Abstract:
A wiping system for removing liquids such as lubricant and coolant liquids from the surfaces of a metallic strip. The system comprises upper and lower wiper rolls for wiping the upper and lower surfaces of the strip. The wiper rolls each comprise a metal core and a porous resilient covering. At least one upper backup roll for said upper wiper roll and at least one lower backup roll for said lower wiper roll providing support for said wiper rolls; urging said wiper rolls against their respective strip surfaces resulting in the formation of a liquid bead on each surface of said strip at the entry end of the wiper roll nip; and engaging their respective wiper rolls at contact zones at the entry ends of which beads of oil squeezed from said porous wiper roll covers are formed. A suction assembly is provided for each bead to remove liquid therefrom. The upper and lower backup rolls may be replaced by substantially identical clusters each comprising two intermediate or backup rolls and three sets of caster bearings.

Description:
TECHNICAL FIELD 
     The application relates to a roll-type system for wiping liquids from the surfaces of strip material, and more particularly to such a system wherein the wiping rolls have porous resilient coverings from which accumulated liquid can be squeezed by one or more back-up rolls for vacuum removal. 
     BACKGROUND ART 
     In the cold rolling of metals it is normally necessary to supply copious quantities of a liquid to provide lubrication and cooling for the rolls and the rolled strip. The energy of deformation of the rolled product appears as heat, which must be removed by the coolant in order to avoid excessive temperature of the strip and of the rolls. When rates of deformation are high, the rate of heat generation is high, and high coolant flow rates are necessary. For example, a Sendzimir mill rolling 50 inch wide stainless steel typically uses a coolant flow rate of around 1000 gallons per minute. 
     In general, the coolant medium is oil based, and typical types used are straight mineral oil, and water/oil emulsions, (usually containing about 5% to 12% oil) either based upon mineral oils, or upon vegetable oils such as palm oil. It is usual to incorporate chemical additives in the oil, such as extreme pressure (E.P.) additives to increase fill strength, anti-oxidants, anti-rust compounds (in case of water/oil emulsions), anti-foam compounds and the like. 
     Subsequent to the rolling process the strip is frequently transferred to a process for which it is necessary to have little or no coolant (or additives) remaining on its surface. For example, when coils are batch annealed, surface oil can cause &#34;stickers&#34; (where adjacent laps of the coil stick together) and &#34;staining&#34; (discoloration of strip surface due to impurities or additives in the coolant). In some cases the strip can be cleaned before being transferred to the next process, but even then, cleaning is an additional cost to the strip processing operation, and elimination or reduction of the requirement for cleaning is a very worthwhile objective. Furthermore, even coiling of strip with an oily surface is hazardous, particularly at light gauges, because &#34;telescoping&#34; of the coil can readily occur. &#34;Telescoping&#34; is a term of art used when adjacent laps of the coil slide over one another in an axial direction, causing the strip emerging from the rolling mill to be forced to the side, thus producing a mill wreck. Surface oil can also adversely affect the measurement accuracy of strip thickness measuring equipment. 
     For these reasons, it is usual to provide cold rolling mills with strip wipers, which have the function of wiping the oil from the surface of the strip as it emerges from the mill, usually before the strip reaches the strip thickness gauges. 
     U.S. Pat. No. 4,551,878 describes the various types of strip wipers that were in common use at the time of that patent&#39;s publication (1985). These types were (1) bar wipers, (2) air flow type wipers and (3) roll wipers. Roll wipers were commonly two roll wipers and three roll wipers, both types utilizing metal (usually steel or bronze) rolls. 
     Since 1985 a number of strip wipers have been installed around the world, usually of the two roll type, but in some cases of the three roll type, wherein the wiper rolls have consisted of a metal core with a covering of a porous resilient (i.e. sponge-like) material, which more readily conforms to the profile of the strip. 
