Abrasive Blasting 101
Direct Pressure abrasive delivery is a process that uses a pressure pot to pneumatically push abrasive to the blasting nozzle inside a blast cabinet.
Before we get any further, we need to clear up a common misconception about how pressurized delivery works. While you use the pressure pot to push the abrasive, gravity is used to deliver the abrasive. A simple mixing system is used to allow gravity to flow the abrasive into the abrasive hose that then pneumatically pushes the abrasive to the opening at the end of the hose, which is called the blasting nozzle. This is the same concept behind ballistics – expanding gas behind a bullet pushes the bullet out the end of the barrel. Similarly, direct pressure abrasive delivery systems have more than one atmosphere of pressure behind the abrasive, expanding and pushing it out the blasting nozzle.
ProTip: If you turn a pressure delivery system upside-down the abrasive delivery stops! Some confuse liquid hydraulic delivery with direct pressure compressed air delivery systems, the latter of which use a pressure pot assembly to push the abrasive.
Direct pressure is very effective at push heavy abrasive, and not-so-heavy abrasive, too. With External Abrasive Storage used in the Power Strip Direct Pressure Model, steel abrasive is seldom used because the pneumatic conveyor velocity used to remove and store the abrasive outside the cabinet does not have the speed needed to lift the steel abrasives vertically. For those applications requiring steel abrasive, we offer the Power Peen Direct Pressure Model with Internal Abrasive Storage.
Direct pressure is also used for blasting into blind holes or cross drill holes. This can be helpful when de-burring a cross-drill hole in a huge locomotive crankshaft, or a diesel truck crankshaft to extend total miles and remove build-up deposits inside the crankshaft oiling system. The reason direct pressure can be used is simple, you can place the nozzle against the part and the part becomes the nozzle and if the hole is smaller than the nozzle the part then determines the abrasive and airflow.
Direct pressure is also used to eliminate heavy, difficult-to-remove coatings. This works because the direct pressure spray patter is very tight raising the frictional heat and also works well with large abrasives. The same abrasive delivered with siphon delivery machine creates a much wider cooler blast pattern when using the same velocity and compressed air amounts. If you don’t understand this statement, which many people won’t, just know this: the blasting pressure used with direct pressure is half the pressure used for siphon with the same abrasive speed! Key to the machine design is raising the frictional heat generated by the concentrated pattern.
Real World Example
Consider two shotguns and one shell with the same powder and shot load. An 18-inch barrel will fan out and slow down faster than a 32-inch barrel that holds a tight pattern and travels a long distance. Both are using the same shotgun shell but each deliver a different result. If you’re not sure which delivery type is best for your application just ask us – we offer both types and will make sure you have the information to choose the right machine the first time.