Patent Application
20090227184
The disclosure pertains to a process for removing undesirable surface material from flat materials either in sheet or continuous form, and from narrow tubular material. In particular, the disclosure pertains to an apparatus and method for removing scale from the surfaces of processed sheet metal or metal tubing by propelling a scale removing medium, specifically, a liquid/particle slurry, against the surfaces of the material passed through the apparatus, and controlling the slurry blasting process in a manners to produce a resultant material that exhibits rust inhibitive properties.
As will be described in further detail below, the methods and apparatuses disclosed herein provide advantages over the apparatuses and methods used in the prior art. Sheet steel (a.k.a. flat roll) is by far the most common type of steel and is far more prevalent than bar or structural steel. Before sheet metal is used by manufacturers it is typically prepared by a hot rolling process. During the hot rolling process, carbon steel is heated to a temperature in excess of 1,500° F. (815° C.). The heated steel is passed through successive pairs of opposing rollers that reduce the thickness of the steel sheet. Once the hot rolling process is completed, the processed sheet metal or hot rolled steel is reduced in temperature, typically by quenching it in water, oil, or a polymer liquid, all of which are well known in the art. The processed sheet metal is then coiled for convenient storage and transportation to the ultimate user of the processed sheet metal, i.e. the manufacturers of aircraft, automobiles, home appliances, etc.
During the cooling stages of processing the hot rolled sheet metal, reactions of the sheet metal with oxygen in the air and with the moisture involved in the cooling process can result in the formation of an iron oxide layer, commonly referred to as “scale,” on the surfaces of the sheet metal. The rate at which the sheet metal is cooled, and the total temperature drop from the hot rolling process effect the amount and composition of the scale that forms on the surface during the cooling process.
In most cases, before the sheet metal can be used by the manufacturer, the surface of the sheet metal must be conditioned to provide an appropriate surface for the product being manufactured, so that the sheet metal surface can be painted or otherwise coated, for example, galvanized. The most common method of removing scale from the surface of hot rolled or processed sheet metal is a process known as “pickling and oiling.” In this process, the sheet metal, already cooled to ambient temperature following the hot rolling process, is uncoiled and pulled through a bath of hydrochloric acid to chemically remove the scale formed on the sheet metal surfaces. Following removal of the scale by the acid bath, the sheet metal is then washed, dried, and immediately “oiled” to protect the surfaces of the sheet metal from oxidation or rust. The oil provides a film layer barrier to air that shields the bare metal surfaces of the sheet metal from exposure to atmospheric air and moisture.
Virtually all flat rolled steel is pickled and oiled. Because flat rolled steel is so commonly used—its typically used in automobiles, appliances, construction, and nearly all of our agricultural implements—pickling and oiling, either as an end result pickled product or pickled to produce other common materials such as cold roll, prepaint, galvanize, electro galvanize, etc, is also very common. To illustrate the scope of the practice, one of the largest steel producers in the world operates a very large steel mill that has 16 pickle lines each running about 90,000 monthly tons. Some estimate that there are approximately 100 pickle lines in the U.S. alone with several thousand more located abroad.
The “pickling” portion of the process is effective in removing substantially all of the oxide layer or scale from processed sheet metal. However, the “pickling” portion of the process has a number of disadvantages. For example, the acid used in the acid bath is corrosive; it is damaging to equipment, it is hazardous to people, and is an environmentally hazardous chemical which has special storage and disposal restrictions. In addition, the acid bath stage of the process requires a substantial area in the sheet metal processing facility. Pickling lines are typically about 300-500 feet long, so they take up an enormous amount of floor space in a steel mill. Their operation is also very expensive, operating at a cost of approximately $12/ton-$15/ton. A “pickling and oiling” line with a tension leveler costs approximately $18,000,000.00. Also, it is critical that the sheet metal be oiled immediately after the pickling process, because the bare metal surfaces will begin to oxidize almost immediately when exposed to the atmospheric air and moisture. Oftentimes, free ions from the acid solution (i.e., Cl−) remain on the surface of the metal after the pickling portion of the process, thereby accelerating oxidation unless oiled immediately.
Oiling is also effective in reducing oxidation of the metal as it shields the bare metal surfaces of the sheet metal from exposure to atmospheric air and moisture. However, oiling also has disadvantages. Applying and subsequently removing oil takes time and adds substantial cost both in terms of material cost of the oil product itself, and in terms of the labor to remove oil before subsequent processing of the steel. Like the pickling acid, oil is an environmentally hazardous material with special storage and disposal restrictions. Oil removal products are usually flammable and likewise require special controls for downstream users of the steel product. Also, again, it is critical that the sheet metal be oiled immediately after the pickling process, because the bare metal surfaces will begin to oxidize almost immediately when exposed to the atmospheric air and moisture.