     It is essential for the covering material to be porous--tests with polyurethane covering material of various degrees of hardness have been made, and it is found that a hydrodynamic oil film develops readily between this covering and the strip which is so free of friction that the wiper rolls (mounted in roll bearings) do not rotate as the strip is passing through, and thus not only do not wipe the strip very well, but can cause scratches if any metal chips embed themselves in the covering. Using a porous covering seems to prevent the formation of a hydrodynamic oil film, probably because as the hydrodynamic pressure starts to develop, it forces the oil into the covering. 
     Commercially available porous resilient materials are usually made from non-woven fabrics, such as those supplied by 3M Co. (3M Brand Mill Rolls, 3M Abrasives Division), and by Armstrong Koverkwik of Pittsburgh under the designation Toho &#34;NON-TEX&#34; roll coverings. 
     In general, strip wipers utilizing rolls covered with porous resilient materials have performed quite well, particularly when used for wiping water/oil emulsions from the strip. For wiping mineral oil (used as a coolant on many mills) the performance is not so good, probably because the surface tension of oils is much lower than that of water, and the effectiveness of the wiper rolls in removing liquid from the strip is at least partially dependant upon capillary action, which is governed strongly by surface tension. 
     In trying to improve the performance of such wipers, U.S. Pat. No. 4,769,924 teaches the use of a hollow tubular core which is provided with radial holes. A vacuum is provided within this core so that any liquid absorbed into the porous covering will be sucked into the core and so removed by the vacuum generating device. 
     Although such a technique may work in some situations, we believe that, in the presence of particular contaminants that are generated by the rolling process (such as small metallic particles) the porous roll covering will act as a very effective filter which will trap the contaminants as the oil flows from the outer surface of the covering to the core, and the filter will become clogged with such particles, thus making the vacuum ineffective. 
     It is therefore a primary object of the present invention to provide an improved roll type strip wiping system which overcomes the above-noted problems of prior art systems. 
     DISCLOSURE OF THE INVENTION 
     According to the present invention there is provided an improved wiping system using rolls consisting of a metal core with a porous resilient covering, the improvement consisting of the provision of at least one metal backing roll for each wiper roll, which provides the functions of supporting the wiper roll and of generating a pinch point for wringing any absorbed oil out of the porous roll covering, and of the provision of suction devices for removing oil which has accumulated on the strip ahead of the nip and at the entry to the pinch point. The backing roll provides the additional advantage of reduced deflection under load, because it can be made much larger than the metal core of the wiper rolls, and enables the wiper rolls themselves to be much smaller and therefore more efficient and less costly than would otherwise be the case. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary elevational view, partly in cross-section, of an exemplary prior art two-roll wiper assembly. 
     FIG. 2 is a simplified cross-sectional view taken along section line 2--2 of FIG. 1. 
     FIG. 3 is a fragmentary cross-sectional view, partly in cross-section, of one embodiment of the roll type strip wiping system of the present invention. 
     FIG. 4 is a simplified cross-sectional view taken along section line 4--4 of FIG. 3. 
     FIG. 5 is an end view of the structure of FIG. 3, as seen from the left of FIG. 3. 
     FIG. 6 is a simplified cross-sectional view of another embodiment of the roll type strip wiping system of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIGS. 1 and 2 a prior art two roll wiper system is shown. The prior art system comprises an upper wiper roll 8 and a lower wiper roll 9. The upper roll 8 consists of a porous resilient cover 11a mounted upon a core 12. The lower roll consists of a porous resilient cover 11b mounted on a core 13. The cores 12 and 13 of upper and lower rolls 8 and 9 can be either a solid core like core 12 of upper roll 8 or a hollow core like core 13 of lower roll 9. It will be noted that core 13 is provided with perforations 14 through which liquid can be drawn out of cover 11b by the application of vacuum, which is applied by means of rotary coupling 20 and pipe 21. It will be understood that FIGS. 1 and 2 are for illustrative purposes only. In practice, both the upper and lower wiper rolls 8 and 9 would have either a solid core 12 or a perforated hollow core 13, together with rotary union 20 and pipe 21 to connect each hollow core 13 to a vacuum source (not shown). 
