic operation, sandblasting should be done in a very methodical manner. So, yes, definitely there is an efficient way to do it.
Start by double-checking that the blast nozzles are configured correctly for current air pressure and volume. Once you are sure of that, start blasting the difficult areas within the surface, like curves or bumps.
The operator must make an effort to achieve the surface profile defined in a methodical way. Depending on the conditions of the surface this can be done at a speedy or slow pace. If blasting outdoors the weather conditions will also influence the way the operation is carried out. Never go against the wind.
When talking about efficiency at sandblasting we need to take into consideration too the conditions for the operator. They must have appropriate personal protective equipment which includes ears and eyes protection. They also should use masks to protect themselves from the dust cloud formed in the area. Only by sandblasting in a healthy and safe way, we can ensure the operators will be able to keep doing it day in and day out.
Step 5: Recover the media and get ready both equipment and media for the next blasting session
Most continuous sandblasting operations count on two operators in place in order to recover the media as is blasted. In other cases, only one operator is available, so he himself sees the need to stop his blasting to recover the media in the ground.
In the case of aluminum oxide, which is our example in this article, since it does not oxide can be used immediately after being recovered, when wet blasting, without the need for any downtime to dry. Another advantage is that the dust cloud is less, so the downtime to recover is also lower, because the environment is not so polluted.
Now, in the case that you decided to go with other abrasive media (or actually is needed, due to the type of surface) this downtime for recovery might vary. Any media that can be recycled will imply some recovery time that has to be included in your cost calculations.
Immediately after the sandblasting, the surface must go to painting. This will prevent the surface from oxide again, and having again the need to be blasted.
Blasting equipment, whatever the size and capacity, are expensive. Make sure that the operators or specialized personnel take care of the one you own, by cleaning it immediately after each use. A regular maintenance program should be put in place to ensure a long equipment life.
You are not alone in this
In a summary, the five steps to prepare surfaces with aluminum oxide are:
- Step 1: Prepare the area and the surface to be blasted
- Step 2: Choose the right blasting, media, and recovery system equipment
- Step 3: Test in a small area
- Step 4: Blast the surface in an efficient way
- Step 5: Recover the media and get ready both equipment and media for the next blasting session
These steps do not vary if you have a lot of experience in sandblasting. But what if you want to dig more into how to prepare surfaces with aluminum oxide? What if you are not sure whether aluminum oxide is the right abrasive media for your surface? What if you have different surfaces to blast in a continuous manner? Feel free to contact us with all your questions. Our consultants have decades of experience on this subject.
