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Blast Pattern 101

What is a Blast Pattern and how does it affect the performance of my machine? Every blast wheel has three basic components.  Let’s begin by describing their roles:

NMA-Centrifugal-Blast-Cleaning---Impeller-Bolt,-Cage,-Blades

Impeller

The impeller is the first part of the wheel assembly to come into contact with the abrasive.  The impeller drives the abrasive through the opening in the control cage and ensures the correct timing of abrasive delivery onto each blade.

Control Cage

The most critical wheel component is the control cage.  Every control cage has an opening that allows the abrasive picked up by the impeller to be admitted to the blades.  The position of this opening controls the location of the blast pattern.

Blades

The blades propel the abrasive.  Even blade wear ensures the abrasive flows smoothly down the surface of the blade and onto the part(s) to be cleaned.

Whether your machine has one blast wheel or multiple blast wheels, a properly set blast pattern is critical to the cleaning process.  Longer than normal cleaning times, inadequate cleaning, and higher than normal maintenance costs can usually be traced to loss of control over the blast pattern.

So, what is the blast pattern?

After being picked up by the leading edge of the blade, the abrasive is rapidly accelerated and leaves the end of the blade in the form of a blast pattern with a relatively narrow width and variable length that must be properly focused on the work surface to be cleaned.

The blast pattern is approximately 40” in length.  A portion of this pattern is called the “Hot Spot” and is typically 8-10” in length.

The Hot Spot receives a greater portion of the abrasive blast.  It is sometimes visible by a discoloration created by the frictional heat generated during the blasting process and will feel warm to the touch immediately after blasting.

Generally, the hot spot should be directed towards the center of the blast chamber to provide the most effective cleaning.  In most blast wheel assemblies, the Hot Spot is approximately 170° opposite the opening in the control cage.

To verify the control cage pattern is set properly, the blast pattern should be checked regularly.  The goal of a blast pattern test is to verify the Hot Spot is directed toward the center of the blast chamber.

To locate the Hot Spot (and verify the blast pattern), place a metal plate in the machine and blast the plate for one minute.

Locating the Hot Spot: Post-Blast Inspection Methods:

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After blasting, the plate will be hot.  Be sure to wear gloves.

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Visually inspect
the plate

If a rusted or painted piece of metal plate is used, this method can be used to visually locate the center of the blast pattern.

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Use a thermal
imaging camera

This method provides a clear image of the blast pattern and Hot Spot.

As the internal wheel parts wear, the blast pattern (and Hot Spot) will shift. As little as a 10% error in the location of the hot spot can reduce cleaning efficiency and increase blast time cycles by as much as 25% or more.

When maintaining your blast wheel and setting its pattern, refer to your Operation & Maintenance Manual for detailed instructions.  Every blast wheel has its own characteristics and special tools may be required.

Tips to keep in mind while setting/checking blast patterns:

1. Verify the abrasive storage hopper is full.

2. Monitor the amperage draw on the blast wheel during blasting. The amperage should be close to the full load-rated amperage on the motor spec plate.

3. Clearly mark the location of the control cage after confirming the hot spot is adjusted properly.

4. Make incremental changes. Even small adjustments can change the blast pattern location dramatically.

Don’t let poor blast patterns slow you down. Regular maintenance and proper adjustment of your blast wheels can significantly improve your cleaning efficiency and reduce operational costs.

Want to learn more about maximizing
your blast wheel’s performance?

Take the first step towards improved efficiency. Our Bronco team is ready to help. Send us a message or call us at 262-330-0006

Visit us at CastExpo 2025 on April 12-15th - Booth #1104

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