The methods and apparatuses disclosed herein eliminate pickling lines and the need to put oil on the product after pickling. The methods and apparatuses disclosed herein produce a rust inhibitive product, whereas conventional shot blasting and other blasting techniques do not produce a resultant product with rust inhibitive properties, and thus do not replace the need for pickling and oiling. A processing line incorporating the methods and apparatuses disclosed herein avoids the many disadvantages of a pickling and oiling line. For instance, a processing line incorporating the methods and apparatuses disclosed herein is about 100 feet long, thereby saving significant space in a facility. The methods and apparatuses disclosed herein allow for recycling of many of the materials used in the process, without the use of harmful chemicals and acids. Operating costs associated with a processing line using the methods and apparatuses disclosed herein are $5/ton-$7/ton, which is significantly lower than the operating costs of approximately $12/ton-$15/ton associated with a “pickling and oiling” line. The capital cost of a typical line utilizing the methods and apparatuses disclosed herein is about $6,000,000.00, whereas the capital costs for a typical pickling line are about $18,000,000.00.
Further features of the apparatuses and methods described herein are set forth in the following detailed description and in the drawing figures.
Referring to
A leveler 18 of the apparatus 14 is positioned adjacent the sheet metal coil 12 to receive the length of sheet metal 16 uncoiled from the roll. The leveler 18 is comprised of a plurality of spaced rolls 22, 24. Although the a roller leveler is shown in the drawing figures, other types of levelers may be employed in the processing line of
From the leveler 18, the length of processed sheet metal 16 passes into the descaler or descaling cell 26. In
An upstream end wall 32 of the enclosure or box 28 has a narrow entrance opening slot 34 to receive the width and thickness of the length of sheet metal 16. An opposite downstream end wall 36 of the box has a narrow slot exit opening 38 that is also dimensioned to receive the width and thickness of the length of sheet metal 16. The entrance opening 34 is shown in
A pair of driven centrifugal impellers 68 are installed in lined casings, shrouds or cowlings 58,62 (see
A pair of electric motors 64 is mounted on the pair of shrouds 58,62. Each of the electric motors 64 has an output shaft 66 that extends through a wall of its associated shroud 58,62 and into the interior of the shroud. Impeller wheels 68 (
The descaling cell impeller wheels and their associated shrouds may be formed from a high strength corrosion resistant material. The descaling cell impeller wheels and their associated shrouds may also be coated with a polymer material to increase the release characteristics of the slurry being propelled from the vanes of the impeller, to increase wear resistance to the grit component of the slurry, and improve the impeller wheel's temperature stability and resistance to chemical oxidation. One type of polymer that has proven effective is a metallic hybrid polymer supplied by Superior Polymer Products of Calumet, Mich., under the designation SP8000MW. A polymer known commercially as Duralan has also been found effective.
As shown in
A supply of slurry mixture 104 communicates with the interiors of each of the shrouds 58, 62 in the central portion of the descaling wheels 68,84 and may be injected into the impeller wheel in the manner described in the earlier-referenced Lehane patent, or being injected through an elliptical nozzle at the side of the impeller wheel. The supply of the scale removing medium 104 is shown schematically in
The upper pair of descaling wheels 68 propels the slurry 105 downwardly toward the length of sheet metal 16 passing through the descaler cell 28 impacting with the top surface 106 and removing scale from the top surface. In one embodiment, each pair of descaling wheels will rotate in opposite directions. For example, as the length of sheet metal 16 moves in the downstream direction, if the descaling wheel 68 on the left side of the sheet metal top surface 106 has a counter-clockwise rotation, then the descaling wheel 68 on the right side of the sheet metal top surface 106 has a clockwise rotation. This causes each of the descaling wheels 68 to propel the slurry 105 into contact with the top surface 106 of the length of sheet metal 16, where the contact area of the slurry 105 propelled by each of the descaling wheels 68 extends entirely across, and slightly beyond the width of the length of sheet metal 16. Allowing the discharge of the impeller wheels to extend slightly beyond the edges of the strip ensures the most uniform coverage. This is depicted by the two almost rectangular areas of impact 112, 114 of the scale removing medium 105 with the top surface of the length of sheet metal 16 shown in
