60/120,572 filed 02/18/99.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to rolling mills having work rolls mounted in cantilever fashion on the ends of roll shafts, and is concerned in particular with an improvement in the tapered sleeves used to secure such rolls on taper neck sections of the roll shafts.

2. Description of the Prior Art In the typical finishing block of a modem day high speed rod mill, ring-shaped carbide work rolls are mounted in cantilever fashion on the exposed ends of roll shafts.

The shaft axes of successive roll pairs are offset by 90° to effect twist free rolling. The work rolls have grooved outer surfaces, and smooth cylindrical bores received on tapered neck sections of the roll shafts. Taper sleeves are inserted between the tapered shaft neck sections and the cylindrical roll bores. The taper sleeves serve to concentrically locate and radially support the work rolls, and to transmit torque from the roll shafts to the rolls.

When the roll grooves become worn, the work rolls must be removed and either replaced (or in the case where the rolls have multiple grooves, reversed). This entails extraction and reinsertion of the taper sleeves, which in turn subjects the interior and exterior sleeve surfaces to wear, pitting and corrosion.

As the taper sleeves wear, their ability to adequately support and transmit torque to the work rolls is gradually compromised to the point where they must be discarded, at considerable cost to the mill operator. Useful sleeve life during normal service will typically range from 6-12 months. Failure to make timely sleeve replacements can lead to roll slippage or breakage, resulting in product cobbles and even more costly mill down time.

The objective of the present invention is to significantly increase useful sleeve

life, thereby providing mill operators with a beneficial savings in operating costs.

SUMMARY OF THE INVENTION In accordance with the present invention, a wear and corrosion resistant coating is applied to at least the critical interior and exterior sleeve surfaces in contact respectively with the tapered neck section of the roll shaft and the cylindrical roll bore. The coating is selected from the group consisting of titanium nitride, titanium carbonitride and chrome nitride, with titanium nitride being preferred, and with the coating being applied to an optimum thickness to achieve the desired result, typically not more than about 0.0025mm. The resulting increase in surface hardness significantly improves resistance to wear, pitting and corrosion.

These and other objectives and advantages of the present invention will now be described in greater detail with reference to the accompanying drawings, wherein: BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a sectional view taken through a typical cantilevered roll mounting assembly; and Figure 2 is a partial longitudinal sectional view on an enlarged scale of the tapered sleeve shown in Figure 1, with the wear resistant coating thickness exaggerated for purposes of illustration.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT With reference initially to Figure 1, a typical cantilevered roll mounting assembly is generally depicted at 10 comprising a roll shaft 12 journalled for rotation in a sleeve bearing 14 fixed within an eccentrically bored cartridge 16. The cartridge 16 is in turn rotatably supported in a roll housing 18.

The roll shaft has a tapered neck section 20 leading to a reduced diameter end 22.

A ring-shaped carbide roll 24 has a cylindrical bore 26 and an outer surface grooved as at

28. The roll 24 is mounted on the shaft 12 by means of a taper sleeve 30 axially wedged between the roll bore 26 and the tapered neck section 20.

A seal end plate 32 and seal assembly 34 serve to retain lubricant in the housing 18 while excluding external contaminants such as cooling water and entrained dirt and mill scale. An end cover 36 and retaining bolt 38 completes the assembly.

The sleeve 30 locates the roll 24 concentrically on the tapered neck section 20, provides radial support for the roll, and also serves as the means for transmitting torque from the shaft 12 to the roll. Each of these functions is dependent upon a precise fit between the tapered neck section 20 and the tapered interior surface 40 of the sleeve, as well as between the cylindrical outer surface 42 of the sleeve and the cylindrical bore 26 of the roll.

As the sleeve surfaces 40 and 42 undergo wear as a result of the sleeve being extracted and reinserted during roll changes, this precise fit is gradually compromised and eventually lost, requiring the sleeve to be discarded.

The sleeves are typically machined from alloyed carbon steel or stainless steel, with a through hardness of about 360-380 BHN. As mentioned previously, useful sleeve life during normal service will typically range from 6-12 months. If sleeves are allowed to remain in service for longer periods, roll slippage and/or breakage may occur because of sleeve wear.

In accordance with the present invention, and as can best be seen in Figure 2 where thickness dimensions have been exaggerated for purposes of disclosure, a wear resistant coating 44 is applied to at least the sleeve surfaces 40 and 42. The coating material is selected from the group consisting of titanium nitride, titanium carbonitride and chrome nitride, with titanium nitride being preferred. Coatings are applied to a thickness which is sufficient to achieve the desired hardness and resistance to wear, and preferably does not exceed about 0.0025mm, resulting in an increase in surface hardness to at least about 700 BHN.

Experience thus far with titanium nitride coated sleeves has shown that useful sleeve life is extended for as much as three times the life of uncoated sleeves operating under the same conditions.

I claim: