There is a common phrase that size does not matter. In the case of sizing abrasives for a particular application size certainly does matter and plays an important role in the cost and economics of a blast cleaning operation.

In abrasive blasting the rule of thumb is to use the smallest possible abrasive to achieve the job of cleaning the part and leaving the required profile or surface finish. When buying abrasive it is human nature to assume that bigger is better and if a bigger abrasive is bought it is going to break down into a smaller size anyway so it must make sense to buy as big as possible.

But what this does not consider is the blasting speed of the abrasive. For any given volume or mass smaller abrasives contain a lot more particles than bigger abrasives. For example 1kg of G18 steel grit contains approx. 30,000 particles. By comparison 1kg of G40 steel grit contains approx. 240,000 particles. Abrasive blasting equipment works as a result of the weight of abrasive thrown, ie in any given set up the weight of abrasive thrown, within a given time period, will be the same regardless of the abrasive size.

So for the above example if we assume blasting for one hour the same weight of abrasive will be thrown. The differnce will be in the amount of particles thrown. There will be 8 times more G40 particles than G18 particles. 8 times more particles mean 8 times more abrasive soldiers doing their work in cleaning and etching the surface. This can have a profound effect on the cleaning speed. The cleaning speed will not be 8 times, but there will be a noticeable difference. So if G40 steel grit meets the required surface profile requirements, and is capable of removing whatever contaminants are being blasted from the surface, this is the abrasive size that should be used. The small saving in abrasive consumption of buying a bigger abrasive will be more than offset by the faster cleaning speed.

Abrasive life is only one of the parameters in establishing abrasive blasting costs. More important is the production rate and this should be maximized as much as possible. At the end of the day it is the work going out the door that pays the bills, and the faster it goes out the door the more the money comes in.

So next time someone tells you size does not matter, you can confidentially advise them they are correct, smaller is better as long as it can achieve the result.

 

Author: Chris Charlton
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