High velocity compressed air blow-offs are especially useful if parts don’t need to be “super dry” (as completely free of water) or if there is a requirement to remove “excess” water or other liquid from a part prior to final drying using another means such as hot air or radiant drying. They are also used when there is a benefit of leaving some residual liquid on a part as in the case of a rust inhibitor. There are parts that, under certain circumstances, can be completely dried using only compressed air as well. Compressed air for blow offs is best delivered by using specialized nozzles designed for use with air or by devices called air knives. These products “amplify” the flow of air to reduce energy costs. Regardless, in many facilities, compressed air is expensive and is often in limited supply. This is especially important as effective compressed air blow-offs consume a relatively large volume of air. This has caused many facilities to consider the use of blowers instead but in many applications, the blow-off performance is simply not adequate and blowers themselves have added maintenance costs and noise levels which can be detrimental to the working environment that offsets energy saving.
An effective air blow-off requires that the surface to be dried is relatively close to the blow-off nozzles. The velocity of air diminishes rapidly as the distance from the nozzle is increased. A distance of about 3″ from the nozzle to the part is a good target for drying parts completely using compressed air although some items such as air knives have been used up to12″ with adequate results although much closer is recommended. Access to blind holes and enclosed spaces is difficult but special blind hole cleaning devices can work in this case. After blow-off, if there is still a need for additional drying then other techniques need to be performed.
For all its limitations, compressed air blow-offs remain a valuable tool in reducing the load on other subsequent drying techniques. It makes sense that the any reduction in the amount of water or other liquid that needs to be evaporated or removed from a part by another method results in a faster, more reliable, and frequently less costly and more efficient process overall.