Abstract:
Apparatus and methods of texturing the surfaces of work rolls and the rolls produced thereby which are used in the manufacture of sheet metals and other sheet materials. The working surface of each roll is textured in a series of process steps which include the steps of media blasting and controlled surface modification. Media blasting can precede or follow controlled surface modification and intervening process steps can be used. Either or both process steps of media blasting or controlled surface modification can be carried out once or more than once as long as each process step is used at least once. The work rolls produced by the method exhibit improved performance and extended life.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is related to two additional patent applications filed on the same day as this application and having the titles: “WORK ROLLS HAVING AN ENGINEERED SURFACE TEXTURE PREPARED BY CONTROLLED SURFACE MODIFICATION AFTER CHROME COATING” and “CONTROLLED SURFACE MODIFICATION AS AN INTERMEDIATE STEP IN THE SURFACE TEXTURING OF WORK ROLLS.” 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention has to do with apparatus and methods for improving the surface characteristics of work rolls which are used in the manufacture of sheet metals and other sheet products. More specifically, the invention relates to the use of media blasting and controlled surface modification process steps in various combinations during the roll surface preparation process. Work rolls processed according to the invention exhibit enhanced mill performance and extended life.  
         [0004]     2. The Related Art  
         [0005]     In the manufacture of sheet steel, sheet aluminum and other sheet metal products, paper, plastics and other sheet materials, steel work rolls or cylinders (referred to herein as “rolls”) are employed in the finishing process, for example, in a steel mill, a paper mill or the like. The roll shape and surface are machined to a high degree of accuracy. Traditionally, the roll surface is textured by processes such as electrical discharge texturing (EDT), electron beam texturing (EBT), laser texturing, chemical etching, media blasting, such as sand blast, shot blast and shot peen and the like, as well as embossing. In some cases the roll surfaces are then coated by chrome deposition or chrome plating as a final step before the roll is sent to the mill to be used in the manufacture of sheet materials.  
         [0006]     The superfinishing process has been applied to roll surfaces following the EDT process in order to improve surface texture as described in published patent application No. 2005/0227594 A1. However, it has not previously been thought necessary to apply superfinishing or other controlled surface modification processes at certain other stages of the roll surface preparation process. We have now discovered that media blasting, for example, sand blasting or shot blasting the roll surface prior to or following controlled surface modification, whether or not there are intermediate process steps, unexpectedly enhances mill performance, extends roll life and extends the usefulness of other methods of texturing previously thought to be outdated.  
         [0007]     For many years, some form of media blast technology has been used to clean or texture work roll surfaces. The texture created by media blasting and/or the other process steps described herein helps with grip or bite in the mill and, for example, in the case of sheet steel used in automotive body applications, produces a strip or sheet having a better surface for paint adhesion and appearance, as well as better formability properties for deep drawing and stamping. Now we have discovered that controlled surface modification before or after media blasting improves work roll performance and extends work roll life. The process of the invention provides cleaner surfaces and makes it easier to place rolls previously run in a mill back into production. This allows for lower costs associated with less stock removal during subsequent grinding operations and, consequently, extended roll life. We have also discovered that the roll surface can optionally be chrome coated before or after media blasting and/or controlled surface modification, either before or after running the roll in a mill to make a sheet product.  
         [0008]     The term “controlled surface modification” is used herein to describe one or a combination of belt grinding, superfinishing, honing, microfinishing, micropolishing and other highly refined and controllable machining processes. The term “chrome coating” is used herein to describe any process of chrome plating or chrome deposition.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides apparatus and methods for applying a combination of a media blasting process step and a controlled surface modification process step to various stages of the roll surface preparation process. Controlled surface modification can be carried out before or after media blasting or before and after media blasting. Media blasting can be carried out before or after controlled surface modification or before and after controlled surface modification. Either or both process steps can be carried out more than once in order to obtain the desired surface characteristics on a work roll. Either process step also can be used as the final texturing step before a roll is placed into service at the mill, or the first texturing step after the roll is returned from the mill for reprocessing. In some cases, rolls textured according to the present invention can be reprocessed by media blasting or controlled surface modification and returned to the mill without the need for any further processing steps. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic elevational view of a sand blasting or media blasting apparatus for cleaning or texturing the working surface of a work roll.  
         [0011]      FIG. 2  is a schematic elevational view of a superfinishing apparatus for modifying the working surface of a work roll.  
         [0012]      FIG. 3  is a side view of a superfinishing apparatus in close proximity to a work roll.  
