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This invention relates to transfer roller tables such as are employed in hot strip mills for the production of steel strip and the rolls for such tables. It is concerned in particular with the arrangement of rolls in a transfer table.
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During the production of strip steel it is desirable to limit as far as possible the cooling of the transfer bars from which the strip is produced by successive rolling passes. For this reason insulating thermal panels are often placed around the material path along the transfer roller tables between which the transfer bars are passed.
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It is known that relatively high efficiency thermal insulating panels can be provided employing a thin-walled construction which has a low thermal mass so that a heat resistant alloy membrane of the panel facing onto the path of the transfer bars is quickly heated to the temperature of the bars. An example of such a thermal panel is described in GB 1603428, for example.
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Although such insulating panels can partially shield the transfer table rolls from the heat of a transfer bar, they may not be able to offer sufficient protection to avoid damage to the supporting bearings at the ends of each roll. Various forms of cooling have been devised to avoid this known problem.
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Thus, it is known to cool transfer table rolls by a water spray but this cannot be done if thin-walled thermal insulating panels are present. The hot membranes of such panels are susceptible to damage from cooling sprays with the result that the useful working life of the panels is severely reduced. That problem can be avoided by providing internal cooling channels in the rolls but it is a very costly solution.
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It has also been proposed to cool the ends of the rolls externally, between each end bearing of a roll and its main body, by means of water jets. Although the water is not sprayed onto the main body of the roll, it is apparent that the known arrangements may not provide a satisfactory solution either. It is found that they do not prevent water from reaching the main body of the roll when the roll is rotating, and the water is then flung off by centrifugal force to impinge on the heat-insulating panels.
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According to one aspect of the present invention, there is provided a roll arrangement for a rolling mill having a roll comprising a main roll body having a neck at one or both ends of said main body, means on the or each said neck for locating the roll in a supporting bearing, a collar on the or each roll neck between said bearing location means and said roll body, and means for delivering a cooling liquid to said roll neck or necks comprising a cover or cowl over the or each said neck and within which the liquid is supplied, the side of said collar facing the main roll body having a tapering form that reduces towards said main body.
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In another aspect of the invention a roll is provided for use in a roll arrangement as aforesaid, said roll having a generally cylindrical main roll body having neck portions extending from opposite ends, said neck portions having means for locating the roll in supporting bearings, between said bearing location means and the roll main body each neck portion being provided with a collar, the side of said collar facing the main roll body having a tapering form with a radial dimension that reduces towards said main body.
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Preferably, said side of the collar facing the main body is generally conically tapered towards the main body. The taper angle is preferably in the range 40°-50°, although it may be possible to obtain satisfactory results with angles ±20° from a most preferred angle of 45°. The presence of the tapered side face has the effect that water clinging to the face is subjected to a centrifugal force gradient that increases towards the maximum diameter of the collar and thus urges the water away from the main body of the roll. The opposite face of the collar may be normal to the roll axis or it may also be inclined.
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It is also preferred to arrange that the major diameter of the collar is not substantially less than the diameter of the main body of the roll. With current roller table travel speeds, this can ensure a correspondingly large centrifugal force is applied to water on the surface of the collar near that region to cause it to be flung off within the cover and run safely to waste.
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In another preferred feature, the tapering form of said side of the collar extends axially of the roll beyond the cover or cowl.
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The invention will be further described by way of example with reference to the accompanying drawings, in which:
- Fig. 1 is a partially sectioned view at one end of a roll of a known roll arrangement on a transfer roller table,
- Fig. 2 is a similar view to Fig. 1 of a roll arrangement according to the invention, and
- Fig. 3 is a side view of one end of a roll illustrating a modified arrangement according to the invention.
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The known arrangement in Fig. 1 is illustrated by one roll 2 of a series of similar rolls of a transfer roller table supported on the table base frame 4 through rotary bearings 6 on mountings 8 at opposite sides of the base frame. For this purpose at each end the roll has an integral neck 10 on which the bearing 6 is fitted. The bearing is located on the roll neck 10 by keepers 12 which are themselves located in the mounting 8 by end plates 14 secured by through bolts 16. The other end of the roll can be arranged similarly to the illustrated end and one end of the roll may also be provided with drive means.
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In the operation of the table, the heat from the transfer slabs on the rolls can cause excessive temperatures in the roll bearings that would cause them to break down. Between each bearing 6 and the cylindrical main body 18 of the roll, means are therefore provided to deliver cooling water so as to moderate the temperature of the bearing against the influence of hot transfer slabs on the roller table. The water is delivered by a pipe 19 into a cowl 20 secured to the inner end plate 14 of the mounting 6. The cowl 20 is shown with a port 22 in its underside to allow the water to escape freely to the flumes (not shown) that run in the usual manner under the base frame 4. The cowl covers a collar 26 on the roll neck and comprises an axially inner end wall 24 that, in co-operation with the collar shields the main body 18 of the roll against water spray.
