| MadSci Network: Engineering |
Hi Megan Sandblasters are very useful tools in industry and art. Sandblasters are used to remove rust and and unwanted finishes from metals, wood and even plastics. Sandblasters can be used to etch designs into glass and metal as well as reduce glare from glossy surfaces. Sandblasters work much like a perfume atomizer. The perfume atomizer works by forcing air across the open top of a tube that is sticking into a container containing the perfume. The air flowing across the top of the tube creates a low pressure area. The higher atmospheric pressure presses down on the surface of the perfume and pushes it up the tube. The perfume then mixes with the fast moving air and tiny droplets form (this is called atomization) that are carried out out with the fast moving air. The effect of fluid velocity on fluid pressure was discovered by an man named Bernouli and is known as the Bernouli principle. This is the fundamental basis for aerodynamics (and incidentally is exactly how automotive carbuerators and airbrushes work). Here is a simple experiment to demonstrate the principle of atomization. a.) Put about 300 mL water in a 400 mL beaker and add some food coloring. b.) Cut a plastic straw with a knife or scissors but leave a slight hinge connecting the two pieces. Bend the one half at a 90° angle. c.) Lower the vertical portion into the water. Blow through the open end of the horizontal part of the straw. d.) Aim the atomizer at a piece of white paper a few centimeters away. Observe what happens. e.) If you have difficulty getting it to spray, cut the straw through thoroughly and try moving the horizontal part slightly with respect to the vertical straw. The sandblaster works very much like a perfume atomizer except the air pressure is much higher, 80 to 90 PSI, and the perfume is replaced with an abrasive media such as sand, ground up walnut hulls, glass or ceramic beads, even ground corncobs. A high pressure air supply replaces the bulb of the perfume atomizer (or your mouth in the experiment) and causes a very high velocity flow at the nozzle of the sandblaster gun. This high velocity flow causes a very low pressure to develop at the end of the sand supply tube (similar to the tube sticking in the perfume bottle) and the abrasive is drawn up the tube and sprayed onto the object being blasted. In short a sandblaster is sort of a cross between a perfume atomizer and sandpaper. If you are interested in learning more about the Bernouli principle you might check out this web page (this is where the experiment came from): http://www.fortbragg.k12.ca.us/AG/PhysSci/bernouli.html I hope this is helpful. Greg
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