The axially staggered positions of the upper pair of wheels 68 also axially spaces the two impact areas 112, 114 on the surface 106 of the sheet metal. This allows the entire width of the sheet metal to be impacted by the slurry without interfering contact between the slurry propelled from each wheel 68. In addition, the pairs of descaling wheels 68,88 may be adjustably positioned toward and away from the surface 106 of the sheet metal passing through the descaler. This would provide a secondary adjustment to be used with sheet metal of different widths. By moving the motors 64 and wheels 68 away from the surface 106 of the sheet metal, the widths of the impact areas 112, 114 with the surface 106 of the sheet metal may be increased. By moving the motors 64 and their wheels 68 toward the surface 106 of the sheet metal, the widths of the impact areas 112, 114 with the surface 106 of the sheet metal may decreased. This adjustable positioning of the motors 64 and their descaling wheels 68 enables the apparatus to be used to remove scale from different widths of sheet metal. An additional method of width adjustment of the area of slurry impact with the sheet metal surface is to move the angular position of the inlet nozzles 104 relative to the impeller casing/shroud. A third option is to rotate the pair of impellers about axes 116 normal to their rotation axes relative to the strip travel direction so that the oval area of slurry impact from each wheel, although staying the same length, would not be square or transverse to the sheet metal travel direction. The movement away and toward the strip will also change the impact energy of the flow, and consequently, the effectiveness of the scale removal and surface conditioning for producing rust inhibitive material.
In addition, the angled orientation of the axes 78,82 of the descaling wheels 68 also causes the impact of the slurry 105 to be directed at an angle relative to the surface of the sheet metal 16. The angle of the impact of the slurry 105 with the surface of the sheet metal 16 is selected to optimize the effectiveness of the scale removal and surface conditioning for producing rust inhibitive material. An angle of 15 degrees has been proven satisfactory.
As shown in
Preferably, the top surface and/or bottom surface impeller wheels 68,88 operate at a wheel velocity which is relatively lower than wheel velocities using in conventional grit blasting operations. Preferably, the top surface and/or bottom surface impeller wheels 68,88 rotate to generate a slurry discharge velocity below 200 feet per second. More preferably, the slurry discharge velocity is in arrange of about 100 feet per second to 200 feet per second. Even more preferably, the slurry discharge velocity is in arrange of about 130 feet per second to 150 feet per second. In conventional shot blasting, the discharge velocity of the grit is greater than 200 feet per second, and may be as high as 500 feet per second. The inventors have discovered that by slurry blasting at a low velocity, and controlling other operating parameters as discussed below, the processed sheet metal may exhibit rust inhibitive properties after passing through the descaling cell thereby obviating the need for secondary processing, for instance, pickling and oiling.
Another operating parameter, which the inventors have found to be important in processing the sheet metal so that the sheet metal exhibits rust inhibitive properties, relates to the type and amount of grit used in the slurry mixture. The type and amount of grit along with the discharge velocity of the slurry mixture are preferably controlled to allow the descaling cell to produce a rust inhibitive processed sheet metal with a commercially acceptable surface finish (i.e., roughness). Controlling the type and amount of grit along with the discharge velocity of the slurry mixture reduces the probability of scale or grit particles being imbedded into the softer steel surface of the processed sheet metal. A relatively low wheel velocity for propelling the slurry and an angular grit has been found efficient in removing the scale oxide layers from the processed sheet metal strip and producing rust inhibitive properties for the processed sheet metal. By propelling the slurry at velocities below 200 feet per second, the angular grit will not fracture to a significant extent, and will gradually become rounded in configuration as it is spent through repeated impact with the processed steel sheet. The rounding of the grit that occurs in the descaling process results in some of the grit becoming smaller in size. A blend of grit sizes assists in ensuring more uniform surface coverage of the processed sheet metal.
With the foregoing in mind, forming the slurry mixture from water and a steel grit having a size range of SAE G80 to SAE G40 has proven effective. Forming the slurry mixture from water and a steel grit having a size of SAE G50 has also proven effective. To ensure the efficacy of the slurry mixture, the grit to water ratio is preferably monitored and controlled. A grit-to-water ratio of about 2 pounds to about 15 pounds of grit for each gallon of water has proven effective. A grit-to-water ratio of about 4 pounds to about 10 pounds of grit for each gallon of water has also proven effective.
