Abrasive Blasting – A Complete Guide
You may wonder what abrasive blasting is, what it is used for, the equipment required, safety considerations and more related to abrasive blasting. Fortunately, this complete guide to abrasive blasting will cover all of this and more links within the article go into further depth on each topic mentioned.
What Abrasive Blasting Is
abrasive blasting involves the act of propelling an abrasive material (usually called blast media) at a high speed and under pressure at a surface to create changes in the surface. Common changes that are achieved by abrasive blasting include smoothing a rough surface, roughening a smooth surface, and cleaning a previously contaminated surface (more on abrasive blasting applications will come later). The process was first patented on October 18, 1870 by Benjamin Chew.
Abrasive blasting involves a variety of methods that can provide a variety of results with some being mild and others being aggressive. Common options for abrasive blasting include compressed air propelled blast media or mechanically slung blast media which is done by a centrifugal wheel blaster. In addition to how the media is propelled, there are a variety of common blast medias that are used in abrasive blasting. The more aggressive blast medias include aluminum oxide, steel shot, steel grit, and sand (though sand has a variety of dangers that make it not ideal). Moderately aggressive blast medias include options like walnut shell, corncob, crushed glass, glass bead, garnet, coal slag, and others. The type of blast media will play a significant role in the profile you achieve and how fast you are able to clean a surface. Gentle blast medias that do not leave much or any profile in the surface include options like soda blasting, plastic bead, and dry ice blasting.
Types of Abrasive Blasting
Compressed air blasting
compressed air blasting is the most common form of abrasive blasting used. Whether you’re using a blast cabinet or using a blast pot compressed air blasting takes the force of the compressed air and seats blast media into the air delivering it to a surface to either clean or profile the surface. Compressed air blasting is fast and efficient at cleaning rust and other undesirable contaminants like weld splatter from a products surface. Equipment needed for basic compressed air blasting includes a properly sized air compressor and a sandblast pot outfit. The larger Cubic Feet of Minute (CFM) a compressor is the faster you can sandblast.
Wet blasting is similar to compressed air blasting but in addition to compressed air water is injected or added to the blast media and air. The primary benefit that wet blasting gives over compressed air blasting is that it helps keep dust from sandblasting down, it also rapidly cleans, and softens blast media impact with the surface which can reduce issues with surface impregnation of blast media. However, due to the blast media impacting the surface with less force it can sometimes be a little slower than standard air blasting. The water also can cause a surface of a product to corrode so you typically have to have a way to coat a wet blasted product relatively quick after its blasted or use a rust inhibiting agent in your wet blast water source. More on the Pros and Cons of Wet Blasting. The reduced dust makes it helpful if you are in an area where dust and blasting is problematic and the faster surface cleaning make it a nice way to prep and clean the product surface in a short amount of time.
Bead blasting uses round sphere blast media whether it’s glass or plastic bead to impact a surface. Common applications for bead blasting include removal of coatings or light corrosion. It is used with substrates that there’s concern that an aggressive blast media like sand or steel grit will create unfavorable alterations to the surface of the product your sandblasting.
Wheel blasting or centrifugal blasting as is often referred to as uses a mechanical swinging arm to propel media at high speed, this is in contrast to the other forms of blasting use air pressure from the compressor to propel the blast media. Common blast medias that are used with the wheel blaster include recyclable blast medias like steel blast media. In Specialized applications plastic beads can be used in a wheel blast inside of a cryogenic chamber for very delicate surfaces like cleaning plastics or rubbers. A size of wheel blaster you select will depend on the product size and with increased size will come increased costs. The major benefit to wheel blasting is that it will create a uniform finish extremely well on a smooth flat surface. This can make will blasting of the great option for automating repetitive abrasive blast process that is using primarily flat surfaces. However, if your product has nooks and crannies or is not uniform in shape wheell blasting can have limitations.
Automated Abrasive Blasting
automated abrasive blasting can be applied to a variety of applications from a sandblast cabinet to automating blasting of large equipment through the use of robotics. The important considerations that should be addressed when considering automating abrasive blasting include the uniformity of parts that will be blasted, how many parts are planned to be blasted at a given time, and the blast profile results you are planning. Additionally, for blast automation, you typically will want to work with the blast equipment company that will sample process your product in an automated system to ensure that the automated abrasive blast system that is proposed will work effectively.
