When using recyclable abrasives it is natural to think that the bigger the abrasive is when it is new the longer it will last as it is recycled and breaks down. This is a true assumption but it comes at a cost, and the cost is productivity. Productivity is expensive and is the worst cost to increase. Remember when you are operating a blasting facility, aside from quality, the most important thing is productivity. You need to achieve the maximum productivity possible out of your facility in order to reduce the per square meter cost. All your fixed costs are already paid for, factory rental, labour, overheads, etc. Whether you produce 1 or 50 square meters per hour of blasted parts these costs are the same and already paid for. Of course variable costs for electricity and abrasive consumption will increase with increased productivity, but the increase in these variable costs is a faction of what is returned by means of higher productivity. So the most important thing is to max out the on the productivity front.

Here's why it will cost you productivity to use a larger abrasive vs a smaller abrasive. Provided the size of the abrasive in use is big enough to remove the coating or mil scale from the surface being blasted, and will provide the required surface profile, the abrasive size that should be selected is the smallest size. Smaller abrasive sizes provide much higher productivity rates than larger abrasives. This is due to the amount of particles in a given volume of abrasive. For example 1 kilogram of steel grit G-40 will contain approx. 240,000 grains of abrasive. Increase the size of the steel grit by just to sizes to G-18 and the amount of particles in 1 kilogram drops down to a measly 30,000. This is a factor of 8:1. Having 8 times as many steel grit grains blasting the surface of the part will produce a lot faster production rate. This is not just an "on paper" theory. In actual use the cleaning speed of a finer abrasive is like night and day and is noticeably different. You can blast an item with a large abrasive and literally watch each indentation on the surface being formed. Change to a smaller abrasive and the blast cleaning production rate can visually seen to increase dramatically.

One caveat with this is it must always be remembered that the abrasive size must be big enough for the particles to have enough kinetic energy to remove what ever needs to be removed from the surface being blasted, old paint, rust, corrosion, mil scale etc. If the abrasive size is too small there is not enough kinetic energy in the abrasive particles and the opposite effect occurs and production slows down. So for maximum productivity always use the smallest size abrasive that will do the job.

 

Author: Chris Charlton
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