     As can be seen in FIG. 1, cores 12 and 13 extend past the end of their respective roll covers 11a and 11b and are provided with bearings 15a-15b and 15c-15d. The bearings 15a and 15b of upper roll 8 are mounted within chocks 16a and 16b, respectively. Similarly, bearings 15c and 15d of lower roll 9 are mounted in chocks 16c and 16d, respectively. Chocks 16a and 16c are guidably mounted in frame-like housing 18a, while chocks 16b and 16d are guidably mounted in frame-like housing 18b. The lower chocks 16c and 16d of lower roll 9 are supported on blocks 19a and 19b within frame housings 18a and 18b, respectively. The upper chocks 16a and 16b of upper roll 8 are connected to piston rods 22a and 22b of cylinders 17a and 17b, respectively. The cylinders 17a and 17b are used to raise and lower the assembly of the upper wiper roll 8, its bearings 15a and 15b and its chocks 16a and 16b, in order to open and close the wiper system to allow threading of strip 10 between rolls 8 and 9. As this assembly is raised and lowered, it is guided by the chocks 16a and 16b sliding within the housings 18a and 18b, respectively. 
     In operation, the wiper rolls 8 and 9 are closed upon the strip 10 which passes through these rolls as it emerges from the rolling mill or other device which applies liquid to the strip. Cylinders 17a and 17b are required to apply sufficient force that the wiper rolls 8 and 9 are pressed firmly against the strip 10. In an exemplary situation, a force of about 100 pounds per inch of strip width may be applied. As a result, cores 12 and 13 bend, and it is necessary to grind a crown on the outside covers 11a and 11b to achieve uniform pressure between wiper rolls 8 and 9 and strip 10 at every point across the width of the strip. 
     Because all points on the surface of covers 11a and 11b are driven by the strip 10 at the speed of the strip, the center portions of the covers, which, because of the crown are at a larger diameter than the end portions of the covers, tend to rotate at a smaller angular speed. This produces a twisting torque on each cover 11a and 11b and it is essential to key or bond the covers to their respective cores in order to transmit the twisting torque to the cores and thus prevent twisting of the covers, themselves. 
     In FIGS. 3, 4 and 5, there is shown a two-roll wiper according to one embodiment of the present invention. In the arrangement of FIGS. 3-5, the wiper rolls 29 and 30 comprise metal cores 32a and 32b (which can be either solid or hollow, as described above) and porous resilient covers 31a and 31b. The cores 32a and 32b extend beyond the length of their respective covers 31a and 31b. Core 32a is provided with bearings 50a and 50b mounted in chocks 46a and 46b, respectively. The core 32b is provided with bearings 50c and 50d mounted in chocks 46c and 46d, respectively. Wiper rolls 29 and 30 are supported by back-up rolls 43a and 43b, respectively. Upper back-up roll 43a may comprise a hollow body 43c with stub shafts 44a and 44b welded to each end thereof. Similarly, lower back-up roll 43b may comprise a hollow body 43d to the ends of which stub shafts 44c and 44d are welded. The stub shafts 44a and 44b of upper back-up roll 43a are mounted by means of anti-friction (ball or roller) bearings 45a and 45b within upper back-up roll chocks 42a and 42b, respectively. Similarly, the stub shafts 44c and 44d of lower back-up roll 43b are mounted by means of anti-friction (ball or roll) bearings 45c and 45d within lower back-up roll chocks 42c and 42d, respectively. Upper and lower back-up roll chocks 42a and 42c are guidably mounted within frame-like housing 47a, in which they are free to slide up and down. Similarly, upper and lower back-up roll chocks 42b and 42d are guidably mounted within frame-like housing 47b in which they are also free to slide up and down. Chocks 42c and 42d for lower back-up roll 43b sit on spacers 49a and 49b, respectively at the bottom of the windows 51a and 51b defined by each housing 47a and 47b, respectively. These spacers are located in recesses in lower back-up roll chocks 42c and 42d and the housings 47a and 47b in order to locate the lower back-up roll 43b axially within the housings 47a and 47b. The chocks 42a and 42b of upper back-up roll 43a may be raised and lowered by hydraulic cylinders 48a and 48b, respectively. Cylinders 48a and 48b have piston rods 52a and 52b, respectively, which are attached to chocks 42a and 42b by retainers 53a and 53b. Cylinders 48a and 48b are mounted on housings 47a and 47b, respectively. 