Dry Ice Blasting
dry ice blasting uses air and dry ice propelled at a surface. Frozen carbon dioxide particles hitting at high velocity remove contaminants from the substrate but the dry ice is evaporated in the process leaving no residue or abrasive media behind. This makes dry ice blasting a good solution when having any residual media left after the blast process is problematic or you need to ensure that no damage occurs to a product surface during the blast process and it can be food safety approved making it helpful for food related blast applications.
Vacuum blasting is and abrasive blast unit that has a pressure blast along with a suction return system which provides you the ability to blast a surface and simultaneously pick up the blast media that is used while blasting. Vacuum blasting is highly effective for doing blast work in open areas indoors whether concerns of blast media being build up inside the facility or you’re doing touchup work and need to be able to not have to deal with dust being created. There are a few main drawbacks to vacuum blasting. First is that vacuum blasting requires even more compressed air than standard compressed air abrasive blasting. Second, vacuum blasting is a lot slower in comparison to standard compressed air blasting because you have to wait for the vacuum reclaim on the blast unit to pick up blast media that has been expelled prior to being able to move on to another part of the surface you plan on blasting.
Other Surface Preparation Methods
In addition to abrasive blasting, you can also prepare a surface through a variety of other methods. For example, there are pneumatic tools like a needler that allow you to remove rust or you can use a grinder to remove weld splatter and similar light surface contaminants.
Common Abrasive Blasting Equipment
Open Air Portable Abrasive Blasting Blast Pots
For Open Air Abrasive Blasting it is typical to use a standard abrasive blast pot. The size blast pot you use will be important in determining the length of time you can blast before running out of blast media. Additionally, standard blast pots come with a variety of options like abrasive cut off switches to turn off blast media, and different blast media valves to accommodate different blast medias. For more check out this guide on sandblast pot buying.
Abrasive blast cabinets offer a contained blast area and can prevent blast media from leaking out as well as offer efficient and effective cleaning for a variety of small to medium-size parts. Abrasive blast cabinets are offered in both suction or pressure feed options. Pressure feed blast cabinets are faster and can remove more stubborn contaminants from the surface but also are more expensive. Meanwhile, suction blast cabinets are slower in comparison to pressure cabinets but cost less. Blast cabinets also vary significantly in price ranging from those used in the hobbyist shop for a few hundred dollars up to thousands of dollars for an automated blast cabinet. In addition to pressure or siphon fed blast cabinets you can also have a soda or wet blast cabinet. Soda blast cabinets offer the ability to remove contaminants without altering the product surface and are well suited for food grade cleaning needs. Wet blast cabinets offer the primary benefit of not impregnating the surface or altering the surface when blasting but are typically slower when compared to a standard dry siphon or pressure blast cabinet. Wet blast cabinets are well suited for applications where heat associated with traditional dry blast media is problematic or where there’s a concern for altering the substrate of metal during blasting. You can learn more about wet and dry blast cabinets here and you can also learn more about blast cabinet prices and choosing the correct blast cabinet for you here.
Abrasive Blast Rooms
Blast rooms are used for large abrasive blast operations that have higher volumes of blasting that they will do. Common uses for abrasive blast rooms include production facilities, fabrication facilities, and manufacturers. A blast room incorporates a blast pot as well as blast media recovery equipment which allows for Blast Media like steel grit, aluminum oxide, or other blast media to be ran through an abrasive blast media cleaner which removes contaminants from the media and allows you to continue to reuse it for multiple times before it is disposed of. Common blast media recovery options can range from a hopper to a full screw or even a belt recovery system. In addition to blast media recovery, it is critical to consider proper dust collection in your abrasive Blast Room. Dust collection for abrasive blast rooms is based on the type of blast media you use and the size of the blast room. For more on abrasive blast rooms, abrasive blast media recovery, and dust collection for abrasive blast rooms this article provides additional details.
Air compressors for Abrasive Blasting
In addition to the typical equipment that is needed for abrasive blasting, one of the most critical components is having sufficient compressed air for your abrasive blasting needs. The larger the air compressor you have, the faster you will be able to blast. The chart below highlights air requirements needed for abrasive blasting. Common options for abrasive blasting compressors include Toby Heinz their used in the field as well as electric driven shop compressors. Abrasive blasting air compressors are almost always two stage compressors it can range in horse power from 25 200+ horsepower to deliver anywhere from hundred or more CFM of air.
