Horton utilizes various applications using the best performing materials to produce small and medium size rolls and to serve the needs of various types of mills, while maximizing productivity. We discuss in detail the strengths of each method and the criteria for producing the best results. We are proud to highlight our efficient melting practices; modern casting methods (whether through static means or through advanced centrifugal casting systems to produce Duplex Rolls); well-equipped heat treatment shops; flexible roll machining, process control using world-class equipment, testing procedures and service; and efficient and correct water cooling processes to prevent fire cracks and roll breakage.

Melting:

All melting is by variable frequency induction furnaces. These modern furnaces have automatic power input to maximize melting efficiency, and close computer control of composition and temperature of the charge.

Casting:

Our foundries are well equipped and specially designed to cast small and medium size rolls either by the static or centrifugal methods.

1. Centrifugal Casting

Due to the expanded requirements and demands of modern mills on rolls, since the mid-1990's an advance centrifugal casting (CC) system was introduced to our foundries to produce double pour (Duplex) rolls.

Double pour duplex rolls have been adopted as primary rolls for flat product rolling. The main reason for using duplex rolls is the flexibility to select the best performing material on the working layer. As for the necks and core, a high strength, softer, ductile material is used. The best wear resistant materials for the working layer are normally much harder, more brittle and of lower strength.

There are various methods to produce duplex rolls, but all duplex rolls from Horton are spun cast, meaning the shell material is always centrifugally cast. This is the most modern and effective method to produce duplex rolls.

In the horizontal centrifugal casting the shell metal is poured into a spinning horizontal chill. After shell solidification, the chill is raised to a vertical position and the core and neck metal is introduced.

Unlike static casting and because of the much reduced cross section of the shell metal, a faster cooling rate is obtained thereby ensuring the uniformity of the microstructure. The hardness penetration pattern becomes more consistent throughout the entire shell depth. This translates into finer and more evenly distributed graphite nodules giving a higher thermal fatigue resistance; less continuous carbide content and higher crack resistance; the dendritic pattern is more directional giving higher wear resistance.

Radial comparison of static and centrifugal cast microstructure 3X 1% nital etching.

A significant improvement of the core and neck strength can be achieved by introducing a softer, stronger, more ductile metal. This metal will contain evenly distributed graphtic nodules in a well balanced pearlitic-ferritic matrix. Unlike some high carbide static cast rolls that exhibit hard and brittle cores, which may be more prone to breakage, the high strength neck and core will withstand higher load. It is very seldom that a CC Duplex roll will break.

The centrifugal system permits extremely precise metallurgical control over the roll composition, enabling Horton to "tailor make" special quality or harder rolls to meet the customer's specific needs.

Centrifugal Cast Duplex Roll Advantages

Improved performance in:

.Increase rolling campaign．Improve tonnage output．
.Increase productivity．
.Better surface finish of rolled products．

Resulting in:

.Reduced down time.
.Less frequent and reduced dressing.
.Can withstand higher rolling loads with no breakage problem.
.Lower roll stock levels

2. Static Casting

Metal moulds are used for chill casting the barrel to ensure rapid solidification and develop a carbide rich hard material. The roll journals are sand cast so that the metal solidifies slowly to form a graphite rich soft iron.

Rolls are poured from the bottom through a tangential ingate. This induces a rotating movement which produces a vortex of liquid metal segregating the impurities to the feeder head, ensuring cleanliness and soundness of the working layer of the roll.

For the manufacture of steel and steel base type roll, the static route will be the same as iron except that the mould design will be different. The barrel will be cast in sand lined chills while the journals are designed for adequate feeding to ensure complete soundness.

The differing structures and hardness required for various applications are obtained by heat treatment processes.

Static Roll Advantages

.Static cast rolls are in the majority monobloc castings and limited to only standard qualities with low alloy contents and at lower hardness.
.Ability to roll heavy and deep sections.
.More readily available at lower prices.

Heat Treatment

Our heat treatment shops have installed modern bogie type hearth furnaces with temperature control by microprocessors at both high and low temperatures. Most furnaces are heated by natural gas with high velocity burners. Some furnaces are equipped with electric radiation units and fans for better circulation of the furnace atmosphere.

The temperature and cycle times are capable of maintaining temperature distribution and accuracy to plus and minus 2.5 degrees C.

There are rotating quenching machines used to quench rolls after re-austenitizing with high velocity fans and water mist sprays.

Roll Machining

Our plants are well equipped with lathes, milling machines and grinders to meet all requirements on tolerances and surface conditions.

Process control

All process data are carefully tested and documented and are available for each individual roll. The equipment is state of the art and maintained by scheduled inspection and service.

The Quality System is in accordance with ISO 9002.