TUESDAY, FEBRUARY 18, 2014
Some abrasive-blasting mistakes are more costly than others. Take these:
If any of those practices sound familiar, you may be spending more time and money on abrasive-blast cleaning than you need to, experts told a standing-room-only session Wednesday (Feb. 12) at SSPC 2014.
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| Photos: Jerry and Brad Gooden |
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Make sure you are checking the pressure at the nozzle, using a good gauge, after the blaster has been blasting for at least one minute. |
"Lowering the Total Cost of Surface Preparation" reviewed what presenters Jerry and Brad Gooden of Blast-One International called the top five mistakes made when abrasive blasting.
In fact, the Goodens said, some cost-saving measures can backfire.
Here are their don'ts for blasters.
Don't assume that the actual blasting pressure is whatever the compressor pressure gauge is reading.
A lot of pressure can be lost between the compressor or blast pot and the nozzle, the Goodens say. The nozzle pressure is what matters. Use a relatively new nozzle pressure gauge, don't test the pressure until the blaster has been blasting for at least one minute, and test all of the blasters, they say.
Another job revealed adequate compressor strength for one blaster, but not for the four that were eventually working at the same time. In that case, the Goodens said, a more powerful compressor was in order.
Don't overuse blast nozzles.
Nozzles can also wear out quickly, depending on the materials from which they are made, the Goodens said.
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A nozzle used just once dropped the psi on one job from 125 to 85, Brad Gooden said. A new nozzle restored the psi to 125 and reduced the eight-week job to six weeks.
The first nozzle may not have worn that much in one job, he added, but it may have been a poor nozzle to begin with.
A new venturi nozzle can double the speed of an abrasive used with a worn nozzle, the presenters said.
Don't use small blast hoses.
Large blast hoses are heavy and difficult to move around, but can increase productivity dramatically, the presenter said. The difference between a 1.5-inch and 2-inch blast house can save "days and even weeks" on a large blasting project, even if set-up takes several days, the presenters said.
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One common mistake, they added, is to confuse the OD of the blast hose as the ID. Always verify the size of the hose with the supplier or by checking the markings on the base.
Don't use small air-supply hoses with restrictive couplings.
Big nozzles need big hoses, the Goodens said. A too-small air suppply hose can kill productivity.
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A too-small air delivery hose will choke the air supply and reduce blasting productivity, the presenters said. |
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For any blast nozzle bigger than a 7/16 inch (#7), use an air supply hose that is at least a 2-inch ID. "Any smaller air-delivery hose will simply be choking the air supply," the presenters said.
Large ID air lines from the compressor to the blast pot will reduce friction loss. Also, make sure hose and pipe fittings are at least as large in bore as the hose size.
Don't choose your abrasive based on price alone.
Some abrasives blast faster than others, and some have lower consumption than others, the Goodens note. Using less abrasive (even if the material is more expensive) may substantially reduce blasting time and disposal challenges, they said.
One abrasive doesn't fit all, and "sometimes, the cheapest abrasive is the most expensive abrasive you can use," said Jerry Gooden.
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The U.S. Navy's formula for blasting cost per square foot indicates that the per-pound price of abrasive is just one of many factors. |
When choosing an abrasive, the Goodens advise, consider:
"With resing regulations and more stringent standards, the cost to perform abrasive blasting projects is ont h rise," the Goodens report. "However, these rising costs can be combated with some very simple changes to an abrasive blasting system and the way the project is managed."
Tagged categories: Abrasive blasting; Quality control; Surface preparation; Surface Preparation