Compressed air chart courtesy of Clemco Industries
Abrasive Blast Media
Besides the time you blast and pressure you use while blasting, the abrasive that you use is one of the key determinants in how fast, how efficient, and the result you achieve sandblasting. There are a variety of blast medias available that will offer a variety of benefits and drawbacks. Abrasive Blast media is typically rated using a Mohs scale. The harder an abrasive blast media is, the faster it will remove contaminants and in general the deeper profile it can potentially create given a certain amount of time blasting. Additionally, blast media comes in a variety of grit sizes with lower numbers representing larger particles of blast media while higher grits are smaller particle sizes. Larger particles leave greater impressions on the surface but are actually often slower in removing contaminants from a blast surface. To learn more about abrasive blast media selection you can refer to this guide here but for now will continue to list common abrasive blast medias.
Coal Slag Media
Coal slag is a common blast media is made out of crushed coal. Is well suited for removal contaminant as well as profiling products for paint application. In general, it is relatively affordable blast media.
Glass Blast Media
Glass blast media comes in both crushed or bead formats and can be used to remove surface contaminant as well as profile a surface. Glass blast media can also be used without creating too much of a profile making it slightly less aggressive than coal slag medias.
Aluminum Oxide Blast Media
Aluminum oxide blast media is one of the most aggressive abrasive blast medias that are available in can quickly remove significant amounts of contaminants from the surface as well as create strong profiles rapidly. However in comparison to other recyclable blast medias like steel grit or steel shot blast medias aluminum oxide cannot be reused as many times.
Steel Blast Medias
Steel blast medias come in both grit shot. Steel grit is often used for profiling as well as removal of contaminants of the surface like corrosion or paint. Steel shot is typically reserved for applications like ball peening where the objective is to actually create reinforced steel by compressing a surface and making it more rigid
Agricultural Blast Medias
Agricultural blast medias include options like corncob or walnut shell blast media. These medias are relatively effective at removing surface contaminant but are also not harmful to the environment when they are not contaminated from the blast surface. They are less aggressive than blast media’s like coal slag or steel or aluminum oxide but can still be effective for light profiling and removing coatings.
Synthetic Abrasive Blast Medias
Synthetic blast medias include options like sodium bicarbonate (Soda blasting) and plastic bead. These types of blast medias are most often used when you want no change to occur to underlying surface while blasting but still need to be able to remove contaminant from the surface.
in certain countries sand to sandblast may still be allowed, but there are a variety of safety concerns for sandblast thing with silica sand. Silica sand has been this shown to cause issues like silicosis which is very deadly disease wear over time you lungs stop working due to inflammation in the lobes of the lungs. Silica sand is very effective at removing contaminant but due to the health concerns associated with using it should be avoided if possible. In certain countries it is illegal to use. If you are going to use silica sand you have to be sure that you are extra conscious of safety requirements. This article covers safety concerns as well as safety requirements associated with silica sand for abrasive blasting in greater detail.
Safety Requirements for Abrasive Blasting
it comes to abrasive blasting primary safety concerns include air purity, staying free from dust contamination, protecting the worker from auditory as well as physical injury, and more. In the United States primary safety organizations that are critical to ensure compliance with include OSHA. OSHA provides a thorough documentation of abrasives blasting safety requirements here. Critical things to ensure that you have though to ensure your safety while blasting include a way to make sure you’re not passing carbon monoxide on through your blast hood respirator which most often requires the use of a carbon monoxide monitor. Additional critical safety equipment includes a blast hood respirator that is properly designed for abrasive blasting respiratory protection. Blast hoods should be certified to meet NIOSH standards. The air you feed your blast operator will have to meet grade D blast air standards which you can learn more about what grade d breathing air is and how to meet the standards here In addition there are requirements related to ventilation depending on if your blasting indoors and what your blasting off. You also have requirements related to protecting the blast operator from harm from blast media. These are the most common abrasive blasting regulations but their are others included those related to hearing protection and more.
While these are general safety requirements, each country may have more or less strict requirements which will be important for you to verify before blasting.
Typical Abrasive Blast Applications
Abrasive blasting is used in a variety of applications including the following:
– rust removal
– surface profiling for better adhesion of coatings or another material
– cleaning molds
– cleaning food trays
– removing mill scale
– removing heat treatment
– restoring cars
– artistic glass work
– Cleaning boat hulls
– Creating 3 D signs
– Cemetery stone markings
These are all just a sampling of applications for sandblasting. Ultimately abrasive blasting has a variety of applications and requires a lot of knowledge around blast media, abrasive blast equipment, and technique. However, it is a great effective way to achieve cleaning a surface as well as creating a profile to improve adhesion and many other applications. This guide is hopefully served to give a great overview of the variety of applications for abrasive blasting.