Media – Finally, let’s get something done.
Media refers to anything picked up by the airstream and launched out the nozzle at the workpiece. Some common media used in Texas Blasters include:
Most of these are available under various name brands and many can be found at box stores in most towns. But, this is by no means a comprehensive list. In fact, you can use just about anything that meets a couple of rules: it has to fit thru the nozzle and it has to be dry.
To say it has to fit thru the nozzle is a bit of an understatement. The rough guideline we use is media particle diameter needs to be at least 5 times smaller than the nozzle orifice diameter (see image). If the particles are too large, even if they are smaller than the nozzle opening, they can jam if too many try to go thru at once. There really isn’t a limit on how small they can be only how large. Coarse grits are larger than fine grits and require larger nozzles to work without jamming. Contact your media manufacturer and they may have guidelines or suggestions for nozzle size.
The next rule is, and it is important, the media must be dry. If you take home nothing else from this lesson, take this: the media must be dry to work in the blaster. Any moisture in the media will cause it to stick in the tank, hose, and at the nozzle. Moisture gets into the media in two ways: the media is wet when it’s added to the tank or it gets wet from moisture in the compressed air.
The first is easily prevented. DO NOT put wet media in the blaster.
The second is more of a pain. Water in compressed air is an effect of compressing the air around us to a higher pressure. As you know, air contains an amount of water vapor. When the amount of water vapor in air exceeds the amount of water vapor the air can hold it falls out, it rains. The compressor exaggerates this by forcing a higher percentage of water into a smaller space. The process of compression also raises the air temperature and warm air holds more water than cool air. Then when the air moves thru the blaster the water starts to settle out. Water has a habit of settling in the low spots. In a media blaster, this is near the grit valve where media enters the airstream. This causes clogs and stoppages at the grit valve. Water in the airstream will moisten the media as it travels through the blast hose, jamming the nozzle.
How much of an issue depends largely on your location, climate, and media. Water-soluble media (soda) is more sensitive to moisture than non-soluble media (sand).
Moisture Issues: March 2018, 11:52AM, Cloudy, 67°F, 57% Humidity
The best way to deal with water and media blasting is to keep them separated. There are several ways to do this: refrigerated air dryers, desiccant, specialized piping, coolers, and filter/separators. We find the best balance between cost, ease of use, and dryness are filter/separators. Texas Blaster is located on the Texas Gulf Coast where humidity is always high. Sometimes when it’s really humid, we will even use two filters in series.
Those are the rules we tell people and those are the rules we follow. But, if you’ve read this far, you will know that there is always a little more…
Choose media based on the project. Some medias polish (corn cobb, shell), some are mild abrasives (soda), some peen (steel shot), and others cut (coal slag, sand).
Choose grit based on the nozzle size and finish quality. Coarse grits are larger than fine grits. Remember, the nozzle has to be larger than the media.
Some media/situations work better at different pressures than just 90psi. This is why the Compressor Nozzle Match lists various CFM@psi recommendations.
OK. That pretty much sums up the basics. We hope you gained a little insight into the considerations of media blasting. Media blasting is really very simple. All the above information is just to better equip you with the knowledge that may help you if something is not working just right or just weren’t quite sure what you needed. Don’t forget to finish your education with some simple tips on Technique and Compressor Nozzle Match.
As always you can contact us here at Texas Blaster to answer your questions and help in any way we can. Or you can go purchase a blaster and get blasting….