         [0013]      FIG. 4  is a top view of the superfinishing apparatus of  FIG. 3  in close proximity to a work roll. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     The rolls prepared according to the present invention are metal rolls that can be made from various ferrous or non-ferrous materials or combinations of both. In practice, the rolls are predominantly made with steel but they may optionally have an outer shell of copper or nickel. They also may be made from cast iron, tool steels, various alloys, titanium, tungsten carbide, combinations thereof and the like.  
         [0015]     The optional chrome coatings are well known in the art and can be carried out using the chrome deposition process or a traditional hard chrome plating bath. The coating thickness of the chrome coating required for particular applications is also well known to those having ordinary skill in the art.  
         [0016]     Media blasting is preferably performed inside a chamber but it can be performed in an open environment. Compressed air is the preferred means to deliver media to the surface of the roll in a manner which assures uniform coverage of the entire working surface of the roll. For example, the roll may be rotated or moved in some manner and the nozzle discharging the media may be moved. The media can be metallic, non-metallic, ceramic, plastic or chemical or some combination thereof. Some examples of media include sand, sodium bicarbonate, glass beads, aluminum oxide, cast steel shot, angular steel shot, cast steel grit and others. The term media blasting is used generically hereafter in this specification to include sand blasting, shot blasting, shot peen and the various methods and media referenced above and other methods and media known in the art.  
         [0017]     Electrical discharge texturing (EDT), also referred to as spark electroerosion or electroblast texturing, is a known process for texturing the working surface of a roll. The process involves the computer controlled spark erosion of the roll surface. Either the roll is partially or completely immersed in dielectric fluid or the electrodes are dammed off and covered with dielectric fluid or the end of the electrodes are flooded with dielectric fluid near the roll and controlled electrical current is generated and discharged through the dielectric fluid producing ionic charges or sparks of either positive or negative polarity which contact the roll surface. This charge melts the extreme outer layer of the roll, forming microscopic craters proportional in size and spacing to the energy supplied and frequency of generation. The result is an extremely precise, predictable and controllable texture on the roll surface.  
         [0018]     The use of electron beam texturing (EBT), laser texturing and chemical etching and embossing are also known to those having skill in the art.  
         [0019]     Referring to  FIG. 1 , roll  1  is rotatably mounted on journal bearing mounts  2 . Rotation is controlled by drive motor  3  through gear box  4  and driver  5 . Sand blaster  10  is provided with a hopper  11  for receiving media, inlet pipe  12  for compressed air input and nozzle  13  which can be controllably moved laterally in the directions of arrow  14 . During the media blasting process step, roll  1  is rotated either clockwise or counter-clockwise and media is blasted with compressed air through nozzle  13  as the nozzle laterally traverses the working surface  6  of roll  1 . Rotation of the roll  1  and lateral traversal by the nozzle  13  are controlled in coordination to obtain a uniform texture over the entire working surface  6  of the roll  1 . The working surface  6  can optionally be chrome coated prior to or following media blasting.  
         [0020]      FIG. 2  illustrates a superfinisher  20  mounted in close proximity to roll  1 . The superfinisher  20  laterally traverses the working surface  6  of roll  1  along guide rods  7  (one shown) in the directions of arrow  8 .  
         [0021]     The superfinishing apparatus  20  of the present invention is a type of continuous indexing belt finisher wherein fresh belt is continuously supplied to the surface being finished/ground/machined. The finishing belt, which comes in various grit sizes and configurations such as 9 μm to 100 μm Finishing Film or 2 μm to 30 μm Lapping Film, usually has a width from about 4 to 8 inches and a length from about 10 to about 60 yards is wound on a feed reel. As shown in  FIG. 3 , the belt  21  is fed from feed reel  22  to a guide roller  23 , a contact roller  24  and then to a take up reel  25 . The contact roller  24  is rotatably affixed to a spring loaded arm  26  which allows the contact roller  24  to apply a contact pressure to the belt  21  and thereby to the working surface  6  of the roll  1 . Accordingly, when the superfinisher  20  is processing the working surface  6 , the belt  21  is pressed against working surface  6  by contact roller  24 . The belt  21  moves continuously so that a fresh unused belt surface can be continuously applied to the working surface  6  of roll  1 . Guide holes  27  receive guide rods  7  (see  FIGS. 2 and 4 ) which facilitate lateral controlled movement of the superfinisher  20  along the working surface  6  of the roll  1 . The finishing belt can optionally be oscillated during some or all of the controlled surface modification steps to produce the desired surface characteristics.  
