Patent Application
20080216925
1. Field of the Invention
The present invention pertains to a method and apparatus for producing sheet metal that is substantially free of iron oxide scale. More specifically, the present invention pertains to a method and apparatus for strip casting sheet metal and then conditioning the surfaces of the sheet metal to remove iron oxide scale by first brushing the surfaces with stainless steel brushes and then brushing the surfaces with aluminum oxide brushes.
2. Description of the Related Art
Processed sheet metal is used in the manufacturing of a wide variety of goods. For example, the constructions of goods such as aircraft, automobiles, home appliances, file cabinets, etc., contain at least some component parts constructed of processed sheet metal. Before the sheet metal can be used by the manufacturers of these goods, the sheet metal must be processed to flatten the sheet metal to the desired thickness and to condition the surfaces of the sheet metal to the desired smoothness.
Sheet metal is typically formed to its desired thickness by a hot rolling process. During the hot rolling process the carbon steel of the sheet metal is heated to a temperature in excess of 1,5000 Fahrenheit (815° C.). Once the hot rolling process to reduce the sheet metal thickness is completed, the hot rolled sheet metal is cooled to an ambient temperature, typically by quenching the hot rolled sheet metal in water, oil, or a polymer. As a result of reactions of the sheet metal with oxygen in the air and the moisture exposure during the cooling process, an iron oxide layer or scale is formed on the surfaces of the sheet metal. This scale must be removed from the sheet metal surfaces before the sheet metal can be used by goods manufacturers.
The most common method of removing all oxide scale from the surfaces of hot rolled sheet metal is a process known as “pickle and oil.” In this process, the previously cooled sheet metal is pulled through a bath of hydrochloric acid (typically about 30 percent hydrochloric acid and 70 percent water) to chemically remove the scale from the surfaces of the sheet metal. After the scale has been removed, the sheet metal surfaces are then washed, dried, and immediately oiled to protect the surfaces from iron oxide scale or rust again forming on the surfaces. The oil provides an air barrier to shield the bare metal surfaces from exposure to air and moisture. It is critical that the sheet metal surfaces be oiled immediately after the pickling process, as the bare metal surfaces will begin to oxidize very quickly when exposed to air and moisture. The “pickle and oil” process is effective in removing substantially all of the iron oxide scale from the surfaces of the sheet metal, and results in surfaces that are suitable for most coating applications. However, the “pickle and oil” process has a number of disadvantages. For example, the oil applied to the sheet metal surfaces after pickling of the sheet metal must be removed before coating the sheet metal surfaces. The process of removing the oil is time consuming. Also, the hydrochloric acid used in the pickling process is an environmentally hazardous chemical which has special storage requirements and special disposal restrictions. Still further, the oil coating on the surfaces of the sheet metal interferes with some manufacturing processes, such as welding, and causes stacked sheets to stick together. The oil also gets into machine parts during manufacturing processes. In addition, while the pickling process is effective in removing substantially all of the iron oxide scale from the surfaces of the sheet metal and produces sheet metal surfaces that are suitable for most coating applications, the pickling agent, or hydrochloric acid, tends to leave a clean but slightly coarse surface.
Other methods of removing iron oxide scale from the surfaces of processed sheet metal have been tried, but these other methods have proven to be more costly than the “pickle and oil” process. For example, sheet metal processors have attempted to use brushes to completely remove scale from the surfaces of sheet metal. By this method, the sheet metal is passed between a pair of counter-rotating large cylindrical brushes. The bristles of the brushes impact against the surfaces of the sheet metal to remove the scale from the surfaces. However, it was found that brushing the surfaces of the sheet metal alone would not adequately remove the iron oxide scale from the sheet metal surfaces. In addition, when the brushes were used aggressively to remove the iron oxide scale from the sheet metal surfaces, the wear on the brushes was increased. This required a frequent replacement of the brushes which substantially increased the costs of removing iron oxide scale using brushes alone over the cost of removing iron oxide scale by the prior art “pickle and oil” process.
There remains a need for producing sheet metal having surfaces free from iron oxide scale in an economical manner and in an environmentally friendly manner.
The apparatus of the invention and the method of using the apparatus produce sheet metal having smooth surfaces substantially free of iron oxide scale without requiring a “pickle and oil” process. The apparatus of the invention is a novel combination of a strip casting assembly and a sheet metal processing assembly that uses a novel combination of brushes instead of “pickle and oil.” The sheet metal processing assembly employs pairs of stainless steel brushes and pairs of aluminum oxide brushes to produce sheet metal with smooth, scale-free surfaces in an economical and environmentally-friendly method.
The apparatus of the invention comprises a substantially conventional strip casting assembly. The strip casting assembly includes a pair of counter-rotating rolls that receive molten steel from a refractory core nozzle of the assembly. The counter-rotating rolls produce a sheet of metal from the molten steel. The sheet of metal is passed through a stand of hot rolling rollers that flatten the sheet metal and form the sheet metal into a desired thickness. The sheet metal is then water cooled and passes into the scale removal and processing assembly of the invention.
