Abrasive Blasting 101
When you boil media blaster cabinet costs down to the basics, it’s all about cleaning speed, frictional heat created, the dust collector size and maintenance costs. If you’re comparing two machine models, and one is much less expensive than the other, here are three things you should consider. Doing your due diligence before you buy could save you time and money in the long run.
To understand why there is so much confusion in air compressors, let’s look at their history. Years ago, three basic cabinet gun sizes were designed to match the three piston air compressor sizes available in the market place. A 5 horsepower (hp) air compressor running on single phases power, the power you can run in your home garage, would produce 20-25 cfm at 175 psi. If you wanted more air, you could opt for either the 10 hp or 20-25 hp compressor. Back then, very few 7-1/2 hp air compressors were sold for operation of a blasting cabinet because they were simply too larger to operate on single phase power, meaning they drew too high an amperage, and were nearly the same price as the 10 hp compressors. The result was about 4.5 cfm of compressed air per horsepower for piston air compressors.
After the piston air compressor came the “fake-me air compressor.” This was essentially a smaller compressor pump, driven faster to produce more air volume, which then reduced the cycle to less than 100% to allow the overheated smaller air compressor to cool. Two things happened, you did get more air but it also used more motor horsepower. Manufacturers created a new scale for motor horsepower and started advertising just the motor size, 6-1/2 hp, 8 hp 5-3/8 hp etc., and not the air volume.
Now everyone was using the motor horsepower and not the cfm volume. People stopped looking at the volume of air produced and started looking only at the motor horsepower. Air Compressor Manufacturers were adding a huge air storage tank to the compressor to look massive, but in small print you would see small cfm volumes.
ProTip: every air compressor tag shows two air volumes measured in cubic feet of air per minute (cfm). The displacement is the mathematical amount the compressor will create in theory when you multiply the compressor rpm speed times the piston volume size. This gives you displacement of the air compressor running in a vacuum or Outer Space, which is not helpful for real world applications. The second cfm number is the air volume produced with air pressure in the tank – this is the number that you care about! Almost all companies list this number at 90 to 100 psi, which is typically the pressure you need to run a blasting cabinet.
Frictional heat and more abrasive being delivered are the key to how long it takes to accomplish any blasting project. A 20 cfm gun delivers 5 pounds per minute and a 40 cfm gun delivers 7-1/2 pounds and an 80 cfm gun size delivers 10 pounds per minute. A 20 cfm siphon gun develops about 175 F-degrees, 350 F-degrees for the 40 cfm and 500 F-degrees for the 80 cfm gun size.
Real World Example
If you are using a 20 cfm air compressor and cleaning a metal box 4″ x 4″ x 4″ and it take 3 minutes to clean using the 1/4″ 20 cfm gun size what happens with the 40 cfm gun size? It will clean 3 boxes in three minutes and the 80 cfm gun will clean 9 boxes in the same three minutes.
How does the 80 cfm gun clean nine times the parts as the 20 cfm gun size? The frictional heat is much higher at the same blasting pressure. When you push down harder on sandpaper it sands faster because you create more frictional heat. Using more air volume does the same thing with blasting equipment.
Based on the compressed air used, speed and frictional heat, machines need properly sized dust collectors. It comes down to creating the right system to increase productivity and reduce maintenance.
If you want to process 9 parts in the same time as someone doing only one part, you need the machine, controls and dust collector to handle the load. Blasting, or trying to blast, a large part in a small cabinet works in reverse. Because the machine is small it cleans slower, lots slower, so you blast lots longer and (likely) will overload the small, less expensive dust collector. This results in a big mess and machine malfunction unless you clean the dust collector at regular, short intervals.
Yes, some media blasting cabinets are much more expensive than others. For some applications, operators can get away with smaller, less costly models; however, there is nothing worse than trying to make a too-small cabinet perform outside its capacity. Just because a part CAN fit inside a smaller cabinet doesn’t mean it’s the right cabinet for that project.
When you see a blasting cabinet being sold that touts a very large cabinet size you can place a car fender into, almost no compressed air usage because your air compressor is too small, and little information about the dust collector and blower size, take a second look… and think about painting your house with a 1-inch paint brush!
Give us a call if you need help purchasing a blasting cabinet that matches the cabinet size, dust collector and gun cfm size that your application requires. We’ll help you buy the right machine the first time.