     Wiper roll chocks 46a, 46b, 46c and 47d are slidably mounted in back-up roll chocks 42a, 42b, 42c and 42d, respectively. Since the back-up roll chocks 42a, 42b, 42c and 42d are constrained to move up and down only by their guidable mountings within housings 47a and 47b, the wiper roll chocks 46a, 46b, 46c and 46d are similarly constrained by their guiding within the back-up chocks, it will be understood that the wiper rolls 29 and 30 will be prevented from moving in a horizontal direction parallel to the direction of movement of the strip 10. 
     During operation of the wiper system of FIGS. 3, 4 and 5, the strip 10 passes between the wiper rolls 29 and 30, and is squeezed by the wiper rolls by the hydraulic cylinders 48a and 48b acting through back-up rolls 43a and 43b. A squeezing force of the order of 100 pounds per inch of strip width is applied. The incoming strip 10 has a coating of liquid on its upper and lower surfaces, and the squeezing action of the hydraulic cylinders 48a and 48b on the wiper rolls 29 and 30 causes the porous coverings 31a and 31b of the wiper rolls 29 and 30 to compress against the strip 10 and also against back-up rolls 43a and 43b. 
     This has two effects. First, the wiper rolls 29 and 30 act as a dam which prevents the liquid on the strip from passing through the nip. As a consequence, beads of liquid 38a and 38b build up on the top and bottom surfaces of strip 10 at the entry side of the nip (see FIG. 4). Secondly, any liquid which has soaked into the porous coverings 31a and 31b is squeezed out by the pressure of the respective back-up rolls 43a and 43b on coverings 31a and 31b of the wiper rolls, thus forming beads of liquid 33a and 33b at the entry side of the contact zones between back-up rolls 43a and 43b and coverings 31a and 31b of the wiper rolls, as shown in FIG. 4. 
     Suction headers 39a and 39b are used to remove liquid from beads 38a and 38b, respectively. The headers 39a and 39b extend across the full length of their respective wiper roll coverings 31a and 31b and the body portion of their respective back-up rolls 43a and 43b. The headers 39a and 39b include interior flow channels 40a and 40b, respectively, which are connected to an external vacuum source (not shown). A series of slots or holes 41 extend along the full length of header 39a, through which liquid from bead 38, together with some ambient air, is drawn by the action of the vacuum source into flow channel 40a and towards the vacuum source. It will be noted in FIG. 4 that header 39b is provided with a similar series of slots or holes 41b, serving the same purpose as slots or holes 41a. 
     In a similar fashion, suction headers 34a and 34b are used to remove liquid from beads 33a and 33b, respectively. Headers 34a and 34b extend across the full length of their respective wiper roll coverings 31a and 31b and the bodies of their respective back-up rolls 43a and 43b. The headers 34a and 34b are provided with flow channels 35a and 35b which are connected to an external vacuum source (not shown). As in the case of headers 39a and 39b, the headers 35a and 35b are provided with a series of slots or holes 36a and 36b, respectively, extending the full length of the headers and through which liquid from the bead 33a and 33b, together with some ambient air are drawn by the action of the vacuum source into flow channels 35a and 35b, respectively, and toward the vacuum source. 
     In FIG. 3, only the lower suction header 34b has been shown, for purposes of clarity. It can be seen that the header 34b extends across the full length of back-up roll body 43d and wiper roll covering 31b. A pipe 56 extends from one end of the header 34b, connecting flow channel 35b thereof to the external vacuum source (not shown). 
