WORK ROLLS HAVING AN ENGINEERED SURFACE TEXTURE

PREPARED BY CONTROLLED SURFACE MODIFICATION

AFTER CHROME COATING CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to two other patent applications filed on the same day as this application and having the titles: 'WORK ROLLS SURFACE TEXTURED BY MEDIA BLASTING AND CONTROLLED SURFACE MODIFICATION" and "CONTROLLED SURFACE MODIFICATION AS AN INTERMEDIATE STEP (N THE SURFACE TEXTURING OF WORK ROLLS."

BACKGROUND OF THE INVENTION Field of the Invention

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 work rolls having a surface coating of hard chromium metal wherein the hard chromium metal surface texture has been modified to produce an engineered texture that is highly accurate, consistent and controlled. Work rolls processed according to the invention exhibit enhanced mill performance and extended life. The Related Art

In the manufacture of sheet steel, sheet aluminum and other sheet metal products, paper, plastics and other sheet materials, 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.

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 oilier stages of the roll surface preparation process.

For many years, chrome deposition or chrome plating have been applied over textured work roll surfaces to increase hardness and lubricity and extend roll life. It has been established and is well known to those skilled in the art that all chrome plating processes including chrome deposition have a propensity to produce a nodular deposit. Although process parameters have been developed to minimize their occurrence, the presence of nodules can have a deleterious effect on the roll performance in the mill by changing mill force requirements, finish transfer characteristics, strip quality and roll life.

We have now discovered that controlled surface modification of the roll surface following chrome deposition or chrome plating, whether or not there has been a prior application of controlled surface modification as intermediate process steps, improves roll performance unexpectedly and further extends roll life. This controlled surface modification also will provide the same results and benefits on any coating applied to the roll surface, for example, nickel, electroiess nickel, nickel iron, cobalt, tungsten carbide, alloys, just to name a few.

Media blasting, for example, sand blasting, is another roll surface treatment process step that can optionally be used with the present invention to clean or texture the roll surface. 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. The process of this invention improves roll life, 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, fewer grinding operations and, consequently, extended usable roll life time. The term "controlled surface modification" is used herein to describe one or a combination of belt grinding, superfinishing, honing, microfinishing, micropoiishing and other highly refined and controllable machining processes. The term "chrome coating" is used herein to describe any process for coating chrome on a substrate including the processes of chrome plating or chrome deposition. The term "texturing" is used

herein to describe any process used to produce a random surface or pattern of peaks and valleys that is not grinding, such as EDT, laser texturing, media blasting, EBT, chemical etching, embossing and the like.

SUMMARY OF THE INVENTION The present invention provides apparatus and methods for applying a combination of a chrome coating process step and one or more than one controlled surface modification process step to various stages of the roll surface preparation process. Controlled surface modification is carried out after chrome coating. Either or both the controlled surface modification or chrome coating process steps can be carried out more than once in order to obtain the desired surface characteristics on a roll. In some cases, roll surfaces prepared 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 Fig. 1 is a schematic elevational view of a sand blasting or media blasting apparatus for cleaning or texturing the working surface of a roll.

Fig. 2 is a schematic elevational view of a superfinishing apparatus for modifying the working surface of a roll.

Fig. 3 is a side view of a superfinishing apparatus in close proximity to a roll. Fig.4 is a top view of the superfinishing apparatus of Fig. 3 in close proximity to a roll.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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.

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.

When the optional process step of media blasting is employed, it 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 rofl 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 in this specification to include sand blasting, shot peen and the various methods and media referenced above and other methods and media known in the art. 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. The use of electron beam texturing (EBT), laser texturing and chemical etching and embossing are also known to those having skill in the art.

Referring to Fig. 1 , roll 1 is rotatabiy 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 be chrome coated following media blasting, if a media blasting step is used. Controlled surface modification can be optionally carried out prior to chrome coating and, according to the present invention, is carried out following chrome coating.

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.

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 and it 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 engineered controlled surface modification surface.

A suitable superfinishing apparatus is the Loser Model SF 100 available from Waldemar Lϋser KG Machinenfabrik, Postfach 1609, Boschstrasse 5, D67346 Speyer, Germany, or a GEM 04150-M or 08150-C Superfinisher available from Grinding Equipment & 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, Michigan 48901 USA or 3M Microfinishing Systems, Building 251-2A-08, 3M Center, St. Paul, Minnesota 55144-1000 USA. Another example of suitable equipment is the centerless cylindrical finishing system available from Rand-Bright, 2900 S. 166th Street, New Berlin, Wisconsin 53151 USA or Supfina Maschinenfabrik Hertzen GmbH & Co. KG, Postfach 100854, Greulingstrasse 33, D-5630 Remscheid, Germany.

Fig. 4 is a top view of Fig. 3.

The process of the present invention modifies the surface texture, characterized by various parameters as Ra, Rp, Pc, Rpk, Rpk*, Rvk, Rz, Rt, Rmax, tp, 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.

In addition to chrome coating 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 usually but not always after an initial grinding operation to produce a roll having the desired shape:

1. Texturing, chrome coating and then controlled surface modification;

2. Controlled surface modification, chrome coating, and then controlled surface modification; 3. Controlled surface modification, texturing, chrome coating and then controlled surface modification;

4. Texturing, controlled surface modification, chrome coating and then controlled surface modification;

5. Texturing, controlled surface modification, texturing, chrome coating and then controlled surface modification;

6. Texturing, controlled surface modification, texturing, controlled surface modification, chrome coating and then controlled surface modification.

The foregoing lists only a few examples of the combinations of processing sequences that can be used according to the invention. The invention can be carried out using the combination of chrome coating and controlled surface modification in any order and either process can be used once or more than once as long as one controlled surface modification process step is carried out following chrome coating. In some cases, a roll surface may be textured or controlled surface modification processed, or both, to clean it or texture it after it has been used (run) in a mill.