What is Sandblasting?
Sandblasting uses air to force an abrasive toward the surface of a work item. This removes surface debris, smooths, engraves, and so much more. Sandblasting is a process known by many names like abrasive media blasting or bead blasting. Before we dig in, let’s set the scene and talk about sandpaper. Bear with us on this. We know sandpaper is abrasive and is used to rub against a surface. Doing so removes something such as paint, or it makes the surface smoother. Although sandblasting is a little more involved, it’s the same theory. Let’s take a closer look at the components of blasting.
Bead? Media? Shot? Abrasive? Blasters?
As we will see, a sandblaster is a common name for the machine itself. These abrasive cabinets are also know as bead, media, sand shot blasters. These names really refer to the media that is used inside the cabinet and not the machine itself. We may refer to it in various ways as well, and will explain along the way. Let’s move on to some major areas of abrasive blasting cabinets.
The primary components of blasting are as follows, and we will look closer at each one:
Abrasive Blasting Cabinet
What is Sandblasting – Cabinets
There are blasting rooms and blasting systems that don’t require a cabinet, but for our discussion we will focus on blasting done inside a cabinet. An abrasive blasting cabinet is simply a leak proof container. The cabinet is designed to contain the work pieces, blasting system, and of course the abrasive media. Blast cabinet design is very important. Some cabinets are plastic and some are steel. Many have bolt on or pop-riveted legs. Others have plastic doors, some have steel doors. Do not sacrifice on cabinet design. This is where your work is going to take place. It’s the “chassis” of the blasting system. But, why does all this matter?
Quality Construction Matters
A cabinet literally has the weight of the world on its shoulders. Well, really on its legs. It carries the weight of the parts you put inside, the abrasive you add to do the work, and often the weight of the person leaning against it during use. As a result, this weight adds up and can make lesser built cabinets less sturdy. Abrasive cabinets that are built with pop rivets, or bolt on legs can teeter or wobble with all that weight. Wobbling can be dangerous and frustrating as the user tries to accomplish precision in their work.
Don’t Forget About the Side Doors
A steel door is also an important consideration. An all steel cabinet (including the door) ensures a sturdy quality seal. Any hole or space between the cabinet and the air outside will push dust and debris outside the cabinet. This can be messy as well as dangerous. Plastic doors, over time, can “flex” and lead to potential leaks. Solid latches and tight seals on doors are critical to successful and safe blasting.
What is Sandblasting – Blasting System
OK, in our quest to answer the question “what is sandblasting” we now know we need a sturdy “box” to contain things. Now, we need a way to blast! Here is where things a little scientific. We promise, it’s easy to grasp and will be fun – in fact it will be a “blast”. There are two basic means of blasting: pressure and siphon. There are variations in the term siphon, sometimes you’ll hear it called gravity fed. For our discussion we will use the term siphon.
Most internet definitions specify a siphon as a device. In most circumstances it’s a tube that can move air or liquids from one container to another using a combination of gravity and atmospheric pressure. The reality in abrasive sandblasting is that a siphon fed sandblaster “technically” isn’t siphoning anything. The name stuck and is familiar. Instead, there are a few physics principles at work. After all, when we talk about “what is sandblasting” we are really talking all about chemistry (abrasive media) and physics (the action of the sand blast gun).
These crude shapes represent a non pressure sandblast gun. As air moves into the system (from an air compressor) it moves across an area that connects to the pickup tube. The pickup tube is a special device that sits within the abrasive media and connects to the abrasive sandblasting gun. It is specially constructed to allow media to flow up and air flow in and around it. Enough detail will be provided to give a basic understanding of the process.
In “Step 1”, there is no airflow. Your trigger or foot pedal is not active. Therefore, there is no blasting – or your air compressor isn’t on. Just kidding. Notice those red stars. They are your abrasive media and in Step 1 notice that without air flow they are not going anywhere. At this point we’re ready to blast, but before you do, always review your safety checklist before blasting! This is different for everyone, but at minimum read and ensure you follow all safety directions! Now that we are safe and secure let’s move on to “Step 2”.
Step 1: No Airflow
No airflow, no motion.
Step 2: Airflow
Initial introduction of airflow…
For Step 2, notice that we just pulled our sandblast gun trigger or depressed our foot pedal. The air from the air compressor is starting to move through our system. In Step 2 we are looking at a “snapshot” of air moving into the system. Things happen fast when you put air into a sandblast system, so we are simply looking at a point in time where the air begins to move. Let’s move on to “Step 3”.
Step 3: Airflow Causes Change in Pressure
Here is where the action happens! What is often referred to as a siphon, is actually some really cool physics, just like what happens to an airplane wing to give it lift. Notice the curved arrows at the bottom of the pickup tube, they play an important role. As the air flows through the blast gun and over the top of the pickup tube, a change in pressure takes place. We actually LOWER the pressure at the top of the pickup tube. Because air pressure around us is constant, a change in one area is always filled by pressure from another area. What? Let’s look at the picture for “Step 3” and say that again.