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The collar 26 is in the form of a cylindrical flange located within the cowl 20 and overlapping the inner end wall 24 of the cowl radially. As the arrows A indicate, one function of the collar is to deflect water from the nozzle towards the bearing housing and it also blocks any direct path for spray past the cowl end wall onto the main body of the roll.
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It is found, however, that when the transfer table is operated water tends to escape past the collar 26 and onto the main body 18 of the roll, from where it is flung off by centrifugal force as indicated by the arrows B and C, and can thus land on an adjacent insulating panel (not shown). It appears that although the side of the collar 26 facing the bearing 6 performs its intended function and any water that reaches the outer rim of the collar is normally flung off by centrifugal force when the roller table is in operation, whether onto the cowl or direct to a drain below (not shown), that does not prevent the passage of water towards the main body of the roll. It can be expected that although the water is allowed to drain away freely, it is splashed about inside the cowl 20 and much of the water landing on the upper region of the internal peripheral wall of the cowl will fall back onto the roll. Some of that water will fall onto the necked portion 32 of the roll between the flange and the main body. Because of its smaller diameter, less centrifugal force is generated on the surface of the necked portion 32 the water therefore clings to the surface. Perhaps due to surface tension at least some of this water spreads along the surface until it reaches the end face of the main body 18 of the roll where, because of the increase of diameter, it is finally flung off by the centrifugal force, with the potentially damaging effect already referred to.
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Fig. 2 illustrates an alternative roll arrangement according to the invention which is intended to counter the problem described. Parts identical to those described with reference to Fig. 1 are indicated by the same reference numerals.
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The arrangement according to the invention has an alternative form of collar 36 on each end of the roll. In particular, the collar 36 has an axially inner side 38 facing the main body 18 of the roll which is conically tapered towards that main body. It is preferred that the taper extends beyond the inner end of the cowl 20 towards the body.
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Being located between the water jet entry and the main body of the roll, the collar 36 functions in the same way as in the first-described arrangement in the manner in which it deflects the incoming water jet towards the bearing mounting 8. Water thrown against the inner peripheral face of the cowl 20 can fall back onto the roll, as already described, but it now falls upon the conically tapered surface 38. Although for at least some of its extent the surface 38 may not have a diameter sufficient to throw the water off again by centrifugal force, its tapered form results in that force creating a pressure gradient which acts on water clinging to the surface. That surface water is thereby drawn towards the outer rim of the collar 36 until it experiences sufficient centrifugal force to be thrown off the collar. The arrangement thus operates throughout the time the roll is being driven to move a hot transfer slab along the roller table to drive water away from the main body of the roll, thereby reducing or eliminating any spray that might fall on adjacent heat insulating panels.
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Arrow D in Fig. 2 indicates a water path, from the top of the cowl interior onto the tapered face and thence along that face towards the maximum diameter of the collar. As a result, the final escape path E of the water is thereby concentrated in the region between the bearing mounting and the maximum diameter region of the collar. The cowl 20 illustrated in Fig. 2 is in fact of an alternative configuration, in the shape of an inverted -U- entirely open to its underside, but the form of cowl shown in Fig. 1 can be employed if desired.
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By extending the tapered surface 38 of the collar axially inwardly beyond the cowl 20 it is also possible to capture water spray leaving the cowl on paths oblique to the roll axis.
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To create the maximum centrifugal force the outer diameter of the collar 38 is at least close to that of the main body of the roll. The taper of the inclined surface 38 of the collar is determined by a number of factors. It must have sufficient axial extent to collect the water that might escape towards the main body of the roll but there are space and cost penalties if the axial length is increased excessively. The illustrated example has an angle of taper of 45° and the preferred range is 40° to 50°. It is possible, however, to employ taper angles in a range of 25° to 65°.
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The axially outer surface 40 of the collar is shown normal to the roll axis but in some applications it may be slightly coned and it preferably has a substantial radius at the base of the collar to reduce stress concentrations.
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Although the roll 2 can be machined from the solid with the tapered collar, it is also possible to provide a fabricated sheet collar 46, as shown in Fig. 3. Such a collar is particularly suitable as a modification of an existing roll, such collars being welded or bolted to the necks of the roll to form a roll in accordance with the present invention.
