Matching Nozzle Size and Grit Size

Question: I would like to know if there is a standard for matching Nozzle opening size to media size. I am just starting out and I am not sure what size media I can use with my sand blaster. The literature on the blaster doesn't say. Can you help?

Response: Generally, the nozzle size you use should be at least 3-4 times the diameter of the grit size.

{If the grit is still getting stuck in the nozzle, try reducing the blasting pressure (psi) and making sure there is no moisture in the system.}

Motorcyle Parts

Question: I want to clean /polish an aluminum motorcycle engine. Would walnut shell be the best media for the job? I want a clean, lightly polished look typical of stock bikes.

Response: Walnut Shell Grit will clean the surfaces relatively well but will not have an impact on the surface finish. A Medium-Fine or Fine Glass Bead will clean the metal and leave a satin-like finish on the surface.

Aluminum Oxide

Aluminum Oxide (a.ka. aluminium oxide, alumina, aloxite, corundum) is generally sourced from bauxite ore. While bauxite is the primary ore for aluminum metal, Aluminum Oxide is extracted using the Bayer Process to remove unwanted impurities.

Aluminum Oxide is a very hard, versatile blasting media that can be used in a variety of applications for removing oxidation and scale off metals to etching stone and glass surfaces. The pure (>99%) White Aluminum Oxide is used when surface non-contamination is critical like when blast cleaning medical parts.

The hardness and large grit sizes available also make Aluminum Oxide an excellent choice for non-skid flooring. Aluminum Oxide is commonly used as an abrasive for sandpaper.

I'll bet you didn't know that precious stones like rubies and sapphires are simply Aluminum Oxide (corundum) crystals contaminated with other metals like chromium, titanium and iron.

Four Times is Twice as Big

Just one more quick comment on CFM, nozzle size and blasting...

I discussed a little about the differences and relationship between CFM and PSI in a previous post. PSI is basically the amount of force you blast with. CFM is the volume of air being used during blasting.

It is sometimes suprising to realize how much air (CFM) is required during blasting. At a given PSI setting, the amount of air needed is directly related to the nozzle size being used. The larger the nozzle, the more air that is required. This also means that if you want to use a large nozzle, you will need a large compressor.

For example, at 80 psi, a 1/8" nozzle will require 20 CFM. At the same pressure a 1/4" nozzle will require 85 CFM and a 1/2" nozzle will demand 340 CFM. A basic chart that shows the air requirements for different nozzles at different pressures is on the PPB Series page.

Rule of thumb: double the nozzle size, quadruple the CFM required.

Corn Cob Grit hard as Iron!

All solid materials can be measured for hardness on the Mohs scale. The scale was created in 1812 by Freidrich Mohs and is based how easily one substance can scratch another. Diamond is the hardest rated at a 10 while talc is a very soft 1.

Suprisingly, Corn Cob Grit and iron have the same hardness at about 4.5. Even more amazing is that Corn Cob Grit is harder than brass (3-4), copper (2.5-3) and aluminum (2-3).

The really cool thing is that blasting with Corn Cob Grit won't frost or pit glass and can be used to absorb grease, oils and water from metal surfaces. Corn Cob Grit is also great for blasting on wood surfaces (more to come on that). I wouldn't recommend using iron grit near glass or on wood!