Pollution Prevention Opportunity

Costs and solid waste generation can be reduced by selecting the most efficient blast media for blast cleaning prior to painting.

Background

Blasting is done to remove weld splatter and scale from steel to improve appearance and paint adhesion prior to painting. Bottom ash or slag is often used as a blasting media due to its low cost and low dust generation. However, bottom ash can usually be used only once or twice prior to disposal (due to fracturing of the ash particles), thus increasing costs.

Alternative Blast Media

There are many alternative blast media available that could directly replace bottom ash. Sand, steel grit, plastic and glass are several types commonly available for use in pressure type sand blasters.

Cost Savings

Cost savings can be achieved by using an alternative to bottom ash. For example, assume a blasting operation uses approximately one pound per minute of bottom ash and that eight square feet of surface area can be cleaned in one minute. Given an annual blasting surface area of 500,000 square feet, 32,000 pounds of bottom ash is consumed annually. At an estimated cost of $0.04 per pound for bottom ash, the annual media cost equals $1,280. Disposal cost is assumed to be $50 per ton or about $800 annually.

The table on the back lists several common blasting media and their associated costs in comparison to bottom ash. Steel grit, plastic, and glass bead media can all reduce waste due to their ability to be reused. Plastic and steel media can reduce both waste and cost.

Media	# Times Used	Cost/lb.	Annual Use/Cost	Annual Disposal Cost	Waste Reduction	Cost Reduction
Bottom Ash	2	$0.04	32,000 lbs. $1,280	$800	None	None
Glass Bead	15	$0.40	8,300 lbs. $3,320	$210	23,800 lbs.	None (+$1,440)
Plastic	15	$0.50	1,120 lbs. $560	$200	30,980 lbs.	$1,324
Steel	50	$0.30	1,240 lbs. $372	$200	30,860 lbs.	$1,512
Sand	5	$0.02	124,000 lbs. $2,400	$3,100	None (+91,900 lbs.)	None (+$4,416)

The amount of media required annually was calculated by comparing the density of the medium compared to bottom ash, and factoring in the reuse potential.

There will be differences in the abrasiveness of each medium. Steel will be much more abrasive than bottom ash or plastic. The amount actually used to blast the steel fabrications may be less than indicated for the steel and glass media. The amount of plastic used may actually be greater. The blasting pressure would have to be adjusted to compensate for the abrasiveness of the medium used.

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