The grit to water ratio may be controlled in a slurry recirculation system of the blasting cell and may include the use of a system of eductors and pumps to meter the concentration of grit and liquid. For instance, the slurry mixture from the blast cabinet may be directed to a system of settling tanks, filters and magnetic separators where grit of a size and shape suitable for reuse is removed from the slurry for later recombination, and the remaining liquid mixture is filtered and separated to remove expended grit, and scale, debris and other metals particles. The liquid may be directed to a system of divided settling tanks with magnetic skimmers to ensure the liquid is predominately free of solids. The previously removed grit may then be re-mixed with the filtered liquid to form the slurry mixture before injection into the blasting cell. The U.S. patent to Lehane (U.S. Pat. No. 5,637,029) shows one embodiment of slurry recirculation system, the principles of which may be modified and incorporated into a descaling cell as described above.
Corrosion inhibitors, for example, those marketed under the trademark “Oakite” by Oakite Products, Inc., may be added to the slurry. Additive(s) may also introduced to the slurry to prevent oxidation of the steel grit. While additives may remain on the sheet metal after processing in the descaling cell, and provide a measure of rust protection, the inventors have found that sheet metal processed under the conditions described above exhibits satisfactory corrosion resistance without the addition of such corrosion inhibitors. Also, other additives may be added to the slurry to prevent the formation of fungi and other bacterial contaminants. An additive having the brand name “Power Clean HT-33-B” provided by Tronex Chemical Corp. of Whitmore Lake, Mich., has proven effective, providing both anti-bacterial and rust inhibitive qualities for the processed sheet metal and grit. An additive may be chosen based on the subsequent processing requirements of the sheet metal and the level of protection required. Also, if the incoming material has any oil on the surface, commercial alkaline or other cleaning or degreasing agents can be added to the slurry without changing the efficiency of the slurry blasting process.
As described in the related applications, the processing line may be configured such that the electric motors coupled to the impeller wheels in the first cell shown to the left in
Although an end user may desire sheet metal with rust inhibitive properties, the end user may also desire sheet metal with a top surface texture different from a bottom surface texture. It should also be appreciated that the opposite surfaces of the length of sheet metal may be processed by the apparatus differently, for example, by employing different scale removing medium supplied to the wheels above and below the length of sheet metal passed through the apparatus, and/or using any of the techniques discussed above. Different target textures on the opposite surfaces of the sheet metal strip is often a requirement where an inner surface of a part has a major requirement to carry a heavy coating of lubricant for drawing and then to support a heavy polymer coating for wear and corrosion protection, and the outside surface needs to provide an attractive smooth painted surface. For example, body panels for luxury automobiles often have this type of requirement. The ability to adjust the surface texture of the sheet is important because a rougher surface texture normally increases a coating's adhesion, but requires more coating. The adjustability feature enables the operator of the processing line to adjust the surface texture for the condition desired, i.e., adhesion or coating, while providing the desired rust inhibitive properties for the surface.
To assist in control of the processing line, an in-line detector 160 may be used to detect a surface condition of the top and/or bottom surfaces of the processed sheet metal after passing through the descaling cell(s), and an output of the in-line detector may be used to assist the processing line operator in adjusting any one or more of the following to obtain a desired surface condition: (i) pivoting, rotating, angling, and/or positioning the top surface impeller wheel(s) of the first blasting cell; (ii) pivoting, rotating, angling, and/or positioning the bottom surface impeller wheel(s) of the first blasting cell; (iii) pivoting, rotating, angling, and/or positioning the top surface impeller wheel(s) of the second blasting cell, (iv) pivoting, rotating, angling, and/or positioning the bottom surface impeller wheel(s) of the second blasting cell, or (v) increasing or decreasing the processing line speed. The in-line detector may be positioned between the two blasting cells 26 or may be positioned after the second blasting cell as shown in
In another embodiment of the descaling cell, the detector 160 may be provided with automatic feedback mechanism that allows for automatic control of processing line operating parameters based at least in part of the detected surface condition. For instance, based upon the detected surface condition, the rate of slurry impact may be controlled to produce a specific surface condition, for instance, a surface finish less than about 100 Ra. The rate of slurry impact may be varied by varying the discharge velocity of the propelled slurry or by varying the processing line speed, i.e., the speed at which the sheet steel is advanced through the line. Thus, based at least in part of the detected surface condition, a rate of advancement of the sheet material through the descaling cell may be changed as desired. In addition to or in the alternative, a discharge rate of slurry being propelled against the side of the sheet metal may be varied as necessary based at least in part upon the detected surface condition. For a system involving centrifugal impellers, the impeller wheel velocity may be changed based at least in part of the detected surface condition. Generally speaking, to obtain a desired surface condition, any one or more of the following may be changed based at least in part upon the detected surface condition: (i) pivoting, rotating, angling, and/or positioning the top surface impeller wheel(s) of the first blasting cell; (ii) pivoting, rotating, angling, and/or positioning the bottom surface impeller wheel(s) of the first blasting cell; (iii) pivoting, rotating, angling, and/or positioning the top surface impeller wheel(s) of the second blasting cell, (iv) pivoting, rotating, angling, and/or positioning the bottom surface impeller wheel(s) of the second blasting cell, or (v) increasing or decreasing the processing line speed. One or more detectors may be used to detect a surface condition of the top surface and bottom surface of the sheet metal, and a top surface detected surface condition and/or a bottom surface detected surface condition may provide input to the automated processing line control system.