As the air passes OVER the pickup tube, we reduce the pressure around the pickup tube. Then, the pressure around the pickup tube forces air UP the tube. And what comes with that air? You guessed it, the abrasive media begins to flow up with the air. A siphon operates in a similar fashion (for liquids and certain gasses), where surrounding air pressure and gravity cause movement from one vessel to another.
Step 4: Pressure Change Causes Abrasive Flow
Step 4 is the result of the process. Abrasive media is drawn up the pickup tube and out the end of the sandblast gun. Overall a very simple process, but one that is effective for a huge number of tasks.
That’s really a close, but not too close, look at a “siphon” abrasive blast system. Let’s take a quick look at what a pressure, also called direct pressure, system looks like. Then we will move on to abrasive media.
A pressure blasting system provides a much more intense blast stream over a siphon system. And we expect that with a name like pressure blasting. The key difference is that with pressure blasting systems we normally see a pressure vessel. The vessel is fed air from a compressor until a predetermined level. The user opens a valve and releases the air within the vessel. Finally, when the valve is opened, the air inside the vessel and the media in the vessel both leave at a high velocity. A high velocity abrasive particle carries a higher kinetic energy. Simply put, a high velocity, high energy particle impacts a surface and can do more work (or faster in some cases).
Pressure blasting begins with a certified pressure vessel. We feel it is important to specify a certified vessel. When it comes to containing pressure safety is very important. Cyclone uses ASME certified vessels in all our pressure systems. A good pressure vessel is built to accept a specific amount of air pressure, related to the ASME certified rating. All Cyclone pressure blasters also have a safety release valve if the pressure in the tank gets too high. Now that safety is first, we can talk about the firs step in pressure blasting.
In step 1, the usual process is to put abrasive media into the pressure vessel. This varies by model, but in most cases the media is put into an opening into the top. This opening usually has a special method of sealing. Once the media is in the unit, and a safety check is performed, an air supply is connected to the vessel. Finally, air is added to the vessel.
In step 2 the pressure is shown by the red arrows inside the vessel. This pressure has nowhere to go because the blast valve is closed. As shown in the picture, the red arrows indicate that the air in the vessel is trying to get out but has nowhere to go.
In Step 3, the user has opened the blast valve. While closed, the air has nowhere to go. Once opened, the air will take the only path it has to escape. Along with the air, the abrasive media is pushed outward. The abrasive media escapes at a very high velocity. This high velocity also means the abrasive media has a lot of kinetic energy. More kinetic energy means a bigger impact on the work. This does not always mean the work goes faster, just that it has more energy.
What is Sandblasting – Abrasive Media
Abrasive media and what is sandblasting? Isn’t it just sand in a “sand blaster”? No. Absolutely NOT. Sand was used many decades ago, hence the most familiar name “sandblasting”. But do not use sand when sandblasting. It is a cheap means of blasting, but there are serious health risks associated with blasting with sand. For an in depth lesson on silicosis, read more here. Silicosis is a serious health hazard found associated with blasting with sand that contains silica. Although there may be sand labeled “silica free” we do not recommend it. Never have and never will.
With many affordable and safer abrasive media, we wanted to get safety out in front and be clear about some of the risks. We take care to emphasize the word safer. No media in a blasting environment is 100% safe. Always read all warnings, safety data sheets for your media in use and respect the equipment and media. You ultimately are responsible for your own safety – so know what you are doing.
There is a vast assortment of abrasive media such as: glass beads, garnet, aluminum oxide, and many more. We won’t go into what media is best in what situation. You can read about that here if you need to know application specific media usage. For now, we are simply introducing the concept of abrasive media. Earlier on we used the terms media, bead, and shot blasting. Remember that these are just names applied to the machine or process itself. Glass (sometimes plastic) beads are used in blasting, hence the term “bead blasting.” Shot blasting, is almost always referring to steel shot which is a very durable media. And finally, media blasting. This is a mostly generic term for the process itself.
Remember the comparison to sandpaper? Rubbing sandpaper against a surface wears away small layers of the surface. With abrasive blasting, the media of choice is forced by air toward the surface being blasted. As the media impacts the surface, it removes loose material. It could be rust on a metal panel or even wood. The media is what actually gets the work done. How quickly the work is done depends on the media and air velocity and other factors too.
What is Sandblasting?
In this post, we tried to give some details associated with the question, “What is sandblasting”. In this effort we took a high level approach. We did not go into extreme detail, and there is definitely detail with abrasive blasting. We hope you found this article interesting, and if you have comments, questions or ideas for us we would love to hear from you.