This disclosure is directed to a method of descaling stainless steel using a descaling apparatus as disclosed in U.S. Pat. No. 7,601,226, the disclosure of which is incorporated by reference herein. In particular, the disclosure is directed to using such a descaler in a processing line having other machinery configured for pushing or pulling the stainless steel strip through the line.
Generally speaking, hot rolled carbon steel HRCS may be processed in a processing line having machinery configured for pushing or pulling the hot rolled carbon steel strip through the line. In these types of lines, the strip lengths of the hot rolled carbon steel are generally not welded or stitched together to form an endless strip, but are pushed or pulled through the line strip-by-strip. This allows small lots to be processed and provides some flexibility in production planning.
A typical push-pull pickling line PPPL for processing hot rolled carbon steel HRCS is shown in
For each production run, the hot rolled carbon steel strip HRCS may be uncoiled from the uncoiler 10 and threaded through each machine and station in the line to the coiling machinery and tension reel 36. In particular, the hot rolled carbon steel strip may be threaded through the pickling tank 16 containing a hydrochloric acid pickling solution so that the strip is immersed in the solution. Typically, the tanks 16 are formed from a granite material that not only withstands the reactivity of the hydrochloric acid pickling solution but also the wear induced by the leading edge of the steel strip during the process of threading the hot rolled carbon steel strip through the line during each coil's production run.
Hot rolled carbon steel HRCS may also be processed in a semi-continuous pickling line SCPL as shown in
As shown in
While hot rolled carbon steel HRCS may be processed in a push-pull pickling line PPPL or a semi-continuous pickling line SCPL depending upon the steel grades, the production quantity required, and the strip product dimensions, the processing of stainless steel strip involves different procedures and processes, which result in different processing line configurations, and traditionally exclude push-pull configured lines.
To descale stainless steel, an acid pickling solution is used that is more reactive than that used for hot rolled carbon steel. For instance, hydrofluoric acid is commonly used to pickle stainless steel. However, the use of hydrofluoric acid requires different design considerations for the processing line than lines using hydrochloric acid in hot rolled carbon steel processing. Hydrofluoric acid generally degrades granite, and thus the granite tanks that are traditionally used in lines processing hot rolled carbon steel must be replaced with other materials, for instance, plastic tanks. While plastic tanks are capable of withstanding the higher reactivity of the pickling solution used in lines processing stainless steel, such plastic tanks cannot withstand the wear induced from the leading edge of the strip during threading processes at the beginning of production runs. Thus, threading processes are often minimized or avoided in lines processing stainless steel to avoid premature reduction of the expected lifespan of the acid pickling tanks. Because threading processes are minimized in lines processing stainless steel, stainless steel is not traditionally processed in a push-pull processing line. Processing stainless steel in a push-pull processing line would require threading processes for each coil's production run, and the excessive threading processes would rapidly decrease the expected life of the plastic acid pickling tank. To avoid the issues associated with threading processes, stainless steel is traditionally processed in a semi-continuous or continuous processing line. The hydrofluoric acid traditionally used to pickle the stainless steel may be contained in plastic tanks, and because there are no repeated threading operations involved, there is diminished risk to damage to the plastic pickling tanks.
U.S. Pat. No. 7,601,226 describes a descaling apparatus that eliminates scale from the sheet metal and eliminates the pickling process that is used to remove scale from the surface of sheet metal. While U.S. Pat. No. 7,601,226 generally discloses a descaling apparatus that allows for descaling of both hot rolled carbon steel and stainless steels, U.S. Pat. No. 7,601,226 teaches such descaling by replacing the acid pickling tanks in a processing line with such a descaling apparatus. For instance, U.S. Pat. No. 7,601,226 and its child patents (including U.S. Pat. Nos. 8,062,095, 8,066,549, 8,074,331, and 8,128,460, the disclosures all of which are incorporated by reference herein) teach removing scale from hot rolled carbon steel and replacing the pickling tanks previously used in such processing lines with descaling apparatuses. Given the decades long practice of processing stainless steel in a semi-continuous or continuous processing line, U.S. Pat. No. 7,601,226 and its child patents merely suggest use of the disclosed descaling apparatus in a semi-continuous or continuous processing line, for instance, retrofitting a semi-continuous or continuous processing line with such a disclosed descaling apparatus. It was heretofore unappreciated that stainless steel may be processed in a push pull stainless steel processing line with such a descaling apparatus. The disclosure is directed to push-pull stainless steel processing line with a descaling apparatus, rather than the replacement of pickling tanks with a descaling apparatus in a conventional semi-continuous or continuous stainless steel processing line.
