The Best Angle for Blasting
Proper surface preparation is essential for better adhesion of coatings on substrates. With blasting, some elements contribute to effectively achieving the optimum blasting performance. One of these factors is the blasting angle, which will be discussed in this document.
The blasting angle is an underestimated factor that can significantly affect productivity depending on the surface’s original state and the substrate’s characteristics. When the nozzle is pointed directly at the target (90-degree angle), it causes the abrasive to rebound, leading to reduced performance and creating the most significant roughness. Roughness decreases proportionally to the sine of the angle between the nozzle and the part (see graphic 1).
Graphic 1. Roughness Vs Nozzle angle: Results from tests performed blasting at 60 PSI with 50-micron aluminum oxide abrasive at 2″ using a 0.060″ nozzle. Source: (Comco sales and support, 2016)
Abrasive particles transfer the most impact energy when the nozzle is positioned at 90° to the target. However, abrasive particles ricochet at this direct angle which crowds and slows the stream. Therefore, when cleaning or eroding surface material, hold the nozzle at or near a 75° angle to the target. Abrasive particles will strike the target with a strong impact but have enough clearance to make room for incoming abrasive.
Created by: Mario Carvajal / NACE level 2, Cert 51611 Reviewed by: Scott Menzies / NACE level 3, Cert 34395
Figure 1. Abrasive ricochet crowds and slows the stream when the nozzle is held at 90°.
Source: (Comco sales and support, 2016)
The peak removal rate tends to happen at 75°. Therefore, as the nozzle angle to target increases, the impact energy increases, increasing erosion. Moreover, as the nozzle angle to target increases from 75° to 90°, ricochet and backscatter block incoming particles, decreasing erosion.
Graphic 2. Erosion Rate Vs Nozzle angle: Results from tests performed blasting at 60 PSI with 50-micron aluminum oxide abrasive at 2″ using a 0.060″ nozzle. Source: (Comco sales and support, 2016)
Alternatively, angles between 80° and 90° may be the most effective in extreme cases such as heavily rusted or pitted surfaces. When removing old paint, 45° to 60° is typically used, and general cleaning is recommended at 60° to 70°. (Halewood, J. 2020).
Please note that the measurements shown in the charts above should be used as starting points when dialing your process, not as concrete rules.
Created by: Mario Carvajal / NACE level 2, Cert 51611 Reviewed by: Scott Menzies / NACE level 3, Cert 34395
References
Harmon, P. (2016). How to improve your sandblasting speed.
Created by: Mario Carvajal / NACE level 2, Cert 51611 Reviewed by: Scott Menzies / NACE level 3, Cert 34395
