Series MVP, Javier Baez of the Chicago Cubs, stealing home through the legs of Dodger Catcher, Carlos Ruiz, during Game 1 of the 2016 NLCS. (Image: Brian Cassella/ Chicago Tribune.)
Peak roughness tends to happen at 90°*
- Peak removal rate tends to happen at 75°*
Let’s unpack the key points.
Chart 1.1- Results from tests performed using a Comco AccuFlo® MicroBlaster blasting at 60 PSI with 50-micron aluminum oxide abrasive at a distance of ~2 inches using a 0.060” Hi/Performance nozzle.
Erosion rate depends on nozzle angle in 3 competing ways:
- As nozzle angle to target decreases, blast area increases, increasing erosion.
- As nozzle angle to target increases, impact energy increases, increasing erosion.
- As nozzle angle to target increases from 75° to 90°, ricochet and backscatter block incoming particles, decreasing erosion.
Abrasive particles transfer the most impact energy when the nozzle is positioned at 90° to the target, but abrasive particles ricochet at this direct angle, crowding and slowing the stream. 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.
Abrasive ricochet crowds and slows the stream when the nozzle is held at 90°.
Chart 2.1- Results from tests performed using a Comco AccuFlo® MicroBlaster, blasting at 60 PSI with 50-micron aluminum oxide abrasive at a distance of ~2 inches using a 0.060” Hi/Performance nozzle.
Texturing? Know this about roughness:
- The surface roughness (Ra value) is highly dependent on the angle of the nozzle with respect to the part.
- Roughness is greatest when the nozzle is pointed directly at the part (90º angle to target).
- Roughness decreases proportionally to the Sine of the angle between the nozzle and the part.
Abrasive ricochet does not present the same issues during texturing. The energy lost by the ricochet is less than the energy lost by tilting the nozzle at an angle. Plus, the spray pattern is more uniform at 90°, so start with your nozzle perpendicular to the target as you dial in your process.
THERE ARE EXCEPTIONS!
- Covering multiple surfaces at once?
- If you need to cover multiple surface faces on a part, holding the nozzle at a 45° angle should allow abrasive to cover two or more sides at once, omitting the need for heavy nozzle manipulation. Increase your blast pressure as your angle decreases to maintain surface roughness.
- Need a sharper delineation?
- A slight step below a 90° angle to the target should improve the delineation on one side of the blast pattern. For instance, hold the nozzle at a 65-70°angle on dental implants that require a very sharp delineation on the collar end. No masking is necessary at this angle.
Sample test 1: Nozzle held at 90° angle to texture section at left. The delineation between textured and untextured area is decently sharp, but overspray is evident in the unblasted area.
The sample benefitted from a 60-70° nozzle angle (bottom left and middle). These samples have excellent sharp delineations and no overspray.
Sample Tests 2-7: 90°= sharp delineation, but overspray / 60-70°= sharp delineation & good coverage / 50°= mostly sharp but incomplete near boundary / 30-40°= delineation is not sharp, poor coverage
-Click to Enlarge-
Like Shining a Flashlight on the Ground
Your nozzle angle determines your spot size, depth, and shape. The best way to demonstrate this idea is with a flashlight. Hold a flashlight perpendicular to a level plot of ground and chances are you are going to see a perfect circle of light with almost uniform saturation throughout. As you tilt the flashlight to an angle, the light cast becomes an oval shape that is brighter at the end closest to the flashlight bulb.
The same is basically true in MicroBlasting. Notice below how the end of the spot closest to the round nozzle has a thicker saturation of white, indicating that part of the surface receives more of the abrasive stream.
Nozzle angle determines spot size, shape and depth. Coverage is the most complete closest to the nozzle.
The spot shape on slide #2, where the nozzle was held at a 75° angle, is not as symmetrical as slide #1, but the bore is deeper. This illustrates that spot size grows longer and shallower as the nozzle gets closer to a horizontal position, decreasing its angle to the slide.
Slides L-R: nozzle held 90° to target, 75°, 60°, 45°, 30°, 15° to demonstrate the relationship of nozzle angle to spot profile.
-Click to enlarge-
Automation that is Flexible
“Do Simple Better”
MicroBlasting may not be as exciting as baseball, but the trademark wisdom of Cubs’ Manager, Joe Maddon, is applicable across industries: get a handle on the basic details and establish a plan for experimentation. Fortunately, we are here to help you eliminate the guesswork. Arrange a sample test with our Applications Lab if MicroBlasting looks like a good solution for your production challenges.
Contact our Technical Sales Team via email or call us at 800-796-6626 to schedule sample testing.
How far should I hold the nozzle from the targeted part?
Learn the ideal distances for certain applications, what influences spot size, when to hold the nozzle close, and when to hold the nozzle farther away. Continue reading