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From the World of Blasting

##### Are You Sure You Are Using the Right Size Abrasive?

Figure 1. Estimated KE of abrasive given throwing speed

Figure 2. Estimated particle count by abrasive size

“If it ain’t broken, don’t fix it,” right? Maybe you’ve been using a certain sized steel shot ever since you started in your company’s abrasive blasting operation. It has never given you any problems before, so why change, right? Well, there might be a couple of things that are worth looking at to either validate your current choice or prompt you to consider another abrasive size.

Throwing speeds of wheel blast machines have increased. Newer and upgraded wheels are throwing well over 300 feet per second (around 100 meter per second). Older wheels had throwing speeds of 260 f/s (73 m/s) to 280 f/s (92 m/s). As the velocity of abrasive increased, so did the kinetic energy of the abrasive. Thanks to this, a smaller particle of abrasive traveling at 320 f/s (105 m/s) can deliver the same energy as a larger particle travelling at the lower speed of 260 f/s (73 m/s). Given the chart below, S390 traveling at 325 f/s (116 m/s) delivers roughly the same energy as S460 traveling at 275 f/s (90 m/s).

So now you’re saying, “Ok, so I’m getting more impact energy with the abrasive size I am currently using…that’s better, right? I still don’t see a reason to change.” To which I will answer, “Let me toss one more thing out there for you…coverage.” The two keys to abrasive blast cleaning are impact energy and coverage. If you do not have both, you will not get satisfactory results. So now that we can match the impact energy by throwing smaller abrasive at faster speeds, using the smaller size, we will also see an exponential increase in the number of particles thrown (coverage). Maybe you have intricate parts to clean, the smaller and increased number of particles are more likely to reach those nooks and crannies.  This will result in a more complete clean in Figure 2.

If the above has not convinced you, let me toss out one more reason to consider a smaller abrasive: increased productivity. Throwing more abrasive at higher speeds will clean faster, allowing for the possibility of reduced cycle time and increased production. At many facilities, the blast cleaning operation tends to be a bottleneck in the production line. Increasing the productivity of this area will ease some of that pain.

Whether or not this article has convinced you to consider another abrasive size, I hope that it has at least convinced you to occasionally evaluate your operation and implement some process checks that will help you to ensure that you are maximizing the efficiency of your blast machinery. Until next time…

Contact:

chris.prouty@winoa.com

Written by chris prouty, Contributing Editor for MFN and Technical Advisor at Winoa