In the scale removal and processing assembly, the sheet metal first passes between a pair of counter-rotating stainless steel wire brushes. Although the stainless steel brushes would not typically remove scale on conventionally processed sheet metal, the combination of the stainless steel brushes working on the surfaces of the cast strip sheet metal removes all of the iron oxide scale from the surfaces of the sheet metal. However, the stainless steel brushes acting against the opposite sides of the sheet metal rough up the sheet metal surfaces. This undesired effect on the surfaces of the cast strip sheet metal is corrected by the sheet metal next passing through the aluminum oxide brushes. Pairs of counter-rotating aluminum oxide brushes act against the surfaces of the sheet metal from which the scale has been removed by the stainless steel brushes. The aluminum oxide brushes smooth and further clean the surfaces of the sheet metal. As a result, cast strip sheet metal that is free of scale is produced. This cast strip sheet metal can be coiled or cut into sheets for further processing.
Because the apparatus of the invention employs a substantially conventional strip casting assembly, the strip casting assembly of the invention is represented schematically in
The apparatus of the invention shown in
As the liquid metal 26 contacts between the pair of casting rolls 22, 24 the metal begins to cool. Two metal sheets are formed on each roll 22, 24 as the metal cools. The counter-rotating casting rolls 22, 24 bring the two metal sheets together to form one continuous cast metal strip 28 as the two sheets are brought together between the rolls 22, 24. This continuous strip of metal 28 exits from between the casting rolls 22, 24 and pass through a hot rolling stand 32.
At the hot rolling stand 32, the sheet metal strip 28 is passed through a pair of counter-rotating reduction rolls 34, 36 where the strip is reduced to the desired dimensions. Although only one hot rolling stand 32 is shown in
Following the passage of the strip 28 through the hot rolling stand 32, the strip 28 is then passed through a water cooling station 38. At the water cooling station 38 a plurality of nozzles 42 spray water against the opposite surfaces of the metal strip 28 to cool the strip. The water cooling station 38 reduces the temperature of the metal strip 28 from its rolling temperature to a temperature that is suitable for the further surface conditioning of the strip to be described.
The cast strip 28 is next passed through the scale removal and processing assembly 48 of the invention. The scale removal and processing assembly 48 is comprised of at least one pair of counter-rotating, metal wire brushes 52, 54 and at least one pair of counter-rotating conditioning brushes 56, 58.
In the preferred embodiment of the invention, the counter-rotating metal wire brushes 52, 54 are stainless steel wire brushes. Although stainless steel brushes would not typically remove scale on conventionally processed sheet metal to a degree comparable to a “pickle and oil” process, the combination of the stainless steel brushes 52, 54 working with the surfaces of the cast strip sheet metal 28 removes all of the iron oxide scale from the surfaces of the sheet metal strip. The metal wire brushes 52, 54 have axes of rotation 62, 64 that are positioned parallel to each other and transverse to the direction of travel of the cast metal strip 28 between the brushes. It is preferred that the stainless steel wire brushes 52, 54 be constructed of 0.012 of an inch crimped wire. The stainless steel wire brushes 52, 54 are also preferably constructed with an outside diameter dimension from 10 to 18 inches, and most preferably with an 8.625 inch inside diameter, and a 14 inch outside diameter with heavy density stainless steel crimped wire.
As the metal cast strip 28 passes between the pair of counter-rotating stainless steel wire brushes 52, 54, the wire brushes remove substantially all of the iron oxide scale from the surfaces of the strip 28. However, the stainless steel brushes 52, 54 acting against the surfaces of the sheet metal strip 28 rough up the surfaces of the strip. This undesired effect on the surfaces of the cast strip sheet metal 28 is corrected by passing the sheet metal through the pairs of conditioning brushes 56, 58.
The drawing figure discloses two pairs of conditioning brushes 56, 58 in the scale removal and processing assembly 48 of the invention. It should be understood that this number of conditioning brushes is illustrative only, and one pair of the conditioning brushes could be used, as well as additional pairs of conditioning brushes. In the preferred embodiment of the invention, the counter-rotating conditioning brushes 56, 58 have axes of rotation 66, 68 that are parallel to each other and are positioned on opposite sides of the cast strip 28 in transverse orientations to the direction of movement of the cast strip. It is also preferred that the conditioning brushes 62, 64 be aluminum oxide brushes. An example of such a brush is offered by the 3M Company, brand SPR-22838C aluminum oxide 7A fine clean and finish XDR brush. As the scale-free cast strip 28 is passed through the opposing pair of conditioning brushes 56, 58, the conditioning brushes smooth and further clean the surfaces of the cast metal strip 28. As a result, the cast metal strip 28 that exits from the scale removal and processing assembly 48 is free of scale and has smooth, clean surfaces.
Although the apparatus and method of the invention have been described above by reference to a specific embodiment of the invention, it should be understood that variations and modifications could be made to the invention described without departing from the intended scope of the following claims.