         [0022]     A suitable superfinishing apparatus is the Loser Model SF 100 available from Waldemar Löser KG Machinenfabrik, Postfach 1609, Boschstrasse 5, D67346 Speyer, Germany, or a GEM 04150-M or 08150-C Superfinisher available from Grinding Equipment &amp; Machinery Co., Inc., Box 2747, Youngstown, Ohio 44507 USA. Other equipment that can be used for controlled surface modification according to the present invention includes microfinishing systems and machines available from Industrial Metal Products Corporation, 3417 West St. Joseph Street, P.O. Box 10156, Lansing, Mich. 48901 USA or 3M Microfinishing Systems, Building 251-2A-08, 3M Center, St. Paul, Minn. 55144-1000 USA. Another example of suitable equipment is the centerless cylindrical finishing system available from Rand-Bright, 2900 S. 166 th  Street, New Berlin, Wis. 53151 USA or Supfina Maschinenfabrik Hertzen GmbH &amp; Co. KG, Postfach 100854, Greulingstrasse 33, D-5630 Remscheid, Germany.  
         [0023]      FIG. 4  is a top view of  FIG. 3 .  
         [0024]     The process of the present invention modifies the surface texture, characterized by various parameters as Ra, Rp, Pc, Rpk, Rpk*, Rvk, Rz, Rt, Rmax, t p , Rsk, etc, measured in micro-inches in the English system or micrometers in the metric system, that was present prior to the start of the controlled surface modification. The surface texture can be modified and tailored as required for optimal performance in different applications.  
         [0025]     In addition to media blasting and controlled surface modification, the working surface of the roll of the invention is normally subjected to other processes in order to achieve the desired texture. For example, the working surface of a roll can be processed in various combinations of sequential steps as follows but not always after an initial grinding operation to produce a roll having the desired shape:  
         [0026]     1. EDT, controlled surface modification and then media blasting;  
         [0027]     2. EDT, controlled surface modification, media blasting and then chrome coating;  
         [0028]     3. EDT, chrome coating, controlled surface modification and then media blasting;  
         [0029]     4. EDT, controlled surface modification, chrome coating and then media blasting;  
         [0030]     5. Media blasting, controlled surface modification, run in the mill and then media blasting;  
         [0031]     6. Media blasting, controlled surface modification, chrome coating, run in the mill and then media blasting;  
         [0032]     7. Controlled surface modification, run in the mill and then media blasting;  
         [0033]     8. Controlled surface modification, chrome coating, run in the mill and then media blasting;  
         [0034]     9. Controlled surface modification, EDT, controlled surface modification and then media blasting;  
         [0035]     10. Controlled surface modification, EDT, controlled surface modification, media blasting and then chrome coating;  
         [0036]     11. Controlled surface modification, EDT, chrome coating, controlled surface modification and then media blasting;  
         [0037]     12. Controlled surface modification, EDT, controlled surface modification, chrome coating then media blasting;  
         [0038]     13. Embossing, controlled surface modification, run in the mill and then media blasting;  
         [0039]     14. Embossing, controlled surface modification, chrome coating, run in the mill and then media blasting;  
         [0040]     15. Embossing, controlled surface modification, EDT, controlled surface modification and then media blasting;  
         [0041]     16. Embossing, controlled surface modification, EDT, controlled surface modification, media blasting, chrome coating;  
         [0042]     17. Embossing, controlled surface modification, EDT, chrome coating, controlled surface modification and then media blasting; or  
         [0043]     18. Embossing, controlled surface modification, EDT, controlled surface modification, chrome coating and then media blasting.  
         [0044]     The foregoing lists only a few examples of the combinations of processing sequences that can be used according to the invention. Other process sequences can be used and other texturing processes, for example, EBT, laser, chemical etching and/or embossing also can be used instead of or in addition to EDT or at any other stage of the process. The invention can be carried out using the combination of media blasting and controlled surface modification in any order and either process can be used once or more than once. Media blasting or controlled surface modification can be the final texturing step before the roll is sent to the mill or the first step when it is returned from the mill for reprocessing. Media blasting or controlled surface modification can precede chrome coating or one or both of media blasting or controlled surface modification can be carried out following chrome coating in cases where a chrome coated roll is needed.  
         [0045]     In some cases, a roll surface may be media blasted or controlled surface modified, or both, to clean it or texture it after it has been used (run) in a mill.