Shot blasting machines are widely used for surface preparation and finishing structural steel components for a variety of industries. In addition to specifically designing machines able to accommodate large, heavy, and bulky structural steel workpieces,  Rosler Metal Finishing also expertly designs the turbines within these machines for precise results.

Blast turbines accelerate and throw the blast media against the workpieces. They are for shot blast machines what the engines are for cars and trucks. Both determine the performance of the respective machine or vehicle including the speed of a sports car and the torque of a heavy-duty truck.

Like vehicle engines, the specifications of different turbines directly influence the performance of a shot blasting operation. This installment of our Structural Steel FAQ series will answer How do different blast turbines affect the quality of shot blasting results?

Blast Patterns

Blast patterns are the size and shape of the area where blast media strikes a workpiece as it progresses through the machine. The area of impact is also referred to as a “hot spot.” Long blast patterns are required to accommodate the large size of structural workpieces.

Concentrated blast patterns are often used in shot peening, but would not offer enough finishing coverage for structural steel applications. Similarly, the normal blast patterns used for casting and forgings are also not effective for structural steel.

Throwing Speeds

Because of the large workpiece envelope, the travel distance of the blast media between the turbine and workpieces can be very long. To generate the impact energy required for blast cleaning of such large components, the acceleration or throwing speed of the media by the turbine must be considerably higher than in smaller shot blast machines.

Turbines with curved throwing blades generate a substantially higher media acceleration than straight-bladed blast wheels and are the preferred blast turbines for large structural steel components.

Rosler’s Gamma^® G is an innovative turbine with curved throwing blades. Compared to straight-bladed, conventional blast wheels, a Gamma^® turbine of the same size and running at the same speed, generate up to 25 percent higher throwing speeds of the blast media. This improves the overall blast performance by 15-20 percent.

Other benefits offered by the Gamma^® G turbine include:

• Use of both blade sides, reducing maintenance costs and increasing equipment uptimes.
• Significantly lower energy consumption compared to conventional blast wheels.
• Quick blast pattern adjustment by changing the impeller position.

Turbine Placement

The correct placement of the turbines around the blast chamber is another critical consideration affecting the performance of blast machines for structural steel components.

Their placement must ensure that complete blast media coverage is achieved on the workpieces without any “dead” spots where the media does not reach. Please note: In the case of large, complex weldments, the prevention of dead spots may not be possible. In such cases, manual touch-up is required. We will address this topic in Part 10 of this series.

The turbines opposite from each other must be somewhat offset so that they are not blasting into each other. This would not only produce poor blast cleaning results but would also cause extensive, premature wear.

The turbine placement can be determined by computer simulation and allows for the evaluation of all faces of exposure.

The Rosler Way

Whatever your structural steel media needs are, you can count on Rosler Metal Finishing to help you find a better way and the best machine. Contact ustoday to discuss your unique challenges.

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The complete Structural Steel Series includes:

• Part 1 – Why Surface Preparation is Necessary.
• Part 2 – Methods of Surface Preparation.
• Part 3 – Evaluating Rust and Mill Scale Pre- and Post-Blast.
• Part 4 – Evaluating the Presence of Dust.
• Part 5 – Assessing Surface Profile.
• Part 6 – Blast Media’s Influence on Surface Profile.
• Part 7 – Comparing Commonly Used Blast Machines.
• Part 8 – Are All Turbines Created Equal?
• Part 9 – Removing Residual Blast Media and Dust.
• Part 10 – Blast Rooms for Touch-Ups.
• Part 11 – Preservation Lines.
• Part 12 – Material Handling Options.

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