     It will be noted that gaps 55a and 55b exist between the upper and lower roll coverings 31a and 31b at each side of strip 10. One of the problems with prior art wiper rolls is that liquid passes through these gaps 55a and 55b and builds up on the outer surfaces of wiper roll coverings 31a and 31b. Eventually, this build up of liquid transfers to the edge of the strip 10 exiting the wiper system, forming a bead on each strip edge which is undesirable. 
     In the system of the present invention, the squeezing action of back-up rolls 43a and 43b against the coverings 31a and 31b of wiper rolls 29 and 30 prevents this surface liquid from passing through the contact zone between the back-up rolls and their respective wiper rolls, and causes the surface liquid to accumulate in beads 38a and 38b from which the liquid is extracted by the vacuum action of manifolds 39a and 39b, as described above. Thus, the build-up of liquid on the outer surface of wiper roll coverings 31a and 31b at each side of the strip is prevented, greatly improving wiping efficiency at the edges of strip 10. 
     Another embodiment of the present invention is shown in cross-section and in simplified form in FIG. 6. In this embodiment, the back-up rolls 43a and 43b are replaced by substantially identical upper and lower clusters. The upper cluster comprises intermediate rolls 62 and 63, and three sets of caster bearings 64 spaced at intervals across the width of the intermediate rolls 62 and 63, and mounted in a carrier 65. The carrier 65 is spring mounted via spring 66 to frame 67. Upper frame 67 can be raised and lowered relative to lower frame 67a by means of hydraulic cylinders (not shown) to provide a gap between the wiper rolls for threading the strip. Additional sealing is provided by elastomer seal 68 which prevents the liquid on the surface of strip 10, as it enters the wiper assembly, from splashing over the top of intermediate rolls 62 and 63, thus by-passing the wiper roll 29. These features are similar to those disclosed in commonly owned U.S. Pat. Nos. 4,551,878 and 4,843,673, the teachings of which are incorporated herein by reference. It will be understood that the lower cluster is substantially the same as the upper cluster and like parts have been given like index numerals followed by &#34;a&#34;. Thus, the lower cluster comprises intermediate rolls 62a and 63a and three sets of caster bearings 64a spaced at intervals across the width of the intermediate rolls 62a and 63a and mounted in a carrier 65a. The carrier 65a is spring mounted to frame 67a via spring 66a. The lower cluster is provided with an elastomer seal 68a similar to the seal 68. 
     Because the porous resilient wiper roll covers 31a and 31b are too soft to be adequately supported by caster bearings spaced at intervals therealong, it is necessary to use hardened steel intermediate rolls 62, 63, 62a and 63a to support wiper rolls 29 and 30. It will be noted that intermediate rolls 62 and 63 are of the same length as the cover 31a of wiper roll 29 and intermediate rolls 62a and 63a are of the same length as the cover 41b of wiper roll 30. Because of this, the intermediate rolls provide continuous support for their respective wiper rolls. As indicated above, intermediate rolls 62 and 63 and intermediate rolls 62a and 63a are supported by their respective sets of caster bearings 64 and 64a. As a result of this, the wiper rolls 29 and 30 and the intermediate rolls 62, 63, 62a and 63a are fully supported in horizontal and vertical planes. Most importantly, this construction enables smaller (and therefore more efficient) wiper rolls to be used, than is the case with respect to the embodiment of FIGS. 3, 4 and 5. 
     In the embodiment of FIG. 6, manifolds 39a and 39b serve the same purpose as manifolds 39a and 39b of FIG. 4. Manifolds 34a and 34b remove beads 33a and 33b, respectively. The bead 33a is formed between wiper roll 29 and support roll 63. Similarly, manifold 34b removes the bead 33b formed between wiper roll 30b and support roll 63a. It should be noted that since there are two support rolls for each wiper roll, it is primarily the exit side support rolls 63 and 63a which provide the squeezing force which forces the liquid which has soaked into wiper roll coverings 31a and 31b to be squeezed out, thus forming beads 33a and 33b which are removed by suction manifolds 34a and 34b. 
     Modifications may be made in the invention without departing from the spirit of it.