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September 13 - September 19, 2015

What are the pros and cons of specifying sieve sizes for abrasives?

Selected Answers

From Robert Ikenberry of California Engineering on November 6, 2015:
Abrasive size selection is generally left up to the contractor as part of their "means and methods" of achieving the specified cleanliness and profile. Unless an unusual abrasive is required, for example, aluminum oxide, where contractors may be unfamiliar with the abrasive, specifying a particular size may just end up causing conflicts with other criteria, increasing costs, confusion and contentiousness.

From Duane Hough of Champion Painting Specialty Services, Corp. on November 6, 2015:
Specify the desired surface profile. Specifying sieve size is unnecessary and falls into the means and methods territory. The various abrasives have different sieve sizes to achieve profile depending upon the hardness of the abrasive, and even the same type can vary (alluvial versus mined garnet, for example.) Specify the proper surface profile for the coating system and let the contractor be responsible for meeting the specification.

From Peter Bock of Energy Designs Houston on November 6, 2015:
The commonly held belief that coarse or medium-to-coarse abrasive does a better job of blasting off mill scale from steel to produce an SSPC-SP  6 or SP10 surface is not necessarily true. On a recent coating RFP, we were asked for a recommendation which would remove mill scale from sheet steel and provide a one-mil anchor profile. I asked a very large, global distributor of garnet blasting abrasive and a manufacturer and lessor of vapor blasting equipment for their recommendations. The garnet guy recommended 200 mesh garnet. He said that this very fine abrasive actually did a better job of removing mill scale, because the fine abrasive particles broke the mill scale into smaller patches, allowing removal with less grit, less labor and less time required. The downside (normally) was that the 200 mesh garnet only produced a 1 mil anchor profile. The vapor blast equipment lessor said almost the same thing. He recommended 200 mesh or 120 mesh garnet in a vapor blast setup. The fine abrasive worked better at removing mill scale, required less time and effort and had an added benefit that there was less wear and tear on the vapor blast machinery, hoses and nozzles. Again, only a 1 to 1.5 mil anchor profile would be the result. So if you need SP 6 or SP 10 but don’t need a 3-mil anchor profile, go with a 200 mesh abrasive and save yourself and your customer time and money.

From robert kogler of rampart llc on September 30, 2015:
The only obvious reason to specify sieve sizes would be to achieve a specific profile or surface roughness as abrasive size heavily influences resultant roughness; however, this issue can be overcome by specifying SSPC AB-1, which includes the classification of the abrasive by "Grade," which requires abrasive manufacturers to test blast with the given abrasive and report the profile that results. This aspect of AB-1 is very useful and makes the SSPC spec more useful than MIL-A-22262.

From Michael Halliwell of Thurber Engineering Ltd. on September 29, 2015:
Warren hit the nail on the head...the pros are all about production and proper profile and might help a less experienced contractor. (It's all about getting the job done cheap, right?) Great if your spec writer has experience and knows what needs to be used. But if your spec writer is out to lunch, you're opening up the possibility of reducing productivity and making all manner of headaches for the project.

From Warren Brand of Chicago Corrosion Group on September 25, 2015:
From a consulting perspective, I can think of no reason to specify sieve size. However, from a contractor's perspective, it may be a good idea. If the sieve size is incorrect, it could seriously reduce production rates and/or may be too large or small to provide the appropriate profile in the specification.

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Tagged categories: Abrasives; Asia Pacific; EMEA (Europe, Middle East and Africa); Latin America; North America; Surface Preparation

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