As disclosed in the related applications, the processing line may also comprise a brusher cell 122 positioned adjacent the blasting cell 26 to receive the length of sheet metal 16 from the descalers. The brusher 122 could be of the type disclosed in the U.S. patent of Voges U.S. Pat. No. 6,814,815, which is incorporated herein by reference. The brusher 122 comprises pluralities of rotating brushes arranged across the width of the sheet metal 16. The rotating brushes contained in the brusher 122 contact the opposite top 106 and bottom 108 surfaces of the length of sheet metal 16 as the sheet metal passes through the brusher 122, and produce a unique brushed and blasted surface, generally with a lower roughness, with some directionality. The brushes act with water sprayed in the brusher 122 to process the opposite surfaces of the sheet metal, adjusting or modifying the texture of the surfaces created by the blasting cells 26. Alternatively, the brusher 122 could be positioned upstream of the blasting cells 26 to receive the length of sheet metal 16 prior to the descalers. In this positioning of the brusher 122, the brusher would reduce the workload on the blasting cells 26 in removing scale from the surfaces of the sheet metal 16. However, it is preferred that the brushers be positioned downstream of the descalers. It should be appreciated that the processing line need not have a brushing unit.
The processing line may also comprise a dryer 124 positioned adjacent the brusher 122 to receive the length of sheet metal 16 from the brusher, or directly from the slurry blaster if the brushing unit is not installed or is deselected. The dryer 124 dries the liquid from the surfaces of the length of sheet metal 16 as the sheet metal passes through the dryer. The liquid is residue from the rinsing process. It should be appreciated that the processing line need not have a dryer.
The processing line may also comprise a coiler 126 that receives the length of sheet metal 16 from the dryer 124 and winds the length of sheet metal into a coil for storage or transportation of the sheet metal.
In alternative line configurations/embodiments, the length of sheet metal processed by the apparatus may be further processed by a coating being applied to the surfaces of the sheet metal, for example a galvanizing coating or a paint coating. The length of sheet metal could also be further processed by running the length of sheet metal through the line apparatus shown in
The apparatus may also be employed in removing scale from material that is in an other form than a sheet of material.
To enable the sheet metal processing line to be expanded to support an additional descaling or blasting cell, or other piece of equipment, the components of the processing line, including the descaling cells, may be mounted on a rail or I-Beam system 170 (
The inventors have determined that processing steel sheet metal through the slurry blasting descaling cell described above under the conditions described above allows for the processing of sheet metal with rust inhibitive properties. Carbon steel used in a hot rolling process typically contains trace amounts of the elements Aluminum, Chromium, Manganese, and Silicon. For instance, common hot rolled carbon steel may have a chemical composition: Al—0.03%; Mn—0.67%; Si—0.03%; Cr—0.04%, C—remainder. The inventors have determined that processing steel using one or more of the descaling methods discussed above creates a very thin passivation layer (˜200 Å (Angstroms)) in the steel substrate comprising one or more of the above mentioned trace elements, thus enabling the processed steel sheet to exhibit rust inhibitive properties.
Although the apparatus and the method of the invention have been described herein by referring to several embodiments of the invention, it should be understood that variations and modifications could be made to the basic concept of the invention without departing from the intended scope of the following claims.
This patent application is a continuation-in-part of patent application Ser. No. 12/051,537, which was filed on Mar. 19, 2008, and is currently pending, which is a continuation-in-part of patent application Ser. No. 11/531,907, which was filed on Sep. 14, 2006, and is currently pending, the disclosures of which are incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12051537 | Mar 2008 | US |
| Child | 12418852 | US | |
| Parent | 11531907 | Sep 2006 | US |
| Child | 12051537 | US |
