shot blasting, structural steel components often require some cleaning. The
degree of cleaning depends on the work piece’s condition prior to processing as
well as machine set-up.
This installment of our Structural Steel FAQ series will answer How are residual blast media and dust removed from shot blasted steel components?
Why Remove Residue
Ancillary machine attachments and processes may be
required to remove blast media and dust resting on structural steel components
to ensure surfaces are properly prepared for painting and coating.
The need for a clean and well-prepared surface after shot blasting mirrors that of the pieces surfacing in the first place as discussed in Part 1 of this series.
Practically all plate and profile roller conveyor
shot blast machines are equipped with a media brush-off system at the machine
exit. By adding a rotary brush at the end of the process, residue is removed as
the work piece exits the machine.
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.
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?
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.
Rosler Metal Finishing expertly designs shot blasting machines for these industriesand others to descale, clean, and prepare structural steel for surfaces for end-use. The particulars of each machine largely depend on the size and shape of the specific components in need of preparation.
This installment of our Structural Steel FAQ series will answer What are the most commonly used blast machines for structural steel surface preparation and how do they compare?
Machine Types by Workpiece
Whether surface preparation is needed for steel beams and plates, round bars, pipes and weldments, ship building, pipeline construction, or heavy equipment and machinery, there are machines tailored to produce consistent surface finishing results for each component.
The most common machine types by component include:
Roller Conveyor Machines for Plates and Beams
Round Bar and Pipe Machines
Roller Conveyor Machines for Large, Extra Heavy Components
Spinner Hanger and Monorail Hanger Machines for Large Components
The surface profile created by shot blasting depends entirely on the blast media and the way it is handled. The right media selection and equipment operating parameters are critical for the surface quality of structural steel components being prepared for paint coating. While mineral abrasives play a role for certain air blast applications, the lion’s share of industrial surface preparation is done in highly mechanized turbine blast machines utilizing steel media.
Rosler Metal Finishinghas decades of experience in the turbine blasting field. Through the years, we’ve used and evaluated all kinds of media and resulting roughness or lack thereof. This installment of our Structural Steel FAQ series will answer:
What influence does metallic blast media have on the surface profile
of structural steel?
Besides the degree of cleanliness – the removal of oil and grease, rust and mill scale, dust, and other contaminants – surface preparation specifications must also consider the surface profile and roughness relative to the coating to be applied. Rosler Metal Finishing builds shot blasting equipment to create the right surface profile on structural steel components as well as cleaning them in preparation for coating and painting.
This installment of our Structural Steel FAQ series will answer What is the optimum the surface profile for a structural steel component prior to painting and how is profile evaluated?
Optimizing for Painting
Shot blasting makes a surface rougher to increase the total contact area between paint and a work piece substrate and generally improves paint adhesion. A surface that is too smooth poses the risk of inadequate paint adhesion, while a surface that is too rough may not cover the peaks. The degree of surface profile required depends entirely on the coating to be applied.
Blade Technology: Straight vs. Curved Blades Explained
As an expert in the shot blasting industry,Rosler Metal Finishing knows about blade technology. All shot blasting machines require blades to propel media towards workpieces. While both straight and curved blades are used, each type offers advantages and disadvantages.
What’s the Difference?
Straight blades are, as the name suggests, blades that do not have curvature when viewed from the side and do not possess tangential curvature with respect to the turbine. Curved blades are blades that have some degree of curvature when viewed from the side.
As the newer design, curved blades are generally better than straight blades, but they also have some drawbacks related to longevity, maintenance, and cost of ownership.
As an expert in the surface finishing industry, Rosler Metal Finishing knows that all the expertise in the world won’t do any good if the surface of the work piece is not properly prepared. When it comes to structural steel, we receive many frequently asked questions about preparation. This installment of our Structural Steel FAQ series will answer How is the presence of dust on shot blasted structural steel components evaluated?
The Dangers of Dust
Blast-cleaned structural steel surfaces must be completely free of dust to ensure proper coating and painting.
Residual dust will reduce the adhesion of subsequently applied coatings and, by absorbing moisture, may promote the corrosion of the blast‐cleaned steel surfaces. The potential accumulation of dust is especially critical on horizontal surfaces, the interior of pipes, and in structural cavities.
Special inspections must be carried out to ensure that such areas are adequately cleaned and free from dust before painting.
Shot blast machines are often a considerable investment for companies. When these highly specialized and high investment pieces of equipment start to show signs of wear and underperformance, expert surface finishing companies such as Rosler Metal Finishing can help prolong the life and effectiveness of your investment by repairing and rebuildinga machine instead of replacing it.
Cost is often the biggest factor considered when rebuilding a shot blasting machine. Generally, rebuilds offer shorter turnaround times than buying a new machine. Rebuilds also come with the added benefit of not needing to integrate a new process since the process already includes a proven shot blasting process.
Levels of Rebuilds
The extensiveness of the rebuild process depends on your specific machine, its condition, and your expectations for longevity versus quick repair.
Different levels of rebuilds fall into three categories:
Surface preparation can account for up to 40 percent of structural steel painting and repainting jobs. As Rosler Metal Finishing’s Structural Steel FAQ series has already established, the life of anti‐corrosion coatings on a steel surface depends to a large extent
on how thoroughly this surface has been prepared for painting.
Properly evaluating the surface of structural steel surfaces for coating before and after shot blasting will help balance the cost of preparing, repairing, and monitoring structural steel throughout its impressive lifespan.
This installment of our Structural Steel FAQ series will answer How are rust and mill scale evaluated pre‐ and post‐blast?
Widely used standards were developed to visually assess the initial surface conditions and the quality of the required surface preparation relative to the initial steel surface conditions.
The dominant standards for evaluating rust and mill scale are ISO 8501‐1:2007 (based on the Swedish standard SIS 05 59 00), SSPC Vis 1‐89, and NACE. While different in some minor details, these standards are practically identical.
Shot blasting is a specialized surface finishing process where small metal (or mineral) pellets, called blast media, are thrown onto the surface of a work piece at incredibly high speeds, ranging from 200-800 feet per second. The impact on the work pieces from this process is what produces the desired surface finishing effect.
Shot blasting can help achieve surface cleaning, surface preparation, descaling, deburring, deflashing, and shot peening.
The process components of a shot blasting system include a shot blast machine, raw and finished work pieces, blast media, dust, and other byproducts.