Eco pickled surfaces ( EPS ) is a process applied to hot rolled sheet steel to remove all surface oxides (plant scale) and clean the steel surface. EPS-treated steels obtain a high level of resistance to the development of surface oxides (rust), as long as they are not in direct contact with water vapor. EPS was developed by The Material Works, Ltd., which has filed several patent applications covering the process. This is primarily intended to be a substitute for the acidification process of a known acid in which the steel strip is immersed in a solution of hydrochloric acid and sulfate to remove the oxide chemically.
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Ikhtisar proses EPS
The EPS process (see Figure 2) begins with a hot rolled steel strip in the form of a coil. This steel is free of uncoiler, then through the machine that serves the purpose of "scale-breaking", "generalize" or both. This machine (see Figure 2) works the material between the hardened roller sets. It has the effect of removing the curvature of the strip ("coil set") and releasing the outer layer of the mill scale that encloses the steel strip.
After passing the "screw/leveler" machine, the steel strip enters the first "EPS slurry slurry cell". Slurry blasting is an abrasive wet blasting process that combines fine metal particle abrasives with "carrier fluid" (the most common being water). This abrasive slurry mixture is fed into a rotating impeller that pushes it at high speed across the object to be cleaned (see Figure 3). Slurry blasting is a method to remove rust/scale, to clean out explosions and shoot peening. The cleaning agent can be inserted into the carrier fluid to reduce smoke and help prevent rust.
The EPS slurry blast cell consists of eight slurry exhaust heads shown in Fig. 3-4 for the upper surface and four for the underside of the lane. In the blasting cell of the slurry, the water jet clears both the coarse particle steel strip and the mill scale off. The EPS production system can use multiple EPS slurry decay cells arranged simultaneously, so the steel strips move from one cell to the next, then to the next, and so on. Some cells increase the exposure of the steel strip to the flow of the slurry burst, thereby allowing the strip to move faster, but still achieving the required scale removal rate. The speed of the strip and, therefore, the system output increases in rough proportion to the number of EPS slurry blast cells used.
This strip comes from the final blasting cell and is dried with a high-speed air blower. At this point the strip passes under the camera of the real-time oxide detector, which provides feedback to the line control to ensure full oxide removal is achieved.
To conclude the process, the strip may, optionally, have the oil film or lubricant applied, then it will retreat. Noteworthy is that the stress created by the recoiler force that pulls the strip through the scale breaker/leveler serves to flatten the strip, eliminating arcs, edge waves and small windings. Also, not shown in FIG. 2 is a pulping shipping/recirculation/filtration system. This closed-loop system collects carrier fluid, abrasive scales and is removed, removes deleted scales, other contaminants and "abrasive" abrasive particles, and returns the blended slurry that has been cleaned back to the blasting cell.
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Characteristics of EPS processed steel strips
Steel that uses the EPS process to remove the surface scale shows some differences from the steel using acid preservatives to remove the surface scale. Downstream industrial processes such as galvanizing, cold reduction and painting of EPS-treated steel strips show it can be interchangeable with acid acidified steel strips. This also applies to general sheet metal fabrication processes, such as laser cutting, plasma cutting, stamping, welding, bending, and roll formation - there is no significant difference between the steel strips using the EPS process and the steel strips using acid preservation.
An area where the difference between EPS-treated steel strips and acidified acid strips is evident is the visual appearance. EPS-treated steels show a more uniform and shimmering appearance, as shown in Figure 4. In the EPS process, the impact of the abrasive particles on the steel surface serves to "smooth" small surface imperfections such as scratches, holes, scrolling marks and silicone lines.
Another difference between EPS-treated steel strip and acid acidified steel strip is rust resistance. Conventional acid-pickled steel strips are often coated with a thin film of oil to serve as a barrier to contact with oxygen thus preventing rusting. EPS-treated steels are inherently rust-resistant and, therefore, do not require oil or other coatings to prevent rusting. Many "downstream" processes and steel fabrication processes must have a layer of steel oil (or other surface contaminants) removed as a precursor step of the process. The use of EPS-treated steels in these processes precludes the need for the "oil stripping" precursor step, thus simplifying the process.
The rust-block property of the EPS-processed strip
The corrosion resistance of EPS-treated steel strips is superior to the pickled acetic acid strip mainly because acid preservation imposes corrosion "punishment" on steels not processed by the EPS process. This penalty is the result of chemical reactions that occur after acid preservation and serves as a catalyst for oxidation. The main preservative agent is hydrochloric acid (HCl). Although the steel strips were completely rinsed with clean water after immersion in HCl immersion, some residual amount of chlorine (Cl) remained on the strip surface. Chlorine reacts very easily with oxygen to form chloride, so Cl is free to act as something of a "magnet" for oxygen. This mechanism makes acetic acid steels more susceptible to taking oxygen, whereas there is no comparable mechanism in the workplace with EPS preservation techniques.
In addition to the free Cl, a compound known as "chloride salt" remains on the acid surface of acidified steel in small amounts, even after rinsing. The chloride salt reacts quickly with water vapor and accelerates the oxidation of iron on the steel surface. To prevent iron oxidation in the acid strip of acar, a thin layer of oil is applied to the surface to serve as a barrier between Cl, chloride salt and free oxygen. No such protective barrier is required for EPS-treated steels, since no free Cl or chloride salt is present.
However, the additives used in the explosive slurry carrier EPS slurry to reduce the "smut" otherwise would remain on the surface and bore the appearance of the EPS-processed strips. This additive contains rust inhibitors, a number of residues remaining on the surface even after rinsing. It is believed that the presence of rust inhibitors adds to the capabilities of an EPS-treated line as a whole for rust resistance. Additives have been shown to have no impact on paint performance.
EPS process instead of acid preservative
The EPS process produces a free-scale steel strip that can be interchangeable with a pickled-acid steel strip, but the EPS process contains lower capital and operating costs (variables) than equivalent acid-preserving output lines. For this reason the EPS process is considered as a direct replacement of acid preservation.
In addition, the EPS process is considered less environmentally destructive than pickling acids for these reasons:
- lower energy consumption;
- no hazardous/acidic substances used in the process;
- there is no potential exposure to acid fumes for people, equipment, or buildings;
- there is no harmful output or pollution or by-product of the process with a disposal or smoke stack.
Apps
Pickled pickle surface technology has been tested and approved for use as a substitute for acidified acid by automotive manufacturers General Motors and Chrysler. The Eco Pickled Surface process is a finalist of the American Iron Market Award (AMM) 2013 for Steel Excellence.
Note
References
- Voges, K.; Mueth, A. (May 2007). Eco-Pickled Surface: A Profitable Alternative to Conventional Acid Preservation (PDF) . The Iron & amp; Conference and Exposition of Steel Technology . Retrieved 2014-12-22 .
- Voges, K. (2009). "Strips And Conductive Surface Stress By Eco Pickled Surf Technology". International Metallurgy and Technology Factory (2) . Retrieved 2014-12-22 .
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