To complete the descaling process, the processing line may be provided with one or more descaling apparatuses 96 as disclosed in U.S. Pat. No. 7,601,226, and its child patents including U.S. Pat. Nos. 8,062,095, 8,066,549, 8,074,331 and 8,128,460. The descaling apparatus 96 may be operated in such a matter to propel the scale removing media against the stainless sheet metal to substantially remove all of the scale from the sheet metal. U.S. Pat. No. 7,601,226 and its child patents describe methods and parameters that which may be used in connection with descaling. The scale removing media may include a slurry comprising a grit and liquid. The scale removing media may also comprise a grit.
After the stainless steel strip leaves the descaling apparatuses, the material may pass through a drying table 98, a crop shear machine 100, and through a take up reel 102. The take up reel may comprise a recoiler, for instance, a recoiler as described in U.S. Pat. No. 8,707,529, the disclosure of which is incorporated herein by reference. U.S. Pat. No. 8,707,529, the disclosure of which is incorporated by reference herein.
The desclaling apparatus 96 may be designed, promoted, sold, or distributed as a separate machine to be included in a push pull processing line for stainless steel. A push pull processing line may be designed, promoted, sold, or distributed with a descaling apparatus included, for instance, integrated therein. In connection with the sale, promotion, design, or distribution of the descaling apparatus 96, the user, e.g. purchaser of the descaling apparatus, may be instructed that the purpose of the descaling apparatus is to enable descaling of stainless steel in a push pull sheet metal processing line. The user is induced to install the descaling apparatus in a push pull sheet metal processing line and process stainless steel in a push pull sheet metal processing line. The user may be induced to substantially remove all of the scale from at least one surface of the stainless steel sheet metal using at least on the scaling apparatus. In connection with the sale, promotion, design, or distribution of a push-pull processing line with a descaling apparatus 96 included therein, the user, e.g. purchaser of the push-pull processing line, may be instructed that the purpose of the push-pull processing line is to use the descaling apparatus 96 to descale stainless steel. The user is induced to purchase the push pull sheet metal processing line and process stainless steel in a push pull sheet metal processing line with the descaling apparatus 96. The user may be induced to substantially remove all of the scale from at least one surface of the stainless steel sheet metal using at least on the scaling apparatus.
In connection with inducing the user to perform one or more of the aforementioned steps, the user may be instructed to perform one or more of the aforementioned steps or may be directed to perform one or more of the aforementioned steps. The user may be induced to operate the descaling apparatus 96 to control the rate of impact of the scale removing media against the at least one surfaces of the stainless steel strip such that the impact of the scale removing media along substantially removes all of the scale from a surface of the stainless steel sheet metal. While U.S. Pat. No. 7,601,226 and its child patents disclose rotating impeller wheels to propel the scale removing media against the surfaces of the stainless steel sheet metal, other methods may be used to propel the scale removing media against the surfaces of the stainless steel sheet metal. The user may be induced to position the first and second impeller wheels in such a manner to propel the scale removing media against the sheet metal and substantially remove all of the scale from the stainless steel sheet metal. A pair of impeller wheels may be provided to propel the scale removing media against the sheet metal top surface and a second pair of impeller wheels may be provided to propel scale removing media against the bottom surface of the sheet metal. The number of descaling apparatuses may be selected as needed to provide a desired level of scale removal, surface finish, and sheet metal processing throughput time.
As described herein, a push-pull processing line for stainless steel sheets or strips using a descaling apparatus may replace a semi-continuous or continuous acid pickling processing line. A continuous or semi-continuous acid pickling processing line has extensive equipment that requires a very large amount of plant space. Additionally, a continuous or semi-continuous acid pickling processing line represents a significant capital investment and relatively high, long-term operating costs. These issues may be avoided with a push-pull processing line for stainless steel sheets or strips including a descaling apparatus, as described herein.
Further, generally speaking, continuous or semi-continuous acid pickling processing lines for stainless steel have as much as a 15%-30% rejection rate due to unacceptable surface condition or finish. Any rejected coils are generally reprocessed through the same continuous or semi-continuous acid pickling line. This results in additional expense in re-pickling the rejected coils. A push-pull processing line for stainless steel sheets or strips including a descaling apparatus, as described herein, may be used in the same plant as a continuous or semi-continuous acid pickling processing line. Any rejected coils may be processed on the push-pull line which is much less expensive to operate, rather than the continuous or semi-continuous acid pickling processing line.
As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.
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