Increasing the nozzle slot length, the flow rate and the distance betweenthe nozzle and the melt bath surface increases the probability of formation of the thickness non uniformity across the strip width. The design of the roll plays a major role in the formation of the cross-sectional shape of the strip: a convex profile is produced by bending of the rolls whilst a concave profile results from thermal expansion of the rolls, in the case of a thick, water-cooled sleeve. Theshape of the pressure profile betweenthe rolls depends on the ratio strip width to roll length. Optimisation of the sleeve thickness, diameter and length of the roll is one of the possibie ways of improving the cross-sectional profile and the flatness of the as-cast-strip.

The rolls are one of the most important components of the twin-roll casting process, determining not only strip quality, but due to their expense, add to the price of the as-cast strip. The potential for reducing operational cost and ensuring required strip quality may be achieved through a reduction in wear of the roll surface and hence reduced frequency of roll surface reconditioning and replacement. To achieve this, it is imperative to understand the mechanisms of roll surface wear which occur during casting operations.The present study was aimed at determining the influence of liquid metal, roll separation force and strip incline from the vertical casting direction on the wear of the roll surface in a twin-roll casting process.It was found that roll wear in the twin-roll casting process is accompanied by removal of material from the roll surface and redistribution of topography of the roll surface. Applying high roll separation forces lead to increase erosion of the roll surface and coarsening of the roll surface topography. Roll surface wear caused by deformation occurs by imprinting of the strip surface on the roll surface as well as grinding of the roll surface by the strip. Even with the application of high roll separation forces the highest contribution to wear of the roll surface is by the interaction of the melt with the roll surface in the very early stages of solidification.KEY WORDS: rapid solidification process; twin-roll process; strip casting; wear; surface roughness.surface. To achieve this, it is imperative to understand the mechanism of roll surface wear which occurs during casting operations. It is of particular interest to relate the influence of liquid metal attack, roll separation force and effect of strip incline to the roll surface wear.The term wear remains a subject of some debate, 22) so to avoid confusion in this discussion the term wear in this work is accepted as "damage to a solid surface, generally involving progressive loss of material, due to relative motion between that surface and a contacting substance or substances". 23) Experimental Equipment and Procedure Twin-roll Casting ProcessAn experimental investigation was carried out on a twin roll caster 24,25) schematically showed in Fig. 1. Steel melt was prepared from 50 kg ingots which were melted under an argon atmosphere in an induction furnace, yielding the following composition: 4.5% Si, 0.0013% Cu, CϽ0.007%, PϽ0.010%, NiϽ0.07%, TiϽ0.02%, CoϽ0.02% and AlϽ0.01%.The superheat was maintained at ϳ30°C and the melt entered the gap between the rolls through a slot in a ceramic nozzle. The cylindrical, water-cooled rolls constructed from Cu-Cr sleeves were ϳ440 mm in diameter and 150 mm in length. The casting speed was 7 m s Ϫ1 and the thickness of the as-cast strip 0.1-0.2 mm.The roll surface before casting was treated with an emery wheel. The roll surface obtained in this manner was further treated with fine emery paper to obtain a roughness of the roll surface, R a ϭ0.4 mm.The roll separation force per unit length of the ro...

One of the common technological schemes for the laser processing of metal parts is laser «glazing» of the deposited thin layer of powder on the substrate, which makes it possible to obtain microcrystalline and amorphous structures in thin surface layers of parts. Pulse melting of small volumes of metal on the surface provides homogeneous liquids (melts), which, after crystallization, can fix the structure of a liquid with unique properties.The presence of three energy input ranges for pulsed laser surface treatment (ILPO) has been established. At an average level of energy input, a process of laser surfacing of the material occurs, while a high adhesive bond between the coating and the workpiece is fixed. The deposition of an amorphized iron-based alloy coating on a metal base of St3, 45 20X13 steels begins at a laser radiation density on the treatment surface of 1800–2000 W/mm2, and alloying at 3500–4000 W/mm2. With ILPO, the laser exposure zone (ZLV) has a layered structure – the fusion zone (ZO), the heat-affected zone (HAZ), and the source material zone. To obtain an amorphous-crystalline structure of the coating, the laser pulse frequency should not exceed 3–8 Hz.

Exposure to laser radiation leads to a change in the temperature field of the substance being treated. The nature of heating, which is determined by the rate of change of temperature, temperature gradients, the time to reach the temperatures of structural and phase transitions, is different depending on the properties of the material being processed and the processing conditions.When modifying the surface layers by high-energy processing by changing the power and time of exposure to laser radiation, you can get a wide range of structural states of the treated surface areas of the material.It is shown that the shape of TVP diagrams and cooling curves of precision alloys on the surface of a two-layer metal system after heating them with laser radiation are determined by the competition of two processes acting in opposite directions: an increase in the driving force of the crystallization process with an increase in supercooling and a decrease in the surface of atoms.The method of surface modification by moving laser radiation allows to obtain amorphous functional layers of precision alloys on the surface of metal products.